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Old 24th May 2011, 03:19 PM   #51
M Gregg is offline M Gregg  United Kingdom
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Quote:
Originally Posted by Alastair E View Post
Output impedance will increase....

'Reflected Imp'. normally refers to Transformer coupling...

Miller shouldnt be an issue, the drive signal is strong enough anyway...
Yes sorry (No Tx) wrong terminology,

I was thinking about the change in output impedance and power transfer to the 8 Ohm / 6 Ohm speaker.

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M. Gregg
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Last edited by M Gregg; 24th May 2011 at 03:30 PM. Reason: Rough day..LOL
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Old 24th May 2011, 03:52 PM   #52
M Gregg is offline M Gregg  United Kingdom
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Ok,

I'll start collecting parts and think about chassis design.

Should be interesting!


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M. Gregg
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Old 24th May 2011, 06:46 PM   #53
CSlee is offline CSlee  United Kingdom
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Would be very interested in following your project M. Gregg, hope you document it here.

Cheers
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Old 24th May 2011, 07:52 PM   #54
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Quote:
Originally Posted by M Gregg View Post
Yes sorry (No Tx) wrong terminology,

I was thinking about the change in output impedance and power transfer to the 8 Ohm / 6 Ohm speaker.

Regards
M. Gregg

If you want to reduce the effects of single-cathode operation and lower the O/P impedance, a nominal amount of global-feedback can be applied into the grid of the first stage, a la Tim-Mellow OTL.

Use a 33K in series with the vol-pot wiper to G1, and a 470K from O/P to the G1 of the first-gain stage.....

Ive tried this, and although it does reduce the overall gain somewhat, it will minimise the effects of a higher o/p impedance using 6C41C or single-cathode 6C33C operation at lower powers

Try it with, and without GNFB, Vary the amount even--See which you personally like the best, Thats the great thing about DIY-Audio....
Personally, I think I prefer without, but I'm giving it a few days listening now with to decide....
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Old 24th May 2011, 09:55 PM   #55
M Gregg is offline M Gregg  United Kingdom
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Is this correct position for the 33K?


Or is it between the grid and the 470K?


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M. Gregg
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File Type: jpg OTL feedback a.jpg (44.3 KB, 947 views)
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Old 24th May 2011, 10:31 PM   #56
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Aye, Thats it....
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Old 24th May 2011, 11:19 PM   #57
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Here you go, Ive re-drawn the scheme, tidying it slightly and including the 22K omitted and the nfb loop....
--Just noticed, during cleanup, ive not put correct value for R15. This should be 4.7Meg, not 100K
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Last edited by Alastair E; 24th May 2011 at 11:23 PM. Reason: correction
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Old 25th May 2011, 06:55 AM   #58
M Gregg is offline M Gregg  United Kingdom
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Thank's,

I notice the 120 - 120V Tx is not so easy to find.

Have you ever used Airlink Tx's

Transformer Manufacturer UK - Airlink Transformers - Home Page

Wondered if they HUMMMM like a wasps nest?

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M. Gregg
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Old 25th May 2011, 10:25 AM   #59
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A quick look, and Ive found this--

9639 : 300VA 230V 1 x 110V toroidal transformer

You would need 2, one for each 150V rail, but they will happily supply both channels...

Prob cheaper than using/getting made a custom jobbie...Being toroidal, noise/hum should be minimal...
--I'll look around for summit better anyway....

There's this one too, bit bigger and more expensive, but has 115-0-115V, so you'll only need the one...
-It seems to have a pretty good spec and shielding etc, looks like it was originally made for some fairly noise sensitive equipment rather than general use. Should be nice and quiet...

http://www.airlinktransformers.com/t...ransformer.asp

Last edited by Alastair E; 25th May 2011 at 10:37 AM. Reason: addition
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Old 25th May 2011, 04:42 PM   #60
M Gregg is offline M Gregg  United Kingdom
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Any ideas,

How much current drawn on each channel on the 350VDC supply?


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M. Gregg
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