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Old 25th January 2010, 09:59 AM   #11
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Quote:
Originally Posted by juma View Post
Thanks Vladimir,
I found another one (I think it says Pd max = 50W, transconductance = 2 S ):
The place you have found is even better, good luck with buying. Pd max = 50W is a result of (150 - 25deg)/2,5 = 50W. I dissipated nearly 50W on them during measurements, no problem happened.
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Old 27th January 2010, 10:28 AM   #12
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For me it is clear why triode-like features of output devices of power amp is good, because speaker is a complex load. But how one can imagine sound improvement due to triode-like devices in preamp? Can backward EMF from loudspeaker be delivered to preamp output?
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Old 27th January 2010, 10:39 AM   #13
Stefano is offline Stefano  Italy
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Have you seen this: ‚’ep
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Old 27th January 2010, 11:00 AM   #14
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Originally Posted by Stefano View Post
Have you seen this: ‚’ep
I know this site for a long time, but the simple ciclotron schematic with 2SK183 is very interesting, thanks. However, I see no hint whether SITs (not like the huge 2SK183) are good for preamps.

A friend of mine says that it is important for preamp to have an idle current 150mA or more, but can't explain why.

Last edited by VladimirK; 27th January 2010 at 11:23 AM.
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Old 28th January 2010, 04:58 AM   #15
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Originally Posted by analog_sa View Post
... How about an active load ...
Theoretically an active load is better than resistor, since current consumption becomes fixed and signal current does not go through the power supply. But in this case one must employ NFB for achievind desirable gain of the stage. I tried an arrangement like a combination of Zen2 and Zen9, with 2SJ162 lateral transistor in the current source, without input buffer, and the resulting sound was not very detailed.
The present simplest resistive load, though impose tuff requirements to power supply quality, sounds good. I used Elna Cerafine 470uF + 2,2uF polypropilene at the end of regulated PS (from 25V to 15V) for the buffer stage, and 10000uF Samwha + 15uF polypropilene + 2,2uF polypropilene at the end of double (connected in series) PS (150V to 125V to 100V) for the SIT amplification stage.
Rectifiers in the PS are Shottky diodes.
Of course, PS as a part of signal chain becomes complex, but it is a payment for the gain stage simplicity and NO NFB.
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Old 1st February 2010, 04:31 AM   #16
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I have addes Solen 80uF polypropilene to the power supply of amplification stage, now can state that the SIT-preamp overtakes JC2 in every aspect.
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File Type: jpg Preamps Being Compared.jpg (112.4 KB, 762 views)
File Type: jpg SIT Preamp Inside.jpg (123.2 KB, 658 views)
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Old 12th February 2010, 05:02 AM   #17
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Thinking about further possible improvemens of simple SIT Preamp schematics, I plan to make parallel stabilizer with current source on the top of it for the amplification stage. Could somebody comment it, especially the choice of active components ?
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Old 12th February 2010, 09:28 PM   #18
mos57 is offline mos57  Italy
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Active device 2SJ200 are very good as old Hitachi L-mos. I don't like the zener diode as voltage reference. Try Norton equivalent as J. Curl. However, i think is better to put a big capacitor in parallel at the output of the 2sj200 to close the AC path of the output stage.

Also sincerely i think your amp is almost a SE Power amp than a preamp.

Are there other little russian SIT devices ( about 1-10 W) that you can employ?

Otherwise i am finding for those little Sit
I not understand russian language: can you tell me about?

Francesco
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Old 15th February 2010, 03:46 AM   #19
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Originally Posted by mos57 View Post
Active device 2SJ200 are very good as old Hitachi L-mos. I don't like the zener diode as voltage reference. Try Norton equivalent as J. Curl. However, i think is better to put a big capacitor in parallel at the output of the 2sj200 to close the AC path of the output stage.

Also sincerely i think your amp is almost a SE Power amp than a preamp.

Are there other little russian SIT devices ( about 1-10 W) that you can employ?

Otherwise i am finding for those little Sit
I not understand russian language: can you tell me about?

Francesco
Francesco, thanks for your comments. Indeed, this schematics could be considered as a current amplifier (Rout=200 ohms) for speakers like Fostex etc. It sounds good, but some doubt is remaining that with shunt type power supply it could be even better. Now I escape from the power supply modulation only due to big polypropylen cap. I should also check the Norton equivalent.
As of medium power SITs, there are nothing among russian parts. I guess the only one in the world is 2SK79, indicated in the poat #4.
There is very good medium power russian j-FET, KP903A, N-channel, P=6W, Io=450...700mA, S=85mA/V, Ciss=15pF, Uds max = 20V. They look excellent in cascoded mode for driver stages of Pass Aleph like schematics, and for capacitorless buffer preamps.
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Old 15th February 2010, 07:45 AM   #20
mos57 is offline mos57  Italy
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Quote:
Originally Posted by VladimirK View Post
Francesco, thanks for your comments. Indeed, this schematics could be considered as a current amplifier (Rout=200 ohms) for speakers like Fostex etc. It sounds good, but some doubt is remaining that with shunt type power supply it could be even better. Now I escape from the power supply modulation only due to big polypropylen cap. I should also check the Norton equivalent.
As of medium power SITs, there are nothing among russian parts. I guess the only one in the world is 2SK79, indicated in the poat #4.
There is very good medium power russian j-FET, KP903A, N-channel, P=6W, Io=450...700mA, S=85mA/V, Ciss=15pF, Uds max = 20V. They look excellent in cascoded mode for driver stages of Pass Aleph like schematics, and for capacitorless buffer preamps.
T4 act as a current generator and T5 as a voltage generator.
Yes i like your amp, it is a current amplifier or as i prefer to call it "transconductance amplifier". (see my site also)

Other little V-FETs are 2SK63 (equiv. to 2SK79) 2SK69/2SJ19, 2SK78/2SJ24 and 2SK75 as medium power, but all they are very scarce (i have 2sk79 only).

Thanks for your advice about KP903A but at this moment i need a P-CH type.
Is there a similar jfet as KP 903A in a P-channel type?

Francesco
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