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Buffalo II & transformers

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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...
 
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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).
 
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Et voilà! 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.
 
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 :p
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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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
 
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.
 
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?
 
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.
 
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 :p
 
Sorry but that is a completly wrong way to output a dac chip.
I dont want to be rude, but please consider following facts,
First:
the reactive element like interstager has to be driven by the VERY low resistance
generator. Which dac chip is NOT. theese 200ohms are simply much to high.
And, dthe very same dac chip is not ment to be the driver of anything but only a DAC...
Second:
the hard step up transformer have a lot of capacitances
because on the output we have large #n secondary turns which have lerger capacitances + on square x C of the primary layers... Tis capacitance deserves very low internal resistance driver before. And it is the problem to compensate large capacitances at the output...
third:
this arangement is after all not have capability to drive the next stage like preamp
even with low electrodes capacitances like tube.
And these topology have all the same sound signatures.
.
forth:
in the topology of the Riv + transformer at very end of the dac
current is partially converts trough the Rdc of the primarry inclouding the reactive
load to the DAC chip directly.
fifth:
if the buffer have very low resistance, thereis no need to use higher primary inductive transformers, so the less turns in primary is needed, and capacitances are decreasing rapidly like allover reactive range... Note: 2sk170 has 40 ohm rds on, which is 5 times smaller value then dac chip has.
...
there is more but there are some basics.
.
The solution is to:
1. convert current after dac chip
2. use low input capacitance + very low output resistance buffer
3. use 1:1 intrestage transformer
4. after the transformer use gain unit
5. buffer on se output to drive the cables, and preamp
...
the main point is that DAC chip and interstage should be separated with a buffer
and the interstage is preferably 1:1 or not high step up ratio
gain has to be acheived with some amplifinig device not the interstage
the role of the interstage is to put galvanic isolation, and to merge down the phases for the SE output from ballanced.
...
cheers
 
enjoy fishing :)
sorry there is no dogmatic in my statements
everything argumented, and could be checked by calculations, spice simulations, measurements, and listening tests.
.
ideologic is laying rather in the concept using a interstage transformer
without proper drive, termination and compensation.
using a reactive element without measuring the coupling factor
and all basic things like primary indictance, eventualy capacitance and so
to determine neded drive minimum output resistance...
that story repeating trough the years and can be called black-white?
...
another thing to add
the galvanic isolation with interstage transformer is complet
ONLY if it is present galvanicaly separated power supplys for active units before trafo and after the trafo...
So AVCC 3.3V and electronic after the dac, but before interstage, can be suplyed from one power trafo branch, and all the modules after the interstage should be suplyed with another power transformer PS unit.
.
more that could be of use:
I did 2 switches in addition,
first to swich chasses fround schucko to the chases or lifted off,
another to choose connection of the audio ground possition
(with isolated transformer-chasses) to ground at primary side or to ground secondary side. In my case there is no any hum in any position of the ground switches.
...
also digital branch should have own PS with own transformer
with parallel RC network of 1meg ll 100nF from digital ground to shucko TAP power
(does not have to be tha chasses in same time, because of the simple switch shucko tap lifted from the chasses i mentioned before...)
from the dac side. if it is not some AC value will be present between the power transformers cores and it is also notiable with the scope... With EI cores it is easy to measure
but toroid cores should have a wire from the core to outside to measure this.
...
cheers
:)
happy building, listening
and sorry for the long inputs
 
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enjoy fishing :)

...that story repeating trough the years and can be called black-white?
... another thing to add the galvanic isolation....

Amen on the positive aspects of galvanic isolation - but most won't know what you are talking about. :confused:

Still here, loading up the car and was just about to turn the computer off...

Maybe I was a little rash, but I like to think I am a free thinker and sometimes able to get things done by thinking outside the square - interstage stuff does indeed interest me, a lot in fact, and maybe I think a little differently. I do roll my eyes when somebody tells me on the phone about a problem, that they have been told by somebody else, that it was caused by an "impedance mismatch" - oh boy, does that throw-away line hide quite a few sins.

Off to catch that Snapper...

Cheers, Joe
 
Hi mars2, put in the way You like to, but these are the facts
I wroted, and I didnt have a notion to disturb anyone from personal
tryouts.
.
just one more fact to add:
Passive simple Riv I-to-V conversion
with a single resistor used = phase shift of voltage
so vhen on +Iout loads Riv the -Vout is expected
and for the +Iout = -Vout is after the Riv
...
There is more ways to converting current to voltage
some of them are to put I buffer after the dac chip
sum all Iouts from the same phases, and then
externaly convert this current to voltage, following the buffer low impedance stage,
then interstage trafo, again SE out buffer and RCA conn.
:)
 
There is more ways to converting current to voltage

Absolutely!

It's all about management, there are going to be a number of variables, some pluses, others minuses, and the best balance and identifying degrees of importance, these will all affect the outcome.

I do NOT favour "virtual earth" solutions, even though on paper they seem desirable to some. They rely on large amounts of feedback in an environment that is ripe for slew rate type distortion. Indeed one well-known designer told us that it is one of the primary causes of "digital sound."

Passive I/V has near infinite overload characteristics, are easy to apply passive filtering (especially if you establish a dominant pole) and using low-noise and even zero feedback circuits (like the types we use in Moving Coil Phono Stages), we have a real high-end solution where the positives outdoes the negatives. The fact that such a solution can also implement DC circuitry and no capacitors, easy with the ES9018 as it can be pulled to ground safely, unlike many other DACs.

Cheers, Joe
 
for the passive filtering i am using if there is a need for
zanden style LRC multi network.And that is depemding on a chrs of the interstage transformer.
.
And i think that You pointed right. Why use transimpedance OP circuits on the end
when we was listened to them for last decades in a same way from 99% of digital equipment?
:(
When I asked Dustin Foreman long tme ago about the Riv issues.
He said simply, put whenewr you want gnd, or +Avcc, os some +Vref in between...
So this dac has no classic output stage like old type models where the offset is have to be low.
.
I spot significant improvement in sound when I change to NON-inductive-hand made resistors from isotan wire...
But maybe it is a subjetive impression?
.
 
Maybe you won`t believe it Zoran, and sure there are also subjective resp. psychological reasons:

I tried the Isotan (have an old bobbin of 0.1mm one at hand) - it sounds very good.
When you have a piece of for example 0.1mm (or even thinner) copper wire
or to top the whole silver wire - provided that you have a top clock, separated supplies, careful grounding ans so on, as it is seems the case in your project.

This will bring things to light and shine out...
 
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