Specific transformer based I/V

matejS · 7th October 2007, 09:18 PM

Hi!

First the facts:
- AD1865 DAC (Iout => likes "zero" ohm load), 1mA max out
- balanced 22k input preamplifier (actually it has adjustable input impedance)

I was thinking of using 1:6.4+6.4 transformer as I/V conversion (Sowter 9762).
It would be connected directly to Iout (no resistor used).

Using calculation 22k / 6.4^2 * +/-1mA = +/-561mV p-p on preamp. Using 2 Iout per channel I will get +/-1.12mV p-p = 0.4mV RMS

Am I correct?
It's a little low, but I this will do, I guess this is the one of the best possible I/V conversions.
I did not have a change to compare it with other I/V solutions (Sowters are not cheap and I did not buy them yet) - does anybody have experience with this method?

Thanks,
Matej

oshifis · 8th October 2007, 05:50 AM

Hi Matej,

Your calculation is wrong. 22 k will be transformed to 537 ohms. That is most probably too much for the DAC. Try loading with lower value. In this case you will need higher gain in the preamplifier stage.

You can also consider a similar circuit:

Laszlo's Valve Output Stage with Lundahl transformer

Laszlo

7th October 2007, 09:18 PM	#1
matejS diyAudio Member Join Date: May 2007	Specific transformer based I/V Hi! First the facts: - AD1865 DAC (Iout => likes "zero" ohm load), 1mA max out - balanced 22k input preamplifier (actually it has adjustable input impedance) I was thinking of using 1:6.4+6.4 transformer as I/V conversion (Sowter 9762). It would be connected directly to Iout (no resistor used). Using calculation 22k / 6.4^2 * +/-1mA = +/-561mV p-p on preamp. Using 2 Iout per channel I will get +/-1.12mV p-p = 0.4mV RMS Am I correct? It's a little low, but I this will do, I guess this is the one of the best possible I/V conversions. I did not have a change to compare it with other I/V solutions (Sowters are not cheap and I did not buy them yet) - does anybody have experience with this method? Thanks, Matej

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8th October 2007, 05:50 AM	#2
oshifis diyAudio Member Join Date: Mar 2004 Location: Budapest, Hungary	Hi Matej, Your calculation is wrong. 22 k will be transformed to 537 ohms. That is most probably too much for the DAC. Try loading with lower value. In this case you will need higher gain in the preamplifier stage. You can also consider a similar circuit: Laszlo's Valve Output Stage with Lundahl transformer Laszlo

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