Well before going any further, i realized that the right board had extensive repairs done, but using the manual i checked for the bias and on my left channel it's within normal range, but the right i am reading double it's value, compared to my left channel, so should i put it at the same value as my left channel ? i am reading a bit over 30mv on r87 and r 49 comparec to 13mv on r87 and r49 on my left board....Anyways as usual a litle help is appreciated... Getting there....
Thanks...
Thanks...
Hi pjaneiro,
The bias is supposed to measure 3.4 mV across the two emitter resistors. You can stick one probe on each emitter terminal on the socket.
Please correct both bias currents post haste.
-Chris
The bias is supposed to measure 3.4 mV across the two emitter resistors. You can stick one probe on each emitter terminal on the socket.
Holy! Man is that ever high!
Okay, an idiot has been loose in your amplifier. That is almost 10X too high. That poor amplifier has put up with a lot plus whatever hacking has been done on the board. Just think. The bias is 150 mA on the high channel when it was designed to be 17 mA. A little off I'd say.
Please correct both bias currents post haste.
-Chris
Huh ?, the way i was mesuring the value is that i have my ground probe on the R87 and the positive probe on the top of R49 , am i doing this wrong ?, but either case my left channel looks pretty original, but my right one, had a lot of work done, resistors have been replaced (correct values) transistors have been replaced with equivalents, as i said the channel (sounds fine), but on the display and at hear you can notice a difference...
Ok my bias has been set equal on both channels, Thanks, i now have the same results on both channels, i've checked all the power ratings on all output transistors and both channels now match exactly, but i still have the issue, my right channel still plays louder, i even removed my input board and directly soldered my y connector to the volume pots, same effect, i am starting to think the guy who messed with the amp previously was on illegal substances most of the time, the solder joints are awfull on some resistors, i have redone just about everything, and yes without a scope i realise that i am shooting in the dark, could it be that some of the transistors that were replaced (not talking output ones) cause this ? i feel like going out and replacing them all (both boards) just to be sure i have the same from the same batch......
Thanks Anatech, and all of you helping me on this, I'am actually starting to enjoy the challenges these amps are giving me...
That Bob sure knew how make something great, but oh so complicated
Thanks...
Thanks Anatech, and all of you helping me on this, I'am actually starting to enjoy the challenges these amps are giving me...
That Bob sure knew how make something great, but oh so complicated
Thanks...
Hmmmmmm one channel louder than the other?? Didn't Carver used to put a "transconductance" pot in those? I remember some kind of pot like that that always got dirty and always made the gain go crazy. ...that and bad coupling caps. Is there a pot in addition to the bias pot in the amp sections?
Hi mrshow4u,
No coupling cap problems. There is the fact that heavy components + vibration = cracked joint(s).
Hi pjaneiro,
There is either an open cap in the feedback network or some incorrect resistor values. How much of a gain differance do you have? Are you using the front panel meters to measure this?
-Chris
It was a variable damping pot. They caused motorboating. The fix was to use a lower value pot and padding resistors. This amp does not use this feature. I mentioned it earlier.
No coupling cap problems. There is the fact that heavy components + vibration = cracked joint(s).
Hi pjaneiro,
There is either an open cap in the feedback network or some incorrect resistor values. How much of a gain differance do you have? Are you using the front panel meters to measure this?
-Chris
Hi pjaneiro,
You may be chasing ghosts now.
Input a sine wave, very boring but easy to measure. If you do not have a really good meter, use 400 Hz. Measure the two output voltages at various volumes. Both volume controls should be set at maximum.
Do not trust the front panel meters on any equipment. They are there as a rough guide. Even Vu meters are only really accurate around 0 Vu if they are calibrated.
-Chris
You may be chasing ghosts now.
Input a sine wave, very boring but easy to measure. If you do not have a really good meter, use 400 Hz. Measure the two output voltages at various volumes. Both volume controls should be set at maximum.
Do not trust the front panel meters on any equipment. They are there as a rough guide. Even Vu meters are only really accurate around 0 Vu if they are calibrated.
-Chris
Hi pjaneiro,
Try with no load first. There is no need to do this at high levels. You can connect a load later just to see the difference.
At 400 Hz and lowish levels, I can't see how this would be harmful to your amp. Try a level between 4 and 16 watts by the meters on the front panel. Run both channels through a "Y" connector and log the output voltages.
-Chris
Try with no load first. There is no need to do this at high levels. You can connect a load later just to see the difference.
At 400 Hz and lowish levels, I can't see how this would be harmful to your amp. Try a level between 4 and 16 watts by the meters on the front panel. Run both channels through a "Y" connector and log the output voltages.
-Chris
Just finished my testings, even at equal bias on both channels, the right one is still louder, i plugged in the voltmeter and at equal volume with a mono source on both channels the right channel has a higher value, not by much but enough to trigger the leds, i can even trigger the right channel to have two of it's leds light up when the left only has one, at that precise moment there is about 80mv difference between the channels, i don't want to give up on this one, but i do aknowledge that i need help, it's probably something very simple and stupid, as both channels have the same values on each output transistors, so i guess it's within the input gain part of amp board...
Thanks...
Thanks...
Check the T's for odd hfe specs?
Some one put in a substitute transistor on the reparied side of the amp with a higher HFE than the required transistor. Find it, it must be there. You may find an ECG cross reference/substitute book to be handy to check this. Compare left channel transistors to right channel transistors and list the variances here on the DIY. It sounds like one channel has too much gain and it is most noticable when the error is made in the pre section.
I may be right, I may be wrong but this has happened to me before working on previously serviced gear. If the work is sloppy usually the substitute transistors don't even "jive" with the require devices.
Cheers,
Shawn.
P.S. Working on opening some high bandwidth upload options!
Some one put in a substitute transistor on the reparied side of the amp with a higher HFE than the required transistor. Find it, it must be there. You may find an ECG cross reference/substitute book to be handy to check this. Compare left channel transistors to right channel transistors and list the variances here on the DIY. It sounds like one channel has too much gain and it is most noticable when the error is made in the pre section.
I may be right, I may be wrong but this has happened to me before working on previously serviced gear. If the work is sloppy usually the substitute transistors don't even "jive" with the require devices.
Cheers,
Shawn.
P.S. Working on opening some high bandwidth upload options!
Hi Shawn,
hFE will not make this difference. Op amp front end.
Component tolerance. Easily within range if you figure on 5% parts. If you convert the mV into dB I think the figure may turn out to be okay. We do need to know what the reference level was.
-Chris
hFE will not make this difference. Op amp front end.
Component tolerance. Easily within range if you figure on 5% parts. If you convert the mV into dB I think the figure may turn out to be okay. We do need to know what the reference level was.
Not even close. Burn them all. They are ...... the book of lies!
-Chris
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