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Old 21st September 2003, 01:44 PM   #11
Pedja is offline Pedja  Serbia
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Default AudioNote I/V stage, pros&cons.

Quote:
Originally posted by Kuei Yang Wang
The note on my DAC Project was included after AUdio Note asked for it and threatened legal action. I did not feel like having a court battle over this at the time although I must note that I am certain that a court review of AN's patent would see it dismissed for reason of obviousness.
So we can only imagine under what threat is Sowter which, imagine, manufactures such (I/V?) transformers. Or Sowter paid/pays license fees to Audio Note to do that? Or Audio Note only needs its name on Konnichiva San's DAC project page?

Pedja
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Old 21st September 2003, 02:38 PM   #12
Previously: Kuei Yang Wang
 
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Default Re: Re: Transformer I/V stage, pros&cons.

Konnichiwa,

Quote:
Originally posted by Peter K

Maybe this discussion can be focussed on Brian's question. I am (and I am sure others are) also interested in a technical explanation.
The explanation is simple. As there is no such thing as an "I/V" transformer there is nothing to discuss. The use of a transformer to match impedances os well known and documented. If you use a transformer with a stepup you trade Voltage Gain for Current Loss.

If we took (for arguments sake) a PCM1704 DAC and a Transformer with a 1:10 ratio and a nominal (load) impedance of 25k we find that the +/-1.2mA current send into the transformer primary become +/- 0.12mA in the secondary. A 23k5 Resistor will convert this current to +/-2.8282V (2V rms). The output impedance of the Circuit will be in effect that of the I/V resistor, so 23k5. A last check, the load on the DAC is appx. 1/100 of the Secondary load, so the load seen by the DAC output is around 235 Ohm and the Voltage on the DAC output is around +/-0.283V.

Absolute standard.

Now an output impedance of 23k5 Ohm is rather unpractical in most systems and cannot tolerate long interconnects, that is the price you pay for being passive and simple. I would hence think that the Transformer and I/V Resistor should be mounted inside the Preamp/Amplifier to avoid exposing the output of the transformer to undue loads. The input impedance of the Pre/Amplifier needs to be accounted for in the 23k5 Resistance as well. This suggests a fully dedicated connection between CDP/DAC and Amplifier with a dedicated input and a dedicated defined interface that makes sure for the system to be completely incompatible with other equipment.

Another option would be to follow our 1:10 Transformer with a Gainstage and place an added resistor in the primary to reduce the Voltage on the DAC's output and subsequently the transformer secondary. An ECC88 SRPP (lower cathode resistor unbypassed) has a gain of around 16 (24db). If we place a resistor of around 16R on the 1:10 transformers primary we will have an effective load on the DAC of around 15R, giving +/-18mV on the transformer primary and +/-180mV on the transformer secondary. After being amplified 16 Times by our ECC88 SRPP gives us a Voltage of +/-2.88V on the output, in essence the common 2V RMS.

As can be seen, all this is the most basic and simple transformer behaviou, calling it EE101 is really stretching it, probably around 8th grader physics....

Sayonara
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Old 21st September 2003, 04:27 PM   #13
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Default Re: Re: Re: Transformer I/V stage, pros&cons.

Quote:
Originally posted by Kuei Yang Wang
The explanation is simple. As there is no such thing as an "I/V" transformer there is nothing to discuss.
How do you figure? Isn't that ultimately what a transformer is, an I/V converter?

A transformer works by way of magnetic field coupling.

The time varying magnetic field produced by the primary is the result of the current flowing through it (just as it's current, not voltage which causes a loudspeaker cone to move as you've said in your writings on current drive for loudspeakers).

That time varying magnetic field then cuts across the windings of the secondary and, according to Faraday's Law, induces a time varying voltage (or EMF if you prefer) across it.

So how can a transformer ultimately be anything OTHER than an I/V converter?

Quote:
As can be seen, all this is the most basic and simple transformer behaviou, calling it EE101 is really stretching it, probably around 8th grader physics....
Are they teaching Faraday's Law in 8th grade these days?

se
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Old 21st September 2003, 05:22 PM   #14
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Default Re: Re: Re: Re: Transformer I/V stage, pros&cons.

Konnichiwa,

Quote:
Originally posted by Steve Eddy


How do you figure? Isn't that ultimately what a transformer is, an I/V converter?

A transformer works by way of magnetic field coupling.

The time varying magnetic field produced by the primary is the result of the current flowing through it (just as it's current, not voltage which causes a loudspeaker cone to move as you've said in your writings on current drive for loudspeakers).

That time varying magnetic field then cuts across the windings of the secondary and, according to Faraday's Law, induces a time varying voltage (or EMF if you prefer) across it.

So how can a transformer ultimately be anything OTHER than an I/V converter?
I will not grace this with a comment. Read again what you wrote and think about it, if you must re-red the textbook from Uni....

Quote:
Originally posted by Steve Eddy
Are they teaching Faraday's Law in 8th grade these days?
Dunno what they do elsewhere, when I went to school (in Germany) we covered it in 8th or 9th grade, including practical experimentes with coils and cores and observing the different votages etc.... School physics went right up to basic semiconductors, though not neccearily the detailed innner function, but we finished the Labs with making simple crystal detector radios with following amplification stages to miniature speakers. This primitive suff amused me no end as I had exhibited in the 6th or 7th grade a Home-made Stereo using an Amp based around some early chip Amps and preamp control chips and an FM Tuner with digital frequency readout, all build from Kits we could get....

Sayonara
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Old 21st September 2003, 06:30 PM   #15
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Default Re: Re: Re: Re: Re: Transformer I/V stage, pros&cons.

Quote:
Originally posted by Kuei Yang Wang
I will not grace this with a comment. Read again what you wrote and think about it, if you must re-red the textbook from Uni....
Ok.

I read again what I wrote. I thought about it. And I checked up on Faraday's Law via several references, including several university websites.

After all that, I still see that a transformer boils down to the same thing; current through its primary produces a magnetic field which induces a proportional voltage across its secondary.

Now, I'm no Ph.D., but that sounds suspiciously like current-to-voltage conversion to me.

So what am I missing here?

se
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Old 21st September 2003, 11:50 PM   #16
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Default Re: Re: Re: Re: Re: Re: Transformer I/V stage, pros&cons.

Quote:
Originally posted by Kuei Yang Wang
Konnichiwa,



The same DIY'er also wrote within this thread:

"There is no such thing as Transformer I/V nor can there be, certain patent claims nonwithstanding."

The note on my DAC Project was included after AUdio Note asked for it and threatened legal action. I did not feel like having a court battle over this at the time although I must note that I am certain that a court review of AN's patent would see it dismissed for reason of obviousness.

Sayonara

Quote:
Originally posted by Steve Eddy


Ok.

I read again what I wrote. I thought about it. And I checked up on Faraday's Law via several references, including several university websites.

After all that, I still see that a transformer boils down to the same thing; current through its primary produces a magnetic field which induces a proportional voltage across its secondary.

Now, I'm no Ph.D., but that sounds suspiciously like current-to-voltage conversion to me.

So what am I missing here?

se
The magnetisation or flux of the core is not depedant on current.
It is voltage (and frequecy) dependant. As an example, a 240V
mains tranny may be designed to work at 14kGauss @ 50Hz.
This flux will not change (theoretically ideal TX) with varying
current loads. The current is merely transferred from load to
source inverse to turns ratio. WRT flux Vs frequency, when freq
is halved, flux is doubled.

So KWY is exactly right, it is an I-I and V-V converter.

Cheers,

T
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Old 22nd September 2003, 12:51 AM   #17
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Default AMTRACK...

Hi,

Quote:
So KWY is exactly right, it is an I-I and V-V converter.
And so he was right from post #2, I think.

For a DAC and likewise for a MC cartridge the I/V is done by the loading resistor on the primary side of the Xformer; voltage is than further transformed by the xformer to higher value depending on ratio and effeciency into a given impedance at the secundary side.

There are other important advantages to using a xformer in this situation, not having read the entire thread I assume these have been covered.

Cheers,
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Old 22nd September 2003, 02:21 AM   #18
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Default Re: Re: Re: Re: Re: Re: Re: Transformer I/V stage, pros&cons.

Quote:
Originally posted by Terry Demol
The magnetisation or flux of the core is not depedant on current.
It is voltage (and frequecy) dependant. As an example, a 240V
mains tranny may be designed to work at 14kGauss @ 50Hz.
This flux will not change (theoretically ideal TX) with varying
current loads. The current is merely transferred from load to
source inverse to turns ratio. WRT flux Vs frequency, when freq
is halved, flux is doubled.
How does any of that change the fact that the magnetic field which causes the whole thing to work in the first place is the result of current? No current, no magnetic field. No magnetic field, no induced voltage. I don't see how, just because you're feeding the transformer from a voltage source (where the current will be dependent on the reflected impedance), that any of that changes.

What we're talking about here is mutual inductance, which pretty much every definition I've seen boils down to this:

Mutual inductance is the property of two electric circuits whereby an electromotive force is induced in one circuit by a change of current in the other. It can also be defined in terms of the number of flux linkages set up in one circuit per unit of current in the other.

So, if current in one circuit induces a voltage in the other, how is that not ultimately current-to-voltage conversion?

se
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Old 22nd September 2003, 02:56 AM   #19
SY is offline SY  United States
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Semantics. You can't have a current without a voltage. You can't measure a voltage without causing a current.

Chickens. Eggs.
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Old 22nd September 2003, 04:49 AM   #20
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Default Re: Re: Re: Re: Re: Re: Re: Re: Transformer I/V stage, pros&cons.

Quote:
Originally posted by Steve Eddy


How does any of that change the fact that the magnetic field which causes the whole thing to work in the first place is the result of current? No current, no magnetic field. No magnetic field, no induced voltage. I don't see how, just because you're feeding the transformer from a voltage source (where the current will be dependent on the reflected impedance), that any of that changes.

What we're talking about here is mutual inductance, which pretty much every definition I've seen boils down to this:

Mutual inductance is the property of two electric circuits whereby an electromotive force is induced in one circuit by a change of current in the other. It can also be defined in terms of the number of flux linkages set up in one circuit per unit of current in the other.

So, if current in one circuit induces a voltage in the other, how is that not ultimately current-to-voltage conversion?

se
Because it is a current to current AND voltage to voltage
converter.

The traditional current to voltage conversion when applied to
a DAC referres to the fact that the DAC feeds an ideal virtual
ground and there is NO voltage swing at the DAC OP. This was
how traditional R2R ladder DACs were designed and attained
best linearity, with NO voltage swing. In it's ideal form, the I-V
converts ONLY current with NO voltage swing (at the - opa IP) to
a voltage at it's OP.

With a transformer I-V, the conversion to voltage from the DAC's
OP current HAS ALREADY HAPPENED before, with or without the
transformer. The transformer IS NOT responsible for the
conversion to a voltage, the low value R at DAC OP is.

The transformer does NOT reflect a load back to the DAC OP
which is solely responsible for conversion to voltage, it merely
amplifies that existing voltage that is already at the IP.
The only load reflected in a so called "transformer I-V" will be
that of a possible snubber network and the following stage.
These are relatively light loads compared to the I-V resistor at
the DAC OP.

I hope this clarifies things.

Cheers,

Terry
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