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Old 6th March 2013, 03:41 PM   #441
Coris is offline Coris  Norway
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I think that all that long wires around the chip and transformers, is not a very good idea at all.
There is an special method to wound an resistor to not have inductance in that component. Googling about it may bring some results (non inductive wounded resistor, or so...).
I should do it in other way. It may be better to use an isolated thin (teflon) tube over that wire, or an already isolated silver wire. I bought a such silver wire which is destined to make electrodes for medical reasons. This wire is 0.2mm, the purest silver as possible, and it have an very thin teflon isolation on it. 7m for 80 euros.
I should make an zig-zag of that wire in one plane only. Then I should use something to make an (as small area as possible) compact sandwich of all construction, so that resulting object will be an quite flat thin pack. On both sides of that sandwich I will use some shieldings (µmetal or some high frequency shielding) material, connected to an GND point.
It may result in this way an resistor which it may have a quite big capacity to GND/shielding, but this is possible to be adjusted, and anyway it may be better and more compact than an resulting coil resistor...

Last edited by Coris; 6th March 2013 at 03:47 PM.
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Old 6th March 2013, 03:44 PM   #442
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Or just use a good quality low-value thin film resistor off the shelf....
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Old 6th March 2013, 08:15 PM   #443
Coris is offline Coris  Norway
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I do not know actually why that resistor it should be made of silver wire... A such large quantity of material to have an low value resistor, it alter many other parameters of that circuit is used for.
I will of course use one (or many) very good (thermic stable) SMD resistor(s).

Last edited by Coris; 6th March 2013 at 08:19 PM.
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Old 6th March 2013, 09:32 PM   #444
rolls is offline rolls  Switzerland
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Originally Posted by mars2 View Post
Et voilą! Ready are the new copper I/V-resistors (uuufffhhh...).
Powering things up and...yeah - near dead silence!!!
Congratulation! I have 0.04 as well, but could barely see it, so I took 0.07. Of course you get the best sound out of the thinnest and shortest wire possible. The problem with your 5cm is, that a difference of just 1mm is already 2%. You have to solder very precisely. And, by the way, did you solder the midpoint to earth? Otherwise the chip is not in (nearly) current mode.
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Old 6th March 2013, 10:02 PM   #445
mars2 is offline mars2  Switzerland
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Originally Posted by Vbenonisen View Post
Are you using the Lundahl transformers in 1:8 or 1:16 and can you please tell us what kind of tube output stage you have?
I use the LL1933 in an 1:16 matter, mainly because of the risk of adding additional noise to the tube input with such low impedance values.
After a lot of experimenting with different topologies and tubes, I ended up using a 6E6P-dr parafeed with an LL7903 (yes one transformer more) wired 4:1 as output.

Taking silver wire must be some kind of transfigured romantic attitude in my case - I understand your raised eyebrows Brian.
Call me crazy, but there`s such a lot associated with silver: it`s historical, mythological and even mystical and magical charged - it`s used for several medical, chemical and technical reasons
...and it sounded so beautiful
So who wants to use a good quality low-value thin film resistor off the shelf?
Seriously: I don`t claim that such an usual resistor, maybe even better as SMD, Coris, wouldn`t do it...

@rolls:Thanks. This small tolerance is also a reason, why I tensioned the wire in a zig-zag manner trough the wholes of an experimental printed circuit board with precisely predrilled wholes and prefabed solder points. So it should be as precise as it can get with soldering it by hand. A really accurate Meter would help to test the result. I didn`t solder the midpoint to earth yet, but that`s what I`ll do tomorrow.

P.S. The sentence with the "purely passive silver bullet" is insofar an ironically hint. It comes originally from Russ in this thread and I used it out of context (please excuse me).
He stated that "there`s no purely passive silver bullet" referenced to a specific transformer I/V - stage with feedback. Seems even true for the silver I/V output...buuhhhuuu!

But wait! What about thinner wire? Saw some 0.05mm pure silver on the net. Resistance should be around 8Ohm/m, so less than 10cm will do...
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Last edited by mars2; 6th March 2013 at 10:22 PM.
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Old 2nd April 2013, 02:54 PM   #446
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I'm transitioning from balanced dual-mono B2 to balanced dual-mono B3SE. I have been using B2 in voltage mode with Audio Consulting 1:2 Silver Rock transformers driving battery-powered LME 49600 buffers. I would like to try the Silver Rock in balanced current mode without using buffers, loading the primary with two resistors to ground as per Joe R's schematic. What R values would you suggest? The transformer is 200R across the primary and 400R across the secondary.

Thanks,
Dave
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Old 3rd April 2013, 03:07 AM   #447
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Quote:
Originally Posted by David Garretson View Post
What R values would you suggest? The transformer is 200R across the primary and 400R across the secondary.

Thanks,
Dave
I would say, generally as low as you can get away with. Just keep in mind, the lower the value, the lower the output from the DAC. It all depends on the gain architecture post DAC output. Have you got enough gain?

Cheers, Joe R.
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Old 3rd April 2013, 01:42 PM   #448
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Thanks, Joe. My preamp could handle perhaps a halving of source output. I'd prefer passive tfx gain in the DAC. The preamp is an Atma-Sphere MP-1 modified with VSE superregulators. The stock series stepped attenuator was replaced with a 100K balanced LDR shunt attenuator. The working range of the LDR attenuator is -30db to -70db, though with tweaking it would be possible to operate closer to unity gain.

I'd like to hang onto the 1:2 AC Silver Rocks, but maybe the optimal approach for current mode is to substitute a 1:20 or higher trans as suggested by others in this great thread. Has anyone experience with the Lundahl silver step-ups?
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Old 3rd April 2013, 09:11 PM   #449
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Sounds like you know what you are doing. I am currently using 2 x 3R and of course have a lot of gain after that. That works for me and also means that getting the best out of the Sabre DAC IMO. But others have used up to 330R, they are usually using 1:1 transformers. So this being DIY, there is an amazing scope for variations that absolute no other DAC chip is capable of. Almost infinite number of combinations and variations possible, and some that have yet to be thought about?

Cheers, Joe R.
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Old 5th April 2013, 11:50 PM   #450
mars2 is offline mars2  Switzerland
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Originally Posted by David Garretson View Post
I'd like to hang onto the 1:2 AC Silver Rocks, but maybe the optimal approach for current mode is to substitute a 1:20 or higher trans as suggested by others in this great thread. Has anyone experience with the Lundahl silver step-ups?
The only doubts I would have are about noise, with the typically low signal voltage levels in current mode.
When you use the Silver Rock with its 1:2 step-up ratio, this would be a 1:4 transformation impedance wise.
Now, taking Joe`s 3R case as example you will have 12R on each half of the output, which is much too low.

Think there`s a rule of thumb for impedance matching with tubes and signal sources to avoid noise increasing (apart from complex calculations):
If the impedance (~noise resistance) of the signal source is equal or greater than the equivalent noise resistance of the input tube, then it should keep noise increasing under 40%!
But not to forget, that the noise resistance values stated in tube data books usually refer to HF-signals. They can increase a lot with decreasing frequency!

It seems that the Atma-Sphere MP-1 is equipped with a differential input stage with cathode current source. This is certainly the best way to build differential stages - but the noise situation at the input changes for the worse, due to the additional (serial) resistance in the cathode leg.

I think these are the reasons, why several people suggest min. a 1:16 step-up transformer for current mode.

If you insist on current mode, I can only suggest to give the Lundahls a try. I currently listen to the LL1933, it plays really delicious...
not to mention, that there`s a silver version
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