Simplistic NJFET RIAA

[RCruz]

Coax really matters when we are using TT.

My system is hum free but I experienced some trouble with hum in my previous systems.

Fo instance, before CD appeared (my first one was a Sony CDP1) I was allreday determined to mod everything so I decided to "improve" my B&O tangencial tonearm TT by replacing the 5pin din outputs by RCA so I could use better cables.

While I was at it, I did not know about coax virtues so I used unshielded high purity copper inside the TT connecting the cart to the RCA. Those wires had 5cm max lenght and the hum was unbearable.....

Recently I tryed my CD cables (Nordost flat unscreened) in my TT and while I get some speed improvements, I can not avoid the hum.

Now I am using some silver VDH cables (screened) on the TT and it is sounding wonderfull.

You progress looks good Lee

Ricardo

[Thomo]

I didn't replace any wires with coax. But as an experiment I did wrap the internal wires in the preamp with copper foil and ground that. It has seemed to help. The arm is now grounded also with a length of wire to the phono stage, which helped massively.

I will figure some way of shielding the remaining wire soon. I rewired the tonearm (an SME Series III) with high purity copper litz cable. This is silk insulated and was a good improvement on the original wire. The single lengths run right from the cartridge pins to the phono input of the pre/phono stage. I believe once I move the nasty transformer out of the TT into a separate box, and feed regulated power to the TT the hum will have gone completely.

I will also be attempting to adapt the phono stage board layout I did to accommodate these rather large Russian Military Silver Mica and paper in oil caps. Thanks for the nice hint there Salas, they seem to sound great even without burn-in.

Regards, Lee.

[Salas]

Hey, Lee, what's up? Made the whole thing with PSU? Listened at all?

[Thomo]

Hi Salas. I've done as much listening as I could, but I've not had time to test the shunt yet!

I am getting some distortion on vocals, which I assume is down to the cart mis-tracking, as it only seems to be on vocals. There is some sibilance on treble sounds too. I will re-align with a different template later on today, and once the Christmas tree is up, I'll have a go with the shunt reg too.

Cheers, Lee.

[RCruz]

What cart / arm are you using Lee ?

[Thomo]

The arm is a SME Series III, and the cart is a Grado Prestige with a Prestige Gold stylus.

I have rewired the arm and added some mass to the arm with Blu-tak and a 5 pence coin on the headshell, lol. I started a thread asking for mods advice about this arm here

I need a new arm I think, but funds are very tight so it'll have to wait.

Lee.

[Salas]

See about VTA too. It can give a harsh edge if the rake angle is too forward tilted.

[kstlfido]

...and it works! Can't listen too much- neighbors won't like it at 4:30 AM! I built Sala's 56db gain one on post 110.

Of the 2SK170's I got, the best 4 were all 8-8.16 mA Idss. Used PRP resistors throughout. Siemens ps for 47n Laclanche ps for the 100n, and Multicaps for the 16n. All the parts were better than 1% except for the multicaps, they were all over the place.

El chepo 'lytics I had on hand for the 470uF. I used a Solen and a Vitamin Q for the 1.5uF output couplers. I have more of the vit Q's so that will go in. Solen sounds 'tizzy' on first impression.

Built on old turret boards- tube style!

Using four 9v batteries as the PS parts have not arrived. It's an alligator dog mess at this point, but sure sounds great! Quiet! Airy! Bit thin on the bass.

Salas, I set my trimmers all to 40 ohms. How do I measure the Idss in circuit? I'm a big newbie to silicon. One board pulls 8.5mA; the other 8.6mA. That sound right?

To think of the tubes I would have to go thru to find quiet ones.... this is so much easier. Now for the break in. Tomorrow.

Thank you, Salas!

-Kent

[Salas]

Hi Kent,

You just adjust the source trimmers so to read 8.1V on top of every FET where it meets its load resistor. There is no such thing like in circuit Idss. Its just that the stronger the FETS for Idss are, the stronger they pull current in a given circuit and the stronger they gain. If you equalize the voltages you will be OK.
I hope that you are not driving an impedance under 50kOhm and you notice lean bass just because you did not employ an additional buffer stage and/or the output capacitors are rather small for what you drive.
Otherwise, the somehow thin bass must be due to 9V batteries and alligator clips. Much added PSU impedance as is.
This Riaa sounds noticeably good on bass normally. Especially when you employ the shunt PSU, that I highly recommend as it is a very successful partner. You will notice a strong sonic lift.
You will be fully OK when you properly supply it and connect it for sure.
The best thing is that already you made it quiet which could be a main trouble part. Let me know more of your system, line in impedance, and progress. Congratulations, nice start. I like the construction style too.

[Salas]

P.S.

Originally posted by kstlfido
Airy! Bit thin on the bass.

-Kent

I saw something on your picture that is going to tilt the response somewhat up towards the highs and will surely contribute to a false tonal balance. That capacitor looks smaller than the 16nF asked by the circuit, at a measured 14.31nF. You must do something about that, by adding some small one in parallel.