Two Noisy amps need repair. - diyAudio
Go Back   Home > Forums > General Interest > Car Audio

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 21st August 2009, 12:38 PM   #1
Luke352 is offline Luke352  Australia
diyAudio Member
 
Join Date: Jul 2006
Send a message via MSN to Luke352
Default Two Noisy amps need repair.

Hi Guys,

I currently have two old Coustic Design Reference amps a 505 and a 514, which I'd really like to be able to use in my current install, problem being they both have noise problems. When hooked up in the car or out of car to a seperate 12v Power Supply I'm getting a hissing noise and it's loud enough to be heard in the car even with the engine running. Now since I've tested these out of car that has basically outruled everything but the actual amps themselves.

Now I'm lead to believe that this kind of noise can sometime be caused by dead capacitors in the Power Supply something to do with ones related to noise filtration. Is this true, and is it the most likely cause? And is it case of just replacing all the Electrolytic caps throughout the amp, or just the ones throughout the Power Supply section or does it involve more then that?

Here are some links to pics on Ampguts , the 514 http://ampguts.realmofexcursion.com/...DR/inside1.jpg
the 505 http://ampguts.realmofexcursion.com/...DR/inside1.jpg

Thanks for any help.

Luke
  Reply With Quote
Old 21st August 2009, 09:42 PM   #2
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Replacing all of the electrolytics capacitors with the proper types/sizes/ratings would be a major job.

You stated that the noise was audible when the engine was running. In many vehicles, you can't tell if the engine is running or not so that doesn't tell us much.

Is the noise affected by the gain settings on the amp?

Is it affected by any of the other controls on the amp?
  Reply With Quote
Old 21st August 2009, 10:03 PM   #3
Luke352 is offline Luke352  Australia
diyAudio Member
 
Join Date: Jul 2006
Send a message via MSN to Luke352
The first thing I did after trying a few things in car was take it out and bring it inside to put on a test bench running of a 12V PSU and the noise is still there, so it has nothing to do with the car. My engine although not loud is definitely audible at idle.

Adjusting the gains does not appear to make have any effect that I can tell, weather they are at min, just of min, or cranked right up.

The only other controls are the Balanced Input OFF/ON switch as the amps has two RCA inputs per channel and also has a separate gain per channel. I'm using it in unbalanced configuration so I'm only using the + RCA inputs with the Balanced switch in the OFF position.

But what I did try was to make up some muting/shorting plugs and I tried the amp in unbalanced as well as balanced set-up, and the noise doesn't change, nor did the muting plugs make any difference.

These are old amps they were produced in the mid 90's, and they have been sitting around for at least a yr, probably much longer infact.

Last edited by Luke352; 21st August 2009 at 10:06 PM.
  Reply With Quote
Old 21st August 2009, 10:21 PM   #4
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Do you have an oscilloscope?

If not, what multimeter do you have?

If you set the multimeter to AC volts, do you read any voltage on the speaker terminals?

If so, how much?

If the meter isn't auto-ranging, set it to the lowest range.
  Reply With Quote
Old 22nd August 2009, 04:01 AM   #5
Luke352 is offline Luke352  Australia
diyAudio Member
 
Join Date: Jul 2006
Send a message via MSN to Luke352
No, no oscilloscope.

I just have a cheapie multimeter but it does do AC.

I'll try all this later, I'm just about to go back out and lay down another layer of fibreglass on my Midbass floor enclosures.

Thanks for the help.

Luke
  Reply With Quote
Old 22nd August 2009, 05:58 AM   #6
Luke352 is offline Luke352  Australia
diyAudio Member
 
Join Date: Jul 2006
Send a message via MSN to Luke352
OK so I hooked the amp up to my PSU and measured 0.1v AC on the speaker connections. It doesn't seem to stay constant it swings bak and forth from 0 to 0.1 but in saying that my DMM probably doesn't have very high resolution. It's only a very cheap one see here http://www.jaycar.com.au/productView...T&SUBCATID=546 .

I'm not sure if I should be seeing anything?

On a side note what DMM would you recommend, I should get a better one and I'll most likely buy one from here http://www.jaycar.com.au/productResults.asp?FORM=CAT is there any in that list you would recommend, though I'd like to not spend much more then $50.

EDIT: seems the second link doesn't work but if you select test equipment and then General DMM's you'll see the list I was looking at.

Last edited by Luke352; 22nd August 2009 at 06:00 AM.
  Reply With Quote
Old 22nd August 2009, 12:03 PM   #7
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
I can't suggest any of those meters because I've never worked with any of them. You would probably need a meter with good high frequency sensitivity for this. Even if you have a meter that can read high frequency AC, I don't know if it will work to troubleshoot these amps. It may require an oscilloscope.

Can you borrow a meter? If you could borrow something like the Fluke 87V, it would be able to measure the higher frequencies and has very high resolution.
  Reply With Quote
Old 22nd August 2009, 09:34 PM   #8
Luke352 is offline Luke352  Australia
diyAudio Member
 
Join Date: Jul 2006
Send a message via MSN to Luke352
OK,

I'll ask some of the I&E techs at work if they have any Multi's like that one, i'll also ring a local car audio shop I'm friendly with to see if they have an oscilloscope I can go in to use or borrow for a few days.

Does it have to be any particular type of O scope?


Thanks for all your help, it may take me a few days to track down the right testing equipment so I may not reply in here for a few days.

Luke
  Reply With Quote
Old 24th August 2009, 08:11 AM   #9
Luke352 is offline Luke352  Australia
diyAudio Member
 
Join Date: Jul 2006
Send a message via MSN to Luke352
Well I will be able to get use of an O scope one way or another, so what I'm I looking for and what settings do I need to use when I get access to one.

Thanks

Luke
  Reply With Quote
Old 24th August 2009, 01:53 PM   #10
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
You'll need to use the ground wire that connects to the end of the scope probe. It needs to be no longer than ~6-8". Keep it away from the transformers when looking for noise.

With...

* the amp powered up with no input signal

* the scope timebase set to ~2ms (or as far counter-clockwise as possible while maintaining a steady trace)

* the probe ground wire connected to a non-bridging speaker terminal

* the tip of the probe on the same point as above

1. How low do you have to set the vertical amp (v/div control) to have the trace on the scope to deflect 1 vertical division?

2. If it never deflects that far, how far does it deflect above/below the reference line at the lowest vertical amp setting?

3. If you move the tip of the probe to the various bridging speaker terminals, how low do you have to set the vertical amp to see a deflection of 1 vertical division?

You should move the ground wire to the non-bridging speaker terminal that's used (when the amp isn't bridged) with the bridging speaker terminal being tested.
  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
For Sale: Lot of 6 American-made car amps for parts/repair SixFoFalcon Swap Meet 0 22nd April 2009 07:54 PM
For those that repair amps:What brands or problems do you prefer to stay away from? spooney Car Audio 25 20th November 2007 10:02 PM
What is the best flux/rosin/colophony for car amps repair? valterdaw Car Audio 4 11th September 2006 12:09 AM
noisy noisy noisy noisy noisy tube dsavitsk Tubes / Valves 50 20th February 2006 04:07 PM
Pass' amps way too noisy? peranders Pass Labs 35 4th July 2002 03:11 AM


New To Site? Need Help?

All times are GMT. The time now is 05:28 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