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Aikido 24V headamp

post #1 of 570
Thread Starter 
Has anyone built their 24V hybrid Aikido yet?
post #2 of 570
I'm nearing completion of mine. Prolly be next week before its running I'd say. Easy enough build so far and the quality of the board is excellent.

This is my second 24V aikido, the first one being a regular pre, ie not a headphone amp and I can say that the sonics are excellent. Well worth throwing a few nice caps into C1, C3 and C4 if you had something like blackgates. Wimas elsewhere.

post #3 of 570
The work for this is coming along nicely. I have the chassis done, PCB is mounted and the PS stuff is all done. I need to do the input/output wiring next and then she should be ready to rock.

More in a day or 2

post #4 of 570
2 pics to show some progress:

post #5 of 570
I have one of these boards as well, and have made up a half-way complete bom for it. I'm really unsure of when I might get to it, though.

-edit- I also have a s11 board I plan to use for it. I've got the resistors in my bom to put it at ~25.2v.
post #6 of 570
OK, I did some more on this tonight and I have it up and running. The linestage part is AOK, but I have some DC (50mV and 30mV left and right) on the HP output. Have to go back and look at that (I emailed JB about it too).

I used a 24V Tx into a tread regulator from tangent. What I did then was adjust it for the heaters to 25.2VDC. Then I put in an extra CRC filter (10uF motor run/15R/1500uF) for the B+ which drops the B+ rather nicely to 23.95VDC. By my reckoning there should be little enough drift from this once its settled in as all the DC comes from the tread first. The tread is only $17 for the kit, a no brainer if you didn't have something already to hand. The heatsink on it hardly gets warm.

When I get the DC issue sorted out, I'll post the solution.

post #7 of 570
Awesome, fran. I look forward to hearing about your results.

-edit- What value did you use for C7-C10?
post #8 of 570
I'm going through my BOM and fleshing it out. It's essentially done, but upon looking for places to buy 6GM8's, I found how scarce they are. I guess I'll have to budget out enough cash for at least two sets of tubes...I'd hate to need to replace them a year or two down the road and not be able to find any. I've found them to range in price from $5-25, depending on which of the 3 places I found to have it in stock I'm looking at.

Does anyone have any suggestion on a good source for these tubes?
post #9 of 570
Fierce freak:

C1 are those 2 metal PIO caps towards the back of the amp, 4uF ones and they are bypassed with 50000pF polystyrenes. I have tried those actual caps in my other aikido and they are indistinguishable from blackgate Ns.

C4 is 3300uF nichicon VXm, C3 is 2.2uF PP and that is again bypassed a second time by one of TomBs russian PIO 0.22uf from my Max build.

I used 1000uF nichicon UPW caps for C7-10, but I don't know how important that is (heater string).

Radiodaze has those tubes and Jim McShane does too. Not that dear either.

I connected in my K501s and it sounds pretty good. Never heard bass like it from 501s before! Very impressive. can't wait to get it inside to the main rig and see how it runs with the 650s and 701s and vs the max. Hurry up and build it! I think this amp could be a great amp.

More on that DC offset later - but I think its all OK.

post #10 of 570
I figured out C1 and C3 after I posted. Thanks for the info, though

Glad to hear it's making music! I look forward to your impressions of it with the HD650s (what I currently have, though I plan to repurchase some RS-1s in the future). I've been really wanting to put this thing together for a long time, but funds just haven't been cooperative Hopefully that'll be taken care of soon.

What other nice amps have you heard?
post #11 of 570
Yep, its definitely worth putting together.

Other amps are Little Dot 2, LD MkIII, revmh millet, millet max, original master, DIY ECL82 amp - after that some portable stuff for on the go. Cans are HD650s, K501s and k701s, ER6i.

I know its not an exhaustive list!

On the DC offset issue: I think I was making a mountain out of a molehill in a way. Just like the millet, there is a DC offset at turn-on, which rapidly drops. With no headphones plugged in this remains about 20mV or so. Plug in some cans and it drops to zero right away.

I've spoke to John Broskie about this. His explanation is that:

What happens is that the electrolytic capacitors leak a small current which against the 10k terminating resistor ends up equaling a fairly big voltage. But that same amount of current against 32 or 300 ohms makes for a 32/10k or 300/10k as much voltage offset.

He talks about using a jack like some musicians use where when nothing is plugged in the tip and ring are shorted to ground. This would dissipate the DC quickly. He says that instead of using a short directly to ground to use say a 10R instead.

Of course you could just put in a e12 delay too.

Overall the build was pretty easy. I recommend using the tread from tangent - it simplifies so much (or one of linear power one supplies off ebay). There are a good few parts to buy - it probably isn't the cheapest one to build, but it is good! BTW he recommends panasonic FM series for C4 bypassed with a polystyrene.

Anyone else out there doing one of these? You get a full function preamp along with a headphone amp too. SQ from the pre is excellent - I can speak on this as this is the second one I've built and it will take on any comers. The headphone amp sounds great to my ears, but I would like a little more time to compare it to say, the max.

post #12 of 570
I hope it's clearly better than the Max. The Max is a good amp, but I prefer my B22 so hope that the Aikido can be on roughly the same level (I've heard a full voltage non-hybrid aikido headphone amp before, and it was killer).

Thanks for the info on the DC offset About the cap in the C4 position...I was planning on using an Elna Silmic II there, but perhaps I'll purchase some FM's as well, to test. I do plan to bypass C3 with a polystyrne (Multicap RTX), but are you saying that C3 itself should be polystyrene?

-edit- forgot to ask, in C11 the lead-spacing is 10mm, correct?
post #13 of 570
From his last email to me, yes it would seem that C3 should be polystyrene with FMs in the C4 position. He spec'd panansonic FM 25V 1800uF.

Highs are excellent with the nichicon/PP/PIO combo that I used though.

C11 - I'm not sure but 10mm sounds about right. I used a leftover nichicon cap from the max build and I think the leads might have been a shade close together so that the cap wouldn't sit right down on the PCB.

I've used the e12 - and in fact I have a spare e12 kit in the workshop, but I'm reluctant to use it, just because I don't like relays in the signal path. Had a bad experience with them one time. (even though my max has one and my revMH too!)

post #14 of 570
Awesome, great info. Thanks, fran

I'm hoping to start ordering parts for this in the coming few weeks, so I should be able to update then. I've got everything picked out, minus an enclosure (and I'm wavering on the volume control).

I look forward to hearing any further impressions you have, Fran. I have one last question for you (I hope ;D): next time you're doing some work on the amp, would you mind measuring the height of the populated board? I'm assuming the tubes are the tallest components and that the total height including board and standoffs might be ~75mm.
post #15 of 570
I make it 72mm approx to the top of the tubes - thats with the board on 9mm/3/8" standoffs. And when I had to open, that C11 does look like 10mm lead spacing. I'm using a 35V1500uF nichicon (mouser # 647-UPW1V152MHD6) from the max BOM and I had to bend a lead to fit it in. I also dropped R17 to 5K to up the idle current and give a bit more gain. My heatsinks are the aavid thermalloy ones (mouser #532-513102B25). They don't hardly even get warm. He specifies a 1" hole spacing for the heatsinks, but those ones the pins are a shade to big and while they sit into the holes, they don't seat home fully. You will get away with it, they go in enough to solder them but just they don't sit down all the way.

There is another thing you should really spring for. Its a LDR based volume control that a fella in australia sells as a kit. His site is SKA Audio and the kit is AUS$27(incl shipping). Beats the crap out of an alps blue. It'll run easily off the 24V aikido supply (you resize a resistor - tell him and he will include it for you). He calls it optivol. I don't think he has it listed on his site, but email him and he will get back to you. I'm going to replace the stepped one i have in my max with it and I've used it now in 2 preamps and it works perfectly.

Original idea posted here:

and ska audio forum:

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