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Old 19th January 2007, 06:23 AM   #1241
Nixie is offline Nixie  Canada
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I'm only using ~600 VA EI transformers for 100 W/ch monoblocks (~300 W power draw). Double the VA rating seems plenty, despite that current is drawn in surges in the case of a C-input filter.
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Old 19th January 2007, 06:29 AM   #1242
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metalman, where do you buy your L's? I can't find power chokes locally for a good price. What size did you use for your Aleph-X?
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Old 19th January 2007, 11:08 AM   #1243
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Default 6) the good ,the bad and the ugly

Well I did not purchase any transformers -- The good
I did purchase heat sinks suitable for a 15 V rail--- The bad
Now Im not sure If I should stay with 15 v rail---The ugly
Oh boy-- R and D surplus.

On a serious note, Whe modeling the Aleph x using PSUD what do you
use for a lod, When I use a current sink/source I get poor results.
I use 4.5 amps bias per mono block.

Thanks
J
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Old 19th January 2007, 12:16 PM   #1244
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There's a simple solution to the heatsink issue. My own heatsinks are only half the size of a passive cooling system. Use a quiet large fan at a significantly lower voltage, driven by a separate small transformer. At low speeds it will be inaudible. A capacitor can be added to pass a higher voltage pulse on turn-on to guarantee the fan starts, which may not happen if you have very low voltage. It's even very simple to add speed regulation to the fan based on heatsink temperature. Still have the heatsinks vertical so that convection helps, but with the fins facing each other making a tunnel for the fan.

I'm using beryllium oxide wafers to attach the output devices to the heatsinks (eBay), and highly recommend them. They're great electrical insulators yet more heat conductive than the aluminum of the heatsink instead. Just don't breathe in the dust while machining them and put a warning sticker on the inside of the amplifier chassis.
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Old 19th January 2007, 02:14 PM   #1245
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Don't blame a "sometimes" hum on the transformers. Check your power line for DC at those times. I've started having trouble in the last year or so. Used to happen at 13:00 every afternoon, but now it's at intervals throughout the day. So far I've just endured it, but the time is coming when I'm going to have to do something about it.

Grey
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Old 19th January 2007, 04:45 PM   #1246
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Quote:
Originally posted by Nixie
metalman, where do you buy your L's? I can't find power chokes locally for a good price. What size did you use for your Aleph-X?
I used the Hammond 15B chokes (1.5mH, 5A) which I got from partsconnexion for around CDN$15 a piece. Locally I couldn't find anything for a decent price.
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Old 20th January 2007, 01:38 AM   #1247
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Well, if you have DC on your powerlines, just use a DC trap. Or don't use toroids -- EIs are much more tolerant of DC.
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Old 20th January 2007, 02:49 PM   #1248
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Default bias vs distortion

After reading som threads It seems that the distortion and capacitance
in the mosfets decreases as the rail voltage and bias increases. This is due to the fact that you are operating the device in a different region.

My delima is that I feel somewhat comfortable building the original version (+- 15~ 16 v rail) But may be a bit skidish building the high power version with my level of experience. The power difference does not concern me I use full range speakers(fostex 166 bhl) most of the time. What does concern me is the distortin. Just how much is the difference? something to be concerned about?

j
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Old 20th January 2007, 04:14 PM   #1249
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Default Re: bias vs distortion

Quote:
Originally posted by tenderland


What does concern me is the distortin. Just how much is the difference? something to be concerned about?

j

The amplitude-related distortion is improved with the increased bias while the frequency-related distorsion is improved when the gain mosfet has low capacitance. Nevertheless, before soldering and listening, nobody can conclude the actual relation between the distortion and the sound.

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Old 20th January 2007, 06:23 PM   #1250
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I think the lower powered AX sounds great, just don't overdrive it. Also, keep your power supply as clean as possible.

I used to use my AX to drive my high frequency horns. This kept the power output low, which lead to great sound--very direct, if I recall.

It's a nice amp.

As an aside, you can always explore different input/output transistors.
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