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Old 28th March 2008, 11:01 PM   #21
Cappy is offline Cappy  United States
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Location: Southern Willamette Valley
Fran,

That looks quite good.

I like the look (and sound!) of an aluminum and wood chassis. Your chassis design looks like it would be fairly straightforward to build. I may need to re-evaluate my current plan which is to prototype on wood boards and then agonize over what to do about the case for two to three years.

Could you explain some of the parts in the chassis I don't recognize such as circuit board to left of Aikido board, small circuit board on top of Aikido board, and boxy things behind Aikido board.

Bill
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Old 29th March 2008, 12:39 AM   #22
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Hi Cappy,


yes this is an easy chassis to build. Side cheeks are wood with a threaded insert. The front and back panels bolt to this. Supports along the front and side panels support the base on which everything is mounted. All you need is the ability to cut the cheeks, drill holes and cut the alu sheet.

When you are assembling the amp you can start with the bottom sheet of aluminium and mount everything on that and then just slot it into the rest of the chassis for the wiring up. I have a rule - I make the chassis first! Otherwise I'd never have something I could bring into the house.

In the pic:

On the left is the PS board - this runs at 24V so its a low voltage regulator based on a LM317. Its set to 25.2v (6.3 x 4) and I then added another CRC filter (just to the left of that board) to filter the B+ a little more and drop it to 24V. Its one that JB is going to put into production. An alternative would be the tread regulator from tangentsoft.net.

The boxy things to the back - they are PIO 4uF caps - the linestage output caps in this case. They are bypassed by 50,000pF polystyrene ones. These are fly wired back to the main board.

The little board mounted on JBs aikido board is a muting delay. Basically at turn on, theres a relay on the board that receives its power from a cap that charges through a resistor. The sizing of the resistor and cap slows that charging of the cap so that the relay doesn't click for about 15 secs after turn on. This allows nearly all of the DC to drain away on the headphone output and protects the headphones from the DC offset (which can be high just after turning it on). The muting delay is available from www.amb.org its called e12 on his site.

Other than that you can see the input and output wiring and the "pot" in the middle is an LDR based attenuator - optivol from www.ska-audio.com.

Very pleased with it - I have another non-headphone enabled 24V aikido and it too sounds excellent. I have yet to bring this one down to the main system - it has stayed beside the PC where I listen when surfing (through headphones).


Fran
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Old 29th March 2008, 05:40 AM   #23
Cappy is offline Cappy  United States
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Fran,

I assume you compared the "Optivol" with other volume controls? It looks cool and isn't all that expensive...
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Old 29th March 2008, 10:32 AM   #24
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Well, it certainly, no question, hands down beats the living crap out of an alp blue velvet. Its like putting cotton wool in your ears by comparison.

Beats a stepped attenuator (DACT type one from ebay - see other recent thread on stepped vs regular pots) on 2 grounds:

I don't think it gives up much sonically to the stepped pot, but I think that

1, the stepped pot can be a bit noisy due to grounding. In the last pre I built (poindexters excellent 6T4 moebius) I could not get the grounding resolved with the pot. All I got was silence when I put in the optivol.

2, I'm not a big fan of the feel of the steps. I found the only way to make the stepped pot "feel" good was to put a big heavy knob on it. I used one that I made myself, turned it on the lathe and tapped it out. I guess its about 35mm by 35mm steel. If you don't use something like that, the steps are kinda rattly and it feels cheesy.

So as I see it, the alps is out on sonics and the DACT type stepped is out on the basis of grounding and it being a PITA. So in my case, in my system, the optivol wins out. YMMV, but I think its worth a try.


Fran
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Old 1st April 2008, 04:03 AM   #25
Cappy is offline Cappy  United States
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I'm putting together a BOM for resistors and capacitors.

I'll probably end up using different resistor brands to try to balance colorations and hopefully get a synergistic effect.

One of the resistor types I'd like to use is Kiwame. I read this interesting post from Pete Millet a few months ago.

So I'll get some of those cheap "Kiwames" here.
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Old 20th April 2008, 05:43 AM   #26
Cappy is offline Cappy  United States
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Let's see if I can get a screen shot of one of my Duncan Labs Power Supply Designer II simulations posted here.

It is an LCLC power supply. This is the response moving the supply current down 10% from 50mA to 45mA:
Attached Images
File Type: png aikido promising a impulse response.png (33.3 KB, 1290 views)
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Old 20th April 2008, 06:06 AM   #27
Cappy is offline Cappy  United States
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Here is another screen shot of the same power supply. It is a static view. Note the B+ is about 213v and the ripple on I1 is 7.50 mV.

I'll discuss the techniques I'm using to analyze this LCLC supply shortly. I would be quite interested if anyone has other PSU II analysis techniques for looking at the acceptability of a supply. I'm also looking for feedback by more skilled power supply practioners on the goodness of my design for use in the Aikido.
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File Type: png aikido promising a static.png (30.3 KB, 1238 views)
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Old 20th April 2008, 06:20 AM   #28
Cappy is offline Cappy  United States
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This LCLC supply is similar, but with a second choke that has less resistance. The C's are tweaked a bit too. The lower resistance means the B+ is about 219v, right near my target of 220v. The ripple is 10.9 mV.
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File Type: png aikido promising c impulse response.png (35.4 KB, 1211 views)
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Old 20th April 2008, 06:23 AM   #29
Cappy is offline Cappy  United States
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Second screenshot for the power supply. Some would argue this isn't a true choke input LCLC supply because of the small cap after the power transformer. Lynn Olson calls this a "transitional" supply.
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File Type: png aikido promising c static.png (44.5 KB, 1209 views)
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Old 22nd April 2008, 07:15 AM   #30
Cappy is offline Cappy  United States
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I ran across this post by John Swenson on AA a few months ago:

http://db.audioasylum.com/cgi/m.mpl?...on&r=&session=

It made a lot of sense to me. I had only messed with one power supply previously, the B+ supply in my modified Lite DAC 50, a PCM63 based DAC. I had tuned this power supply by ear. I went back and measured the 10% step response like John suggests and damn if it didn't have the quick move up and the slight overshoot, then the quick damping.

So the above PSUD II charts I posted show an impulse after a 10% step move in current. Basically I am trying to get 1) a non-ringing step response that has 2) a decently quick impulse move, and that is 3) not overdamped or underdamped -- overshoots but damps down quick, and 4) has low ripple.

An overdamped power supply might have a lot of resistance and capacitance in it. The impulse curve has no overshoot and the more damped the slower the move is. These power supplies can sound dull and boring, from my limited experience working with my DAC anyway.

It takes a fair amount of dicking around to come up with a non-ringing LCLC supply (and there may still be impedance or other problems with the supply, more on that in the next post). It is easy to create something nasty like this:
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