Hello,
I made a DAC with a 6N8S tube output and I don't know why there is such a drop at lower frequencies? The power supply is 114-0-114 VAC through the EZ81 tube and the filter is CLC: EZ81-C30uF-L16H/480ohm-C100uF. Ra=7k5, Ua=120V, Ug=-4.6V, Rk=1K, Ia=4.6mA.
The DAC is ES9018 (voltage output 1Vrms=3Vpp) and input to the grid is via a 4uF capacitor. Without grid stopper. Output capacitor is 1uF, connected to 100K pot. I am attaching the freq. characteristic.
Does anyone have an idea why there is such a drop on low freq. (100Hz=-1dB, 50Hz=-3dB, 20Hz=-7dB)?
Thank you.
I made a DAC with a 6N8S tube output and I don't know why there is such a drop at lower frequencies? The power supply is 114-0-114 VAC through the EZ81 tube and the filter is CLC: EZ81-C30uF-L16H/480ohm-C100uF. Ra=7k5, Ua=120V, Ug=-4.6V, Rk=1K, Ia=4.6mA.
The DAC is ES9018 (voltage output 1Vrms=3Vpp) and input to the grid is via a 4uF capacitor. Without grid stopper. Output capacitor is 1uF, connected to 100K pot. I am attaching the freq. characteristic.
Does anyone have an idea why there is such a drop on low freq. (100Hz=-1dB, 50Hz=-3dB, 20Hz=-7dB)?
Thank you.
Attached.
I measure with Behringer UCA202 USB DAC/ADC and REW. When I measure other amps results are flat line (Onix 31L, Sansui G5500) or near flat line in my DIY SET KT88 + 6n6p .
I measure with Behringer UCA202 USB DAC/ADC and REW. When I measure other amps results are flat line (Onix 31L, Sansui G5500) or near flat line in my DIY SET KT88 + 6n6p .
I also try with silicon rectifier using 2x 114Vac to get B+ 300Vdc and CCS load (IXYS10M45S). It sound better with CCS but measurment returns same low-freq. drop.
Im not sure whether the bottom 4uf is in place, but if it is, 4uf and 1K makes an rc high frequency filter with 40hz pole.
Sorry for sneaking in, I am planning to build a similar circuit these days.. well done btw.
Would this mean that for best result (same corner frequency) the caps on the plus input should be 360x smaller than minus input cap?
Would this mean that for best result (same corner frequency) the caps on the plus input should be 360x smaller than minus input cap?
I get that thank you, I was planning to use 10uF caps on plus and minus input.. will try to go to something like 0,1-0,47uF on the grid and 20uF on the cathode later on..
Is your final schematic/voltages something like this? I'd like to compare waveforms and distortion results vs simulation.
