This is the basic output stage of a typical wah-wah pedal. You can see that the pot that controls the bandpass frequency is connected not only to the output jack but also to the input of a buffer transistor that feeds back part of the signal to the first stage.
This will make the wah sensitive to the load that is placed on its output. It can also cause an adverse reaction with a low impedance input of the next stage, such as with a fuzzface type cicuit. The FF can break into oscillation with the frequency changing as the wah treadle is moved.
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The Tillman jfet booster circuit is widely known in the DiY effects community and often recommended for certain guitar fx applications. I recently saw the circuit posted on a guitar forum and realized that it could be built on my Multi-Purpose pc board.
I’ve modified the instruction page for the pcb to show how to use it to build the Tillman. The instructions and parts list are on the site that is emailed to everyone that buys one of the boards. Ordering info:
AMZ MultiPurpose PC Board
The Proco Rat has become a classic pedal that has a legion of fans among guitar players. I have 3 of them, two Rat2 and a Turbo Rat.
The Rat is designed to have a large amount of gain and a significant treble boost. This is part of what gives it a characteristic sound, but also makes some players dislike the tone it produces.
The resistors R6 and R7 along with the capacitors C7 and C6, are the main determining factors for the low frequency rolloff.
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The slightly dusty pcb from my Epiphone Valve Jr. amp…
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My new Epiphone Valve Jr. amp head
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audioXpress is the only do-it-yourself audio magazine currently published in the USA. I’ve been a subscriber since the late 1970s and have a nice collection of back issues.
Their web site has plenty of free info so check it out… better yet, subscribe today and support DiY!
http://www.audioxpress.com/
An example of a recent project is the Hybrid Valve MOSFET SE Amp by Stephen Moore, published in the Oct and Nov 2007 issues. They are online for free download:
http://www.audioxpress.com/magsdirx/ax/addenda/media/moore2355.pdf
http://www.audioxpress.com/magsdirx/ax/addenda/media/moore2844.pdf
Vox amPlug Headphone Guitar Amp
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My new Epiphone Valve Jr. amp head
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This has to be the cool project of the month… it has a bit of a “steampunk vibe” with the copper panels and screwheads… very cool. You can read more about this unique amp at the link shown below.
http://www.head-fi.org/forums/showpost.php?p=2891866
