Technics Class A Bias Circuits

[sdman]

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.

Thanks
SDMAN

 

[ppl]

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]

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.

Sam

 

[Nelson Pass]

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]

Mr Pass,

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

Atiq

 

[tiefbassuebertr]

Technics patent #4,115,739 old German diy project

From the topologies about
Power amplifier
or
Efficient high fidelity audio power amplifier
or
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:
http://www.diyaudio.com/forums/solid-state/23590-audiotek-69-technics-se-a1.html
http://www.freewebs.com/mondaca/AMP-TUNER1978_07.jpg
http://www.freewebs.com/mondaca/135.jpg
http://www.hcmy.com/oneand.html

 

[ojo]

Hi gentlemen, i know this has been a longtime thread. Just want to ask about my friends technic
su-v6x.
Since you are all specialists in super a technics. My question is, is the amp really difficult to fix? It has blown output transistors, 2 drivers, and i think 7 diodes which i cannot find in the market. OA90 and MA27w-a. Found a thread that says replace them with 2 in4148 in series. But to no luck. What equivalent diode can i use to stabilize the voltage bias?

 

[Iomis]

Hello,

I can only help with a start searching point...
Few years ago, I changed (in a SU-V8) 2OA90 with Ge diode 1N60 bought from here. And in a SU-V90D, MA29WA with 2x1N4148 in series indeed (from Vishay). Both amps are working fine.

Best regards,
Cosmin