Cant figure out this switching.

[swever]

Breadboarded this http://www.diystompboxes.com/smfforum/index.php?topic=77456.0

I really like how it sounds and now I have an idea to make a pedal with two footswitches where one would bypass the whole thing and the other switch between with and without the emitter cap thing. Piece of cake so far. Then I realized that I would love to be able to have an extra toggle that would switch between the tonestack engaged all the time AND only engaged when the emitter cap mod is engaged.

Will be happy to see any ideas, directions or ready solutions.

PS I have 3PDT footswitches, DPDT on-on and DPDT on-off-on toggle switches.

[GibsonGM]

I think you could do this with a DPDT.  "Left side" of DPDT has a wire going from above the emitter R in to the middle of the switch...."bottom" lug goes to the cap, to ground.  The "top" lug is empty....when the top is selected, the run to the cap goes nowhere so you just have the resistor in circuit.

"Right side" of DPDT would be set up to SHORT across the SWTC at the same time the cap is NOT engaged...can you picture what I'm getting at?  You can jump over the SWTC with a piece of wire, and the switch opens the jumper when you want SWTC in the circuit.

[GibsonGM]

Here, nearly illegible drawing, LOL  http://doodle.ly/doodles/583201e38dd49e6240f6225c

On left is emitter resistor, and on right is SWTC components. Likely you have the volume control after that?   You'll have a volume loss when SWTC is engaged...

[swever]

Thanks, Mike! It's funny how it becomes so obvious onсe you see it 

I used a 3pdt footswitch instead of dpdt in your drawing. It's great for rhythm/lead/chorus/verse variation.
I also added a spdt to switch between tonestack always on/only on when cap mod engaged.

There is no noticebale volume difference between with/withoug SWTC. At least when it's fully open.

The whole thing works great - quite flexible and versatile and has a great tone character for such a simple circuit.

[GibsonGM]

Awesome, I'm glad it works!   With the 3PDT, you could have a status LED...I still get buggery over switching options like this, ha ha.  I just draw them out.

Yeah, fully open the SWTC isn't really "in", so it would be as you're cutting highs that any vol. loss would occur, and may not be too bad, compared to more advanced tone controls.   

Some good ideas you've incorporated into your pedal, Swever!  Enjoy it 

[swever]

Just finished stuffing this bad boy into 1590B. I think I will use a BB next time I build anything with two footswitches - there just is not enough surface on a B for controls and fs's. Still, this one is perfectly usable, just have to take care not to stomp on the knobs while switching. And I am very satisfied I managed to fit it all 

Need to add indication. Can't make up my mind if I should "waste" one of the RGB LEDs or order some bicolros and wait 

You were actually right about the volume drop, Mike. It is there. Also "vanilla muff fuzz" mode is ever so slightly louder (higher peak-to-peak) than "emitter cap mod" mode. Those two factors make for quite noticeable volume difference between the modes. Switched back to the "tonestack on in both gain modes" and it's almost even. Maybe I should substitute the "tonestack bypass" to slight level reduction on "vanilla" mode if I ever build this again. Or even add a separate volume control for the second mode.... so many ideas so little time 

[GibsonGM]

Very nice, clean build, Alexander!  Mine are VERY messy, after 15+ years, LOL!  I can't fit more than one 3pdt in one of those...

You could add a resistor to the 'tone stack bypass' line, to drop ITs level as well, if the volume drop of the SWTC concerns you...I'd probably consider just putting a voltage divider in there - use a pot to find out what resistors to use, replace with fixed values...

good work! 

[swever]

https://youtu.be/Di3PBg-p3Pk

Please excuse my sloppy playing 

I think I have to do something with the volume difference. It's a bit exaggerated on the vid (probably because of dynamic processing in the camera being more sensitive to low freqs that are more pronounced in "red" mode") but it's still there. I think I will omit the "tonestack bypass in green mode" thing and substitute it for a voltage divider to lower the output of the green mode a bit.

Agian, I'm having a trouble warping my head around this stuff. Does it look right on this drawing?

[GibsonGM]

Hey, the playing wasn't bad, LOL - good noodle, try the pedal out stuff, man!  We're not auditioning on here...
Like how it sounds, it was definitely a useful mod!    The vol. difference isn't bad, but yes, it might be cool to adjust it. You COULD just use an internal trimmer to do so....like, 100k....

let me think on what I think you're trying to do, Alexander - I will get back shortly with a drawing.    You want "emitter cap plus tone stack", and if that is off, "voltage divider on", correct?

[GibsonGM]

Ok, I have thought a bit about what you're trying to do...."green mode" is no bypass cap/tone stack jumped, and "red mode" is bypass cap inserted/tone control in, right?

We need some basics.....OK - a bypass cap allows AC frequencies to.....bypass...the emitter (or cathode in a tube circuit).  They work nearly the same in either type circuit.    Without the cap, you don't have as much GAIN.  This is due to a lot of (somewhat complicated) stuff, but you could think of it as....there is a feedback path from emitter (cathode) to base (grid) which 'stabilizes' the signal.   Putting the cap on the emitter (cathode) prevents the emitter (cathode) from 'following' the base (grid)...it smooths out AC variation, holding the bias steady, and therefore the stage can realize its full gain potential (or nearly so).   You can use this to boost volume, 'drive' (distortion), or both...sounds like here, you're using it to increase fuzz....

Ok?  You're 'cranking' the transistor with the cap.    A BIG cap (several uF, or 10's of uF) will allow ALL audio frequencies thru, so it all gets boosted.  If we make that cap SMALLER (like, .22uF, .1uF, etc...) we start cutting bass out.   So, we can use it to shape tone!!

To make this long story short - do you need to make the green channel more quiet, or do you need to put a smaller cap in there to cut some bass, make the tone less muddy and so on?   Maybe if you lower the value of the cap. the channels will seem more balanced, as the low end will be less and less boosted....I'd try it, rather than adding a fix to fix what we already fixed, ha ha!   

A divider WOULD work, but then we'd probably be adding bypass caps to THAT, as it may seem not bright enough after!!! 

If a smaller cap doesn't get you what you want, maybe ALLOW the tone control on green mode, too...there are many ways to approach this

You could switch between 2 different caps, too....a 10u and a .1u, or something, he he...

[swever]

Thanks for the suggestions!

In fact I already ditched the idea of disabling tonestack in green mode (the mini switch to enable it is still there on the board though). It not only worsens the volume difference but is also pretty much pointless - this tonestack is more of a corrective type rather than something that adds character so it makes sense to have in on in both modes. What you see in the vid is tonestack enabled in both green and red.

Changing the emitter bypass cap value is not something I want to do here. I have tried many different values while this was on breadboard and found that 22uF gives the tone character I liked the most, so I'd rather keep that.

That probably means that a trimmer to cut the green mode's output a bit would be the best option. Gotta figure out how to implement that. Does the drawing in my previous post look right to you (if I change the two resistors for a trippot)?

[GibsonGM]

Hi dude,

I'm not seeing how you do what you want with just the 1 switch.   I've used this setup to get 2 different volume pots with one effect, with success.     Now, if you used a 4PDT, you can use the extra pole to bypass the cap, and then you're all set!!!

You can't just pop in a voltage divider and away you go, because the output is between the resistors - and with it out of circuit, the output would then be 'below it'...you would have more than one output to move (if that makes any sense).  Not enough poles, and over-complicating this stuff isn't too smart as if it gets messed up you have difficulty in tracing things.

With the setup in the pic,  the pots could be replaced with fixed resistors (or just on one side), if you like.

A 4PDT will give you the final switch that you'd wire up to your cap.

Then, after you play with the 2 pots, you may wish to jump the 'lower volume one' with a bypass cap to retain highs, LOL - it never ends....

[swever]

Well thats not really good news for me 

Anyway, after more tests I find that there isn't much volume  difference between green and red. What you can see in the video is the camera's compression triggered by red mode's lows. In reality red is a touch more loud most of the time, but because it has less mids a certian range of notes does sound somewhat quieter. I think it's not a problem at all and I am almost sure it shall get evened out by a cranked power amp in any "loud" situation which I will check tomorrow at a jam.

Thanks for the useful informaion, Mike!

[GibsonGM]

No problem, glad it worked out!   I accepted long ago that 'different sounds appear to have different volume levels'...and that shaping the tone can go a long way to how you perceive something (cutting bass, increasing mid, etc)...down the road you might mess around with some of that, maybe you can get more out of this or another project.