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Old 3rd Apr 2019, 6:41 pm   #1
Robert Gribnau
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Default "Aikido" headphones amp

A photo and the schematic of the headphones amp i finished building today (except for the housing). The amp part is from a design of John Brosky (GlassWare), the high voltage supply from a design of AudioXpress (May 2008).

Some more information (in Dutch...) and photos in this and older postings on my site: http://otl800.blogspot.com/2019/04/h...amp-klaar.html
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Old 4th Apr 2019, 12:24 am   #2
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Default Re: "Aikido" headphones amp

The audio side is interesting but the PSU looks like pointless overkill!
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Old 4th Apr 2019, 5:45 am   #3
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Default Re: "Aikido" headphones amp

Well, the PSU can't hurt either. Part of my fun with tubes is to try to use a given chassis to the max. And even with these numbers of tubes in my projects, i still will not succeed in using all the tubes i have gathered over the years.

Greetings,
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Old 4th Apr 2019, 10:56 am   #4
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Default Re: "Aikido" headphones amp

True. And it's fun to play around with unusual circuits. It helps not having the bean counters to worry about, too.

Was there any particular reason for the ECC40 rather than, say, ECC81?

What was the chassis from? Looks like it had IFTs on it sometime.
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Old 4th Apr 2019, 12:18 pm   #5
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Default Re: "Aikido" headphones amp

I like the ECC40 and have a small number of them. I allready used the ECC81 in other projects. I also noticed that John Brosky mostly uses double triodes with moderate mu in the first stage . So that is why i chose the ECC40.

The chassis is from a dismantled Philips radio (B6X43A or B7X43A). When i rediscovered this hobby, i was a bit respectless towards radio's. However, during my time as a volunteer at the Rotterdams Radio Museum, i got to understand and appreciate radio's. I will not take one apart again except for a 'total loss'. I am even planning to make an AM radio and a small AM transmitter (with a triode and an ECL80).

Greetings,
Robert
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Old 4th Apr 2019, 12:43 pm   #6
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Default Re: "Aikido" headphones amp

Thanks for the info. I've not used many (any?) salvaged chassis for my odd valve builds. Biscuit tins, chocolate sample tins and recycled diecast boxes have featured, though.....


A flat plate of 20 gauge ally fixed on top does wonders for the appearance though not perhaps for the eccentricity factor
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Old 4th Apr 2019, 9:17 pm   #7
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Default Re: "Aikido" headphones amp

Hi Robert, can you post some details on the Rotterdam radio museum please.
We pass that way in summer from Europort

Thanks, Ed
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Old 4th Apr 2019, 10:24 pm   #8
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Default Re: "Aikido" headphones amp

The adress of the museum is:

Rotterdams Radio Museum
Ceintuurbaan 104
3051 KD Rotterdam

The museum is open on Thursday till Sunday from 13.00 till 16.00 hours. Entrance is for free.

By train: Go to station “Rotterdam Noord” (one stop from station “Rotterdam Centraal”) and then it’s only a one minute walk.

By car: There’s a big parking place and parking is for free.

The website of the museum: https://www.rotterdamsradiomuseum.nl/

Some photos i took in the museum in 2015: http://otl800.blogspot.com/2015/01/r...io-museum.html

The museum is sponsored mainly by Correct, a big electronics warehouse in Rotterdam. The museum is also housed in buildings of Correct. I have read that the museum has to shrink by giving up the part where now most of the old radio’s and old record players are. That building used to belong to either the national train service or the Rotterdam tram service and is old and made of wood so expensive to heat and maintain.

The part of the museum in the big building just across the street where Correct is also housed, is much bigger. There the tv’s, broadcast equipment, HiFi equipment and computers are on display. Some of the computers can be used for playing old school games. If i understood it correct, the radio-part of the museum will move to that part.

Greetings,
Robert
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Old 5th Apr 2019, 2:40 am   #9
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Default Re: "Aikido" headphones amp

I must say that the museum looks beautifully presented. There are LOTS of goodies to see.

best regards

Joe
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Old 5th Apr 2019, 7:17 am   #10
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Default Re: "Aikido" headphones amp

Interesting, how does it sound? Did it meet your expectations? The PSU as Chris says is OTT, but it's nice to use valves for other circuits than audio and if they're sitting in a box unused, you may as well use them, though some folk would swoon over the use of two Philips ECC83's in a PSU! : )

Did you measure it's THD + N, IM, frequency response, etc?

Nice work, Andy.

PS like the schematic BTW.
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Old 5th Apr 2019, 8:31 am   #11
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Default Re: "Aikido" headphones amp

Thank you for your compliments Andy.

It sounds great to me but i allways find it difficult to describe how something sounds. I use it with my AKG K240 (600 Ohm) headphones. It has plenty of headroom (i think the volume will never pass the halfway point; 1/3 is allready loud).

The two ECC83's are the only tubes in the amplifier which were allready used (but they tested good).

I did not measure the parameters you describe. Conducting those kind of measurements is a part of electronics i am not familiar with yet. I have some oscilloscopes and signal generators but i do not have distortion measurement equipment.

Greetings,
Robert
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Old 5th Apr 2019, 8:25 pm   #12
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Default Re: "Aikido" headphones amp

Hi Robert, thanks for the information, Ill try to visit in June when I'm returning to Europort from Austria.

Ed
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Old 6th Apr 2019, 11:45 am   #13
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Default Re: "Aikido" headphones amp

I've built the Aikido Cathode Follower part of that circuit, using ECC82 'cos thats the valves I had plenty of.
I'd be hard pressed to say that it works any better than a standard "Bootstrapped" CF output stage, but it does perform well and drives very long connecting leads to power amps. I think it's main advantage is the active load on the cathode helps somehow with stuff like PSRR and minor voltage fluctuations so yes, the PSU is a bit of a step too far but hey why not if all it's cost you is a bit of time?

A.
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Old 6th Apr 2019, 1:35 pm   #14
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Default Re: "Aikido" headphones amp

I must say that the museum looks beautifully presented. There are LOTS of goodies to see.

best regards

Joe


The person mostly responsible for the presentation of the museum will surely appreciate your compliment. Untill his early retirement, he worked fulltime at Correct as the interior designer. Now he is one of the volunteers of the museum.

The museum was a personal hobby of the late mr. de Jong, the owner and son of the founder of Correct. The museum was opened by the late mr. Frits Philips, son of Anton Philips (who, with his brother Gerard, founded Philips).

I am glad that his children, who now run Correct, continued the museum, but to me they did not seem to be so interested in old electronics as their father was. And the museum costs Correct money (20 visitors on a day in the museum was a lot so it does not attract that much extra potential buyers) while competition in their business is very tough. The upcoming shrinking of the museum, together with a couple of half yearly special events that have been cancelled in the past years, is not good news.

Greetings,
Robert
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Old 6th Apr 2019, 1:48 pm   #15
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Default Re: "Aikido" headphones amp

I've built the Aikido Cathode Follower part of that circuit, using ECC82 'cos thats the valves I had plenty of.
I'd be hard pressed to say that it works any better than a standard "Bootstrapped" CF output stage, but it does perform well and drives very long connecting leads to power amps. I think it's main advantage is the active load on the cathode helps somehow with stuff like PSRR and minor voltage fluctuations so yes, the PSU is a bit of a step too far but hey why not if all it's cost you is a bit of time?

A.


I am now thinking of making an Aikido power amplifier with triode connected PL36's, PL504's or something like that for my 800 Ohm speaker systems, but probably not with a regulated PSU (or? with E130L's as pass tubes like in the early Studer Recorders, one for each channel?).

Greetings,
Robert
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Old 7th Apr 2019, 6:57 am   #16
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Default Re: "Aikido" headphones amp

Frequency response is easy, feed a 1khz sine in, scope the OP with a dummy load ( two 1k2 R's in parallel) centre the trace on the scope so the trace comes between two division lines then flip the sig gen x 10, x 100 switch, IE do a manual sweep from 50hz or lower to 20khz or higher. The OP trace should stay the same amplitude if the freq response is flat, if not note at what freq the amplitude is roughly half the original amplitude, this gives you a rough 3dB point at either end of the scale.

Distortion is trickier to measure, but there are several PC based free software that do the job. A good book to check out is the the Tektonix cookbook - https://vintagetek.org/wp-content/up...udio-Tests.pdf

Andy.
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Old 8th Apr 2019, 3:53 pm   #17
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Default Re: "Aikido" headphones amp

Shouldn't the -3dB amplitude be 0.707 (1/√2) of the starting value? 1/2 would be -6dB.
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