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Old 27th May 2008, 12:17 AM   #41
Cappy is offline Cappy  United States
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The other components in the power supply are the 4 100 ohm resistors to create the virtual center tap for the 6.3 volt supplies, and the voltage dividers to get the B+/4 voltage potential.

These will all be 2 watt KOA SPR2 resistors, otherwise known as Kiwame.

Question for the group: I am not sure whether I need the 0.1 uF cap that Broskie shows in the manual from the virtual center tap to ground. Do I? He mentions different approaches to biasing the heater supply voltages -- I'm not sure if the 0.1 uF cap is needed for my scheme, or if it is just for the floating heater supply scheme.
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Old 27th May 2008, 06:39 PM   #42
Cappy is offline Cappy  United States
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One potential problem with the Angela power transformer is that the 6.3 volt secondary is only 3.5 amps. The 6CG7s/5687s just by themselves will draw 3 amps. This should be ok for AC heaters but with DC there is probably not enough headroom. So in that case a separate filament transformer would be necessary.

I happen to have a filament transformer in my parts drawer, so I'll still consider the Angela. Others may have different requirements.

One nice thing about the Angela transformer is that in addition to the 320 volt secondary there is a 380 volt center tapped secondary. This could come in handy if using an LC-Regulator configuration, since a shunt regulator could easily burn the extra volts.

I also notice there is a 55 volt bias tap on the Angela transformer. This could come in handy to dispense with the B+/4 voltage divider resistors, it seems close enough.

That brings up another question. The Lundahl LL1683 transformer has a 48 volt secondary. I wonder if that be used for biasing the heater supplies? It is two wires out, probably 24 volts each, so not quite like the Angela bias tap which could just be run to the heater supply virtual center tap.

Thinking about this more, the 55 volt bias tap is AC, not DC. I have no idea if this would work plugged into the virtual center tap. Thoughts?
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Old 2nd June 2008, 05:04 PM   #43
Cappy is offline Cappy  United States
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Here is a picture of the power supply prototype with parts laid out on the board. Swapping between the Lundahl and Angela power transformers will give possible 260, 320, and 380 volts AC input. This seems like a good range as a test bed for various vacuum tube output stages I might want to try. For the Aikido, it will allow voltages from 200 to 300+ volts:
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Old 2nd June 2008, 05:22 PM   #44
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Cappy,

Looks great, so far. I have to remark that those Obbligato power filter caps are just freakin' huge. My own Aikido build is nearing completion, but being my first build of much of anything it's turned out much simpler than your own efforts. I built a Maida-type regulator and have eschewed any choke on the input.

The results, so far, have been great. My question to you is, given the very good PSNR figures on the Aikido, why spend so much effort in reducing noise that will be nulled by the topology anyhow? Note that this isn't meant to bait you, I'm genuinely curious.

--k
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Old 2nd June 2008, 06:07 PM   #45
Cappy is offline Cappy  United States
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Kool,

That's a reasonable question.

First, I'm becoming a big believer in having the best power supply possible, based on my own experiments and listening to other people's stuff. And that reducing ripple is important, but there is more to it than that - current delivery, impulse behavior, no hash from power supply back on power lines, no electrolytic caps, etc. etc. The Aikido will null ripple, but I think that other attributes of a good power supply are worth pursing and will positively effect the Aikido. My power supply definitely isn't state of the art on ripple reduction anyway.

Last weekend at VSAC I listened to two of Jeffrey Jackson's amps with power supplies that make my power supply look like a children's toy. And both those amps sounded tremendous.

Secondly, I don't know much about the subject, so my goal is just to learn more -- it's possible your compact power supply would beat or match mine. Knowing that in itself I would find an interesting result. I just read a quote I liked that is somewhat applicable:

"An expert is a man who has made all the mistakes which can be made, in a narrow field." -- Niels Bohr

So is a choke input supply really worth the trouble? Part of this exercise is to determine the answer to that question empirically. Also, how can I bullshi* effectively in audio forums if I haven't made the experiments.

Second, I've been wanted to explore the area of choke input supplies for a while, since they don't often appear in commercial gear, just for fun.

Third, I am aiming for this power supply to be a semi-universal solution for my future projects such that I can just change a few things and get the power I need for a variety of B+ voltages. For example, I've been wanting to try a DHT Dac output stage --- now that will require some clean power.

One of Jeffrey's amp prototypes. Note, this is honkin' bigger than it looks in the picture:

Click the image to open in full size.

Here is another picture -- for scale that is a subwoofer in the corner with an 18" Hartley driver:

Click the image to open in full size.

Cheers, Bill
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Old 2nd June 2008, 06:30 PM   #46
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Wow. Everything about that first picture just screams, "do not touch me. you will die"

Not a place for curious cats or hedgehogs.
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Old 2nd June 2008, 06:36 PM   #47
Cappy is offline Cappy  United States
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Yeah, 1000 volts exposed.

I think if hotel security knew what was going on we would have seen Defcon 1 type behavior.

I pulled those photos from:

http://www.jenalabs.com/shows/shows.html
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Old 3rd June 2008, 07:24 AM   #48
tomsyl is offline tomsyl  United States
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Default You're collecting an audience

I just got my 5687 Aikido kit in the mail and am planning to use it as a DAC output stage, just like you are. I like the idea of an inductor-based PS; some claim that is one of the reasons why the Ayre gear sounds so good.

I want you to finish this project without trauma, so before going farther I suggest you listen to this lecture on Electricity.

%^>
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Old 3rd June 2008, 05:24 PM   #49
Cappy is offline Cappy  United States
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Tomsyl,

Thanks for the link, I enjoyed listening to it. I never thought Hunter S. Thompson could be so... sobering.

Keep us posted on the progress of your Aikido for your DAC.

Maybe we need a name? How about:

D'aikido.
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Old 3rd June 2008, 05:50 PM   #50
Cappy is offline Cappy  United States
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Hmm, maybe a little obscure.

Dackido?
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