Samuel Groner said:
But even your test bench can't measure 180 dB... 8)
JR
transformer for I/V conversion in DAC?
- Thread starter dirkwright
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But even your test bench can't measure 180 dB... 8)
JR
Samuel Groner
Well-known member
I have little hope that -180 dB will be necessary. 
Samuel
Samuel
Jonte Knif
Well-known member
Last winter I suddenly felt the need to find an use for a pair of extra Sowter 1:7 mic input trannies and decided to mod my CD player, an old ES-series Sony, just for fun. I don't remember the chips in it, but the DA-output surely was current output and symmetrical. I tried a couple of different I/V-resistor values, and surely it is easy to see that too much voltage will cause trouble. Anyhow I was able to get pretty clean 1V peak output with only 1:7 trannie, so staying under 100mV per phase was enough for that particular chip. Some 3rd harmonic can be seen. I only have simple j-fet buffers after the trannies. Noise is surely low enough.
I wish I had another unmodded player to compare the modded one to. But when it comes to the use of that particular player, enjoying music at home, the sound really seems to be good enough for me and the mod job was fun. I do tend to believe that the set of dubious capacitors and cheap OP amps didn't *improve* the sound from the chip, but I should have another player to do quick comparisons to really know. How ever, I did expect the sound to be a bit darker and less detailed in the treble with the transformer conversion, but did not hear that no matter how hard I tried. Quite the contrary. There is plenty of detail present. That particular trannie with those resistor values made a decent low pass filter, but I did add some passive filtering before the trannie, (I can not remember what, perhaps just shunt caps) and any conversion noise should not get through the system now. It certainly did without the extra filtering, so I would not blindly trust that any trannie is enough filtering.
Just my 2 cents.
-Jonte
I wish I had another unmodded player to compare the modded one to. But when it comes to the use of that particular player, enjoying music at home, the sound really seems to be good enough for me and the mod job was fun. I do tend to believe that the set of dubious capacitors and cheap OP amps didn't *improve* the sound from the chip, but I should have another player to do quick comparisons to really know. How ever, I did expect the sound to be a bit darker and less detailed in the treble with the transformer conversion, but did not hear that no matter how hard I tried. Quite the contrary. There is plenty of detail present. That particular trannie with those resistor values made a decent low pass filter, but I did add some passive filtering before the trannie, (I can not remember what, perhaps just shunt caps) and any conversion noise should not get through the system now. It certainly did without the extra filtering, so I would not blindly trust that any trannie is enough filtering.
Just my 2 cents.
-Jonte
dirkwright
Well-known member
- Joined
- Mar 24, 2012
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- 83
I apologize for being a hot head in my previous posts. I did some work on this for a while and have now shelved it, mostly because I've been busy with other projects.
I did try a zero field transformer input with a low impedance transformer (I can't remember which one I used but it was not a mic transformer with high step up ratio but instead a 1:1 output transformer I think) but didn't get good results in real life. I only tested the zero field I/V converter, not the entire chain including the DAC. In theory, the zero field transformer input could present a very low impedance to the DAC. I got the idea from Lundahl. I modified their version of the circuit to provide some damping the subsonic frequencies at that cost of slightly higher input impedance. The only advantages for the transformer over non-transformer circuit in this case would be DC isolation and RF attenuation. The disadvantages would be more distortion (but not much) and higher cost. Lundahl makes an output transformer that has extremely low winding resistance, so it was part of my plan to use it but the results with the real life zero field circuit were disappointing.
I also designed and built a low impedance active I/V circuit that performs well, but haven't got around to making anything usable and real. Thanks for all the inputs and opinions. Transformers have their place in my opinion, but maybe not here.
I did try a zero field transformer input with a low impedance transformer (I can't remember which one I used but it was not a mic transformer with high step up ratio but instead a 1:1 output transformer I think) but didn't get good results in real life. I only tested the zero field I/V converter, not the entire chain including the DAC. In theory, the zero field transformer input could present a very low impedance to the DAC. I got the idea from Lundahl. I modified their version of the circuit to provide some damping the subsonic frequencies at that cost of slightly higher input impedance. The only advantages for the transformer over non-transformer circuit in this case would be DC isolation and RF attenuation. The disadvantages would be more distortion (but not much) and higher cost. Lundahl makes an output transformer that has extremely low winding resistance, so it was part of my plan to use it but the results with the real life zero field circuit were disappointing.
I also designed and built a low impedance active I/V circuit that performs well, but haven't got around to making anything usable and real. Thanks for all the inputs and opinions. Transformers have their place in my opinion, but maybe not here.
