Tube Zone

[Chuck D. Bones]

Next in the queue is the M I Audio Tube Zone (Valve Stem). A friend of mine brought this now out-of-production pedal to my attention. I put this board on the Wish List a while back... lo and behold! my wish was granted. It's kinda like two DS-1's ganged together with a few extra tone controls and a booster at the end. I don't usually buy a board before the Build Docs are released, but I already had a schematic so I knew what I was getting. Between that and the silkscreen, I constructed a parts list. I had created an LTSpice model quite a while back, so I had a pretty good idea what to expect from this pedal. About the only thing I plan on changing is the tuning of the PRESENCE control. In the production models, PRESENCE was an internal trimpot. PRESENCE is another treble cut at the very end of the circuit and it does more-or-less the same thing as the BRITE control. I'm moving the PRESENCE control's cutoff freq out about an octave and a half so the two controls are staggered. Everything else looks pretty damned good as-is. I'm socketing the opamp so I can try others. About the only other change I might consider is changing the DRIVE pots to A100K dual for an extra 12dB gain. Not sure that's necessary...

Here's a schematic I found on a Russian site:



Happy New Year everyone!

 

[BurntFingers]

The character control, that would be a blend between the 2 caps? Like the Timmy's bass pot.

That's a very minimal mid control too. I'm guessing that's working as a high pass filter going between 340hz and 3.4khz? Or band filter is probably more accurate.

Love your work, mr bones.

 

[Chuck D. Bones]

Thanks, Man.

CHARACTER is a bass cut before the distortion stages, just like the Timmy.

I ran a simulation and 22nF is way too small for C5. The 220nF shown in red is more like it, that's what I ended up using. I went with 10uF for C4, although it hardly matters unless CHARACTER is dimed.

The MID control looks to be pretty effective in simulation; I'll let you know how it performs in real life.

 

[BurntFingers]

Yeah man I like that mids schematic. If it works well that's pretty cool. I'd be tempted to limit its reach to under
3k but that's just me.

Or split it into 2 pots: one for lower mids, one for upper. Throat and teeth.

 

[cooder]

Excellent and another interesting circuit to wrap the head around. Thanks again Sir Chuck! Will follow this with interest.

 

[Chuck D. Bones]

Yeah man I like that mids schematic. If it works well that's pretty cool. I'd be tempted to limit its reach to under
3k but that's just me.

Or split it into 2 pots: one for lower mids, one for upper. Throat and teeth.

I'd like to think that between TONE, MID, BRITE and PRESENCE, this pedal has the mid and treble ranges pretty well covered. We'll know for sure when the build is complete.

 

[Chuck D. Bones]

And here is it! Top row: VOLUME, PRESENCE, DRIVE. Bottom row: BRIGHTNESS, TONE, MID, CHARACTER. Nice tones. Plenty of smooth sustain. Still exploring all of the tone controls. MI Audio provides a user manual on their website. PRESENCE was in internal trimmer on the production models. I made five little mods:
1. Corrected a routing error. PedalPCB is aware of this and is working on a revision.
2. Changed C17 from 22nF to 6.8nF. This tunes the PRESENCE control to a higher register.
3. Changed C5 from 22nF to 220nF in accordance with the Russian schematic, above.
3. Subbed 2N5089s for the BC549Cs. Note that the pinout is reversed.
4. Subbed NOS FD100 diodes for the 1N4148s. The curves are almost identical and the FD100s look cool.

 

[cooder]

Very nice, Sir!

 

[Barry]

Looks great!

 

[Chuck D. Bones]

Thanks, guys. Yellow was not my first color choice. I screwed up the drilling on the first chassis, so this was my 2nd try. That's one of the risks in building before the Docs come out. I'm planning to do a pour over the yellow.

 

[music6000]

Thanks, guys. Yellow was not my first color choice. I screwed up the drilling on the first chassis, so this was my 2nd try. That's one of the risks in building before the Docs come out. I'm planning to do a pour over the yellow.

Did this get a Swirly finish or did the Pour pedal stay as is!???

 

[Chuck D. Bones]

Never did an acrylic pour on this one. Or label it...

 

[notTHEwillienelson]

Never did an acrylic pour on this one. Or label it...

@Chuck D. Bones Sorry to dredge up an oldie, but did you happen to audition any other opamps in this one?

 

[Chuck D. Bones]

I did not. Since this circuit can drive the opamps to saturation, different opamps will sound different. I may have to dig this one out of the pile and give it a try...