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Old 22nd September 2008, 03:34 PM   #1
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Default All FET Aikido

Hi,

I should propably post this in solidstate forum, but aikido is more known to tube related guys so....

I would like to built aikido headphone amplifier with FETs and with some buffer on the output to drive most variety of headphones.

But I do not have any clue about schematics, what type of FETs to use, what B+ voltage, what are the currents requierements.

Thank you.
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Old 22nd September 2008, 03:58 PM   #2
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First off: John Broskie, whose design the Aikido is, has almost certainly touched on this subject once before, and if he has my guess is that he concocted a (probably untested) schematic to go with the idea. I would check his blog.

Secondly, however, I would ask: what's the point? The Aikido exists because it is a flexible circuit that balances the imperfections of tubes against those of other tubes. You get good PSNR and a number of other benefits as bonuses; but if you're going to make a deal with the silicon devil for your headphone amplifier, I imagine that there are better topologies.

By no means let my comments stop you from experimenting. You may come up with an amplifier that does a darn good job. All that said, though, I don't view "taking a good tube circuit and replacing the tubes with transistors" as valid design strategy.

-k
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Old 22nd September 2008, 04:02 PM   #3
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Hi,

I want have FET version because of smaller voltages, cost, space. I already have tube aikido in my system. I mainly listen to speakers, but sometime headphones are handy, so I would like to built the headphone aikido topology in simpliest way.
Aikido topology should also work with FETs (or other amplifying device), not just tubes.

I will check tubecad.com for some more info.
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Old 22nd September 2008, 04:05 PM   #4
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Koolatron is right: in various blogs Broskie already wrote about the inclusion of sand in the aikido, mostly as current output buffer in addition to the standard aikido, but I remember there was also a schematic using sand in the second stage. So the first thing would seem to be to go through the blogs again.

To keep it 'tube like' and simple I would start looking at depletion mode Mosfets.

Erik
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Old 22nd September 2008, 05:51 PM   #5
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Hi,

I know this isn´t the Aikido and I will absolutely support the opinion of Erik de Best and the other tube-fellows.

Have you considered the Borbely FET headphone amplifier?. It might not be the simplest thing in the world to make, but Mr. Borbely has a very good reputation indeed.

Have a look at his circuit here:

http://www.borbelyaudio.com/pics/Web309line.pdf

At the Borbely-site you can find prices for his different kits as well.

If you really feel that your headphone-amp must be with FETs I am quite sure that you will get a lot of positive reactions and advice in the solid-state forum.

Good luck

Karsten
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Old 22nd September 2008, 11:07 PM   #6
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To fake a Pentode, use depletion FETs. I do
not think you can make a straightforward
solid state Aikido in this way. The "Triode"
region of a starved FET is not sufficiently
like a real Triode for a proper Aikido either.

To make a FET misbehave Triode like, abuse
an enhancement FET. And bias the gate from
voltage divider strapped from drain to source.
This is the basic building block of the FETron.
Now you might be able to get somewhere.

A bit like O.H.Schade (RCA)'s Triode emulator
of 1938. Abusing the 6L6 Pentode with screen
referenced to B+ rather than Triode strapped.
Plate negative feedback interacting with G1
through an external network.

Honestly, I don't see the point. I believe other
circuit topologies than Triode emulation may be
more optimum for a FET. But there is certainly no
reason an Aikido could not be done if you were
merely trying to prove something.
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Old 23rd September 2008, 01:55 AM   #7
flg is offline flg  United States
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JFETs ???
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Old 23rd September 2008, 02:25 AM   #8
lineup is offline lineup  Sweden
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Default Re: All FET Aikido

Quote:
Originally posted by kacernator
Hi,

I should propably post this in solidstate forum, but aikido is more known to tube related guys so....

I would like to built aikido headphone amplifier with FETs and with some buffer on the output to drive most variety of headphones.

But I do not have any clue about schematics, what type of FETs to use, what B+ voltage, what are the currents requierements.

Thank you.
Quote:
Originally posted by flg
JFETs ???
In type of semi conductor N-JFET is similar to Triode.
Most any circuit using triodes could be built with N-JFET.
At suitable lower voltages of couse.

Should not be very diffincult to make one Aikido JFET Clone.
The performance would not be the same. But may not be at all bad.
In fact, it is very probable, it may be real good!

There are N-JFET with current ratings from 1 mA and as high as 100 mA.
Even there are a few Higher Power JFET
Lovoltech LU1014D power JFET
Lovoltech LU1014D power JFET

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Old 23rd September 2008, 03:39 AM   #9
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FET JFET whatever. They essentially behave like Pentodes.
And the "Triode Region" is not the same thing as a Triode.

If you sub in depletion FETs (or JFETs), even if you get it
"working", it will not behave the same as an Aikido. Aikido
relies upon the low plate resistance of real Triodes for the
whole noise rejection thing to cancel out properly.

FETs won't do that without additional external feedback.
You have to fake the intrisic Mu feedback of a real Triode
or you can forget about Aikido as a viable FET topology.

I've already drafted a schematic just to prove to myself
that Aikido with FETrons is do-able. But I'm not going to
show it here without a real tube in it somewhere. I may
post to solid later. I am tired right now, its not a priority.
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Old 24th September 2008, 12:00 AM   #10
lineup is offline lineup  Sweden
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Default JFET Aikido with 4 N-JFET and great working!

I setup one circuit in my simulator
Using 4 common N-JFET and 24 VDC.
Most anybody with some knowledge of Spice can do this.
I has expected to see somebody here doing this before myself.

What is Aikido?
- first stage one input device with constant current collector load
- signal to output follower from the collector of input device
- output follower biased by one constant current source
Two N-JFET for first stage. Two N-JFET for second stage.
That's all.


At a voltage gain same as Aikido, +15 dB, and 1 Vrms output
my circuit shows just great performance!
In fact, simulates so great,
I have decided not to 'give away' this circuit here.
Will be one 'goodie' for my dear members at my own place.

Lineup
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