Dave Slagle (Intact Audio) is building for my Audionote Kit DAC 4.1 a couple of permalloy-core I/V transformers to replace the original ones from ANK.
I will add more details and my listening impressions once I have them in my hands and I have a chance to try them.
I will add more details and my listening impressions once I have them in my hands and I have a chance to try them.
Transformers don't do I/V conversion; resistors do.
But a dac current output loaded with a resistor and transformer works quite nicely.
https://www.diyaudio.com/community/threads/transformer-i-v-stage-pros-cons.20523/
But a dac current output loaded with a resistor and transformer works quite nicely.
https://www.diyaudio.com/community/threads/transformer-i-v-stage-pros-cons.20523/
@daanve you are 100% correct. I called it IV transformer because it's in the IV section (and that's how everyone seems to call them) but yeah the resistor does the I/V conversion. If you wanted to remove the resistor, you could use a transformer with winding resistance high enough to generate the desired output voltage, although I don't think that would bring much of an advantage compared to a discrete resistor; plus such transfomer would also have a very high capacitance for the DAC to drive.
@20to20 Good question. I remember reading in some forums that the "IV" transformers of the ANK DAC 4.1 are a major bottleneck, so I decided to try out some of Slagle's nickel transformers. I am not sure how they will perform and I won't know until I try them out. And even then, it will be a subjective opinion.. although I could set-up a test system to measure BW, square wave response and distortion.
@20to20 Good question. I remember reading in some forums that the "IV" transformers of the ANK DAC 4.1 are a major bottleneck, so I decided to try out some of Slagle's nickel transformers. I am not sure how they will perform and I won't know until I try them out. And even then, it will be a subjective opinion.. although I could set-up a test system to measure BW, square wave response and distortion.
Current to voltage conversion using a transformer and a resistor; I/V conversion . . . Yes.
Take an EL84 pentode (a current source . . . if you do not bypass the self bias resistor).
(& drive the grid versus the bottom end of the self bias resistor).
Connect the EL84 plate to an output transformer primary, & the other end of the primary to B+.
Connect a load resistance across the output transformer secondary
= guess what? A Current to Voltage Convertor
Done
Take an EL84 pentode (a current source . . . if you do not bypass the self bias resistor).
(& drive the grid versus the bottom end of the self bias resistor).
Connect the EL84 plate to an output transformer primary, & the other end of the primary to B+.
Connect a load resistance across the output transformer secondary
= guess what? A Current to Voltage Convertor
Done
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The resistor do the conversion and the trafo multiplies it , make a build with an trafo without any resistor , make a measurement of it and come back to report 😎
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If you have a voltage output a resistors dos not any conversion.
A transformer always transform ( a 1:1 wil give the same output , limited but the physics of the transformer) .
You can only use a resistor if there is a current source to get a change in voltage. A transformer (with a resistor) is more versitile.
A transformer always transform ( a 1:1 wil give the same output , limited but the physics of the transformer) .
You can only use a resistor if there is a current source to get a change in voltage. A transformer (with a resistor) is more versitile.
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Bottom end would be ground. Don't you mean top end of the bias resistor....in other words the cathode?
actually You have 2 cases, simplified.
1. Dac + Iout + Riv Transformer + Rload. (The IV going on the Riv Before transformer and ac voltage is on the transformer.)
2. Dac+ Iout + Transformer + Riv. (AC current going to the transformer and after on the secondary IV going on Riv, also a load R...)
.
1. Dac + Iout + Riv Transformer + Rload. (The IV going on the Riv Before transformer and ac voltage is on the transformer.)
2. Dac+ Iout + Transformer + Riv. (AC current going to the transformer and after on the secondary IV going on Riv, also a load R...)
.
Ten years ago Ibuolt a complete dac with Twisted pear full kit Sabre
In out I use a 10-15 ohm for conversion and a beautiful 3575 occ from Sowter
Then a tube stage gain+cf
It works perfectly
The coupling working on R gives you also different (little) changing in freq response that helps a lot to kill noise and residual image of conversion
In addition there is a galvanic isolation between stages
Walter
In out I use a 10-15 ohm for conversion and a beautiful 3575 occ from Sowter
Then a tube stage gain+cf
It works perfectly
The coupling working on R gives you also different (little) changing in freq response that helps a lot to kill noise and residual image of conversion
In addition there is a galvanic isolation between stages
Walter
Bass Horneman,
Perhaps I did not describe the current source adequately, or current sink if you look at it that way.
Example:
Use a 300B, -61V bias, 300V plate to filament, and plate current 60mA.
Then rp = 700 Ohms.
We can self bias with a 1k self bias resistor, and bypass the self bias resistor with a cap.
rp will be 700 Ohms.
The 300B is a very poor current source.
The signal drive is between the grid, and the bottom of the self bias resistor (ground).
300B u = 3.85
Then remove the bypass cap.
1000 Ohms x u = 3850 Ohms.
The New plate resistance, rp, is 700 Ohms + 3850 Ohms = 4550 Ohms,
The 300B still not a current source, but it is coming closer to it.
Again, the signal drive is between the grid, and the bottom of the self bias resistor (ground)
Now, start with a Pentode or Beam Power tube, and a self bias resistor and bypass cap, it might have an rp of 20k Ohms.
If you remove the bypass capacitor, it will have many times higher rp than 20k Ohms.
The trick is to refer the bottom of the grid resistor, Rg to ground; and to refer the bottom of the cathode self bias resistor, Rk to ground.
That makes self bias work, and if Rk is Not bypassed, it makes the tube a current source with much more than 20k Ohm plate impedance.
Again, for the pentode or beam power tube that has self bias, the signal drive is between the grid and the bottom end of the self bias resistor, at ground. (whether the self bias resistor is bypassed, or is not bypassed).
Perhaps I did not describe the current source adequately, or current sink if you look at it that way.
Example:
Use a 300B, -61V bias, 300V plate to filament, and plate current 60mA.
Then rp = 700 Ohms.
We can self bias with a 1k self bias resistor, and bypass the self bias resistor with a cap.
rp will be 700 Ohms.
The 300B is a very poor current source.
The signal drive is between the grid, and the bottom of the self bias resistor (ground).
300B u = 3.85
Then remove the bypass cap.
1000 Ohms x u = 3850 Ohms.
The New plate resistance, rp, is 700 Ohms + 3850 Ohms = 4550 Ohms,
The 300B still not a current source, but it is coming closer to it.
Again, the signal drive is between the grid, and the bottom of the self bias resistor (ground)
Now, start with a Pentode or Beam Power tube, and a self bias resistor and bypass cap, it might have an rp of 20k Ohms.
If you remove the bypass capacitor, it will have many times higher rp than 20k Ohms.
The trick is to refer the bottom of the grid resistor, Rg to ground; and to refer the bottom of the cathode self bias resistor, Rk to ground.
That makes self bias work, and if Rk is Not bypassed, it makes the tube a current source with much more than 20k Ohm plate impedance.
Again, for the pentode or beam power tube that has self bias, the signal drive is between the grid and the bottom end of the self bias resistor, at ground. (whether the self bias resistor is bypassed, or is not bypassed).
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