RJM Audio Emerald Phono Stage Help Desk

rjm

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Joined 2004
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Hi,

So first thing is you are unlikely to be able to use the OPA827 for IC1 on account of the output offset voltages being too high. (75 uV typ vs 25 uV typ for the OPA27). You can get away with just about it if you keep the Emerald in MM mode as you propose. 60 dB DC gain means 75 mV (150 uV datasheet max). In MC mode that would increase to 750 mV / 1.5V...

In MM mode the first stage gain is about 3x or 10 dB. It depends a little on which BOM configuration you choose an you can calculate it as (totalMMgain - 30 dB) as the second stage is always 30 dB.
 
Opa827 (75uV/150uV) x 1000 = 75mV/150mV max, ...but even so, it's probably a lot

OP27EPZ (10uV/25uV max) x 1000 = 10mV/25mV max, - price 9,53€ / 3 nV/√Hz at 1khz
AD797BRZ (10uV/40uV max) x 1000 = 10mV/25mV max, - price 17,20€ / 0.9 nV/√Hz at 1khz

Richard, could I also use the AD797 at positions IC1 and IC2 ?
 

rjm

Member
Joined 2004
Paid Member
1. The DC gain of the Emerald configured as a MM stage with 40 dB midband gain is 60 dB before the output coupling cap brings it to zero.
2. No, the AD797 is unlikely to work with the Emerald because the boards and circuit layout are not designed with this very specialist IC in mind. (The last time someone experimented with this was back with the Phonoclone, but nothing fundamental has changed that would indicate any different result here.)
 
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I will be using an external PSU that provides ultra low noise +/- 12V.

I will be wiring them to the V+, V- and REF pads, or to the relevant pad in Q5 and Q7.

I will be omitting the marked section in the PCB, but my question is whether I should also omit C6-C13 or are they required for local bypass?
Hello,
I am also thinking of connecting an external PSU (linear) like you. Did your idea of connecting an external PSU come true? If you did, how did it happen? I would be very happy if you share it.