Simplistic NJFET RIAA

[le´flu]

Hi,

thanks for your rating. I think i´ll try the itch.
Is there a later Version or ist revision 1.2 the newest one?

https://www.diyaudio.com/forums/analogue-source/140635-valve-itch-phono-157.html#post3802065

And the PSU ist still as in #3 ?

Greetings

 

[Salas]

There's no more than 1.2 & yes PSU is #3. Good luck in making it as it takes 100% handcraft and let us know how it went in its thread. Be careful with high voltage, but you already know that.

 

[le´flu]

Hi Salas,

thanks. As it is noch my first valve-Project i´m not afraid of high voltages.
And no problem with handcraft - valve-projects need less parts ;-)
What gain can be expected from the Ref. 1,2Version without the SUT?

 

[Salas]

Says on the schematic 45dB after the SUT meaning the circuit's gain alone

 

[MASantos]

I got myself a rega RP8 with dynavector XX2mk2 and a rega aria phono stage.

I will be changing my simplistic for MC duties and then try to compare them side by side.
My amplifier has the means for input level matching so I'll be able to do some rudimentary A/B testing.

Would a splitter RCA cable be a problem when connecting the cartridge to 2 different phono stages? Would the loading resistors in one influence the circuit in the other?

 

[vgeorge]

Would a splitter RCA cable be a problem when connecting the cartridge to 2 different phono stages? Would the loading resistors in one influence the circuit in the other?

Just think about that arrangement. The loading resistors will be parallel.
I would avoid that. Even a switch after the cartridge.

 

[anatech]

Hi vgeorge,
I agree completely! The wiring to the cartridge shouldn't be messed with at all. It's hard enough to get the resistance and load capacitance right. Adding anything to that signal will probably turn out to be a disaster.

-Chris

 

[MASantos]

Just think about that arrangement. The loading resistors will be parallel.
I would avoid that. Even a switch after the cartridge.

this i what I thought, thanks for confirming it.

 

[aive]

Hi Salas, I’ve measured roughly 20mv pk channel imbalance with 1khz sine test signal. Is this worth worrying about? If so where should I start looking to remedy this?

Note - unsure if it’s relevant but I measured roughly 20 mv difference between the LED strings of each channel.

Thanks as usual Salas.

 

[Salas]

The gain matching between channels in this circuit depends on the transconductance similarity of JFETS in their first and second stages. You could tweak R8 to bit higher value so to drop an output. But make sure that the test method is consistent. Verify the signal levels with a DMM set for AC RMS. Don't rely on a digital scope's numerical indication because it reads an average of the wave peaks drawn on the screen, its not measuring a signal, it sees pixels.

In the end you would want no more than 1-2% error which is what you can not better on a pristine cartridge's channel balance spec when a TT is IDEALLY leveled and set for anti-skating. Or you can offset the tracking system's channel imbalance by keeping a difference in the phono and use it for matching cart channels and gain outputs properly with a test record.

 

[aive]

The gain matching between channels in this circuit depends on the transconductance similarity of JFETS in their first and second stages. You could tweak R8 to bit higher value so to drop an output. But make sure that the test method is consistent. Verify the signal levels with a DMM set for AC RMS. Don't rely on a digital scope's numerical indication because it reads an average of the wave peaks drawn on the screen, its not measuring a signal, it sees pixels.

In the end you would want no more than 1-2% error which is what you can not better on a pristine cartridge's channel balance spec when a TT is IDEALLY leveled and set for anti-skating. Or you can offset the tracking system's channel imbalance by keeping a difference in the phono and use it for matching cart channels and gain outputs properly with a test record.

Thanks Salas

 

[Salas]

Better keep using the same channel from the generator so to ensure the input signal is the same when measuring each phono channel's output RMS. Especially when its a PC signal generator.
The sound chip in the computer can have worse tolerances than a calibrated bench type dual output generator from Rigol, Siglent, GW Instek, Keysight etc. Given the high gain of the phono, any small input differences will multiply and mislead.

 

[aive]

Thanks Salas

 

[Salas]

By the way Dimdim recently bought a new model rather affordable Rigol dual gen and he told me he is happy with it. Its fanless and has touch screen. He had made an unboxing and playing around with the controls video too:

Rigol DG822 Arbitrary Waveform Generator Unboxing & Brief Demo

 

[rickmcinnis]

could such a device produce an inverse RIAA sweep?

 

[Salas]

I don't know if it can be instructed to also vary amplitude as it sweeps frequency. You can find most of those generators instruction manuals freely available in their manufacturers and distributors websites.

 

[aive]

By the way Dimdim recently bought a new model rather affordable Rigol dual gen and he told me he is happy with it. Its fanless and has touch screen. He had made an unboxing and playing around with the controls video too:

Rigol DG822 Arbitrary Waveform Generator Unboxing & Brief Demo

Nice, definitely need to check this out.

Multimeter measurements indicate 1% to 1.5% output deviation between channels.

Should I increase R8 by roughly 1% on the higher channel Salas? Aim for a 50 ohm?

 

[Salas]

No, don't bother in my view, that's an excellent matching result for an open loop phono's channels. Very well picked active components and very good voltages adjustment led to this. 1-1.5% deviation in 300mV nominal is 0.086-0.129dBV. No worries. The vinyl tracking system and the loudspeakers matching exceed such a channels level error already.

 

[aive]

No, don't bother in my view, that's an excellent matching result for an open loop phono's channels. Very well picked active components and very good voltages adjustment led to this. 1-1.5% deviation in 300mV nominal is 0.086-0.129dBV. No worries. The vinyl tracking system and the loudspeakers matching exceed such a channels level error already.

Hehe, thanks Salas

 

[fmena]

Quick question.....for LED1 in the PSU board Tea-bag provided would a 10mA (2.2V) LED be ok? can't find in the BOM where the value is listed and I have a bunch of these orange LED's already. I assume it doesn't matter that much as long as the output voltage of the PSU is with-in spec?
Thanks
Frank M