Bypassing tone switch on Rotel RA-931 and RA-930AX - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 9th June 2012, 10:59 AM   #1
lars667 is offline lars667  Norway
diyAudio Member
Join Date: Nov 2007
Default Bypassing tone switch on Rotel RA-931 and RA-930AX

Hi there.

I've got two amps with the problem that one of the channels drops out/crackles after playing for a while. This goes for all inputs and both speakers and headphones. I've read that I should try bypassing the tone bypass switch circuit by doing this (quote from another member here, don't remember who):

For the left channel : cut J62 and J69. Link from the north end of J69 to the north end of J62.

For the right : cut J66 and J37. Link from J66 E to J37 N.
Now, I've located all the jumpers apart from the J69, which seems to be gone on both of my boards. It looks like it should be behind/underneath C515, but there's nothing. Should I then just make a jumper between the hole slightly north of C515 to J62N?

I'd appreciate any input, as I can't figure it out for sure. I have found schematics for the circuit boards af004111a (ra-931) and af004111 (ra-930ax), however my ra-931 uses af004111-b.

Please have a look at the schematics here if you would be so kind:
RA-930AX and RA-931

  Reply With Quote
Old 9th June 2012, 11:47 AM   #2
diyAudio Member
east electronics's Avatar
Join Date: Jan 2006
Location: Athens GREECE
From your sayings i guess someone with low experience in things like that ...but i might be wrong .

It could be wise to clean the all amplifier first switches and pots before start messing with it ...

Tone switch might also be bypassed in other ways but still i recon that you start from there ....
  Reply With Quote
Old 9th June 2012, 11:55 AM   #3
lars667 is offline lars667  Norway
diyAudio Member
Join Date: Nov 2007
Yes, I've cleaned all switches etc. earlier on the RA-931, which I will try to fix first. I have earlier built a small guitar amplifier, a couple of effect pedals etc., but only from write-ups. I lack a bit in the theoretical department, and am not very experienced no.

I will be changing power amp electrolytics etc. too, but I reckon those should not affect the sound of the headphone output. Therefore I've concluded that something's wrong in the preamp section, and have heard of this tone switch being a weakness.

I'd be grateful for any writeups on how to bypass the tone circuit on this particular amp, but will try the first method on the ra-930ax, since I've got two amps anyway.
  Reply With Quote
Old 9th June 2012, 01:06 PM   #4
diyAudio Member
Join Date: Mar 2001
Location: Brazil
Bypassing a tone section is relatively easy and it's already provided in the Rotel, with the S3 tone switch.

You can choose going through the Bass and Treble stage or not. Maybe that switch became noisy.

You may try a new bypass, directly wiring from before C515 to before C601, where you would have to cut the pcb track. Same thing on the other channel.
  Reply With Quote
Old 9th June 2012, 08:51 PM   #5
lars667 is offline lars667  Norway
diyAudio Member
Join Date: Nov 2007
Hm, my point was to bypass the tone bypass, so to speak, as to always include the tone section.

However, the mod I mentioned didn't seem to work, or at least didn't solve my problem. After the mod, I've got sound on the left channel, but no sound on the right.
  Reply With Quote
Old 9th June 2012, 09:20 PM   #6
lars667 is offline lars667  Norway
diyAudio Member
Join Date: Nov 2007
I was wrong. Actually, the amp works on both channels now, however the tone controls are out of the circuit. And when I look on the original advice, that is exactly what the mod did. Not exactly sure if that's what I wanted, though.
  Reply With Quote
Old 10th June 2012, 03:39 PM   #7
lars667 is offline lars667  Norway
diyAudio Member
Join Date: Nov 2007
I put the tone controls back into the circuit, and now the RA-931 works. I also cleaned the pots more thoroughly. It actually seems to be working, and has been working without problems for a couple of hours.

Also, I haven't had the problem recurring on the RA-930AX, which I only cleaned. Haven't tested that long yet, though. Difficult to know for sure with intermittent faults like this!

I will report how it goes.
  Reply With Quote


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
rotel ra-930ax repare. fozy_50 Solid State 2 17th February 2011 01:23 PM
Rotel Ra-931 argonrepublic Solid State 3 23rd June 2009 06:43 AM
Rotel RA 931 argonrepublic Chip Amps 0 20th April 2009 01:26 AM
Rotel RA-931 problem njholland Solid State 3 16th July 2006 04:01 PM
Rotel RA-931 Transformer captaintact Solid State 1 13th July 2005 08:42 AM

New To Site? Need Help?

All times are GMT. The time now is 05:03 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2