Simplistic NJFET RIAA

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#14,601
C4, C3 Low f attenuation

Salas,

I'm populating the MM version with 2 inputs, one for MM and one for MC and with a 8x or 16x step-up transformer. I'm still undecided about the 40dB or 43dB version.

The output will go right into a line-input transformer so I want to skip C4 and let C3 drop 1/f around 10Hz. In the PDF you recommend only 100nF for C3 in the low gain version, is 1/f all too high with 47nF?

Thanks
 
#14,603
tannat said:
Salas,

I'm populating the MM version with 2 inputs, one for MM and one for MC and with a 8x or 16x step-up transformer. I'm still undecided about the 40dB or 43dB version.

The output will go right into a line-input transformer so I want to skip C4 and let C3 drop 1/f around 10Hz. In the PDF you recommend only 100nF for C3 in the low gain version, is 1/f all too high with 47nF?

Thanks
Click to expand...

Use 8x and 43dB for a typical 61dB MC gain total. 16x will shorten overload spec. Not desirable. 43dB will not typically overload enough with 5mV on the other hand. Still in bounds for THD.
There is also a difference in R4 value for the 40dB config only that has to do with the C3 recommendation. So a 47nF would lighten it rather much. When with 43dB config will remain fine.
 
#14,604
Salas said:
Use 8x and 43dB for a typical 61dB MC gain total. 16x will shorten overload spec. Not desirable. 43dB will not typically overload enough with 5mV on the other hand. Still in bounds for THD.
There is also a difference in R4 value for the 40dB config only that has to do with the C3 recommendation. So a 47nF would lighten it rather much. When with 43dB config will remain fine.
Click to expand...

Makes perfectly sense, thanks!
 
#14,608
Pretty late in joining this project. I recently purchased Tea Bag's and Salas's kit for phono preamp. Making a present to my son - a vinyl lover. All is well, I am done and everything went as it should be all the way up to biasing, but would need some advice here please.

To start with configuration first: Cartridge and needle are Sure White label with 6mV output. Based on that I configured

Rx1- Rx4 = 33.K, 10K, 20K, 33K

Did not populate Q2, R3, used for R2 - 91ohm, for R13 5.6K 1 W, for R4 1.8K

C3 = 100nF

Power supply is providing 54V for each channel fed by two 2 x 18 V 50VA transformers.

The problem I am having on one channel - voltage between rail and ground is max 31 V at max trimmer position. Measurement btw. TP1 and TP2 is 4.1 V at max trimmer adjustment. In another word, I cannot make any more adjustment to achieve, requested in manual, voltages - 3.6V btw. TP1 and TP2, or 34 - 38V on Rail + and ground. All of the major parts are from matched Tea Bags kit, which means they are all matched properly and accurately.

The second channel manages to make max 33V and I am able to adjust 3.6V btw. TP1 and TP2.

Any advice how to bring it to spec values would be very appreciated.

Thank you

AR2
 
#14,614
P.S. 54V raw DC input is on the high side. If there is a chance it will go beyond 55.5V on your mains, better use some power resistor between the rectifier the and large filter cap to cut 5-10V. No harm, it will filter ripple also.
 
#14,617
Salas said:
P.S. 54V raw DC input is on the high side. If there is a chance it will go beyond 55.5V on your mains, better use some power resistor between the rectifier the and large filter cap to cut 5-10V. No harm, it will filter ripple also.
Click to expand...

Would that be in the RD/Link position on the PS board? I did try to have resistor there to see if I could lower some voltage but I recall it did not do much. I tried 1 ohm. I will try some other values, I did not work hard enough on that aspect I have to say.
 
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