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Help New TAC US 12A crossover distortion.
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Old 8th February 2008, 01:13 PM   #1
spirod is offline spirod  Australia
diyAudio Member
Join Date: Sep 2006
Default Help New TAC US 12A crossover distortion.

Anyone heard of TAC or Proffessional Amplifier Co?

I have just bought a Brand New TAC US 12A 400w x 2 amp on ebay.

Manufacturers link:

This amp is quite a beast, and has more than enough power to drive a pair of humble vifa 6.5" mtm's

I guess that is the problem. I am only planning on listening at normal sound levels. and this amp has quite high crossover distortion. Sounds like there is no biasing on the output devices at all.

Question is. (and very tempting). Should I have a peek inside and see if there are any biasing pots to adjust?
Does any one have a schematic to help decide?
Can any of you guys with PA equipment experience suggest the likely hood of there being any adjustments I can make?

I am trying to decide if i should risk opening up my new amp only one day old

any input would be great. (no pun intended)
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Old 9th February 2008, 04:34 PM   #2
spirod is offline spirod  Australia
diyAudio Member
Join Date: Sep 2006
FYI. In case anyone else has this amp,
I ended up opening the unit up and yes there is a biasing pot

I adjusted it so that it read 3.5 mV across one side of the power resistors on the output. Which is about 40mA total bias current in the output devices.
The crossover distortion is gone now
Also I would have to reccomend this amp to anyone thinking about a DIY power amp. for the price around $300 AU new on ebay, the unit is very good value, and would not be able to make one for that price.
highly reccomended.

That said, I do think my gain clone amp does sounds a little smoother, but never the less it will be getting replaced by the TAC as the G.C. cant quite drive my vifa 4ohm MTM's at full volume for long without the SPIKE kicking in.
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