Bob Cordell's Complementary IPS-VAS topology - diyAudio
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Old 5th May 2013, 03:48 PM   #1
danny92 is offline danny92  Portugal
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Default Bob Cordell's Complementary IPS-VAS topology

Hi everyone,

I'm simulating this circuit that is based in one circuit found in Bob Cordell's book, this circuit has good characteristics, but this is really stable in the real world, does anyone tested something like this ?
I'm thinking about using a thermal shutdown network connected to the mute network, using Schimitt Trigger configuration, and I should also use a S/C protection circuit, but I don't know if I should use a single slope VI limiter, or a multislope VI limiter.

Thank you very much for your support
Best regards,
Daniel Almeida
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Old 5th May 2013, 04:01 PM   #2
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I am doubtful that this circuit would work in practice. And yes, use a VI limiter; send me your email address and i'll send you an article on VI limiters. What sort of Schmitt trigger do you intend to use?

You could use the VI limiter connected to opto-coupled transistors to trigger a bistable latch that remains triggered ounce VI limiting is invoked until power is cycled.
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Old 5th May 2013, 04:08 PM   #3
danny92 is offline danny92  Portugal
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This circuit won't work? why?

My email adress is: danielgpsalmeida@hotmail.com

Best regards,
Daniel Almeida

Last edited by danny92; 5th May 2013 at 04:18 PM.
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Old 5th May 2013, 04:20 PM   #4
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Because I am not certain that second stage standing current would be well controlled in reality. But I think you should consult the circuits author on this point.

Check your mail.

Last edited by michaelkiwanuka; 5th May 2013 at 04:22 PM.
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Old 5th May 2013, 04:25 PM   #5
danny92 is offline danny92  Portugal
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Can suffer from quiescent bias current instability in the VAS, right?
Bob Cordell said that the 47kohm shunt resistor in the differential pairs should solve the problem, but I'm no sure about that, I've written in Bob Cordell's book thread.

Thank you for your help,
Best regards,
Daniel Almeida
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Old 5th May 2013, 04:28 PM   #6
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Quote:
Originally Posted by danny92 View Post
Can suffer from quiescent bias current instability in the VAS, right?
Bob Cordell said that the 47kohm shunt resistor in the differential pairs should solve the problem, but I'm no sure about that....

Yes, you need to establish from Bob Cordell whether he's actually built the circuit to verify this.
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Old 5th May 2013, 04:36 PM   #7
danny92 is offline danny92  Portugal
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Can you send me your VI limiter articles, please?
I'm thinking about using the mute network connected to a Schmitt trigger comparator, and then comparing a resistive voltage divider's voltage, with NTC voltage divider's voltage, the window will shutdown the amplifier at nearlly, I don't know, some temperature between 70 and 100 șC and the device will only be reactivated at a lower temperature between 60 and 90 șC, I don't know if that is possible, if so, what model of comparator I should use?

Best regards,
Daniel Almeida
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Old 5th May 2013, 04:48 PM   #8
danny92 is offline danny92  Portugal
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Thank you very much for the articles

Best regards,
Daniel Almeida
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Old 9th May 2013, 08:47 PM   #9
Struth is offline Struth  Canada
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Hi Guys

Yes, the idle current in the VAS is predictable and stable with the above circuit. The third Q in each mirror, Bob calls a "helper transistor'. This Q establishes the voltage on one side of the mirror. If the mirror balances, then the voltage at the output side is identical, with zero current through the 47k.

In the end, the diff tail current sets the voltage drop across the emitter Rs in the mirror. The voltage across these Rs is identical to that across the VAS emitter R, so VAS current is set by resistor ratios and the diff-amp tail current.

The same applies to the front-end of Bob's mosfet amp from 1983.

Have fun
Kevin O'Connor
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Old 9th May 2013, 09:36 PM   #10
danny92 is offline danny92  Portugal
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Ok, thank you for your help,

Best regards,
Daniel Almeida
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