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From: Allen Bong on 4 May 2010 02:15
Hi,

I have been playing with op-amp for the past few weeks and I came
across this circuit

http://www.flickr.com/photos/11236051(a)N08/4577591378/sizes/o/

If I am correct, the gain of op-amp U1:B is 2, as (R1+R18)/R18 = 20/10
= 2.

But what's the gain of op-amp U1:A ? I cant find the resistor which
is going to ground.

TIA,

Allen
From: Tim Wescott on 4 May 2010 14:21
Allen Bong wrote:
> Hi,
>
> I have been playing with op-amp for the past few weeks and I came
> across this circuit
>
> http://www.flickr.com/photos/11236051(a)N08/4577591378/sizes/o/
>
> If I am correct, the gain of op-amp U1:B is 2, as (R1+R18)/R18 = 20/10
> = 2.
>
> But what's the gain of op-amp U1:A ? I cant find the resistor which
> is going to ground.

Complicated, and variable. Does that help?

The answer isn't leaping out at me, but I'm guessing that the three pots
are either tone controls or that this is some sort of a distortion
effect and they control that. Do you know what the circuit is supposed
to be?

Simulating it with Spice might be helpful -- put a signal in, twiddle
the pots, see what happens.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
From: John Larkin on 4 May 2010 15:44
On Mon, 3 May 2010 23:15:29 -0700 (PDT), Allen Bong
<allenbsf6502(a)gmail.com> wrote:

>Hi,
>
>I have been playing with op-amp for the past few weeks and I came
>across this circuit
>
>http://www.flickr.com/photos/11236051(a)N08/4577591378/sizes/o/
>
>If I am correct, the gain of op-amp U1:B is 2, as (R1+R18)/R18 = 20/10
>= 2.
>
>But what's the gain of op-amp U1:A ? I cant find the resistor which
>is going to ground.
>
>TIA,
>
>Allen

Wow, that is one ugly circuit!

John

From: Allen Bong on 4 May 2010 18:08
On May 5, 2:21 am, Tim Wescott <t...(a)seemywebsite.now> wrote:
> Allen Bong wrote:
> > Hi,
>
> > I have been playing with op-amp for the past few weeks and I came
> > across this circuit
>
> >http://www.flickr.com/photos/11236051(a)N08/4577591378/sizes/o/
>
> > If I am correct, the gain of op-amp U1:B is 2, as (R1+R18)/R18 = 20/10
> > = 2.
>
> > But what's the gain of op-amp U1:A ?  I cant find the resistor which
> > is going to ground.
>
> Complicated, and variable.  Does that help?
>
> The answer isn't leaping out at me, but I'm guessing that the three pots
> are either tone controls or that this is some sort of a distortion
> effect and they control that.  Do you know what the circuit is supposed
> to be?
>
> Simulating it with Spice might be helpful -- put a signal in, twiddle
> the pots, see what happens.
>
> --
> Tim Wescott
> Control system and signal processing consultingwww.wescottdesign.com

The circuit is a acoustic guitar active pickup circuit. It was in a
small metal case mounted to the side of the hollow guitar powered by a
small 9V battery. the 4 volume controls are tone controls each taking
care of a range of frequencies.

The circuit was actually traced by me and drawn for easy
troubleshooting. The problem was one of the strings was having very
low output so I suspect one of the tone controls was not working
correctly. This particular circuit was made in Indonesia. I've seen
that some Yamaha guitar are also having the same pickup built in.
I'll try to get one and trace out the circuit.

Anyway thanks for your reply.

Allen
From: Allen Bong on 4 May 2010 21:07
On May 5, 3:44 am, John Larkin
<jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> On Mon, 3 May 2010 23:15:29 -0700 (PDT), Allen Bong
>
>
>
>
>
> <allenbsf6...(a)gmail.com> wrote:
> >Hi,
>
> >I have been playing with op-amp for the past few weeks and I came
> >across this circuit
>
> >http://www.flickr.com/photos/11236051(a)N08/4577591378/sizes/o/
>
> >If I am correct, the gain of op-amp U1:B is 2, as (R1+R18)/R18 = 20/10
> >= 2.
>
> >But what's the gain of op-amp U1:A ?  I cant find the resistor which
> >is going to ground.
>
> >TIA,
>
> >Allen
>
> Wow, that is one ugly circuit!
>
> John- Hide quoted text -
>
> - Show quoted text -

John,

I agreed with you the design is messy. Do you have a better one that
does the same job? It must be compact and simple.

Allen
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