The one shown at post 6315 powered in 2.5 v , routed on 4 layers , I tried it on 2 layers it works but it is very noisy
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Thanks Zoran.
I think I have finally figured out what I want to do:
The tube stage is Bartola 801A that has been up and running (wonderfully!) as a preamp since last summer.
1) Parallel TDA1541A; motivated by findings of audio enthusiasts from early 2000's, e.g. Andrea Galavotti or AquaBlue TDA1541A
Balancing would not give the DC cancellation, my Jensen SUT unfortunately is not bifilar wound so balancing would just require extra circuitry in the digital domain with own problems and uncertain reward. I already have the PSU ready for 2 chips so why not try paralleling.
2) Passive I/V with John's DC cancellation scheme from post #7981 adopted to the situation, coupled to Jensen 347. My first guess is about 18R, giving
72mVmax before the transformer and 0,576Vmax at the grid. Although SUT should stand it (specs say -10dBu=0.35Vmax@20Hz), this may be too much gain but the parallel connection allows to experiment with very low I/V values, below 10R, which give low harmonics: MVLabs IV selection I can also try connecting SUT secondaries in parallel to make it 1:4.
3) I need raw voltage for the +15V and this is my headache now as I don't seem to have a free line anywhere and -15V line is wher the offset current sinks to so cannot use it, right?
4) Another, more crazy idea is to follow John from #7981 and make use of the +200V that I already have at the output tube:
We discussed it also here #7574. I guess what John ment with CCS being grainy was using just CCS to output pin, while here I'd have both CCS and 50k resistor. For some unknown to me reason in the previous discussion in 2020 I opposed connecting the DAC AGND to the tube ground, which killed the HV bias idea, but I can't find any good reason why I did so. Both DAC and 801A stage will share the same housing, all the connections are short, internal runs so connecting the grounds shall not be a problem.
Comments welcome
I think I have finally figured out what I want to do:
The tube stage is Bartola 801A that has been up and running (wonderfully!) as a preamp since last summer.
1) Parallel TDA1541A; motivated by findings of audio enthusiasts from early 2000's, e.g. Andrea Galavotti or AquaBlue TDA1541A
Balancing would not give the DC cancellation, my Jensen SUT unfortunately is not bifilar wound so balancing would just require extra circuitry in the digital domain with own problems and uncertain reward. I already have the PSU ready for 2 chips so why not try paralleling.
2) Passive I/V with John's DC cancellation scheme from post #7981 adopted to the situation, coupled to Jensen 347. My first guess is about 18R, giving
72mVmax before the transformer and 0,576Vmax at the grid. Although SUT should stand it (specs say -10dBu=0.35Vmax@20Hz), this may be too much gain but the parallel connection allows to experiment with very low I/V values, below 10R, which give low harmonics: MVLabs IV selection I can also try connecting SUT secondaries in parallel to make it 1:4.
3) I need raw voltage for the +15V and this is my headache now as I don't seem to have a free line anywhere and -15V line is wher the offset current sinks to so cannot use it, right?
4) Another, more crazy idea is to follow John from #7981 and make use of the +200V that I already have at the output tube:
We discussed it also here #7574. I guess what John ment with CCS being grainy was using just CCS to output pin, while here I'd have both CCS and 50k resistor. For some unknown to me reason in the previous discussion in 2020 I opposed connecting the DAC AGND to the tube ground, which killed the HV bias idea, but I can't find any good reason why I did so. Both DAC and 801A stage will share the same housing, all the connections are short, internal runs so connecting the grounds shall not be a problem.
Comments welcome