DON'T USE DC-DC step down/buck switching converter circuits for H+

[doqmemory]

Interesting, good enough for a U67 style mic?

Not if you want to use the negative heater scheme...

 

[RuudNL]

Interesting, good enough for a U67 style mic?

No, the U67 needs a negative filament voltage. (The grid bias is derived from this voltage).
The only way to do it is to use two of these voltage converters fed from separate transformer windings.
The outputs have a common ground and both outputs are positive referred to ground.

The same answer at the same time!

 

[rock soderstrom]

The outputs have a common ground and both outputs are positive referred to ground.

That's a pity...

 

[rock soderstrom]

I’ve used step-down converter for H+ of my V76 mic pre. Not a ready-made module, but designed around some switcher chip (don’t remember the number off the top of my head).
Input and output were filtered (CM and DM chokes on the input and LC at the output). It was also designed to run in CCM, and switching frequency was around 100k.
No traces of noise whatsoever. And very efficient compared to LM317.

Yes, if someone with your skills designs a solution, it will be really good. The question is, beyond efficiency, is it necessary? Is the old solution really significantly worse in terms of sound?
I'm not a professional gear producer, I'm a hobbyist. For me, tried and tested DIY solutions definitely have advantages. It's also about what I can realise myself at home.

There can be different perspectives on this topic, and now you know mine.

 

[rock soderstrom]

I have used a Chinese DC/DC converter (output 6.3 V and 150-280 V) for a tube microphone without any problems.
View attachment 113292

Ruud, how much current can you draw from the B+ and F+ rails? Link?

 

[Aleguitarpro]

Ruud, how much current can you draw from the B+ and F+ rails? Link?

I’m not Ruud but specs are:
1500mA for 6.3V
15mA for B+
https://www.ebay.it/itm/403434596856

 

[rock soderstrom]

Thank you. I will order a module to test it. A small mic pre amp would also be possible. Nice.

 

[Ilya]

Yes, if someone with your skills designs a solution, it will be really good. The question is, beyond efficiency, is it necessary? Is the old solution really significantly worse in terms of sound?
I'm not a professional gear producer, I'm a hobbyist. For me, tried and tested DIY solutions definitely have advantages. It's also about what I can realise myself at home.

There can be different perspectives on this topic, and now you know mine.

Actually, the solution is not that difficult. You can find another variation in Merlin Blencowes tube preamps design book. The components used are all through hole and easy to get. The circuit may even be available at Merlin’s site.

Before resorting to switcher I assessed the regular 317 option. But for V76 I had to provide around 1.2 amps for all tubes. Power dissipation was too high for a linear reg. I could’ve used a pair of regs to distribute heat load, but the amount of dissipated heat doesn’t change. For a single tube it may be tolerable to use 317 reg because the load is much lighter.

 

[kingkorg]

I have used a Chinese DC/DC converter (output 6.3 V and 150-280 V) for a tube microphone without any problems.
View attachment 113292

Indeed, there is a solution for every problem

 

[elskardio]

I have used a Chinese DC/DC converter (output 6.3 V and 150-280 V) for a tube microphone without any problems.
View attachment 113292

Out of curiosity, have you tested this DC/DC converter with a simple 9-12v wall wart?
It could be a super compact solution to power a tube mic.
thanks

 

[Delta Sigma]

Out of curiosity, have you tested this DC/DC converter with a simple 9-12v wall wart?
It could be a super compact solution to power a tube mic.
thanks

I wouldn't try this unless you have another source for earth ground.

 

[Newmarket]

Wrt LM317 - while I like them, there are now LDO regulators that are quieter.