Tone stack for DOD 250

[notneb]

HELP!! I'm such a newb. Built the DOD 250 overdirve, ala Beavis audio, (doesn't he do the easiest-to-read schematics?), and I love the way it sounds with 2 LEDs replacing the stock diode matrix. I'm trying to incorporate the VOX tone stack as per the Tonestack Calculator from Duncan and it sounds like crap so far. The bass is super muddy and the treble is very "tinny"/ AM radio sounding. Really killed the gain, too. Already tried the Marshall and it had almost no effect. How does it wire into the pedal circuit? Duncan's diagram has the signal on the left, the top of which I took from just before the main volume pot on the pedal and grounded the bottom. ?!? They have the output at the top (and rather ambiguous to a newb like me) with no point of contact indicated so I ran that back into the volume pot. The load resistor R5 has me confused. Don't kick me off the board for asking such a dumb question, but is that "load" as in, it represents the load that the pedal should be showing to the tone stack, or a resistor across the output, parallel with the pedal as a buffer of something?

[GibsonGM]

Hi Ben,

No apologies necessary, man!  It's tough being new.  One thing you could do is post a link to the schematic when you have a question so we can just click it, but that's ok.  The Schem. is HERE  http://www.beavisaudio.com/schematics/DOD-250-Overdrive-Schematic.htm

Ok, what you have is a case of trying to crowbar something into a place where it won't work  that good.    Which is cool, it's called "experimenting" and is a wonderful thing!  I remember the same "WTH???" feeling when you work at something and this happens.

What seems to be the trouble is that when you sim the tone stack in TSC, it expects a certain input and output impedance.    The "Load" resistor is simulating the input impedance of your pedal or the rest of an amp, yup!   So you are really mismatched, and the parts in the stack won't do what they're told to.  It makes a big difference what comes before and after filter circuits, since they will interact.  That's the simple answer.     Plus, you lost tons of volume, called INSERTION LOSS, because there wasn't enough voltage there to drive the thing AND keep a good signal level.    Try changing the load resistor from 600K to 10K and see what happens!!!!   The lower resistance 'sucks' the level away on you.

SO:  we need additional gain stages and/or buffers.   Look at THIS bad boy:  https://www.generalguitargadgets.com/pdf/ggg_mgv_sc_guv.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a      This is what the 250 became over time, when other designers got their hands on it. 

There is another gain stage there, and the values of resistance/capacitance in the tone stack have been tweaked to work well with the input impedance of the pedals or amps that may follow the Guvnor. 

You CAN put a WHOLE stack in your 250, but to do so, you'd have to add a recovery stage or buffer after the stack, turning it into something a lot more like the Guv.     So the question is, do you WANT to, or do you want to just build a Guv?

If you just add a tone stack to a 250, you'd want another gain stage and to use the values shown on the Guv.

Hope that helps!

[notneb]

Thanks, Mike, for the speedy response! BTW, I didn't post the link because I wasn't sure if that was allowed. I really like the Beavis Audio site and didn't want to over step. I expected to lose some gain with the tone stack and assumed I'd have to bring it back up, but figured I'd have to try it out to find out just how much I'd lose. Found out real quick. I really needed to know if I was hooking the ins and outs correctly so I'd know if I had a starting point to start tweaking. Seeing the GUV schematic throws some perspective on it. While we're at it, is it necessary to use log B pots, or will linear of the correct value work? I expect a difference in "feel" when turning the pot but as long as the value is the same it should have the same overall effect, correct? Thanx again.

[notneb]

  OK, while looking at the GUV, I'm struck by how similar it is to the DOD. Just add tone and another gain stage and whoopee. And compare the DOD to the MXR... well you get my point. I realize they are very basic circuits, and you can't really patent a super basic, "common knowledge" idea. I posted a question a while back about how different designs have to be to not infringe on someone else' design. I guess there's no simple answer, but it seems like they're so similar that these guys would be fighting over who did what first, and who's ripping who off. I guess it's like Eddie being accused of ripping off Clapton, being accused of ripping off Hendrix.... yada yada yada. Analogy correct?

[bufferz]

Ya, you will be hard pressed to find novel ideas - a lot of these ideas can be found on the data sheets provided by the parts manufactures. I wouldn't worry too much about infringement, just continue to be be honest about where you are getting your ideas from and have fun

[gjcamann]

For the dod250 and dist+ look for the article by Brian wampler about mods to this pedal. He shows some good ways to tweek the tone. I think it was in guitar player mag online.

[TGP39]

Mike, I wanted to thank you for the above explanation you offered. It helped another newbie tremendously. Steve.

[GibsonGM]

Wow, very glad to hear that, TGP )   In some ways, we're ALL newb's at certain things! Depends what you spend your time doing, I think....you can't know everything about EVERYthing in this hobby! 

There's always something to learn 'round these here parts! 

>>>  I missed Ben's last post up there from last week!   Usually you use "B" pots, which are linear.  A few designs might vary from that, but I'd stick with linear tapers for the most part.

[notneb]

Thanks again for the info Mike. I tried the simple tone stack at the very bottom of the page here- http://www.generalguitargadgets.com/richardo/distortion/  Interesting though, I originally wired it as shown and couldn't hear any discern-able effect. Then I tried putting it in series, (swapped 2.2nf for 1nf) between the diodes and C6 before the output and got a sweeeeet, usable little tone control. Nice roll-off on the highs without any mud in the low mids. Overall, I'm tickled with the sound I ended up with. Nice classic-hard rock pedal. Not metal, but that wasn't what I was shooting for with this one.