Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

Help to fix C-Audio RA3000 Amplifier
Help to fix C-Audio RA3000 Amplifier
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 26th November 2008, 12:15 PM   #31
AudioSystemsEng is offline AudioSystemsEng  England
diyAudio Member
 
Join Date: Dec 2007
Hi Lee,

I'm finally back in the workshop with this naughty RA3000.
To Refresh you, this one seems to be slew rate limiting.
Both channels behave identically 80V and 100V rails are good.
feeding with a 100Hz sine wave i get full amplitude sine wave out of it (with or without load).
As I increase the frequency, the response rolls off at about 200Hz !
If I increase the signal amplitude, I get a near perfect Triangle suggesting there is some integration going on somewhere.

Last time I was in the amp, I replaced a few of the small electrolytics (suspecting the C56/R98 filter on the feedback line). I also replaced C54/C60 and C55 while i was in there for no real reason except that they might've dried out.

I have tested the signal between the level pots / Input buffer, and the fault is definately somewhere after that.

Any ideas ?
regards,
jonathan
  Reply With Quote
Old 2nd February 2009, 09:58 PM   #32
kevvywevvywoo is offline kevvywevvywoo  United Kingdom
diyAudio Member
 
Join Date: Aug 2008
Does anyone on this thread know much about the TR850? I'm having a merry dance with a faulty one here. It's elderly but would be a shame to scrap it as it has had a few famous users ;-)
  Reply With Quote
Old 2nd February 2009, 10:09 PM   #33
AudioSystemsEng is offline AudioSystemsEng  England
diyAudio Member
 
Join Date: Dec 2007
ha ! - you again ;-)

Lee is the man for that.. he used to work in c-audio tech. but i don't know if he's reading this board - his number is on here somwhere.


i have cct. layouts somewhere, but there were several revisions.
the ones i had didn't work very well and had to go back for mods.
  Reply With Quote
Old 3rd February 2009, 06:20 PM   #34
kevvywevvywoo is offline kevvywevvywoo  United Kingdom
diyAudio Member
 
Join Date: Aug 2008
Yeah I did briefly exchange emails with Lee but then the thread seemed to go cold, I guess he's a busy guy trying to make a living like all of us!
  Reply With Quote
Old 3rd February 2009, 06:59 PM   #35
AudioSystemsEng is offline AudioSystemsEng  England
diyAudio Member
 
Join Date: Dec 2007
yeah - i haven't tried calling him because i guess he must be busy - i've got this ra-3 with a bizzare fault.

just out of interest, what problems are you having with your TR ?

i think one of the revisions was the addition of a resistor in the base of each output device... but we're talking about 15 years ago.

j
  Reply With Quote
Old 5th February 2009, 06:15 PM   #36
kevvywevvywoo is offline kevvywevvywoo  United Kingdom
diyAudio Member
 
Join Date: Aug 2008
First of all there's a few non-matched output transistors fitted from a previous repair. One channel appears heavily repaired and has a 200mV output offset compared to the working side, the offset pot runs out of room before it's gone below 150mV. Secondly, when you put it into standby (a dedicated switch) the relays drop out then after a few seconds start to buzz, getting louder till eventually they come back in again! The standby circuit has had alot of components changed and bits bodged in here and there by the phantom dabbler.
  Reply With Quote
Old 5th February 2009, 06:35 PM   #37
AudioSystemsEng is offline AudioSystemsEng  England
diyAudio Member
 
Join Date: Dec 2007
Wow ! - I hate it when they let the monkeys play with the goods !

sometimes... and i only do this with my own stock (not customer's amps), I completely strip an amp down and turn it into a 'kit', removing all transistors, and one end of all diodes. This leaves an RC network on the PCB which can be meter-tested.
then i test the transistors off board, and re-build the amp.
very time consuming... did you know an EV P1200 has over 100 transistors ?
haha !

In your case, i'd definately test all the output devices out off the board.
and i'd pull the bias ladder apart and test the components off board too.

I'm not due back to my workshop for a few weeks, but i'll dig out the schematics for you if it helps.

The ones we had seemed to have a badly designed thermal control system... even if the amps were idling, the multicolour LED would cycle through green-red-green - often within a 10 second period - the cooling fans ramped up and down accordingly.
  Reply With Quote
Old 14th November 2010, 07:01 PM   #38
AudioSystemsEng is offline AudioSystemsEng  England
diyAudio Member
 
Join Date: Dec 2007
Default Weird RA3000 behaviour

Quote:
Originally Posted by AudioSystemsEng View Post
Hi Lee / anyone ?

I'm back in the workshop, after sorting out an RA3001 i picked up on eblag, i decided to have another look at this RA3000.

To Refresh you, this one seems to be slew rate limiting.
Both channels behave identically 80V and 100V rails are good.
Feeding with a 100Hz sine wave i get full amplitude sine wave out of it (with or without load).
As I increase the frequency, the response rolls off at about 200Hz !
If I increase the signal amplitude, I get a near perfect Triangle suggesting there is some integration going on somewhere.

Last time I was in the amp, I replaced a few of the small electrolytics (suspecting the C56/R98 filter on the feedback line). I also replaced C54/C60 and C55 while i was in there for no real reason except that they might've dried out.

This time, i injected the test signal directly into the 1k Power amp input resistor. (with the preceding circuitry dis connected) I also removed the drive limiting zeners and checked that the 6v2 zeners in the phase-splitter had the correct voltage across them.

I mentioned that the problem seems to be slew limiting / lack of drive to the mosfets. Tests today seem to confirm this, as increasing the input amplitude at frequencies above 1kHz has no effect on the output amplitude.

Any ideas ?
regards,
jonathan
  Reply With Quote
Old 14th November 2010, 07:02 PM   #39
AudioSystemsEng is offline AudioSystemsEng  England
diyAudio Member
 
Join Date: Dec 2007
actually.. that wasn't all meant to be a quote :-/
  Reply With Quote
Old 2nd October 2011, 11:57 AM   #40
noizyboy is offline noizyboy  United Kingdom
diyAudio Member
 
Join Date: Aug 2011
Dear sir, please forgive me for interupting in this discussion, only I too have an RA3000 which I aquired with the softstart circuit disconnected also the LED boards missing. The amp works fine on both channels but I would like to re-connect the softstart circuit. I am reading these posts to find a solution to my amp shortcommings. Please could anyone help with a sketch of the softstart circuit sent to me?

Noizyboy
  Reply With Quote

Reply


Help to fix C-Audio RA3000 AmplifierHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Schematic: Audio Innovations, The first audio amplifier maartentje Tubes / Valves 28 12th July 2016 12:41 PM
Help to fix C-Audio RA3000 Amp Kevin.Frost Solid State 10 15th November 2007 05:31 PM
Audio Amplifier wkahc Introductions 1 31st August 2007 06:01 PM
Audio amplifier Darksog Solid State 26 18th January 2006 02:17 AM
Audio Amplifier Help pls silverferro Everything Else 0 26th August 2004 10:15 AM


New To Site? Need Help?

All times are GMT. The time now is 03:00 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki