Tubeworks Tube Driver sounds like ripped speaker

[Randall]

Got a 3 knob Tube Driver that sounds like a ripped speaker, just nasty. Can find no bad connections, or otherwise obvious problems. I don't even know where to start with this. Tried a new 12AX7. Anyone have any suggestions?

[mozwell]

Is the sch any of these ?

If it is....
We get 12VAC from the transformer secondary, so are all the power supply voltages ok
There are clamping diodes to voltage rails at various points, are all these ok
What is the voltage at B+ B-, these power the TL072, more than +/-18V and the TL072's may be gone.
What is the voltage at A+ A-
Are the power supply caps ok ?

Inject a suitable signal & follow the circuit through

(sorry i cant be more help)

If you have the sch & its not one of the ones i posted, then post it here for all of us to see

[Jazz P Bass]

Send BK an email.

Technical questions: tech@butleraudio.com

[Randall]

I don't think it is any of those schematics mozwell, and I haven't yet found one that looks correct. It has no model number on it that I can see, only 910-C on the board. Perhaps I'll try that email route.

[Jazz P Bass]

Here is what I could find, pedal wise.

The 910-C may be the newset version.

TubeWorks Pedal.zip

[Randall]

Jazz, that's the same set of files as above.

[guitician]

Sounds like voltages are out of spec somewhere. Or, the op-amp has failed. Is the 9v wall transformer DC output? Check it with a meter for AC voltage out. The capacitor in it may have failed.

[Randall]

Gawd, this thing is kicking my butt!! I replaced a cracked output pot, so now it's a lot louder, but I still don't think it is supposed to be so ratty and raspy sounding, almost like a fuzz pedal. Here is the schematic I am working off, it's not exact, some values are different, but it's such a simple circuit.


Were I am focusing on is the tube circuit. I am feeding a tone through it, and tracing with a scope. If I dial up the drive pot about half until the sine at the output at the second stage of the 4558 just starts to clip, and follow it across the .1uF and grid resistor (mine is 4.7K), I see a slightly smaller version of the sine on the first grid. So far so good.

But then it gets strange. I see a 2.5v p-p clean sine on the first grid and a 4.8v p-p with the top clipped on the first plate. On the second grid I see the same wave as the first plate, and a 3v p-p sawtooth on the second plate. The 68K, 470K and 100K resistors check out, and I tried replacing the 0.047 coupling cap. I lifted the 2.2K resistor that feeds the output with very similar results.

Here are the voltages I see:

8.3vdc at the junction of the plate and grid resistors.

on the tube:

1. 4.6v
2. -1.6v
3. 0v
4. 10.1v
5. 0v
6. 5.1v
7 -0.6v
8 0v
9 5.1v

Why are my grids negative? Also worth noting is the zener at the top is at 1.7v, but the other side of the 2.2K is at 10.1v, so I don't think it's the problem. I don't really quite understand how a tube can run on a 9v supply, so maybe this is why I don't see what is wrong. I have also replaced the op amp and tried different tubes, and it's quite a bit louder with some tubes than others.

Enlighten me please.

[The Dude]

I can neither confirm nor deny this, but found it on another forum. (copied and pasted)

"The 3 knobber is the Tube Works Tube Driver, Chandler made only 4 knobbers. On the original transformer power supply, it is stated as '120v, 60 hz, 15w input, 24vac@6va output'."

Since you said you are "working off" the schematic you posted, I am wondering if it's the wrong one and you simply don't have the correct power supply? If the above statement I copied is correct and the supply should be 24vac, there should be some sort of rectifier circuit in your unit.

[Randall]

Dude,

The one I have is the BK Butler Tube Works 3 knob. It is the 9vdc external Power Supply version.

[g1]

Scope the 220uF in the supply. Is it the same sawtooth that you see on the second plate?

[DrGonz78]

Why are my grids negative?

Shouldn't the grids have a negative voltage? I am not positive but is that part of how the tubes are biased?

[Enzo]

I don't know what we expect it to sound like. We have a 12AX7 with only 4v on the plates, instead of 100-200v. With a 9v B+ supply, 4v is about where we'd expect the plates to sit. The cathodes are grounded, so if we have any bias at all, it is grid leak, but with 3.3k tells me that is unlikely. So it isn't remotely a hifi stage. In your drawing, the second grid has a 470k resistor to B+, which if accurate, ought to put positive voltage on the grid. otherwise the drawing is missing a grid return.

The zener? Look at the circuit. The 9v input - or 10v is that is what yours is - fed to the 2.2k resistor, the other end is at the zener to ground, wwhich limits the voltage across the LED to whatever the zener says. The zener has no other function and doesn't affect the audio circuits.

The op amp? Look up top for the VR in a circle - voltage reference - note it is a 1/2 voltage divider (two 22k in series) across the 9v. SO VR should be about half 9v or 4.5v. That is used to bias the op amps. So is the output of the op amps hovering at around 4-5v?

[Randall]

Nope. The power supply is clean. But I'm sure now that the schem I have is not exact to this board. I have a message out to email Jazz provided requesting the correct one. And we shall see.

[MarkusBass]

Why are my grids negative? Also worth noting is the zener at the top is at 1.7v, but the other side of the 2.2K is at 10.1v, so I don't think it's the problem. I don't really quite understand how a tube can run on a 9v supply, so maybe this is why I don't see what is wrong.

If you are supplying the circuit with +9V, there is not way to get negative voltage on a grid. The only explanation is that you are not measuring the voltages referenced to the ground, or the ground track is broken. I think that the schematic that you posted is not the best one. First, suplying the heaters with 9V is a very bad idea - I would supply it with 12V. Then, the grid of the second triode connected to V+ is also a very bad idea.
Please note that other versions of the effect were supplied with AC voltage, they had both positive and negative rails, and the second grid was connected to the ground or negative rail with resistor. And it made sense.

Mark