Simplistic NJFET RIAA

[Salas]

Just try some coaxial shielded instead of the Mundorf 1% gold single strand I see in your pics. Don't strap the MM input RCA grounds together. Only coax from RCA to input load resistor on Riaa.

 

[Salas]

Is your arm grounded? Here is what to do for some initial hum busting, by looking at your pic. Maybe there is more to do.

 

[jonners]

Salas -

Now that I have added a buffer stage to my RIAA I'm aware that I have more gain than I need for my DL110. How much output can I get without overloading it? (33V supply, 6k8 drain and 39R source). Can I lower the gain by simply reducing the supply volts and adjusting the source resistors to keep 8V on the drains?

John

 

[Salas]

What is the gain of your amp, and the sens of your speakers? What kind of a buffer did you prefer to test?

 

[Thomo]

Hi Salas. Thanks for the suggestions, I'll start on those tomorrow. The arm isn't grounded now, as the connection was removed when I rewired it. I'll have to find a way of doing it again.

Cheers, Lee.

 

[jonners]

What is the gain of your amp, and the sens of your speakers? What kind of a buffer did you prefer to test?

I'm using a 2SK170 source follower buffer. I think my amps have 20dB gain, speakers are around 90dB.

 

[Salas]

You think like you need roughly half the subjective ear volume for same pot rotation?

 

[jonners]

Yes, about that much.

 

[Salas]

Try 21V B+. One parallel 6k8 per existing one. 3k4 resultant value for each Rload for stage 1 & 2. Rs stay 39 R. You must get 7.7V-8V Vd and proper gain. Its a rough estimation, trying to imagine your situation, try and tell me to tune it more if not ok.

 

[jonners]

Many thanks Salas, and goodnight - sleep well. (Do you sleep?)

John

 

[Salas]

Thanks. I sleep in weird patterns.

 

[Salas]

I'm using a 2SK170 source follower buffer

What circuit? Rsource or B1 style, or White follower? Did you notice it at all sonically, apart the drive boost?

 

[Salas]

Ah, Jonners! I almost forgot. If you find the new gain nicely usable in your system, change the series Riaa filter original resistor (82k//82k) to a single 47k new one, the 6k8 vertical one that leads to the 47nF cap remains the same. Else it will sound toned up in treble.

 

[jonners]

Thanks. I sleep in weird patterns.

Kalimera Salas! Weird patterns are good - very creative! ''

What circuit? Rsource or B1 style, or White follower? Did you notice it at all sonically, apart the drive boost?

Buffer circuit is as below. I didn't notice a sonic difference when I installed it.

Thanks for mentioning the 47K resistor - I had been wondering about that.

 

[Salas]

Hi,

If you try at 21V and like the gain, better feed the buffer with a 470R or 1k//1k=500R. It will restore its about original quiescent conditions when it was with higher B+. 11.20ma (151% Idss)

 

[jonners]

B+ is now 22V, and a 910R dropper keeps the buffer nicely warm at 11mA

I had no more 6K8 res to hand, so I used 8k2 in parallel with each drain res, giving 3k7. Drains are near 8V.

Playing nicely, gain is adequate, and a +15dB modulation from my test record into the DL110 gives an output at the buffer of 1.1VRMS.

Thanks again for your help, Salas.

 

[Salas]

Good to know. Its nice that we hit it with one try. Happy listening!
You not only rotate your volume knob more nicely now, you listen with less noise, which is what excessive gain only contributes to a system, along a short throttle.

 

[Salas]

Yet another one. The non cascoded 0.5mV 2 stage version and Vbe Mosfet shunt. Michael made it for his friend that has a Pink Triangle Anniversary with a Roksan Arm. He used a Goldmund pre with phono input, but it is up for sale now.

 

[Thomo]

Nice work there. This morning I built the shunt reg on stripboard, and I'll be testing later.

My hum appears to be a number of things. The armtube isn't grounded. It also seems to be caused by the TT itself! I shall build an external psu for it one day soon, and add lots of damping to the plastic underside too.

Cheers, Lee.

 

[Salas]

Hi Lee,

Do that coax thing I showed to bring a part of your hum down at least for now. I will be happy to know your impressions about the shunt later.