W-Audio PSR-8A

bfisk · 20th June 2011, 07:19 PM

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

pacificblue · 21st June 2011, 05:34 PM

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.

bfisk · 21st June 2011, 06:13 PM

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

bfisk · 1st July 2011, 02:57 PM

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

20th June 2011, 07:19 PM	#1
bfisk diyAudio Member Join Date: Aug 2004 Location: London	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

21st June 2011, 05:34 PM	#2
pacificblue 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)

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21st June 2011, 06:13 PM	#3
bfisk 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

1st July 2011, 02:57 PM	#4
bfisk 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

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