XS 4300 Schematic or service manual

[mtxmow]

Hello everyone, first post on the site.
I picked up a XS 4300 in a pawnshop the other day and was testing the outputs AC voltage on my oscope and dmm. The outputs are putting out between 15.50 to 16.50 vac each before clipping with a 1khz test tone but there's about a volt difference between the 4 channels. I noticed on the board four trimmers. Does anyone know what they're for? Bias or balance controls?
DC offset is pretty low but again not the same on all four channels.

Also the Dale crossover DIP is 180K so that works out to 100hz crossover which is stock I believe.
Here's a good picture of one
:


Are there schematics or a service manual available?

thanks

[trickyricky]

PG never released schematics or service manuals. They are highly confidential, therefore making them impossible to have/share.



15.5-16.5 SOUND EXACTLY correct. So I wouldn't mess with any trimmers inside, especially if the dc offset is very low...below 30mv.



If your replacing the Rnets make sure you get the correct ones, if you install the wrong configuration then you will get loud static/hum noise and could damage the amp and your comps.

[mtxmow]

Well I measured the DC offset on the four different channels and came up with:
LF -3.35
Rf 5.00
LR 0.98
RR 16.55

I'm testing it using a little 3.0A 13.8vdc regulated PS I have.

Are these values normal on these amps? I debating whether or not to take it back to the pawnshop for a refund.

[trickyricky]

Is that dc? The numbers don't appear to be correct. Is the dmm set at milli volts?

[mtxmow]

I should of specified, yes those numbers are for dcmv.

[trickyricky]

That amp is good to go if you ask me, 0.016vdc on the RR is the highest and that still is not over 0.030.

Also keep in mind that 3amp power supply is only enough to power it up not to test it. As soon as you apply speakers/load and some music it will shut off due to the small power supply.

If you think you got a deal on it, then keep it no reason to return it unless you changed your mind and want something else.

[mtxmow]

I paid 50.00 out the door, so not a screaming deal.
Yeah, the little PS is just more convenient then pulling out amps out of my truck for testing with no load. Although this amp must pull a couple of amps just idling.
I'm wondering if the trimmers themselves are maybe a little dirty. And are they for bias or adjusting dc offset?

[trickyricky]

Am pretty sure they are for the bias not offset. So i wouldn't mess with them unless you had to replace the whole channel (repair). 50 bucks is not bad, would of been a killer deal if it was a 4600.

[mtxmow]

I snagged it because it just because it's an old school amp.


Is there any info or specs at all about setting the bias on the amps? It's hard to trace the PCB with the black mask on there.
I did measure the voltage drop across the 3 big grey resistors and two sets out of the four are different.


Here's an article about how replacing the bias trimmers improved the dc offset.
http://www.tnt-audio.com/clinica/bias_e.html

[mtxmow]

I snagged it because it just because it's an old school amp.


Is there any info or specs at all about setting the bias on the amps? It's hard to trace the PCB with the black mask on there.
I did measure the voltage drop across the 3 big grey resistors and two sets out of the four are different.


Here's an article about how replacing the bias trimmers improved the dc offset.
http://www.tnt-audio.com/clinica/bias_e.html

[trickyricky]

The thing is that these XS amps do not use the cheap crap pots....its sealed and of good quality (They are not premium top of the line, but they are great for their purpose). I suggest you leave them alone, don't even try to adjust the original settings.