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L'Amp: A simple SIT Amp
L'Amp: A simple SIT Amp
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Old 5th March 2018, 07:10 PM   #2901
atmasphere is offline atmasphere  United States
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If you use an effective CCS you may find that equalizing the currents through the differential amplifier is not needed.

I usually use a pair of devices wired in series, with the top gate referenced to ground via a zener diode, and the bottom gate tied to -V with the source. A biasing resistor is needed for the zener diode, and a second biasing resistor in the source circuit of the bottom device to set the current.

You should see measurably better bandwidth, lower distortion and greater gain with this setup.
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Old 6th March 2018, 12:19 PM   #2902
maxlorenz is offline maxlorenz  Chile
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Great. Thank you.
A very fast CCS is needed, so cascoded be it.
The good thing about resistors is that they do not have a slew to worry about...or am I wrong?
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Old 6th March 2018, 01:02 PM   #2903
maxlorenz is offline maxlorenz  Chile
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Already studying CCS's (source/sink) like mad.

I'll probably also replace the big R for the VFET with a good one soon.
More rejection and more power with one move. We'll see if the "electronic microscope" effect is retained or lost with that mod...
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Old 1st May 2018, 09:17 AM   #2904
qwertyl is offline qwertyl  United Kingdom
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I have 2 spare 400VA transformers, but they are 2 x 22VAC, not 18VAC. Can I still use them to build 193V version? Any adjustments need to be made to the original schematic?
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Old 2nd May 2018, 04:10 PM   #2905
plasnu is offline plasnu  United States
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Quote:
Originally Posted by qwertyl View Post
I have 2 spare 400VA transformers, but they are 2 x 22VAC, not 18VAC. Can I still use them to build 193V version? Any adjustments need to be made to the original schematic?
Easiest way to drop the voltage would be adding a few more resistors at CRC filter.
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Old 2nd May 2018, 04:26 PM   #2906
Zen Mod is online now Zen Mod  Serbia
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L'Amp: A simple SIT Amp
4V more is nothing to worry about

just set output node higher, accordingly
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Old 2nd May 2018, 06:34 PM   #2907
qwertyl is offline qwertyl  United Kingdom
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Quote:
Originally Posted by Zen Mod View Post
4V more is nothing to worry about

just set output node higher, accordingly
What do you mean? Should I set bias a bit lower than 2A?
I suppose I can always drop a couple of volts by adding another RC in power supply filter...
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Old 2nd May 2018, 08:34 PM   #2908
Zen Mod is online now Zen Mod  Serbia
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L'Amp: A simple SIT Amp
output node means point where output cap is connected ...... I'm pointing on drain voltage practically

you have more than enough info in thread , regarding Iq and output node voltage


what I was saying is - go ahead with your xformers , rail voltage isn't carved in stone
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Old 3rd May 2018, 07:25 AM   #2909
qwertyl is offline qwertyl  United Kingdom
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Ok, thanks. I will do a bit more digging
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Old 8th May 2018, 10:02 AM   #2910
sontero is offline sontero  Italy
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Originally Posted by maxlorenz View Post
Dear all,

L' Amp style amps, while being wonderful, may be seen (at least I see) as starting points in the learning experience and I cannot avoid wondering about many experiments to be done, like CCS, cascoded CCS, cascoded VFET, which are some of the steps to add to my already modded amp.

I have been using my Tokin amp with a differential amplifier for the input and it really improved a lot.

As some may know, I am experimenting with Peufeu's recommendations for diminishing (putative) thermal memory distortion effects, like the cascoded-CFP input pair. Well, yesterday I replaced the input pair differential with a "cascoded-compound CFP" pair of units, using Toshiba's SK170 as both, the cascodying element and as the "driver" of the CFP pair and a BC560 PNP as the "emitter follower" of the pair, with a 1K resistance on its emitter. I confess I studied some academic articles about this compound Szicklai but they were too much for me, so I took the plunge as the good Lord seemed to advice me...and it worked!

First listening tests are very encouraging.

I attach picture of the cascode-compound CFP units and a diagram of the target amp...

I hope you like it.
M.
Hi Max
Also me have a pair of sk180 as a soon experiment with l'Amp.
For now i have build a pair of MoFo monoblock....very great amplifier.
Waths is the gain of your interesting CFP?
Waths bias have the sk180 for 50v B+?
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