Simplistic NJFET RIAA

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#17,265
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?
 
#17,269
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.
 
#17,270
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.
 
#17,271
Salas said:
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.
Click to expand...

Thanks Salas 🙂
 
#17,272
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.
 
#17,277
Salas said:
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
Click to expand...

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?
 
#17,278
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.
 
#17,279
Salas said:
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.
Click to expand...

Hehe, thanks Salas 🙂
 
#17,280
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
 
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