Moskido - Hybrid Aikido/MOSFET amplifier

[the_manta]

Thanks for your post and schematic, i'm also interested in building a project like this.
But I want to use another tube stage, because I don't like Aikido because it's so popular now Don't take amiss, but I hate mainstream

Now I have two questions: I'm sure it would be possible to use a bipolar Power supply and to leave out the decoupling capüs at the output. What should I change therefore ?
And for another Tube driver stage, I have to know the gain for the amplifier. The Mosfet-Amp is a source follower and has unity gain. The B+ is 2 x 20V (+20V and -20V) Can tell me what Signal voltage teh Mosfets need ?
Since I only have good knowledge in tube engeneering, I can't calculate on my own. Are the Mosfets working into an resistive load or an inductive load ?
Many questions...
regards, Simon

[marsupialx]

http://www.tubecad.com/2007/05/blog0107.htm

This is a link to John Broskie's 'Capacitor-Input Cathode Coupled Amplifier'.
If I were concerned with the popularity of the Aikido, I'd build this. Fabulously simple. It would be great if somebody would build it and report back.

[marsupialx]

By the way, the 'Capacitor-Input Cathode-Coupled Amplifier' is the last circuit before 'Next Time'. Way at the bottom.

[beau2317]

But I want to use another tube stage, because I don't like Aikido because it's so popular now

Well hardly popular. Maybe a few dozen people have made one. And for good reason...it's staggeringly good (go read John's posts on it).

I think the reason this sounds so darned good is actually down to how good the aikido is. If you go ahead and build please post the voltage amp you use as I am curious as to what a less-used-than-aikido stage looks like. It would have to be a pretty unique design!

As for using a bipolar supply, yes it would be possible but I think it would involve having some kind of DC servo to keep the output voltage at zero.

As I mentioned, the gain of the tube stage I used is about 30. The gain you need depends on the input level, the power you require and the impedance of your speakers

[beau2317]

If I were concerned with the popularity of the Aikido, I'd build this

Ah yes I had not thought of this. I liked the look of that. Now if only John would make some PCBs for that. Darn you John for making so many good circuits

[marsupialx]

Any cool suppliers for Buz901?

[beau2317]

I got mine from RS components, but also you can pick them up on EBAY

Well you can get BUZ900/905 at the moment for $15.75 ea

I asked John whether it was OK to use the BUZ900/905 instead of the 901/906. The specs are identical except the 901/906 pair have max voltage of 200V while the 900/905 are 150V

Given the rail was 65V it did not seem necessary to use the high voltage part.

And John confirmed this. Also they are cheaper.

(and the slightly thinner gate leads to a more faster more rhythmic treble and a more solid bass ) Or something like that

[JoshK]

One could also try the pentode aikido, where a pentode is used for the first position (EF86, 6AU6, 12HG7, etc) and the Aikido followere thereafter. Its a less used but proven design. I'd like to try this one in a 813 SET design with the 12HG7 or something like that.

[marsupialx]

This is an idea that I'm thinking about.
You have probably read about TVC (transformer volume controls).
Let's say I have the Aikido configured with 12sl7/12sn7. This may be too hot to use as a traditional active pre, so I was thinking about running the input signal through a high grade step-down transformer for the low setting of a high/low switch. Any thoughts on this idea, and what characteristics such a fransformer should have?
What about the idea of using a TVC as a volume control for an Aikido?
-Thanks, Jeffrey Hill (marsupialx)

[marsupialx]

Beau2317,
Can you fill in the value for the mystery resistor from the Hybrid SE schematic?
http://www.tubecad.com/2006/04/blog0058.htm
The only difference for my case will be Buz900 rather than Buz901.
Thank you. - Jeffrey Hill (marsupialx)