Hi everybody,
Pleasee. I have this problem My pre amp, which is old classe dr6. The right channel is softer than the left channel. It is also less clearer and sharper. I have to turn the 'balance' knob to '3-o clock' in order to hear vocal at the center (between the speakers). What is the problem and how do I fix it? Thank you for helping.
Pleasee. I have this problem My pre amp, which is old classe dr6. The right channel is softer than the left channel. It is also less clearer and sharper. I have to turn the 'balance' knob to '3-o clock' in order to hear vocal at the center (between the speakers). What is the problem and how do I fix it? Thank you for helping.
debug procedure
I don't have a schematic of a dr6, and don't know what is in it, but here is a general debug procedure for balance. My PAS2 had a balance problem, so first I swapped tubes right for left. The soft channel was still right. If you have soldered in transistors, do this after the resistors and capacitors, described below. Then I measured the volume potentiometer resistance with a meter. Both sides measured the same at a couple of positions. Then, because it was over 25 years old, I replaced the electrolytic capacitor. Electrolytic capacitors dry up after a while, the seals leak the fluid out. Before doing this, if you have tubes, read the safety sticky thread at the top of the tube forum about not killing yourself with electricity, electrolytic capacitors over 25 V rating can kill you with the power unplugged. That helped hum a little but not the balance. If your preamp is transistor or IC based, you may have a lot of electrolytic capacitors, they are little aluminum cans, sometimes with a plastic wrapper.After 1967, some tantalum electrolytics look like peanut M&M candy. Early ones lasted less than 2 years. (Make sure you mark the plus on the pcb for electrolytic capacitors, if you replace them, they explode if installed backwards). (Cheap electrolytics don't last 25 years, they can start going bad in a year or two and some vendors sell unused outdated short life ones on auction websites. Buy 2000 hour up life electrolytics from a regular distributor so you don't replace them again). Then I unsoldered one leg of each resistor on the section that was unbalanced, the magnetic phono balance section, and measured them. One was 25% off, I replaced it, it only helped a little. I also replaced some carbon composition resistors at that time with metal film resistors, that helped the hiss a little but didn't help the balance. Then I replaced all the paper dielectric capacitors in the mag phono section, they were less than $15 and a capacitor meter would be over $100. That fixed the problem. One of the paper capacitors had the wax case burned through in 1961 when it was installed, and the builder had installed the burned part on the bottom where you couldn't see it. Didn't keep moisture from getting in and changing the capacitance value. I used plastic film capacitors, polyprophylene dielectric is supposed to be the best, but I also used polyethylene ones. Now the PAS2 sounds better than it ever did. Good luck on your preamp.
I don't have a schematic of a dr6, and don't know what is in it, but here is a general debug procedure for balance. My PAS2 had a balance problem, so first I swapped tubes right for left. The soft channel was still right. If you have soldered in transistors, do this after the resistors and capacitors, described below. Then I measured the volume potentiometer resistance with a meter. Both sides measured the same at a couple of positions. Then, because it was over 25 years old, I replaced the electrolytic capacitor. Electrolytic capacitors dry up after a while, the seals leak the fluid out. Before doing this, if you have tubes, read the safety sticky thread at the top of the tube forum about not killing yourself with electricity, electrolytic capacitors over 25 V rating can kill you with the power unplugged. That helped hum a little but not the balance. If your preamp is transistor or IC based, you may have a lot of electrolytic capacitors, they are little aluminum cans, sometimes with a plastic wrapper.After 1967, some tantalum electrolytics look like peanut M&M candy. Early ones lasted less than 2 years. (Make sure you mark the plus on the pcb for electrolytic capacitors, if you replace them, they explode if installed backwards). (Cheap electrolytics don't last 25 years, they can start going bad in a year or two and some vendors sell unused outdated short life ones on auction websites. Buy 2000 hour up life electrolytics from a regular distributor so you don't replace them again). Then I unsoldered one leg of each resistor on the section that was unbalanced, the magnetic phono balance section, and measured them. One was 25% off, I replaced it, it only helped a little. I also replaced some carbon composition resistors at that time with metal film resistors, that helped the hiss a little but didn't help the balance. Then I replaced all the paper dielectric capacitors in the mag phono section, they were less than $15 and a capacitor meter would be over $100. That fixed the problem. One of the paper capacitors had the wax case burned through in 1961 when it was installed, and the builder had installed the burned part on the bottom where you couldn't see it. Didn't keep moisture from getting in and changing the capacitance value. I used plastic film capacitors, polyprophylene dielectric is supposed to be the best, but I also used polyethylene ones. Now the PAS2 sounds better than it ever did. Good luck on your preamp.
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in picture 015.jpg, on the right top are the xlr outputs (top and the one below it) and besides these are the rca outputs. If I use the XLR, the difference in loudness is less noticeable....I don't know why. In picture 016.jpg, the black box on the left is the volume pot and the one besides it is the 'balance' pot.
You have a lot of electrolytic capacitors, some rated 100V, some rated 400V. This is pretty high voltage for a transistor amp, but can kill you just as dead as tubes. Read about making a capacitor discharging tool in the tube forum new user thread, and learn to measure the voltage (under 10v) before you replace them. 5 mf and 10 mf capacitors are usually electrolytic, I can't tell how big those yellow caps are, but they would have to be huge to be film dielectric (and long life). The line on one end is minus. The blue ones with the pinched end are definitely electrolyic, but the big ones are more likely to be power supply caps (and cause hum) than filter/coupling caps (that cause imbalance and poor sound). The little pinched end caps would be the first ones I would replace, they are probably in the signal path and probably electrolytic. Some of the .1's on the board have a plus on one end of the board, that is a dead giveaway of electrolytic. Replace with film dielectric(either end plus). Signal path coupling and filter caps, try to match the value and tolerance. Power supply caps (near the transformer) can be up to 35% bigger in value. Voltage should be the same or up to 25% higher on electrolytic caps. Higher voltage is okay on film caps, if it will fit.
The blue "RN55" and "RN60" devices are metal film resistors, probably.
The blue "RN55" and "RN60" devices are metal film resistors, probably.
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These are the ones which needs to replace first? These resistors probably need not change. Should I check the volume pot first?
Seems like a lot of capacitors to be replace. Should I change the transistors? Can't see what are they...hidden in the heat sink
capacitors are cheap
Capacitors are cheap, time of a repairman is expensive. If it is over twenty years old, replace all the electrolytic caps. I gave up on a sony TC250 tape deck I was using as a preamp, not because I couldn't get the parts, but because there were over 100 electrolytic caps in there that needed replacing. Your yellow Passd Audio caps are rated X/Y/Zv, Z is obviously voltage rating, X is probably value, Y is weird. Three slashes is unusual. I would suspect Y is tolerance. I would do the Passd Audio caps last, they may be film. Your circled electrolytics are the first pair I would replace. But if one electrolytic is drying out, they all are the same age. Cut the number of shipping charges you pay and order a bunch of them at once. But only change 2 parts at a time (pairs of identical ones) so that if you make a mistake, you don't have to buy an oscilloscope and debug that way to figure out what you did wrong.
Film resistors don't change much unless overheated, I wouldn't look at those until all electrolytic caps are changed. Measuring volume pot is a good idea, they wear out due to use.
Capacitors are cheap, time of a repairman is expensive. If it is over twenty years old, replace all the electrolytic caps. I gave up on a sony TC250 tape deck I was using as a preamp, not because I couldn't get the parts, but because there were over 100 electrolytic caps in there that needed replacing. Your yellow Passd Audio caps are rated X/Y/Zv, Z is obviously voltage rating, X is probably value, Y is weird. Three slashes is unusual. I would suspect Y is tolerance. I would do the Passd Audio caps last, they may be film. Your circled electrolytics are the first pair I would replace. But if one electrolytic is drying out, they all are the same age. Cut the number of shipping charges you pay and order a bunch of them at once. But only change 2 parts at a time (pairs of identical ones) so that if you make a mistake, you don't have to buy an oscilloscope and debug that way to figure out what you did wrong.
Film resistors don't change much unless overheated, I wouldn't look at those until all electrolytic caps are changed. Measuring volume pot is a good idea, they wear out due to use.
To test the volume pot, disconnect the middle terminal of both sides. Leave it at a level that you have balance problems. Measure resistance (ohms) from one end terminal the the middle one. If the two sides (using the same end terminal for each side) are about the same, then it is okay. Before resoldering the middle terminal, also measure the resistance from the other end terminals to the middle ones. Should also be about the same, +-5%.
If your yellow 5 mf capacitors are about 4 or 5 cm long, they are probably plastic film dielectric and most likely are not a problem. Electrolytic capacitors are the ones that go bad based on time. Concentrate on replacing electrolytic capacitors. How old is this device? Really good electrolytics last 20-25 years, really cheap ones less than a year, some are shipped bad from the factory. Your yellow capacitors look really expensive, so I don't expect cheap electrolytics.
Some of your capacitors show "400v" rating. This is pretty extreme for transistor circuits and may not be required. Measure the voltage of the power supply when turned on to make sure it is under 100 or so (the others are rated for). Then you can buy capacitors that are that voltage or what the old ones are rated at, which would be cheaper and smaller and easier to find than 400 V ones.
If your yellow 5 mf capacitors are about 4 or 5 cm long, they are probably plastic film dielectric and most likely are not a problem. Electrolytic capacitors are the ones that go bad based on time. Concentrate on replacing electrolytic capacitors. How old is this device? Really good electrolytics last 20-25 years, really cheap ones less than a year, some are shipped bad from the factory. Your yellow capacitors look really expensive, so I don't expect cheap electrolytics.
Some of your capacitors show "400v" rating. This is pretty extreme for transistor circuits and may not be required. Measure the voltage of the power supply when turned on to make sure it is under 100 or so (the others are rated for). Then you can buy capacitors that are that voltage or what the old ones are rated at, which would be cheaper and smaller and easier to find than 400 V ones.
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If it is an alps black beauty (volume pot) it may be finally entering failure mode. They can go like that.... and those long handled switches tend to go as well. They are miniatures, IIRC, but with very long handles. The long paddle is what gets them. If the switches, or any of them are board mounted, that might be it.
I have a vague recollection of the DR6 having such a similar failure mode...but my brain has not yet found the neural pathway that goes to the answer. Sorry.
I have a vague recollection of the DR6 having such a similar failure mode...but my brain has not yet found the neural pathway that goes to the answer. Sorry.
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The yellow caps are film - polypropylene if I'm not mistaken. The meaning of 5.0/10/100 is: 5.0uF, 10% tolerance, 100V. DO NOT replace these, at least until all the electrolytics (blue sleeved) are done. Indianajo is right to advise replacing these. 10 years is too old, even if they measure fine. Even bad quality guitar amps show an improvement if 10-year old electrolytics are renewed.
The Panasonic AM series audio electrolytics are very cheap (Farnell sells them) and will work for all the caps I can see in that picture. Any caps below 2.2uF (or 4.7uF) can be replaced by MKT or even better film types, if you are feeling more adventurous.
" You have a lot of electrolytic capacitors, some rated 100V, some rated 400V. This is pretty high voltage for a transistor amp, but can kill you just as dead as tubes. "
"Some of your capacitors show "400v" rating. This is pretty extreme for transistor circuits and may not be required. Measure the voltage of the power supply when turned on to make sure it is under 100 or so (the others are rated for). Then you can buy capacitors that are that voltage or what the old ones are rated at, which would be cheaper and smaller and easier to find than 400 V ones. "
I'm afraid you have rather missed the point here!
They are 400V rating NOT because that is necessary, but that is (was) all there is in that value. Very often true for small films from the age of tubes.
The OP should get a generator and 'scope and MEASURE the difference between the channels rather than the wholesale slaughter of all the caps!
"Some of your capacitors show "400v" rating. This is pretty extreme for transistor circuits and may not be required. Measure the voltage of the power supply when turned on to make sure it is under 100 or so (the others are rated for). Then you can buy capacitors that are that voltage or what the old ones are rated at, which would be cheaper and smaller and easier to find than 400 V ones. "
I'm afraid you have rather missed the point here!
They are 400V rating NOT because that is necessary, but that is (was) all there is in that value. Very often true for small films from the age of tubes.
The OP should get a generator and 'scope and MEASURE the difference between the channels rather than the wholesale slaughter of all the caps!
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