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Old 4th September 2011, 03:51 PM   #181
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How much the IV transformer cost?
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Old 4th September 2011, 04:50 PM   #182
ichiban is offline ichiban  United States
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They better be goooood!!! eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices $1030.00 !!!
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Old 4th September 2011, 06:00 PM   #183
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Please contact Bunpei for price. He is on this forum.
http://www.diyaudio.com/forums/members/bunpei.html

They are very, very good.


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How much the IV transformer cost?
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Old 4th September 2011, 08:54 PM   #184
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Wow!!! That gonna cost me arm and leg. It would be nice to have it but I'm not ready at this economic situation. Thanks for the info though.
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Old 5th September 2011, 10:19 AM   #185
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Default Current versus Voltage - a Transformer Compromise?

My experience with the Sabre DACs have mainly been with Oppo Players, the older BDP-83SE and now the newer BDP-95, ES9016 in the former and the ES9018 as in in Buffalo.

I have tried transformers but preferred the I/V approach. As Russ has stated, the 195R output Z means that the ideal load should be a near short or at least a very small fraction of 195R. No doubt that ESS sees Virtual Earth as the solution. I beg to differ, being somebody who wants and explores non-NFB solutions.

Based on what I hear and others have expressed, the transformer/voltage solution gives a lighter tonal balance, but nice and open.

To me, the I/V approach has a better tonal balance, but it requires some serious active circutry and associated power supplies. No wonder transformers look attractice.

But that lighter tonal balance... can something be done?

Something that retains the ease of transformer, yet puts some more body into the presentation.

Please look at the two examples below. It basically boils down to one or the other. You have to choose either Current or Voltage.

Click the image to open in full size.

A: This represents my preferred way, using two very low value resistors straight to ground. They are a fraction of the value of 195R and so means we have avoided Virtual Earth but this doing it the current way.

But some may note this: There is a 1.65V offset voltage on the output of the DAC, but pulling that straight to ground we have exchanged offset voltage for offset current, the maths is simple:

1.65V/195R = 8.5mA

The beauty of this approach is that I can now make a differential direct-coupled non-NFB amplfier with suitable gain and get the expected 2V RMS output target.

Mind you, I am not one of those who gets nervous if falling short of 2V.

B: Don't you just look at the simplicity and from a DIY point of view, it is so attractive. Try different transformers, you don't need a engineering degree to experiment...

NOW TRY THIS:

Click the image to open in full size. C:

What you might call this, I don't know. It is not current I/V in the regular sense. But do note that we now have traded some of the offset voltage for current offset. Again the maths is simple, same as above:

1.65V/(195+330R) = 3.1mA

The offset voltage will be just above 1V DC. That DC will not go through the transformer, only AC current will be seen by the Primary. Looking AC wise, it also looks like a voltage divider:

(330R(195R+330R))*2.1VRMS = 1.3VRMS

But there is also another way of looking at it: The 3.1mA DC current offset is at least less that a tenth of the peak AC current required on the Secondary of the 1:1 transformer in pretty much all circumstances. The Sabre DAC is essentially modulating that current. Think of it as an iddle current being modulated.

Some kind of current processing is going on, but not in the sense of a proper I/V converter - which I still believe to be ideal, but maybe we are not looking for the ideal, just a better compromise for transformer use.

Bottom line, IF only 1.3V RMS output does not ruffle your feathers (it does some, but shouldn't), then like any good soup, how does it taste?

The general impression is that some of the missing sense of body comes back and very little that the transformer does so nicely is lost.

So guys, all it takes is a few resistors!!!

Some transformers will require a Zobel network on the secondary. I have tried my own QuadFilar transformers, they do not require a Zobel. But most others will. I have also tried another and less expensive transformer (my secret for now) that did require 10n/2K7 Zobel. I would recommend 600R:600R transformers, probably about 100R total DCR on Primary and Secondary. Also: That 330R resistor value can of course also be lowered (not much point increasing). But your output will go further down, but try it, maybe find a compromise that suits you.

How about this as another possibility: Use just 3R, as used in my I/V converter above, would give only 31mV RMS. Then you would need 50x gain amp on the Secondary, but it can be a single-ended circuit, ground one side of the Secondary, because the summing has already been done on the Primary. This could be done with tubes. Who said you couldn't do a proper I/V converter with tubes? With a 1:1 transformer you could.

For now, get some hands on four 330R resistors and tell the rest of us what you think, did you get a better tonal balance or anything else?

Cheers, Joe R.
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Last edited by Joe Rasmussen; 5th September 2011 at 10:31 AM.
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Old 5th September 2011, 10:50 AM   #186
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Default Transformer-Tube I/V Converter

Just thought I'd add this:

Click the image to open in full size.

This is proper I/V Converter. The input to the Tube Stage will see no DC - a variety of tube circuits could be used, but decent gain, low noise, are minimum requirements.

Cheers, Joe R.
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Old 5th September 2011, 03:22 PM   #187
Bunpei is offline Bunpei  Japan
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Default Offering of free evaluation opportunity in EU region

To staccatiss,
We much appreciated your detailed and complete review on Feastrex line transformer specially developed for ES9018 DAC.

The designer and manufacturer of the transformer intend to provide a better product by employing an innovative core material than those conventional ones in the market.

However, actual listening is believing.

The Feastrex company offers an opportunity for some audiophiles in EU region to evaluate the pair. Please send an usual e-mail ( NOT a private messaging of this forum) to my following address;
bunpei<at>ta2<do>so-net<dot>ne<jp>,
if you are interested in the evaluation.

"staccatiss" in Sweden will forward the pair to you. We may require a certain evidence information that identifies you and ensures your trustworthiness.
After your two or three week evaluation period, we request your shipment to the next evaluator in EU region or send back to Feastrex compnay in Japan with your expense. When you want to buy the pair after your evaluation, a discounted price can be expected.

Bunpei
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Old 5th September 2011, 06:06 PM   #188
joemana is offline joemana  United States
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Hi Bunpei,

Any chance of circulating that Transformer to the U.S for evaluation?

Thanks,

Joe
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Old 6th September 2011, 02:59 AM   #189
fulken is offline fulken  United States
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Quote:
Originally Posted by joemana View Post
Hi Bunpei,

Any chance of circulating that Transformer to the U.S for evaluation?

Thanks,

Joe
Hello Joe,

I will look into a way with Bunpei and Feastrex Japan.

Kenji@Audio Feast (Nashville TN)
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Old 6th September 2011, 09:37 AM   #190
Ciu is offline Ciu  France
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Quote:
Originally Posted by Joe Rasmussen View Post
Just thought I'd add this:

Click the image to open in full size.

This is proper I/V Converter. The input to the Tube Stage will see no DC - a variety of tube circuits could be used, but decent gain, low noise, are minimum requirements.

Cheers, Joe R.
Hello Joe

Newbie question
Each output (+ , -) can sink or source the signal ....
So why the center 3R connected to ground ?
What's the value of the current from +- to Gnd ?

Thanks!
Richard
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