Mosfets are 4-terminal devices with a gate that controls the conduction of the drain to source channel. The body (or substrate) of the typical n-channel enhancement mosfet is a P-type material with the drain and source formed from N-type materials.
The oxide layer insulates the metal gate connection from the other layers. There are holes in the oxide layer left for the metallic contacts of the drain and source.
My new Epiphone Valve Jr. amp head
I sometimes get the question “Does a pulldown resistor affect input impedance?”. The short answer is “Yes”.
As we see here, the guitar pickup is modeled as a signal source in series with an output impedance (Z1).
When you add the pulldown resistor at the input of a pedal circuit, that new resistor becomes the maximum impedance (Z2) into which the pickup is looking. It can never be higher than the value of the pulldown, even if the circuit input impedance is infinite. (more…)
I added a couple more mods for the TS-9 tone control:
Delay pedal (prototype)
Expanding the TS-9 Tone Control…
New article in the Lab Notebook!
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!
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:
RoHS = Restriction of Hazardous Substances
Its impact in pedal construction has to do with banning lead from being used in solder, circuit boards and chip construction.
Read the 12 Myths about RoHS: