Get a little more boost from this?

[anotherjim]

Kylie don't mean Crocodile. Cathode Ray Oscilloscope. Some still say CRO even if it's LCD/OLED fancy new things.

Simple circuits, especially discretes, tend to assume plenty of interaction with what is before and what comes after. Part of the fun, or frustration, depending on your personality.

It is good engineering to design loading that don't change the source  - but - it's a well known tonal effect with magnetic guitar pickups that the loading they get doesn't only result in simple hf roll-off, there is a response peak too at the roll-off corner. That peak can get pushed down towards the mids depending on load.
So it's possible that raising input impedance will leave you with a tone control that won't sound how it did no matter how you fiddle the R's and C's.
As Kylie sang "I should be so lucky, lucky, lucky lucky...."

[Ben Lyman]

Oh, one of those... no, I didn't get one yet. The guy with all the vintage ones says he wants $100 each, take my pick but I don't know how to test them before I buy one. Make a pocket sized signal generator and take it with me to the shop?

[Ben Lyman]

Hey again everybody, I'd like your opinions on the impedance of this arrangement. Since I still had the Duende on board (thanks again Plexi) I decided it would be worth trying to get my treble filter (as I like to call it) to work on the output, and it does. You'll notice I changed the input gain control/bias thing, I didn't like the way the distortion characteristics were changing on the original schematic when I turned the 1M pot. I thought it might be better to go with a fixed 1M on the gate instead. You'll also notice R2 33K just because I've been told its a good safety practice. What about my Dirt pot R1? Seem okay like that? No need for a pull down resistor like this. R3 24K gave this J201 exactly 4v5 and the tone knob works great

[anotherjim]

Neat solution Ben.
Input impedance is now 500k to 1M depending on Dirt pot (R2 & C1 impedance is negligible).
Tone control should work ok so long as you don't plug into anything less than 500k.

Testing CRO.
There should be a signal generator built into every 'scope. It only does square wave at 1Khz. By all means take your own if you want.

[antonis]

Tone control should work ok so long as you don't plug into anything less than 500k.

IMHO, not less than 5M (10%), Jim..

With succeeding impedance of 500k (and Tone pot full on) tone control out will be "degraded" by -6db..

[GibsonGM]

Oh, one of those... no, I didn't get one yet. The guy with all the vintage ones says he wants $100 each, take my pick but I don't know how to test them before I buy one. Make a pocket sized signal generator and take it with me to the shop?

If you can find out the model you're interested in, the manual for it is probably online. You can look at it ahead of time to see what they say to set the controls at for calibration (we won't be doing the whole thing, just want the timebase and volts/cm settings).  Set the O scope to those settings and put your probe to the calibrate port as Jim is showing in the pic.  You should see the square wave.  Do it for each channel.

Then you can vary the volts/cm to see if the wave gets bigger/smaller* (don't go wild, a click either side is probably sufficient. Doubt the cal signal can be hot enough to pop anything, but you never know).    Vary time base to see the wave 'spread out'.  Vary 'focus' to see if the wave goes from fuzzy to sharp.   Old Tektronix boxes tended to buzz, and that is ok.  Don't ever allow a 'spot' to stay on the screen, turn the brightness down to nothing until you have something to look at.

A wave that does not "stand still", and you can't make it stand still with the controls, is an issue (triggering).  But some settings can cause this to happen, so you have to be sure where it is set.

I got mine for $100, one channel not working, and had to put a transistor in to act as a low-capacitance diode that had popped.  *Someone had fed it too large a signal for the volts/cm setting.  It's fine since, and well worth what I paid.  So be aware of that setting!   Really, if both channels are working, showing a nice wave, you can see the amplitude matches what you are measuring, triggering looks OK (stable presentation) and you can adjust wave size and wavelength...worth $100. 

[Ben Lyman]

IMHO, not less than 5M (10%), Jim..

ooh, that's pretty high. I have only tried it straight into my amp but it might not work so well into a pedal...
Is this why so many pedals (like the Rat) have output buffers? I really want this to go in front of an OD/dist pedal for cutting the lows off and tightening up the sound. Especially with hum buckers or neck pickup into something like a Big Muff or Rat, it gets a little muddy.

edit: I just tried it with a few pedals and it seems to be doing it's job, tested with Rat, Tone Bender MKII, Plexi-Drive and Big Muff.
I would still like to know if there is a better way to set the output impedance anyway.

Here's how it is now, sort of going back to the original with no volume pot. At first I thought it would be cool to have a master volume but it isn't doing much so I thought I'd just give it a fixed resistor. Instead of 100K like the Duende, I am trying out a 47K. Is that gonna make a difference in the output impedance at all?

[antonis]

@Ben: Neither me, nor Jim said it wont work..
(despite our different estimations for impedance of whatever comes next..)

That kind of tone control is kind of "tricky" because of its impedance in conjuction with its specific placing in the circuit..
(you've already seen the problem of placing it before BJT amp..)

The current placing issue "prescibes" for significantly lowering Tone pot value (from circuit output impedance point of view) vs simultaneously significantly raising its impedance (from total Drain resistance point of view)

For general purpose use, a JFET output buffer should be advisable..

[anotherjim]

Well, the output pot was 100k. Ben found the tone control acceptable with that loading it. Presumably, Ben is listening to it from some amp with 1M input. 1M is typical of guitar pedals and amps. 1M fits the x10 loading rule over that 100k pot. It don't change the value of 100k or the pot taper by a musically relevant amount, even if the math tells you it does.
At worst the loading rule is only x5. That's why I suggested 500k minimum (some electronic bypass pedals are about that).
As a tone control, you tweak it to taste depending on situation. As long as allows you to obtain the desired effect, it's a good tone control in my book.
Dropping the load to 47k, if the tone control range still sounds right to you, means the x10 rule is satisfied into those 500k(ish) pedals. A penalty may well be reduced output level, if over-driving is something you want your pedal to do.
Drain resistance is 24k. x10 rule suggests total load on output of 240k. At worst x5, the 100k pot original wasn't so bad.

We know that to avoid different sources and loadings changing the planned effect of the circuit, it really ought to have a fixed, high input impedance with full bandwidth and a fixed low output impedance with full bandwidth. Everything that the pedal does, should happen between these 2 buffers. Everything it does it will always do and never be affected by whatever is plugged into either end. That said, there are hundreds of popular pedal designs that pay no heed. Guitar > CryBaby > FuzzFace > Amp is a classic example of input and output interdependence producing an overall effect that millions love.

[Ben Lyman]

Thank you so much guys, this is a very big help. I think it is doing the job, it sounds good with all the distortion pedals I have placed after it, especially the Plexi-Drive.
I decided to nix the master volume because I wanted to make it a 2-knob pedal, just a simple booster with a high pass tone control seems like what I need.

Antonis- I was seriously considering an output buffer but of course I want to keep the parts down to a bare minimum if possible.
I wonder how a JFET buffer would affect the tone control, being that I couldn't make the tone control work in front of the JFET one page ago, as explained by Jim.
Maybe I'll try it and find out, or maybe a BJT buffer.

Jim- yes, probably a 1M input, it's a Fender Champion 600. The next step is to try it with some bigger amps and find out how it sounds.
I could change the 47k R5 back to 100k but it still has enough boost to overdrive a pedal or tube amp, maybe I'll change it back to 100K anyway, I dunno yet.
I think it will probably work with most pedals although I do recall some version of the OCD may have an input impedance as low as 330K, can't remember for sure though.

Not only did I decide only 2 knobs but I felt most of the time either the dirt knob or the boost knob was always full on, while the other was 1/2 way or more.
In either case there was always some grittiness to the tone without the ability to be a very "clean" boost. This is again the original problem I faced with wanting more volume but that's okay.
It sounds nice, the JFET does have a nice break up as compared to my original BJT booster attempt so I think it'll work out fine.

edit:
Just tried a JFET buffer and then BJT buffer and didn't like how they affected the tone control (surprise, surprise, eh?)
Anyway, I don't want to overthink this whole impedance thing but what do you think about a 100pF from ground to junction R2 & C1?
I see it a lot and I think one of you told me it is there to filter RF but won't affect impedance in the guitar range frequencies.

[anotherjim]

J-FET does not have to have a high input impedance. The gate resistor can be any value, it only has to connect the gate to the reference voltage. You found the load of a 100k pot suited the tone control, so that can be the gate resistor. 100k isn't hard to achieve with a BJT buffer bias network either, so it don't have to be a FET.

[Ben Lyman]

Thanks Jim, it's all starting to make sense now. I just tried the JFET buffer with a 100K gate resistor and the thing just came alive.
Sounds great with a Rat. Rat filter knob cuts the highs and the booster cuts the lows leaving whatever I want in the middle.

Here it is with the possibility of adding C4 100p near the input for RF filter. 
Is C7 necessary? Sound wise, there isn't any difference without it but I don't know if it's important to the buffer.
I put a 47K R5 on the output because I've seen it in a lot of pedals that have an output buffer with no volume knob.

[anotherjim]

Is C7 necessary? Sound wise, there isn't any difference without it but I don't know if it's important to the buffer.

C7 can go. C2 & C3 are already blocking the DC out of the first stage.

I put a 47K R5 on the output because I've seen it in a lot of pedals that have an output buffer with no volume knob.

Value of the pull-down will set bass cut corner frequency with the output cap. 47k is going to be changed some by the following load. So plugging into low impedance inputs will raise the bass cut frequency. As it is, driving a 1M input will give a bass cut around 30Hz. I would raise the output cap. 220n will drop down an octave for safety, but I would fit 470n which will keep full bass all the down to 10k loading.
Keep C7 and reduce it some less than 100n if you want bass cut that isn't changed by following load.

[Ben Lyman]

Thanks again Jim, this thing sounds great. Here's the way I have it set up right now

[Ben Lyman]

I slapped it together in time to use at a gig last night and it made a world of difference.
I know it would've fit in a much smaller enclosure but this suits me and it was really quick to build.
I like it more than my Ge Rangemaster clone because it doesn't give it that "wah wah" tone (which is also cool) but this just takes away all the flubbiness and mushiness,
brings clarity and helps me cut through the mix. Can't really tell much from my lame vid, it really worked great last night though.
I'm calling it the Color Booster in honor of the Colorsound pedal (whatever that was called, I can't remember)

[pinkjimiphoton]

to make it a little louder? ditch the fuzz pot off the e and ground it directly. move the fuzz knob to the input of the circuit and make it bigger... say, 50-100k. then the q will be set up for max gain and you can control the drive via the moved pot, which will now be more of an attack control. you even lose one component.

DOUBLE the output pot. use a reverse audio.

you can even add a treble cut to it that won't take all its balls away. use my monkey balls trick. ya gotta add three components, but can have more output, better gain control and tone all with one q.

for the tone control, think of it as a snubber cap between b and c. but make it variable. try like, 22p on pin 1 of a 100-500k pot and 3.3n to pin three. tie the free ends of the caps together, and stick the whole mess so that wiper connects to base and the caps connect to collector. or maybe backwards. been a while, i'm burnt toast and have the memory of an eggplant.

that will let you sweep between almost no snub... the 22p to a substantial treble cut ... the 3.3n. you won't lose volume like you will with most tone stacks that are out there. it just cuts the treble somewhat.
47-68n instead of 100 for the input will focus it more in the mids and treble and may make it a bit louder too.

just the kinda shit i would probably try if it was me. i LOVE seeing how much shit i can get out of a single transistor.

[Ben Lyman]

Awesome, thanks Jimi! I guess you are referring to the first schematic I posted, I may have to revisit that one and see what I can do. For now though, I really love the current version.
I need to make a new demo vid because that vid above ^^^ doesn't show how awesome the pedal is

[pinkjimiphoton]

yeah, sorry ben, one of them late nite barely conscio kinda things. as i was posting the reply i noticed it had evolved. oops!
when i get back later i'll look a little closer.

i love simple stupid one or two q fuzzes that kick ass