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A lot of people suggest buffers with a 1M input impedance and a 100R output impedance. In the Buffer Board, it appears to have the 1M input impedance. Is the output impedance set by R3? If I want the 100R output impedance can I just change R3 from 100K to 100R or are any of the other components contributing to the output impedance? Thanks in advance, Hank
Many people including myself have built it as is with no adverse affect so I’d build it per the build doc, it being a blend and buffer circuit rather than just a buffer
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Billy, Thanks. I was just curious about which components govern the output impedance. Thanks for the response!
I checked the data sheet for the TL071 and confirmed that the output impedance is 125R. This will be the impedance sent out when the Buffer Board is bypassing the effect board.. When activated, the output of the buffer feeds into the input of the attached effect board and the output of that board will determine the final output impedance. I hope this helps.
Wilkie, Thanks! I’m assuming if I build it as a stand alone with no foot switch (jumpered for always on) that the input is then 1M and the output is 125R…would that be correct? I’m thinking of building an interface box with input and output buffers (before and after the pedalboard).
Thanks again, Hank
No. As i said, when the Buffer Board is BYPASSED the output impedance is 125R.
When it is active, the final output is provided by the attached effect board, NOT the Buffer Board. Look at the schematic and you can see this. If the effects board has a buffered output, then you would not need an additional buffer.
Wilkie, thanks. I think my intent may not be clear. I want to build an always on “buffer only” much like the BonaFide by TC Electronics that isn’t tied to an outboard circuit with just an input and output that is always on (sans foot switch). I would jumper the foot switch holes on the Buffer Board and use the board in and board out for my input and output jacks. Nothing in the box but the Buffer Board (actually 2 separate buffers, each with its own in and out). In that case, doesn’t the 1M in and 125R out apply?
Yes. Simply jumper the footswitch so that the Buffer Board is always bypassing the effect board in and out. That way the buffer is always on. You will use it as an extra effect olaced at the end of your board. The input impedance will be 1M and the output impedance will be 125R.
Wilkie, Perfect! Thanks
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