Amplifier troubleshooting, one channel weak - Page 3 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 3rd November 2010, 05:35 PM   #21
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Voltages are normally with respect to ground.
If the output is at zero volts DC and the output stage is drawing current (volt drop over the 0.47 ohm emitter resistors) then that 99% checks all is OK dc wise. You can check things like the constant current sources and calculate the values expected but low gain is more typical of an AC fault.
Is the sound OK... just lower in volume. Not lacking bass at all ? Might be worth linking points 36 and 38 (inputs to power amps) with a wire to be absolutely certain each channel is receiving the same signal, just to be 100% sure it really is a power amp problem.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 3rd November 2010, 07:03 PM   #22
JanErik is offline JanErik  Finland
diyAudio Member
 
Join Date: Aug 2010
Location: Vasa
Yes, both channels output stages are running around 100 mA measured on the .47R resistors. I tuned that as well as the outputs' offset to zero.

I have the signal connected directly to those points. There is an input (XP1, 5-pole DIN) on the back that goes directly to the power amp. And input signals are the same amplitude after C1 and C2.

I would say it is lacking a bit bass, but treble is low too. At 1 kHz, this channels unloaded output amplitude is around 1/3 of the other, on the scope. Otherwise undisturbed sinewave both loaded and unloaded.

Last edited by JanErik; 3rd November 2010 at 07:10 PM.
  Reply With Quote
Old 3rd November 2010, 07:20 PM   #23
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
So you have a 'scope

So don't overlook anything... check the input as measured on the junction of R5/C1 comparing for both channels.
Carefully while applying the sinewave (1khz) scope each end of the electroylitics in the signal path and confirm the same signal is on both ends. Lack of bass on the faulty channel points to a dried out cap. Not treble though. C5 the 120 pf worth checking it's not leaky and shunting input signal. Same for C11 (feedback network). Check resistors R48, R11 and R5 and R9 as these determine the gain. R48 and R11 would have to go low in value though to reduce gain... unlikely. C13 worth checking by bridging.
Have you scoped the output at the emitter resistors in case of problem from amp to sockets... don't overlook anything however unlikely.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 3rd November 2010, 07:37 PM   #24
JanErik is offline JanErik  Finland
diyAudio Member
 
Join Date: Aug 2010
Location: Vasa
I only have a soundcard scope but that should be enough, except that it does not show DC offset.

Yes, input signals are similar at C1/R5 and C2/R6 junctions.

I have measured on the cases (collectors) of the output transistors and they are similar.

And the output waveform is not distorted neither with nor without speakers connected. Just too low amplitude.

In the weekend I will have time to take a look at it again... Will also try 100 Hz and 10 kHz to see how it behaves with those.
  Reply With Quote
Old 3rd November 2010, 08:10 PM   #25
SPL db is offline SPL db  United States
diyAudio Member
 
Join Date: Sep 2004
Location: Omaha NE
Okay, stupid question time...

1. Have you checked the balance knob to make sure it is installed on the control correctly?

Meaning, if you move the control it's even on both sides?

Maybe the knob is off center.

2. Have you tried swapping the speaker inputs around to make sure it's not the speaker at fault?

Sorry if this has been answered already, I just jumped the gun and replied.

Scott
  Reply With Quote
Old 4th November 2010, 03:40 AM   #26
sregor is offline sregor  United States
diyAudio Member
 
Join Date: Jan 2006
Location: massachusetts
Gain is set by R48 and R7 + R1 parallel R2 on one channel, and R49 and R8 on the other. R2 is a trimmer to adjust the gains of the first channel, but shouldn't make this much difference. R8 and the R7 combination go through C4 and C3 100 uf caps, which may be dried up and causing the gain to go down. Try changing C3 or C4. (If you want to check there should be no signal on them if they are good). Unless I am misreading the circuit, and assuming the schematic is correct. Good luck with it.
__________________
Steve
  Reply With Quote
Old 4th November 2010, 06:53 AM   #27
JanErik is offline JanErik  Finland
diyAudio Member
 
Join Date: Aug 2010
Location: Vasa
Quote:
Originally Posted by SPL db View Post
Okay, stupid question time...

1. Have you checked the balance knob to make sure it is installed on the control correctly?

Meaning, if you move the control it's even on both sides?

Maybe the knob is off center.
The signal goes directly to the input capacitors. Scoped after them both channels still have the same amplitude.

Quote:
Originally Posted by SPL db View Post
2. Have you tried swapping the speaker inputs around to make sure it's not the speaker at fault?

Sorry if this has been answered already, I just jumped the gun and replied.

Scott
Yes, and seen on a scope the output signal is lower on one channel both with and without speaker connected.
  Reply With Quote
Old 4th November 2010, 05:45 PM   #28
diyAudio Member
 
astankov's Avatar
 
Join Date: Dec 2009
Location: Pernik
"Regulkrdva usilenija" means roughly Amplificaton Adjust
  Reply With Quote
Old 4th November 2010, 05:51 PM   #29
osscar is offline osscar  Latvia
diyAudio Member
 
osscar's Avatar
 
Join Date: May 2009
Location: Riga, LV
Hi -

here is link to schematic in djvu format.

http://www.rw6ase-dok1.narod.ru/arhi...u010instr.djvu


and there info about odissei and other soviet amps (in russian, but with pictures )

Стереофонический усилитель ''Одиссей У-010 стерео''.

oh, sorry - you have it. my mistake.
__________________
If time is money then I'm out of time
  Reply With Quote
Old 11th December 2010, 02:48 PM   #30
JanErik is offline JanErik  Finland
diyAudio Member
 
Join Date: Aug 2010
Location: Vasa
Got it fixed. Replaced C4 and C14, then scoped and started wondering... wasn't it this channel that was weak? Then replaced C3 and C13 (equal on the other channel) and now both are equal.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Carver M4.0t with weak channel sjdemark Solid State 13 25th June 2014 11:18 AM
Ideas on weak left channel with static? matt82609 Tubelab 4 13th June 2010 07:28 PM
Weak sound on L channel - Carver TFM 45 power amplifier rontay Solid State 0 4th April 2008 08:54 PM
Heathkit Ar-15 one channel weak ar15guy Solid State 0 27th March 2008 01:54 PM
NAD 3240PE VERY weak right channel danter Solid State 1 14th January 2008 02:43 PM


New To Site? Need Help?

All times are GMT. The time now is 11:09 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2