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Old 5th November 2011, 07:06 PM   #1291
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by Jay View Post
... even tho bipolar sound is not my cup of tea.
do you really believe bipolar has a 'sound' ? I thought that the topology and operating points and power supply are going to have a bigger impact on the sound than choice of FET verses BJT - although I haven't the experience you have, I thought that both of them can be employed to achieve the results you are looking for.

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... the SSA is simple and perfect physically.
I have this strange irrational feeling that really good amps are imperfect in some way - technically speaking that is. It's part of the 'Art' as you have said

The SSA has it's weaknesses - thermal stability is one of them - in my opinion, and use of zeners (noisy things). And I think it will sound better if it's NOT actually symmetrical - an easy thing to achieve and I hope to try this out with my TGM5 version.
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Old 5th November 2011, 07:16 PM   #1292
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I would just like to ask, off-set is measured with reference to what? Obviously 0V reference which is dictated by the power supply. If the positive rail caps are slightly more leaky than the negative rail, or if the transformer windings are a few mV difference which is very likely, you are actually offsetting your amp deliberately to compensate for the power supply.

When the signal is applied and the one rail drops in relation to the other, won't there be an immediate dc offset besides the signal. You all talking DC states, you don't listen to DC do you?
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Old 5th November 2011, 07:18 PM   #1293
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Hi Salas
We might be looking for similar results on an amp, I too find the need for some help in the lower region that the F5 can't deliver fully at least with my speakers.

Are you planning to parallel output devices at the end?

Tony

Last edited by apassgear; 5th November 2011 at 07:23 PM.
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Old 5th November 2011, 07:58 PM   #1294
Sheldon is offline Sheldon  United States
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Quote:
Originally Posted by Lazy Cat View Post
Guys, no worries please, you can always do something like this.
Simple Symetrical Amplifier

If I have a single output pair for the FC100 buffer, can I do thermal comp. like this? I've left out stoppers and bypass caps for simplicity of display. The 1N diodes are standard small signal diodes, the ones labeled NJL are the Thermatrak diodes.
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Old 5th November 2011, 08:04 PM   #1295
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Apassgear,

No disrespect intended, I always get a little concerned by power nuts. It is always a good measure to make the SSA as it was intended, familiarize yourself with it quirks, shortfalls and advantages, and most importantly get a feel for its sound whether it lives up to your expectation before pouring a bucket of transistors into it.

It is relatively easy to expand when you are satisfied that it is the amplifier that you want to live with.
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Old 5th November 2011, 08:13 PM   #1296
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Sheldon, that method is feasible. It will compensate for ambient as well using it like you indicate.
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Last edited by Nico Ras; 5th November 2011 at 08:17 PM.
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Old 5th November 2011, 08:15 PM   #1297
Salas is offline Salas  Greece
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Quote:
Originally Posted by Nico Ras View Post
I would just like to ask, off-set is measured with reference to what? Obviously 0V reference which is dictated by the power supply. If the positive rail caps are slightly more leaky than the negative rail, or if the transformer windings are a few mV difference which is very likely, you are actually offsetting your amp deliberately to compensate for the power supply.

When the signal is applied and the one rail drops in relation to the other, won't there be an immediate dc offset besides the signal. You all talking DC states, you don't listen to DC do you?
No problem if the DC values will stay at safe margins in the long run. For the time being this amp can easily give me the creeps some times during on off eratically. Building another channel now to see if its a trend or an error.
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Old 5th November 2011, 08:17 PM   #1298
Salas is offline Salas  Greece
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Quote:
Originally Posted by apassgear View Post
Hi Salas
We might be looking for similar results on an amp, I too find the need for some help in the lower region that the F5 can't deliver fully at least with my speakers.

Are you planning to parallel output devices at the end?

Tony
Don't know, got to listen to it critically first when I will have a satisfactory stereo build on hand, hopefully soon.
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Old 5th November 2011, 08:33 PM   #1299
sonnya is offline sonnya  Denmark
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I have a solution to the drift...

1. You Can use it or not. The 2 input transistor should be feed by an current mirrors feed by a shared currentsource Like cr200..

2. the cr200 Will give an idle current of 2mA +/-10%.. this Will reduce the basiscurrent and remove the heat. The baseresistor for the next stage has to be 5x larger..

This solution is taken from my mirand AMP.

I have a drift starting at 300mV falling to ~50mV. And i Will ADD the circuit above
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Old 5th November 2011, 08:38 PM   #1300
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Quote:
Originally Posted by Salas View Post
No problem if the DC values will stay at safe margins in the long run. For the time being this amp can easily give me the creeps some times during on off eratically. Building another channel now to see if its a trend or an error.
Maybe it is a possible error or unsymmetry caused by the fet current source because of its voltage drop ...

Mine SSA BIGBT has no power on thump-pop whatsoever (scope shows 200mV positive jump for the first 0,2 s for no loaded amp) and its thermal DC offset drift inside +/-10 mV over cold to 70°C.

More important issue is an output bias thermal stabilization which can be realized successfully in many ways, already suggested here and in TGM5 thread, how to hold the amp at a certain thermal working conditions.

According to my oppinion the most important feature by this design is its no frequency compensation need as a result of the SSA feedback nature and consequently the sound quality result.
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