Carver C4000 Preamp Help....!

nadude98

nadude98

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Help!!! I went to play an album last night and I noticed something wasn't right with the system. It had been fine last time I used it but the sound was not right and I had no right channel.. I had to turn it up too much. It was just off! Well after playing around with it I realized what I had done. I ran a line from tape monitor out to my subwoofer but didn't unplug the one from my surround sound receiver. I forgot about it and later I turned on my surround sound to watch tv and the preamp was still on. I must have sent a signal into it.

Symptoms on the preamp are no right channel, a pop whenever I push the auto-correlator button, sonic holography or peak unlimiter buttons. If I hit mono I have audio out of both speakers. It doesn't matter what source I use. I replaced IC1 and IC2 on the tone amp board and I got rid of the pop but when I took it back to the man-cave and plugged it in I still had no right channel audio and then when I started testing the buttons again, the pop returned..
I've screwed something up but not sure where to even start.

Another painful lesson! I hope someone can help me.... :banghead:
 
orange

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Are you sure you have all the inputs and outputs back in the right places, don't have the right ch lines crossed?

If you have that many things to control, an audio switch box added to one tape monitor line would be a sound idea. You shouldn't have to rewire every time you need to add and subtract gear.

By using one of the monitor loops (you do have two, correct?) you can use the tape loops to send out to external AV stuff or bring them in for stereo (and use the AV thing to switch other audio sourced from video etc)...

I know it sounds silly but that's what you do when you love old stereo gear and their bastid AV stepchildren :)

It's like building Frankenstein's monster (but that's FRON-KEN-STEEN)...:shaking2:
 
nadude98

nadude98

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orange said:
Are you sure you have all the inputs and outputs back in the right places, don't have the right ch lines crossed?

If you have that many things to control, an audio switch box added to one tape monitor line would be a sound idea. You shouldn't have to rewire every time you need to add and subtract gear.

By using one of the monitor loops (you do have two, correct?) you can use the tape loops to send out to external AV stuff or bring them in for stereo (and use the AV thing to switch other audio sourced from video etc)...

I know it sounds silly but that's what you do when you love old stereo gear and their bastid AV stepchildren :)

It's like building Frankenstein's monster (but that's FRON-KEN-STEEN)...:shaking2:
Click to expand...
I was just testing something out... I still get some distortion when playing loud.. can't figure out if it's my amp, Magnepan's or what... Just the heavy bass and mainly the newer more compressed recordings... I have no way to test the amp under load and neither did the shop I had taken it to so they could look at the signal with a scope.
I need a scope and some 250 watt dummy loads.. Which I actually found at Michael Percy Audio but they are about $75 ea. http://percyaudio.com/Catalog.pdf

Actually I have two mains out, I should have been using the second, which I will do the next time if I get the preamp fixed. Then I would have volume control to the sub. I will also add a switch box when I'm ready to do it full time.. Like I said I didn't intend to leave it, just got distracted and I forgot to disconnect it.
 
grapplesaw

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Just a thought try cleaning the volume pot. I have had lots of problems with Carver getting grainy and was due to dust in the pot. Also check power supply transistors solder joints.
 
nadude98

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Well, on a good note. Out of all the gear that I picked up that need repair, the one I put off because of how difficult it would be was the Carver TFM-24. I plugged it into the variac and slowly turned up power. No issues so I hooked up an antenna and plugged in my headphones and tuned in a station. Lo and behold I heard music.. out of one channel. I played with the headphone jack and I had both channels. Tried out the bass and treble and when I turned either up left would decrease in volume and right would increase.. both controls. Took it apart and cleaned all the controls and everything worked as it should afterwards. Put it all back together and took it in and hooked it up to my turntable and the WOPL and I have tunes. I also notice it seems a lot more dynamic that the C4000 did... also don't have to turn up the volume like I did either.. Evidently the Carver has had issues for quite a while.. I believe it has not been right even when I got it back from a place out west...!

Good news is I have Music!!!

Bad is the C4000 needs a hospital!
 
nadude98

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Peak Unlimiter LED working all the time!

Well, I did some work on the 4000 last night, I replaced TL074 IC1 on phono board with an upgrade to OPA4227 and replaced the 4136's on the peak unlimiter board with the brown dog upgrade... because I had them. Also replace IC1 and IC2 on the tone amp board with upgrades, brown dog on IC2 and OPA2134 on IC1.

Now the preamp seems to be working now, however now the peak unlimiter led acts works just like I have the button pushed in all the time. I do noticed a difference in sound when I do push in the button so I think it's working as it should otherwise...

Anyone know what might be going on? I have gone through the schematic and I'm a little lost..
 
nadude98

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So I was reading Jason's Phase Linear P3600 thread and I'm wondering would the C4000 benefit from bypass caps on the upgraded opamps I put in? I also see where there are electrolyic bypass caps on the bottom of a couple of opamps that were already in there.. change to film?
 
laatsch55

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No electrolytics were used to bypass op-amps in Jason's 3600. You shoud bypass V+, V- to ground with Wima POLY-PRO .047uf...
 
laatsch55

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Wima makes a good 1uf poly, but I would ask Joe about the value. It may be doing more than bypassing at that value...
 
nadude98

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C7L and C7R on peak unlimiter board calls for 2.2uf 6.3v electrolytic cap. It is right in the signal path.. it had 4.7uf's in it originally.. one was a 50v and one was a 63v.. I can't find any info and I can't find a electrolytic any lower than 25v..
 
NavLinear

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laatsch55 said:
So what's your question?
Click to expand...
I believe that he's not sure what he should do.

Typically with capacitors you can up the voltage without compromising the circuit - changing the value is a different issue. I would suggest replacing the electrolytic capacitors with Wima because the capacitors you want to replace are in the signal path. I'll go out on a limb here but I'd guess that the caps you're replacing are radial so the spacing can be an issue with the Wima capacitors as the ones stocked by Mouser generally have short legs.
 
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