I have an article by Erno Borbely from WW 1982, in which he describes an amplifier using Hitachi lateral MOSFETs. It looks very much like son of DH-200. I can scan it and post, if there's any interest... the circuit discussion is interesting. Pm me if you'd like to see it.
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Any Borbely articles are worth reading. I think you're thinking of this one from 1983?
If not, post away ...
https://worldradiohistory.com/UK/Wireless-World/80s/Wireless-World-1983-03.pdf
If not, post away ...
https://worldradiohistory.com/UK/Wireless-World/80s/Wireless-World-1983-03.pdf
That's the one!
Looking at J162/K1058, they seem to be very similar to 2SK135 and 2SJ50, thoughts?
I only have a very tatty paper photocopy of the article. Great to see the entire mag, thank you for that. Just look at the price of toroidal transformers...
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I looked at the design, he used a cascode in the push-pull VAS and did not buffer the drive to the mosfets. Compensation is done in the IPS and the feedback loop. Something to test out in simulation.
He used the plastic package versions of the hitachi mosfets, similar to currently manufactured exicon devices
He used the plastic package versions of the hitachi mosfets, similar to currently manufactured exicon devices
He cerainly is:
"Talking about feedback, I would like to make a couple of comments, as this subject seems to be perennial in TAA and other audio publications. First of all, treat feedback like a friend, not an enemy. Just as with friendship. rely on it when you need it, but never strain it. Applying the right amount of feedback in a well-controlled manner cannot hurt anybody; but when you try to cover up a bad design with a lot of feedback, it may turn sour on you"
If you try to build the 60W, it's an error in Fig. 7: R20 should be connected to R9 and R22, and not to ground.
I must say that his designs are simply brilliant in many ways.
I made a modified Servo 100. Higher rail voltage and some other smaller changes, and 6 pairs SJ55/SK175 per channel, biased to 1 amp it also gives some class A output. It produces 250w in 4 ohms, and I measured distortion to 0.0034%.
It sounds fantastic.
/Figge
I made a modified Servo 100. Higher rail voltage and some other smaller changes, and 6 pairs SJ55/SK175 per channel, biased to 1 amp it also gives some class A output. It produces 250w in 4 ohms, and I measured distortion to 0.0034%.
It sounds fantastic.
/Figge
what are the possible replacement for Bipolar transistors in Servo 60 or 100?
I have couple of spare Mosfets that I can try
thanks
I have couple of spare Mosfets that I can try
thanks
Mr. Pavel Dudek developed in 1992 year the Borbely-Lender schematic in the family of DPA audio amplifiers.
Here you have the old DPA110 project:
Here you have the old DPA110 project:
Attachments
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Erno refined things a bit for his later Servo 50 design. I built one years many ago and it's been a favorite amp for many years - one of the few projects I built that I didn't later disassemble to use the parts elesewhere.
🙂
Anyone planning to build any of these amps would do well to look for and read the Servo 50 amp articles. One of the nice touches was to add regulators for the front-end circuitry.
🙂
Anyone planning to build any of these amps would do well to look for and read the Servo 50 amp articles. One of the nice touches was to add regulators for the front-end circuitry.
DPA110 looks like the front end of the 60W mosfet design with bipolar output stage.
I notice it has DC offset adjustment. Has this proved necessary in the Borbely mosfet designs? Is it not sufficient to match hfe of the input transistors?
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I notice it has DC offset adjustment. Has this proved necessary in the Borbely mosfet designs? Is it not sufficient to match hfe of the input transistors?
edited for spelin
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