Shaka Tube debug - I'm Stumped!?!

[Pushtone]

I used Paul Marossy's project file for the dual opamp since it is the latest revision.
The web page is here.

This is a direct
link to the file I used.
The build went so clean I totally expected it to work right off. But it dosn't and I can't figure it out. Please help.

I'm powering the circuit with a wall wart displaying  a rating of 12VAC 830mA.
It meters at 14VAC. The tube heaters are also getting 14VAC.
The tube doesn't seem to be any hotter than normal. Warm to the touch.

I'm feeding the circuit a 1k tone. There is no sound at the output of the circuit.
I can probe sound up to the 0.01uF cap that follows the opamp.
There is no sound on the other side of this cap.
The output of the opamp (pin-1) sounds like a synth, motorboats, and drops over an octave
in pitch as the DRIVE pot is lowered. At max DRIVE it sounds like the input 1k tone, but distorted.

Here are my voltages.

Power supply
V- : -9.27VDC
V+ : +13.15VDC
BIAS: 0.04 (trimmer adjusted)


12AX7 Tube
Pin-1: -4.79VDC plate
Pin-2: -7.63VDC grid
Pin-3: -8.31VDC cathode
Pin-4: 14VAC
Pin-5: 0
Pin-6: -5.99VDC plate
Pin-7: -7.56VDC grid
Pin-8: -8.17VDC cathode
Pin-9: NC


TL072 Opamp

Pin-1: 0
Pin-2: 0
Pin-3: 0
Pin-4: -9.23VDC
Pin-5: 0
Pin-6: -7.87VDC
Pin-7: -7.87VDC
Pin-8: +13.14VDC


Any suggestions would be much appreciated.

Dave S.

[Pushtone]

I've meter a behavior when powering up from a "cold start" with the caps fully discharged.
Pin-1 and 6 on the 12AX7 go to positive 12.95 volts for a few seconds, then drop slowly to the neg voltage posted above.
Pin-2 and 7 also go positive to +3.21 volts for a few seconds then drop into the neg voltage and sits there.

Dave

[Paul Marossy]

Huh, that's some kind of strange symptoms. This layout is basically what I built my own Shaka Tube from.

Here's a few thoughts:

1. AC voltage is too high. I used a 100 ohm resistor in series with the AC power supply to drop it down closer to the 12.6 VAC. You can go +/- 10% on the heater voltage, but more than that should be addressed.

2. Bad or worn out tube.

3. Something is miswired at the tube socket, or at the V+/V-/Bias connections. I suspect something in the bias wiring since that is what sounds the most screwy.

4. Perhaps the opamp is faulty. Have you tried any other ones to see what happens?

5. Are you sure there isn't a mistake on the power supply board - like a backwards diode or cap?

[Pushtone]

3. Something is miswired at the tube socket, or at the V+/V-/Bias connections. I suspect something in the bias wiring since that is what sounds the most screwy.

Uh? Isn't bias supposed to be around 0 volts?!?
The trimmer can swing the bias between +13V and -9V.
Should bias be trimmed to another reading?

Thanks Paul. I'll go thought your list of things to check.

[Mick Bailey]

Bias is favourite. Some builds omit the bias and hard wire to V-. Unless you have sufficient negative voltage, you won't get any output. Try it hard overt o the negative side as a starting point and check from there.

Your V- looks too low considering the input voltage. the V+ also looks a little low.

Try disconnecting the cap on the tube side and audio probing there to isolate the op-amp stage.

[Paul Marossy]

Uh? Isn't bias supposed to be around 0 volts?!?
The trimmer can swing the bias between +13V and -9V.
Should bias be trimmed to another reading?

That seems correct. But the bias shouldn't be around 0V, AFAIK.

In my own Shaka Tube, at the time that I had built it, I had measured these voltages:
V+ = +11.8V
V- = -14.6V
Bias = -13.6V

Hope that helps...

[Pushtone]

Got it working AND loaded into the box.

SOUNDS GREAT!


Thanks Paul, Aron, Jack.


Too tired to tell you all the debugging drama. It was a combination of things.
Getting the heater voltage down to 12V was key though.
And the PSU voltages from Paul helped too.

Here's a pic.



And an inside shot of the non-working pedal.
Looks pretty much the same now except there is a big 5W 10ohm ceramic crammed in next to the tube to lower that heater voltage.


Yes that is an extra "vanity" LED to light up the tube from the inside.
I cut that bit out while trouble shooting.

Thanks all for the comments. It kept me poking at it. Another successful DIY debug session.
Dave S.

[Paul Marossy]

Awesome! Beautiful looking build, too. 

[Pushtone]

Hey Paul,

Where did you hook up the LED on yours?

I soldered the +side of the LED to the long horizontal jumper in the middle of the board. Seems to work OK.

Dave

[Paul Marossy]

Hey Paul,

Where did you hook up the LED on yours?

I believe that I have it inline with one leg of the AC power coming from the power jack.

[aron]

wow, that's one amazing pedal!!!!!!  WOW!

[Pushtone]

Thanks Aron. And thanks for the whole Shaka circuit line.

The tone is great. I might have to build everything with shaka in the name!


Paul, thats how I had my LED wired. Thought it might be part of the problem.
That was one of the things I changed thinking it would be better to get the +V for the LED after its been made DC.

[Paul Marossy]

Dunno.... mine worked fine. In any case, glad you got yours working. 

[Paul Marossy]

I was originally thinking of doing something like you did, but I never felt like the tube was going to be protected enough, so I put it inside the enclosure.

[Pushtone]

My take on the ST is totally meant to be eye candy trophy pedal with the tube on top because thats what I wanted.

Pedals with tubes sticking out of them are like flames painted on a car.
Not very practical but sure looks cool.

Paul, I thought about making your bracket. It is well designed and simple to make.
I totally geek-out at how the tube mount is secured by the footswitch. Brilliant box layout!
One can not help but be inspired after looking at your DIY engineering.


Anyone looking into a Shaka Tube build will certainly want to check out Paul's build report and layout on his web site. www.diyguitarist.com



And to think you thought about shutting it down. tsk tsk tsk

[tranceracer]

Actually that tube thru-enclosure facade is great conversation piece.  I've already had one person ask me "is that a "real" tube in that pedal?" on my li'l Matsumin OD pedal.  My answer is uh-huh it shore is!   ...and I show them the dim glow!  I see a big and then an ...oooh!  I lol to myself! 

[Pushtone]

Then let them touch it so they can feel the burn, all 12 volts. Ahh tube powered at last! 

  I lol to myself! 

You laugh out loud to yourself??
You are obviously a deranged individual.

[Paul Marossy]

Paul, I thought about making your bracket. It is well designed and simple to make.
I totally geek-out at how the tube mount is secured by the footswitch. Brilliant box layout!
One can not help but be inspired after looking at your DIY engineering.

It was one of those moments where I actually had a good idea, a revelation, a "Eureka!" moment... 

[tranceracer]

You laugh out loud to yourself??
You are obviously a deranged individual.

... I hear laughing, screaming and the voices... those gaud awfol voices ...  !!!   

[awitee]

hey guys, i also built the shaka tube
its not working!! darn it
how do you measure for the v+ v- and bias voltage? with the black probe on ground? coz when i measure mine the values are all postive and the values of bias range only from 6+v to 10+ v when adjusting the trimpot while the v+ and v- dont seem to change at all, am i measuring it wrong?
the v+ v- and bias from the power pcb is supposed to be connected to the v+ v- bias on the tube/opamp pcb ryt? with v+ going to v+ and so on?
the 12vac and ground of the tube and the power pcb are connected to the dc jack ryt?
darn it, cant get it to work
the in ground, out ground, dc jack ground, tube ground, 3pdt ground, power pcb ground, are all connected ryt?
pls help guys... i would really appreciate it.. thx
im am using a ecc832 tube btw
im using a regulated 12v power supply, dc