Stereo boost?

[Kipper4]

I've noticed that you have pin 4 going to +9v.
I thought pin 8 went to 9v on a tl072
Plus pin 5 is the inverting input not pin 6.
I'd use a single voltage divider to power both sides of the op amp too.
I'm no expert but it looks fairly low output impedance, but then I guess it depends what your feeding it into.
No input pop stopper resistor either.
I'm sure it will evolve on the breadboard.
Have fun

[therealfindo]

I've noticed that you have pin 4 going to +9v.
I thought pin 8 went to 9v on a tl072
Plus pin 5 is the inverting input not pin 6.
I'd use a single voltage divider to power both sides of the op amp too.
I'm no expert but it looks fairly low output impedance, but then I guess it depends what your feeding it into.
No input pop stopper resistor either.
I'm sure it will evolve on the breadboard.
Have fun

oh.. yeah.. I realised pretty quickly that the pinout in the diagram was wrong... and will put a pop resistor inthe final one.

What's a voltage divider, and why do I need it? Doesn't the chip have a single voltage input?

[nocentelli]

Your diagram already has two voltage dividers - the two pairs of 2M2 resistors that divide the 9v supply down to 4.5v to bias the non-inverting inputs (should be pin 3+5). You could use a single pair of 10k resistors (one from +9v, one from ground, meeting at a point which has a 22uF cap to ground) and run two 470k resistors from this meeting point to each inverting input. It saves a couple of components and will be a bit quieter (search for "noise-less biasing").

[therealfindo]

Your diagram already has two voltage dividers - the two pairs of 2M2 resistors that divide the 9v supply down to 4.5v to bias the non-inverting inputs (should be pin 3+5). You could use a single pair of 10k resistors (one from +9v, one from ground, meeting at a point which has a 22uF cap to ground) and run two 470k resistors from this meeting point to each inverting input. It saves a couple of components and will be a bit quieter (search for "noise-less biasing").

ah... ok, thanks!

[therealfindo]

Your diagram already has two voltage dividers - the two pairs of 2M2 resistors that divide the 9v supply down to 4.5v to bias the non-inverting inputs (should be pin 3+5). You could use a single pair of 10k resistors (one from +9v, one from ground, meeting at a point which has a 22uF cap to ground) and run two 470k resistors from this meeting point to each inverting input. It saves a couple of components and will be a bit quieter (search for "noise-less biasing").

Umm... actually, I don't think I've understood properly.. like this (those 100ohm resistors should be 470K, of course, forgot to change the value):



?

Do I connect the two inputs after each 470K resistor? How do I keep the two inputs isolated if the resistors meet?

[waltk]

I think this is what you want...

It's a stereo version of the circuit described here: http://www.diystompboxes.com/smfforum/index.php?topic=75862.0

[therealfindo]

I think this is what you want...

It's a stereo version of the circuit described here: http://www.diystompboxes.com/smfforum/index.php?topic=75862.0

Will it be a problem running this on 9V instead of the 5V on the schematic?

[duck_arse]

the points marked "+5V" are all connected to the voltage divider between "V+" and "GND". because R2 and R3 are equal value, V+ is divided by 2.

so, to answer your question, yes, 9V is ok, connected at "BT1". the opamp positive supply pin, pin 8, must be connected to the "V+", and not the +5V. (+5V would be better called Vref in this circuit).

in this circuit, the inputs are biased to half the supply with 1M resistors instead of 470k. this means the op-amp only loads the input signal by 1M, ie almost nothing. this effectively isolates the opamp from the signal.

[Kipper4]

It needs a +9 volt supply depicted in the schematic as a battery and 9volts DC jack.
The 5v is created by the voltage divider ie: 2 x 10k resistors.
thats the purpose of the voltage divider is to create a half supply voltage in this case actually 4.5v (not 5v)
the voltage divider makes a V referance point that powers the signal going to each individual op amp via the !k resistor to the op amps inverting input (minus side, pins 2 and 6)
the op amps gain is determined by the two resistors attached in the feedback loop so 1k resistor R1 and 10k resistor R10
which should give a gain of 11.
R1xR10+1   =  1 x 10 + 1 = 11
if im not mistaken.
I'm still a bit of a newbie and i might not have desribed it well but i'm pretty certain this is whats going on here.
I hope this helps.
Rich

[waltk]

Will it be a problem running this on 9V instead of the 5V on the schematic?

What duck_arse said is all true.

The points labelled +5V are really the Vref, 1/2 power supply formed by the 10K voltage divider, R2 and R3.  BT1 represents the battery or other power supply, which could be a 9V battery, or any other reasonable power source.  When I drew this, I wasn't planning for anyone else to see it.

Everything labelled U2 is part of the opamp. So the rectangular symbol shows pin 8 connected to V+ and pin 4 connected to ground (V-).

The diode is a schottky for polarity protection.

The gain of each channel is set by the ratios of R10 to R1 and R9 to R6, and is fixed at 11.

The volume pots are intended to be a dual pot with one shaft to control the output level (best for your purposes), but could also be just two separate pots.

This circuit was built and it works fine.  If you use a TL072 or similar JFET input opamp, it's a great clean boost pedal.  I've also successfully used it as a headphone amp by substituting a 5532 opamp (and I think that's why the output caps are so big).

-Walt

[waltk]

I guess Rich (Kipper) and I were typing at the same time... we're all saying the same thing.

If you look at the thread I referenced above, there's a lot more information about how the circuit works (and also many dumb questions from me - as I was just beginning to learn this stuff at the time).

[therealfindo]

I guess Rich (Kipper) and I were typing at the same time... we're all saying the same thing.

If you look at the thread I referenced above, there's a lot more information about how the circuit works (and also many dumb questions from me - as I was just beginning to learn this stuff at the time).

Thanks everyone for the info!

I've already etched (following a successful breadboard) the circuit I posted earlier (with the correct pinout however) so I'll finish that, and then try this one out..

[therealfindo]

And here's my planned wiring for Millenium Bypass and a 4PDT footswitch:

[Kipper4]

Did you do a working breadboard of it yet?

[therealfindo]

Did you do a working breadboard of it yet?

I was a bit lazy and only breadboarded one half of the circuit.. both halves are the same, so I just went straight to soldering up a pcb, and it works.

[Kipper4]

excellant news.
you shoulodnt need a millenium bypass if you put 1m resistor from inputs to ground as suggested earlier. that should cope with defeating any pops you might get when turning it on.
this looks like an over complicated switching for a stereo booster too or are you treying to create a kind of loop out of it?
Confused now!!!!!!!!!!

[therealfindo]

excellant news.
you shoulodnt need a millenium bypass if you put 1m resistor from inputs to ground as suggested earlier. that should cope with defeating any pops you might get when turning it on.
this looks like an over complicated switching for a stereo booster too or are you treying to create a kind of loop out of it?
Confused now!!!!!!!!!!

The Millennium Bypass is because I want an LED.. unless I'm missing a way to wire this switch to get an LED without millennium bypass?
I'm using 1M pulldown resistors on the input anyway..

[therealfindo]

Here's the finished box:

I'll try and post the final schematic and pcb etc. sometime..

[Kipper4]

Good job
I'm glad you have a nice transparent working unit.
It sounds like it pops a little when you engage the switch. does it? or is it just the camera picking up the switches mechanical noise?
Either way good job thanks for reporting back.

[therealfindo]

Good job
I'm glad you have a nice transparent working unit.
It sounds like it pops a little when you engage the switch. does it? or is it just the camera picking up the switches mechanical noise?
Either way good job thanks for reporting back.

It's just the camera - if you watch in a section where the camera is muted (no talking bits) there's no pop in the circuit as far as I can tell. It's a pretty stiff 4pdt though..