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VSSA Lateral MosFet Amplifier

Hi there, would need some help please :)

I m turning in circle with the TR1 & TR2 of the VSSA adjustment;

when I organize to have 120mv on TP1 then I have 200+ mv on the speaker out.
then playing with TR1 (or TR2) to brings that down to 0, then the VAS bias falls and I read 50mv instead of 120mv...

FYI, I have set TR3 so that the overall curent is arounf 180 ma roughly, but still, playing yoyo !!!

and I have same difficulty on another module

any feedbacks on similar experience welcome
cheers
 
More than that, I was, on my side, very surprised by the *low* price of those modules, if you consider how it should cost to order the parts on Internet, plus the saved time to list them, build them and tune the amps...
And, if we consider both the incredible quality/price ratio and the time spend by L.C. to design those fine amps, it is, really, just a gift.

Lc said he was having hundreds of these modules built. That brings the parts cost really down, specially if you build stock for future manufacturing! Costs a lot but brings the price down! I once built 25 units of a dac, and the parts price reduced by almost 50% compared to building a single unit.
 
oops, ok now I have the bias and the offset :)
in fact just need to be relax and play a bit with each pot :)
dont drink too much cofee before suc exercise

what I did : put TR1 to the max I could.
then reduce TR2 so that the value is on V1 is 150mv
then reduce TR1 to 135mv
then adjust TR2 for the offset to 0
then by magic the V1 was showing 125mv
breath , wait, and double check

cheers
 
maxidcx, nearly same as "steering the car, wife telling something, phone beeps, police at behind", difficult.
Balance, see picture :)
 

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maxidc, try to preadjust the potmeters so that you read ~200R on both R9 and R10. After that power up the module and adjust slowly and in small steps, just as BYRTT has pictured up.
In my XVSSA case it helped me a lot soldering 470R on top of both R9 and R10, so the adjustment range was reduced to more useful values..
Good luck and try to get most of patience before this step ;)
 
I want to buy a Talema Nuvotem toroidal transformer 2x30V - 300VA.
Is this transfomer big enough to power both channels ?..........
Yes, many members used transformer with such data for VSSA.

..........Are Talema Nuvotem good for audio apps ?..........
Don't no, but why not.

Else some trend goes with SMPS PSU's. LC tested and recommend HYPEX +/-45V SMPS400180 unregulated, 1xSMPS to 1xVSSA module, little expensive setup. Some have used Connex regulated +/-45V SMPS300R and SMPS500R (these are cheaper than HYPEX). If I remember correct one member run stereo modules from one SMPS500R, this setup will though have some power limit (lack of current at high output).
 
hello..

sorry if my question kinda silly..

i only have 2SJ118 and 2SK413 mosfets here.can i use them to this circuit?.if yes, how much i should bias the mosfet?.and how to check the bias since this amp has no source resistor.a 10Ohm resistor across the final supply?.

i couldn't find 2SC3503/2SA1381 here.can i use MJE340/350 instead?.

thanks in advance!
 
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Hi. I got problem with VSSA amp. Amp have little seasound in otput. Caps in powersupply are normal, intput cable is enought good, biasing is also in place (maybe +-4mV is variaton). In PSU i have 300VA toroidal transformer, and 12x 10000uF caps, but if there is something wrong, I must hear in output 50/100Hz?
Interesting case...
 
Hi Elektrohoolik and LC.
Attach picture where input cable seems to be braided with speaker cable, is that okay.
Also possibility that the blue bypass cap makes resonance, this said because after first entry for PSU spades at VSSA module there's 1mF electrolytic also bypassed, here by 1uF.
 

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Intput cable I already put other way (not twisted with output cables) to input. Plastic washer must also be between PCB ann screw (exepted output mosfet)? But i can't hear in output 50/100Hz sound (Ok maybe littlebit). Hmmmm. Blue caps, i gonna remove tomorrow , lets see what then happens, russian caps are sometimes like cristhmas present, you dont know what is inside... And if still noise is in output, i put output GND wire to GND connector at PCB. But interesting is that it it like digital noise, or like sea, not 50/100Hz.

Sorry about my language.
 
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Elektrohoolik yes it's funny the noice is seasound. Bypassing can make resonance with certain unlucky values, maybe that little blue one do that, it's cheap trying desolder one end. I can't see the input pair (BC550C/BC560C) in your pictures, you haven't put any metal art around their case to couple them thermal, then take that off and use non metal or glue them together.
Should be interesting to hear what coursed the noice.