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Got my Tube driver going, got a couple questions


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1/29/2001 3:15 AM
Ben S
Got my Tube driver going, got a couple questions
All righty!! I got my tube driver going tonight and I am very pleased. I used a used tube socket and had to retension it to get the thing working (love/hate and salvage parts)but it works.  
 
 
 
First impressions are that it is very buzzy. I'm gonna even say it sounds solid state. I don't know the brand of 12ax7 I had in there so I pulled it and remembered that some had had better luck with their TD's and 12au7's. Just happened to have one on the bench to try it out. Much better distortion sound. Much better. I like it a lot more this way but... It still isn't heaven yet. Oh and the low tone control is totally non-functional. Gotta track that down..  
 
 
 
SO, 'bout that starved plate stuff...  
 
 
 
Iam wondering if rasing the voltage between plate and cathode might make these pedals less choosey about the tubes they use.... Any body got any comments on how to go about this????  
 
 
 
Can I use a separate power supply for the tube as long as they share a ground??? I have several tranny's that could be used to raise the B+. One would go as high as 200vdc. What kinda problems am I in for???  
 
Another tranny would put the B+ at about 50vdc. That'd give about 65volts between - and +. That's about double what I have now. Whattya think folks? Will this work to homogenize the pedals' response to different tubes? How do insure proper bias???  
 
 
 
God I'm fulla questions. Guess I'm a little excited at finally getting around to completing my TD breadboarding
 
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1/29/2001 2:04 PM
Doug H

quote:
"First impressions are that it is very buzzy."
 
 
Which one did you build? The 9V version or the 12V BKButler version that John Greene drew up?  
 
 
 
 
 
quote:
"Iam wondering if rasing the voltage between plate and cathode might make these pedals less choosey about the tubes they use.... Any body got any comments on how to go about this???? "
 
 
You might consider "upverting" the dc voltage. Check this out:  
 
 
 
http://members.aol.com/sbench101/#Power  
 
 
 
There might be an idea in there.  
 
 
 
I proto'ed the BKButler Tubedriver back before the holidays. I discovered one of the keys to getting a decent tone at these low voltages is to keep the input Z of each tube stage really low. This circuit uses these 10K (!!) grid shunt resistors. I tried increasing them to 470K and yowww! Buzz city!  
 
 
 
This thing didn't sound buzzy to me. It was warm and sustainy, but not a hi-gain tone at all. My only complaint is it had some intermod distortion that caused some blatty harmonics when I cranked up the gain and played chords with my neck p/u. I tried various & sundry ideas including some RC filtering in the cathode circuits but couldn't get it to go away. My conclusion is it's not a bad circuit, but as overdrives go I've been able to rival (and surpass) it in some ways with SS stuff I've built.  
 
 
 
Now, having said all that... FWIW, I've come up with a pretty significant mod to this thing that I really like. It solves all the aforementioned problems and then some. I want to do a couple sound samples and then I'll put up the schematic. I think you guys will like this, I think it's fairly unique for these starved plate circuits.  
 
 
 
Doug
 
1/29/2001 5:58 PM
Ben S

>I proto'ed the BKButler Tubedriver back before the holidays. I discovered one of the keys to getting a decent tone at these low voltages is to keep the input Z of each tube stage really low. This circuit uses these 10K (!!) grid shunt resistors. I tried increasing them to 470K and yowww! Buzz city!<  
 
 
 
Glad to have your comments.  
 
 
 
>This thing didn't sound buzzy to me. It was warm and sustainy, but not a hi-gain tone at all. My only complaint is it had some intermod distortion that caused some blatty harmonics when I cranked up the gain and played chords with my neck p/u.<  
 
 
 
I think I have a little of this happening too. I wonder if it is due to the low voltage operation of the tube? Why would you run the tube on low voltage like this(other than the fact that 12v transformers are cheaper than HV trannies)  
 
 
 
 
 
>I tried various & sundry ideas including some RC filtering in the cathode circuits but couldn't get it to go away. My conclusion is it's not a bad circuit, but as overdrives go I've been able to rival (and surpass) it in some ways with SS stuff I've built.<  
 
 
 
>Now, having said all that... FWIW, I've come up with a pretty significant mod to this thing that I really like. It solves all the aforementioned problems and then some. I want to do a couple sound samples and then I'll put up the schematic. I think you guys will like this, I think it's fairly unique for these starved plate circuits  
 
 
 
Doug<  
 
 
 
Oh man, I'm drooling. I am really pumped up to figure this bugger out. I'll trace out the tone stack tonight or tomorrow, home improvement chores allowing, and get back to ya.  
 
 
 
BTW what tube did you use. I was surprised at how well the 12au7 worked.  
 
 
 
Later, Ben S
 
1/29/2001 6:14 PM
Doug H

quote:
"Why would you run the tube on low voltage like this"
 
 
Mainly I was just curious. I had heard so much about the BKButler Tube Driver, Eric Johnson likes his, etc, etc... I had built a starved-plate circuit back in the 80's (from a GP article, I believe) and it sounded terrible. I just wanted to try this one after hearing so much about it.  
 
 
 
quote:
"(other than the fact that 12v transformers are cheaper than HV trannies)"
 
 
I used a $5 12VAC transformer wall wart I got from Mouser. It simplifies PS construction and has the added bonus of physically isolating the transformer from the rest of the circuit - very low noise and no hummmmm...  
 
 
 
quote:
"BTW what tube did you use. I was surprised at how well the 12au7 worked."
 
 
I liked the sound of my telefunken 12ax7. But it worked with a 12au7 as well. When I had the tone stack problem, it sounded bad with a 12ax7 but decent with a 12au7. That's why I suspected that may be your problem too.  
 
 
 
Doug
 
1/29/2001 8:07 PM
Ben S

Cool, I'll look into the tone stack when I get home.  
 
 
 
'bout the low voltage comment, I should say "Why would anyone use this starved plate approach?" I didn't just mean you in particular, Doug.  
 
I built mine due to hype from articles about Eric Johnson and David Gilmour. I think that their overdiven sounds are awesome so you can see why I'm so interested.  
 
 
 
Have you done a PCB for yours or is it still on the breadboard?  
 
Later, Ben S
 
1/30/2001 1:25 AM
Doug H

Nope, still on the breadboard. PCB layout is almost finished.  
 
 
 
I think the appeal of the low-voltage stuff was lower cost and easier to build safely into a pedal. For me, it's easier to tweak than HV stuff because I can slap it on a breadboard. With the safety considerations of HV it takes a lot longer to tweak with (although I love tweaking with my amp).  
 
 
 
Doug
 
1/29/2001 3:58 PM
Doug H
Check your tone stack wiring
Ben,  
 
 
 
I didn't catch this the first time:  
 
 
 
[QUOTE]First impressions are that it is very buzzy.[...]  
 
Oh and the low tone control is totally non-functional. Gotta track that down..[/QUOTE]  
 
I remember a similar problem when I first wired up mine. Check and double check how your tone stack is wired. I seem to remember having my 22k or 330p wired incorrectly- no lows, *very* buzzy. You might find fixing the tone stack will remove the buzz.  
 
 
 
Doug
 

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