Guitar pre-amp built for small practice/studio amp

[anotherjim]

Built this almost a year ago. I like it. Could say it's tube sound, but after using it for a while I prefer it to any small tube amp I've ever had the use of.

Not a high gain thing at all - that's what your other pedals are for and it responds very nicely to overdrive. Generally Fender-ish sound. Dynamic, chords chime, single notes have a nice thickening.

Another CD4007 based thing of course. Eat it Yum!



To get the amp out of the way first, I used the LM386 while developing. In the end it was built with a TDA2003 power amp instead. Stock data-sheet circuit running off +/- 12v dual supply. 8R speaker/cab optimal.
With D1 omitted, the preamp supply used was from a 78L08 regulator off the +12V keeping similar volts to 9v with D1 included. I had 78L08 in the drawer that needed using D1 is really only needed if made as a standalone pedal.

The reverb send & return connect to a simplified version of Merlins' Equinox - it doesn't need pre-amp or wet/dry mix so the op-amp wasn't needed at all. Surprisingly effective that Equinox. You might almost expect it to go "boing" if you hit it.

The preamp...
Bias trim adjust for 1/2 supply volts at U1 pin5 should get the sound going.

Tone is Big Muff 1 knob, but the Boost bypass stops it being as boring as would otherwise be. The "bass" side of the control is more interesting with the switch on.
2nd mosfet stage is a P-channel source follower - no gain, it's just buffering the tone control and providing onward drive.
Finally, the Inverter biased as an amplifier ( is THE reason I bother to use the 4007 chip) emulates the power stage "tone".

[Kipper4]

Are those mosfet SRPP on the input  and output of the tonestack Jim?

[anotherjim]

Not SRPP. It may be a short step to that. I think I've seen something like that from one of the boutique pedal brands - the upper mosfet is working but with a drain resistor for the lower mosfet across it. It might have been Catlinbread SCOD, but I'm not 100% on that.
No, I've just tied off the unused channel of the complementary pair. I'm pretty sure it's having no effect shorted out like that, although it do look a little odd.
At any rate, I'm not too convinced it's possible to get good sounding high gain out of a single 4007 without other, more suitable, parts providing most of the grunt.

[tca]

Is the P-mosfet connected  correctly (done on purpose)? Shouldn't the source be connected to +9V?

[anotherjim]

If you mean pins 1 & 2 shorted? Yes, it is deliberate. Also pins 9 & 12. With the channel shorted across, just imagine that mosfet is not there at all. However, since it's in the package, it isn't ignored. The unused channel drain and source is tied to the substrate voltage, which is +supply for a P-channel and 0v for an N-channel. The fact that the gate of the disabled mosfet is connected and active has no effect.

If, say, pins 1 & 2 were left completely disconnected, then that mosfet channel would be floating at high impedance & possibly able to build up a very high static charge. That said, you would probably get away with leaving them disconnected since every pin on the 4007 has a protection diode network. I have left nothing to chance by making those connections.
On the subject of mosfet safety, those protection diode networks mean no need for extra zeners or whatever you see on discrete mosfet inputs. The protection diodes will stop any pin exceeding supply + and - by more than about 0.5v. Resistor R3 limits current in the protection diodes if input overvoltage happened.

[tca]

Ok, my bad, didn't see the short.

Cheers.

[swever]

I've just finished building one from another thread and now here's this! The description sounds very intriguing to me and I'd really love to try it. BUT my spare experience, limited knowledge and very modest intellectual abilities  don't allow me to fully understand this schematic.

May I ask to explain what are +IN, -IN, VEE, VCC and +UB.
What kind of power source do I need for this? Will it work off a 9v battery?

Any other noob friendly information is greatly appreciated! I want to build it as a separate box to use with a power amp.

PS okay I could try to guess that the VEE and VCC are points to power the power amp. Is that correct?

[anotherjim]

May I ask to explain what are +IN, -IN, VEE, VCC and +UB.
What kind of power source do I need for this? Will it work off a 9v battery?

Different names to stop pcb software from auto-routing the power connections to one connection. Not that I've ever made a pcb layout that way, still it just seems a good idea to use some separation on the scheme.
+IN and -IN is the DC supply input. 9v expected as drawn. VCC & VEE are power amp supplies. +UB is a supply name that comes with the pcb software - some parts of the world use U instead of V for voltage - so it is the bias voltage from the trimmer pot.
It certainly "can" run off a 9v battery, but current consumption may be a couple of milliamps more than those schemes using JFETs, due to the inverter pair passing some current right through the mosfet channels. .

[swever]

I guess I see now. Powering is no different than any other fuzzbox - basicaly there is only +9 and negative ground. Right?

Found a locally available russian substitute for CD4007 - К176ЛП1. Will see if it's going to work when I get it.