L'Amp: A simple SIT Amp

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juanitox

juanitox

Member
Joined 2006
Eventually, you'll want to get your voltage references working. These really shine with no degeneration, and I think you'd do well to focus your effort there. I have, after all, posted a working schematic which you can easily build on perfoboard.
Click to expand...

michael , i came back with this but i want to be sure there is no misunderstanding , fig 11 without bypass cap on source res sounds very bad i agree but with a 47000uf and 22ufMKP on it , it's sounds as good if not better than my first version with negative bias..

anyway i will retry fixed bias cause i had not the CLC power supply that i have now :rolleyes:
 
Zen Mod

Zen Mod

Official Court Jester
Joined 2003
zenmod.in.rs/
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M

Michael Rothacher

Pass DIY Apprentice
Joined 2001
passdiy.tv
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juanitox said:
michael , i came back with this but i want to be sure there is no misunderstanding , fig 11 without bypass cap on source res sounds very bad i agree but with a 47000uf and 22ufMKP on it , it's sounds as good if not better than my first version with negative bias..

anyway i will retry fixed bias cause i had not the CLC power supply that i have now :rolleyes:
Click to expand...

I understand. Have you considered the possibility that the difference might be attributable to a problem with your original voltage reference setup?
 
juanitox

juanitox

Member
Joined 2006
sure it was because now even if the R-core still make a little mechanical noise there is nothing out with the head inside the 102db horn .. so perhaps it was the lm337 bias module which had ground loop with my ancient power suplly.

also when i turn on the new PS with this module they explose immediatly perhaps because it makes a short circuit somewhere , i'm lost...:confused:

as for the fixed bias VS auto-bias i'm used to that with SET tube amp , and i don't know why as in theory fixed bias is better in practice you get a more 'tubey" sound with bypass resistor on cathode..
 
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nicoch58

nicoch58

Member
Joined 2004
juanitox @ lundhal have nice filament choke....
catode bias drop the B+ on the catode resistor on transient a sort of limiter/compressor...fix don't have the big bad caps plus without the limiter can fly better...
not too expert but probably the tube sound are the elko on catode at last on my driver stage the silmic do this vs PP or oscon
 
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flg

flg

Member
Joined 2005
When I was experimenting with ZV9, with a choke load, there was this other interesting enthusiast we havent seen much of lately. Maybe some of you have not seen before "The Donut". I'm not sure what to call it? If you know Magura, you know:) If this is new to you???
ZM!, what is it I want to send them to. A monster differential choke loaded donut borrowing from ZV6, 7 & 9?
 
M

Michael Rothacher

Pass DIY Apprentice
Joined 2001
passdiy.tv
Paid Member
ra7 said:
Q. What controls the amount of current through the CCS? Is it the bias voltage on the SIT or the Vgs of the IXTH? Or both?
Click to expand...

It does feel a bit "chicken or the egg" doesn't it?

As ZM points out, the MOSFET is self-biased, and we're using the adjustable voltage reference to balance the currents and put the SIT drain where it needs to be. You could use a slightly smaller source resistor and run with higher current, but I found that wasn't really necessary as it didn't have a big impact on performance. Also, the bigger source resistance helps stabilize the CCS a bit. I included a spot for RTRIM, a trimming resistor, in the drawing in case you want to really fine tune things.
 
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