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Old 2nd April 2004, 12:06 AM   #11
AKSA is offline AKSA  Australia
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A cap coupled output using modern electros with a little judicious bypassing with a Black Gate is incredibly transparent, and guarantees you'll never monster a driver with DC. Believe me, this cuts the worry factor to zilch...

Offset control will require some sort of servo; this is not so bad, but it introduces complexity into a hugely elegant, simple circuit.

A +19V/-3V supply cannot be properly supported from a center tapped winding because, by definition, it's not a center tap! Such an arrangement sets up unequal flux across the winding which may cause transformer noise problems with the larger currents proposed here. A better idea is to use two separate windings, say 15Vac and 3Vac, each with a separate rectifier, then place the DC in series. This will give you a sufficient voltage margin to incorporate chokes into the supplies to assist with filtering and greatly reduce the size of the filter caps and lessen the current pulse load on the transformer; 22,000uF should be quite enough.

The DCR of the 100mH audio choke could be set to 1R, so that three amps will drop precisely three volts. If the gate is then biased for zero offset, exactly three amps will be flowing into the choke.

These SE amplifiers - significantly NOT balanced - sound very, very good. I have one, though it's efficiency is only marginally higher than a steam engine since it's loaded with a CCS. I have heard Circlotron's choke loaded SE Mosfet and it is sensational.


Cheers,

Hugh
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Old 2nd April 2004, 12:45 AM   #12
Fuling is offline Fuling  Sweden
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I agree with AKSA here: Take the best īlytics you can find, bypass them with some serious film caps and go ahead and play some music!
Definitely the easiest way to deal with the problem.
Many Zen versions are cap coupled and I donīt hear much complaints about them
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Old 2nd April 2004, 04:35 AM   #13
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Default coupling caps?

so, with say a 20vdc supply, a 3A bias, 100mh 1ohm choke.

do i need non-polarized or polarized coupling caps?

The top of the choke is at 3v.

I think I will go with the choke and cap arrangement.


I just need to find a 100mH choke..... any ideas?
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Old 2nd April 2004, 06:47 AM   #14
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Quote:
Originally posted by Fuling

Maximum teorethical efficiency for an CCS loaded SE amp is 25% versus 50% for a chokle loaded design.
When I had my "choked" follower running I got 30W out @ 80W power consumption.
Hello Fuling,

Correct, theoretically that is the maximum for an “ideal” amp. But regarding Vg_th and you can’t drive the Fet to have zero voltage across it, losses in the choke/transformer, and the low supply voltage you may be glad to have 20 to 25% in the end at reasonable low distortion.

But you are more an expert with Zen amps I understand, so what did you actually measure in the end at say 0.5% distortion?

Regards
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Old 2nd April 2004, 10:18 AM   #15
Fuling is offline Fuling  Sweden
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Quote:
you may be glad to have 20 to 25% in the end at reasonable low distortion.
30/80= 37,5% efficiency. Thatīs what I measured in my amp.

Not a Zen expert at all, Iīve never even buit one. I just meant that alot of people seems to use them and like them even though they are cap-coupled.

AudioGeek: No, I donīt think youīll need bipolar caps. Just ordinary lytics (ok, the best ones you can find), bypassed with something good

Letīs see, you need a pair of 100mH 3A chokes, huh?
Are EI transformer kits available in your area?
If so, get a pair of >250VA kits, remove the primary windings and fill the bobbin with 1,4mm wire.
The core must be assembled with an airgap, talk to Circlotron about how to adjust that.

OR: Have a look at hammondmfg.com.
Following pieces might be of interrest:
195T5
193V
159ZE (three or four in series)
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Old 2nd April 2004, 12:20 PM   #16
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Default Re: yeah!.

Quote:
Originally posted by AudioGeek
thinking of 50mH - 100mH 1ohm choke. 3A bias.

would this be adequate for 8 and 4 ohms?

what should my power supply voltage and my source voltage be to have symmetrical clipping from a choke load?????
3 amps will let you swing to -24v into 8 ohms The supply rail will need to be +24v plus a couple of volts extra so the mosfet when swinging positive doesn't have to turn on too hard, going into it's nonlinear region, but don't go nuts. I use 27.7 volts @ 3.5 amps, 80mH.

Make sure you use a 220 ohm or so gate resistor on the mosfet - on mine I have the gate lead and the resistor lead each cut to about 4mm before being overlapped and soldered.

Once you have it going you will wonder how you put up with anything else before. You will =not= be disappointed.
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Old 2nd April 2004, 03:35 PM   #17
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Default circlotron:

what kind of power supply do you use? How do I wind my own 80-100mH chokes?

28vdc it is then.

so I would only need 25v BG caps??? or 50v???

which series?
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Old 2nd April 2004, 03:49 PM   #18
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Default chokes found.

Digikey has those BIG *** 195T5 chokes (100mH 0.67dcr 5A) for 57.00 each.

would these work???

So... 3x0.67 is 2v across the choke.

hmmm since these are not enclosed, would they emit tons of interference???? or should I really be looking for enclosed chokes?

Thanks!!!!

p.s. these weigh 14 lbs each.
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Old 2nd April 2004, 04:52 PM   #19
Fuling is offline Fuling  Sweden
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195T5 should work fine.
Donīt worry about them not being enclosed, most audio chokes and transformers arenīt anyway.

Since they can handle 5A you have the opportunity to crank up the bias as much as the heatsinks and PSU can handle, not being locked to 3 A. No such thing as too much bias, soundwise.
Heat is an issue, though!
No such thing as too big heatsinks either!

2V across the choke is nothing. I dropped 4,8V @ 3A when my amp was up and running. Just calculate for it when you design the PSU.

14 lbs, thatīs nice
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Old 2nd April 2004, 05:10 PM   #20
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Default bias at choke current handling

is there any issue with choke saturation running the bias so close to the choke rated current?

If my bias is say 4A... and the choke is rated 5A... do I have only a +1A to -1A available output swing??

lemme see.... 3A x 28v = 84W.... toasty.

I have a heatsing that was running 2x 12v x 3.25A = 78W so they should work fine. (Yes they were HOT to the touch, but mosfets worked fine and lasted).

What coupling cap should I use??? 4700uf good enough?

next got to work out a bias scheme.... probably run from the ground of the IT coupling to the gate.

thinking around 6v bias (2v across choke + 4v for 3.25A at 28v).

make it adj. of course.
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