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Old 17th September 2011, 02:43 AM   #821
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Quote:
Originally Posted by Nico Ras View Post
Esperado, read your PMs
I had 1, already answered ?
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Old 17th September 2011, 07:12 AM   #822
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Hi Bigun

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Originally Posted by Bigun View Post
More power dissipation - why is that bad ?
It is not bad, just different. Good for someone, not so good for the others.


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I don't understand why Cbc is going to have much influence since unlike the VAS there isn't much of a voltage swing on the collector of the input devices ?
More explanation here.


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Originally Posted by Bigun View Post
Did you try listening to both ?
For a long time I didn't built an amp without cascoded input, see it as an advantage but I fully aware that the sound signature is simply different.

P.S. How is doing your SSA built? I am very enthusiastic about the quality of your sch especially with compound output drivers.
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Old 17th September 2011, 08:51 AM   #823
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Exclamation SSA Full Balanced Input

SSA full balanced input current feedback front-end. Maybe I'll try it someday.
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File Type: jpg SSA Balanced Input.jpg (190.2 KB, 841 views)
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Old 17th September 2011, 09:11 AM   #824
gfle is offline gfle  Greece
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VERY inspiring design LC
I might try SSA bipolar version, scaled down for headphones , 32-55 ohm @+/- 24V reg.PSU with MJE150xx output.
In simulator works like promised!
I have also simulated (don't laugh!) SSA quasi. Not so symmetrical, I admit, but I have many power NPNs left from past century
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Old 17th September 2011, 10:18 AM   #825
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Quote:
Originally Posted by gfle View Post
VERY inspiring design LC
I might try SSA bipolar version, scaled down for headphones , 32-55 ohm @+/- 24V reg.PSU with MJE150xx output.
In simulator works like promised!
I have also simulated (don't laugh!) SSA quasi. Not so symmetrical, I admit, but I have many power NPNs left from past century
Try the circuit shown at the bottom of the page, the original JLH circuit, sounds great, use cfp for the outputs and highish beta input transistors. With HD600 phones only 2nd and 3rd harmonics with dominant 2nd and no high order harmonics. THD is exceptionally low. Youll be hard pressed to find a better sounding headphone amp.

http://www.tcaas.btinternet.co.uk/jlhphones.htm
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Old 17th September 2011, 12:49 PM   #826
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Quote:
Originally Posted by Lazy Cat View Post
SSA full balanced input current feedback front-end. Maybe I'll try it someday.
May-be need of a trimer in the input to tune the common mode rejection. Once again, i do not understand the cap between the two emitters lines. Their trans are feed by a constant current, not ?
Beautiful, as habit, the way you mix the two first stages. Can be implanted on all the boards, as you can simply remove the two transistors and 4 resistances of the - stage if you do not need-it.

By the way, there is just one version missing to explore all possible combinations: with fets both in input and output.

I had spend hours with LTspice, trying in vain to make working a design witch work in the real life. What a piece of sh... and a lossy interface !....
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Last edited by Esperado; 17th September 2011 at 01:19 PM.
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Old 17th September 2011, 02:03 PM   #827
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Quote:
Originally Posted by Esperado View Post
Once again, i do not understand the cap between the two emitters lines. Their trans are feed by a constant current, not ?
In theory the potential between middle points of a splited feedback loop-bridge is DC. All AC variatios should be in phase so zero difference, in theory. So the capacitor is there to bring the bridge to near the ideal theoretical conditions.


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Originally Posted by Esperado View Post
Beautiful, as habit, the way you mix the two first stages. Can be implanted on all the boards, as you can simply remove the two transistors and 4 resistances of the - stage if you do not need-it.
Yes universal unbalanced/balanced SSA PCB fit the needs for RCA or XLR inputs as well.

Last edited by Lazy Cat; 17th September 2011 at 02:09 PM.
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Old 17th September 2011, 02:08 PM   #828
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Quote:
Originally Posted by homemodder View Post
Try the circuit shown at the bottom ... hard pressed to find a better sounding headphone amp.
I appreciate your cooperation, you're wellcome, but please this is SSA thread and we are discovering implementations in accordance to SSA principle.
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Old 17th September 2011, 04:29 PM   #829
Bigun is offline Bigun  Canada
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Hi Bigun
Thanks for the quick reply!

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Originally Posted by Lazy Cat View Post
More explanation here.
yeah - I got the bit about reduced miller capacitance, but.... with my limited experience I am relying on what I read about Cascodes. I read that they are helpful, even compulsory, for JFET inputs because these little fellas can have high capacitances from gate to drain which hurts freq. response. I read that cascodes work wonders on the VAS, in fact I may yet use one, because this is where the vast majority of the voltage gain is being made, and hence it's where the miller-multiplication rears its ugly head. But for a BJT input device I don't see a lot of miller multiplication and I don't see that theres too much h.f. roll-off. In simulations I find it hard to see any benefit from the cascode of the input device. The OLG plots for with and without appear the same.

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Originally Posted by Lazy Cat View Post
For a long time I didn't built an amp without cascoded input, see it as an advantage but I fully aware that the sound signature is simply different.
This is where I was heading with my question. There has to be something more to it than a marginal 'engineering benefit'. But 'different' doesn't imply 'better' and so I am left with the thought that the cascode is not 'earning it's place' in the design yet ? - not that I doubt your experience but I like to question things in order to learn.

Quote:
Originally Posted by Lazy Cat View Post
P.S. How is doing your SSA built? I am very enthusiastic about the quality of your sch especially with compound output drivers.
Progress is a bit slow due to my day-job. This week they sent me off to a 1-week training course (which was excellent by the way).

I am absolutely confident in the design of the amplifier, with or without cascodes. I don't have any doubt it will serve my application well. So I'm looking at a pcb layout design rather than prototyping the amplifier first. This means learning some new things, not only how to use Eagle software but also different way of layout and mounting of power devices. I am considering incorporating a speaker protection circuit on the pcb so I'm playing with some simulations of this part of the design today.
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Old 17th September 2011, 04:48 PM   #830
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Default Beauty in Simplicity

Lazy Cat,

While reading this thread I'm so amazed with Yours pure genie simplicity, and Yours target . . the beauty of
purest sound playback possible.... Congratulation to You on such effective simple circuit with such great performance.
While You mention the SSA variants possible, there is the top one to be realised in future, an X Balanced version, similarly like F5. Perhaps unmatched performance especially if implemented with Lateral Fets in a BIBGT stile. A Holy Grail of Amp.
Thank You for all Your great share to the Audio community.

Best regards,

Andrew
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