Adding mic. transformers

[spectrasound]

I have purchased a Midas Venice 320 analog console to use on remotes, multitrack...but mainly for recording ACOUSTICAL jazz straight to 1/2" 2 TRACK. I understand that Midas has left room (and PCB lands) for adding a mic. transformer manufactured by Sowter (?) Has anyone done this....or what would transformer "specs" be for this application? Also. anyone have a schematic of the preamp? Thanks in advance!

[Jim Williams]

It's for the small can Sowter 600/600 line transformer. I've seen them installed in Soundcraft 8000's.

I don't recommend it for jazz. They saturate badly in the low end and sound very English rock and roll.

The best choice if you must use one is the Jensen JT-11-P1, also 600/600 ohms line transformer. Keep in mind that although they will offer galvanic isolation from faults and electrical shorts, they will degrade the mic preamps' EIN noise specs a couple of db's, if you can live with that.

[spectrasound]

I was wrestling with this for a while...I understand about the saturation..just thinking about best CMMR. Transformer will have better rejection than electronically balanced, right? And the Jensen will have more headroom than the Sowter? Anything by Lundhal?

[Jim Williams]

CMRR is typically -70 db for Jensens. It degrades at higher frequencies from winding leakage. If you bother to match up the resistors in the mic pre and select and match transistor pairs, you may be able to best that spec without using the transfomer. My preamps do -90 db CMRR, 20~20k hz without transformers and my EIN noise is -133 at 50 ohms. Transformers would degrade those specs and add color.

[nosebleedaudio]

Jim, which Jensen???
The JT-16 that I use the CMRR is 117dB @60 Hz, and 85dB @ 3KHz..
Far better than ANY Transformerless Pre I have seen...

[theBF]

In order to beat a Jensen transformer balance you would have to match resistors to an extremely small difference on a transformerless input. I have done things like this with a trim pot but even then stray capacitance still caused problem at high frequencies.

Just my experience

BF

[nosebleedaudio]

Originally Posted by theBF

In order to beat a Jensen transformer balance you would have to match resistors to an extremely small difference on a transformerless input. I have done things like this with a trim pot but even then stray capacitance still caused problem at high frequencies.

Just my experience

BF

It's more than that, match the input caps too..even then those caps will not change value together over time...If you know what I mean...Something most NEVER mention...
But like I said, I have yet to see ANY transformerless pre that beats the Best Jensen...JT-16.

[Jim Williams]

Originally Posted by nosebleedaudio

Jim, which Jensen???
The JT-16 that I use the CMRR is 117dB @60 Hz, and 85dB @ 3KHz..
Far better than ANY Transformerless Pre I have seen...

Guess you havn't seen mine. -90 db CMRR 20~20k hz or better. No iron. -136 db EIN with a shorted input, 2000v us slew rate, 30 mhz bandwidth, .00015 % IMD.

[nosebleedaudio]

Originally Posted by Jim Williams

Guess you havn't seen mine. -90 db CMRR 20~20k hz or better. No iron. -136 db EIN with a shorted input, 2000v us slew rate, 30 mhz bandwidth, .00015 % IMD.

I have seen it..See, not even close to the 117dB on the Jensen...
-136dB Shorted input? Never seen a Mic that can drive a shorted input
Tried to check the noise on your pre, did NOT like an unbalanced load..
Also it had some design issues IMHO..

[theBF]

Originally Posted by Jim Williams

Guess you havn't seen mine. -90 db CMRR 20~20k hz or better. No iron. -136 db EIN with a shorted input, 2000v us slew rate, 30 mhz bandwidth, .00015 % IMD.

I have seen engineers that worked for me test CMRR like this at a company that built test gear. It always looks pretty good in the lab.

Try this test. Get two remote trucks, one audio one video production on a live shoot. They are connected to the power grid by the electrician on the shoot in some way you have no idea about, the day before.

Then bring an audio feed from the audio truck over to the video truck , so the vidiots can hear the mix, using your preamp as the input device for the video truck, and tell me what you will hear. hmmmmmm...

That's my real world experience. Transformer input device won every time. Now that was 17 or more years ago. Has something improved with tranformerless input devices?

Not slamming anyone. I just really would like to know more about progress in this area since I am a long time away from it.

BF

[spectrasound]

I agree with BF....xformers have saved by recordings many, many times. At a minimum, when all else fails, I bring out the iso's. 600/600 with a good ground lift has never left me down.