Sharing a power supply between multiple components

SoaDMTGguy

Member
Paid Member
2021-07-31 3:41 am
Sacramento, CA
I am interested in building a preamp by combining a line stage and phono stage in one box. Specifically, I'm looking at the Aikido boards from GlassWare Audio Design:

Aikido Octal Stereo PCB
Aikido PH-2 Phono Stage

The descriptions for these two boards both suggest their PS-21 power supply. "Great" I thought, "I can use the same power supply for both boards".

I assume it can't be as simple as branching the various +V rails to the two amplifier boards. I imagine I would have to increase supply capacity (transformer? rectifier capacitors? both?). I also assume there are grounding concerns to address. Are there other issues with such an idea?
 

rayma

Member
2011-04-29 8:37 pm
Generally with a shared supply, you would want some decoupling between the line stage and the phono stage,
to lower phono hum and noise, and to reduce the possibility of LF instability. Provision for decoupling
may be on one or both of the boards.
 

kodabmx

Member
Paid Member
2011-10-31 1:00 am
Toronto
It will only supply 50mA of HV current, and last I checked those boards use different voltages (not that you couldn't make the line stage run at the higher voltage he uses on the phono stage)... That isn't enough for both boards. There also won't be enough heater current unless you run 12V tubes.
 

SoaDMTGguy

Member
Paid Member
2021-07-31 3:41 am
Sacramento, CA
It will only supply 50mA of HV current, and last I checked those boards use different voltages (not that you couldn't make the line stage run at the higher voltage he uses on the phono stage)... That isn't enough for both boards. There also won't be enough heater current unless you run 12V tubes.

Ohh, so even though each board can use the same power supply, they have to be configured differently to provide different voltages.

Ok, stupid question time: Could I modify the power supply to produce more current? That's assuming the voltage wasn't an issue.
 

SoaDMTGguy

Member
Paid Member
2021-07-31 3:41 am
Sacramento, CA
Yes, but complete dual mono is better.
You answer an extremely high number of my questions… let me know if you’re ever in Sacramento, I think I owe you a beer or 12.

Is it silly to make a single preamp if my linestage and phonostage don’t share a power supply or transformers? I guess there are still benefits of a single case and fewer interconnects.
 

rayma

Member
2011-04-29 8:37 pm
Not likely in the near future, but thanks.

It's never silly to build audio component(s). If you mainly listen to phono, I'd build a standalone phono stage
with its own power supply. Maybe even use a SMPS medical supply with extra HF filtering like has been done
in diyAudio for near zero hum. I personally don't care for line stages, and just go with a volume control.

However, the phono stage could share a case with the line stage if done carefully, and if you use other sources routinely. Unplugging cables to swap components is no fun either. One switch contact in the selector switch is a fair trade off,
for one less audio cable and two pairs of RCA sockets, but use a really high quality selector switch.

But consider whether you really need a line stage with gain at all. Maybe you can use a unity gain buffer,
or even just a pot or switched resistor volume control by itself.
 
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SoaDMTGguy

Member
Paid Member
2021-07-31 3:41 am
Sacramento, CA
use a really high quality selector switch.

I was thinking of using something like this for my input switcher: https://www.mouser.com/ProductDetail/Grayhill/71B30-01-4-03N

I'm still unclear if I should use a shorting switch or not, and whether I should one deck/many poles or one pole/many decks.

I'll be primarily switching between phono and DAC inputs. My phono cartridge is mid-output and I think a line stage with gain will be necessary unless I use a step-up transformer or find a way to get a lot of gain out of my phono stage. Also, I have all the parts for a line stage amp sitting in a box next to me on the desk waiting to be assembled :p
 

rayma

Member
2011-04-29 8:37 pm
I'd keep the channel grounds separate throughout the circuit, and only connect them together
at one point chosen for the lowest hum, usually in the power supply.

I've never used two sources at once, but some used to record one source while listening to another.
But if you leave the DAC playing and switch to phono, it could bleed through.