That is good idea, I will prepare the parts list soon.
By the way the boards are on the way from China.
Here is the BOM with summary of needed components for one board at the end of the list.
If someone can double check if it's OK?
Damir
With vac231 help here is corrected BOM with summary of needed components for one board(dual mono).
Recommendations for building the preamp
Hi Damir,
are there any recommendations for matching the transistors. If yes, which transistors should be matched (PNP-PNP, NPN-NPN, PNP-NPN). I was wondering, why you use 0,1 % resistors for the emitter resistors.
Is it ok to increase R19 to 221R for a gain of 10 dB. Are there any poblems to exspect for this modification?
D1 LED sould be a standard LED,no high efficiency LED (2mA)?
BR
Günni
Hi Damir,
are there any recommendations for matching the transistors. If yes, which transistors should be matched (PNP-PNP, NPN-NPN, PNP-NPN). I was wondering, why you use 0,1 % resistors for the emitter resistors.
Is it ok to increase R19 to 221R for a gain of 10 dB. Are there any poblems to exspect for this modification?
D1 LED sould be a standard LED,no high efficiency LED (2mA)?
BR
Günni
Hi Gunni,
There are some requirements for transistors matching:
Vbe matching:
Q11/Q12, Q3/Q4, Q15/Q16, Q13/Q25, Q14/Q26
hfe matching:
Q1/Q5, Q2/Q7
Those 0.1% resistors are in Current Mirrors and distortion is greatly influenced by theirs mismatch. You can use 1% resistor but match R5 with R6 and R14 with R16 to 0.1% tolerance.
Transistors matching is not overly critical, DC offset will be corrected with DC servo and distortion will go up a bit if not perfectly matched.
The LEDs are just indicator that CCSs work, you can use even green one if you prefer the color.
You can use 221R for R19, the preamp will be perfectly stable.
BR Damir
TME has J111 (instead 2N5286) and J112 (instead 2SK170BL) but I never used them in GainWire. You can buy them, they are cheap, and try in CCS configuration with 15V power supply(or similar), to see what source resistor values are for requested CCS current, adjustable between 1 to 3 ma for J112 and 8 to 12 mA for J111.
This is an important post that should be linked from post 1. Otherwise will get buried as time goes by.
OK, done.
By the way, the boards somehow are held up at the Customs office here in Croatia (still slow bureaucracy from Yugo time). I have to pay some Customs duty, and hope I will have the boards this week.
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You don't need to match jfets for this preamp.
Just choose Idss you need. to do that connect the gait to the source and then connect 10V DC between a drain and a source(+ to the drain if nfet) and measure Idss.
