Siemens U274 Mic preamp

[MikkelM]

Just got a Siemen U274 preamp today:
I am planning to rack it up with a 20db pad feature, and phantom power by using a part of Bo hansen's API PSU.
http://w1.316.telia.com/~u31617586/

I am not used to work with trannie stuff, so place let me know if I am going to stirfry anything.

Cheers

Mikkel Meyer

20DB Attenuation

 

[sismofyt]

This is one of my alltime favs! I've racked a few, what do you want to know?

Are you planning to run linelevels into it? I use a mictrannie wired backwards for that. Also check this;

www.digital-synthologie.de/siemens_u274/index.html :thumb:

The diodeclipper is one mean fukker for drumz :grin:

 

[MikkelM]

I want to use it as a mic preamp.
Amplification starts at 44db and I want it to be lower if necessary.

The Line level thing sounds quite interesting.

 

[sismofyt]

I don't use these as preamps, I use them to distort, clip & compress the living **** out of linelevelsignals. They're quite dirty. Not the best Siemens/Telefunken preamps. Very colourfull. Not hifi..

I keep the original front on mine when I rack them. I also keep the original switches, the comp on/off switch have unused pins. I wired a LED to those so I can see if the switch is engaged or not.

Also, check ALL caps. You'll find some leaky ones for sure. DC leaky that is, not the snot inside them.

I like 'em a lot. The last ones I bought of ebay were like 90euros I think.

The pad should work fine. You could also pad the output if you wanted some distortion from the amp.

 

[sismofyt]

Just a note on that schematic, none of the units I got use SST 117/1 transistors. Don't even know what the hell those are :? They all have BCX 45s instead. Any TO-5, hfe=40 will do I guess. Also don't mess with the trannie wires, they're quite fragile :shock:

 

[MikkelM]

Thanks for the info.. I got mine for 80 ?..

Do you know what the R14 pot is for?

 

[sismofyt]

It's for setting the gain/feedback operating point. Don't mess with it. Old trimmers tend to get really sticky, and it'll probably **** up if you try to turn it.

 

[MikkelM]

I leave it then.. Damn! I like to screw on knobs.
The caps looks quite good, and the module isn?t that greasy.
It is in a quite good shape.
I got a SoundCraft mixer there had been 3 years on a closed but wet balcony, and before that it was used as a coffee table.

 

[sismofyt]

I like to screw on knobs too :grin: :wink:

You cannot see if the caps are leaking DC. I'm not talking about that gooye **** inside, but caps tend to pass DC when they age. That'll make switches go click'n'pop. I've gone through +50 modules by now, and they pretty much all needed some caps changed. Those luvly ol' Frakos are crap after 35 years. They also loose the capacistance, so you'll get a weaker lowend and incorrect working point.

I prefer to use ordinary caps for recapping, not the new fancy low impedance/graphite stuff.

 

[MikkelM]

OOHHH! Recrapp Ups! Recapping.
I have finished 3 months recapping and troulbeshooting a couple of months ago. Yep! the mixer. I have currently capfobia!

Are you a piece of Danish pastry sismofyt shalimar?

 

[sismofyt]

Please call me sismofyt or Ole :wink: yeah, I'm danish too, not a 'kage' though.. haha.. recapofobia.. I know that. I recapped a console last year. I have nightmares after putting in hundreds of vertical caps. Originals were axials.. :twisted:

 

[MikkelM]

Lot of Danes in here. Great!
Is the Sismofyt a Ole B. Ørsted?

 

[sismofyt]

No, who is that?

 

[sismofyt]

A Google turned up a director of a porn movie.. could have been me, he :green:

 

[MikkelM]

Haha! Have just checked the your web.
Ole B. Ørsted has been building synths and audio stuff from the 60's and forward.
Århus gangster..... My girlfriend is from Århus.

 

[sismofyt]

I used to be an Århus gangster for real, but now I'm a good boy. Used to live in Odense before. I have also lived four years in Copenhagen. Born in boring Herning though..

May I ask who you bought the U274 from?

 

[MikkelM]

One of theese hiphop guys? hehehe!

www.vintagecity.de

 

[sismofyt]

They're great! I've bought from them before. I have good luck on ebay as well. Some vendors charge silly money for shipping, private sellers usually don't.

You need a W295 EQ to go with that U274 :thumb: Make a PSU that can power both. It's okay since all modules have local filtering and decoupling.

Hmm, I need to take some pics of my Siemens/TABs as well..

 

[MikkelM]

UUhh! I have just spend too much on the mixer, and some Danish Radio speakers.

 

[sismofyt]

Kewl! I got some old DR discrete preamps in Danner cassettes. I wonder how much gear they made themselves in the 60's & 70's? Do they still have DR auctions in Kbh?