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Old 1st April 2012, 06:03 PM   #71
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Apart from the JFETs, I found a similar circuit here, which is essentially the same. (better sub-circuit to talk about)

Cheers,
E.
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Old 1st April 2012, 06:17 PM   #72
KSTR is offline KSTR  Germany
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OK, then Pavel's (PMA's) DisPre variants would count too, wouldn't they?
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Old 1st April 2012, 08:32 PM   #73
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Schematic?
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Old 1st April 2012, 08:49 PM   #74
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Pavel Macura audiopage
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Old 1st April 2012, 08:58 PM   #75
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Thx KSTR.

The basic topology is the same, i.e. a TIS gain of just 1x, but the freq. compensation is totally different.
edit: > different: not input stage inclusive compensation.

Cheers,
E.
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Old 2nd April 2012, 02:47 PM   #76
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Quote:
Originally Posted by myhrrhleine View Post
it looks like one of the circuits developed by Hawksford.
see his distortion correction for audio amplifier circuits paper.
Hi myhrrhleine,

Do you mean his paper about the enhanced cascode?
(i.e. "Reduction of Transistor Slope Impedane Depedent Distortion in Large-Signal Amplifiers.")

Cheers,
E.
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Old 2nd April 2012, 08:11 PM   #77
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Default stability issues

Quote:
Originally Posted by keantoken View Post
I meant THD @20KHz at +-1V at the output.

I considered building this circuit yesterday, as I have several BC847DPN, which are dual npn/pnp pairs with "good Hfe matching". Unfortunately I don't have any same-polarity pairs I could use for the current mirrors or LTPs.

I will test the latest improvements in simulation... Good work Edmond.
Hi Keane,

If you really are going to build that circuit, beware of possible stability issues from the cascodes at the input stage. See: 182MHz Oscillations :-0 for a remedy.
According to my sims, collector stoppers of 100 Ohms (or base stoppers) seem to cure this problem.
Regarding the matched duals of the same gender, just use BC547 respectively BC557 or so, and (hand) match them to a delta VBE <10mV.

Cheers,
E.
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Old 4th April 2012, 04:40 PM   #78
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Default Update

I've updated my website with a comparison between the Super TIS and a more traditional symmetrical front-end, i.e. one of the Randy Slone circuits with additional (Hawksford) cascodes and a CMCL to stabilize/define the VAS Iq.
See: http://home.tiscali.nl/data.odyssey/Super_TIS.html

Cheers,
E.
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Old 4th April 2012, 10:10 PM   #79
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Default Stuff

Hello Edmond,

Congratulations on your excellent and thorough work , do you plan to include the Alexander type of front end or will it be excluded because it uses an opamp and is not discrete.
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Old 5th April 2012, 05:55 AM   #80
Bonsai is offline Bonsai  Taiwan
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Edmond,

yes, more excellent stuff from your side - thanks for sharing.

Any thoughts on using your front end with say 5-8 pairs of bipolar to create a big 200-250W amp, and, same question again wrt mosfets.

My concerns with bipolars are I have not seen a working design that uses HEC probably because of the low BE forward voltages make it more difficult to implement without losing headroom, or having to provide higher supply voltages to the front end.

EF3 goes some way to solving the linearity issues, but, my practical experience (both on the Ovation 250 and on my new e-Amp I am working on) shows that thermal lags across the EF3 completely dominate short term distortion - and here I talk about seconds to minutes. I am wondering if HEC can solve this issue (but maybe then we only need an EF2 again ;-) WRT mosfets, how effective is HEC when a lot of devices are paralleled, and what about the current sharing issue in linear mode?
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