[pix] [finished] Germanium Preamp

[analag]

Beautiful work, classic DIY.

analag

 

[Moby]

Thanks Kubi.

No. We're not talking 100GHz SMD stuff here.
At least I'm sure I can't hear or measure the difference.

I was thinking about hum and buzz but when you say that you can't hear it it's OK 

Hope so. The preamp works for me and I assume I didn't make any mistakes drawing the schematic.

Looking good but if you have some time take a look. 

 

[emrr]

No hum and buzz in the originals right next to two open frame linear PSU.

 

[Moby]

Great emrr I tried to simulate Kubi's schemo. Hmm, something is wrong. I went with bc550...

 

[Moby]

What's wrong, Moby? Is the signal distorted? lost along the way?
BTW: Please, use BC560 or a similar PNP-transistor instead of the ASY26, not the BC550 which is NPN.

Sorry I made typing error, yes BC560 pnp  ;D . I'm still looking for possible error, but I have just one half of amplitude at the end 
Maybe I made some value error, because it's stated as a list separately. 

 

[Moby]

Maybe I made some drawing mistake.  :-[ I checked few times, but please correct me if I did .

 

[Moby]

Yes Kubi. I was too fast  :-[ I was just redrawing but left my brain somewhere else  ;D . Thanks, now it works.  Can you please tell me transformers ratios U used? I remember that you mentioned that circuit will work with pretty low load at output (API type). Am I right?

 

[[silent:arts]]

oh, this would be a first nice Project for the GroupDIY51XAlliance formfactor ... ;D

 

[Moby]

oh, this would be a first nice Project for the GroupDIY51XAlliance formfactor ... ;D

Hehe, go ahead and design the board 

 

[[silent:arts]]

oh, this would be a first nice Project for the GroupDIY51XAlliance formfactor ... ;D

Hehe, go ahead and design the board 

will do ;D

 

[Moby]

Cool, than I will wait for you. You are better than me 

 

[Moby]

I'm sure that I saw somewhere which UTC tx can be used for this pre. (input xt) but can't find it now  :-\ Can somebody refresh my memory  ;D

 

[Conductor]

UTC AR-535
( http://audio.kubarth.com/jensamp/10.JPG )

 

[emrr]

UTC AR-535
( http://audio.kubarth.com/jensamp/10.JPG )

That would be the original RCA input transformer.

 

[hitchhiker]

In case no one has made this clear in this thread.

All the BA71 versions wire the transformer as 1:3.2 input.

The same input transformer is on the BA73 line amps (and others too IIRC) but then wired 1:1.58

The BA71 schematics show al the options.

 

[jensenmann]

Lance, your´re aware that you are the one who brought this ball into rolling 

cheers
Jens

 

[Moby]

UTC AR-535
( http://audio.kubarth.com/jensamp/10.JPG )

Thanks, yes I know for original one, but I'm thinking about some possible model to use like substitute. I think that somebody wrote that somewhere.... :-\

 

[hitchhiker]

Hey Jens!  I'm guilty it seems.

I have a 6 transistor BA71a on a breadboard but no longer have an original RCA
output transformer because I sold all my BA71c preamps.

When I tested it with a UTC A-20 wired for 1:2 output the breadboard version sounds good but has headroom issues. It didn't have this problem with the real RCA 1:2.45 output.

What output ratios are you and Kubi using ?

 

[Moby]

Wow Kubi, this is great  8) How about self etching files?  ;D Or maybe it will be better to organize some finished PCB's. Volker? 

 

[3nity]

These boards will not work inside Purusha's cases
and if he sold you a PCB, it might be faulty and will not be supported in any way!

And before this ****** sucker even asks: NO, it's not ok with me if you produce Jensamp-cases.

What the heck hapenned?
the board looks very pro BTW!!!

Altough i thing that you should do something like the Great River MP-2 pcb.
transformers outboard for more options!

Thanks Kubi.