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sdman 13th October 2001 05:38 PM

Hi, Been doing some research on Class A bias techniques and
ran across Technics Class A Synchronous bias and their
balanced bridge network using two amps {Voltage class A)and
(Current Drive). I would like to know how effective these
aproaches were in attaining Class A operation,(Sound Quality)etc,etc. I think some of these models were SU-V7,8,
SE-A100 etc,etc.
Also I see where Nelson Pass had some good ideas and patents
on the subject.


ppl 14th October 2001 06:26 AM

I Bought an SU-V8 way back in the 80's The Syncro-Bias works wery well at reducing Crossover Distortion. This Amp is a real sleeper Dual transformers on each Channel Good Topology. and a High gain Power amp section that allow the Power amp to be Directly Connected to the Source with No Preamp or Coupling capacitors in Between. Just a Volume Control. Or you can use the Via tone Mode and have all the Preamp features. I no longer use this amp since i need a Transformer for one Channel. But when and if i Find one Ill get this up and running. I did some Mod's to dramictcaly improve the sound like reduce the ampont of Neg Feedback by reducing the Open loop Gain. Bypassing the PS Capacitors with 4.7uF Solens. and Phono Preamp Mods. Yes this Amp has a Wonderfull sounding and quiet Phono Preamp. In short if you find one of these used get it.

sdman 15th October 2001 05:10 PM

Technics Class A Bias Circuits
Thanks ppl,
I agree that the amp is a sleeper. A friend gave me this one
and at the time wasn't interested in it,just didn't want it thrown away. Recently I pulled the "the old boy" out of the closet and hooked the thing up just to have something to do
and was plesantly suprised at the sound it produced,the program source was a CD player. So this is how I got interested in Class A circuits because on the front of the
unit it had (New Class A Syncro Bias),so this got my interest and started doing some research on the subject.
So my query to the Forum was to see what the Pro's and Con's
are with his type of circuit. I do have a Service Manual on the unit now and it does explain how the circuit works. Seems though that there always is a downside to innovations
of this type. The unit does sound good and stays on all day
in my shop with an FM tuner as it's source.
I am interested in the mod's you did on the feedback and phono section,any info would be welcome.


Nelson Pass 15th October 2001 07:16 PM

The Technics amps I have actually seen on the market
looked to be a variation on Dynamic Bias; in fact an
alternative approach to my patent #3,995,228.

Far more interesting is the amplifier based on the
1977 Sano et al patent #4,115,739, which corresponds
roughly to the above descriptions.

In any case, I pay Sano, Hirosha, and Hirota the
highest compliment: I wish I had thought of it.

atiq19 9th January 2009 11:06 AM

2 Attachment(s)
Mr Pass,

could you explain briefly how technics bias is achieveing sliding mode?


tiefbassuebertr 1st July 2010 05:58 PM

Technics patent #4,115,739 old German diy project
1 Attachment(s)
From the topologies about
Power amplifier
Efficient high fidelity audio power amplifier
Power amplifier circuit

I have found by chance an amplifier diy project in Germans magazine Elektor (see attachement).
Are there more of such diy projects here on diyaudio?

From commercial products I have found this from Technics SE-A1:

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