Double balanced microphone preamp project

I'm sorry for the off-topic W&G-stuff, it's getting a bit out of hand here :grin: . And the pic above to which I linked seems a computer-thing to me, so a really bad example and precisely not what's about.

They showed some pinguin(sp?)-animated-movie in front of the main act (W&G) and imnsho it was so lifeless when compared to the W&G-claynimation. Like digital vs analog recording ? Ah, that's somewhat back again on topic. :wink:

Forget about the "double balanced preamp", let's talk about Wallace & Gromit. :grin:

I didn't see the new cinema movie but I'm a big fan of the original clay animation, especially "The wrong trouser" episode. Absolutely briliant!

Wallace and Gromit is my all time favorite animation. Interesting is, that first time I saw "The wrong trousers" about ten years ago and it was on the Hungarian television. Unfortunately I didn't catch it from the beginning, so I had no idea about the title. I was so impressed but later I discoverd that I had no idea about the name of the animation and the caracters. More than eight years I had no idea how to identify the animation. Two years ago I discovered the picture in my avatar on an internet page, and was very happy to see again that smart dog, but still no info about it.
About a year ago, a friend of mine who studied sound engineering in UK saw my picture (avatar) and he said: Hey that is Gromit from Wallace and Gromit. I done some google and found their homepage with pictures and clips. Since then I had the possibility to watch again "The wrong trousers" and some episodes and I'm still impresed about how expresive are the caracters and how the whole story is built. Brilliant!
:grin:

chrissugar

[quote author="chrissugar"]...I saw "The wrong trousers" about ten years ago and it was on the Hungarian television...[/quote]
Was it on Channel One or Channel Two? :thumb:

BTW, there is a board on the works for the JFET version (output modified though) of the Cohen circuit by and unnamed Brazilian. :green:

Hey Tamas

I always had the intention to ask you if you speak hungarian, because of your name.
If I remember well it was on Channel1 (MTV1).
[quote author="tk@halmi"]
BTW, there is a board on the works for the JFET version (output modified though) of the Cohen circuit by and unnamed Brazilian. :green:[/quote]
That is good news but I would be curious about the details in implementation. In a way I'm tempted to build a variation on Fred's design because I trust his work.

chrissugar

In the Fred version of the Cohen circuit there are missing parts values for RGain, the two common mode adjust pots as well as the resistors marked TBD that is off of the CMRR pot wipers. Anybody have a suggestion as to what those values should be??? This circuit is really interesting to me cuz I have a box of 2SK389 FETs sitting above my bench!

Probably a 5K pot is Ok because the gain depends only on the values of the two resistors between the FET sources and the outputs of the first two OPA604s ( 2K ) and the value of the pot.
The formula would be:

for single ended out - Gain= (Rg + 2K + 2k)/Rg

for balanced out - Gain= 2x(Rg + 2K + 2k)/Rg

Rg the value of the pot

chrissugar