One Knob Tonebender help please?

[petemoore]

Do you recommend me buying a breadboard?  There's a few spare dollars at the end of the week and I think it might be cheaper to figure out how things work without spending tons of dough on parts that will be stuck to a non-working board.  Although I gather from the forum that just because it works on breadboard doesn't mean it's going to work on perf.

Having never worked with trimpots, I would be interested in finding out which trimpot I should purchase.  Any recommendations?

What's a node?

Which resistor is the Q2 collector resistor? 
  >>It's the resistor connected to Q2's collector, has an output cap and a 1k or so...[depending] resistor connected 'above'.
  >>That'd be the 10k, or 8k2, and a trimpot lets you dial in bias, otherwise it's possible, but a 'longer road' and directions thereto...
  As nice as it was to have an introductory tutorial to stripboard, without the schematic I definitely feel like I was just painting by numbers without a big picture perspective on what the various components on stripboard do.
  Just redrawing the circuit, or drawing up your own perf layout, and building on perf.. [see ROG for a printable perfboard template], will increase your understanding of a FF, I built a couple from memory in the last couple days.
  I will definitely measure every resistor on my multimeter prior to installing it.  What setting should I use to measure capacitors and transistors on a DMM?
  >>[Caps generally don't get measured by DMM's] Capacitors...well...I 'measure' capacitors by socketting input [output?] caps, then I take a cap marked 104 [.1uf], and one marked 103 [.01uf] and after a bit of swapping/listening, the decimal point is 'idendifiable by sound', then I just use the other markings to determine where the inbetween values 'are'...or just swap 'till I drop or pick one I like...
I'll work on my layout for the perf and submit it as an image to this thread for you take a look at by Thursday.  Chances are the build won't actually start till next week though, cause I have to get the parts from Small Bear.  Thanks for your help.
  >>Read GEO "Technology of the Fuzz Face", ROG has some FF articles, and Fuzz Central's schematics and related texts are great FF reads.
  >>A node is where two *or more component leads are to be connected, when looking at nodes, it is helpful to simply count the connections at each node on the schematic, [and orientation of any polarized components],  and figure your build in that area accordingly...this way your'e less likely to have to 'tack on' or thread the needle to add that component as an afterthought. Counting node connections on schematic and comparing that to what the board has is an old first trick to try when looking for a 'missing' or 'one too many'...connections counting.

[somasix]

So here's my first attempt at a hand drawn schematic for Dragonfly's one-knob tonebender.  The basic layout was modified from the Vox Tonebender schematic available in the GEO "Technology of the Fuzz Face" article you pointed me too.  Drawing the schematic definitely helped me understand the circuit better, although I'm going to have to read the article about ten more times.

If you could, please guide me to what is specifically right and wrong with my schematic, any theory explanations would be appreciated also.



Here are some specific questions or points of interest I have about my schematic:

Is there any specific reason why the 1M resistor and the 100u electro capacitor go straight to the ground?

Are there clues within the schematic that I should look for when choosing a ground point?

What would be the pros/cons of a 10K trimpot versus a 20K trimpot?

Having completed the schematic, I went back to my veroboard attempt and noticed that a small amount of solder had bridged from the 9V + wire to a separate copper strip.  I cleaned up the point and, behold, I got the crackling noise back!  Still no Tonebender, but being able to debug the circuit back to it's ORIGINAL non working condition was a step in the right direction.

Thanks.

[petemoore]

Is there any specific reason why the 1M resistor and the *100u electro capacitor go straight to the ground?
  >>The 1m is a pulldown resistor to 'hold' the input cap at 0V to reduce pops,
  >>The 10uf [that's 10uf, could be 4u7 or 22uf or...] and the 1k resistor go to ground from Q2's emitter/150k feedback resistor, the cap 'feeds' the emitter and smaller values let less bass get amplified, the 1k resistor is partially responsible fro the bias on Q2 and sets the gain of the circuit.
  Are there clues within the schematic that I should look for when choosing a ground point?
  >>all points with the ground marking get connected...[? if that's what you're asking]
  What would be the pros/cons of a 10K trimpot versus a 20K trimpot?
  >>...not much, the 20k will let you adjust between 0k to ~20k, the 10k will be 'finer' adjustment and will most likely have enough range to bias your transistors, adding a 4k7 or so resistor to the 10k trimpot makes dialing in 'fine', and resistances using a 10k + 4k7 allows resistances between 4k7 and 14k7, [20k's not that 'coarse' of adjustment, and you can get a fine bias...]
  Having completed the schematic, I went back to my veroboard attempt and noticed that a small amount of solder had bridged from the 9V + wire to a separate copper strip.  I cleaned up the point and, behold, I got the crackling noise back!  Still no Tonebender, but being able to debug the circuit back to it's ORIGINAL non working condition was a step in the right direction.
  >> I just noticed an 820k as part of Q2's collector resistor for bias.
  >>Check out Fuzz Face schematics of same polarity as this 'tonebender' [which is a Fuzz Face er...that's what I'd call a 2Q Feedback loop amp distorter]..and notice that Q2 biases with ~8k2 [trimpot dials in bias, 8k2 is like...middle of the road or close]...I suspect that resistor is to be 820 ohm...FF's generally have that resistance position coming in at values between 470ohm and 1k2. I go with 1k there usually.

[somasix]

Sorry if these next few questions seem redundant, I just want to confirm some of your recommendations before I put in my order at Small Bear.

>>...not much, the 20k will let you adjust between 0k to ~20k, the 10k will be 'finer' adjustment and will most likely have enough range to bias your transistors, adding a 4k7 or so resistor to the 10k trimpot makes dialing in 'fine', and resistances using a 10k + 4k7 allows resistances between 4k7 and 14k7, [20k's not that 'coarse' of adjustment, and you can get a fine bias...]

-- So here you are recommending I put a 4k7 between the 10k trimpot and the node leading to the .22uf?  Or is it the 10k trimpot, the 4k7, and then the Q2 transistor?

>>Check out Fuzz Face schematics of same polarity as this 'tonebender' [which is a Fuzz Face er...that's what I'd call a 2Q Feedback loop amp distorter]..and notice that Q2 biases with ~8k2 [trimpot dials in bias, 8k2 is like...middle of the road or close]...I suspect that resistor is to be 820 ohm...

-- Looking back at the original schematic, the 820 resistor is actually 820R... Does R mean OHM?  If so, I ordered the wrong 820 resistor.  Could that be the problem?  I read the R as a K when I put in my initial order.

>>FF's generally have that resistance position coming in at values between 470ohm and 1k2. I go with 1k there usually.

-- And this is a recommendation to put a 1K in the 820R position in leau of the 820R?  What affect will this have on the overall design of the circuit. 

>>[which is a Fuzz Face er...that's what I'd call a 2Q Feedback loop amp distorter]

--That's a joke, right? 

Thanks for all your help.  I feel like your advice has driven me to learn in particular directions I don't think I would go on my own.  It's truly appreciated.

Jason

[petemoore]

Sorry if these next few questions seem redundant, I just want to confirm some of your recommendations before I put in my order at Small Bear.
  *>>K
>>...not much, the 20k will let you adjust between 0k to ~20k, the 10k will be 'finer' adjustment and will most likely have enough range to bias your transistors, adding a 4k7 or so resistor to the 10k trimpot makes dialing in 'fine', and resistances using a 10k + 4k7 allows resistances between 4k7 and 14k7, [20k's not that 'coarse' of adjustment, and you can get a fine bias...]

-- So here you are recommending I put a 4k7 between the 10k trimpot and the node leading to the .22uf?  Or is it the 10k trimpot, the 4k7, and then the Q2 transistor?
  *>>Replace Q2CR [the second transistors collector resistor, original FF it was 8k2 or so]..with a variable resistance...adding a stop resistor to the choice of 10 insures you can under/over and bias many transistors easily, coarse enough tuning to bias any 'worthy' candidates, fine enough tuning so when you turn the dial it don't jump over the voltage readings your'e looking for.
>>Check out Fuzz Face schematics of same polarity as this 'tonebender' [which is a Fuzz Face er...that's what I'd call a 2Q Feedback loop amp distorter]..and notice that Q2 biases with ~8k2 [trimpot dials in bias, 8k2 is like...middle of the road or close]...I suspect that resistor is to be 820 ohm...

-- Looking back at the original schematic, the 820 resistor is actually 820R... Does R mean OHM?  If so, I ordered the wrong 820 resistor.  Could that be the problem?  I read the R as a K when I put in my initial order.
  That could an probably is the main problem, I used always to put 470k there, seriously reducing current and causing serious misbias,,,like no-bias.
>>FF's generally have that resistance position coming in at values between 470ohm and 1k2. I go with 1k there usually.
-- And this is a recommendation to put a 1K in the 820R position in leau of the 820R?  What affect will this have on the overall design of the circuit.
  You can basically stick anything between 470 ohm -2k, 1k2 is TONs of output...1k is high output [what I've been using] you get the idea, higher resistance there increases output.

>>[which is a Fuzz Face er...that's what I'd call a 2Q Feedback loop amp distorter]
--That's a joke, right? 
   It has 2 transistors, is a single gain stage, amplifies and distors signal...
   The topology of the FF is able to wring more gain from 2 transistors/simply, as opposed to seriesing two transistor gain stages, the first transistors output of the FF feeds directly to the second transistors input, and from the second transistors 'other output' [emitter] a bit of the boosted signal output is fed back [thru feedback loop] to Q1's input. 

Thanks for all your help.  I feel like your advice has driven me to learn in particular directions I don't think I would go on my own.  It's truly appreciated.

Jason

[somasix]

All right, it works!   I pulled the 820K out of the circuit and put in a 1K I had around, noting your statement about higher resistor means higher output.  Heck, I figured high output couldn't hurt.  I plugged it in and checked to see that all the gain was rolled off on my amp and that the level on the amp was set to 1.  Flipped the switch on my amp (it's solid state) and a deafening squeal filled every corner of the room. 

After my fillings stopped hurting I potted the TB down a bit and tried again.  You were right about the output.  It matched my amps volume at about halfway up.  And it sounds awesome.  SO MUCH FUZZ!  Although I didn't get to rock out too much (it's still relatively early and there's a baby that lives two floors down), I had a lot of fuzz, er... fun. 

I'm very pleased with the project and appreciate all your help.  In my mind I expected it to sound a bit more like I remember my old Vox Tonebender sounding (or the Distortion Booster on the Vox Electronic guitars).  I think it sounds a bit darker than the Vox TB.  Still love the sound though.  When I build this circuit on perf, what could I do to bring a bit more treble into the tone?

Thanks again.

Jason

[petemoore]

  Hope you don't mind me quoting the whole thing here...
All right, it works!
  Happy Time Congraduations !!
     I pulled the 820K out of the circuit and put in a 1K I had around, noting your statement about higher resistor means higher output.
  820k is only 1000x off the mark...lol. 
  >>1k's cool I think, you could always use a longleg 1k and strap a 1k parallel to it to ma .5k [that's 500 ohm]...stick it on a switch or whatever...for a boost if you like...I like 1k cause the volume control rolls off a little bit of the highs when attenuating the increased output the 1k delivers over a 470 ohm...
   Heck, I figured high output couldn't hurt.  I plugged it in and checked to see that all the gain was rolled off on my amp and that the level on the amp was set to 1.  Flipped the switch on my amp (it's solid state) and a deafening squeal filled every corner of the room. 
After my fillings stopped hurting I potted the TB down a bit and tried again.  You were right about the output.  It matched my amps volume at about halfway up.  And it sounds awesome.  SO MUCH FUZZ!  Although I didn't get to rock out too much (it's still relatively early and there's a baby that lives two floors down), I had a lot of fuzz, er... fun. 
I'm very pleased with the project and appreciate all your help.  In my mind I expected it to sound a bit more like I remember my old Vox Tonebender sounding (or the Distortion Booster on the Vox Electronic guitars).  I think it sounds a bit darker than the Vox TB.  Still love the sound though.  When I build this circuit on perf, what could I do to bring a bit more treble into the tone?
  >>Smaller input cap value rolls off lows...so it'll sound brighter...makes treble 'more' of what it amplifies...
  >>Smaller '820' will reduce output, therefore you'll probably be using the volume pot turned up farther...and you'll have smaller resistance between output and output...er...going through the volume pot...turning the volume pot down reduces output of course but also rolls off highs a bit [more in relation to overall attenuation, highs get cut a 'little'] so a smaller resistor may be what you want...so you can have the volume knob turned up and 'not attenuate highs' more than overall volume...this 'subtle' difference may be all you want...
  >>If you're seriously into tweekin of the FF...build a FF 'testboard' with longleg '*big' resistors [enough room above board to solder or clip a parallel resistance reducing resistor to...start with a 'larger' value and work your way down] *the 150k IS big on the FF build you've got...100k is 'normal' I've seen 47k there...the 10k [Q1CR] is 'small'...normal would be the 33k, 47k is fine...you can diddle with any resistance on the board up/down/whatever...
  >Socket the input output and E bypass electrolytic...all caps
  >Socket all transistors Ge .. anyway
  >>Trimpot with stop resistor [4k7 or a little bigger + 10kpot] Q2C's resistor [8k2 or so on most schematics that don't show a trimpot]...this is a must have on a FF testboard.
  >>Use a gainpot...Smallbears FF gainpots work RIght.
  >>Basically you can [I did] diddle with FF's 'till the cows come home [assuming you don't have cows]...so I like to have a couple FF testboards handy...for grabbin' and testin' on transistors 'n such's...then I can build a more permanent FF lifting the values from the testboard...
  >>Or...breadboard.
  >>every part on the FF board changes 'something' a little, or drastically...
 

Thanks again.

Jason

[petemoore]

  C1 socket [smaller values let less bass in]
  Q1 socket [just so you can swap Q's here, gain has big effect on circuit]
  Q1CR make it 33k, 47k, even 100k, longleg it so you can tag parallel another to it, above the board [ez mod] or even easier socket it...I don't care much about this one as long as it's around 33k or so...
  the '820'...you know that that one does...
  the 100k...feedback loop resistor...smaller values allow more feedback...
  the electrolytic cap, smaller values let less bass get amplified in the circuit
  The gain resistor or pot...sets gain of the circuit...in your case by providing limited shunting to ground via feedback loop, ITCase of a gainpot, it shunts what the electrolytic 'has' to ground, reducing gain as resistance to ground here is diminishing...it shunts the 'reinforcing' feedback to Q1base/input to ground.
  Trimpot Q2CR...so you can bias the circuit easily...re-bias after every Q swap BTW.
  Socket the output cap, smaller values here'll limit how much bass gets out.
  I just use 100k volume pots on FF's anymore...50k-500k tried...I like the 'balance between the 1k resistor [as an '820' or between the two *colllector resistors] and a 100k volume pot...you wanted more highs so a smaller *1k will make you want to turn a 100k volume pot up higher to get same output...hence a little bit more highs are let out....because less resistance at output [between volume pot input and volume pot output {wiper and the input from circuit}]
 
 

[petemoore]

  When I perf these FF's, I use a complete 8pin IC socket, one side for input cap, other side for transistors connections [input cap gets 4 lugs], transistor emitter gets bottom lug, base gets second lug up, collector gets top two lugs...that leaves a lug open and connected to the collector...EZ to hit that with the DMM probe when repeatedly checking bias.
  I find using whole 8pin IC's is Very Sturdy, cutting 'em in half...why...just wire the whole thing right in there...

[somasix]

Who needs a breadboard when you can just socket in any variety of parts for a test drive?  Do you have any pictures of your FF testboards lurking around in these pages?  I feel like my overall inexperience keeps me from visualizing an obviously helpful work style that can no doubt be adjusted to other projects.

With that in mind, how many other projects have you used this technique for?  I'm certain that socketing a variety of parts into a testboard would help my understanding of how different capacitors, resistors, and transistors interact with one another.

Thanks.

[petemoore]

Who needs a breadboard when you can just socket in any variety of parts for a test drive? 
  >>For testing out many various circuits..like I did on perf..Idda saved pretty big doin' 'em on breadboard, I have a pile of perfjunk that I scavenge from, but scavenging isn't that fun, not the best either.
  >>For a FF though, a testboard makes pretty good sense, I mean I don't know what you're using for an amp and whether an OA Clipper might beat the FF with it, or what you want, for somebody who turned out to like FF's the way I like these FF's and testboard 'em, build 'em into boxes with sockets, re-voice [I just did a .1uf cap swap to .047uf, at volume isn't always available, and crankin' has proven to be the way to find out what a box actually sounds like cranked, so I like re-voiced it after Fri Gig last week, and Saturday it was really fine, better pick attack and a bit more clarity..it's my new 3 transistor Fuzz...any rate if you like 'em it may be of good service to have that testboard like always there..that frees up a breadboard for possible competition.
  >>I actually have a buncha FF type thangs, boxed with nice switch for A/B testing, I find by racing them I can get one that 'corners' great, and one that saturates even more...not that the ultimate FF could'nt be had with one box, I found A/Bing Voicings helped me figure out over time what 'that does when this is...', stuff like which caps and resistors I like on em.
Do you have any pictures of your FF testboards lurking around in these pages?  I feel like my overall inexperience keeps me from visualizing an obviously helpful work style that can no doubt be adjusted to other projects.
  Nope...my fave is the 8pin IC for input cap and Q1, output cap and Q2 use another 8pin IC socket, 33k, 1k, and 100k are fixed resistors, electrolytic is made fairly EZ to swap if fitted right to the gain pot, 22uf is fine, Trimpot Q2 [I like 10k with 4k7 stop resistances], 100k output pot.
  See 'Axis Face' at Fuzzcentral, the cap across the 1k takes a toucha highs off if you want.
  >>also any resistor can be made a little smaller with a paralleled resistor, I 'longleg' resistors so I have a little room above board to either...check with probe easily, or, solder another resistor right there...I pretty much settled on the above values..you OTOH..might want to check out Joe Davissons Fuzz Face Calculator...see if altering values and fitting them to the hfe's and type transistors you want to try wreaks another FF mile.
  With that in mind, how many other projects have you used this technique for?  I'm certain that socketing a variety of parts into a testboard would help my understanding of how different capacitors, resistors, and transistors interact with one another.
  DIST +
  Many input caps, and some staging caps [series in signal path/that cut bass amount].
  Diodes in clippers
  Anything that uses Ge Transistors...[or Si..lol..I uza lotta socketta...probaly more than necessary]
  Lotta times I 'bridge' above board if it looks like it'll be sturdy..or sorta sturdy..haven't had a pad break from being 'overbridged above board' by too many 'floating components', these perfpads are pretty sturdy, I like partially soldered/bridged above board builds...but I stick my iron in a brick and hold the board 'n solder too...for EZ accurate approaches, board angles etc. /and a HUGE ancient iron that's REAL hot with a copper core wire [from industrial 440v use] wrapped around the tip [this unique thin/long tip is temperature controlled ... lol].
 

Thanks.

[somasix]

Love the idea about adding a switch controlled 500 ohm resistor into the line for that extra boost.  I'm personally glad the One Knob Tonebender didn't work right of the bat.  Now I have a whole thread of fuzzface techniques I can quickly get too.  The testboard sounds good.  I'm definitely going to have to buy a breadboard when I have free cash.  Seems integral for designing variations on circuits.

Regarding the OKTB and highs, I haven't opened it all the way up yet because I live in an apartment.  Today I'll be around a soundproof studio, so I'm going to bring it with the intention of checking out it's sound at full volume.

[petemoore]

  Deffinitely mess with volumes, ouput up can sound alot different than down some on a FF [generally works just great for like a 10-20% boost or unity], all the way up, on mine, with mine, overdrives the amp...cool but I think it's best behaviours are rolled back some, I usually have the volume control at 2/3 - 3/4, which is a boost above unity.