[sdiy] SSM2017P

[Ingo Debus]

"jh." wrote:
> 
> > does anyone here have any experience with the SSM2017P audo preamplifier
> > chip? (claims to be a state of the art, 1 external resistor job). I was
> > thinking of using one as a mic pre (or part of). Any thoughts?

I built six mic preamps with these, they work very well.

If you want pot-adjustable gain, you need a pot with reverse log taper.
This is perhaps not easy to get. I used normal log pots and mounted the
shaft from the back of the pot. This was quite fumbly (does this word
exist?), I wouldn't do it again this way. If you use a pot, don't forget
to put a capacitor (big, electrolytic) in series with it. It'll scratch
terribly otherwise.
Another option is a switch for gain.

> It's a good, low noise preamp. I used it in the Frequency Shifter and in the
> HiFli Clone. I think AD has cancelled the SSM2017P 

Huh, really?
But I think Burr-Brown/TI makes a very similar device.

> > Also, how much can i expect to pay for a reasonable audio isolation
> > transformer (to go between mic phantom power and mic pre, as opposed to
> the
> > four zener diode solutions) ?

What is the four zener diode solution?

One of my preamps has 12 V phantom supply. Many condensor mics today
work happily with 12 V instead of 48 V. Check the mic's data sheet.
IMHO when you just want to connect a microphone you don't need a
transformer. The 2017's specs (CMRR and noise) are so good without
transformer, there isn't much benefit.
Of course it's a different situation when you want to connect other gear
and need the isolation to avoid ground loops.

> Speaking of transformers: Does anybody make a transformer with 10k
> output impedance, and with 600R *and* 10k input impedance ?
> I thought that should be the optimum for a combined Mic / Line input,
> but I haven't found one like this.

600 ohms is a pretty low input impedance for a mic input, usually these
are in the several kOhms range.

Ingo