Home |
Search |
Today's Posts |
|
Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
Reply |
|
LinkBack | Thread Tools | Display Modes |
#1
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
Does anyone have a set of schematics for the C-Audio RA3001 that they could
let me have fairly urgently please ? The links to the service manual on the supposed C-Audio 'website', just seem to take you round in ever decreasing circles via other third party vendors of everthing you can imagine. TIA Arfa |
#2
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
Arfa Daily wrote: Does anyone have a set of schematics for the C-Audio RA3001 that they could let me have fairly urgently please ? It's not a 'head', it's a 19" rack mounting pro power amp with line level inputs. What do you want to know btw ? They are notoriously unreliable. First job is to replace all the PSU caps that have been cooked by the hot exhaust air. Then check how many mosfets are open. I know an awful lot about it, having rejected it as an ODM product for Studiomaster. I think it was that model. The links to the service manual on the supposed C-Audio 'website', just seem to take you round in ever decreasing circles via other third party vendors of everthing you can imagine. Harman UK bought them. And I could tell you a story about that too ! Ask there. Except it's not Harman any more it seems but google that for starters. They've moved to Letchworth. I think most of the C-Audio parts ended up shuffled into a corner (I could tell another story) so they might be willing to get rid of some unwanted and unloved bits. Unless they already put them in a skip (dumpster for USAans) Graham |
#3
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
"Eeyore" wrote in message ... Arfa Daily wrote: Does anyone have a set of schematics for the C-Audio RA3001 that they could let me have fairly urgently please ? It's not a 'head', it's a 19" rack mounting pro power amp with line level inputs. What do you want to know btw ? They are notoriously unreliable. First job is to replace all the PSU caps that have been cooked by the hot exhaust air. Then check how many mosfets are open. I know an awful lot about it, having rejected it as an ODM product for Studiomaster. I think it was that model. The links to the service manual on the supposed C-Audio 'website', just seem to take you round in ever decreasing circles via other third party vendors of everthing you can imagine. Harman UK bought them. And I could tell you a story about that too ! Ask there. Except it's not Harman any more it seems but google that for starters. They've moved to Letchworth. I think most of the C-Audio parts ended up shuffled into a corner (I could tell another story) so they might be willing to get rid of some unwanted and unloved bits. Unless they already put them in a skip (dumpster for USAans) Graham The guy who owns the shop where all this stuff comes from, and who is a musician himself with 'many years in', tends to call anything that's rack mount, line input and 'power', a "head", as opposed to an "amp" for an instrument level standalone unit like a Marshall, or a "combo" for the same thing with speakers built in like an AC30 or Fender Twin. I just follow his lead, and call them the same. What do you describe as a "head"? Anyways, as to what's wrong with it. The "A" channel has an *extremely* asymmetric output. On a sine wave, looks like the output from a half wave reccy with no filter cap on the end. It also 'bounces' in amplitude when the input level, or front panel level, is varied. The problem is right up the front end somewhere. There are pukka sine waves around the TL074 input amp, but soon after, the signal has taken on this asymmetry, which is then faithfully amplified by the output stage. The "B" channel works perfectly, so I guess I can start comparing between the two. Just would have been a lot easier with a set of schematics to see where exactly the signal goes. It's got that nasty 'feel' about it, that says it's going to be something like an o/c resistor, which looks perfect to the naked eye ... I see a couple of bunches of four TO92 transistors, so I think that may be a good place to start looking. Arfa |
#4
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
Arfa Daily wrote: "Eeyore" wrote in message Arfa Daily wrote: Does anyone have a set of schematics for the C-Audio RA3001 that they could let me have fairly urgently please ? It's not a 'head', it's a 19" rack mounting pro power amp with line level inputs. What do you want to know btw ? They are notoriously unreliable. First job is to replace all the PSU caps that have been cooked by the hot exhaust air. Then check how many mosfets are open. I know an awful lot about it, having rejected it as an ODM product for Studiomaster. I think it was that model. The links to the service manual on the supposed C-Audio 'website', just seem to take you round in ever decreasing circles via other third party vendors of everthing you can imagine. Harman UK bought them. And I could tell you a story about that too ! Ask there. Except it's not Harman any more it seems but google that for starters. They've moved to Letchworth. I think most of the C-Audio parts ended up shuffled into a corner (I could tell another story) so they might be willing to get rid of some unwanted and unloved bits. Unless they already put them in a skip (dumpster for USAans) The guy who owns the shop where all this stuff comes from, and who is a musician himself with 'many years in', tends to call anything that's rack mount, line input and 'power', a "head", as opposed to an "amp" for an instrument level standalone unit like a Marshall, or a "combo" for the same thing with speakers built in like an AC30 or Fender Twin. I just follow his lead, and call them the same. What do you describe as a "head"? A 'head' has preamp level inputs. A guitar head has sensitive Hi-Z inputs for guitars, a 'PA' head has mic inputs. The old name for what an RA3001 type amp is a 'slave amp'. Anyways, as to what's wrong with it. The "A" channel has an *extremely* asymmetric output. Typical C-Audio ! On a sine wave, looks like the output from a half wave reccy with no filter cap on the end. It also 'bounces' in amplitude when the input level, or front panel level, is varied. The problem is right up the front end somewhere. There are pukka sine waves around the TL074 input amp, but soon after, the signal has taken on this asymmetry, which is then faithfully amplified by the output stage. The "B" channel works perfectly, so I guess I can start comparing between the two. Just would have been a lot easier with a set of schematics to see where exactly the signal goes. It's got that nasty 'feel' about it, that says it's going to be something like an o/c resistor, which looks perfect to the naked eye ... I see a couple of bunches of four TO92 transistors, so I think that may be a good place to start looking. Unlikely. Do you know how to test Hitachi lateral mosfet output devices ? Not much different from any mosfet except they made true complements. Remove them all. I expect they're TO-3 so easy to get them out and test. You will find a fair few are totally open. Replace these and you're good to go but DO replace the reservoir caps too. They will have been roasted by the searingly hot air passing over the heatsink. Don't even think of using 85C types. One of the worst laid out designs I've ever seen in my entire life. In tests I measured 150C *on the HEATSINK*. God knows what the junction temp was. Your trouble will be getting genuine Hitachi replacements as they stopped making them and the Semelab/Magnatec and Exicon replacements aren't exactly identical.. I may have a few but you WILL pay megabucks for them. Graham |
#5
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
"Eeyore" wrote in message ... Arfa Daily wrote: "Eeyore" wrote in message Arfa Daily wrote: Does anyone have a set of schematics for the C-Audio RA3001 that they could let me have fairly urgently please ? It's not a 'head', it's a 19" rack mounting pro power amp with line level inputs. What do you want to know btw ? They are notoriously unreliable. First job is to replace all the PSU caps that have been cooked by the hot exhaust air. Then check how many mosfets are open. I know an awful lot about it, having rejected it as an ODM product for Studiomaster. I think it was that model. The links to the service manual on the supposed C-Audio 'website', just seem to take you round in ever decreasing circles via other third party vendors of everthing you can imagine. Harman UK bought them. And I could tell you a story about that too ! Ask there. Except it's not Harman any more it seems but google that for starters. They've moved to Letchworth. I think most of the C-Audio parts ended up shuffled into a corner (I could tell another story) so they might be willing to get rid of some unwanted and unloved bits. Unless they already put them in a skip (dumpster for USAans) The guy who owns the shop where all this stuff comes from, and who is a musician himself with 'many years in', tends to call anything that's rack mount, line input and 'power', a "head", as opposed to an "amp" for an instrument level standalone unit like a Marshall, or a "combo" for the same thing with speakers built in like an AC30 or Fender Twin. I just follow his lead, and call them the same. What do you describe as a "head"? A 'head' has preamp level inputs. A guitar head has sensitive Hi-Z inputs for guitars, a 'PA' head has mic inputs. The old name for what an RA3001 type amp is a 'slave amp'. Anyways, as to what's wrong with it. The "A" channel has an *extremely* asymmetric output. Typical C-Audio ! On a sine wave, looks like the output from a half wave reccy with no filter cap on the end. It also 'bounces' in amplitude when the input level, or front panel level, is varied. The problem is right up the front end somewhere. There are pukka sine waves around the TL074 input amp, but soon after, the signal has taken on this asymmetry, which is then faithfully amplified by the output stage. The "B" channel works perfectly, so I guess I can start comparing between the two. Just would have been a lot easier with a set of schematics to see where exactly the signal goes. It's got that nasty 'feel' about it, that says it's going to be something like an o/c resistor, which looks perfect to the naked eye ... I see a couple of bunches of four TO92 transistors, so I think that may be a good place to start looking. Unlikely. Do you know how to test Hitachi lateral mosfet output devices ? Not much different from any mosfet except they made true complements. Remove them all. I expect they're TO-3 so easy to get them out and test. You will find a fair few are totally open. Replace these and you're good to go but DO replace the reservoir caps too. They will have been roasted by the searingly hot air passing over the heatsink. Don't even think of using 85C types. One of the worst laid out designs I've ever seen in my entire life. In tests I measured 150C *on the HEATSINK*. God knows what the junction temp was. Your trouble will be getting genuine Hitachi replacements as they stopped making them and the Semelab/Magnatec and Exicon replacements aren't exactly identical.. I may have a few but you WILL pay megabucks for them. Graham Well, if that's the case, it ain't gonna get done, as he only sold it a couple of weeks ago as a cheapy second hand job. As a matter of interest, does the circuit employ feedback to the front end then ? I wasn't expecting this to be an output issue, as the waveform seems to distort quite early in the chain, but now you suggest this, I guess it makes some sense of the way that the amplitude of the waveform 'bounces' a couple of times before settling, when the level is adjusted, externally or front panel. Arfa |
#6
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
On Nov 24, 7:25*pm, "Arfa Daily" wrote:
"Eeyore" wrote in message ... Arfa Daily wrote: Does anyone have a set of schematics for the C-Audio RA3001 that they could let me have fairly urgently please ? It's not a 'head', it's a 19" rack mounting pro power amp with line level inputs. What do you want to know btw ? They are notoriously unreliable. First job is to replace all the PSU caps that have been cooked by the hot exhaust air. Then check how many mosfets are open. I know an awful lot about it, having rejected it as an ODM product for Studiomaster. I think *it was that model. The links to the service manual on the supposed C-Audio 'website', just seem to take you round in ever decreasing circles via other third party vendors of everthing you can imagine. Harman UK bought them. And I could tell you a story about that too ! Ask there. Except it's not Harman any more it seems but google that for starters. They've moved to Letchworth. I think most of the C-Audio parts ended up shuffled into a corner (I could tell another story) so they might be willing to get rid of some unwanted and unloved bits. Unless they already put them in a skip (dumpster for USAans) Graham The guy who owns the shop where all this stuff comes from, and who is a musician himself with 'many years in', tends to call anything that's rack mount, line input and 'power', a "head", as opposed to an "amp" for an instrument level standalone unit like a Marshall, or a "combo" for the same thing with speakers built in like an AC30 or Fender Twin. I just follow his lead, and call them the same. What do you describe as a "head"? Anyways, as to what's wrong with it. The "A" channel has an *extremely* asymmetric output. On a sine wave, looks like the output from a half wave reccy with no filter cap on the end. It also 'bounces' in amplitude when the input level, or front panel level, is varied. The problem is right up the front end somewhere. There are pukka sine waves around the TL074 input amp, but soon after, the signal has taken on this asymmetry, which is then faithfully amplified by the output stage. The "B" channel works perfectly, so I guess I can start comparing between the two. Just would have been a lot easier with a set of schematics to see where exactly the signal goes. It's got that nasty 'feel' about it, that says it's going to be something like an o/c resistor, which looks perfect to the naked eye ... I see a couple of bunches of four TO92 transistors, so I think that may be a good place to start looking. Arfa- Hide quoted text - - Show quoted text - On the western side of the big pond, "head" can mean what you folks on the eastern side, I believe, call the "Loo". Think it comes from nautical background when the in-ship toilet was at the front/head of the ship/boat. Bob H |
#7
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
|
#8
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
Arfa Daily wrote: "Eeyore" wrote in message snip One of the worst laid out designs I've ever seen in my entire life. In tests I measured 150C *on the HEATSINK*. God knows what the junction temp was. Your trouble will be getting genuine Hitachi replacements as they stopped making them and the Semelab/Magnatec and Exicon replacements aren't exactly identical.. I may have a few but you WILL pay megabucks for them. http://cgi.ebay.co.uk/2SK175-Transis...QQcmdZViewItem http://cgi.ebay.co.uk/2SJ56-Transist...QQcmdZViewItem Probably cheaper to remove all the Hitachis (and sell them ?) and replace all with Exicon or Semelab. http://www.profusionplc.com/pro/gex/...eral%20mosfet# http://uk.farnell.com/jsp/search/bro...questid=473126 You need the 'BUZ' parts. Well, if that's the case, it ain't gonna get done, as he only sold it a couple of weeks ago as a cheapy second hand job. As a matter of interest, does the circuit employ feedback to the front end then ? Oh yeah. I wasn't expecting this to be an output issue, as the waveform seems to distort quite early in the chain, but now you suggest this, I guess it makes some sense of the way that the amplitude of the waveform 'bounces' a couple of times before settling, when the level is adjusted, externally or front panel. It 'might' be something else. You'll only tell by removing the output devices (thankfully easy enough) and testing them but C-Audio have a reputation for eating them. And will do so again if driven hard into 4 ohms. Graham |
#9
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
"Meat Plow" wrote in message ... On Tue, 25 Nov 2008 06:00:02 +0000, Eeyore wrote: Arfa Daily wrote: "Eeyore" wrote in message Arfa Daily wrote: Does anyone have a set of schematics for the C-Audio RA3001 that they could let me have fairly urgently please ? It's not a 'head', it's a 19" rack mounting pro power amp with line level inputs. What do you want to know btw ? They are notoriously unreliable. First job is to replace all the PSU caps that have been cooked by the hot exhaust air. Then check how many mosfets are open. I know an awful lot about it, having rejected it as an ODM product for Studiomaster. I think it was that model. The links to the service manual on the supposed C-Audio 'website', just seem to take you round in ever decreasing circles via other third party vendors of everthing you can imagine. Harman UK bought them. And I could tell you a story about that too ! Ask there. Except it's not Harman any more it seems but google that for starters. They've moved to Letchworth. I think most of the C-Audio parts ended up shuffled into a corner (I could tell another story) so they might be willing to get rid of some unwanted and unloved bits. Unless they already put them in a skip (dumpster for USAans) The guy who owns the shop where all this stuff comes from, and who is a musician himself with 'many years in', tends to call anything that's rack mount, line input and 'power', a "head", as opposed to an "amp" for an instrument level standalone unit like a Marshall, or a "combo" for the same thing with speakers built in like an AC30 or Fender Twin. I just follow his lead, and call them the same. What do you describe as a "head"? A 'head' has preamp level inputs. A guitar head has sensitive Hi-Z inputs for guitars, a 'PA' head has mic inputs. The old name for what an RA3001 type amp is a 'slave amp'. Anyways, as to what's wrong with it. The "A" channel has an *extremely* asymmetric output. Typical C-Audio ! On a sine wave, looks like the output from a half wave reccy with no filter cap on the end. It also 'bounces' in amplitude when the input level, or front panel level, is varied. The problem is right up the front end somewhere. There are pukka sine waves around the TL074 input amp, but soon after, the signal has taken on this asymmetry, which is then faithfully amplified by the output stage. The "B" channel works perfectly, so I guess I can start comparing between the two. Just would have been a lot easier with a set of schematics to see where exactly the signal goes. It's got that nasty 'feel' about it, that says it's going to be something like an o/c resistor, which looks perfect to the naked eye ... I see a couple of bunches of four TO92 transistors, so I think that may be a good place to start looking. Unlikely. Do you know how to test Hitachi lateral mosfet output devices ? Not much different from any mosfet except they made true complements. Remove them all. I expect they're TO-3 so easy to get them out and test. You will find a fair few are totally open. Replace these and you're good to go but DO replace the reservoir caps too. They will have been roasted by the searingly hot air passing over the heatsink. Don't even think of using 85C types. One of the worst laid out designs I've ever seen in my entire life. In tests I measured 150C *on the HEATSINK*. God knows what the junction temp was. Your trouble will be getting genuine Hitachi replacements as they stopped making them and the Semelab/Magnatec and Exicon replacements aren't exactly identical.. I may have a few but you WILL pay megabucks for them. Graham Ran into the Hitachi mosfet issue years ago after acquiring a Sound Code Systems (SCS) rack mount power amp. Had the 2SJ49/2SK134 pairs inside if I recall correctly. I replaced them with J50/K135 devices which at the time were still available. Now adays there are replacements but with a little modification since they are not in a TO3 package. I've had that amp now for 15 years after repair and used it for 5 years as a bass guitar amp strapped mono. Now adays it is the PA amp for my home studio. I've only seen one SCS amp and this is it. IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and T0247, which are still easily available. http://uk.farnell.com/jsp/search/bro...estid=48642 0 Gareth. |
#10
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
"Meat Plow" wrote in message ... On Tue, 25 Nov 2008 18:54:01 -0000, "Gareth Magennis" wrote: IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and T0247, which are still easily available. http://uk.farnell.com/jsp/search/bro...estid=48642 0 Gareth. Good to know when the old J50's and K135's decide to check out. Well, I didn't say the BUZ were replacements for those, but C-audio did use a selection of different devices throughout the years they were in production. Some of the amps were rather prone to RF oscillations, burning out their Zobel networks - attributed to various things like heatsink/ground bonding or layout design, depending on who you talked to and what opinion they had, or how much bull**** they liked to talk. I replaced quite a few BUZ's, and they were expensive back then, about the same as Farnell charge now. Can't remember changing many, if any, reservoir capacitors though. Gareth. |
#11
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
"Gareth Magennis" wrote in message news "Meat Plow" wrote in message ... On Tue, 25 Nov 2008 18:54:01 -0000, "Gareth Magennis" wrote: IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and T0247, which are still easily available. http://uk.farnell.com/jsp/search/bro...estid=48642 0 Gareth. Good to know when the old J50's and K135's decide to check out. Well, I didn't say the BUZ were replacements for those, but C-audio did use a selection of different devices throughout the years they were in production. Some of the amps were rather prone to RF oscillations, burning out their Zobel networks - attributed to various things like heatsink/ground bonding or layout design, depending on who you talked to and what opinion they had, or how much bull**** they liked to talk. I replaced quite a few BUZ's, and they were expensive back then, about the same as Farnell charge now. Can't remember changing many, if any, reservoir capacitors though. Gareth. Oh, and the worst problem they suffered from was (allegedly) smoke fluid (in club installs) being deposited on the PCB behind the fan intake. This would eventually corrode lots of fine tracks running along the board, the most common victim being part of the Protect/Speaker Relay circuit, so the amp would stay in Protect forever. Annoyingly, the corrosive substance would creep under the Speaker relays and eat the tracks under them as well, so repairing these amps properly was either very time consuming and expensive, or just plain uneconomical. And, the 47 ohm 10 Watt ceramic Soft Start resistors would very often need replacing. These had their fair share of design problems, that's for sure. Gareth. |
#12
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
Gareth Magennis wrote: IIRC, the C-Audio RA series commonly used BUZ Mosfets, Not originally. both T03 and T0247, which are still easily available. But best not to mix them I imagine. Graham |
#13
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
Gareth Magennis wrote: "Gareth Magennis" wrote "Meat Plow" wrote in message "Gareth Magennis" wrote: IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and T0247, which are still easily available. http://uk.farnell.com/jsp/search/bro...estid=48642 0 Good to know when the old J50's and K135's decide to check out. Well, I didn't say the BUZ were replacements for those, but C-audio did use a selection of different devices throughout the years they were in production. Some of the amps were rather prone to RF oscillations, burning out their Zobel networks - attributed to various things like heatsink/ground bonding or layout design, depending on who you talked to and what opinion they had, or how much bull**** they liked to talk. I replaced quite a few BUZ's, and they were expensive back then, about the same as Farnell charge now. Can't remember changing many, if any, reservoir capacitors though. Surprised at that. C-Audio's stance was they were a 'service item'. Like the mosfets presumably ! Oh, and the worst problem they suffered from was (allegedly) smoke fluid (in club installs) being deposited on the PCB behind the fan intake. This would eventually corrode lots of fine tracks running along the board, the most common victim being part of the Protect/Speaker Relay circuit, so the amp would stay in Protect forever. Annoyingly, the corrosive substance would creep under the Speaker relays and eat the tracks under them as well, so repairing these amps properly was either very time consuming and expensive, or just plain uneconomical. And, the 47 ohm 10 Watt ceramic Soft Start resistors would very often need replacing. These had their fair share of design problems, that's for sure. Which is why I didn't approve them to be sold under the Studiomaster badge and went on to design the much loved D Series. http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA:IT&ih=011 Siemens ODM'd the RA3001 though IIRC. Graham |
#14
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
"Eeyore" wrote in message ... Arfa Daily wrote: "Eeyore" wrote in message snip One of the worst laid out designs I've ever seen in my entire life. In tests I measured 150C *on the HEATSINK*. God knows what the junction temp was. Your trouble will be getting genuine Hitachi replacements as they stopped making them and the Semelab/Magnatec and Exicon replacements aren't exactly identical.. I may have a few but you WILL pay megabucks for them. http://cgi.ebay.co.uk/2SK175-Transis...QQcmdZViewItem http://cgi.ebay.co.uk/2SJ56-Transist...QQcmdZViewItem Probably cheaper to remove all the Hitachis (and sell them ?) and replace all with Exicon or Semelab. http://www.profusionplc.com/pro/gex/...eral%20mosfet# http://uk.farnell.com/jsp/search/bro...questid=473126 You need the 'BUZ' parts. Well, if that's the case, it ain't gonna get done, as he only sold it a couple of weeks ago as a cheapy second hand job. As a matter of interest, does the circuit employ feedback to the front end then ? Oh yeah. I wasn't expecting this to be an output issue, as the waveform seems to distort quite early in the chain, but now you suggest this, I guess it makes some sense of the way that the amplitude of the waveform 'bounces' a couple of times before settling, when the level is adjusted, externally or front panel. It 'might' be something else. You'll only tell by removing the output devices (thankfully easy enough) and testing them but C-Audio have a reputation for eating them. And will do so again if driven hard into 4 ohms. Graham You are right. One whole bank of FETs is o/c - hence the very asymmetric output. There has been a further development. I rang the shop to tell him the bad news that a set of twelve devices was going to set him back 100 quid, with the possibility of there being some o/c on the other channel (a couple of them seem very cool under drive conditions, compared to their neighbours, so a good indication that they may well be open as well) and then the possibility of some smoothers as well. Turns out that when he sold the guy this one as a s/h unit, he picked up the wrong one. This example was sitting waiting to come to me for checking, so he has now given the customer the right one, and is writing this one off, for the time being at least. Thanks for the useful pointer to the FETs, anyway. Arfa |
#15
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
"Gareth Magennis" wrote in message ... "Meat Plow" wrote in message ... On Tue, 25 Nov 2008 06:00:02 +0000, Eeyore wrote: Arfa Daily wrote: "Eeyore" wrote in message Arfa Daily wrote: Does anyone have a set of schematics for the C-Audio RA3001 that they could let me have fairly urgently please ? It's not a 'head', it's a 19" rack mounting pro power amp with line level inputs. What do you want to know btw ? They are notoriously unreliable. First job is to replace all the PSU caps that have been cooked by the hot exhaust air. Then check how many mosfets are open. I know an awful lot about it, having rejected it as an ODM product for Studiomaster. I think it was that model. The links to the service manual on the supposed C-Audio 'website', just seem to take you round in ever decreasing circles via other third party vendors of everthing you can imagine. Harman UK bought them. And I could tell you a story about that too ! Ask there. Except it's not Harman any more it seems but google that for starters. They've moved to Letchworth. I think most of the C-Audio parts ended up shuffled into a corner (I could tell another story) so they might be willing to get rid of some unwanted and unloved bits. Unless they already put them in a skip (dumpster for USAans) The guy who owns the shop where all this stuff comes from, and who is a musician himself with 'many years in', tends to call anything that's rack mount, line input and 'power', a "head", as opposed to an "amp" for an instrument level standalone unit like a Marshall, or a "combo" for the same thing with speakers built in like an AC30 or Fender Twin. I just follow his lead, and call them the same. What do you describe as a "head"? A 'head' has preamp level inputs. A guitar head has sensitive Hi-Z inputs for guitars, a 'PA' head has mic inputs. The old name for what an RA3001 type amp is a 'slave amp'. Anyways, as to what's wrong with it. The "A" channel has an *extremely* asymmetric output. Typical C-Audio ! On a sine wave, looks like the output from a half wave reccy with no filter cap on the end. It also 'bounces' in amplitude when the input level, or front panel level, is varied. The problem is right up the front end somewhere. There are pukka sine waves around the TL074 input amp, but soon after, the signal has taken on this asymmetry, which is then faithfully amplified by the output stage. The "B" channel works perfectly, so I guess I can start comparing between the two. Just would have been a lot easier with a set of schematics to see where exactly the signal goes. It's got that nasty 'feel' about it, that says it's going to be something like an o/c resistor, which looks perfect to the naked eye ... I see a couple of bunches of four TO92 transistors, so I think that may be a good place to start looking. Unlikely. Do you know how to test Hitachi lateral mosfet output devices ? Not much different from any mosfet except they made true complements. Remove them all. I expect they're TO-3 so easy to get them out and test. You will find a fair few are totally open. Replace these and you're good to go but DO replace the reservoir caps too. They will have been roasted by the searingly hot air passing over the heatsink. Don't even think of using 85C types. One of the worst laid out designs I've ever seen in my entire life. In tests I measured 150C *on the HEATSINK*. God knows what the junction temp was. Your trouble will be getting genuine Hitachi replacements as they stopped making them and the Semelab/Magnatec and Exicon replacements aren't exactly identical.. I may have a few but you WILL pay megabucks for them. Graham Ran into the Hitachi mosfet issue years ago after acquiring a Sound Code Systems (SCS) rack mount power amp. Had the 2SJ49/2SK134 pairs inside if I recall correctly. I replaced them with J50/K135 devices which at the time were still available. Now adays there are replacements but with a little modification since they are not in a TO3 package. I've had that amp now for 15 years after repair and used it for 5 years as a bass guitar amp strapped mono. Now adays it is the PA amp for my home studio. I've only seen one SCS amp and this is it. IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and T0247, which are still easily available. http://uk.farnell.com/jsp/search/bro...estid=48642 0 Gareth. Yes, they are BUZ's and yes, they are in the Farnell book, allbeit with a different suffix letter to what is actually fitted now, but with six N's and six P's in the equation, at 8 quid + VAT a pop, that's 100+ quidsworth trade in devices for one channel, before we even start looking at the other channel to see if any are open there as well. Shop owner has deemed it uneconomic for the moment, so it will go back up the corner to await its ultimate fate ... :-( Talking of Farnell, do you order much from them ? Have you noticed how much they seem now to be rationalising 'on the shelf' stock ? It used to be *very* rare to ever catch them out of stock on any catalogue item. Now, there seems to be something on every order. Also, have you noticed how you get one order in two shipments ? One parcel comes from Leeds, and the other, often something like a single transistor, comes in a box the size of your head, by UPS, from Belgium. Surely, this can't make economic sense, let alone (God forgive me for using the "e" word) ecological sense ? Arfa |
#16
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
"Eeyore" wrote in message ... Gareth Magennis wrote: IIRC, the C-Audio RA series commonly used BUZ Mosfets, Not originally. both T03 and T0247, which are still easily available. But best not to mix them I imagine. Graham This one that I had on the bench used BUZ's, and the soldering on them looks original Arfa |
#17
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
Arfa Daily wrote: "Eeyore" wrote It 'might' be something else. You'll only tell by removing the output devices (thankfully easy enough) and testing them but C-Audio have a reputation for eating them. And will do so again if driven hard into 4 ohms. You are right. One whole bank of FETs is o/c - hence the very asymmetric output. There has been a further development. I rang the shop to tell him the bad news that a set of twelve devices was going to set him back 100 quid, with the possibility of there being some o/c on the other channel (a couple of them seem very cool under drive conditions, compared to their neighbours, so a good indication that they may well be open as well) That's what happens. The weakest or hottest fail first (open) and the relatively large ON resistance for these devices causes assymmetry in the delevered peak voltage to the load. Graham |
#18
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
Meat Plow wrote: Eeyorewrote: Gareth Magennis wrote: "Gareth Magennis" wrote "Meat Plow" wrote in message "Gareth Magennis" wrote: IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and T0247, which are still easily available. http://uk.farnell.com/jsp/search/bro...estid=48642 0 Good to know when the old J50's and K135's decide to check out. Well, I didn't say the BUZ were replacements for those, but C-audio did use a selection of different devices throughout the years they were in production. Some of the amps were rather prone to RF oscillations, burning out their Zobel networks - attributed to various things like heatsink/ground bonding or layout design, depending on who you talked to and what opinion they had, or how much bull**** they liked to talk. I replaced quite a few BUZ's, and they were expensive back then, about the same as Farnell charge now. Can't remember changing many, if any, reservoir capacitors though. Surprised at that. C-Audio's stance was they were a 'service item'. Like the mosfets presumably ! Oh, and the worst problem they suffered from was (allegedly) smoke fluid (in club installs) being deposited on the PCB behind the fan intake. This would eventually corrode lots of fine tracks running along the board, the most common victim being part of the Protect/Speaker Relay circuit, so the amp would stay in Protect forever. Annoyingly, the corrosive substance would creep under the Speaker relays and eat the tracks under them as well, so repairing these amps properly was either very time consuming and expensive, or just plain uneconomical. And, the 47 ohm 10 Watt ceramic Soft Start resistors would very often need replacing. These had their fair share of design problems, that's for sure. Which is why I didn't approve them to be sold under the Studiomaster badge and went on to design the much loved D Series. http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA:IT&ih=011 Siemens ODM'd the RA3001 though IIRC. I own a Studiomaster 700D and would like to replace the quad set of mains filters. These are low profile, I know there is a specific name for them. The tops of these all seem to bubble upwards but when I picked that part off it was just a cover of sorts for the real container both overshod with heat shrink. I don't think they are bad, haven't removed them but the amp works however I'm worried about it being in service as my bass guitar amp. NEVER seen that myself but those amps are getting old now. Original spec parts were Samwha (forget which series but the plastic film was dark green) 3300uF/63V (yes they're overvolted off load @ 67V but we checked that for reliability with Samwha and they sent us detailed info to say it's basically OK, the leakage current just increases very marginally at ~ 5% overvoltage and no load). The alternative part was IIRC, Panasonic (again forget which series). Dumpy little black cans. Looked absurdly small. I expect that's what you've got. I specced the ripple current per cap at ~ 2.7-3A IIRC. You'll find something in Farnell that'll do fine. Use 105C caps if you want to continue using it forever. I assume you're driving a 4 ohm load btw ? Want some more Oomph ? Fit 4700s. It'll reduce the dynamic headroom though. What do you think of the amp btw ? Graham |
#19
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
Meat Plow wrote: I'm also looking for a new speaker binder set as one is broken off. You must have a US model. Those weren't sourced in the UK. That means you have an Indian built one. Can't tell you what they used sadly. Currently I'm using Spec-on connectors. I bought this amp used at a thieves price. They go on ebay for 'reasonable' prices. I just bought one on behalf on my local music pub client for £72. 10 years old and looked almost new inside. Just had some 'rack rash'. Is there a place here in the US for factory parts or do i have to get them from GB? Not at all. I gave data in my other post. Don't scrimp on the ripple current btw. Use good brand caps. I found Samwha to be excellent btw at a reasonable price. My second preference is Panasonic. Graham |
#20
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
Meat Plow wrote: Is there a place here in the US for factory parts or do i have to get them from GB? I'm fairly certain the original spec is the Samwha HC series 3300uF 63V. Yes, this pdf includes the data sheet. The ripple current is in fact 3A. http://www.rapidonline.com/netalogue/specs/11-3100e.pdf Now ask me how I remember that after over 15 years ago. You'll easily find replacements. Graham |
#21
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
"Arfa Daily" wrote in message ... "Eeyore" wrote in message ... Gareth Magennis wrote: IIRC, the C-Audio RA series commonly used BUZ Mosfets, Not originally. both T03 and T0247, which are still easily available. But best not to mix them I imagine. Graham This one that I had on the bench used BUZ's, and the soldering on them looks original Arfa Often C Audio would put little pink or green dots on the transistors, presumably after testing them prior to production. Not the kind of thing a repairshop would do, so this may indicate if they are the originals or not. I often used to find only one or two devices not working or clamping at high voltages, you may not have to replace the lot at all. Gareth. |
#22
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and T0247, which are still easily available. http://uk.farnell.com/jsp/search/bro...estid=48642 0 Gareth. Yes, they are BUZ's and yes, they are in the Farnell book, allbeit with a different suffix letter to what is actually fitted now, but with six N's and six P's in the equation, at 8 quid + VAT a pop, that's 100+ quidsworth trade in devices for one channel, before we even start looking at the other channel to see if any are open there as well. Shop owner has deemed it uneconomic for the moment, so it will go back up the corner to await its ultimate fate ... :-( Talking of Farnell, do you order much from them ? Have you noticed how much they seem now to be rationalising 'on the shelf' stock ? It used to be *very* rare to ever catch them out of stock on any catalogue item. Now, there seems to be something on every order. Also, have you noticed how you get one order in two shipments ? One parcel comes from Leeds, and the other, often something like a single transistor, comes in a box the size of your head, by UPS, from Belgium. Surely, this can't make economic sense, let alone (God forgive me for using the "e" word) ecological sense ? Arfa I order just about all my stuff from Farnell. They don't tend to have much in the way of unusual or older transistors, these I can usually find at Cricklewood Electronics. http://www.cricklewoodelectronics.co...ewood/home.php I get my stuff next day without fail from both Farnell and Cricklewood, nothing is usually out of stock or comes from Belgium. I'm in Leeds, so is Farnell, so maybe that might have something to do with it, but shouldn't really. What kind of stuff is coming from Belgium? Chocolate screwdrivers? Cheers, Gareth. |
#23
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
Gareth Magennis wrote: I'm in Leeds, so is Farnell, so maybe that might have something to do with it, but shouldn't really. What kind of stuff is coming from Belgium? Chocolate screwdrivers? I've seem multiple deliveries from them. Simple explanation. They don't hold all stock in a single place. Graham |
#24
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
"Gareth Magennis" wrote in message ... IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and T0247, which are still easily available. http://uk.farnell.com/jsp/search/bro...estid=48642 0 Gareth. Yes, they are BUZ's and yes, they are in the Farnell book, allbeit with a different suffix letter to what is actually fitted now, but with six N's and six P's in the equation, at 8 quid + VAT a pop, that's 100+ quidsworth trade in devices for one channel, before we even start looking at the other channel to see if any are open there as well. Shop owner has deemed it uneconomic for the moment, so it will go back up the corner to await its ultimate fate ... :-( Talking of Farnell, do you order much from them ? Have you noticed how much they seem now to be rationalising 'on the shelf' stock ? It used to be *very* rare to ever catch them out of stock on any catalogue item. Now, there seems to be something on every order. Also, have you noticed how you get one order in two shipments ? One parcel comes from Leeds, and the other, often something like a single transistor, comes in a box the size of your head, by UPS, from Belgium. Surely, this can't make economic sense, let alone (God forgive me for using the "e" word) ecological sense ? Arfa I order just about all my stuff from Farnell. They don't tend to have much in the way of unusual or older transistors, these I can usually find at Cricklewood Electronics. http://www.cricklewoodelectronics.co...ewood/home.php I get my stuff next day without fail from both Farnell and Cricklewood, nothing is usually out of stock or comes from Belgium. I'm in Leeds, so is Farnell, so maybe that might have something to do with it, but shouldn't really. What kind of stuff is coming from Belgium? Chocolate screwdrivers? Cheers, Gareth. Seems like just about anything I order now can come from the Belgian warehouse. To be fair, it usually comes the next day, as the stuff from Leeds does, but how much must it be costing them to process, pack and ship from Belgium, just one item out of an order of perhaps 10 items ? They also seem to employ no rhyme or reason with determining how exactly the orders are shipped by default. One day, they will deliver a transformer weighing a couple of pounds, in a Jiffy bag, by regular post. The next day, a packet of transistors will arrive in a box a foot square, conveyed by UPS, who don't usually get to me until late afternoon. One thing about UPS *really* irritates me (must be my age). After having got it to the right address, and asked me to sign for it, and after the same bloke delivering the same sorts of packets to me from the same company, for a long time, he still says every time after I finish signing "What's the surname, please ?" Aaaaarrghhh !!! I haven't used Cricklewood for a while. I also hadn't used Grandata for a while until a few weeks ago. They have really gone down the toilet compared to what they were. I needed an STK, and a couple of power transistors for an amp, as well as a few other bits and pieces - fuses and so on. All items showed as in stock on the website, so I went ahead and placed the order, credit card payment and all that. The next day, I was extremely annoyed to get an e-mail informing me that half the stuff was on 3 to 10 day back order. It has actually taken a total of about 5 weeks to finally get everything that was on the order, the last transistor arriving just yesterday ... Arfa |
#25
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
Arfa Daily wrote: Seems like just about anything I order now can come from the Belgian warehouse. To be fair, it usually comes the next day, as the stuff from Leeds does, but how much must it be costing them to process, pack and ship from Belgium, just one item out of an order of perhaps 10 items ? They also seem to employ no rhyme or reason with determining how exactly the orders are shipped by default. One day, they will deliver a transformer weighing a couple of pounds, in a Jiffy bag, by regular post. The next day, a packet of transistors will arrive in a box a foot square, conveyed by UPS, who don't usually get to me until late afternoon. Why do you think they charge the price they do ? The use of 'satellite warehouses' is well established. Someone must have done the sums. You can bet UPS don't get their standard fee for such an operation. Graham |
#26
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
Arfa Daily wrote in message
... "Gareth Magennis" wrote in message ... IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and I haven't used Cricklewood for a while. I also hadn't used Grandata for a while until a few weeks ago. They have really gone down the toilet compared to what they were. I needed an STK, and a couple of power transistors for an amp, as well as a few other bits and pieces - fuses and so on. All items showed as in stock on the website, so I went ahead and placed the order, credit card payment and all that. The next day, I was extremely annoyed to get an e-mail informing me that half the stuff was on 3 to 10 day back order. It has actually taken a total of about 5 weeks to finally get everything that was on the order, the last transistor arriving just yesterday ... Arfa Grandata must have dumped or auctioned-off their back catalog when moving address from Wembley to Ruislip and trading name to Thumbs Up , actually thumbs down, earlier this year A few totals of IC types in 2000 Grandata catalog, 2008 "Thumbs Up" TDA... 760 136 TEA.... 120 14 L.... 370 55 M.... 234 10 Anyone ever get to the Pike auctions in Nottingham? Or is there any other electronic component auctions around since that one in Stroud Gloucester closed down ? BTW yesterday I passed a Maplins store as a pallet load of returns was being tail-lifted on a lorry, well wrapping tape had Returns Centre printed all over it. Does that turn up at Pikes with all the other returns ? -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#27
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
"Eeyore" wrote in message ... Arfa Daily wrote: Seems like just about anything I order now can come from the Belgian warehouse. To be fair, it usually comes the next day, as the stuff from Leeds does, but how much must it be costing them to process, pack and ship from Belgium, just one item out of an order of perhaps 10 items ? They also seem to employ no rhyme or reason with determining how exactly the orders are shipped by default. One day, they will deliver a transformer weighing a couple of pounds, in a Jiffy bag, by regular post. The next day, a packet of transistors will arrive in a box a foot square, conveyed by UPS, who don't usually get to me until late afternoon. Why do you think they charge the price they do ? The use of 'satellite warehouses' is well established. Someone must have done the sums. You can bet UPS don't get their standard fee for such an operation. Graham Farnell don't charge me shipping, and to be honest, I've never felt that their prices are excessive, given the stockholding that they have, and the normal efficiency of their service. Arfa |
#28
Posted to sci.electronics.repair
|
|||
|
|||
C-Audio Power Amp Head ...
"Arfa Daily" wrote in message ... "Eeyore" wrote in message ... Arfa Daily wrote: Seems like just about anything I order now can come from the Belgian warehouse. To be fair, it usually comes the next day, as the stuff from Leeds does, but how much must it be costing them to process, pack and ship from Belgium, just one item out of an order of perhaps 10 items ? They also seem to employ no rhyme or reason with determining how exactly the orders are shipped by default. One day, they will deliver a transformer weighing a couple of pounds, in a Jiffy bag, by regular post. The next day, a packet of transistors will arrive in a box a foot square, conveyed by UPS, who don't usually get to me until late afternoon. Why do you think they charge the price they do ? The use of 'satellite warehouses' is well established. Someone must have done the sums. You can bet UPS don't get their standard fee for such an operation. Graham Farnell don't charge me shipping, and to be honest, I've never felt that their prices are excessive, given the stockholding that they have, and the normal efficiency of their service. Arfa Likewise. I can phone my order for 1 transistor at 6pm if I need to, and it is here, free delivery, next day. That's what I need to be able to do. Certain things, like cable and connectors, are cheaper elsewhere, but for everyday components I order from them exclusively and pay monthly. Parts are usually the smallest part of the bill anyway, and the customer pays for them, so ultimately I am not bothered about trying to save them a few pence if it takes more time and hassle (and possible labour charge) to do so. Neither, I suspect, are they. Gareth. |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Very Odd Audio Common Mode Condition Started Just Before Midnight 12/31--Audio Feedback Oscillation through Power Line? | Electronics | |||
C-audio RA4001 power amp problem | Electronics Repair | |||
how to adjust the staionary control track/mono audio head ? | Electronics Repair | |||
Adjusting audio head on Pana NV-9100 U-Matic | Electronics Repair |