Moskido - Hybrid Aikido/MOSFET amplifier

[beau2317]

Hi

My friend and I have been building a series of hybrid amps based on one of John Broskie's designs. It's an Aikido driving a MOSFET output stage.

The original circuit is here:

http://www.tubecad.com/2006/04/01/ai..._amplifier.png

The description by John is here:
http://www.tubecad.com/2006/04/blog0058.htm

The first one was hashed together mostly with parts that were to hand. It sounded astonishingly good, besting my Nuforce Ref 9.02s and my friends Aikido-driving-300B monoblocks.

So we both built "proper" versions using quality parts. My friend made a pair of monoblocks. I built a huge version using paralleled MOSFETS. I had a dialog with John and he advised me on some things. He also liked the name "Moskido"

Here's some pictures and some details. I can post the full circuit if anyone is interested..

http://www.beausoft.com/moskido1.jpg (during construction)
http://www.beausoft.com/moskido2.jpg
http://www.beausoft.com/moskido3.jpg ( finished )

1) Implementation

I used 4 MOSFETS per channel (BUZ901, BUZ905), each running at 1A idle current (total 2A). With a supply voltage of about 65 volts, this means each side dissipates 130W so it keeps quite warm! It is meant to drive my 4 ohm Magnepan 3.6R. So it produces a quite reasonable amount of Class A power

I used pretty much the best components I could find :

-- Resistors : Audionote Tantalum, Caddock, Riken Ohm
-- Caps : VTV Ultratone for coupling, Blackgate and Auricap for output, Jensen four pole for power supply
-- Bridge rectifiers: FREDs
-- all wired up with Kimber cable
-- 500VA transformer for mosfets, separate transformer for tubes.
-- tubes : Russian special military 6SN7 and 6SL7 (not the normal Russian surplus...these are 1578 and 1579 super tubes..have tried lots of 6SN7 and 12SN7 and these are by far the best..)

It uses a Broskie Aikido PCB, and the MOSFET driver parts are built on some tagstrip on the heatsinks.

2) Sound : incredible. This was the third version of this design. The first two were made by my friend Steve.

But this version comprehensively beats that. It's quite astonishing. I had not realized quite how much my previous amps were leaving out. I've owned and built a fair number of amps in my time. (Nuforce Reference 9s, dual 211 SET, 300B SET driven by aikido driver stage, Gainclone, Meridian 605, Ear 509, plus an assortment of tube amps).

The treble is so delicate and detailed. The dynamics are amazing. Every nuance comes through. And it also seems to make just about any recording sound great. None of this "the amp was so good it made everything but the best recordings sound rubbish"... this amp just makes *music*...even old Beatles or Motown sounds great.

I have planned a couple of visits to local High End dealers. One of them is going to let me try this against some very high priced amps : Lamm 1.2 (also a MOSFET hybrid, about $15000) . Also Pass Labs 350 ( a mere $8000).

I will post the results of the comparison.

If anyone is wanting to build a class A hybrid amp, this is a good one to try. I must say that John's designs are great! If you want a killer line stage, go for an Aikido..(btw I have no commercial interest)

[jacco vermeulen]

Originally posted by beau2317
Sound : incredible.

I bet.
Here's a hybrid from 1988, E83CC and 6FQ7 for the White cathode follower.

[beau2317]

Yes but imho the Aikido is a better performer than the white CF, and the 6SN7 sounds better than any 9 pin tube. This is not idle speculation. I have built and compared both (ie white CF and all sorts of tubes). But I am sure that circuit would also sound good.

Jacco - groetjes, I lived in rotterdam for 10 years.

[jacco vermeulen]

Not meant to compare one with the other.

Just the point that hybrids have been given a bad rap, Counterpoint years, but is able to sound wonderfull.
I've put the Aikido on my project list a while ago.

Groetjes, a surprising number of globetrotters at this gathering, a pleasant surprise.

[Luke]

Beau, I wish you were in Wellington. Sounds like a nice map.

[Andypairo]

Hi Beau,
did you use the Push-pull or the SE circuit?

Cheers

Andrea

BTW I also use a Hybrid with a Aikido frontend (E88CC - 6N6P) into a diamond buffer with OnSemi Thermaltrak devices.

[cheater]

Looks real, real nice.

Schematics please!

Btw, the link to the "original schematics" doesn't seem to work.
It seems it got shortened, it links me to

www.tubecad.com/2006/04/01/a...r_amplifier.png

Thanks

[beau2317]

Push pull.

[beau2317]

http://www.tubecad.com/2006/04/01/ai..._amplifier.png

I hope that URL works...

That's what it's based on, but I need to draw up the actual circuit and PSU I used...give me a day..

[beau2317]

Originally posted by Luke
Beau, I wish you were in Wellington. Sounds like a nice map.

I'm in Pukekohe. If you are up this way you are welcome to listen.

Originally posted by Andypairo

I don't believe in audiophile components - except when I can get them at frugal-phile(tm) prices

Interesting thing is that the 3 versions we made were built with varying components

#1 Basic components
#2 Frugalphile things like russian caps and tubes
#3 Top of the range

The better components do sound better. It seems the most difference is with the tubes. We tried about a dozen or more 6sn7/12sn7 and 3 or 4 6sl7

The Russian special 1578 (6sn7) was the best 6sn7. These were $30 a pair a year ago, but now there is only one guy on ebay selling them, two at a time every week. They go for more than $100 for a pair now.

The bargain though is the similar 6sl7 called 1579. You can pick these up for just a few bucks. They sound or better than any 6sl7 we tried.

Both the 1578 and 1579 are non microphonic completely (if you put them in a preamp where most 6sn7s are hugely microphonic, these are simply not). (I daren't post this info in the tube amp forum...that would be bound to push the price up)