REDD 47 and Gyraf G9 PSU?

[Germanium_Boy]

After some years registered, this is my first post in the forum. It's true that I'm pretty thankful because of all the useful info I found here; without it, I'd have never built some of the gear that I use everyday in my studio!

Anyway, I know more about soldering than about maths and theory, and that is my issue and concern...

I'm thinking about building a 'hybrid' REDD 47 preamp, an idea that I think that some of the buddies of the forum developed time ago... Basically, a REDD 47 with a solid state PSU.

My idea is a REDD 47 with a PSU based in the Gyraf G9 PSU. The issue is that the output in of the last one is about 245v, and the REDD 47 needs 290v... So the question is... Is it possible? What resistors or other components, if the answer is yes, could be changed?

By the way... I have a two-channel clone of the REDD 47 that I really like... But I need something portable, single channel, and more light. The REDD 47, with the tubed-PSU and the iron is pretty heavy, that is the main reason for my idea. A solid state PSU as the Gyraf G9 had, would be perfect!

Thanks in advance, guys.

P.D.: Please, forgive my mistakes, as English is not my first language..

And, on the other hand, here is the schematic for the G9:

http://www.gyraf.dk/gy_pd/g9/g9_sch.gif

The REDD 47 preamp schematic is attached

 

[gyraf]

Should be possible, I don't see why not.

Look up the TL783 data sheet for how to set output voltage.

Please note (and understand) the protection scheme it's wrapped in - the two 2w resistors, the zeners, and the reverse diode.

From there, it's just a matter of finding a secondary-trafo that will give you the needed higher raw voltage.

Jakob E.

 

[ruffrecords]

Change R35 to 390 ohms and R36 to 33 ohms. This should make he Tl783 produce 295V. Change the transformer secondary winding to 250VAC and change C14 and C15 to 400V rated types.

Cheers

Ian

Edit: fixed typo!!

 

[shot]

Ian,

...and change C14 and C15 to 40V rated types

I think you have a typo there... it should be 400V not 40V... right?

Change the transformer secondary winding to 250VAC

And also, I think that the trick of using dual mains transformers back-to-back is to lower the cost and simplify things. It's both in G9 and G7 designs. So rising transformer output to 250V would be impossible without using custom transformer.  Maybe using different secondary (in this case this is used as primary) of the second transformer, like on G7 design, would yield different voltage closer to 250v.  Maybe something like 12VAC (guessing here).




Luka

 

[gyraf]

yes - maybe use a 15V transformer for the first one, and then a 220:10V transformer as the second (stepup)

You'll probably have to experiment a bit with what transformers you can get

Jakob E.

 

[ruffrecords]

If this is a new build there is no need to stick to the two transformer method. There are plenty of off the shelf transformers with 240VAC or 250VAC HT secondaries and heater windings. If you want a very simple HT supply you could use my HT250 board design. It is a simple CRCRCRC design. It is not regulated but with a class A circuit like the REDD47 it is not really necessary. You just adjust the seire R values to obtain the HT voltage you need.

https://drive.google.com/open?id=0B_n67A1hN3qtTEM4eF80cW9MZG8

Cheers

Ian

 

[Germanium_Boy]

Thanks a lot for the answers, guys! I really appreciate your time! It is true that my idea of using the G9 PSU is related with its low-cost, but amongst other things, starting a project from a PSU that I'm sure is effective, reliable and with noise give me a special relief! At the same time, having those 48v for the phantom is an extra, no doubt about it.

I'm gonna take a look to the numbers you gave me. Because, at the same time, it's a chance to learn by myself the theory behind these things, and that it's the most important point in every new project, learning 

By the way, ruffrecords, I save that design, it looks pretty good! I like it!