Balanced Mic Preamp

[seanm]

I have "designed" a very simple balanced mic preamp based on the ssm2141 It was designed for instrument level output and has a gain of about 10dB. I really recommend the 5532 opamp here.



I would really appreciate it if somebody could check/comment on the grounding (or any other part of the design). I initially had the reference opamp going to ground, but seperating ground and Vref seems to make it quieter. I am interested in any gotchas.

More information here: http://seanm.ca/stomp/micpre.html

[StephenGiles]

From the data sheet "The SSM2141 is an integrated differential amplifier intended to receive balanced line inputs in audio applications", so I wonder if it is suited to Mic level?
Stephen

[grapefruit]

The SSM2141 is dsigned as a line level balanced amp. The SSM2017 is the one designed for mic level. It has adjustable gain. The SSM2017 is hard to find these days but the Burr Brown INA217 is equivalent.

Stew

[12afael]

ssm2019, ina106 and ina103 too if I remember well

[seanm]

Interesting points. The SSM2017 et al. are microphone preamps. They replace both chips with one. This chip is unity gain and just converts the balanced to unbalanced. I assumed the input level did not matter.

Really, I used the SSM2141 because my local electronics store had one 

It seems to work well, but I am only trying to get instrument level. It is very very low noise. I think the low gain helps because it is not as sensitive to picking up background noise. Which is good or bad depending on your application.

I may try one of the mic preamp chips though. Smaller part count. However, I am not sure how well they will work at +/- 4 volts.

[seanm]

Hmmm looks like I screwed up, the levels are far too low  Somebody pointed out that I was standing too close to the mic, which is why it worked so well. Hey, I'm not a singer.

With a second stage for +20dB gain, the noise level goes way up. Probably still ok for stage work, but I may have to rethink this.

[12afael]

on some instrumetation amps like the ina217 with a high gain you have less noise.
if you want to use it for mic forget the 9 votls supply. you need more headroom for a good sound.
maybe 2*9volts