7-Band equalizer primer?

[bluefoxicy]

I just grabbed myself an Epiphone Valve Junior, nice little 12AX7 preamp/EL84 power amp box. Tube amp, first time, and holy crap the damn thing responds to ANYTHING. Here's a few things that do absolutely nothing:

• Adjusting the tone knob on a guitar
• Switching between Neck and Neck+Bridge pickups (the bridge pickup by itself does sound vastly different)
• Switching between .6mm and 1mm delron picks (i.e. Dunlop Tortex)
• Picking harder when already striking pretty hard (i.e. digging in instead of just passing through the string really fast)
• Turning the volume up until about 6 (aside from, of course, volume)

... ANY of this causes sound differences, with the tone knob basically acting like a MASSIVE overdrive control particularly, and the Neck pickup sounding vastly different from having both pickups on. Volume on the amp and guitar don't just adjust volume similarly; touching one or the other has different effects. You can kind of tell how I'm playing, what pick I'm using, etc too.

... I LIKE this thing. But it's got one knob, a volume knob. Now, given that the tone knob causes massive overdrive when fiddled with, I think that adjusting the tone is an awesome idea. In fact, adjusting the tone in various bands various ways is an awesome idea. IN FACT, I could drill into this thing and add a 3-band (Bass/Mid/Treb) or 7 band EQ and achieve all kinds of interesting hotness.

I can't find anything googling about how to build a 7 band EQ though. I know it's caps to control the frequencies being handled by the tone pot, and then cross the hot leads with a tank/RC circuit to allow other frequencies to pass (so cap gives you the lower bound, RC gives you the upper bound, pot affects what's in there). I don't know exactly how I should go about building this though, what cap and RC values to use, etc.

I'm going to use push-pull pots to bypass each respective circuit (the associated cap, pot, and RC) to avoid affecting the tone when I don't want this; that being said, that's a pretty easy modification, and cluttering a diagram with that would probably be detrimental to my understanding (I could work through it, but eh...)

Any ideas?

[d95err]

Mesa Boogie used 5-band EQ's on some of their amps. You can find the schematics at www.schematicheaven.com. They used transistors for those EQ's though and it probably wouldn't work too well in a Valve Jr type amp.

I think you should stick to simple well-known guitar tone controls. The classic Fender/Marshall style EQ could work, but you'd loose a lot of gain. Something simpler like the Fender Tweed style tone control is probably a better idea.

Checkout the www.sewatt.com site, they are experts in modding these kind of amps, and can probably give you some ideas for simple tone controls.

[d95err]

Hmm... forget most of what I said above. I forgot the most important part:

In the Valve Jr, almost all distortion will be generated by the poweramp. The preamp will run pretty much completely clean, unless you boost the input a lot.

This means you get the same effect by putting an EQ pedal before the amp as you'd get if you managed to build an EQ into the amp. So if you want a 7-band EQ, go build/buy an EQ pedal.

A simple tone control could be useful though, to shape the distortion. Try a Fender "Tweed" style tone control, or a Vox style "Cut" control (on the input to the power tube).

Here are a few options:
http://www.generalguitargadgets.com/...d=46&Itemid=26

http://www.runoffgroove.com/tonemender.html

http://www.runoffgroove.com/mreq.html