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Old 4th December 2011, 05:33 PM   #271
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If using a pair of Buffalo2's in dual mono, what should the resistor values be with a tube stage after the transformer?

JD

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Originally Posted by Joe Rasmussen View Post
I still think somebody should try this with a Sabre DAC using Tubes.

Click the image to open in full size.

Normally Tubes are only good for voltage DACs, but use a transformer like this and you will have a Tube I/V stage - and it is the Sabre DAC that makes it possible - offset current = 8mA (I wouldn't do this with any other DAC I could think of). It can be pulled all the way to ground on the Primary and the Secondary grounded - and just input to the grid of your favourite Tube - and away you go.

Somebody should try it - requires gain about 50.

Cheers, Joe R.

Last edited by Jeffrey Davison; 4th December 2011 at 05:45 PM.
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Old 4th December 2011, 06:41 PM   #272
fulken is offline fulken  United States
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I would install a 100K POT and find a sweet spot to your taste.
After you find sweet spot, I would swap to the fixed value.

Loading transformer makes huge difference on its sound. The best is subjective and up to your taste.
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Old 4th December 2011, 06:49 PM   #273
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I'm thinking in terms of using a tube stage with gain after the transformer as in Joes schematic and keeping the the two reisitor low. His schematic shows a pair of 3r to ground on the primary for an output of the transformer to 30mv.
My question is would those resistors be the same value or a different value if using a dual mono rather than the single one in the schematic. (just curious)


Another thought I had was just running the Dal Mono Buff2's into a transformer with it's secondary loaded (2v) then into a 6H30 driver / buffer (with no gain).

JD

Quote:
Originally Posted by fulken View Post
I would install a 100K POT and find a sweet spot to your taste.
After you find sweet spot, I would swap to the fixed value.

Loading transformer makes huge difference on its sound. The best is subjective and up to your taste.

Last edited by Jeffrey Davison; 4th December 2011 at 06:55 PM.
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Old 4th December 2011, 06:56 PM   #274
fulken is offline fulken  United States
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Hi JD,

I do not know about the theoretical value, and theoretical value is a good starting point. I would still do the same thing with a POT to my taste. All the transformer is not same and small change makes big difference in this area.
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Old 4th December 2011, 07:56 PM   #275
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oops,

meant to say "before" the transformer (on the primary side) where the two are mated to ground. Would the dual mono setup need to have the 3R resistors changed to another value to get the same 30mv out?

JD
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Old 5th December 2011, 02:18 AM   #276
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JD,
I agree with fulken's suggestion but if you don't want to do this, you can use 1.5ohm resistors since you are running dual mono. You should still get 30mV if you're using a 1:1.
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Old 5th December 2011, 03:50 AM   #277
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Quote:
Originally Posted by ihear21khz View Post
JD,
I agree with fulken's suggestion but if you don't want to do this, you can use 1.5ohm resistors since you are running dual mono. You should still get 30mV if you're using a 1:1.
No, you will get 15mV RMS. Each phase of ES9018 will produce 1V RMS. Use Ohm's Law calculation:

2*(1.5/195) = 0.015384

I think 1R would be low enough to claim proper current mode, but the subsequent gain would need to be very high and low noise. That's the other consideration if using a tube gain stage, noise. If you want 2V RMS final out, then gain = 200.

Cheers, Joe R.
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Old 5th December 2011, 04:04 AM   #278
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Joe, JD is running dual mono. He has 8 Dacs per channel. Output impedance should be half the 195 you used in your calculation. Cheers DF
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Old 5th December 2011, 04:20 AM   #279
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Quote:
Originally Posted by ihear21khz View Post
Joe, JD is running dual mono. He has 8 Dacs per channel. Output impedance should be half the 195 you used in your calculation. Cheers DF
OK, gotcha on that one. That will indeed double up.

But something came to mind, that means the 195R gets halved, but also means that a lower Z is required for same 'level' of current mode, as the ratio between that Z and the load Z defines current mode. In theory it should be infinite and that means the ES9018 should only see its own Z and no more. But real world...? I have used 3R (stereo) and 1R5 (8 channel) and it works well - but didn't use tubes and no tx as I had a differential input with a gain of about 70 and very low noise.

But tx is a good idea when you have a single-ended input tube stage. I haven't done it, but a friend/client is soon to try.

Cheers, Joe R.
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Old 8th January 2012, 03:49 AM   #280
dheming is offline dheming  United States
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Just wanted to say thank you to everyone in this thread, it's been a great resource to me. I'm currently building my Buffalo III and decided to go with Sowter 3603 transformers with the OCC wire option. There will be a build thread for it soon, but this is where I'm at so far:

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