072 Buffer Circuit

Posted: May 10, 2012 in 072, Build Your Own, FX
Tags: , , , , ,

So, here’s the circuit I used to create the 072 with. It is pretty much as basic as you can get, especially as it is always on but it is very effective at its job.

D1 is for reverse polarity protection incase people use a positive center adaptor instead of negative center (or vice versa depending how you wire it). R1, R2 and C2 form the voltage divider which provides the reference voltage for the opamp. R1 and R2 don’t have to be 47k, they can be anything (I would stick between 10k and 100k though to ensure the divider is reasonably stable) as long as the values are equal. C1 helps prevent any noise while  C3 prevents and DC from the circuit leaking into the amp and R3 limits the current so the LED doesn’t burn out. You could get away with something like a 680r resistor for R3, but the I like the 2.2k because I have a load of them, and they are commonly used for this purpose! I would hook up pin 7 (the output for the second side of the opamp) of the TL072 to ground as it isn’t going to be used.

And that is really all there is too it. Fits nicely in the 1590A enclosures, providing your layout fits. On the only 072 I have built I had quite a big vero layout and it still fit, but I redesigned it after to be that bit smaller to allow slightly more room in the enclosure for everything else.

Parts:

R1    47k

R2    47k

R3    2.2k

R4    1M

C1    100nF

C2    10uF

C3    10uF

D1    1N4001

D2    3mm LED

U1    TL072

And the all important circuit:

You can pretty much drop this into other builds, and if they require an opamp you will probably have a reference voltage you can tap into to get your Vr, which cuts out the whole voltage divider section. There are many, many mods you can do to this circuit, but this is meant as a simple low noise, low part count buffer in a small package.

Revision 04/02/2013: I have updated the circuit and added a vero:

Revised Circuit Vero

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Comments
  1. Karuzaku says:

    Hi,

    nice work, any chance to put a 3PDT foot switch to turn on/off the buffer?, that will be very helpfully if you want to know the difference between the buffered and unbuffered signal,

    thanks

    • 0xdfx says:

      Hi – you could do that easy enough, it bumps the price of building one up considerably though as the 3PDT is the most expensive component and requires a bit extra work. It is also by far the most unreliable component. Funnily enough toneking are bring out a buffer (line doctor?) that has a footswitch. It is something I’ve never really got – to me the buffer should be always on, and if the difference is not night and day by using one you probably don’t need it!

      Cheers

      Ben

  2. Max says:

    Hi! Input and output jacks are drawn wrong. The signal should come from and to pin 1

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