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Old 21st September 2012, 07:34 AM   #51
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I received the transistors yesterday. Man thanks, Sonny.
Now I can start to build it :-) I will report my results...
Boris
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Old 22nd September 2012, 11:25 AM   #52
mikelm is offline mikelm  England
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Well, if anyone here thought that the formula for retrieval of maximum detail was to take a reasonable topology and then increase OLG and FB then this amp may well disabuse you of your notion. ( as someone famous here once said )

My TSSA 1.6 CLG is 27dB, I think OLG is around 47db with my o/p devices so my FB is only about 20db ! - Sonny can you correct this if necessary.

I never heard so much detail before ! Sometimes today I was just laughing. It's quite holographic.

Sounded pretty dreadful during "run in". I think the worst is over now but I'll give it a few more dummy load silent "full on" sessions to make sure.

I remember someone once said that you never can match the detail of an o/p stage that is the VAS when you use a follower o/p stage. Also JLH noted that symmetrical designs tend to have a more detailed sound than SE ones - so with TSSA we seem to have a formula for ( almost ? ) maximum resolution of detail.

Might not be to everyone's taste and may not be ideal if you have cheap dac but this amp is certainly not lacking in the vitality & fun department !

more later . . .

Last edited by mikelm; 22nd September 2012 at 11:38 AM.
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Old 22nd September 2012, 07:28 PM   #53
mikelm is offline mikelm  England
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Default A SUGGESTED MOD

Sonny,

Listened quite a lot today and even though the sound was smoother now there was something about it that seemed somewhat surreal - somehow larger than life, exaggerated detail and over etched imaging - then, I played a particular track and realised - at least to my ears - something was not right - it just didn't sound natural.

So I did a mod that I always do on my designs but didn't want to do on this design until I had tried it in standard mode first.

I removed the PSU bypass caps and replaced them with epcos stacked film 4.7uF 100V caps in series with 0.2R ( 10mm lengths constantan resistance wire ). These caps are about the same size as the caps you suggested but are now mounted on the solder side of the board between the original ground pad and the pad where the pos & neg rails meet R32 & R33. ( I will post a photo when I have daylight tomorrow )

This mod eliminates a resonant circuit formed between the two caps and the inductance between them.

The amp is still stable. 10khz into 8R & 0.1uF looks more or less the same as before but interestingly, I think clipping is now a bit better than before.

I noticed a few days ago that the onset of clipping was somewhat asymmetrical on the negative cycle and when I checked again after the mod I thought it looked a bit more even.

My feeling is that subjectively this changes the character of the amp for the better. Before I made the changes the amp was making me laugh - after the changes I think it could much more easily make me cry and now all the the amazing qualities this design has seem able to flow more naturally.

I hope you try this mod and let me know what you think. I can send you constantan wire if you would like some, or give you the suppliers address.

I use this type of resistor for all low values for 2 reasons

1) it sounds very good
2) cost of each resistor is virtually nothing.

but I'm sure other good quality 0.2ohm resistors will sound good as well

The caps are available from Farnell.

that's it for now

cheers

mike

Last edited by mikelm; 22nd September 2012 at 07:32 PM.
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Old 22nd September 2012, 10:32 PM   #54
mikelm is offline mikelm  England
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Final comment before close of play . . .

Before I did the mod this amp sounded quite extraordinary but I noticed I relaxed more when I switched back to my DC linked fetzilla. Fetzilla gave less insight but was more refined & relaxed.

After the mod, and using my simple choke supplies, this TSSA 1.6 is the best amp I have ever heard by quite a bit margin. Now extremely insightful and quite refined.

I think there is still room for some more small refinements but already quite outstanding.

I now intend to do design a regulated supply - which I think this design will benefit from - and generally explore the whole field of 2 stage amps to the fullest extent possible.

Thanks Sonny - quite a masterpiece . . . You have opened up a new audio universe for me and I hope you enjoy the little suggestion I offer

Last edited by mikelm; 22nd September 2012 at 10:38 PM.
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Old 22nd September 2012, 10:38 PM   #55
sonnya is offline sonnya  Denmark
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Nice to hear. I have never Said that This AMP plays neutral. My feeling has always been that This AMP colours a bit.

That has to be clear.
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Old 22nd September 2012, 10:40 PM   #56
mikelm is offline mikelm  England
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Ahh - we post same time - haha - the mod makes it more nuetral ( in a wonderful way )
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Old 22nd September 2012, 10:40 PM   #57
sonnya is offline sonnya  Denmark
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But it was amusing to read i am really happy right now!!!
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Old 22nd September 2012, 11:51 PM   #58
Salas is online now Salas  Greece
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Just to know if I got it right, are we talking replacing C6,C7 bypasses with 4u7+0.2R each when C8,C9 electrolytics remain?
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Old 23rd September 2012, 12:09 AM   #59
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@Mikelm

There are C4,C5 470n bypasses on C2,C3 AC/DC split gain feedback electrolytics. Did you experiment on those too? Starting without any direct bypasses and then compare bypass solutions maybe its an acceptable practice also. I remember when I had been suggested to bypass my LCR 15000uF PSU capacitors in a JLH 80W amp with MKPs. The tone got pinched and I ditched them very soon. Snubbing is best but needs original PCB space. Your constantan wire does the trick neater though.

P.S. What speakers you got and how is bass with TSSA at ~20dB feedback?
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Old 23rd September 2012, 04:32 AM   #60
mikelm is offline mikelm  England
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Quote:
Originally Posted by Salas View Post
Just to know if I got it right, are we talking replacing C6,C7 bypasses with 4u7+0.2R each when C8,C9 electrolytics remain?
Correct
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