I just hooked my TH Custom tube driver up to my test rig, and it worked, but was very quiet. I pulled it off, reflowed and checked for bridges. When I hooked it back up to test again, the power pulses at a rate of about 4 times a second, The LED in the tube socket flashes like its on an LFO. I haven't taken voltages because I'm afraid it will hurt it to connect power for long. I did try another test rig, just to be sure, and it is the circuit, not the rig.
Also had a couple questions on this build...
1. Which way does the voltage regulator orient? It is cropped out of the pictures on the build doc, and I guessed at it.
2. Whats with the omitted components? R2, R9, R24 and C18 were left empty because I didn't know what to put there. The build doc just omits mention of them, or has "--" where the value should be.
Thanks.
(https://dl.dropboxusercontent.com/u/13215910/Web%20Images/20150418_161014_resizeda.jpg)
(https://dl.dropboxusercontent.com/u/13215910/Web%20Images/20150418_160914a.jpg)
I'm now seeing that my use of 40106BE may be a problem. Build doc calls for 40106N.
Quote from: AntKnee on April 18, 2015, 10:04:22 PM
I'm now seeing that my use of 40106BE may be a problem. Build doc calls for 40106N.
I used the 40106BE in mine so that is not the problem. Triple check every diode orientation, then reflow everything around the power section (40106 and all diodes). Start with that and I can pull mine apart and get proper voltages for you, etc.
There are two different things.
1) the led is directly connected to the 6v regulator, so the voltage multiplier has nothing to do with it.
Is your psu strong enough to power it?
2) the multiplied voltage can be meassured after the last multiplier diode. It should be appx 60 v
Thanks, man, but no need to get voltages now. I decided to replace the 40106, but upon removing it discovered I had put the socket in backwards, which led me to put the IC in backwards. Oops! That issue is solved.
Now I am noticing that my bass knob does nothing and the effect is very bright.
Quote from: Thomas_H on April 18, 2015, 11:10:04 PM
There are two different things.
1) the led is directly connected to the 6v regulator, so the voltage multiplier has nothing to do with it.
Is your psu strong enough to power it?
2) the multiplied voltage can be meassured after the last multiplier diode. It should be appx 60 v
Why are the part values so different between the BOM and the schematic? I'm trying to double check my values and they are very different in some cases.
Thats because the initial circuit is build with calculated ot default values -which is what is in the schematic.
Afterwards the circuit is tweaked to work better/sound better - thats what is in the BOM.
The BOM is whats in the lead when it comes to,values.
R2 and R9 aren't necessary, but you'll need to install R24 for the bass pot to work. The BOM calls for 220k in that position. C18 can be used to roll off some fizziness. If you install some socket pins, you can try different values in that position starting with 1n, or just leave it out if it sounds OK as is.
Quote from: oldhousescott on April 19, 2015, 02:24:24 PM
R2 and R9 aren't necessary, but you'll need to install R24 for the bass pot to work. The BOM calls for 220k in that position. C18 can be used to roll off some fizziness. If you install some socket pins, you can try different values in that position starting with 1n, or just leave it out if it sounds OK as is.
Thanks, mine is a bit fizzy, I'll play with it. As for R24, it is installed, but bass doesn't work. Does R23 need to be installed? It has no value for it on the BOM.
Yes, R23 should be installed. It's not perfectly clear from the BOM, but R23 looks to be grouped with R10..R16 and should be 10k.
Quote from: oldhousescott on April 20, 2015, 12:37:43 AM
Yes, R23 should be installed. It's not perfectly clear from the BOM, but R23 looks to be grouped with R10..R16 and should be 10k.
Holy missing cel outlines! You're right!
I completely missed that.
Thanks!
Quote from: AntKnee on April 20, 2015, 01:00:56 AM
Quote from: oldhousescott on April 20, 2015, 12:37:43 AM
Yes, R23 should be installed. It's not perfectly clear from the BOM, but R23 looks to be grouped with R10..R16 and should be 10k.
Holy missing cel outlines! You're right!
I completely missed that.
Thanks!
Indeed that R23 is crucial for the baxandal stack. I played a lot with the tonestack values to warm it up. Pretty happy with the results overall.
Quote from: pryde on April 20, 2015, 02:28:11 AM
Quote from: AntKnee on April 20, 2015, 01:00:56 AM
Quote from: oldhousescott on April 20, 2015, 12:37:43 AM
Yes, R23 should be installed. It's not perfectly clear from the BOM, but R23 looks to be grouped with R10..R16 and should be 10k.
Holy missing cel outlines! You're right!
I completely missed that.
Thanks!
Indeed that R23 is crucial for the baxandal stack. I played a lot with the tonestack values to warm it up. Pretty happy with the results overall.
Do you recall what values you settled on?
So I had the tone stack caps socketed and started with a standard baxandall arrangement:
C28: 470p
C29: 4.7n
C30: 330p
C31: 3.3n
This will get you a dead-flat EQ in the bass/treble at 12 o'clock position with full mid-hump CCW and full mid-scoop CW.
Try these and see if you are happy. I upped C30 to 1n and C31 to 4.7n to knock treble freq down even more and kept C28/C29 at above values.
Tube choice is also VERY important as well. A 12AY7 or 12AT7 still had a lot of gain and reduces harshness.
The end result of mine with demo:
http://www.madbeanpedals.com/forum/index.php?topic=20371.msg198804#msg198804
You can dink around with Bax tone stack values using the Duncan Amps Tone Stack Calculator (http://www.duncanamps.com/tsc/). Use the James tab (which is the passive version of Bax circuit).
Thanks, guys!
As far as tubes, I have a 12AX7, 12AT7, and 12AU7. Tried the AT, but it was VERY driven. I will try the AU. I was hoping this would act more like a tube preamp, and not be so much of a distortion pedal, but it is what it is. Would a different IC help clean it up? Maybe a TL071, or a TL061?
A chip change won't do much. Instead, remove R10 and replace it with a 1M pot wired as a variable resistor. This will allow you to reduce the gain between the two tube stages. If you don't want to permanently leave in the pot, find a position on the pot that gives you the best compromise in conjunction with the Gain control, remove the pot and measure the resistance at that position, then substitute the closest value resistor back into R10.
Starved plate tube designs, like this one, are inherently more distorted than full voltage designs for a given input signal level.