Easiest way to get both 15v and 35v DC from 120vAC? GK 700RB

Frequently asked questions regarding powering your pedal.
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jerrymcdougal
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Post by jerrymcdougal »

Hello,

I plan on rehousing the preamp board from a Gallien-Krueger 700RB-I to be used as a standalone preamp/DI. (I upgraded to a 700RB-II preamp) Schematic and image of board (RB-I board on top) attached.

I need to feed it 35v and 15v. One thing I'm a little confused about is how the schematic lists the J3 (the connector that feeds the board power) voltages. The -35v and +35v just denote positive and negative right, not some sort of other trickery? If so, why the additional ground?

What the easiest way of accomplishing this? Should I just get a 120vAC to 35vdc and 120vAC to 15vdc transformers (or build my own rectifiers) and feed them 120v, or is there an easier solution. I'm also not sure how much current and filter capacitance I'll need to provide. Any ideas?

J3-1: +35v
J3-2: +15v
J3-3: Ground
J3-4: -15v
J3-5: -35v
J3-6: Power LED
J3-7: Protect LED (won't be used)
GK 700RB-I Preamp Board (Top)
GK 700RB-I Preamp Board (Top)
206-0105-F.pdf
GK 700RB-I PreAmp Schematic
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Dirk_Hendrik
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Post by Dirk_Hendrik »

Build a +/-35Vdc power supply using a +/-24VAC transformer. 2*2200 uF should be plenty as filter caps.
Use 2 15V 1W zeners + 3W resistors to make the 15VDC from the 35Vdc. The resistance of these resistors should roughly a little less than what is required by the current consumption of the +/-15VDC circuitry.
Sorry. Plain out of planes.

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Post by jerrymcdougal »

Dirk_Hendrik wrote:Build a +/-35Vdc power supply using a +/-24VAC transformer. 2*2200 uF should be plenty as filter caps.
Use 2 15V 1W zeners + 3W resistors to make the 15VDC from the 35Vdc. The resistance of these resistors should roughly a little less than what is required by the current consumption of the +/-15VDC circuitry.
This is great! Thanks Dirk!

How do I get 35dc out of 24ac? Do I need to use a charge pump or something? Or maybe once rectified the dc is more than the source ac?

Would the zeners be in series or parallel? I'd imagine series right? Or maybe one zener/resistor per +/- "side"? Maybe I'm misunderstanding.

What's the best way of determining the current consumption of a circuit?

Many thanks!

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Post by Dirk_Hendrik »

jerrymcdougal wrote:
Dirk_Hendrik wrote:Build a +/-35Vdc power supply using a +/-24VAC transformer. 2*2200 uF should be plenty as filter caps.
Use 2 15V 1W zeners + 3W resistors to make the 15VDC from the 35Vdc. The resistance of these resistors should roughly a little less than what is required by the current consumption of the +/-15VDC circuitry.
This is great! Thanks Dirk!

How do I get 35dc out of 24ac? Do I need to use a charge pump or something? Or maybe once rectified the dc is more than the source ac?

Would the zeners be in series or parallel? I'd imagine series right? Or maybe one zener/resistor per +/- "side"? Maybe I'm misunderstanding.

What's the best way of determining the current consumption of a circuit?

Many thanks!
A rectified 24VAC will result in approx 35Vdc ;)

As for the Zeners:
Image

googlegoogle
with a transistor it gets even prettier!
Image


And the other way around for the minus supply.

Determining sucks. In your case personally I'd make an educated guess of approx 50mA and fine tune if the zener current is really high. With the above transistor version that issue is out of the way anyway.
Sorry. Plain out of planes.

http://www.dirk-hendrik.com

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Post by jerrymcdougal »

Dirk_Hendrik wrote:
jerrymcdougal wrote:
Dirk_Hendrik wrote:Build a +/-35Vdc power supply using a +/-24VAC transformer. 2*2200 uF should be plenty as filter caps.
Use 2 15V 1W zeners + 3W resistors to make the 15VDC from the 35Vdc. The resistance of these resistors should roughly a little less than what is required by the current consumption of the +/-15VDC circuitry.
This is great! Thanks Dirk!

How do I get 35dc out of 24ac? Do I need to use a charge pump or something? Or maybe once rectified the dc is more than the source ac?

Would the zeners be in series or parallel? I'd imagine series right? Or maybe one zener/resistor per +/- "side"? Maybe I'm misunderstanding.

What's the best way of determining the current consumption of a circuit?

Many thanks!
A rectified 24VAC will result in approx 35Vdc ;)

As for the Zeners:
Image

googlegoogle
with a transistor it gets even prettier!
Image


And the other way around for the minus supply.

Determining sucks. In your case personally I'd make an educated guess of approx 50mA and fine tune if the zener current is really high. With the above transistor version that issue is out of the way anyway.
Wow, thanks Dirk! I'll update when I get started.

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