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Channel switching
#1
Hi Guys

Channel switching is the most common requirement in guitar amps as far as having any kind of "switching" system. It is truly quite simple, but can be made "too simple" sometimes impairing the ergonomics for the player.

As we know from "The Ultimate Tone" (TUT) series, ANYTHING can be put on a switch and once you've done that, all the switchable things can be synchronised and/or be made remotely accessible, all at the whim of the builder or player.

London Power offers a range of switching kits and has a PDF to make selection easier.

Switching can be done using relays, transistors (BJTs), jfets, mosfets and even tubes, depending on what needs to be switched. Sometimes the simplest circuit can turn out to be tricky to design or to get working reliably, but we will show step-by-step methods of design and get you to a satisfying finish.

Have fun
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#2
Great to have a section of the forum dedicated to switching! I have yet designed or built a two-channel amp, but I want to do so in the near future. Something like a LPSP with the two channels sharing the first gain stage (and maybe staying separate from there; but who knows). My plan is to start as simple as possible.

I like the form factor of the ERK, but are there disadvantages to using jfets (say, instead of relays)?
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#3
Hi Guys

There are pros and cons for every switching element.

Jfets are inexpensive, require no power to be on or off, and come in a wide variety of capability. For switching, you want low on-resistance and suitable voltage rating for the circuit point. Using them as shunt switches is simple but as series switches they require a bipolar supply, which you may find easy or difficult to employ. The gate control voltage is not 100% isolated from the channel, so a small amount of care must be taken in the placement of parts.

Relays require a bit of power to energise and this current has to come from somewhere. Supplying the coil is usually the biggest hurdle in using relays. otherwise, relays provide negligible on-resistance and near-infinite isolation between poles and to the coil, so the coil control circuit can be at any voltage, as can be the contacts. Relays cost a lot more than jfets regardless of what deals you might come across. The contacts can be configured for series or shunt switching with no effort at all.

Have fun
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A warm welcome to those interested in tube and hi-fi audio! Fans of Kevin O'Connor's The Ultimate Tone (TUT) book series form a part of our population. Kevin O'Connor is the creator of the popular Power Scaling methodology for amplifiers.
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