Behringer A500 power amp problem, please help? - 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 14th December 2009, 12:12 PM   #21
diyAudio Member
 
Join Date: Feb 2008
According to the schematic it is 10u/50V. What would I win by putting a 100V-capacitor on the input? In my head there is just about 2V there.

Best regards,

/Bo
  Reply With Quote
Old 14th December 2009, 03:09 PM   #22
KISS is offline KISS  United States
diyAudio Member
 
Join Date: Jan 2007
True. The key is it should be a non-polarized one and probably isn't. 2x the power supply rail of the OP amp. 50 V is a good number. Usually the higher the voltage, the better the reliability. The lower the voltage the better the ESR (Effective Series Resistance)

Neither matter much in that area. If it does turn out to be that cap, you might replace the other one.
  Reply With Quote
Old 14th December 2009, 03:31 PM   #23
diyAudio Member
 
Join Date: Feb 2008
I don't have any non-polarized ones to try with. How about 2 22u/50V back to back?

Best regards,

/Bo
  Reply With Quote
Old 14th December 2009, 03:49 PM   #24
KISS is offline KISS  United States
diyAudio Member
 
Join Date: Jan 2007
Use a polarized one to test. Check the other channel for a band or a marking for polarity.

I've seen a lot of amps that used polarized caps there and they fail eventually. Typically I saw 1 uf electrolytic caps when they should have been metalized polyester which is NP.

What really should go in there is a 10 uf 63 V metalized polyester cap. Digikey has them for about $4.50 each. I did't think they made them that high.
  Reply With Quote
Old 14th December 2009, 04:03 PM   #25
diyAudio Member
 
Join Date: Feb 2008
OK. I'll start with the polarized test and work from there.

I can get metalized polyester from elfa.se:

Click the image to open in full size.

10u/63V is about $3. But it's nearly an inch long, so it probably won't fit.

Best regards,

/Bo
  Reply With Quote
Old 14th December 2009, 09:48 PM   #26
diyAudio Member
 
Join Date: Feb 2008
Inspection shows that C11 is definately a bipolar (non-polarized) eletrolytic. I really doubt a 50V lytic on the input would fail. It's not possible to desolder and resolder without disassembling the cooling fins, so it's a bit of a job.

Best regards,

/Bo
  Reply With Quote
Old 16th December 2009, 01:41 PM   #27
diyAudio Member
 
Join Date: Feb 2008
I dismounted Channel A completely from the cooling fins. I will now be able to reach all solder points on this channel.

Where do you suggest I start? I have never done any troubleshooting before (apart from my LYNX amp, which blew up a couple of times). I have scope, signal generator, multimeter and schematics.

The problem again: As I turn volume up, noise is immediately present at the output. When volume knob reaches a certain point, output increases by itself, clipping occurs (visible at the led on the PCB as well as the indicator on the front), the circuit resets, then starts again. It's a sort of slow oscillation.

Any hint is obviously extremely welcome!

Best regards,

/Bo
  Reply With Quote
Old 2nd January 2010, 10:51 PM   #28
diyAudio Member
 
Join Date: Feb 2008
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
  Reply With Quote
Old 2nd October 2010, 04:29 PM   #29
KP11520 is offline KP11520  United States
diyAudio Member
 
KP11520's Avatar
 
Join Date: Apr 2007
Hi All,

My guitar teacher brought his A500 over for me to look at, as his A500 has one normal channel (2 or Right) and one channel (1 or Left) that is faint and doesn't appear (by listening) to be distorting but with no bass. Both Gain Pots are at max.

Although I have been visiting here over the years, I might need a little hand holding. So can anyone make suggestions as where to look. My only Test Equipment is a nice DMM (Agilent U1242A).

I checked all the mechanical things like the jacks, etc. and that all seems intact.

Also any cheap and easy mods that improve it would be appreciated too.

Thanks!

Regards//KP
__________________
If Wile E. Coyote had enough money to buy all that ACME ****, why didn't he just buy dinner?
  Reply With Quote
Old 5th October 2010, 02:45 PM   #30
KP11520 is offline KP11520  United States
diyAudio Member
 
KP11520's Avatar
 
Join Date: Apr 2007
Bump

Quote:
Originally Posted by KP11520 View Post
Hi All,

My guitar teacher brought his A500 over for me to look at, as his A500 has one normal channel (2 or Right) and one channel (1 or Left) that is faint and doesn't appear (by listening) to be distorting but with no bass. Both Gain Pots are at max.

Although I have been visiting here over the years, I might need a little hand holding. So can anyone make suggestions as where to look. My only Test Equipment is a nice DMM (Agilent U1242A).

I checked all the mechanical things like the jacks, etc. and that all seems intact.

Also any cheap and easy mods that improve it would be appreciated too.

Thanks!

Regards//KP
__________________
If Wile E. Coyote had enough money to buy all that ACME ****, why didn't he just buy dinner?
  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 183 11th December 2014 05:00 AM
Blown power transistor SAP15 on a Cambridge A500 jmillerdoc Solid State 8 3rd April 2009 01:13 AM
Phonic Max250 or Behringer A500 for speakers 93db?? Brit01 Solid State 13 29th July 2008 08:54 PM
cambridge audio a500 amp problem tim0850 Solid State 3 1st March 2005 09:13 PM


New To Site? Need Help?

All times are GMT. The time now is 09:47 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