Aikido line stage results? share yours

[Craig405]

Hi,

I have just finished and tested 2 aikido amplifiers using 12AX7's in gain stage and 12AT7's in buffer.
PSU is 375V 150mA transformer, 5Z4 rectified with plenty of capacitance and a 20H choke.
Each channel is seperatly tube regulated using 2x0D3 and 2x0C3 giving 265V per amp.

Tubes used in the Aikido are 12AX7's for gain and 12AT7's for buffer.
I get about 2mV PSU junk/HF junk on output of each channel which is ok i guess.

My frequency response is from almost DC to 50Khz (-3dB).
Gain is around 15 but my tubes are dodgy and old so it might be completely different.

Will a transistor CCS before the regulators help the 2mV noise?

What specs is this amp supposed to have and what specs have people got from building it?

How much thump do you get turning it on, i get about 5V on and 3V off (enough to mash my speakers ,when i eventually hook it up ) is this normal?

Output offset is about 30mV.

I would be interested to know what success people have had with this amp as i have heard it is very popular.

long post hehe

Cheers
Craig

[J Epstein]

Craig - I'm no help w/measurements for my unit (which is 6SN7/6SN7), but in any case I'd expect that there may be something up with yours: gain should be more like 50 than 15.

Subjectively I'm very happy with mine, no plans to change it anytime soon at all.

Re: turn-on, did you use the "safety" voltage dividers Broskie added in a later blog? They should help with turn-on (although those voltage regs do turn-on quite suddenly, that might be the issue.)

Best,

-j

[Craig405]

J Epstein, yea i used the dividers.
I might recheck the gain, that is a massive difference, although i dont know the gain of the tubes you used.
I havnt actually listened to mine yet (lackng my power amp for a bit) but i hope its as good as some people have said.
i might create a mute using Jfet's to short the o/p ofter the capacitor for a few seconds at turn on and maybe at turnoff too.

Craig

[dave dove]

mine is quiet turning on and off
no noise i can hear at output either
but i'm just using two 20H chokes
choke input with two 470uf caps
and a 1k>470uf RC stage to drop the voltage

i have run mine with 12ax7 > 12at7
that had way too much gain
but sounded ok
though not as good as with 12au7 CF

i'm now using 6n1p > 6n6p and it is wonderful

dave dove

[dmcgown]

Just a few comments regarding Aikido power supply...

First, I recommend using a CCS in place of a resistor feeding the shunt regulators, it will help reduce noise and grunge even though the Aikido supply is fairly good in doing this intrensically.

Regarding a turnon thump, I would strongly recommend installing a mute switch or time delay relay that will ground the outputs until the regulators light off. That being said, the sound is really just annoying, it doesn't do any damage, at least in my system.

Also, I have found that power supply capacitor quality and size is clearly audible, even with shunt regulation with CCSs (I am using a similar arrangement with series 0A2s for a 300V B+). I would recommend using as small value as you can get away with without comprimising the hum or hash on the outputs). If using electrolytic caps, bypass them with signal quality film or oil caps.

That being said, the Aikido circuit is capable of very low level resolution, the naturally low PSRR means that meticulous attention to PS quality will reap great benefits in resolution.

Just one comment to Dave Dove, regarding the problem I was having a few weeks ago concerning excessive noise that I thought was attributed to the safety resistor divider, I subsequently found that the 12FQ7s I was using at the time had a problem with poor heater insulation that was producing excessive buzz noticable through my 105dB efficient horn speakers. Using a different tube solved the problem. Thanks for all the thought and effort in your comments to me on the problem.

David

[Craig405]

Dave, nice thanks for the reply 6N1P are pin compatible i take it? I might give them a try, what cathode resistors do you use with them and HT voltage.

dmcgown,
I will certainly add a CCS then, definatly solid state because i dont have much room left inside my case after all those regulators .
My PSUcaps (~80uf per channel) consist of 3 smaller caps in // with a 340nf cap accross their output.

I think Jfets are a good solution to the thump, more compact and reliable than relays but to get the output muted on turnoff might be tricky.

Thanks for your posts.

Craig

[heater]

dmcgown:

"That being said, the Aikido circuit is capable of very low level resolution, the naturally low PSRR means that meticulous attention to PS quality will reap great benefits in resolution."

I don't understand your comment. I thought the whole point of the Aikido concept was to have a very good PSRR.

[Bas Horneman]

I don't understand your comment. I thought the whole point of the Aikido concept was to have a very good PSRR.

True..I guess that is what he meant.

[dave dove]

craig45

6n1p and 6n6p are not pin compatible with 12at7 etc
they have 6.3v heaters on pins 4 and 5 with pin 9 to ground

simple enough if you have 6.3v source

i am using JB's original circuit for 6n1p and 5687
220vHT 430Rk
i feel no need to mess

dmcgown

you're welcome

dave dove

[Peter Clements]

I have been working on a SN7 Aikido breadboard.
Very, very good sound.Open and airy sound. Very transperent.
I used another of Broskie's ideas as well, works great. 18.9 volt heater transformer with 21 ohm resistors on each valve. I can plug in any 6,8 or 12 volt SN7 or such. Then I used 19AX7 damper diodes off the same transformer. These diodes are cheep as chips and sound good.
I found the power supply quite critical. The sound of caps quite noticeable. I now have ..10H , 10uf Solen, 10H, 20uf Solen, 500ohms 30uf Solen, 10H, 50uf motor run, 10H 100uf motor run.Sounded better than NOS oils or Cerafines and or a less complex supply.
Mucking around with volume pots was interesting. Vishay 1M cermet law faked with carbon comp 50k is very transperant. Will try it as a series conection next.
Cheers.