This is important because it could be the first good way to give a tube output to the many 5V V-out DAC's.
Does this give CMRR ?
Does this give CMRR ?
tubes are used with ccs bellow and floating grid decades ago ;
that's completely normal and common way for using either tubes , jfets or bjts for floating differential output ;
Maybe but its the first I've seen on the web especially DC coupled to the DAC chip with its 2.5V offset. It is important if it has good CMRR.
BTW nearly all the commercial DAC's with tube or discrete buffers are using one rail of the V-out DAC outputs. So its not that well utilized.
BTW nearly all the commercial DAC's with tube or discrete buffers are using one rail of the V-out DAC outputs. So its not that well utilized.
LTP stage have good CMRR by virtue , especially if having CCS in tail .
that's their flaw , if using DAC's differential output is possible .
So Poynton (Andy) has built something close years ago, but does not remember his schematic. He used a low powersupply voltage...and an E88CC tube. Can we reverse engineer his circuit and come up with something someone can simmulate or prototype? Seems like there is quite a bit of interest for people with differential DAC outputs.
DAve
DAve
Dave,
Poyntons circuit is as I understoodfrom the CD63-thread somewhat simpler than the one I presented in post #1. To use an ECC88(mu=33) together with a voltage DAC that has ca 1V out could be problem. To make it work you have to add local feedback as seen there. Personally I would also add a CF to lower Zout so you will need 3 ECC88 in total. Also Zen Mod has shown his solution with local feedback. I can adjust my circuit to suit your needs. Need to know your DAC and the output level you expect from the buffer.
Poyntons circuit is as I understoodfrom the CD63-thread somewhat simpler than the one I presented in post #1. To use an ECC88(mu=33) together with a voltage DAC that has ca 1V out could be problem. To make it work you have to add local feedback as seen there. Personally I would also add a CF to lower Zout so you will need 3 ECC88 in total. Also Zen Mod has shown his solution with local feedback. I can adjust my circuit to suit your needs. Need to know your DAC and the output level you expect from the buffer.
Differential White Cathode Follower
Lookie how it kills both CMRR (450Hz) and PSRR(120Hz)!
Lookie how it kills both CMRR (450Hz) and PSRR(120Hz)!
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I have a EZ DAC kit from Evan (ShinyMetal) and I was planning to build this when time permits. He uses a PCM1794 or 1798. This chip uses differential output. I would like to have a tube output and a regular output. I would prefer to grab the signal prior to the differential amplifier. However, this seems to be the issue. I'm not designer, and since I don't have it built yet, I can't prototype the tube output. Any thoughts would help.
Thanks,
DAve
Well this would be a good match, you could reduce the EZDAC's I/V resistor in porportion to the extra gain you get in this new tube stage, you could probably pull the input right off the top if the I/V resistor.
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