Cheap tube mic preamp power supply

[13engrsapper]

FWIW we never send out client gear with house-built or non-certified power supplies. Yes, we build super quiet ones for ourselves, but the liability is just not worth it with paying clients as @emrr and @JohnRoberts have stated. Most of the potential liability is in that power supply.

I will have to look up the model switching supply (for tubes) we tried here on an old Raytheon preamp. The noise level was so high the preamp barely could cover it at full tilt, also I do not think it actually put out its rated current on either side. I knew it would need some filtering, but man it was really bad. Some nice motorboating too, I had to put on a life jacket just to listen, it was quickly removed. I will find the brand/model so we can all avoid it. It is possible we got a bad one, that happens. This was not a situation where I grabbed 100 of them thankfully.

-Tony

P.S. I will be up your way again soon @emrr, Kernersville area around the 1st of May, you have been warned, lol. Hoping we have time to meet up quick this time. Again, you have been warned.

 

[ruffrecords]

To power a few preamp tubes for a single ended mic pre, why can't I build a simple power supply like the ones used in these circuits? (but modified to use a grounded 3 prong power cord and no death cap of course)

No reason at all. Many of us do it all the time. Hammond makes a wide range of mains transformers for just this kind of thing.

Cheers

Ian

 

[Brian Roth]

No reason at all. Many of us do it all the time. Hammond makes a wide range of mains transformers for just this kind of thing.

Cheers

Ian

Antek is another source ....

Bri

 

[k brown]

Best trick I found for lo-cost tube curcuit supplies is using two generic, inexpensive 110v>12v transformers back-to-back; tapping the heater supply off where the two 12v secondaries connect.

The rest of the parts in a linear supply are quite inexpensive.

 

[GussyLoveridge]

Can someone please suggest a simple quiet safe preamp power supply circuit I could build instead? Or one I could buy?

I built a bench top supply from a PCB that @ruffrecords sold to me. It supplies 48VDC regulated for phantom power, 12 VDC regulated for heaters and 360 VDC unloaded for HT/Anode.

The most significant expenses were the transformer and the case. I'm sure both could be done cheaper.

https://groupdiy.com/threads/valve-mic-preamp-design-incoherent-rambling.77747/page-11

See post #218.

I am very happy with the results and the build documentation is thorough.

 

[rock soderstrom]

I've ordered this slightly larger module, I'm curious to see what it can do.

The SMPS module arrived today and I gave it a quick test run.



I loaded the heater voltage rail with 2.1 Ohm, the voltage was (stably regulated) 6.39V, a current of 3A flowed.

B+ is unregulated and increased from 278V to 289V(!) during the test period. Approx. 25mA flowed via an 11200 Ohm load.

The test period was approx. 15 minutes, the SMPS module became slightly warm, at higher loads I would mount it upright with the two cooled semiconductors at the bottom on a metal plate/housing. Thermally this load was no problem for the module.

For my desk it was a bigger load, the two resistor pairs got very hot as expected. The burn marks are from the two 1 Ohm resistors, I moved the test setup twice as you can see.

 

[rock soderstrom]

The switching frequency is quite low, otherwise it tests well.

I'm going to install the SMPS module in a Gibson Skylark clone tomorrow, I'm curious to see how it performs.

 

[13engrsapper]

Antek is another source ....

Bri

I use and stock several of the ANTEK toroidal transformer types, never had an issue, highly recommended. There are probably 20-30 of them here at any time.