Giovanni Stochino's ultra fast amp - diyAudio
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Old 26th March 2001, 04:57 AM   #1
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I have built Giovanni Stochino's ultra fast amp as published in Electronics World and I am very impressed with its performance. My previous ss amp was mid-80s design from Sydney Uni which featured nested differentiating feedback loops. Again, I liked this amp. What do others think of this Stochino's design vs other ss amp designs?
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Old 26th March 2001, 05:02 AM   #2
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Is the circuit published anywhere on the web?

Grey
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Old 26th March 2001, 05:16 AM   #3
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Default Not officially, but....

this guy is currently building it and a schematic is provided on his site.

http://www.soton.ac.uk/~apm3/diyaudio/Poweramp.html

If you are interested I can post some pics of mine...
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Old 26th March 2001, 07:04 AM   #4
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Just for fun, you might want to take a look at the link for The Leach Amp under Amplifier-Projects. This is the current incarnation of one of the earliest low TIM (i.e. high slew rate) amps. I heard one of the older versions a long time ago--frankly don't remember being much impressed, but time may have played tricks on my memory and, at any rate, the circuit has been updated many times since then.
The circuit on the link you provided looks to be much simpler, which to me is a good sign.
One thing that occurs to me is that the Stochino circuit might benefit from some parts upgrades. Several of the small signal transistors used are, I believe, classed as 'general purpose.' Judicious substitution of MPSA18s/MPSA42s/MPSA92s might further improve the performance, but to do a good job would probably entail adjusting resistor values, etc., quite likely more trouble than it's worth.
Some of the lads on this site seem to get their jollies by running up software simulations of circuits and comparing them. Talk one of them into running a head-to-head between the Leach and Stochino amps. It wouldn't be the same as listening, which is my preferred way of tilting at windmills, but it might prove interesting.
I'll try to take another gander at it when I have more time.

Grey
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Old 26th March 2001, 08:55 AM   #5
djk is offline djk
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The circuit at http://www.soton.ac.uk/~apm3/diyaudi...no_circuit.jpg has some errors in it.The IRF640s are drawn wrong.The 12V zener diodes need to be on the outputs not the drivers. Miller capacitance from drain to gate when driving an inductive load will hit the gates hard and decrease the life of the outputs.Active current sources are noisey and don't sound good.A resistor from a regulated supply ala Leach works better.An active current source as a load really pushes the open loop gain.It is better to trade gain for frequency response.The resistor between the emitters of the cross-coupled diff inputs is a nice touch and could be easily added to the Leach.The Leach can go faster if you go from a tripple to a double output stage and substitute MJE15030/31 30Mhz drivers and MJ1302/3281 30Mhz outputs.The Leach would benefit from a regulated voltage for the front end too.A .33 ohm source resistor doesn't do much for equalizing currents on an IRF9640 with an Rds on of .5 ohms, the Vgs need to be carefully matched in this design.
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Old 5th April 2001, 03:35 PM   #6
Alex M is offline Alex M  United Kingdom
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Default Stochino schematic

DJK wrote:

"The circuit at http://www.soton.ac.uk/~apm3/diyaudi...no_circuit.jpg
has some errors in it.The IRF640s are drawn wrong. The
12V zener diodes need to be on the outputs not the
drivers."

Actually the Zeners are correct, at least according to
the most recent EW article. Sorry if the MOSFETs are
drawn wrong - this was a tediously hand-drafted copy of
the original using Illustrator.

I'm afraid I still can't offer any comments on the
performance of this amp as I'm still working on my preamp.
I have completed the PCBs and built the chassis for the
power amps, but haven't got around to putting the
(substantial) power supply together yet.

Alex

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Old 6th April 2001, 07:43 AM   #7
djk is offline djk
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The error in your drawing is easily forgiven.I only pointed it out in case some inexperienced person tries to build it from this schematic.The placement of the gate protection zener diodes is a design issue as are most of my other remarks.I earn my paycheck analyzing design flaws and making suggestions on how to improve said designs.If I seem overly critical it is because it has become second nature to me.
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Old 6th April 2001, 08:19 AM   #8
Alex M is offline Alex M  United Kingdom
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I'd certainly like to see pictures of any other
implementations of this amplifier.

Alex
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Old 9th April 2001, 07:00 PM   #9
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This circuit reminds me of the Sansui ultra-high-slew
"Diamond Differential Amp" of the 70's, where the
input system is capable of tossing a lot of extra
drive current under high speed conditions.
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Old 27th April 2001, 12:47 PM   #10
ppl is offline ppl  United States
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I Built A Circuit Similar to this one and the Leach Amp Years Ago. It still Works Fine. I was wondering what the Concerns were with using a Constant Current Source For the Diff. Amp? I Thought that the CMRR is improved by Constant Current vs Just a resistor? Also What Advantage is the Resistor and capacitor from the Pos. Diff amp to the Neg. Diff amp for the Emitter sides. TIA
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