In article , Eeyore
wrote:


Nick Gorham wrote:

Ian Iveson wrote:

and the voltage reg will try and regulate that away, with a current
reg, the signal is common mode, so not affected.

UH ?

Can only speculate at this point as I have never tried using these circuits
for heaters in audio amps. However...

With 'direct' heating the heater psu is - I presume - connected to the
same physical place as the cathode signal. Having a 'constant current' PSU
means the PSU looks like a high impedance connection, so will be less
likely to have a loading effect on signal drive to the cathode if the PSU
common mode isolation is poor. i.e. the problem is that the cathode signal
has to drive any loading it sees due to the PSU, so a high impedance might
be preferred.

Slainte,

Jim

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