Mpp

[Joachim Gerhard]

Good idea Scott. This noise discussion got a mess.

[Salas]

From a 56dB gain 1 jfet input build non cascode, just Rload drain, I got this for noise floor ref 0dBV=1V out. I used a 1/200 10k series 50R parallel attenuator to obtain 0.5mV from 100mV Emu Tracker Pre usb box generator and I put the phono in its loop. Without Lpad, gen's output is rather noisy under 500mV and can't be controlled precisely under 50mV for asked output. That high frequency blip is an artifact, most of the times isn't there. Is this noise floor result possibly fake?

P.S. I found the output impedance of the card at 580 Ohm when I calibrated the levels for different loads.

[syn08]

Originally Posted by Salas

From a 56dB gain 1 jfet input build non cascode, just Rload drain, I got this for noise floor ref 0dBV=1V out. I used a 1/200 10k series 50R parallel attenuator to obtain 0.5mV from 100mV Emu Tracker Pre usb box generator and I put the phono in its loop. Without Lpad, gen's output is rather noisy under 500mV and can't be controlled precisely under 50mV for asked output. That high frequency blip is an artifact, most of the times isn't there. Is this noise floor result possibly fake?

Not sure how your attenuator is built, but for noise measurement purposes you'd better repeat the measurement with the input shorted to ground. The generator and the attenuator may add much more noise than the pre itself.

[Salas]

Just L pad, 2 resistors. 10k series, 50R shunt. Will do with short also. Thanks.

[scott wurcer]

I just remembered that I did an S parameter complex noise figure spreadsheet 15 yr. ago that might apply here. The problem then was ultrasound transducers connected at the end of lossy coax. An Aglient box was used to extract S parameters at frequencies of interest. Here we could just use the lumped R/L/C and find the best front end termination/amp combination.

EDIT - Still HP at the time.

[SY]

In spreadsheet form, that would be awesome.

Just curious if any of you low output users run your cartridge-to-preamp connection balanced?

[Holger Barske]

The Eminent, My Sonic Lab is interesting with 2 Ohm, 0.5mV output. Unfortunately very expensive.

Second best cart I ever had my hands on. Topped only by the Hyper Eminent.

[Joachim Gerhard]

My commercial Goldstandard is balanced. The good thing is that this needs no ground wire so works even when the groundwire is connected to the tonearm and is not seperatetely put out like in some Rega turntables. Hum and noise in unbalanced Head-Amps can be very low nevertheless even with low impedance cartridges. The Goldstandard sounds very clean, but if that is the result of the ballanced connection i can not say. I have also an experimental ballanced stage with INA163 that works fine but the necessary gain resistor in the intrumentation amp reduces the noise performance to something like 1.4nVQHz.

[syn08]

Originally Posted by scott wurcer

I just remembered that I did an S parameter complex noise figure spreadsheet 15 yr. ago that might apply here. The problem then was ultrasound transducers connected at the end of lossy coax. An Aglient box was used to extract S parameters at frequencies of interest. Here we could just use the lumped R/L/C and find the best front end termination/amp combination.

EDIT - Still HP at the time.

Interesting idea, I'll look into this, it shouldn't be to difficult. I can do it directly, unfortunately only from 300KHz up to 6GHz, so not really useful here.

What was the reference impedance for your measurements?

[scott wurcer]

That work was done at 50 Ohms. A series of equvalent two ports was very easy to set up, i.e. an X ft. piece of RG58 at a given f was a simple two port. For this problem I would start with simple lumped parameters. Several mirowave design texts have tables of two port equivalents for R-L-C networks even transformers. Voltage and current noise were simple sources.

The problem remains what do you do when the best noise performance has a cartridge time constant well into the audio band (and not one accounted for as with MM).