HK 770 pwr amp input caps - Replacement suggestions

[crispycircuit]

I'm trying to squeeze a little improvement in sound out of this amp. The input cap is 100uf 10v electro bypassed by a .1uf 50vmylar. What would you recommend?

[jeffreybehr]

What's the load-resistor value?

[crispycircuit]

Input to caps then a 1K to 330pf to grd, then 34K to grd.

[anatech]

Hi Mr. crispy ,
The 100uF is overkill to begin with. But the more important point is that the input cap type will not affect the sound quality anywhere near what you might wish for - or expect.

My guess is that the input impedance is a bit less than 34K (transistor input impedance in parallel with the 34K resistor). Things that can really affect how a circuit sounds ranges from the PCB layout to some of the parts used. Even how closely certain parts are matched will affect how much distortion and sense of smoothness an amplifier may have. You may certainly try and experiment with the input capacitor. You may even find some improvement (try lower capacitance and a film type capacitor, like maybe a 10uF or so of the type used for crossovers). Don't discount the effect of older capacitors that need replacing though. If you replace those older capacitors with modern ones of a similar type (brand names are not important here), you may experience a large improvement in performance. Once it's working to spec again, you can play with other types.

HK tends to run everything hot inside the chassis, so expect the original smaller capacitors to need replacement. The main filter caps may be perfectly fine though, just check the AC ripple with a 'scope to answer that question.

-Chris

[Zen Mod]

nice to see Anatech active again

regarding HK770 ...... even if by sch amp is promising , in reality it is veiled drek ;

I tried some things with mine , but all led to conclusion that major redesign is way to do .

It's sort of easy ( just demands some time , which I still didn't found ) , because physical layout is almost perfect ..... peachy , to say so

search my threads regarding Harman Kardon and Silver , I think you can find some more info

[Zen Mod]

Manu's HK Tower & ZM's Silver Turm