anyone know this?

[mich]

there is this project that i found on the web- its called "project AEM6012"-
wich is a transformerless mic preamp design, using the LM394 matched transistors.ive built a couple of them and they sound very good to my ears...also its a very simple design...anyone tried it?

 

[Svart]

no, never heard of it.. but you have my interest up.. got pics/links/schematics?

 

[gyraf]

http://proaudio.nwz.pl/proj6012.pdf

Looks more or less like a standard design - but there is no gain control? And no phantom blocking capacitors?

Take a look at the SSL9K preamp for something similar, but proved..

Jakob E.

 

[rafafredd]

there´s also this one...

http://www.proaudio.nwz.pl/pre2_rys6.jpg

 

[Guest]

[quote author="rafafredd"]there´s also this one...

http://www.proaudio.nwz.pl/pre2_rys6.jpg[/quote]
There is some serious download stuff on sthat site
Checkout the Focusrite 430 and Red 6 - schematics, PCB/component/jumper diagrams

 

[gyraf]

Yep - lots of good stuff.

But most of it "lifted" from known sources (a lot of it is already on the gyraf/resources pages, or on TK's server)

JAkob E.

 

[mich]

yes...so many thing to do...just need time, money, patience, looking for parts, more patience, more looking for parts...etc... :

 

[kvintus]

[quote author="gyraf"]
But most of it "lifted" from known sources (a lot of it is already on the gyraf/resources pages, or on TK's server)
[/quote]

There's even a couple of broken links to the gyraf website...

/Anders

 

[Guest]

donwloaded the focusrite 430
looking at the mic pre schematic - there are is 12 pos grayhill switch after the trandformer secondary - is this where the variable impendance resitors sit?
Or is this a version without the variable impedance ?

 

[rafafredd]

Yes, this swicth varies the transformer impedance.

 

[gyraf]

I don't think the ISA430 has variable impedance. Should it have?

 

[rafafredd]

I guess it´s like the old neve stuff. It´s just labelled gain, but it in fact change the impedance the mic "SEES". It could also be called an attenuator. But it´s always using the same winding at the input transformer.

The best method for a transformer coupled/variable impedance input would be a multiple tap input transformer, like some of cinemag and UTC stuff.

 

[Kev]

[quote author="mich"] anyone know this?
... there is this project that i found on the web- its called "project AEM6012"-[/quote]
yes
Australian Electronics Magazine AEM
if I remember correctly

One of the Tilbrook boys did this one I think.
(Dave was well known for his Toshiba NO Hitachi !! power amp stuff ... basically the app notes but with an emphasis on low feedback and low TIM he kind of made it his own.)


there is another thread around here where we covered this and posted some related info.
I think It needed a little modification to run with phantom ... yes/no ?

 

[chrissugar]

Fred Forssell has on his page an improved version of this preamp with fet inputs, and OPA604 opamps.

chrissugar

 

[CJ]

I saw a transformerless micpre at the AES show last week that was pretty darn slick. There was an impedance selector for the input , 1K and 2 Meg input impedance. This is manipulated electronically, no taps or resistors.
The output also was tricked out. It had a sensing circuit that automatically adjusted the output stage parameters to match the load. This is done with active circuit elements, no pots or attenuators. This cuts down on distrotion.
Also, the gain is controlled without any negitive feedback or attenuators. The actual signal path is changed depending on the gain setting. Noise was close to minus 130 db.
:guinness:

 

[rafafredd]

WOW!

What was the brand/model, CJ? Don´t tell me you don´t remenber...

 

[NewYorkDave]

It sounds like he might be describing the "Gordon" preamp... I saw it at last year's AES.

 

[Peter Simonsen]

[quote author="gyraf"]I don't think the ISA430 has variable impedance. Should it have?[/quote]

Nope it does not..;-)

Kind regards

Peter

 

[Guest]

[quote author="Peter Simonsen"][quote author="gyraf"]I don't think the ISA430 has variable impedance. Should it have?[/quote]

Nope it does not..;-)

Kind regards

Peter[/quote]
The 430 Mk 11 does...
From the Focusrite web site....

Classic Focusrite transformer-based Mic-pre with variable impedance and ?Air? feature


Look here at the recall sheet
http://www.focusrite.com/downloads/resetsheets/430mkiiresetsheet.pdf
Check out the button on the left which chooses between the following settings...
Low
ISA110
Medium
High

With an additional one labelled - "Mic Air"
The original doesn't...

http://www.focusrite.com/downloads/resetsheets/430resetsheet.pdf