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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. |
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#1
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Valve amps and microcontrollers
Blimey, this had me stumped for a while.
Blackstar valve amp. Unless you insert a plug into the input jack, the Power Amp section is on mute, but I already knew that. So you can't check the Power Amp section by injecting a signal into the FX return or Power Amp In socket, thereby bypassing the pre-amp section, as I normally do, unless you insert a dummy jack. Now this amp has a PIC onboard that (as well as controlling the footswitch functions, also) senses the inserted jack in the input socket. But, in addition, it also disables the Bias control circuitry, so as well as muting the signal to the Power Amp, it also puts -100v bias onto the output valves, thus cutting them off completely, unless a plug is in the input socket. But what I didn't know was that the PIC also gets a signal from the Speaker jack sockets, and will again not take off the -100v bias unless THIS also has a plug in it. So after repairing the faults, I follow my normal procedure of checking HT and bias voltages with no output valves or speaker jacks in place, but I remember to put a dummy jack in the input socket to unmute the amp. But having no plug in any speaker socket means the amp will not come out of the -100v bias position and I think for a long long time there is another problem to fix. Hope that makes sense. Gareth. |
#2
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Valve amps and microcontrollers
Kinda makes sense. I really don't like all this automatic bull****, but it does make saense.
Like a pedal, if there is no inpput, turn off and save the battery. with an amp, if nothing is plugged into the output, wwhy have output ? I reember a car amp a long time ago, simple, transforer based, push pull with a driver transformer. It put out some, and they said to run the main power to oit off an always hot line in the car so you wouldn't overload the ignition switch. The other wire could come from hot in acc or run, ar even the new thing coming out on aftermarket radios, the pink wire that became hot when you tuen on the radio. It also ran some power antennas. The "ON" line for this amp simply supplied the bias circuit. With the bias off, it is pretty much off and that asa that. No relay, no pulling 20 amps though youi ignition switch, none of that. (it went in the trunk (under the boot)) |
#3
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Valve amps and microcontrollers
"Gareth Magennis" wrote in message ... Blimey, this had me stumped for a while. Blackstar valve amp. Unless you insert a plug into the input jack, the Power Amp section is on mute, but I already knew that. So you can't check the Power Amp section by injecting a signal into the FX return or Power Amp In socket, thereby bypassing the pre-amp section, as I normally do, unless you insert a dummy jack. Now this amp has a PIC onboard that (as well as controlling the footswitch functions, also) senses the inserted jack in the input socket. But, in addition, it also disables the Bias control circuitry, so as well as muting the signal to the Power Amp, it also puts -100v bias onto the output valves, thus cutting them off completely, unless a plug is in the input socket. But what I didn't know was that the PIC also gets a signal from the Speaker jack sockets, and will again not take off the -100v bias unless THIS also has a plug in it. So after repairing the faults, I follow my normal procedure of checking HT and bias voltages with no output valves or speaker jacks in place, but I remember to put a dummy jack in the input socket to unmute the amp. But having no plug in any speaker socket means the amp will not come out of the -100v bias position and I think for a long long time there is another problem to fix. Hope that makes sense. Gareth. Whilst it's all very clever sticking a micro in there, realistically, what is the point ? When has a shorted input, as is the case with most amps with a switched input socket, ever caused any kind of problem ? It serves to keep the amp pretty silent, and is simple, and reliable. And if you really want to shut the output stage off along with the rest of the amp, what was wrong with a standby switch ? When I see some of this stuff, I can't help but think that it is design for the sake of the designer's ego. I have a friend that is an ex commercial designer, and his answer is to put a PIC in everything from a toilet seat to a kitchen blender. If ever I happen to mention that I've knocked up some little service aid out of bits in the junk box, his first comment is ALWAYS "If I was designing that, I'd have done it with a PIC ... " Yes, sometimes what he says is valid, but often, when I've achieved the desired result with a couple of transistors and a few other bits, without having to sit down and write and debug code to make it work, I really can't see what the point of the needless complexity would be ... Arfa |
#4
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Valve amps and microcontrollers
Arfa Daily wrote:
Now this amp has a PIC onboard that (as well as controlling the footswitch functions, also) senses the inserted jack in the input socket. But, in addition, it also disables the Bias control circuitry, so as well as muting the signal to the Power Amp, it also puts -100v bias onto the output valves, thus cutting them off completely, unless a plug is in the input socket. But what I didn't know was that the PIC also gets a signal from the Speaker jack sockets, and will again not take off the -100v bias unless THIS also has a plug in it. Whilst it's all very clever sticking a micro in there, realistically, what is the point ? ** None so blind as those who will not see. When has a shorted input, as is the case with most amps with a switched input socket, ever caused any kind of problem ? ** It does not mute nor put the amp in standby. And if you really want to shut the output stage off along with the rest of the amp, what was wrong with a standby switch ? ** Requires an intelligent human operator. When I see some of this stuff, I can't help but think that it is design for the sake of the designer's ego. ** Lucky your mad ideas are not anybody's concern. What the uP does in this examples is useful, clever and makes great selling points too - the number ONE thing a guitar amp has to do is sell well in an extremely oversupplied market. The uP in the Blackstar extends output valve life, biases them precisely and protects them in case of open circuit operation. The only other amps I know with even this last features are some Rivera models - where the output valves cathode connection to ground is open until a speaker plug is fitted. My only worry is obtaining replacement uPs in a few years time. .... Phil |
#5
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Valve amps and microcontrollers
"Phil Allison" wrote in message ... Arfa Daily wrote: Now this amp has a PIC onboard that (as well as controlling the footswitch functions, also) senses the inserted jack in the input socket. But, in addition, it also disables the Bias control circuitry, so as well as muting the signal to the Power Amp, it also puts -100v bias onto the output valves, thus cutting them off completely, unless a plug is in the input socket. But what I didn't know was that the PIC also gets a signal from the Speaker jack sockets, and will again not take off the -100v bias unless THIS also has a plug in it. Whilst it's all very clever sticking a micro in there, realistically, what is the point ? ** None so blind as those who will not see. You said it, Philip ... When has a shorted input, as is the case with most amps with a switched input socket, ever caused any kind of problem ? ** It does not mute nor put the amp in standby. I never said it did put it in standby, did I ? And whilst it doesn't 'mute' the amp, it keeps it quiet enough for all practical stage-use purposes. And a standby switch mutes it totally and absolutely. And if you really want to shut the output stage off along with the rest of the amp, what was wrong with a standby switch ? ** Requires an intelligent human operator. Oh puleese ... It requires any guitar-playing grunt who can flick a toggle switch. Cite me one single case you've ever come across in your long and undistinguished career, where an owner has been too thick to cope with the concept or operation of a standby switch. When I see some of this stuff, I can't help but think that it is design for the sake of the designer's ego. ** Lucky your mad ideas are not anybody's concern. Lucky I'm not just mad, like you, whose ideas really are of no concern to any sane person ... What the uP does in this examples is useful, clever and makes great selling points too - the number ONE thing a guitar amp has to do is sell well in an extremely oversupplied market. The number one thing it has to do is have a well known-name like Fender or Marshall or Vox, and above all, have a reasonable price tag. Baffling features - and these are if you think a standby switch is too complicated for the average user - serve only to attract these amplifiers to musos who have more money than sense, read all the 'right' reviews, and think themselves a lot better than they actually are ... The uP in the Blackstar extends output valve life, biases them precisely and protects them in case of open circuit operation. The only other amps I know with even this last features are some Rivera models - where the output valves cathode connection to ground is open until a speaker plug is fitted. My only worry is obtaining replacement uPs in a few years time. ... Phil Good luck with that. Arfa |
#6
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Valve amps and microcontrollers
Arfa Daily wrote:
"Phil Allison" wrote in message ... Arfa Daily wrote: Now this amp has a PIC onboard that (as well as controlling the footswitch functions, also) senses the inserted jack in the input socket. But, in addition, it also disables the Bias control circuitry, so as well as muting the signal to the Power Amp, it also puts -100v bias onto the output valves, thus cutting them off completely, unless a plug is in the input socket. But what I didn't know was that the PIC also gets a signal from the Speaker jack sockets, and will again not take off the -100v bias unless THIS also has a plug in it. Whilst it's all very clever sticking a micro in there, realistically, what is the point ? ** None so blind as those who will not see. When has a shorted input, as is the case with most amps with a switched input socket, ever caused any kind of problem ? ** It does not mute nor put the amp in standby. I never said it did put it in standby, did I ? ** You are making a false comparison by inventing straw man. And whilst it doesn't 'mute' the amp, it keeps it quiet enough for all practical stage-use purposes. ** Bull****. FX loops are not muted, reverb is not muted and any noise/hum from the input st valve onwards is not stopped. And if you really want to shut the output stage off along with the rest of the amp, what was wrong with a standby switch ? ** Requires an intelligent human operator. Oh puleese ... ** My god you are a ****ing tedious ****wit. When I see some of this stuff, I can't help but think that it is design for the sake of the designer's ego. ** Lucky your mad ideas are not anybody's concern. Lucky I'm not just mad, ** Right, you are an arsehole and a pommy pig too. What the uP does in this examples is useful, clever and makes great selling points too - the number ONE thing a guitar amp has to do is sell well in an extremely oversupplied market. The number one thing it has to do is .. ** Sell well - you ****wit pommy knob. ..... Phil |
#7
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Valve amps and microcontrollers
On 15/03/2015 3:23 AM, Arfa Daily wrote:
"Gareth Magennis" wrote in message ... Blimey, this had me stumped for a while. Blackstar valve amp. Unless you insert a plug into the input jack, the Power Amp section is on mute, but I already knew that. So you can't check the Power Amp section by injecting a signal into the FX return or Power Amp In socket, thereby bypassing the pre-amp section, as I normally do, unless you insert a dummy jack. Now this amp has a PIC onboard that (as well as controlling the footswitch functions, also) senses the inserted jack in the input socket. But, in addition, it also disables the Bias control circuitry, so as well as muting the signal to the Power Amp, it also puts -100v bias onto the output valves, thus cutting them off completely, unless a plug is in the input socket. But what I didn't know was that the PIC also gets a signal from the Speaker jack sockets, and will again not take off the -100v bias unless THIS also has a plug in it. So after repairing the faults, I follow my normal procedure of checking HT and bias voltages with no output valves or speaker jacks in place, but I remember to put a dummy jack in the input socket to unmute the amp. But having no plug in any speaker socket means the amp will not come out of the -100v bias position and I think for a long long time there is another problem to fix. Hope that makes sense. Gareth. Whilst it's all very clever sticking a micro in there, realistically, what is the point ? When has a shorted input, as is the case with most amps with a switched input socket, ever caused any kind of problem ? It serves to keep the amp pretty silent, and is simple, and reliable. And if you really want to shut the output stage off along with the rest of the amp, what was wrong with a standby switch ? When I see some of this stuff, I can't help but think that it is design for the sake of the designer's ego. I have a friend that is an ex commercial designer, and his answer is to put a PIC in everything from a toilet seat to a kitchen blender. If ever I happen to mention that I've knocked up some little service aid out of bits in the junk box, his first comment is ALWAYS "If I was designing that, I'd have done it with a PIC ... " Yes, sometimes what he says is valid, but often, when I've achieved the desired result with a couple of transistors and a few other bits, without having to sit down and write and debug code to make it work, I really can't see what the point of the needless complexity would be ... Arfa **So true. I serviced a (brand and model deleted) power amp awhile back. Simple design, but with high(er) bias switching. It, too, used a micro for muting and switching the bias switching. Needlessly complicated. Particularly in light of the fact that when the amp landing on my bench, it was the micro that had crapped itself. It was one of those mask programmable things, which I had to order from the manufacturer (overseas - New Zealand). Silly buggers sent me the wrong micro, which meant my client had wait even longer for his amp. The amp has three switches. Power (just a big honkin' switch for the mains), a muting toggle and a bias toggle. It could have been far simpler and more reliable to just use simple stuff. If they had wanted to get fancy, then a few gates is all they had to do. For ****'s sake the damned thing was complementary symmetry to boot! -- Trevor Wilson www.rageaudio.com.au --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com |
#8
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Valve amps and microcontrollers
On 15/03/2015 3:43 PM, Trevor Wilson wrote:
For ****'s sake the damned thing was complementary symmetry to boot! **Oops. "That would be QUASI-complementary symmetry..." -- Trevor Wilson www.rageaudio.com.au --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com |
#9
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Valve amps and microcontrollers
** My god you are a ****ing tedious ****wit. When I see some of this stuff, I can't help but think that it is design for the sake of the designer's ego. ** Lucky your mad ideas are not anybody's concern. Lucky I'm not just mad, ** Right, you are an arsehole and a pommy pig too. And you, as ever Philip, are a dopey **** who just can't stop that mealy gob of his flapping. You are just a controversial **** who has to go against anything that anyone says just for the sake of it. Now **** off back under your stone you antipodean arsewipe ... Arfa |
#10
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Valve amps and microcontrollers
On Sun, 15 Mar 2015 12:16:47 -0000, "Arfa Daily"
wrote: ** My god you are a ****ing tedious ****wit. When I see some of this stuff, I can't help but think that it is design for the sake of the designer's ego. ** Lucky your mad ideas are not anybody's concern. Lucky I'm not just mad, ** Right, you are an arsehole and a pommy pig too. And you, as ever Philip, are a dopey **** who just can't stop that mealy gob of his flapping. You are just a controversial **** who has to go against anything that anyone says just for the sake of it. Now **** off back under your stone you antipodean arsewipe ... Arfa Stop beating around the bush Arfa, tell us how you really feel. Eric |
#11
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Valve amps and microcontrollers
wrote in message ... On Sun, 15 Mar 2015 12:16:47 -0000, "Arfa Daily" wrote: ** My god you are a ****ing tedious ****wit. When I see some of this stuff, I can't help but think that it is design for the sake of the designer's ego. ** Lucky your mad ideas are not anybody's concern. Lucky I'm not just mad, ** Right, you are an arsehole and a pommy pig too. And you, as ever Philip, are a dopey **** who just can't stop that mealy gob of his flapping. You are just a controversial **** who has to go against anything that anyone says just for the sake of it. Now **** off back under your stone you antipodean arsewipe ... Arfa Stop beating around the bush Arfa, tell us how you really feel. Eric d:-) Arfa |
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