Yet another Boogey thread. Adding Mark Hammer's stupidly wonderful tone...

[jimmybjj]

I built a couple of these and do not really dig the tmb setup and would like to make it a single tone control. I found this thread http://www.diystompboxes.com/smfforum/index.php?topic=41298.0 What does the stuff after Q4 do? It is referenced as a ROG style sim, does it act as some sort of HPF/LPFfilter? I have built this version from gaussmarkov toneless PCB layout with success and would like to use it for the tone control version so i don't have to build another one, so i will just add a pot with the extra stuff coming directly off the pot, terminal strip style. Does this seem like a good idea? If it is would I leave the ROG stuff after Q4 or would i eliminate this stuff? Again, i would really like to know what the ROG stuff is really doing if someone has time to explain what is going on in those particular components.

Links

toneless thread with reference to ROG sim   http://www.diystompboxes.com/smfforum/index.php?topic=41298.0

toneless boogey   http://gaussmarkov.net/layouts/drboons/project.pdf

stupidly wonderful tone control   http://hammer.ampage.org/files/SWTC.gif

regular dr boogey   http://gaussmarkov.net/layouts/drboo/drboo-project.pdf

thanks for any help.

[Mark Hammer]

Using the gaussmarkov "toneless boogey" as a reference, the networks formed by R13/C11 and R14/C12 are two cascaded lowpass filters, with a rolloff set at around 4.8khz.  Since there are two such networks, that makes for a 2-pole, or 12db/oct rolloff, such that content at 9.6khz is 12db down.  The filters are fixed, and presumably optimized to someone's taste.

The SWTC provides for a variable lowpass, but is only 1-pole or 6db/oct, so the effect is subtler.

If you find the corner frequency of 4.8khz too bright or too dull, there are some things you can do.  One of these is to use an on-off-on DPDT toggle to alter the corner frequency by selecting between cap values.

If you had a second cap of 4700pf between C11 and ground, and C12 and ground, when none of those caps is bypass, you have an effective capacitance of around 1500pf and a rolloff beginning around 7khz (which is effectively full bandwidth for most distortions).  Shunt the 4700pf and you go back to 2200pf and a 4.8khz rolloff.  Flick the toggle the other way and you shunt the 2200pf caps, making the effective capacitance 4700pf and yielding a rolloff at around 2.2khz.

If 4.8khz was too bright for you to start with, then consider replacing C11 and C12 with a 3900pf and 6800pf cap pair.  When neither of the caps is shunted, the rolloff is around 4.3khz.  Shunting the 6800pf caps gives you a rolloff at 2.7khz, and shunting the 3900pf caps gives you a rolloff at just over 1.5khz.  So, there is roughly a one octave change in rolloff point with each switch position.

If this is not enough variety for you, then I suggest replacing R13 and R14 with an 8k2 fixed resistor and dual-ganged 10k pot.  The pots are wired up such that the resistance preceding each cap now varies over a 8k2-18k2 range.

Change the cap values to .0039uf, and the rolloff will be continuously adjustable from around 2.2khz to around 4.9khz.  That might not seem like much but the 12db/oct rolloff yields a lot of effect.  If it is still too bright for you, make those caps 4700pf to shift over to a 1.8khz - 4.1khz range.

EDIT:  Just to note, the SWTC is not MY tone circuit.  I have found it in use in many places (even Z-Vex effects) and simply drew it to people's attention.  So it should be the SWTC.  I'll happily take credit for what is truly my idea, but do not wish to take any credit for what is already out there.

[TimWaldvogel]

 thunk somebody should develope a dr.boogey that's relatively simple. Like something that just rolls off high end like the SWTC. That way they could readjust it for that great boogey tone without the complications

[jimmybjj]

Using the gaussmarkov "toneless boogey" as a reference, the networks formed by R13/C11 and R14/C12 are two cascaded lowpass filters, with a rolloff set at around 4.8khz.  Since there are two such networks, that makes for a 2-pole, or 12db/oct rolloff, such that content at 9.6khz is 12db down.  The filters are fixed, and presumably optimized to someone's taste.

The SWTC provides for a variable lowpass, but is only 1-pole or 6db/oct, so the effect is subtler.

If you find the corner frequency of 4.8khz too bright or too dull, there are some things you can do.  One of these is to use an on-off-on DPDT toggle to alter the corner frequency by selecting between cap values.

If you had a second cap of 4700pf between C11 and ground, and C12 and ground, when none of those caps is bypass, you have an effective capacitance of around 1500pf and a rolloff beginning around 7khz (which is effectively full bandwidth for most distortions).  Shunt the 4700pf and you go back to 2200pf and a 4.8khz rolloff.  Flick the toggle the other way and you shunt the 2200pf caps, making the effective capacitance 4700pf and yielding a rolloff at around 2.2khz.

If 4.8khz was too bright for you to start with, then consider replacing C11 and C12 with a 3900pf and 6800pf cap pair.  When neither of the caps is shunted, the rolloff is around 4.3khz.  Shunting the 6800pf caps gives you a rolloff at 2.7khz, and shunting the 3900pf caps gives you a rolloff at just over 1.5khz.  So, there is roughly a one octave change in rolloff point with each switch position.

If this is not enough variety for you, then I suggest replacing R13 and R14 with an 8k2 fixed resistor and dual-ganged 10k pot.  The pots are wired up such that the resistance preceding each cap now varies over a 8k2-18k2 range.

Change the cap values to .0039uf, and the rolloff will be continuously adjustable from around 2.2khz to around 4.9khz.  That might not seem like much but the 12db/oct rolloff yields a lot of effect.  If it is still too bright for you, make those caps 4700pf to shift over to a 1.8khz - 4.1khz range.

EDIT:  Just to note, the SWTC is not MY tone circuit.  I have found it in use in many places (even Z-Vex effects) and simply drew it to people's attention.  So it should be the SWTC.  I'll happily take credit for what is truly my idea, but do not wish to take any credit for what is already out there.

Mark thanks for the concise explanation, very educational. I think I am going to socket the caps and see if i can find something that works with the filter. Now that i have your explanation i know where to start. If i can't find anything i want to stick with I'm going to try the dual gang option. Do you have any links or can you point me to some educational material that explains what you were talking about (rolloff, 2-pole, corner) I would like to have a better understanding. Thanks again for the response.

[jimmybjj]

...one last question. What does the 27n(c10)  at the Q4 drain do? Does it play a role in the LPF? Thanks.