FETCODED

Now on to the output stage
Analag

Analag, nice work.

Some circuits I was taking in consideration in the last year when thinking about a transformerless fet/tube based preamp.
The input circuit would be a diferencial circuit based on the MC input of the Borbely Audio phono preamp:
http://www.borbelyaudio.com/adobe/phono.pdf
everything doubled and mirrored (2x 2sk389 and 2x ecc88), and with a 10mA current source made with a 2SK170 Jfet. The two MC out points would go to the input of the Fred Forssell tube line driver:
http://www.forsselltech.com/schematics/TLD.PDF
Add some goodies like gain controll, phantom power and a nice PSU and probably we will have a functional preamp.


chrissugar

An ECC88 should be biased around 8ma for best sound, so 16ma is what's needed from the CCS. My circuit will be fully differential, no opamp stuff. Also no adaptation from other schematics, I want to keep it as original as I can, even though that's kinda hard to do.

Analag

Anyway I'm sure Fred saw it and he made no comment, so I take it I'm on the right track.

Click to expand...

There is an interesting application of reasoning in that statement. Nice project name by the way.

[quote author="FredForssell"] Nice project name by the way.[/quote]
nice and original :grin: :grin: :grin:

chrissugar

Check out this link http://www.tubecad.com/october99/page15.html , it was a follow up to a question, I asked John Broskie from Glass-ware.com/Tubecad concerning TT preamps.

Analag

hey Analag,
Just wondering if you have any experience with the 6C33C tube? They look pretty beefy to be used in output stage, in case you haven't seen it....

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=58174&item=7522272754

6C33 is a little over board for me in this application. I have redesigned the schematic some what...I've made it simpler and better at the same time, with better overload charactistic. Will post soon.

Analag

[quote author="analag"]Check out this link http://www.tubecad.com/october99/page15.html, it was a follow up to a question, I asked John Broskie from Glass-ware.com/Tubecad concerning TT preamps.

Analag[/quote]

Yes, we know the tubecad mic preamp and it was discused at the old place, and if I remember PRR had some concernes about this design. Also I think it has a fixed gain and it was something like 45dB (hope my memory is OK), and it is not optimised for noise at every level.

chrissugar

[quote author="analag"]I've made it simpler and better at the same time, with better overload charactistic. Will post soon.

Analag[/quote]

Looking forward to see it! :grin:

The Idea is to create a transformerless input pre based upon the improved concept that Forssell is using.


Analag

Hey Analag,

Is your output stage single ended or balanced. The gain switch is between the posted circuit and the output buffer/line amp ?

chrissugar

> my further improvement.

Noise figure is ~8dB. Working at 8mA ("for sound"?), you could do a lot better.

Yes stepped attenutator is between this section and the other which is a gain stage and buffer. It is fully balanced.

Analag

I'm always fascinated with new concepts in tube design and this is leading me more into hybrid circuitry.

Analag

Revised it a little or a lot depending on how you look at it.
Analag

Would love to see how the unit turns out when you are done.

COOL Bra. :shock:
(A while back I met a friend of a friend and instead of bro he says bra, you can imagine how I felt when I first heard that :shock: kind of people you meet from the westside....)

Look at my avatar .
Where did it go?
Analag

Amplifer section completed , now on to the P.S.