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Old 21st October 2012, 01:07 PM   #141
mikelm is online now mikelm  England
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Quote:
Originally Posted by Salas View Post
Increasing the driving impedance has no side effect because we have driving emitter followers?
Actually from this and past experience I think having a CCS entirely or predominantly as an i/p stage load does tend to smooth out the sound somewhat. I think this may be caused by current lag at higher audio frequencies, but having even a small portion of the current coming through a resistor helps quite a bit to reduce this effect.

I'm going to wait till I have my new PSU before I make up my mind about this.
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Old 21st October 2012, 03:24 PM   #142
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Quote:
Originally Posted by mikelm View Post
I think this may be caused by current lag at higher audio frequencies
Why, if it is fast enough ? Don't you think it is the contrary, and non infinite resistance tend to increase transients ?
Looking at square waves (no overshoot, no rounded corners) at low and high level is enough to make our mind, i presume.
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Last edited by Esperado; 21st October 2012 at 03:29 PM.
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Old 21st October 2012, 06:55 PM   #143
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Well, when I was developing my fetzilla I tried i/p stage load as CCS for a while - with many cheap resistors in the circuit but very good FB resistors this brought big benefits because of the very big increase in Open Loop Gain, but later when I have good resistors in every position the amp sounded much better with a simple resistor in this position - much more immediate & lively sound - by comparison the CCS sounded refined & polite but lacking in vitality.

Later when I researched this in spice I found that the only difference I could see was an earlier phase shift of the current with respect to frequency when using the CCS. Adding a parallel resistor helped to reduce this shift but not 100%.

Last edited by mikelm; 21st October 2012 at 06:59 PM.
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Old 22nd October 2012, 08:54 PM   #144
mikelm is online now mikelm  England
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TSSA 1.6 vs DC linked Fetzilla:

Have to wait a bit for this comparison - the incredibly refined sound of TSSA1.6 made me realise that I had some "housekeeping" to do in my design so I'll report the differences & similarities once I've finsihed - should be in a day or two.

For now all I'll say is that they are both sounding very nice indeed

Thanks Sonny - I'm still learning . . .
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Old 3rd November 2012, 06:03 PM   #145
mikelm is online now mikelm  England
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With some mods now done to my amp I began to do a comparison today but in the end I abandoned it quite soon because I believe to a large extent I would just have been describing the differences between the different PSU arrangements each amp has - it would not have been easy for me to give each topology identical supplies at this stage and for me it is the topologies that I am interested to compare rather than the PSU's.

At present my amp has 2 x 22,000uF shared between two channels + 470uF on the board
TSSA currently has 22,000uF for each channel + 3670uF on the boards.

I believe that both amps will improve will the new supplies I am planning. TSSA should sound smoother & my amp should gain better defined midrange.

Please don't misunderstand me, already both amps sound very nice but I believe the differences I can hear are to a large extent defined by the different PSUs.

I will be travelling for a few weeks this winter so it may be a while before my real comparison gets made.

Last edited by mikelm; 3rd November 2012 at 06:08 PM.
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Old 3rd November 2012, 08:49 PM   #146
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Originally Posted by mikelm View Post
Later when I researched this in spice I found that the only difference I could see was an earlier phase shift of the current with respect to frequency when using the CCS. Adding a parallel resistor helped to reduce this shift but not 100%.
That make sens.
So CCS have to be done with the fastest devices we can find. May-be FET cascoded current source ?
It look like it is a crucial point. Lack of linearity VS lack of response's speed.
An external PSU very high voltage with high Z resistance could help to find the audible limit ?

But i agree with you, PSU is the first to look at.
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Last edited by Esperado; 3rd November 2012 at 08:51 PM.
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Old 25th November 2012, 07:57 PM   #147
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One more TSSA is almost ready.
1A with 26V rails, dual mono.
All the parts came from what I had in my parts bin and the chassis was salvaged from an old class A amp.
For the moment it is on the test bench and doing well. Very stable, easy to adjust seems to work fine.
looks good on the scope too.
Will do some more tests tomorrow and hopefully listen to it.
One question only. Is there a way to make a balanced input for TSSA? It would be handy!
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Old 25th November 2012, 09:06 PM   #148
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Looks like the chassis of a french beast from the 80'es!???

I could design a small frondend for it that would accept balanced input very little or no feedback.

Would that be of interrest.
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Old 25th November 2012, 09:17 PM   #149
vgeorge is offline vgeorge  Greece
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You are right, Audioanalyse A9.
Regarding balanced input, that means another active stage. I don' t know, I may try it.
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Old 25th November 2012, 09:27 PM   #150
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I could make something very transparent with folded cascode and no output buffer.

So this would be like a true 1stage design.
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