Simplistic NJFET RIAA

[Salas]

Which are those face to face TO-92s? There is no dif pair so they better not touch. Using K369?

 

[buzzforb]

Top two transistors are BF245 and BC560. I built the dual 170 version.

Edit:
This one
http://www.diyaudio.com/forums/analogue-source/129126-simplistic-njfet-riaa-839.html#post3221512

 

[Salas]

They better not touch. How did you manage R13 for 2W? It really needs be 2W.

 

[buzzforb]

IT is 2W SMD. I made pad large to help with heat. When speaking of the TO92 touching, is it simply to avoid thermal coupling.

 

[Salas]

Yes, those two are different semis doing different stuff and they must not be thermally coupled. Do you have provision to trim the 15nF RIAA cap with some Mica up to 15.15nF maybe? Cruz went there after some subjective fine tuning he mentioned. But that is not de facto for every system and cart and user of course.

 

[buzzforb]

I have some coming, but not with me. You can see spots on one of the boards for adding trimmer caps. Really just want to get it up and running. There is plenty of tuning to be done. I am runnning the shunts with 10R and 240mA. Here are the skins I am using. Based on the spreadheet, they should be adequate and make for easier isolation.

 

[Salas]

I have seen those two pads under the smaller XO cap that is why I commented on trimming. Not a big deal for now. Did you check the RIAA caps on LCR meter BTW?
Regarding regs, remember NOT to disconnect power rails during tests if not measured very low or zero first after power down. The 1000uF capacitors near the trimmers store enough energy to kill trimmer and kick back to the reg even. They need let to discharge first. Its in the folded PDF but I stress it here again.

 

[buzzforb]

I have seen those two pads under the smaller XO cap that is why I commented on trimming. Not a big deal for now. Did you check the RIAA caps on LCR meter BTW?
Regarding regs, remember NOT to disconnect power rails during tests if not measured very low or zero first after power down. The 1000uF capacitors near the trimmers store enough energy to kill trimmer and kick back to the reg even. They need let to discharge first. Its in the folded PDF but I stress it here again.

I admit I did not check the caps, as I paid Parts Connexion to match them. After I get the whole operation running, I will check the RIAA curve properly. THanks for the tip, I saw that mentioned in the document.

 

[vgeorge]

Nice work Buzz!
I would also try with an electrolyte around 220 - 470uf with BIB in the Vref position.

 

[buzzforb]

You liek better than MKT? I have some Elna Silmics

 

[buzzforb]

Salas,
120R across shunt reg output should give me target laoading of RIAA stage, correct.

 

[Salas]

1000R for 35mA @ 35V to sim one channel with 2x170 input.

 

[buzzforb]

My apologies. I calculated 300mA not 30.

 

[vgeorge]

You liek better than MKT? I have some Elna Silmics

It is recommended for more sensitive circuits like phono.
You can always try with MKT and compare.
Elnas Silmic II are good.

 

[buzzforb]

Ill switch. Must have missed that one in document. Too big a hurry.

 

[RCruz]

Hy buzz... splendid work.

You ordered matched caps... but did the supplier write down the actual values on the caps ?

If you have that info, maybe you also have the actual measured values of the resistors.

If so, would you be so kind to post them.... I love maths you know

 

[buzzforb]

The TNPW are .1% tolerance, one of the main reasons i used them, but ill try to check them all. Gonna have to use a single shunt reg at first. Bent 9530 leg twice and it broke. Any options other than mj bbjt? Did not measure caps. If we like it, i expect to redo the board with some refinements.

 

[Salas]

9240-9140 if they fit for a while.

 

[zeeuw]

Hello Salas

Finished today and connected.
Sounds great,more detial and stage

 

[Salas]

Congratulations. With what cart and system you use it? What you had before for phono pre?