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jarthel 27th April 2007 12:52 AM

my aikido headphone amp - almost there
after a long delay due to priorities/commitments, I've almost completed my aikido

Here are the pics: - In this photo you can see the amp PCB and the DC heater supply for the tube. The tubes used at the moment are RCA 8CG7 cleartops and 6H30. I got other pairs of 6CG7/8CG7 that I can roll.

The volume pot is a cheap-o switch but the Vishay-Dale resistors has been handmatched by myself. In case this one sucks (I bought cause it was cheap and I want to try), I have a stand-by Elma with handmatched resistors to use. I'll be using an extension bar so I can have the volume knob at the front.

The green caps are Russian 2.2uF 400V PIO and the silver looking ones are 0.1uF Russian teflon. The black ones are Solens. They were used in places that are not as important

The caps used in the DC supply are CDE 381LX 56000uF and 4700uF. Very long life and size is smaller than others.

The heatsink is used to cool down the LT1083. It's similar to LM317 except that it has a lower voltage drop-out and it's rated up to 7A. I

Also as you can see the headphone jack has not been mounted. I still need to work on the front panel. It need a 45.5mm hole for the volume knob.

Wires has been color coded as well. blue is right channel while white is left. Except for the AC mains wires, all wires are teflon coated. 18AWG for the B+ and heater supply. 20AWG for the NE555 delay supply and LED. 22AWG for the left and right channels.
Another shot of the amp from a different angle:

Here's the photo of the B+ circuit:

It's choke-input and the capacitor is a 10uF Solen + a 2.2uF Russian PIO. it's not big at all but since it a regulated supply, other people have said it's not much of an issue. The SS parts you see are for CCS. Output current can be set by adjusting the trimmer. It's set at around 82mA at the moment. It was designed by Gary Pimm. He has remove all the DIY stuff from his site but I have a copy in case you're interested.

There was a change of PSU from series to shunt. And then the intended shunt design doesn't seem to work with the tubes that I have. So I decided to buy a few VR tubes just in case.

In the end, I went with the VR tubes bypassed with 2x 0.1uF Russian teflons (the silver tubes in the photo). It has the added benefit of not needing a heater and it glows!

Here's a shot of the chassis top (though it's upside-down since I am testing it):

The silver tubes that you see are 100uF 430VAC ASC motor run caps. The coke-bottle tube is the VR tube while the straight bottle tube is a 5AS4 (which will be replace by a coke-bottle version just because coke-bottle = sexy!)

here's a photo of the other equipment used for testing:

it's our Sony DVD player and a cheap headphone. These were used just because my main CD player is at work and I wouldn't used good headphones when testing a newly built amp!

photo of ground-loop breaker and ne555 delay circuit:

In my experience, ground-loop breaker helps in eliminating/minimizing noise. the NE555 circuit is used to delay the AC supply of the B+. So when the 8CG7 and 6H30 are already hot when the full B+ kicks in.

another photo:

In this photo, the 2 resistors and orange drop are used to reference the DC heater ground to B+. I believe this extends the life of the tube. (Tubes has a maximum rating for heater-cathode voltage)

just a close-up of the DC heater supply:

I would to thank the people who have helped me. Your assistance are very much appreciated and invaluable in helping me build and learn.

jarthel 27th April 2007 01:00 AM

what needs to be done:

I need to drill 2 holes on the front panel for the volume knob and LED.

I am hoping for a black paint mirror finish on the chassis. I've downloaded some guide used to paint computer cases so I'm hoping that is applicable too. I've bought the supply and a buffer to help. In case this fails, there is a place near where I live tha powder paints metal! :)

jarthel 27th April 2007 01:20 AM

results: take note that I'm using a cheap headphone

Initially, only the right channel has sound. So I thought it must the headphones. I installed it on my PC and there was no problem with it. I think it is the adaptor I'm using.

I then connected the jack to the output by putting it beside the wires (not sure if the description is clear but I had to do something to make it work. Think McGyver for the older folks :))

I was very surprised with the sound. soundstage is amazing. possibly some a little harshness but that could be because it still needs break-in or due to the headphone. bass is okay. I was playing something that doesn't have much bass.

Tonight, I'll be using my everyday phones (Beyer DT880) and using the usual selection for testing:

- Metallica's and justice for all and one
- beethoven's 6th symphony (1st movement)
- tschaikovsky's 1st piano concerto (2nd movement)
- vivaldi's 4 seasons (one of the movements in either summer or autumn)
- chemical brothers
- prodigy
- mariah carey - not sure of the title. but it's the 1st track of her "best" CD.

jduffy 27th April 2007 04:07 AM

Hey man, thanks for the pics and the descriptions. Fun stuff!

I could never post pics of my stuff here. They would look so puny in comparison the great work that just keeps amazing me.

BTW I also like you selections in music. Nice.

Stixx 27th April 2007 07:50 AM

Hi Jarthel,

nice story and interesting pics of your built...looks pretty busy there!
I am also about to finish my version of the aikido headphone amp with the same tube compliment and using the Rev.B boards...though with a more or less conventional psu using toroids and regulated DC heaters (using the LM1084).
Tubes haven't arrived yet, but all the other components are ready...and to be put on a breadboard first. This time I definitely want to check everything and possibly try a few things before I cram it into a chassis...;)

Have fun completing your amp ...
and enjoy the music!


Edit: That volume pot very much looks like the ones sold by that guy in Hongkong...true?

jarthel 27th April 2007 02:07 PM


Originally posted by jduffy
Hey man, thanks for the pics and the descriptions. Fun stuff!

I could never post pics of my stuff here. They would look so puny in comparison the great work that just keeps amazing me.

BTW I also like you selections in music. Nice.

hardest part of the project was the chassis!!! :(

it's not as good as others. if you look at the bottom of the chassis, you'll see all the mistakes I made. Good thing they are the bottom :)


Originally posted by Stixx
Hi Jarthel,

Edit: That volume pot very much looks like the ones sold by that guy in Hongkong...true?

yes. it's the same one except that I bought this locally. it's quite cheap. 1 set (including the resistors) is cheaper than an elma switch. so I decided to try. no problems so far. and I do not think I would encounter it since the knob usually stays at 1 position for long periods of time.

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