W-Audio PSR-8A - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 June 2011, 08:19 PM   #1
bfisk is offline bfisk  United Kingdom
diyAudio Member
 
Join Date: Aug 2004
Location: London
Default W-Audio PSR-8A

Hi,

I'm trying to find a schematic for this model of active speaker amp. It has 2x TDA7294's one for the high range speaker and one for the low range.
I picked up three blown units (minus speakers) for one UK pound each at a junk sale and I want to use them for other projects. The faults vary from the chips actually blown apart to various caps blown. They look quite nice units with fan assisted heat sinks and overload compressors. I've searched the web but can only find the user manual which is useless.
I need to know what voltages are supplied for the + and - rails, probably somewhere around 30-40v I suspect.

Many thanks
Bob
  Reply With Quote
Old 21st June 2011, 06:34 PM   #2
diyAudio Member
 
Join Date: May 2008
It is rather the other way round, two TDA7294 for the low range and one for the high range. Up to 30 V is fine for 4 Ohm, up to 40 V for 8 Ohm. Since the two amps for the low range are probably BTL configured, each of them will see half the nominal speaker impedance which means 30 V are the safer choice.
__________________
If you've always done it like that, then it's probably wrong. (Henry Ford)
  Reply With Quote
Old 21st June 2011, 07:13 PM   #3
bfisk is offline bfisk  United Kingdom
diyAudio Member
 
Join Date: Aug 2004
Location: London
There are only two chips and the speaker leads are just marked high and low. There must be some active crossover circuitry built in to the small daughter board that also has the compressor limiter functions.
There is also an extra two pin socket on the board which is unmarked, it could be for a 12v supply to the fan but a schematic would make life much easier.

Bob
  Reply With Quote
Old 1st July 2011, 03:57 PM   #4
bfisk is offline bfisk  United Kingdom
diyAudio Member
 
Join Date: Aug 2004
Location: London
Having some success with repairing these.
One unit, the daughter board had a break between the top and bottom of the board on one of the supply lines at the connector. One output amp therefore had a full supply on the speaker connection. Luckily I was testing into dummy loads!

On all these units the manufacturers have used some gluey stuff to secure the power resistors. Being as these generate a fair bit of heat it turns the substance into a conductive brown film after time. I've been coming across this for years and it amazes me that manufacturers still use it?

The units also need a complete re-cap as they are all rated at 85c and many were dried up. One of the boards a couple had exploded. All replaced with 105c so they should be more reliable.
Lastly the mute and standby function is set by the supply voltage so anything much less than 30v leaves the chips muted. Had me going for a while.

Still would like a schematic if anyone has one.

Bob
  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
remains of Yamaha PSR 620 / 520 Bregg Instruments and Amps 2 14th December 2011 08:46 PM
2SK343 & 2SJ99 Audio Mosfets, 140V, 8A VS Parts 6 16th August 2010 09:26 AM
160v/8a Fob Power Supplies 50 10th December 2008 07:32 PM
YAMAHA keyboard PSR-500 elec972 Instruments and Amps 3 10th January 2008 02:45 AM
Wanted: chip in Yamaha PSR 220 Keyboard efex Parts 0 1st June 2004 11:58 PM


New To Site? Need Help?

All times are GMT. The time now is 06:17 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