Dr. Boogey biasing and tone stack

[MohiZ]

Hello to one and all! My name is Jouni, I'm from Finland and I'm new to this forum. Let me just say what a great forum you have here!

I've just built a Dr. Boogey as my first effect project and after some minor debugging I actually managed to get it to work. And it sounds GREAT! The only issue I have is that I built it with a custom layout on veroboard to try out my skills, and it squeals and oscillates so badly it's hardly usable at all That's why I've decided to try it again according to this layout now: http://gaussmarkov.net/wordpress/circuits/dr-boogey/.

The tone stack seems to be a tad inefficient, the best sound I got was when I put the treble and mid all the way down and bass all the way up. Is there any way to improve this? The circuit seems to have an obscene amount of high end and I wish there was a way to turn it even more down. Also, the middle seems to add treble as well in quite a massive way.

The other question I have is about biasing the J201s. Do they have to be of equal voltage to work the best? Does the bias voltage affect unwanted oscillation? I use normal 1-turn trimmers, and it seems the circuit works fine with each of the trimpots set anywhere from about 9 o'clock to 3 o'clock, although the voltage is substantially different in these positions. Also would it be better to use normal resistors instead in order to reduce hum?

Thanks!

[oskar]

Hejsan!
-tonestack
Check out the tonestack calculator...
http://www.duncanamps.com/tsc/

[MicFarlow77]

Hello to one and all! My name is Jouni, I'm from Finland and I'm new to this forum. Let me just say what a great forum you have here!

I've just built a Dr. Boogey as my first effect project and after some minor debugging I actually managed to get it to work. And it sounds GREAT! The only issue I have is that I built it with a custom layout on veroboard to try out my skills, and it squeals and oscillates so badly it's hardly usable at all That's why I've decided to try it again according to this layout now: http://gaussmarkov.net/wordpress/circuits/dr-boogey/.

The tone stack seems to be a tad inefficient, the best sound I got was when I put the treble and mid all the way down and bass all the way up. Is there any way to improve this? The circuit seems to have an obscene amount of high end and I wish there was a way to turn it even more down. Also, the middle seems to add treble as well in quite a massive way.

The other question I have is about biasing the J201s. Do they have to be of equal voltage to work the best? Does the bias voltage affect unwanted oscillation? I use normal 1-turn trimmers, and it seems the circuit works fine with each of the trimpots set anywhere from about 9 o'clock to 3 o'clock, although the voltage is substantially different in these positions. Also would it be better to use normal resistors instead in order to reduce hum?

Thanks!

Hey Jouni,

Welcome to the Forum! It's nice to see you here.

On my first Dr. Boogey, I had a very small short that kept the tonestack from functioning correctly. It took a while to find it, but it works great when it's right.

Also, on the trim pots, I would certianly use individual resistors. On mine, I actually put sockets in there and use anywhere between 22k and 47k resistors and bias to roughly half of the supply voltage. I just use the one that get's the closest to half and all of mine sound very similiar and there is so much less hiss.

Good Luck on getting yours where you like it! I know I am happy with the ones I build!

Thanks,

Mick

[ayayay!]

Hello and welcome to the forum!  I had the same problem with squeal.  Some shielded cable took care of it.

http://www.diystompboxes.com/smfforum/index.php?topic=71019.0

[Ripthorn]

Regarding biasing, I actually do it by ear.  It is not hard and you can get rather different results just by adjusting some of the trimmers.  Trimmer 1 will have the largest effect on gain, but the other ones shape the sound.  For the tone stack, I haven't noticed problems with mine, but that doesn't help you much.

As for the squealing, this is a very high gain pedal and you should shield the input wires and the wires to the gain pot.  This will make it so that your amplified signal isn't getting back in to your input signal and thus creating a feedback loop (which will squeal like mad).  I use RG-174 mini coax cable for shielded stuff, just run the braid to ground.  There is a good document on it at OLCircuits.com.  Best of luck.

[MohiZ]

Alright! I'll first try with the shielded cable, but if it doesn't take care of the problem I'm prepared to try the gaussmarkov layout. I'll report back how it's going.

[ayayay!]

I don't know if one layout is better than the other.  Some say yes, but I did the electrictabs version and it was incredibly quiet once I got the shielded cabling in. 

BUT, that being said, most people around here have used the gaussmarkov layout so you might get more eager help if you use that one.  The tonestack is scaled down in it.

Personally I'd try the shielded cabling first, then go from there.   

[MohiZ]

I just read from some posts that the gaussmarkov layout is supposed to be quieter than the electrictabs one. Not to mention I just made up my own without having the noise issues in mind  But if it'll work with the shielding, that'll be great!

[PedalBuilder]

I'm going to be be building one of these in the near future (shipments just came in from Mouser and Smallbear and I'm happy as a schoolgirl) and was a bit worried about the noise thing, too.  Is the reason for biasing with a trim first and then using a resistor to kill the noise the variance in different parts?  Otherwise, couldn't a specific resistor be calculated to use for the trims?

[MohiZ]

Ok, I just finished a very tedious process of soldering the piece together with shorter wires and shielded wire for the gain pot, and from the output and input jacks to the DPDT switch as well as from the circuit to the switch.... and... it's AMAZING! I can crank every knob except for the volume which has to be left around 3 o'clock before I get oscillation! Also, if I don't crank all the other knobs, then I can dime the volume without that annoying squeal. So mission (almost) completed for me 

I'm still gonna mess with the bias and eventually switch to normal resistors instead of the trimpots, even though it is surprisingly quiet already. Would it help to use shielded wire for the rest of the controls as well, or is it not worth the trouble? The tone stack also seems to work fine now, I think I may have wired the middle pot wrong earlier on  ..  BTW, is it normal for the presence control to affect the volume? Not that it bugs me, but the volume drops down almost to zero when I turn the presence control all the way down. I used a 27pF capacitor before the presence control instead of the 30pF capacitor suggested in the schematic.

[dschwartz]

27pF??
it should be around 3nF..(i use 47nF!!)

[kurtlives]

Wire the bypass switch for input grounded when bypassed can also help kill oscillation I hear.

Might be worth a try if your not already using that style to get rid of your last little issue.

[MohiZ]

My mistake! Of course I mean 27nF. I use the scaled down tone stack version which calls for a 30nF cap.  What does the 47nF cap affect?

I already use the grounded input method. Still I do get a little oscillation at some settings, and I was wondering if using shielded wire for the treble, middle and presence pot would do the trick of silencing it for good? I thought it would be enough to shield the volume and gain pots, since all the other pots are pretty close together in the signal chain. 

[Ripthorn]

Kurtlives, do you have a reference for that?  I am trying to think of how that would work, but seems like you would need a 3pdt switch, is that right?

[ayayay!]

Yeah, Kurtlives is referring to using a 3PDT.  And I can tell you from experience that does work.   

[kurtlives]

http://www.generalguitargadgets.com/diagrams/switch_lo_3pdt_ig_dcjack.gif    <---Use this style of wiring

http://www.generalguitargadgets.com/diagrams/switch_lo_3pdt_tb_dcjack.gif    <--- You are probably using this style now.

[Ripthorn]

That's pretty slick.  I don't think I would have come up with a way to do that with an LED.  I will have to do this for at least my Double D, it has issues when bypassed on the high gain channel.  Amazingly, my Dr. Boogie has no such issue.