Do all valve amps hum?

Hi,

There is a difference between dipping a transformer into laquer or putting them and hot laquer/wax into a pressure vessel and evaccuating the air from it and leaving the transformer there for 48 Hours before removing it. Most transformers are dipped, few are vaccuum impregnated.

Ciao T

 

Hi,

In some cases, yes. I routinely use them in all of my own designs, few others do.

You can make a nice external setup for a power conditioner incorporating a lowpass based around ferrite beads on conductors and a DC blocker and you get around 40% of the mains conditioning I'm designing into our upcoming gear.

Ciao T

 

Valve amp hum is also related to the design of the circuit and quality of wiring/circuit layout. Most use AC heaters so you have 50Hz all over the place inside. Twisting the heater supply wires helps (good manufacturers do this). Also, some amps have 'hum balance resistors' on the heater supply. These add a centre ground point and are adjusted to effectively cancel hum.

Some amps use regulated DC heater supplies and have very little hum. There is a debate about sound quality differences between AC and DC heaters.

Also, amplifier grounding is an art in itself.

Power conditioners and DC blockers cannot remove audible hum from the amp circuit, but evidently can improve mechanical transformer hum (if this bugs you and justifies the money spent).

Just my 2p worth...

 

While making triode amplifiers for my own use, I have recently been experimenting with the various means of supplying the heaters. AC heating sounds very fluid and natural but even with a hum balancing pot does not allow sufficient hum reduction in most instances to use with the very sensitive speakers I have. Conventional dc heating (again with a pot) does allow the hum to be removed completely but with a very strange and unpleasant effect on the sound. I've tried a few different configurations with and without chokes & regulators but this effect persists. The ac heating even with hum had been preferable. In the last few months I have also had the opportunity to try the Tentlabs boards which give a quiet supply without the downside of putting a big, nasty sounding electrolytic in the signal path. These work very well, keeping the qualities of ac heating without the noise. Has anyone else tried these? Alternatively, are there any other methods I should look at?