Aikido valve microphone preamp - first impressions.

[zebra50]

I finally found a few hours to put together an 'Aikido' tube mic preamp from parts I had kicking around. This is sort of a prototype version, to see if it's worth doing properly.

It's basically this circuit....

...with a Sowter 1:7 input tranny and a 50K pot on the front end. It might be better with 100K to show the mic circa 2K, but I was out of 100k log pots. The tubes at present are a Funkwerk ECC83/12AX7 at the input and ECC88/6DJ8 for the output stage, although I tried 12AY7 and 6CG7 also, which seemed to work fine.

Initial impressions are that it is extremely quiet - hum/ripple are completely inaudible, and hiss/noise seem less than room noise. The sound is good - still definitely tubey, but clean tubey.

At this stage I'd say it seems to be worth spending a little more on parts. I'd also like a little more gain. My plan next is to find a 1:10 input tranny and a goldpoint 250K switched attenuator for the input.

More on the akido here....
http://tubecad.com/2006/08/blog0074.htm

z50

 

[okgb]

Looks good with a part count so low that you can wire directly to
the sockets .
thanks for showing this

 

[jackies]

Good stuff, I been thinking to try that one.
What output tranny you got there, 1:4 or someting?
Is PSU regulated?

 

[zebra50]

Thanks for the comments and ideas.

Yup, the supply is the spare board from the G9, but with a 7806 to give regulated 6V, and 245V for B+. But I think with the noise-cancelling design you could easily do a standard caps-and-resistors network for the high voltage side.

Yes, all the resistors are wired to the socket tags. It's a very simple, minimalist built.

The output tranny is a 3:1, left over from an Altec 1566 clone, which I built and then scrapped.

I hand-matched all the resistors for closest values. Probably worth the effort for this.

 

[DerEber]

Did you do the tube mounting metal by yourselfe?
This kind of metalwork is allways dramaticaly expanding the time and fun i need building something.
Great pice! :thumb:

 

[zebra50]

Yes, it was just some scrap aluminium. I punched a couple of holes and mounted the sockets. No big deal.

I just noticed the picture is before I finished - some wires to connect. And I still need to wire in the on/off switch at the front.

It's just a prototype, but sometimes the prototypes live forever....

 

[3nity]

have you tried or compared against something? G9 or NYD-1B?
Looks interesting....i have 2 NYD-1b channels in a box waiting to be racked...but i'm still up for mods...

 

[zebra50]

Hi 3nity,

It's too soon to tell - I only built it this morning!

I've built 3 G9s of different varieties. The current one has Lundahl input and OEP output trannies, and is really sweet. The only obvious thing to say at this stahe is that the Akido seems quieter, but has less gain so it's hard to make a proper comparison.

My plan now is to tweak a few components, do some proper tests and report back. I'll be auditioning a few different tubes too.

 

[jdbakker]

Good to hear that it works well. It sure looks simple enough, I think I'll try to find the time to build one too.

Just one thing for future searcher's sake: it's called the Aikido, as in the martial arts.

JDB.

 

[Viitalahde]

Looking good! :thumb:

I've got a near finished Aikido-ish thing in an EQ I need to fire up some day & test.. 2C22 into 6SN7.

 

[zebra50]

[quote author="jdbakker"]
Just one thing for future searcher's sake: it's called the Aikido, as in the martial arts.
JDB.[/quote]

My bad! I've corrected the thread title. Thanks for pointing that out!
:thumb:

 

[zebra50]

I had a couple of emails / PMs about this and want to make it absolutely clear that this is NOT my own design. I just added a couple of transformers and fiddled with some components.

The basic circuit is from John Broskie's GlassWare / tubecad site:

http://tubecad.com/2006/08/blog0074.htm
http://tubecad.com/2004/blog0011.htm

Some more Aikido threads

http://www.groupdiy.com/index.php?topic=29463
http://www.groupdiy.com/index.php?topic=13355

Thanks!

:thumb:

 

[john29302]

Ok so enuff of whose it is what were the results of the aikido preamp as a mic preamp? all over the web is this and that how neato torpedo the build is but whats the sound like?? what gain  and mic and mixer and some details about its better than just going straight into laptop,,,no review is on entire web of the aikido...its like this application is a void or dark hole and if most mics are 150 ohm then why the heck are edcor trannies xm series all 600 ohm input??

 

[zebra50]

Hello John,

Welcome to the forum.

As you can see from the dates, I built this mono unit about four years ago, so this is all from memory.

I then went on to make a stereo pair of these using one of the PCBs from John at Glassware and goldpoint switched input attenuators. So I have three channels in all. The stereo unit uses 1:10 Sowter input trannies, and some old BBC output transformers (2:1).

>what gain  and mic and mixer and some details about its better than just going straight into laptop,,

Both units have been in use in our (professional) protools studio since 2009, and they get used regularly as outboard mic preamps alongside the APIs, Littlelabs, RFZs, Gyraf G9s, and a bunch of other stuff. The preamps run straight into the protools hardware (via patchbay).

The sound is very clear and solid, without much distortion. I particularly like them on bass instruments, but they get used on pretty much anything. They have a decent amount of headroom before distortion, and work well with dynamic mics like our RE20s, and also very good with ribbon mics - like our Melodium 42bs and Crowley & Tripp Naked Eyes. 

My unit doesn't have phantom power, and I don't tend to run my tube mics through tube preamps as you can have too much of a good thing. That is not to say that it won't work well with FET condensers - it does. But with our studio setup it is less convenient to do so.

In terms of gain, the best bet is to read the Aikido build manual.  The gain depends on the tubes selected and of course on the transformers used. They stand up well against the API A2D preamps, but my units don't have as much gain as those.

>if most mics are 150 ohm then why the heck are edcor trannies xm series all 600 ohm input??

That's a separate question and I haven't used those particular transformers. The '600 ohm' bit is really a recommended application, and not a fixed value. The mic preamp's input impedance should preferable be greater than the microphone output impedance for best noise performance and frequency response.

In the case of the Aikido circuit above, the input impedance is set by the 100K resistor across the input (in parallel with the tube grid, but we can use 100K for ballpark stuff). But the mic sees this through the transformer, and the impedance goes with the square of the transformer ratio. In the case of my build above, I used a 1:7 transformer, the mic sees 100K / (7*7), which is around 2K ohms. With the 1:10 transformers, I fiddled about with the input stage.

Cheers!

Stewart