Author Topic: How to Convert single supply voltage circuit to Dual +/- voltage supply??  (Read 658 times)

bluelagoon

Hello Fellow Board Members,
                                             I am in a bit of a quandry, trying to properly figure just how to correctly convert the Boss FA-1 circuit from single 9 Volt supply to a Dual rail +/- 9 volyt supply with a centre 0v ground. I realize I shall need an appropriate charge pump to get the dual supply, but really need help to identify just which of the original grounds become -9volt and which stay as 0 volt ground, I understand that the op amp half supply voltage goes to 0 volt just mainly curious on the section circled in orange trying to get my head around, particularly where the 3M3 resistor is supposed to end up either 0V ground or -9volt? also the 1M pull down resistor does it go to --9volt or ground? I see that also the voltage dividing network in there can probably be scrapped just need some sound advice on the matter. the rest of the circuit seems a bit more straight forward, but please chime in with every detail needs correcting for dual +/-v supply.

Please see attached FA-1 Schematic.

Thanks for any help you can offer.

Best Regards,

TTay


iainpunk

Re: How to Convert single supply voltage circuit to Dual +/- voltage supply??
« Reply #1 on: November 19, 2020, 08:25:01 AM »
all the Vr points go to the new ground, that includes the 3M3 resistor.
RPD 1M still goes to ground,
the whole Vr circuit encircled in orange can be omitted,
the rest can stay the same.

cheers, Iain
half man - half snail - 6 feet to scale - Snail man's - not frail - He's been - to jail - snail man is fuccing real
『snailpilled』

antonis

Re: How to Convert single supply voltage circuit to Dual +/- voltage supply??
« Reply #2 on: November 19, 2020, 08:39:46 AM »
all the Vr points go to the new ground, that includes the 3M3 resistor.

Dramatically altering Q1 Gate bias.. :icon_wink:
(as it is, Gate is biased at 3V above GND..)
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

iainpunk

Re: How to Convert single supply voltage circuit to Dual +/- voltage supply??
« Reply #3 on: November 19, 2020, 09:19:26 AM »
all the Vr points go to the new ground, that includes the 3M3 resistor.

Dramatically altering Q1 Gate bias.. :icon_wink:
(as it is, Gate is biased at 3V above GND..)
bruh...
you have 18V of headroom for the input signal, a few volts of mis-bias won't make a damn difference here.

cheers, Iain
half man - half snail - 6 feet to scale - Snail man's - not frail - He's been - to jail - snail man is fuccing real
『snailpilled』

antonis

Re: How to Convert single supply voltage circuit to Dual +/- voltage supply??
« Reply #4 on: November 19, 2020, 09:24:15 AM »
you have 18V of headroom for the input signal..

No, unless you connect R3 to -9V (instead of GND)..
(I didn't see any relevant proposal..)  :icon_wink:
« Last Edit: November 19, 2020, 09:44:07 AM by antonis »
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..


iainpunk

Re: How to Convert single supply voltage circuit to Dual +/- voltage supply??
« Reply #6 on: November 19, 2020, 11:24:19 AM »
you have 18V of headroom for the input signal..

No, unless you connect R3 to -9V (instead of GND)..
(I didn't see any relevant proposal..)  :icon_wink:
shouldn't you bias the base to Vpower/2, which is 0V in the case of a bipolar supply?!
the -9V can be quite noisy with a charge pump, biasing to this point can introduce said noise to the signal.
and we probably only need 3V pkpk headroom anyways since its probably used for instrument level.

cheers, Iain
« Last Edit: November 19, 2020, 03:01:34 PM by iainpunk »
half man - half snail - 6 feet to scale - Snail man's - not frail - He's been - to jail - snail man is fuccing real
『snailpilled』

antonis

Re: How to Convert single supply voltage circuit to Dual +/- voltage supply??
« Reply #7 on: November 19, 2020, 02:16:24 PM »
shouldn't you bias the gate to Vpower/2, which is 0V in the case of a bipolar supply?!

Iain, plz..  :icon_smile:

There shouldn't be any bipolar supply for Q1  with its Source resistor left connected to GND..
As it is, VGS is -1.5V, considering Source at 4.5V..
With R3 to GND & for same Drain current, Source has to lie at 1.5V, leaving only 1.5V for negative undistorted signal headroom..
(actually, much less than 1.5V due to R3 and and succeeding impedance voltage dividing effect..)

« Last Edit: November 19, 2020, 02:51:14 PM by antonis »
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

iainpunk

Re: How to Convert single supply voltage circuit to Dual +/- voltage supply??
« Reply #8 on: November 19, 2020, 02:59:35 PM »
shouldn't you bias the gate to Vpower/2, which is 0V in the case of a bipolar supply?!

Iain, plz..  :icon_smile:

There shouldn't be any bipolar supply for Q1  with its Source resistor left connected to GND..
As it is, VGS is -1.5V, considering Source at 4.5V..
With R3 to GND & for same Drain current, Source has to lie at 1.5V, leaving only 1.5V for negative undistorted signal headroom..
(actually, much less than 1.5V due to R3 and and succeeding impedance voltage dividing effect..)
so i was thinking that it was a BJT, not a JFET, im an idiot for not noticing that earlier. i noticed it when i read the words ''Source resistor''

sorry and cheers, Iain
half man - half snail - 6 feet to scale - Snail man's - not frail - He's been - to jail - snail man is fuccing real
『snailpilled』

antonis

Re: How to Convert single supply voltage circuit to Dual +/- voltage supply??
« Reply #9 on: November 19, 2020, 03:04:48 PM »
 :icon_lol: :icon_lol: :icon_lol:

Cheers but forgiven..!!
(at least, not until I finish your on the house beer..) :icon_wink:
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

antonis

Re: How to Convert single supply voltage circuit to Dual +/- voltage supply??
« Reply #10 on: November 20, 2020, 06:22:19 AM »
In case of OP is confused due to the above argument ..


edited, thanks to Stephen.. :icon_wink:
« Last Edit: November 20, 2020, 03:17:02 PM by antonis »
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..