Borbely-Lender True Symmetry

[buzzforb]

Originally Posted by steph_tsf

You mean this all MOS implementation dating back from 1992 (Audio Amateur) ?

Yes. What are the major differences, other than transistor type?

[steph_tsf]

And now comes the time for me to get excommunicated.

The man who killed (by mistake) the Borbely-Lender amp is no less than Douglas Self. Read his "Audio Power Design Handbook" page 132, chapter 5. See the figure 5.12.

Douglas self writes : " As I said earlier, there is no reason not to adopt current-mirrors when using a double input stage and every reason to do so. This gives us the configuration in Figure 5.12."

Is there litterature available from Douglas Self, where he realizes his mistake ?

If you don't find such thing, you may suspect that he liked to have people getting smoke and flames building the Borbely-Lender amp, blaming the Borbely-Lender amp, then adhere to his own "blameless" topology.

Just tell me.

[steph_tsf]

Originally Posted by wahab

Another ancestor, that might well be the first such design is the Motorola design published in REL 12/1973. Notice the output stage topology.

Bingo ! Look what Erno Borbely is saying to Jan Didden (Linear Audio) : "Anyway, I was wrapping up my work on the 400 at the end of 1972 when I decided to leave Dynaco (...). We moved to Switzerland and I worked as Applications engineer/Application Manager at Motorola Semiconductor. I met John Curl there and we had a good time discussing audio circuitry, and from my position as application manager I was able to provide John with samples of low-noise Motorola semiconductors. I was designing low-noise circuits with bipolar transistors and JFETs, power amplifiers with bipolars, and also an FM tuner with dual-gate MOSFETs."

Is this Motorola design signed John Curl / Erno Borbely ?

[steph_tsf]

I still don't know why Ben Duncan is referring to Lender. Is there a publication from Lender ?

[steph_tsf]

If you dare operating in class A or at a 400mA bias current, you can simplify the schematic to the max and build those three amplifiers, truly symmetric :

Zenquito (evolution)
Buzquito (Mosquito)
Zenotron

See the details here : 2A & DIY

I guess you need a clean power supply. A LTspiceIV simulation is needed for determining what is the actual power supply rejection.

[steph_tsf]

beware MJE-340 and MJE-350
I'm reproducing the post #91 from ACR in Unstable VAS current in amp from Slone book


" Re the MJE340 and 350 - I originally used them as the cascode pair and as VAS buffers in a circuit topology very similar to Anthony Holtons topology. I never got good results and could not get rid of HF ringing, especially on the negative halves of the output waveform. If I drove the amp into light clipping, the ringing was really bad. I put it down at the time to output parasitics - just could not tame them. I abandoned that approach and went for a fully balanced complimentary design (not built yet - still simulating and exploring). I used the MJE340 and 350's again in the cascode amp and as the first transisors in the output triple circuit (a la Self). When I simumlate the amp going into light clipping (a useful test to check for good behavior) I got the same ringing and could not get the amp stable. Suspecting the MJE's, I checked them out in a switichng circuit (2 V square wave input to base via 1k resistor, 10K load resistor, 70V rail). The devices are slow and have very significant base storage issues. I then tried a BF470/BF469 pair - little or no storage problems and they switch damn fast. I replaced these in the amp similation - problem gone. What is actually happening here with the MJE's can be seen on a gain/phase plot - the gain is well behaved through the 0db cross over point, but then actually starts increasing again in the 1-2 MHz range by about 8db. I surmise that when you drive the amp into soft clipping, or you put a real world load onto the output, it's easy to get the amp to misbehave - once you are clipping for example, all sorts of quite high level harmonics are being generated and this triggers the ringing. Again, this situation does'nt seem to exist with the BF469/470's."

[steph_tsf]

John Linsley Hood
Audio amp symmetry
Wireless World Jan 1985 p.31

How to use current mirrors as collector loads in a Borbely-Lender True Symmetry amplifier.

Additional comment from smoking-amp
From post #77 in Unstable VAS current in amp from Slone book
R8 and R9 provide the VAS bias feedback in a convenient manner. R8 and R9 only need to feedback DC info, so can put caps from Q9,Q12 ends of R8,R9 to respective rails. Now can put another 100 Ohm resistor in each emitter circuit (Q9,Q12) to act as conventional degeneration.

[steph_tsf]

Dr. William Marshall Leach Jr.
"The Leach amp", Feb 1976
Dr. Leach's Amplifier and Speaker Projects

[fojica]

we can count in also GrandMOS, still by Jean-Marc Plantefève - very similar with Mosquito/Buzquito - mosfet VAS instead of bjt, more output devices than Buzquito

thanks for schematics
regards,
Tibi

[steph_tsf]

Originally Posted by fojica

we can count in also GrandMOS, still by Jean-Marc Plantefève - very similar with Mosquito/Buzquito - mosfet VAS instead of bjt, more output devices than Buzquito.

Quite unorthodox input stage. Gone are the differential pairs. Why is such unorthodox input stage not widely used ? What if replacing T1 T2 by a low offset JFET opamp ? Are there implementations with current mirrors, with the VAS idle current controlled like the Linsley Hood proposal ?