dmp
Well-known member
I compared heater methods for a tube preamp to see how different options compared for noise performance ( this V76 I built a few years ago )
I had built this with AC heaters with 100 ohm artificial center tap to audio ground. Tightly twisted heater wiring.
The noise spectrum of the preamp was flat without spikes at 60/120 Hz (white noise spectrum) when measured with RMAA
I compared:
- switching from the 100 ohm resistors to audio ground to a humdinger pot
- elevating the artificial center tap to ~50 volts from a voltage divider off the B+ rail
- Switching to DC heaters with the DC ground connected directly to the power audio ground
I didn't see an improvement or any difference in the noise performance with these different setups.
My takeaway is when building a tube preamp with good heater wiring and ground layout, simple AC heaters are just as good as the more complicated options.
But I wonder in what situations would these alternatives show an improvement? Poor AC heater wiring? Or is there a characteristic of certain tubes that allow heater hum to bleed into the audio?
I had built this with AC heaters with 100 ohm artificial center tap to audio ground. Tightly twisted heater wiring.
The noise spectrum of the preamp was flat without spikes at 60/120 Hz (white noise spectrum) when measured with RMAA
I compared:
- switching from the 100 ohm resistors to audio ground to a humdinger pot
- elevating the artificial center tap to ~50 volts from a voltage divider off the B+ rail
- Switching to DC heaters with the DC ground connected directly to the power audio ground
I didn't see an improvement or any difference in the noise performance with these different setups.
My takeaway is when building a tube preamp with good heater wiring and ground layout, simple AC heaters are just as good as the more complicated options.
But I wonder in what situations would these alternatives show an improvement? Poor AC heater wiring? Or is there a characteristic of certain tubes that allow heater hum to bleed into the audio?