Powering 2 G7 mics with one PSU, is it possible??

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Chad

Well-known member
Joined
Jan 29, 2009
Messages
57
Location
Perth, Australia
Im building 2 of Gyraf's G7 mics at the moment and I was thinking of running both of them from the same power stage? Im guessing it's possible but I might have to beef up some of the components.
Or is it just not worth the hassle...?
Thoughts anyone?
 
Yes, it has been done.

Of course you'll be drawing twice the current, so you'll need to adjust resistors accordingly to get the correct B+ voltage drop, and beef up the filter caps. Make sure your transformer is up to the task too.

As some point you'll have to split the supplies, and I'd suggest adding extra filtering caps here for each mic.

(You may be better off with a slightly higher initial AC voltage on the high voltage side, so that you can get efficient filtering without massive caps.)
 
Looking at this...

http://gyraf.dk/gy_pd/g7/gic_s.gif

On the 160V side, simply double the first 470 uF cap (or use two - they often come in packs of 5 so you could even use three here). Then split the supply - so run TWO 10k resistors to TWO separate 470uF caps. Then you can make your voltage dividers for your pattern controls etc. So really you just have two of everything from the 10K onwards, one for each mic.
 
If you're not going to use both mics simultaneously every time then you'll need to have two filament regulators to make sure that you're getting the right filament voltage with the changing load of one mic versus two. There's not much current on the B+ so that shouldn't change much. I don't think you have to worry about that one. I built a dual supply for myself and it has one B+ supply and two filament supplies. I used the G7 power supply boards; both populated with the filament parts and one populated with the B+ parts. Don't forget to put some filtering after your pattern selecting switch so you don't get pops when you change the pattern. A lowpass filter with 1Mohm/1uF should do the trick.
 
http://www.electronics-lab.com/articles/LM317/
http://www.reuk.co.uk/LM317-Voltage-Calculator.htm

If it is a regulated supply, then the voltage should be set by R1 and R2, and not by the filament load. So long as you have a suitable supply before the regulator, it should give you a similar voltage whether you have one mic or two. Did I miss something?

(FWIW, I normally use a 7806, or 7805 and a couple of diodes for tube mic supplies.)
 
zebra50 said:
http://www.electronics-lab.com/articles/LM317/
http://www.reuk.co.uk/LM317-Voltage-Calculator.htm

If it is a regulated supply, then the voltage should be set by R1 and R2, and not by the filament load. So long as you have a suitable supply before the regulator, it should give you a similar voltage whether you have one mic or two. Did I miss something?

(FWIW, I normally use a 7806, or 7805 and a couple of diodes for tube mic supplies.)

No, you're right, you didn't miss anything. I was speaking from my memory of how I built my supply, but I wasn't thinking through it and I didn't explain correctly. The reason I had two filament regulators was because I put some extra RC filtering after the regulator. That's why my voltages were different with one mic versus two mics with only one regulator. Therefore, since I wanted to use that extra filtering, I used two regulators. Sorry to confuse things. Thanks for pointing that out.
 
Awesome!  :D I will try that once the boards get here.
I assume that I can run the second 6.3v Heater and Heater ground without any mods?
 
yosh said:
. The reason I had two filament regulators was because I put some extra RC filtering after the regulator...

Yeah, that would change things - of course it only regulates at the regulator! The extra RC filtering is not a bad thing!

Chad said:
I assume that I can run the second 6.3v Heater and Heater ground without any mods?
:)

Should be able to. Run them in parallel. It would be a good plan to increase the 1000uF caps before the regulator to 2200, or whatever you can fit there! You can also add a 10uF  cap across the H+ for each mic if you like, at the 7 pin XLR to decouple the supplies.
 

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