I have a Denon DCD-1500 on which I replaced the output op-amps. Soldered in 8 pin sockets so I could play with op-amp rolling and tried some opa2134s. But when I plugged it in to play, I got some upper register distortion. Basically it's a fuzzy upper end (e.g. piano parts on Diana Krall/"Peel me a grape"). Low end seems nice and clean. It also happens when I put back the original op-amps.
If I were to guess, the distortion sounds much more analog than digital. It almost sounds like distortion from too much gain or too high an input signal. Though with it applying only to higher frequencies, it could be a sampling problem? I don't have much experience with things digital.
The unit played nicely before the surgery. It sat open for a month or so on my bench while I got distracted by other work. For initial troubleshooting I've blown out dust and cleaned the laser lens. Tried a number of op-amps and RCA cables. Checked soldering with a magnifying glass - joints are good, no bridging - and cleaned with an electronics parts cleaner). All to no avail.
I have the service manual from hifi engine and have done some research online, but for the life of me just don't know where to look next. Digital sources are a black hole to me.
I'd be grateful for any suggestions of where to look for the problem.
If I were to guess, the distortion sounds much more analog than digital. It almost sounds like distortion from too much gain or too high an input signal. Though with it applying only to higher frequencies, it could be a sampling problem? I don't have much experience with things digital.
The unit played nicely before the surgery. It sat open for a month or so on my bench while I got distracted by other work. For initial troubleshooting I've blown out dust and cleaned the laser lens. Tried a number of op-amps and RCA cables. Checked soldering with a magnifying glass - joints are good, no bridging - and cleaned with an electronics parts cleaner). All to no avail.
I have the service manual from hifi engine and have done some research online, but for the life of me just don't know where to look next. Digital sources are a black hole to me.
I'd be grateful for any suggestions of where to look for the problem.
Back up
When doing DIY mods, it is always best to try one step at a time. This is especially important if you knowledge is limited. My advice is just that, back up and take out the sockets. Seems you have looked it over well enough to see any obvious problems. You will not be the first one to have unexplained problems!!!!!!
When doing DIY mods, it is always best to try one step at a time. This is especially important if you knowledge is limited. My advice is just that, back up and take out the sockets. Seems you have looked it over well enough to see any obvious problems. You will not be the first one to have unexplained problems!!!!!!
1. Clean the board arround the sockets with alcohol...
2. Install some film capacitors between each supply pin and ground (back of the board).
2. Install some film capacitors between each supply pin and ground (back of the board).
Thanks, both of you. I did clean the board but will add an alcohol cleaning. I've tested the socket joints and don't get any continuity between adjacent sockets (not sure if the circuit should provide some continuity what with feedback and the like...). I'm reluctant to remove the sockets except as a last resort b/c it just doesn't make sense to me that it's the cause...or if it is, it would seem to be damage to the board which would not be fixed by removing them.
In any case, I see no damage around the op-amps on the board with the possible exception of some exposed traces (tiny spots). May try to upload a clip later so you can hear the distortion. I'll also look at trying caps on the supply pins (I assume you mean both + and - supplies on both sockets). Though why would there be any introduced ripple when there wasn't before?
In any case, I see no damage around the op-amps on the board with the possible exception of some exposed traces (tiny spots). May try to upload a clip later so you can hear the distortion. I'll also look at trying caps on the supply pins (I assume you mean both + and - supplies on both sockets). Though why would there be any introduced ripple when there wasn't before?
If it sat open for a month it could have gathered a lot of contamination on/in the pickup.
First check has to be the RF (eye pattern). A marginal signal can give "distortion" of sorts as the signal is just on the point of being on the threshold of what will work and what wont. The noise is "like" that you might get holding a finger against the rotating CD and slowing it just enough to cause drop out...
If your sure it's in the analogue stages... and it doesn't really make sense... then again you have to scope it and see what's going on. A small cap (0.1uf etc) directly across the supply pins of the opamp (not on the socket or print) will prove beyond doubt that it is/isn't some weird stability or oscillation issue... and I just can't see that tbh.
First check has to be the RF (eye pattern). A marginal signal can give "distortion" of sorts as the signal is just on the point of being on the threshold of what will work and what wont. The noise is "like" that you might get holding a finger against the rotating CD and slowing it just enough to cause drop out...
If your sure it's in the analogue stages... and it doesn't really make sense... then again you have to scope it and see what's going on. A small cap (0.1uf etc) directly across the supply pins of the opamp (not on the socket or print) will prove beyond doubt that it is/isn't some weird stability or oscillation issue... and I just can't see that tbh.
Thanks, Mooly. I will try to clean it further first off. Re your other suggestions, I don't know what you mean by the RF eye pattern (though I've seen you mention it in other posts). If it's simple to explain, can you do so (including where to test it)? I have the service manual so should be able to locate specific points to test. If not, can you point me to a resource to learn about it? Something not too complicated if that's possible. 
As for the cap across the supply pins, do you just mean to touch the cap to the supply pins of the op amps (e.g. pins 4 and 7)? I assume while it's playing? Am I looking for the distortion to stop? Do I need to scope the output in that case? And is this better than capping from the supply pins to ground (sure sounds easier!)?
I have a scope but only know the most basic of ways to use it. It's an old analog scope, so I'm a bit limited in what I can do with it anyway...
As for the cap across the supply pins, do you just mean to touch the cap to the supply pins of the op amps (e.g. pins 4 and 7)? I assume while it's playing? Am I looking for the distortion to stop? Do I need to scope the output in that case? And is this better than capping from the supply pins to ground (sure sounds easier!)?
I have a scope but only know the most basic of ways to use it. It's an old analog scope, so I'm a bit limited in what I can do with it anyway...
It's safer to connect the two caps - one from each power pin to the ground.
I won't go into details, but connecting one cap between power pins is not that effective or indicated.
It's just easyer for some to do 🙂
I won't go into details, but connecting one cap between power pins is not that effective or indicated.
It's just easyer for some to do 🙂
1)Check & see if you still have both power supply rails functioning. Don't have the manual in front of me, but you should have + & -12 or 15v supply lines to the output stage. This era of Denons often had fusible resistors(low value metal oxides) just after or before the supply regulators, and one tiny slip with a tool or etc. could have popped one, and they rarely show visual signs of it, so you have to measure them.
2)If both supply rails are OK, next most likely thing is either defective output muting transsistors or a defect in the controlling voltage to them. Simplest thing is to simply remove them. They serve no good purpose anyway, but to much up the sound.
3)On the off chance that the grunge in the sound happens to correspond in any way to the rotation of the disc, you may have a sluggish platter/spindle motor. On the 1500, I believe it's a simple dc brush motor, in which case it is a simple matter to spray a healthy shot of SILICONE spray lubricant up into it, run it a bit & try it again. Silicone treatment often cures such platter motor problems permanently.
4)Check supply voltages to the dac chips. Unlikely the problem is there, but not inconceivable.
5)If it's none of the above, it's time to get out the oscilloscope.
2)If both supply rails are OK, next most likely thing is either defective output muting transsistors or a defect in the controlling voltage to them. Simplest thing is to simply remove them. They serve no good purpose anyway, but to much up the sound.
3)On the off chance that the grunge in the sound happens to correspond in any way to the rotation of the disc, you may have a sluggish platter/spindle motor. On the 1500, I believe it's a simple dc brush motor, in which case it is a simple matter to spray a healthy shot of SILICONE spray lubricant up into it, run it a bit & try it again. Silicone treatment often cures such platter motor problems permanently.
4)Check supply voltages to the dac chips. Unlikely the problem is there, but not inconceivable.
5)If it's none of the above, it's time to get out the oscilloscope.
I used to have DCD1500 actually, and it was a great player... but which is yours ?
Mine was this one,
Denon DCD-1500 | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine
The manual from this link is poor but the RF is the signal direct from the disc. I seem to remember is was available on a white open plug on the PCB (various test points). You'll soon find it and it must be around 1.2 volts peak to peak amplitude (use a x10 probe for better bandwidth).
Found it in the manual, page 19 TP102 pins 1 and 3 with a picture of what it should look like. That's all you are scoping, forget the other stuff shown on the page.
Mine was this one,
Denon DCD-1500 | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine
The manual from this link is poor but the RF is the signal direct from the disc. I seem to remember is was available on a white open plug on the PCB (various test points). You'll soon find it and it must be around 1.2 volts peak to peak amplitude (use a x10 probe for better bandwidth).
Found it in the manual, page 19 TP102 pins 1 and 3 with a picture of what it should look like. That's all you are scoping, forget the other stuff shown on the page.
This is some great info here, thanks. Mine is the DCD-1500 like yours Mooly - not the MkII version with the digital out. Oooooh, with the "double super linear converter"...who could ask for anything more?
Anyway, I'm currently pretty busy but have some time off soon so will clean it, test supplies (fusible resistors is definitely a possibility which I've read about elsewhere), lube it (if I can) and scope it. All your help is amazing and greatly appreciated. I hate tossing otherwise good equipment, and was enjoying the opportunity to play with modding it as a learning tool...that is if I don't fork it up first.
Anyway, I'm currently pretty busy but have some time off soon so will clean it, test supplies (fusible resistors is definitely a possibility which I've read about elsewhere), lube it (if I can) and scope it. All your help is amazing and greatly appreciated. I hate tossing otherwise good equipment, and was enjoying the opportunity to play with modding it as a learning tool...that is if I don't fork it up first.
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