my poor power amp... :-( - 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 20th August 2004, 10:17 AM   #1
diyAudio Member
 
Join Date: Jul 2004
Location: UK
Send a message via MSN to timfishy
Default my poor power amp... :-(

Hi everybody,
a few months ago i was thinking about building a power amp but i bought one for less than all the parts cost me so... you know how it goes.

Anyway, came home today from a party switched on the amp to hear a nice reasonably loud humming. Well actually its about music listening volume. I turned it off straight away and went and had a word with my brother and he said he hadnt had it up loud and i believe him because he payed halves with me.

Ive had the lid off and done some testing and the humming/buzzing is independent of the two level controls on the front, you can still play the music sort of behind it, my multimeter is showing 108Hz on the speaker outputs.

Im thinking power supply because of all the above.

I'll do some more testing.

I can also supply pictures.

any ideas?

Thanks,
Tim
  Reply With Quote
Old 20th August 2004, 12:11 PM   #2
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Sounds like broken rectifier or smoothing cap(s).
  Reply With Quote
Old 20th August 2004, 12:28 PM   #3
diyAudio Member
 
Join Date: Jul 2004
Location: UK
Send a message via MSN to timfishy
yeah, it sure is, measured DC voltages accross the two psu caps (all dissconected and out of the amp etc) and one of them had no volt and the other had 60V ish

What do you think could have killed it?

it also has no voltage on it so im not sure about ordering another one.
it says....

6800uF 80WV

any ideas? could it happen again?

Would i get any gains out of upgrading them while im here?
  Reply With Quote
Old 20th August 2004, 12:48 PM   #4
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
Measure the AC output of the transformer. Multiply that by 1.414. You need capacitors to withstand that sort of voltage. From the sound of it, you need 80-100V capacitors (the 100V ones are probably going to be the easiest to get).

What make/model amplifier is it ? Any chance of some internal pictures ?
  Reply With Quote
Old 20th August 2004, 01:00 PM   #5
diyAudio Member
 
Join Date: Sep 2003
Location: Illinois
I don't think I would believe your brother, my friend has a harmon/kardon cd player/tape player/preamp/amp shelf system (all seperate parts), and he cranks it pretty loud all the time and his started doing the same thing, a humm in the speaker. He did come up with a good way to fix it, just turn it louder.
  Reply With Quote
Old 20th August 2004, 02:10 PM   #6
diyAudio Member
 
Join Date: Jul 2004
Location: UK
Send a message via MSN to timfishy
yeah wacked a 4700uF 80v cap that i had lying around in and it seems fine. doesnt get warm and the hum has gone. I will buy a replacement that is the same as the previous one.

Yeah its a ProSound 1000w peak into 8 ohm
in a 2u rack mount case weighs a ton
i wasnt expecting to much from it but it has surprisingly good sound

its got a 1000VA transformer (wouldnt want to have to replace that!), 25A bridge rectifier some protection circuits, then on a separate board there is the amp, 16 large transistors on a fan cooled heatsink. level controls on the front and clip indicators etc. speakon outputs etc.

When i switch it on my computer UPS battery backup supply complains about the drop in power for about 1/2 a second on the ring main....

i'll get some pics for you when my brothers finshed with the camera

The fan is good for when you have a party but is annoying when you want to listen to music quietly so i made a controller circuit for it. The fan is off until a certain temperature then it kicks in when its needed. i still want to make a thermal cut-out with a couple of thermal switches so i cant blow it up.

tim
  Reply With Quote
Old 20th August 2004, 02:17 PM   #7
diyAudio Member
 
Join Date: Jul 2004
Location: UK
Send a message via MSN to timfishy
apparently its meant to be

2x400Wrms into 4 ohm but i dont really care too much, you dont need that sort of power in a house.

What has surprised me the most is i can play it so much louder than my old stereo and not even notice because it still sounds clear.

On my old stereo it actually sounded "loud" because it couldnt cope with it.
  Reply With Quote
Old 20th August 2004, 03:09 PM   #8
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
Might be best to replace both of them if one has popped - could be that the originals are from a faulty batch. 6800uF is a bit weedy for such a high power amplifier though, I would have expected at least 2x6800uF per rail.

I would check the bridge rectifiers. If there's a 1000VA transformer in there, i would hope there are two! (one per rail). They should be big 35A jobs bolted to the case. Make sure none of the diodes in the bridge are short.
  Reply With Quote
Old 20th August 2004, 09:37 PM   #9
diyAudio Member
 
Join Date: Jun 2004
Location: Knoxville
How old are these caps? Electrolitics break down with time. Check to see if the tops are bulged up. This can indicate one that is ready to blow.
  Reply With Quote
Old 21st August 2004, 09:53 AM   #10
diyAudio Member
 
Join Date: Jul 2004
Location: UK
Send a message via MSN to timfishy
yeah the bridge rectifier is a big metal one with 4 6.3mm (?) push on connectors. 2 are marked AC and the others are +ve and -ve. bolted to the case, not found it to get even warm yet though.
yeah i double checked it and its fine

no the caps were fine, we did some playing at college connecting caps up the wrong way round and over-voltaging them by about 2 times.... if you put them in a metal tube you can get some distance on them....

i was thinking last night... could i make a separate PCB with lots of caps in parrallel and then link it in with wires or would this introduce lots of noise?

I gather the capacitors smooth out the rectified AC but do they also supply that extra bit of power (quickly discharging) for the loud low frequency sounds? Or do they just have to suply enough power and not leave too much ripple?

Tim
  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
Poor Man's Strad peace brainerd Multi-Way 75 14th August 2012 07:53 PM
poor sound Mission Digital Source 2 25th November 2007 02:35 PM
Poor Quality ... virtu Analogue Source 17 15th June 2003 06:06 PM
(Poor) Box design AvoidTheLloyd Multi-Way 4 31st December 2001 03:39 PM


New To Site? Need Help?

All times are GMT. The time now is 06:21 AM.


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