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Old 3rd July 2012, 01:45 PM   #2711
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Originally Posted by dadod View Post
I think that two pairs of those lateral are not enough if a load drops to low and +-70V is to much for this amp.
I used-it with +-75V in his VFB version for years with 6 Ohms load. (i use to compensate my speakers both motional and zobel to get a near flat impedance on all the bandwitch.).
Well 3 // units on each side would be better to have a perfect value of the impedance hole of the power fets, so: more stable.
Again, i do not see any interest in trying to build this crescendo amp, for those who do not have it yet. Components are obsoletes (for some, it is a pity) printed circuit no more available, etc... The only interest, is to improve this amp for those who have-it yet, on my point ov view.
About sims, i'm of the old school. we do not had this tools, in our laboratories, when i was on the business. Just multimeters, volt meters, osciloscopes, distortiometers. and slide rule

About simulation values, as, on the VFB version, the spice models used give quite good result comparing to the real amp measurements, i do not think there are to far away from my parts.
And, on my CFB amp version, when i tuned-it, the square waves where ok for that kind of slew rate: Limit of my generator.
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Last edited by Esperado; 3rd July 2012 at 01:51 PM.
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Old 3rd July 2012, 03:41 PM   #2712
dadod is offline dadod  Croatia
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Quote:
Originally Posted by Esperado View Post
I used-it with +-75V in his VFB version for years with 6 Ohms load. (i use to compensate my speakers both motional and zobel to get a near flat impedance on all the bandwitch.).
Well 3 // units on each side would be better to have a perfect value of the impedance hole of the power fets, so: more stable.
Again, i do not see any interest in trying to build this crescendo amp, for those who do not have it yet. Components are obsoletes (for some, it is a pity) printed circuit no more available, etc... The only interest, is to improve this amp for those who have-it yet, on my point ov view.
About sims, i'm of the old school. we do not had this tools, in our laboratories, when i was on the business. Just multimeters, volt meters, osciloscopes, distortiometers. and slide rule

About simulation values, as, on the VFB version, the spice models used give quite good result comparing to the real amp measurements, i do not think there are to far away from my parts.
And, on my CFB amp version, when i tuned-it, the square waves where ok for that kind of slew rate: Limit of my generator.
I am old shool too(retired telecomunitation engineer) and Spice simulator is great tool, so I am trying to lern it now.
Simulation with your lateral transistor models shows low distortion too(when I changed CCS zener from 3.9V to 4.7V) but with wrong resistors values. One of them is R33 8ohm resitor, and with 1.13mA of the VAS current produces 138mA per output transistor pair. This impossible in real world, so the models are wrong.
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Old 4th July 2012, 04:39 PM   #2713
Sheldon is offline Sheldon  United States
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Originally Posted by Sheldon View Post
Finally got this thermaltrak version in stereo and housed.

http://www.diyaudio.com/forums/attac...hermaltrak.jpg

Not as neat as LC's fabulous versions, but quite functional. The SSA amps are on the vero board at the rear of the chassis. The other two amps are symasyms - for a four channel amp (still need a set of binding posts and rca jacks for the symasyms). Early listening to the SSA shows no defects that I can hear. Clean, clear music, powering the range above 300Hz so far. I like it.

Technical: Gain of 23dB. No noise at all with 100dB+ speaker. Very slight low frequency blip at switch on (100mV offset, maximum). Not audible with my speakers. No audible blip at shut off. Offset wanders around for a minute or so, but settles down to less than 20mV. Nice square wave at 100kHz - slight, well damped overshoot with a load, a little more pronounced without.

Practical: It takes a while to tune in the bias and offset, as they are interdependent. Once done, it's stable so far. If I were building again, I'd adjust it close, then measure the 500R pots on the current sources. Then I'd replace with a resistor and 50R pot, as it's quite sensitive to small changes and takes some fiddling to get within 10mV. But I'm not highly motivated to order the pots and change now, as I've already done the fiddling. The input transistors are from the same batch and well matched within type, but no matching across types. The driver and outputs are not particularly well matched. They are what I had.
Did some tweaking, as the bias drifted more than I liked. It seemed to be over compensated. As the overall amp warmed up, bias moved down and the spread between start-up and steady stage was about 2 fold. The steady state point tended to go lower when the amp output was increased. With the amp just on the heatsink, I didn't see this, as the input and drive transistors were exposed to room ambient. With the amp all cased up, they were in a warmer environment, and the NTC resistor overcompensated without the 220R (I think that was the original recommendation) series resistor. I tried 180, but that tended to undercompensate, so I settled on 130R in series with the NTC. While I was at it, I substituted 180R and a 50R pot for the 500R pot that sets the CCS current. This made adjusting a lot less touchy. End result is that bias starts out at about 5mV (0R1 emitter resistor) and climbs to about 12mV over a couple of minutes, then stabilizes at about 16mV a few minutes later, and stays there over hours. With a 5W sine wave output, the bias drifts up less than 2mV as the amp temperature goes up a little. That would more than cover any average power requirement that I would need.

I believe that the main issue for compensation is the fact that the input pair, drivers, and CCS, all contribute to the bias drift. The NTC provides a single compensation which must counteract the summed effect of the three contributors. In my case, they each reach equilibrium at different rates and reach different temperatures in response to a change in their ambient setting. If someone were to do a similar version, I would recommend trying to get the input, driver and CCS (bottom of the cascode pair anyway), on a single sink. Then they would all reach similar temperature together and compensation should be fairly easy to get right. The outputs, on the main sink, are well compensated independently.

Scope pictures look good. Only a little overshoot, visible here on a 100kHz square wave (5mV/div, 10x probe). Sine waves don't show it, except a couple mV spike on the peaks at 1mHz - not visible as amplitude is increased. I'm inclined to leave it as is.

Sheldon
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Last edited by Sheldon; 4th July 2012 at 04:55 PM.
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Old 12th August 2012, 06:42 AM   #2714
shaan is offline shaan  India
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Hello everybody!

Glad to see this great thread moving forward(which it should).

I'm here to share the story of my re-incarnated SSA which I built a week ago.

As the pictures show I built the front end and the VAS+cascode on different boards and interconnected them with 7 wires. BC550C/560C as input, same as cascodes, BD139/140 regulars as VAS, 1N4148s for bias setting and 1058/162 Laterals as outputs. The diodes set the bias to a nice 150mA through the FETs with +-25VDC supply. Total Iq is 180mA. 5pF silver mica caps as bandlimiters in the VAS and 5.6pF(Old Philips ceramic) as input RF filter. Offset control with two 10K small pots from +-15V zeners, filtered with 1uF siemens MKT. Power to the VAS and the front end is supplied through two 1N4007s with 1uF before them and 1uF+1000uF after. 100ohm gate stoppers and no Zobel at the output.

The amplifier worked like a charm the very first time it was turned on and after setting the offset I was listening to music within 5 minutes of the first run.

No hum, No noise, No offset problem, No overheating, No bias drifting, No nothing!!!!! What is this amplifier!?

Music didn't stop for two hours. And people, what dynamics, what purity, what bass, what mid and overall, what sparkling treble! The speakers were singing!

Honestly, I think my fullrange drivers are not truly full-range at all. But I didn't realize what they were capable of until they met SSA! I have found the holy grail of amplifiers!

Great vocals, both male and female, sitar, sarod, tanpura, mridangam, sarangi, guitar, piano, drums, flutes, violins, cellos, saxes, kicks, claps, cymbals, crashes, snares, bells, synthetics... EVERYTHING sounds JUST RIGHT... what a pleasure!

Tonal character unchanged from very low volume right upto very high! How does SSA do this? No other amp I have built or listened can successfully show this charecteristic and SSA does it with ease, even with my 4" $2 drivers! How, where's the magic?

The sound is absolutely non-disturbing for long listening trials. I live with my mom and sis. And they are excellent and sensitive natural scopes(:P) for the testing of this very parameter. In the past they have helped me accurately decide an amp's "obstructive" or "intrusive" or "artificial" or "just bad" character. They say that when I play music through a good amp it feels like someone else is present in my room and is singing or like there are real musical instruments being played in my room, feels real from outside. For the SSA, their remarks are "NATURAL" and "LOVELY".

All these with a 5 meter coax from an AC'97 sound card and an input cap which is, ahem, a cheap bipolar 10uF electrolytic.

SSA is a milestone for its simplicity, a benchmark for its speed, a crown jewell for its music.

My drums mentor, the man I respect the most told me that very good things will happen to me this year. One happened a just week ago.

LC, Thank You. We are lucky to have you around.
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File Type: png SSA.PNG (33.3 KB, 473 views)
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Old 12th August 2012, 09:15 AM   #2715
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Originally Posted by shaan View Post
LC, Thank You. We are lucky to have you around.
Hi Shaan, I am flattered, thanks, should rename myself to Lucky Cat

Very very positive impression regarding music reproduction from you Shaan, Nico Ras, Bigun, Esperado, Sonnya, MiiB, Joachim Gerhard, Sheldon, Lazy Cat, Jazzz (SSA owner) and maybe somebody else in background. Still waiting Marc to finish TSSA and of course all others invited.

What surprises me the most, all the guys from above made each their own PCB-s, some even without and some PCB in P2P like you Shaan (pure work of art!) and in spite of all kinds of good amps available still listening to SSA/TSSA.

What can I say, I am honoured to know you all my friends, enjoy the Sunday and good music, regards Andrej
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Old 13th August 2012, 02:17 AM   #2716
Bigun is offline Bigun  Canada
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Old 13th August 2012, 03:26 AM   #2717
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Old 17th August 2012, 01:18 PM   #2718
shaan is offline shaan  India
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After two weeks of daily operation I checked the offset and bias today. Both unchanged. Whoa!

Probably the best fortnight spent with an amplifier. There has only been signal, no noise. So the psychological SNR or satisfaction is infinite mathematically.

I have some questions. I did not feel a hint of distortion from the class-AB SSA. If the SSA with source follower config already sounds(and measures) so well, then why is there the drain follower TSSA with limited power, hot sinks and big Zout? For the fostexes and lowthers? Or is there a noticeable increase in audible and measured performances? Does it sound the same(or better) through the same speaker drivers? Is it an attempt to eliminate as many gain stages as possible? Or is it for demonstrating the scalability of the SSA front end?
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Old 17th August 2012, 04:48 PM   #2719
DIGORA is offline DIGORA  Belgium
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Hi

Esperado is using CSS instead of cascode on the input stage, what is better ?

I would like made an amplifier with lateral mosfet for my Magnepan 1.7 (86db 4ohm)

What do you think about using SMPS sypply for SSA amp ?

Thanks
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Old 17th August 2012, 05:26 PM   #2720
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Esperado is using CSS instead of cascode on the input stage, what is better ?
No way to answer to this kind of question: "What is better". As each circuit has his own sound/advantages/disadvantages.Current mirror brings an advantage on bandwitch: As the frequency of the first stage increase, his efficiency, so his current consumption increase. Then you have some sort of auto-compensation with an increase of the resultant bandwitch. That you will pay at the extreme hight end with a highest Q roll-off., IE phase rotation.
Quote:
Originally Posted by DIGORA View Post
I would like made an amplifier with lateral mosfet for my Magnepan 1.7 (86db 4ohm)
What do you think about using SMPS sypply for SSA amp ?
Again, you'll have to listen, compare, to make your own subjective conclusions. Just remember that, if Current feedback topologies brings-you reduction of distortion as well as increased bandwitch, you will pay it by a worse ripple rejection of the power line. So SMPS will need great filtering care of it switching frequency. But you will win on price, compacity / efficiency, dissipation, regulation. I prefer SMPS for analog amplification, linear power supply on Class D amplification. Some will prefer the contrary ;-)
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