Old school coustic amp (DR 514 ) 4 channel amp need info on DC (offset )

Tony7

Member
2016-03-22 10:32 pm
just got this Coustic Design Reference Amp 514-DR opened the amp and nothing looks bad all Psu and output fets are good did a full recap on it check the rails getting good steady voltage the DC(offset) is not bad i get 37]ma on right and 41]ma left amp runs great i see the bias pots how do i test or adjust them i have a 2 channel as well they claim too be a class"A amp it does sound better than my "alpine mvr340" class A-B any help or info would be helpful i can repair amps have some
Knowledge but just dont understand this amps circuit it use 16 IRF-530 N hexfet for channel outputs four per a channel and no op/amp's all surface mount devices for the drives and gates any one with knowledge on this that can shed some light on this type of circuit they used on these amps iv'e allways seen bipolar sets or pairs transistors or MOSFETs sets as output device's but not all N channel
And 4 irfz44n for the power supply rail voltage is 32 volts
 

Perry Babin

Member
Paid Member
2003-11-20 11:01 am
Louisiana
www.bcae1.com
I don't have the specs for the bias settings. If it's not causing any issues, leave it as is. The bias pots were dodgy in some of the Coustic amps and may go intermittent if you turn them. That could cause the amp to fail.

For other amps (non class A - whatever that means, it rarely means true class A), I set the bias like this:
http://www.bcae1.com/temp/ausettingbias.swf

The DC offset is subjective. Some see 25mv as the maximum. For others it's 50mv. I'd probably never chase it down for 50mv or less.