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GB for Salas Folded Simplistic Phono PCB

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#43
Salas said:
I have included a table for 10-15 mA 2% Idss tolerance 369 matches in the guide. That is I actually tested them on the breadboard with the source pin resistors mentioned.
So its a broad range that should make many samples usable. When they run at about 9mA bias after degeneration with proper Rs they present the same transconductance.
So if you got 13mA samples you know what resistors. 12mA, again you know, etc.
Use the next nearer mentioned resistor for midway Idss. I.e. you got say 12.6mA match use the next higher mentioned Rs. I.e. the one for 13mA. If you got 11.4mA use the resistors of 11mA etc.

P.S. It will even work with same IDSS & Rs table K170s at input but in less gain and bit more noise. A compromise.
Click to expand...

Are these Rs always the same if using one or two fets in the input ?
 
#50
arthur said:
Add me 2 boards 2 minikits and 4 s369 quad
Thanks
Click to expand...

Okay, probably no 4 quads, even if 4 boards are ordered.

It's looking like 25.00+ USD for a quad at this rate, for the amount of unusable <10 and >14ma I get, in addition to looking for matches within that set.

I cannot at this point promise 2% matching across a quad. I don't have lab grade equipment and stable temperatures and no breezes enough to be certain they will measure the same way multiple times under similar conditions. Salas and I settled on 1 min. 30 second measuring time at general room temp, and to when they stablize.

You can purchase the set, and if unsatisfied, send them back for a full refund, re-measured by you but unsoldered. So far, I cannot promise I can even get more until they are in my hands, and then hope I get the same rate of matches.

I have purchased some from Zhoufang on ebay, and they measure just like other ones I have received from another hobbyist. I encourage you to purchase and measure your own for peace of mind.
 
#53
Guys don't get intimidated by the matching thing. When its difficult for a single source guy to produce ideal matches for everybody, the guide's IDSS range and compatible degeneration resistors are quite broad when having a few at hand. In the high MC and MM cases there is even more slack to 5% because the samples gm falls much together by the harder degeneration to reduce sensitivity. Much less thermal drift happens also. Enough left overs are good there. For MC+ HMC MM there are only two 369s needed, remember.
 
#55
In the end its just about not losing significant target amplification and to track gain well between the channels.
Better than a cartridge's channel balance spec at least (0.5dB in expensive ones, 1dB or worse in most).
Even when you match everything IDSS super, you don't really curve trace, and the second stage has play also.
But you don't get bad gain mismatch so easily. Still you can fix the situation if dangerously out of good IDSS stash:
Final weapon is tuning R8 when you get a gross gain mismatch as a result of various tolerances.
It takes 1kHz generator attenuated for cartridge level sine wave, it can be computer audio via 1K:10R Lpad.
And a DMM on AC mode if without a scope. You attenuate the louder channel is best practice. Meaning a higher value R8 there.
 
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