Aikido amplifier topology

piedwagtail · Posted: Wed Sep 13, 2006 6:58 am Post subject: Aikido amplifier topology

I'm currently finishing a tube/valve preamp of this topology and in the initial test it was frighteningly quiet for a tube microphone amp,my voice came out of the darkness.
In its many topographic versions,the main element is the injection of the power supply noise antiphase into the circuit such that it is cancelled out.(See 2M/2M ladder in schematic)
See John Broskie's TubeCad.com for background information.

Tube electronics is a bit like tree surgery compared with the gardening of +/-15V,but
I built a fet version of this topology and it is also unbelieveably quiet.It provides perfect quiet gain for my ribbon mic.
I used 2N3819,unmatched,with an input transformer with a input attenuating pot.
Play with the 6K feedback resistor for overall gain.Can't see any problem with supply from 9-24V apart from headroom,stick a cap on the front if you don't use a transformer to decouple any dc.

If you need a gain stage give it a try.
Robert

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elektro80 · Posted: Wed Sep 13, 2006 8:32 am Post subject:

The tubecad site is awesome.

I love this section:

piedwagtail · Posted: Wed Sep 13, 2006 1:48 pm Post subject:

Funny similiarly how the snooty folks over at groupdiy.org dislike him too.
Only when you've built and heard it do you realize quite how good it is.

Robert

elektro80 · Posted: Wed Sep 13, 2006 4:03 pm Post subject:

I am considering his stepped attenuator thingie. BTW: this one could be developed into some kind of very decent alternative to those mackie, Presonus and Samson monitoring devices. I prefer passive attenuators when the signal path allows it.

Hmm.. is this yet another DIY project .. and could we develop this ourselves into a kind of [i][color=#255293]electro-music.com[/color] group project thing? [/i]

Anyways, I really enjoyed his detailed analysis of the mu follower ( http://www.tubecad.com/articles_2002/SRPP_Deconstructed/index.html ). Quite a read and a lot more entertaining than the complete output of Stephen King. This is a wet T-shirt party for advanced fans.

piedwagtail · Posted: Thu Sep 14, 2006 9:36 am Post subject:

I had a stereo attenuator sat between balanced lines,but the steps were break before make i believe,as i'd get cracks at every click as the shorting was broken.Using a valve amp and Philips 9710M speakers this was never really a problem.But with electrostatics it would not have been ideal Smile

Attenuators are a nice polish,but i need to dedicate time to basics and production before i reconsider them.
Robert

jksuperstar · Posted: Fri Sep 15, 2006 4:25 pm Post subject:

I'm interested in your fet version of the circuit, as I'd like to make a preamp for field recording and this technique sounds promising when using fets/mosfets.. If you have any other info about your experience, schematics, or other, please share! (what gain levels can you get cleanly (0 - 60db?)?) Are you using dynamic mics, or have you modified from this schematic to add phantom or other power for condensers?

piedwagtail · Posted: Fri Sep 15, 2006 6:02 pm Post subject:

I used the schematic above,run from a wallwart dc supply of 12V.Input transformer 600-50k balanced to unbalanced Sowter 9045,run into a100k pot.Rest as shown,i believe i upped the feedback resistor a fair bit,try out various values to suit on gain vs linearity.
My RCA varicoustic ribbon is a devourer of mic gain but this handles it easily.It's normally a balance between adequate gain and infringing noise on a desk with this mic.Gain is mainly from the first bottom jfet,so perhaps a socket in this position,as they can vary .

I don't have any 48V mics,only a tube mic with its own supply.48 V would be added to hot/cold in front of some dc decoupling caps in front of the transformer.The quality of the caps is important as their signature is messing with a small signal.,
I really recommend it,it's an easy build and it is quiet beyond belief.
Robert