Simplistic NJFET RIAA

[RCruz]

I have seen 2SK170s failing for no apparent reason before. There are some weak ones it seems but its not often at all to see them fail randomly when used for under 100mW self dissipation. Still I remember one or two in a friend's builds. He was using a rather heavy soldering iron characteristically, l don't know if that can weaken some for long run reliability or not after they start working OK nonetheless. Your suspect FETs should not show less than 35R across else they have failed shorted or partly shorted.

All fets show 39r

 

[Salas]

They were all selected for same idss originally, hence the same RDS? Its better the top buffer fet to be a bit stronger than the one at its tail.

 

[rclourenco]

Folded C2x

Hi,
Can anyone advise if I can 3,3uF for C2x instead of 4,7uF?
Thanks

 

[Erlend Sæterdal]

Hi,
Can anyone advise if I can 3,3uF for C2x instead of 4,7uF?
Thanks

Salas did that earlier in this tread. Have to be 4,7 because it is a Zobel . Or use a electrolyt and no resistor ( 1,2 ohm)
In that case use a jumper for the 1,2 ohm

 

[Salas]

You don't need a jumper in case of 22uF/50V normal ESR electrolytic bcs I have provisioned it auto skips the resistor position.

4.7uF or 5uF only in case of MKP and the 1.2R populated.

Did you find a TT for a session yet by the way?

 

[rclourenco]

You don't need a jumper in case of 22uF/50V normal ESR electrolytic bcs I have provisioned it auto skips the resistor position.

4.7uF or 5uF only in case of MKP and the 1.2R populated.

Did you find a TT for a session yet by the way?

Thank you both!

 

[Erlend Sæterdal]

You don't need a jumper in case of 22uF/50V normal ESR electrolytic bcs I have provisioned it auto skips the resistor position.

4.7uF or 5uF only in case of MKP and the 1.2R populated.

Did you find a TT for a session yet by the way?

No it is almost Christmas. People are busy. Next week A friend will bring a TT.
I am working hard on a power amp. And also the buffer . I am going to compare it with another one I made when it is finnished.

 

[Salas]

What technology is the other one? Opamp, BJT, tubes, NFB, open loop?

 

[Salas]

The Simplistic's natural class is low active parts count no overall NFB loop circuits. Apples to apples comparisons would be classic structure tube phonos and very few minimalistic SS. Even a Pearl is a stretch. To see what class of circuits sound someone prefers though poses no comparison limit.

 

[Erlend Sæterdal]

What technology is the other one? Opamp, BJT, tubes, NFB, open loop?

Not another Riaa/ MC. Another buffer from Teabags GB. So I will compare two off the buffers with only smalll differences. Did not like the first I made.

 

[Salas]

You will need a 0.7V sensitive amp to have good dynamics from a unity buffer if the source is phonographic.

 

[Erlend Sæterdal]

Will be a dac.

 

[nezbleu]

re: Q2x, Q3x, Q5x
I am not going to get 6 2sk117's with Idss between 3-4mA; in fact I'm not measuring any under 4mA. Assuming a spread from 4-6mA, which spots should have the "stronger" fets, which the "weaker"? I'm assuming a fairly strong one for Q2x is OK to boost the Vf of the LED's a bit; for Q3x and Q5x does it matter which has higher Idss?
Thanks.

 

[Salas]

Use your stronger for Q3X and 6.2K R3x. Use your medium for Q2x and 27R R6x. Your lower ones for Q5x.

 

[Marra]

I had a go at sorting my boards this morning swapping out the four leds and the output caps and reflowing a couple of joints.The phonostage is powered up;no smoke;and I have the following readings.

LEFT RIGHT
VDC 43 43
G/+rail 33.6 33.5
TP1/2 3.43 3.45
G/TP1 7.75 7.75
G/TP2 4.31 4.29

I'll it for a few hours to check things and hopefully will have a good result when I have a listen.

 

[Salas]

Very good readings.

 

[nezbleu]

Use your stronger for Q3X and 6.2K R3x. Use your medium for Q2x and 27R R6x. Your lower ones for Q5x.

Thanks Salas. Now I notice the note on the BOM about the resistor values, and the alternates are in Teabag's excellent minikit. Sorry for the noise.

 

[Salas]

Only a little additional questional noise (new physics LOL) does no harm when aiding builders clarify the guides, still adequate SNR for vinyl replay.

 

[skouliki]

Regarding the 47nf RIAA capacitor i found in ebay some Siemens rectangular polystyrenes with dimensions 12x12x12mm. I was thinking that i could solder these on the underside of the board. Is the extra lead length a problem in a Riaa?

 

[Salas]

Adds inductance. I don't think it will change the audio frequencies curve at all but it will not match the 1837's short legged application in a pulse test either.