Simplistic NJFET RIAA

[Salas]

Originally Posted by Joao@AltheaMusica

Hello Salas,
what about using following RIAA amp design:

1st stage > discrete op-amp with variable gain, i.e. from 20 to 40db, with an transformer coupled, single ended, output stage of 600 Ohm

following into an LCR-RIAA

2nd stage > same as 1st. stage

Regards
Joao

Get JE990 as building block and experiment with whatever you like for filter LCR or not, and/or Trafo coupling between stages and/or the outside world. You are a valve and TT man, you need to work with blocks and their interaction, not their innards. Fastest way for you to a ''different'' phono sound to tune. TT makers love to tune, don't they?

[Joao@AltheaMusica]

Originally Posted by Salas

Get JE990 as building block and experiment with whatever you like for filter LCR or not, and/or Trafo coupling between stages and/or the outside world. You are a valve and TT man, you need to work with blocks and their interaction, not their innards. Fastest way for you to a ''different'' phono sound to tune. TT makers love to tune, don't they?

Sometimes I'm faster in typing than I should do. After some readings in my old documentations ...

You're correct, I'm a valve and TT man, but this doesn't exclude that I'm interested in the innards of circuits. I've learned this in my education and I do this with valve circuits as well. And I do not search, or want, some different phono sound. My reference is the naturalness, the truth - wether valve or transistor.

Already had a look at those amplifiers like the JE990. But they look very complicated. I like more the simple circuits - like I do with my single ended valve circuits as well, and I like the efficiency of transformer coupling!

This brings me back to your circuit. I think it has more potential and it's worth to try them out. For example reduce R1 to 600 Ohm and you can use an LCR-RIAA network - disadvantage, you loose some gain.

[Salas]

In such a case you can experiment with such a way. Only it is SE non GFB, and you mentioned discrete OP-AMP. So I thought to design your own OP-AMP would be consuming.

[Joao@AltheaMusica]

Originally Posted by Salas

In such a case you can experiment with such a way. Only it is SE non GFB, and you mentioned discrete OP-AMP. So I thought to design your own OP-AMP would be consuming.

This was the what I meant with typing to fast. Just an idea of many. Then I recognized the complicated circuitry of OP-AMPs - discrete or as chip. Yes I'll first experiment with the LCR.

What do you think of expand it to a 3 stage design, a 3rd stage - or better input stage - for low output mc carts? Would be interest to compare this stage to a mc transformer. My first thoughts are that the transformer can provide a better S/N ratio.

[Salas]

The wire has its Johnson, adds to en. If its driving triode or jfet input there is a line of use, it helps by upping the source impedance where those two are rated for nVsqrtHz, 1 kOhm will do. With low source Z they would pick up roar towards LF, still the hiss goes higher with the input trafo. If for BJT input, the trafo has no use at all. Its only detrimental. And impairs layout, as well as having some detail loss, no core is perfect. 3 stages are inverting BTW.

[Joao@AltheaMusica]

I agree when we're talking about "normal" cores, but cores like permalloy or nano-crystalline amourpous hiss should be no problem.

But like mentioned above I'll experiment with this ... as well with interstage coupling of the stages. First I have to listen to the original RIAA amp, and maybe it's close or equal to valve phono stages.

When using a 3rd stage follower it will invert the phase, but a non-inerting stage with source-output for lower output impedance will not.

Another idea. Have you experimented with implement the signal to the source as current source - grounded gate?

[Salas]

The hiss is due to the wire, not the core. Detail smothering level or tonal coloring can be due to the core and general construction. Trafos are specialist stuff, you guys know which one suits better what cart etc.

Have listened to it against Steve Bench Cascode, My Valve Itch, and some specialist LCR tube phono. Will be interesting for you too when comparing technologies I think.

That is how the simplistic is now. 3rd stage is a source follower. Non inverting as a whole.

Transimpedance? No, I haven't.

[Joao@AltheaMusica]

Yes transformers are a special issue... I use a low output mc-cart with output voltage of ~ 0.2mV. This means I need some more 20dB more gain. As well I use a passive Line Stage with a TVC, the Power Amps input sensivity is 1Vrms.

Of course it will be interesting to listen to such a phono stage, and I'm just curious. Can you describe some differences in comparison to valve amps?

[Salas]

I could write the Britannica but I avoid.

Severe lack of controls and abundance of differences between systems of no common experience with the asking party. Impossible to convey anything meaningful over the web.

The Simplistic ain't nothing special anyway so it could give some heading. Its just a beaten path concept targeted at easy DIY build, for just basic things to come across right in my subjective preferences order.

[Joao@AltheaMusica]

Originally Posted by Salas

I could write the Britannica but I avoid.

Severe lack of controls and abundance of differences between systems of no common experience with the asking party. Impossible to convey anything meaningful over the web.

The Simplistic ain't nothing special anyway so it could give some heading. Its just a beaten path concept targeted at easy DIY build, for just basic things to come across right in my subjective preferences order.

Agree with your sight of view. When this is your "entry level" how is your highest level in phono amplifiers? Just interested if you will give me / us some short possible forecast on your designs?!