Update for Elektor Crescendo Power Amplifier 1982

[PMik]

Ok ..i had already planned to follow the advice bjornagain has posted and go a little futher
Among others re-locate the gate stoppers so they are soldered directly to the gates of the MOSFET's, the distance from there original placement and for the gates are in my pov./experience to far away to be any good, the optimal RG value has to be determinated by messure and audition tests
compensation of the Cg by add of a 300pF cap. betwin GD of the 2SK135 will also add some stability,
there is difference betwin SJ50/2SK135 (Ciss = 900/600pF)
R1/C2 will be changed for 1K/1nF (160KHz -3dB)
R32/C15 altered for: 5x47R-2W MP/100nF
Removel of the C1,C2
Change of the R1 value to perfect fit of my passive pre-amp
Parr. of all the el-caps will make wonders for the stability and the sound of the Crescendo

[Dusk]

Hi Pmik
I got the update
thanks
Dusk

[bigpanda]

Thanks PMik, mail received.

[ashok]

Can you send me a copy of the circuit PMik ?
Thanks.

Please change (at) and _dot_ .
ashokm(at)sify_dot_com

[PMik]

Article on its way for your inbox

[Samuel Jayaraj]

PMik, article for me too! I have a pair of Crescendo boards, fully assembled and tested. Initial oscillations were tamed. However, I'd like to see the official updates. Thanks.

[PMik]

Samuel ....., I have pure and simple just made a screendump picture of Bjornagain's first post, this to complete the original article

[bjornagain]

The nice thing with the Crescendo is the pure simplicity, I think, and any modifications must keep it that way. I would like to share one idea from a fellow member.

First a more proper way to bias the cascode T8/T10, which will enhance almost everything.

Second R3 is moved and both differential inputs references meets the signal ground at the board entry.

Then I can not see the purpose of C12/C13 more. Suggestions?

The mods is quite simple. Unfortunatly I have not tried them yet, but I will.

Schematics attached!

[bjornagain]

Very fast I entered a simple schema of recent proposed mods, using ECX-devices for which I had SPICE-data for. With shown values calculated THD is 0.005% at rms 40 W 1 KHz, no overshots using square wawe, and nice falling spectrum (2nd larger then 3rd and so on). This is theory.

In practice supply and zener must be bypassed, proper HF-protection at input applied, output filter and HF-impedance loading applied, output device doubled with proper source-resisitors, current limiting applied, and an active dc-servo inserted controlling output offset.



It is still close to the original, with some sonic improvements in theory, and hopefully more stable function.

Still, it all remains to be proven in practice!

[chryslerjay]

Sorry to barge in on your thread, but I thought PMik might be able to help me find an output transformer for my Audio Innovations series 800 Mkiii power amp. Can someone ask him for me? Thanks.
or reply to chryslerjay@excite.com