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I have written a further Workshop Bulletin 5: Improving FET Gain and Lowering White Noise eTap2hw, this fits with the previous 4 bulletins that I assembled, which are on Piet's Blog at http://www.echotapper.nl/wp.

This workaround shows how to improve FET gain, lower bandwidth from 20kHz to a more electric guitar friendly 10.6KHz and significantly reduce output noise.

Number 1 covers improving the positive headroom of the input operational amplifiers section to align with some of the previous suggestions of ChrisG.
Number 2 is a flowchart type procedure for optimising the FETs by changing the bias resistors. Especially useful for those who feel the need to have a sound which can vary from clean to one rich in harmonics. Also of use to those who haven't measured (or can't be bothered to measure) the FET parameters or perhaps can't measure them because the FETs are soldered into the board.
Number 3 is an inductor/capacitor power supply filter to prevent noise being injected into the eTap2hw by the Arduino automation controller.
Number 4 is a design based on Charlie Hall's Cutting Edge Filter and includes a Frequency Response graph and suggestions on how to use it.

Thanks to all my collaborator's for their inputs to the bulletins; Piet Verbruggen, Philip Hawthorne, Johan Forrer and ChrisG.

Further developments will be posted in the same way so keep looking.

Hope you find them useful,

Steve Mitchell

Cheers Steve, good work.

Here's an active link to Piet's blog http://www.echotapper.nl/wp

Phil.

PS You can use the URL button on the toolbar to insert working links

Hi Steve,
Thanks for your helpful bulletins and the other help you have given me. Your help in optimizing the FETS is certainly worthwhile as I have found and I have now modified three of the five etaps I built, all successfully and to the delight of their owners.

Des.