A cheap tube guitar preamp/effects box.

[knockbill]

Nice neat work Paul!!! Dontcha hate it when you have set of knobs but pots don't match!!!! I try to get mainly set screw knobs,, they fit more pots... How's the effects from the preamp? Can you get them with out a guitar?

 

[Lavane]

Nice neat work Paul!!! Dontcha hate it when you have set of knobs but pots don't match!!!! I try to get mainly set screw knobs,, they fit more pots... How's the effects from the preamp? Can you get them with out a guitar?

Some. I was able to get it to sound really dark or really bright if I wanted. There was some distortion when turning the volume on the amp up at a high level. I'm just going to order a few chicken heads so they all match since they have set screws. I could only find the one.

 

[knockbill]

OK,,, the git amp will have more gain than a hi-fi amp, so it should distort all he wants!!! Chicken heads may run into each other on that chassis, ask me how I know!!!! The odd, bigger round one in the earlier pic looks fine to me!!!

 

[Lavane]

OK,,, the git amp will have more gain than a hi-fi amp, so it should distort all he wants!!! Chicken heads may run into each other on that chassis, ask me how I know!!!! The odd, bigger round one in the earlier pic looks fine to me!!!

I thought about that. I ordered a cheap set of round white knobs from Amazon the same diameter as the ones in the preamp now. They should be here tomorrow.

 

[Mr Boochie]

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.

Yeah, I don't like metal knobs on amps and EFXs for instruments. Just another annoyance to deal with.

 

[knockbill]

I thought about that. I ordered a cheap set of round white knobs from Amazon the same diameter as the ones in the preamp now. They should be here tomorrow.

HA,,, yep the ones next to each other always want to fight for the same space!!! and if ya build on used chassis as I do, ya dont get to place the holes!!!!

 

[tubelectron]

Hey @Lavane - I don't know if you ever built such guitar tube preamp device, but if not, I let you discover the intricaties, in the sense that if this Chinese unit is an Audio/Hi-Fi circuit, it will probably not sound very good for guitar, as the requirements are not the same... Modifications in perspective but it's the part of the game, right ?

As suggested by @Mr Boochie - yes you can have a look to the Dumble Overdrive Special preamp section (2x12AX7) for your build otherwise. This is not a super simple circuit as is though, but very performant... My Serial Tone Killer amp uses a custom design modded version :



As a side note, this simple design sounds very good - I have the original at home :



The WESTBURY W-20 "The TUBE" has been produced in Japan for UNICORD (USA) from 1978 to 1982. Here's mine :



It's a very compact unit - reputedly the first Tube Overdrive Stompbox ever made - with ONE drawback : the closeness of the power transformer with the circuit... Avoid this in you guitar preamp design @Lavane, otherwise you will have troubles to get rid of the induced hum !

Another one - with two 12AX7 this time, and conceived as a standalone preamp unit, in the style of what you want to experiment - is the Matchless Hotbox . I never took the time to test it, but he has a good reputation :



Have Fun !

T

 

[Lavane]

Hey @Lavane - I don't know if you ever built such guitar tube preamp device, but if not, I let you discover the intricaties, in the sense that if this Chinese unit is an Audio/Hi-Fi circuit, it will probably not sound very good for guitar, as the requirements are not the same... Modifications in perspective but it's the part of the game, right ?

As suggested by @Mr Boochie - yes you can have a look to the Dumble Overdrive Special preamp section (2x12AX7) for your build otherwise. This is not a super simple circuit as is though, but very performant... My Serial Tone Killer amp uses a custom design modded version :

View attachment 2964835

As a side note, this simple design sounds very good - I have the original at home :

View attachment 2964819

The WESTBURY W-20 "The TUBE" has been produced in Japan for UNICORD (USA) from 1978 to 1982. Here's mine :

View attachment 2964823 View attachment 2964825

It's a very compact unit - reputedly the first Tube Overdrive Stompbox ever made - with ONE drawback : the closeness of the power transformer with the circuit... Avoid this in you guitar preamp design @Lavane, otherwise you will have troubles to get rid of the induced hum !

Another one - with two 12AX7 this time, and conceived as a standalone preamp unit, in the style of what you want to experiment - is the Matchless Hotbox . I never took the time to test it, but he has a good reputation :

View attachment 2964830

Have Fun !

T

Ya I know. I had everything I needed except the cheap board to play with the thing. I did break down and shell out for a cheap $16 chassis in the end just because it didn't look like there would be enough room to add a midrange control in a busted computer power supply chassis i have access to.
If it doesn't work out, I can always use the board to make a two channel preamp.

 

[Mr Boochie]

Hey @Lavane - I don't know if you ever built such guitar tube preamp device, but if not, I let you discover the intricaties, in the sense that if this Chinese unit is an Audio/Hi-Fi circuit, it will probably not sound very good for guitar, as the requirements are not the same... Modifications in perspective but it's the part of the game, right ?

As suggested by @Mr Boochie - yes you can have a look to the Dumble Overdrive Special preamp section (2x12AX7) for your build otherwise. This is not a super simple circuit as is though, but very performant... My Serial Tone Killer amp uses a custom design modded version :

View attachment 2964835

As a side note, this simple design sounds very good - I have the original at home :

View attachment 2964819

The WESTBURY W-20 "The TUBE" has been produced in Japan for UNICORD (USA) from 1978 to 1982. Here's mine :

View attachment 2964823 View attachment 2964825

It's a very compact unit - reputedly the first Tube Overdrive Stompbox ever made - with ONE drawback : the closeness of the power transformer with the circuit... Avoid this in you guitar preamp design @Lavane, otherwise you will have troubles to get rid of the induced hum !

Another one - with two 12AX7 this time, and conceived as a standalone preamp unit, in the style of what you want to experiment - is the Matchless Hotbox . I never took the time to test it, but he has a good reputation :

View attachment 2964830

Have Fun !

T

Agree with Matchless Hotbox. I've restored a VibroBox, which is a Hotbox with tremolo circuit. Very reliable, smooth sounding pedal.

 

[tubelectron]

Agree with Matchless Hotbox. I've restored a VibroBox, which is a Hotbox with tremolo circuit. Very reliable, smooth sounding pedal.

Ah yes, the Vibrobox is even more interesting with the tremolo facility - I should give a go to these Hotbox or Vibrobox one of these days !

I think both are not in the Hi-Gain, but rather in the Mid-Gain or Lo-Gain category - right ? OK, let me clarify first :

Hi-Gain department = Joe Satriani and the like.
Mid-Gain = Santana and most of the 70-80s.
Lo-Gain = Vintage crunch.

T

 

[Lavane]

I've thought about building a Matchless EL84 PP amp. The Spitfire was it I think?

 

[Mr Boochie]

Ah yes, the Vibrobox is even more interesting with the tremolo facility - I should give a go to these Hotbox or Vibrobox one of these days !

I think both are not in the Hi-Gain, but rather in the Mid-Gain or Lo-Gain category - right ? OK, let me clarify first :

Hi-Gain department = Joe Satriani and the like.
Mid-Gain = Santana and most of the 70-80s.
Lo-Gain = Vintage crunch.

T

Low gain. The bypass is perfect on Matchless boxes.

 

[Mr Boochie]

I've thought about building a Matchless EL84 PP amp. The Spitfire was it I think?

They are great amps! The Hurricane is a Spitfire with Tremolo. An original Fender Reverb Unit sound quite nice, going through these amps.

 

[Lavane]

They are great amps! The Hurricane is a Spitfire with Tremolo. An original Fender Reverb Unit sound quite nice, going through these amps.

I read something about the OPT's they used in the Spifire. Supposedly it doesn't have a primary impedance you would expect to be used? People that built clones couldn't get them to sound quite like the real deal.

 

[Mr Boochie]

I read something about the OPT's they used in the Spifire. Supposedly it doesn't have a primary impedance you would expect to be used? People that built clones couldn't get them to sound quite like the real deal.

The early Matchless amps had specially wound transformers to Mark Sampson's specs. Same for Trainwreck amps. This is a large part of the tone of both.

Even hand wound ones have a hard time completely being equal to the originals. Closest fit, in my experience, are the Mercury Magnetics special Tone Clone irons. I bet that the people that founded Mercury were the original custom makers of these boutique amp transformers.

They are expensive, but worth every penny, if you are after that tone.

https://www.mercurymagnetics.com/make/matchless/

 

[Lavane]

I didn't like the mismatched plastic onobs I had on hand knobs I had on hand so I bought some cheap white plastic knobs. Now it's done.

 

[Lavane]

I do have a question, it didn't matter for what I did to this poor 2 channel preamp, but does it look like a hybrid to anyone. There are 4 transistors on the thing. No schematic to follow either.

 

[Mr Boochie]

From video in the first post, look like the unit runs off a 12VAC wall wart. So, maybe those are diodes? I can't really see if they have two or three legs.

Though, I wouldn't be surprised if it had transistors like FETs in certain sections. Those tubes may be simply buffers.

 

[tubelectron]

From video in the first post, look like the unit runs off a 12VAC wall wart. So, maybe those are diodes? I can't really see if they have two or three legs.

Though, I wouldn't be surprised if it had transistors like FETs in certain sections. Those tubes may be simply buffers.

Possibly yes, maybe with a low plate voltage to the 12AX7 (starving plate circuit)... There have been some stompboxes like this :

http://revolutiondeux.blogspot.com/2012/04/dean-markley-overlord-to-b-k-butler.html

I had both for test the Dean Markley Overdlord and the Tube Works Real Tube from y local shop, as long with the Ibanez / Maxon Tube King 999 : deceptive sounding, easily beaten by a Solid-State stompbox like the DOD 250, the OCD, the RAT, etc...

If the target is simply crank the amp that follows the preamp, it should work - even fine with a suitable tone correction to avoid muddy bass tone - but if it is for producing the overdrive effect by itself before the amp, I guess it won't do the job, I'm afraid...

While I write this, having not re-read all the thread, I think that you are in the first case, @Lavane : a preamp just giving extra-gain to overdrive the amp that is following, while I was more focused on a standalone overdrive unit... Sorry.

T

 

[Lavane]

From video in the first post, look like the unit runs off a 12VAC wall wart. So, maybe those are diodes? I can't really see if they have two or three legs.

Though, I wouldn't be surprised if it had transistors like FETs in certain sections. Those tubes may be simply buffers.

There are diodes, but there are two transistors on each side about mid point on the board. The tubes could be used as buffers.
The tube phono preamp board in my main system preamp has a Jfet for the first gain stage.