A cheap tube guitar preamp/effects box.

[Lavane]

I've been scrounging parts out of my bins to build a tube guitar preamp with a few added distortion effects using a cheap two channel Chinese tube preamp board. By running the first channel through the second channel with tone controls between the the two channels and a volume control at the end. I'll also play with adding a small diode circuit on a switch and possibly a simple Klon type curcuit. This preamp will have lots of gain to be able to add distortion.
I saw this preamp used in a couple YouTube video's. The preamp board should be here tomorrow, I have all the other parts rounded up including a small cheap box chassis I found on Amazon. The link below is to one of those video's. It's kind of long, but shows some of the things you can do with this board. The pictures below show the tone stack I'm going to try first along with a simple picture of how this thing wires up.

 

[Mr Boochie]

This is going to be interesting. Now that I think of it, you ever heard of the Dumble Mods?

https://stringjoy.com/dumble-amps/

I've never personally done this modification --- but, I've heard and played through Dumblized Deluxe Reverbs. Super smooth OD tone.

 

[Lavane]

No, I hadn't seen that one before. Mine will be done on the cheap. It just looked like a fun little project to play around with. I have plenty of various pots, caps, resistors, power connectors and such on hand. My son was going to bring me one of those power supllies to gut to use the chassis, but it looked a bit cramped if I wanted to add any more to it. So I bought the cheap $16 chassis with plenty of room.
He has amps with overdrive, presence and other controls he uses, but I thought this might be fun for him to use with some of the small SE amps I built for him with just a volume control.

 

[Lavane]

The preamp board arrived this morning.
I'm going to relocate the film caps under the board and use stand offs tall enough to clear them since the tubes are pretty close to the caps.The board itself is vented to allow some convection around the tubes. Next is some measuring, drilling and hole punching of the chassis.

 

[knockbill]

Looks like you're on your way!!!!

 

[Lavane]

Getting there. I'll probably start masking off and drilling holes today.

 

[knockbill]

Sounds good,,, glad its moving along!!!!! I think it would be cool to hook that preamp up to the 4x 6L6 amp I'm working on!!!!!

 

[Lavane]

It's light enough John, I can ship it to you to try out.

 

[Lavane]

I got all but the holes for the input and output jacks on the back done along with relocating the film caps to the underside of the board and adding a LED pilot light.
The rest is just wiring up the tone stack point to point on the pots and running some wires to the board.

 

[knockbill]

Wow,,, you really made good time with that!!!! Looks good,,, Fire it up by tomorrow???
I may need to put a cap on the input so I dont smoke it for ya!!!!

 

[Lavane]

Maybe. I have to drive out of town tomorrow morning. If I get back early enough I may finish it.

 

[Lavane]

I wired up the tone stack and added the input and output jacks when I got home today. I just wired the tone stack point to point for now. I may be making changes to later.

 

[knockbill]

Very cool!!!!!

 

[Mr Boochie]

Very nice! Are those 6922 tubes?

Good luck with the completion!

 

[Lavane]

Very nice! Are those 6922 tubes?

Good luck with the completion!

Chinese 6J1's. But the GE JAN 5654W's are a really good drop in upgrade.
I bought a couple of the GE tubes a few years ago @ $5 each. Now they go for $25 or more each.

 

[Mr Boochie]

Chinese 6J1's. But the GE JAN 5654W's are a really good drop in upgrade.
I bought a couple of the GE tubes a few years ago @ $5 each. Now they go for $25 or more each.

Never used a 6J1. Tube type is important in effects. You want kinda slow onset of OD. Not an on-off switch effect.

It's good that there are NOS mil spec available.

 

[Lavane]

Never used a 6J1. Tube type is important in effects. You want kinda slow onset of OD. Not an on-off switch effect.

It's good that there are NOS mil spec available.

The JAN's are a night and day difference.

 

[Mr Boochie]

The JAN's are a night and day difference.

I bet.

And they will last forever. As long as the electrical parameters around the tube are correct.

 

[Lavane]

I bet.

And they will last forever. As long as the electrical parameters around the tube are correct.

There are other subs, but the GE's are the go for most people that use them in place of the 6J1's.

 

[Lavane]

I was able to finish up this preamp. The Chinese 6J1's were acually quiet with no microphonics unlike the pair I had in a little hybrid preamp I have.
It works like it should I guess. The real test will be when my son plugs a guitar into it. I used used an old smart phone streaming music through a summing box into one of my amps with a Y cable.
I did have to go with knobs with plastic inserts though since the metal ones caused hum when touched. The 10K midrange pot has a round shaft instead of knurled like the others so for now I'm using a chicken head.
As advertised, it has a lot of gain.