Klon Buffer with higher input impedance

[exabrial]

Hey guys,

I'd like to build this buffer to go inside my acoustic guitar to buffer the piezo. I'm reading that 1mohm _may_ not be enough for a piezo pickup. To up in the input impedance, do I merely change out R1 (1mohm) for a 5mohm resistor? Two questions:

Will the vref voltage need to be adjusted due to the increased voltage drop?
C1 looks like a DC blocking capacitor, does it's value need to be changed however?


Thank you!


Refs:

https://manticorefx.wordpress.com/2015/10/29/klon-buffers-theyre-all-wrong

[slashandburn]

http://www.diystompboxes.com/smfforum/index.php?topic=92228.0

I can't help really, but this thread might.

[PBE6]

Yes, you can just increase the value of R1 to 5M. No other changes are necessary.

[slacker]

That drawing has the pins of the unused half of the opamp floating, this is a bad idea, if you build it connect pins 6 and 7 together and connect pin 5 to 4.5 Volts.

[Frank_NH]

...or use a TL071...

Here's a vero layout:



http://tagboardeffects.blogspot.com/2011/04/klon-buffer.html

[exabrial]

You guys rock! thanks

[ashcat_lt]

Two questions:

But you've actually got 3. 

To up in the input impedance, do I merely change out R1 (1mohm) for a 5mohm resistor?

Yep.

Will the vref voltage need to be adjusted due to the increased voltage drop?

Not with a TL07x or most JFET opamps because its impedance is a whole lot bigger than 5M.

C1 looks like a DC blocking capacitor, does it's value need to be changed however?

A bigger R will make the cutoff of the filter lower.  It probably doesn't touch guitar frequencies already, but...

More importantly, WTF is going on in the lower right corner there?  A non-inverting opamp section unbiased at the input, open loop (infinite gain) and 100% (unity) positive feedback?  That's got to be a huge mess.  It makes a bit more sense if the + and - inputs are reversed, but not a whole lot.


Thank you!


Refs:

https://manticorefx.wordpress.com/2015/10/29/klon-buffers-theyre-all-wrong


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