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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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Intermittent dropouts on phono input
I'm in the middle of a multi-year project to digitize my vinyl collection and
I've got a reucrring problem that's driving me up a wall. I have a Dual CS 528 turntable hooked to a Pioneer SX-201 which is functioning as preamp. My homebrew PC (a dual-CPU 1 GHz Intel server board) sound card (a late-model low-end SoundBlaster) is wired to the tape in/out jacks. A cassette deck is connected to the CD inputs. Most of the time, the setup works fine. It's not audiophile quality by a long stretch, but it works well enough that I hear the music and not the technology. The problem is that without warning, one or the other channel will drop out partially or entirely, with a 60-cycle hum appearing noticeably (but not at full volume). If I pull and reinsert the turntable inputs, it goes back to normal, and pulling and reversing the turntable's power cord also clears it. Thinking that this looks like an intermittent ground loop, I took care to plug the amp, TT and the PC into the same (battery backed-up circuit of the) UPS. Didn't help. One other thing I noticed is that sometimes the signal will drop out when there is a spike on the line (like when the dehumidifier turns off) but I can't say I've noticed that since I put everything on the UPS. I have even replaced both the turntable and the amp and get the same problem. Over the course of the summer the setup was not giving me much trouble, but in the past couple of weeks I have difficulties several times a day. Now I'm wondering if there is some kind of diode effect somewhere that is causing a charge buildup, but at this point I'm just veering into wild speculation because I'm all out of ideas. /ff |
#2
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Intermittent dropouts on phono input
FearlessFerret wrote:
The problem is that without warning, one or the other channel will drop out partially or entirely, with a 60-cycle hum appearing noticeably (but not at full volume). If I pull and reinsert the turntable inputs, it goes back to normal, and pulling and reversing the turntable's power cord also clears it. I'm betting the ground connections on your turntable cables aren't good. Could be corrosion or intermittent cables. -- If John McCain gets the 2008 Republican Presidential nomination, my vote for President will be a write-in for Jiang Zemin. |
#3
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Intermittent dropouts on phono input
"FearlessFerret" wrote in message ... I'm in the middle of a multi-year project to digitize my vinyl collection and I've got a reucrring problem that's driving me up a wall. I have a Dual CS 528 turntable hooked to a Pioneer SX-201 which is functioning as preamp. My homebrew PC (a dual-CPU 1 GHz Intel server board) sound card (a late-model low-end SoundBlaster) is wired to the tape in/out jacks. A cassette deck is connected to the CD inputs. Most of the time, the setup works fine. It's not audiophile quality by a long stretch, but it works well enough that I hear the music and not the technology. The problem is that without warning, one or the other channel will drop out partially or entirely, with a 60-cycle hum appearing noticeably (but not at full volume). If I pull and reinsert the turntable inputs, it goes back to normal, and pulling and reversing the turntable's power cord also clears it. Thinking that this looks like an intermittent ground loop, I took care to plug the amp, TT and the PC into the same (battery backed-up circuit of the) UPS. Didn't help. One other thing I noticed is that sometimes the signal will drop out when there is a spike on the line (like when the dehumidifier turns off) but I can't say I've noticed that since I put everything on the UPS. I have even replaced both the turntable and the amp and get the same problem. Over the course of the summer the setup was not giving me much trouble, but in the past couple of weeks I have difficulties several times a day. Now I'm wondering if there is some kind of diode effect somewhere that is causing a charge buildup, but at this point I'm just veering into wild speculation because I'm all out of ideas. /ff Duals are notorious for output cables going bad. That's my guess. Especially the white and black pairs. Mark Z. |
#4
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Intermittent dropouts on phono input
FearlessFerret wrote:
I'm in the middle of a multi-year project to digitize my vinyl collection and I've got a reucrring problem that's driving me up a wall. I have a Dual CS 528 turntable hooked to a Pioneer SX-201 which is functioning as preamp. My homebrew PC (a dual-CPU 1 GHz Intel server board) sound card (a late-model low-end SoundBlaster) is wired to the tape in/out jacks. A cassette deck is connected to the CD inputs. Most of the time, the setup works fine. It's not audiophile quality by a long stretch, but it works well enough that I hear the music and not the technology. The problem is that without warning, one or the other channel will drop out partially or entirely, with a 60-cycle hum appearing noticeably (but not at full volume). If I pull and reinsert the turntable inputs, it goes back to normal, and pulling and reversing the turntable's power cord also clears it. Thinking that this looks like an intermittent ground loop, I took care to plug the amp, TT and the PC into the same (battery backed-up circuit of the) UPS. Didn't help. One other thing I noticed is that sometimes the signal will drop out when there is a spike on the line (like when the dehumidifier turns off) but I can't say I've noticed that since I put everything on the UPS. I have even replaced both the turntable and the amp and get the same problem. Over the course of the summer the setup was not giving me much trouble, but in the past couple of weeks I have difficulties several times a day. Now I'm wondering if there is some kind of diode effect somewhere that is causing a charge buildup, but at this point I'm just veering into wild speculation because I'm all out of ideas. /ff I had a similar problem on my Dual 505. It turned out to be tarnished contacts on the removable cartridge carrier. No amount of cleaning cured it for long so I solved it by pulling the loom through the arm a little and wiring directly onto the cartridge. HTH Ron(UK) -- Lune Valley Audio Public address system Hire, Sales, Repairs www.lunevalleyaudio.com |
#5
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Intermittent dropouts on phono input
Hello,
I have to agree with Mark Z., the most likely problem is the awful RCA cables that Dual used for years. If the turntable is one of the ones where there are RCA plugs at both ends, simply replace them. If they are soldered at the turntable, or have the slip on lugs, then you can change the RCA plugs, but be careful to get decent quality plugs (I like the Switchcraft 3502) and you have to do a good soldering job. Crimp or screw terminals will be problematic on phono signals. Cleaning head shell contacts might also be a good idea, and Dual headshells sometimes have awful crimps as well. I'd use isopropyl (rubbing) alcohol on a q-tip to clean the contacts. Regards, Tim Schwartz Bristol Electronics FearlessFerret wrote: I'm in the middle of a multi-year project to digitize my vinyl collection and I've got a reucrring problem that's driving me up a wall. I have a Dual CS 528 turntable hooked to a Pioneer SX-201 which is functioning as preamp. My homebrew PC (a dual-CPU 1 GHz Intel server board) sound card (a late-model low-end SoundBlaster) is wired to the tape in/out jacks. A cassette deck is connected to the CD inputs. Most of the time, the setup works fine. It's not audiophile quality by a long stretch, but it works well enough that I hear the music and not the technology. The problem is that without warning, one or the other channel will drop out partially or entirely, with a 60-cycle hum appearing noticeably (but not at full volume). If I pull and reinsert the turntable inputs, it goes back to normal, and pulling and reversing the turntable's power cord also clears it. Thinking that this looks like an intermittent ground loop, I took care to plug the amp, TT and the PC into the same (battery backed-up circuit of the) UPS. Didn't help. One other thing I noticed is that sometimes the signal will drop out when there is a spike on the line (like when the dehumidifier turns off) but I can't say I've noticed that since I put everything on the UPS. I have even replaced both the turntable and the amp and get the same problem. Over the course of the summer the setup was not giving me much trouble, but in the past couple of weeks I have difficulties several times a day. Now I'm wondering if there is some kind of diode effect somewhere that is causing a charge buildup, but at this point I'm just veering into wild speculation because I'm all out of ideas. /ff |
#6
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Intermittent dropouts on phono input
"FearlessFerret" bravely wrote to "All" (09 Oct 05 10:48:26)
--- on the heady topic of "Intermittent dropouts on phono input" Fe From: FearlessFerret Fe Xref: core-easynews sci.electronics.repair:344542 Fe I'm in the middle of a multi-year project to digitize my vinyl Fe collection and I've got a reucrring problem that's driving me up a Fe wall. Fe I have a Dual CS 528 turntable hooked to a Pioneer SX-201 which is Fe functioning as preamp. My homebrew PC (a dual-CPU 1 GHz Intel server Fe board) sound card (a late-model low-end SoundBlaster) is wired to the Fe tape in/out jacks. A cassette deck is connected to the CD inputs. Fe Most of the time, the setup works fine. It's not audiophile quality Fe by a long stretch, but it works well enough that I hear the music and Fe not the technology. Fe The problem is that without warning, one or the other channel will Fe drop out partially or entirely, with a 60-cycle hum appearing Fe noticeably (but not at full volume). If I pull and reinsert the Fe turntable inputs, it goes back to normal, and pulling and reversing Fe the turntable's power cord also clears it. Fe Thinking that this looks like an intermittent ground loop, I took care Fe to plug the amp, TT and the PC into the same (battery backed-up Fe circuit of the) UPS. Didn't help. Fe One other thing I noticed is that sometimes the signal will drop out Fe when there is a spike on the line (like when the dehumidifier turns Fe off) but I can't say I've noticed that since I put everything on the Fe UPS. I have even replaced both the turntable and the amp and get the Fe same problem. Fe Over the course of the summer the setup was not giving me much Fe trouble, but in the past couple of weeks I have difficulties several Fe times a day. Fe Now I'm wondering if there is some kind of diode effect somewhere that Fe is causing a charge buildup, but at this point I'm just veering into Fe wild speculation because I'm all out of ideas. From the description of the sudden mysterious hum behaviour it gets my antennas up for some type of parasitic oscillation. When dealing with parasitics, there has to be enough gain at some frequency. The stage with the most gain is probably the phono input and this narrows the search area. My theory is that the phono cable you are using adds just the right amount of stray capacitance to make the phono input oscillate at VHF. The quick fix is to add a small value resistor (100 ohms to 1K) in series with the input or a ferrite bead through the center conductor of the socket (or cable if impossible but closest to amp). However, the root cause of the hyper-sensitivity to parasitics may be a dried up decoupling electro in the receiver's phono preamp stage. Of course, this theory may be totally out to lunch and it really is simply a dirty connection or broken solder. A*s*i*m*o*v .... A stereo system is the altar to the god of music. |
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