MOTM

hello all,

with a second router now in my possession, my thoughts have turned to
voltage sources and just making one instead of using an adsr all the time.
so here's the plan - a quad voltage source, four pots, four jacks, very
rough & ready

this is probably (yeah right) a silly question, but can i just hook a pot
directly up to the power supply and stick a suitable 1/4W resistor either
side to keep the max levels to within -10v to +10v
or is there something i've forgotten..?
or should i keep levels to within -5 to +5v..?

i think my brains have turned to mush

cheers
paul b

I think (oh dear, not again) that you want to stick to +/-5V... or maybe
0-10V.  I don't think you want a full 20V swing.  The VCO outputs +/-5V, and
the EG generates 0-+5V and 0 to -5V.

I think you might want to use an op-amp (or rather, a quad op-amp) to
isolate yourself from the power supply.  Call it a hunch.

While you're at it, can you hickory smoke your voltage sauce?  It gives it a
more vintage flavor... <grin>

--PBr

> -----Original Message-----
> From:	sikorsky [SMTP:vulture.squadron@...]
> Sent:	Friday, January 05, 2001 11:43 AM
> To:	motm@egroups.com
> Subject:	[motm] voltage sauce !
> 
> with a second router now in my possession, my thoughts have turned to
> voltage sources and just making one instead of using an adsr all the time.
> so here's the plan - a quad voltage source, four pots, four jacks, very
> rough & ready
> 
> this is probably (yeah right) a silly question, but can i just hook a pot
> directly up to the power supply and stick a suitable 1/4W resistor either
> side to keep the max levels to within -10v to +10v
> or is there something i've forgotten..?
> or should i keep levels to within -5 to +5v..?
> 
> i think my brains have turned to mush
>

Of course there's interest, if for nothing other than academic purposes!
Always good to learn...

--PBr

> -----Original Message-----
> From:	J. Larry Hendry [SMTP:jlarryh@...]
> Sent:	Friday, January 05, 2001 1:26 PM
> To:	motm@egroups.com
> Subject:	Re: [motm] voltage sauce !
> 
> Any other interest?  If so I will put it on my web
> site.  Otherwise I will just send the schematic to Paul privately.
>

From: Brousseau, Paul E (Paul) <noise@...>
> I think (oh dear, not again) that you want to stick to +/-5V... or maybe
> 0-10V.  I don't think you want a full 20V swing.  The VCO outputs +/-5V,
and
> the EG generates 0-+5V and 0 to -5V.

yeah, i realised halfway through typing out that email, that +/-5v is a
useful range

> I think you might want to use an op-amp (or rather, a quad op-amp) to
> isolate yourself from the power supply.  Call it a hunch.

ah, a bit more digging then...

> While you're at it, can you hickory smoke your voltage sauce?  It gives it
a
> more vintage flavor... <grin>

only if you connect it up to the wrong side of the power one supply ;-)

cheers
paul b

hello all,

thanks for the reply larry,
i was shying away from the bells & whistles, as i can use my oakley multimix
to attenuate / invert / offset, and as i have two #700 routers, a quad
source would be just right - and keeping it to 1u is pretty important at the
moment (i'd hate to have to start worryng about cabinet #3 prematurely)
i'd love to see the schemo you have to pull off the original buffer idea,
i'm still in the dark when i venture this far into electronics

cheers
paul b

Oh yeah, put it on the web site, please!!!

Thanks!

-Chris-


>>> jlarryh@iquest.net 01/05/01 03:25PM >>>
OK, I'll give you my take on this.

1.  I agree.  I have this on my DIY list.
2.  -5 to +5 for CV range.
3.  Yes you can get the voltage by hooking the pot across the power supply
BUT.....  You have to use something large so the current is not excessive
4.  Yes, you can limit the range with resistors as you mentioned.

The problem as I see it is that your voltage source is unbuffered and the
source impedance is too high.  If your load varies much it will in turn
effect your output voltage.  So, you want to buffer your output voltage to
provide an output with a lower impedance.  My take on that is to use a
simple op-amp circuit.  Since your voltage is static and interaction between
op amps is not critical, you could do the whole thing on one nice little
quad op amp like a TL-074.  The circuit would have the one chip, four pots,
four caps, and 12 resistors for 4 voltage sources.

Now, if I was going to all the trouble to do this, I would add one more cool
feature (cost you one jack and one resistor per voltage source.  I would add
inputs to a couple of the channels.  That way you could use it as a stand
along DC source, or to offset / bias / invert some other AC or DC signal.

I just purchased some very nice small protoboards for $1.95 each that would
be perfect for this job.  Any other interest?  If so I will put it on my web
site.  Otherwise I will just send the schematic to Paul privately.

Larry Hendry

----- Original Message -----
From: sikorsky <vulture.squadron@...>
so here's the plan - a quad voltage source, four
pots, four jacks, very rough & ready

this is probably (yeah right) a silly question, but can
i just hook a pot directly up to the power supply and
stick a suitable 1/4W resistor either side to keep the
max levels to within -10v to +10v or is there
something i've forgotten..?
or should i keep levels to within -5 to +5v..?

OK, I'll give you my take on this.

1.  I agree.  I have this on my DIY list.
2.  -5 to +5 for CV range.
3.  Yes you can get the voltage by hooking the pot across the power supply
BUT.....  You have to use something large so the current is not excessive
4.  Yes, you can limit the range with resistors as you mentioned.

The problem as I see it is that your voltage source is unbuffered and the
source impedance is too high.  If your load varies much it will in turn
effect your output voltage.  So, you want to buffer your output voltage to
provide an output with a lower impedance.  My take on that is to use a
simple op-amp circuit.  Since your voltage is static and interaction between
op amps is not critical, you could do the whole thing on one nice little
quad op amp like a TL-074.  The circuit would have the one chip, four pots,
four caps, and 12 resistors for 4 voltage sources.

Now, if I was going to all the trouble to do this, I would add one more cool
feature (cost you one jack and one resistor per voltage source.  I would add
inputs to a couple of the channels.  That way you could use it as a stand
along DC source, or to offset / bias / invert some other AC or DC signal.

I just purchased some very nice small protoboards for $1.95 each that would
be perfect for this job.  Any other interest?  If so I will put it on my web
site.  Otherwise I will just send the schematic to Paul privately.

Larry Hendry

----- Original Message -----
From: sikorsky <vulture.squadron@...>
so here's the plan - a quad voltage source, four
pots, four jacks, very rough & ready

this is probably (yeah right) a silly question, but can
i just hook a pot directly up to the power supply and
stick a suitable 1/4W resistor either side to keep the
max levels to within -10v to +10v or is there
something i've forgotten..?
or should i keep levels to within -5 to +5v..?

OK, I'll give you my take on this.

1.  I agree.  I have this on my DIY list.
2.  -5 to +5 for CV range.
3.  Yes you can get the voltage by hooking the pot across the power supply
BUT.....  You have to use something large so the current is not excessive
4.  Yes, you can limit the range with resistors as you mentioned.

The problem as I see it is that your voltage source is unbuffered and the
source impedance is too high.  If your load varies much it will in turn
effect your output voltage.  So, you want to buffer your output voltage to
provide an output with a lower impedance.  My take on that is to use a
simple op-amp circuit.  Since your voltage is static and interaction between
op amps is not critical, you could do the whole thing on one nice little
quad op amp like a TL-074.  The circuit would have the one chip, four pots,
four caps, and 12 resistors for 4 voltage sources.

Now, if I was going to all the trouble to do this, I would add one more cool
feature (cost you one jack and one resistor per voltage source.  I would add
inputs to a couple of the channels.  That way you could use it as a stand
along DC source, or to offset / bias / invert some other AC or DC signal.

I just purchased some very nice small protoboards for $1.95 each that would
be perfect for this job.  Any other interest?  If so I will put it on my web
site.  Otherwise I will just send the schematic to Paul privately.

Larry Hendry

----- Original Message -----
From: sikorsky <vulture.squadron@...>
so here's the plan - a quad voltage source, four
pots, four jacks, very rough & ready

this is probably (yeah right) a silly question, but can
i just hook a pot directly up to the power supply and
stick a suitable 1/4W resistor either side to keep the
max levels to within -10v to +10v or is there
something i've forgotten..?
or should i keep levels to within -5 to +5v..?

Sure, post it to your site.

-- 
James Holloway
jimh54@... - email
(972) 993-2023 x1188 - voicemail/fax

> I just purchased some very nice small protoboards for $1.95 each that
> would
> be perfect for this job.  Any other interest?  If so I will put it
> on my web
> site.  Otherwise I will just send the schematic to Paul privately.
> 
> Larry Hendry


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