Behringer A500 power amp problem, please help? - Page 4 - 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 27th October 2010, 02:00 AM   #31
diyAudio Member
 
MurphyUHF10's Avatar
 
Join Date: Oct 2010
Location: Melbourne
Quote:
Originally Posted by bomellberg View Post
Update:

Before Christmas I got some help from a Swedish forum, faktiskt.se. Together with two other guys I found out that the OPAMP on the input stage was faulty. The easy fix would have been to replace the faulty one and be happy.

Instead I found that you can easily bypass the entire input stage and volume knobs, by directing the input signal to the middle pin of the volume knob connector head. I drilled a hole for a new rca-plug on the back panel and routed this to the middle pin and ground.

This mod turns the A500 into a no-nonsense power amplifier, without "input level matching" and volume controls. I only have to solve a ground loop humming problem, but I think this is the way to go.

Some pictures:





I'll be back with more pictures of the complete solution once it's finished.

Best regards,

/Bo

How did you go with your mod??
Judging by the circuit diagram, if you direct the signal to the center pin on the volume control, you are still going through one of the Op amps (IC2)..

If you want to bypass the entire input side, you need to inject signal at junction of C19 & R65.. I'm just waiting for confirmation if this will work form another thread here (Behringer A500 as a DIY project)

I stuffed up the op amp replacement and I' wanting to do the same as you..

Cheers..
  Reply With Quote
Old 27th October 2010, 11:50 AM   #32
diyAudio Member
 
MurphyUHF10's Avatar
 
Join Date: Oct 2010
Location: Melbourne
Quote:
Originally Posted by MurphyUHF10 View Post
How did you go with your mod??
Judging by the circuit diagram, if you direct the signal to the center pin on the volume control, you are still going through one of the Op amps (IC2)..

If you want to bypass the entire input side, you need to inject signal at junction of C19 & R65.. I'm just waiting for confirmation if this will work form another thread here (Behringer A500 as a DIY project)

I stuffed up the op amp replacement and I'm wanting to do the same as you..

Cheers..
Bump for someone on the opposite side of the world..
  Reply With Quote
Old 3rd November 2010, 12:33 AM   #33
diyAudio Member
 
MurphyUHF10's Avatar
 
Join Date: Oct 2010
Location: Melbourne
Quote:
Originally Posted by bomellberg View Post
Update:

Before Christmas I got some help from a Swedish forum, faktiskt.se. Together with two other guys I found out that the OPAMP on the input stage was faulty. The easy fix would have been to replace the faulty one and be happy.

Instead I found that you can easily bypass the entire input stage and volume knobs, by directing the input signal to the middle pin of the volume knob connector head. I drilled a hole for a new rca-plug on the back panel and routed this to the middle pin and ground.

This mod turns the A500 into a no-nonsense power amplifier, without "input level matching" and volume controls. I only have to solve a ground loop humming problem, but I think this is the way to go.

Some pictures:

Click the image to open in full size.

Click the image to open in full size.

I'll be back with more pictures of the complete solution once it's finished.

Best regards,

/Bo
Hi there,

I also have just completed this mod..

Instead, I actually removed all components from the input stage and inject signal directly to pin 6 of IC2 & IC3 (see my diagram) using the volume socket (X6 & X14).. Because I removed all input I was able to use the vacted hole on the connector panel to screw in a new RCA socket.

Input_Bypassed.JPG

I kept a 20K resistor across pin 6 and ground, I'm not sure if I actually needed to? but I thought I would I just keep it as the 4K7 resistors shown in the circuit diagram aren't actually present..

First impression is that the amp now seems 'alive' and more bright. More detail between instruments..

But the amp is not as quiet as it once was!! There is quite a noticable hissing noise from the speakers when no sound is playing.. With sound on low you can still here hissing, but as you turn up the volume on the pre amp you cant here it anymore..

Any suggestions on how hissing has been introduced?
Any solutions to test and eliminate this hissing??

Cheers,
Murphy
  Reply With Quote
Old 7th December 2010, 07:54 AM   #34
diyAudio Member
 
Join Date: Feb 2008
That's great, and it is exactly what I did myself, although I didn't bother to desolder all of the surrounding components.

For clarity: I have added an extra RCA-input per channel. The signal goes to the middle pin of the volume socket, X6-2, shield goes to ground, X6-3. No 20K resistor is used in my case (volume knobs completely removed). I had a humming problem when I used both channels, but since I just use it in bridged mode for now, I'm not bothered by it.

I added a 10K-resistor between the new rca-shield and signal. I also added a 1K-resistor in series with the input signal:
Click the image to open in full size.

Another mod is the addition of a proper soft start:
Click the image to open in full size.

Regards,

/Bo
  Reply With Quote
Old 8th December 2010, 10:42 AM   #35
diyAudio Member
 
MurphyUHF10's Avatar
 
Join Date: Oct 2010
Location: Melbourne
Quote:
Originally Posted by bomellberg View Post
That's great, and it is exactly what I did myself, although I didn't bother to desolder all of the surrounding components.

For clarity: I have added an extra RCA-input per channel. The signal goes to the middle pin of the volume socket, X6-2, shield goes to ground, X6-3. No 20K resistor is used in my case (volume knobs completely removed). I had a humming problem when I used both channels, but since I just use it in bridged mode for now, I'm not bothered by it.

I added a 10K-resistor between the new rca-shield and signal. I also added a 1K-resistor in series with the input signal:
Click the image to open in full size.

Another mod is the addition of a proper soft start:
Click the image to open in full size.

Regards,

/Bo
Hi Bomellberg,

Thanks for getting back to this thread..

Yes, I have the exact same problem!! In stereo mode I get a loud buzzing from the speakers, but in bridged mono it's dead quiet!! I too use them in mono.. I injected the signal the same way as you, and I actually removed all unused components and connectors too.. I have noticed improved sound by replacing stock op-amp with opa2134's.. Also, I put a 20K resistor across pin2 and pin3 of volume input (just to keep the same value as stock unit when the volume is at max)

rca_input.jpg

On one of my A500's I had an interesting issue.. After my initial testing when I mounted heatsink back into case and screwed eveything together, i get a bad distortion, but if i separate the heat sinks from the amp chasis and leave the amp spread out (but still wired up) it sounds great!! So one of my amps I'm using it with case open and heat sinks separated from chasis,, weird??

btw, your attachments are not working??

Cheers..
Murphy
  Reply With Quote
Old 9th September 2012, 12:16 AM   #36
NicoB is offline NicoB  France
diyAudio Member
 
Join Date: Feb 2012
Hi

I made the modification like you ( removing input, inject X6-2, 10K-resistor between rca-shield and signal), but I have to add a 20k resistor in series with the input signal, else I have a powerfull ground loop (I thinks it is).
Shield is direct connect to case for ground, nothing connect in X6-3 or 1.
This resistor can alter hight frequencies ?

Even with this resistor, still have a little noise when no input sound.

I'm in bridged mod, I keep the volume B because if I remove it's look like I loose power of channel B, when you are in bridged mono, what do you do for Volume B ?

Thanks, and sorry for my English
  Reply With Quote
Old 20th January 2013, 01:30 PM   #37
tojoko is offline tojoko  Netherlands
diyAudio Member
 
Join Date: Feb 2009
Default Behringer A500

Hi
Just bought a A500 and wanted to use it as an amp for my Disub Woofer, so i need 2 channels, not bridged, i did a few mods, got rid of the pots, better in and output connectors, when i use one channel at the time, so i unplug the powersupply to one of the 2 boards, all is well, no hum no noise, good quality sound, as soon as i connect both boards, there is serious distortion at relatively low level on both channels, does anyone know a solution to this problem?
thankes for help,
  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
Behringer A500 as a DIY project derouineau Solid State 182 18th July 2014 01:13 PM
Blown power transistor SAP15 on a Cambridge A500 jmillerdoc Solid State 8 3rd April 2009 12:13 AM
Phonic Max250 or Behringer A500 for speakers 93db?? Brit01 Solid State 13 29th July 2008 07:54 PM
cambridge audio a500 amp problem tim0850 Solid State 3 1st March 2005 08:13 PM


New To Site? Need Help?

All times are GMT. The time now is 10:31 PM.


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