Supa Page Bender

kaycee · Post by **kaycee** » 14 Jul 2010, 17:03

A slight moddification of the alleged modded Jimmy Page Tonebender from the 'Don Mare schematic.'

Addition of the Vox Supa Tonebender (Yardbox) tonestack, switchable input caps and bias for Q3 mounted externally.
Schematic:

Stripbaord layout:

Positive ground, 3 x germanium transistors, usual bender gain ranges, nothing special used in mine and it sounds great to me. My build:

kaycee · Post by **kaycee** » 15 Jul 2010, 07:21

Thanks! I'll measure the voltage at Q2 next time I have it open (cocked up the positioning of the transfer so will be redoing that). It works through quite a wide range of the trims adjustment, I usually just tune to ear though. The second external bias is like a fine adjustment.

I used a polarity converter, ICL7660S for polarity conversion and added a 20k trim for sag, so we thought alike there

but I'm only knocking a little off of the input voltage, the most useful adjustment is from the bias IMHO. I went with 10nf as the second input cap on the switch, I like both that and the 10uf though.

RnFR · Post by **RnFR** » 15 Jul 2010, 09:38

is the first transistor just leakage biased? and what's up with that 100K to gr before the i/p cap?

kaycee · Post by **kaycee** » 15 Jul 2010, 16:22

RnFR wrote:is the first transistor just leakage biased? and what's up with that 100K to gr before the i/p cap?

Hi,
dunno, I'm just an idiot who Frankensteins parts of circuits together

Its the same as the CS/Vox Tonebender Mk2 pro as per schematics at Fuzz Central - My assumption on the 100k is that its a pulldown for switching, built as per schematic and using the MBP this doesn't pop when engaging, and believe me it would if it could if my previous experience is anything to go by

Measured the voltages at collector in my two builds - strange

Q2 -0.55 and -0.45. Q3 -3.3 and -1.82 from a voltage of -8.45 on the power line. Taking Q2 over -1v and it fades out, can't get anywhere near -7v on either build, but both sound fine, tons of fuzz and sustain.

Must get around to having a go at that Masterblaster of yours RnFR.

DrNomis · Post by **DrNomis** » 26 Jul 2010, 09:44

That 100k resistor before the input cap really should be going from the first transistors base terminal to ground,this resistor acts as a "pull-down" resistor to get the first transistor to bias correctly,normally,Germanium transistors have a small amount of leakage current that flows through the collector-emmiter terminals,this effectively turns the transistor on so that it goes into "saturation",ie passes the maximum current that is determined by the collector resistor,the 100k "pull-down " resistor is there to turn the transistor off enough so that it biases properly,that is how it works in a stock Tonbender Profesional Mk3.

RnFR · Post by **RnFR** » 26 Jul 2010, 10:58

DrNomis wrote:That 100k resistor before the input cap really should be going from the first transistors base terminal to ground

yeah, that's what i was thinking. i think the schematic may be a bit off. i would make the above adjustment and then see how your build sounds.

DrNomis · Post by **DrNomis** » 26 Jul 2010, 16:31

Yep,that cleaned up scan looks correct,if you want to stop any audible clicking or popping when switching the effect in and out,what i would do is stick a high value resistor in parallel with the .01uf capacitor on the input of the effect,anything from 1M to say 2M2 should work fine,it has no effect on the tone,just the footswitch popping....

DrNomis · Post by **DrNomis** » 26 Jul 2010, 16:33

Not the polarized .01uf capacitor though,the one going to ground....

DrNomis · Post by **DrNomis** » 27 Jul 2010, 10:18

The Tonebender Professional Mk3 is basically a Fuzz Face with an extra gain stage tacked on the front end of it,the collector voltage for the second transistor should be something like .3 to .5 of a volt,germanium transistors normally need about .3 of a volt between the emitter and base terminals for it to conduct current from the collector to emitter,silicon transistors require .6 of a volt.

For a stock Tonebender Prof. Mk3,I've seen an article on Fuzz Central that suggests biasing the collector of the third transistor to 4.5 volts with respect to ground,I built myself a Tonebender Mk3 from the info in the article and it sounded good with transistor 3 biased like that,I had to use what germanium transistors I had on hand,they came out of an old Hewlett Packard Electronic Counter that had Nixie style displays,from memory I selected one with a current gain of 75 for transistors 1 and 2,and one with a current gain of about 100 for transistor 3,I have no idea exactly what the transistors were,but they had 1850 or something like that written on them,but they were germanium transistors,and they seemed to work fine for me anyway,here are the collector voltages for my pedal:

Supply voltage: 9.01V

Transistor 1 Collector: 8.60V

Transistor 2 Collector: 0.57V

Transistor 3 Collector: 4.5V

Note:The collector resistor of transistor 2 is 47k in my pedal.

Hope this helps with getting your pedals biased correctly....

kaycee · Post by **kaycee** » 27 Jul 2010, 16:38

Thanks for the info gents

So, on the whole my voltages weren't that far out after all, and I could probably dial it in on Q3 if I wanted, nice.

Regarding the 100K at the input, so having that before the input cap is isolating it from Q1? As I said, it seems to work and sound fine like that, curiosity piqued I'll have to breadboard another and shift that 100K around and see if I can measure a difference in current at Q1 collector with my DMM.

Heres a clip of mine, the stock version without tone control and with a 10nf input cap:

http://www.mediafire.com/file/7s3w0wu27888v87/MOBY DUCK.MP3

DrNomis · Post by **DrNomis** » 27 Jul 2010, 17:25

It does appear to be doing that,just checked out the clip,your pedal does seem to sound a bit like mine,I should upload a clip of my Tonebender for comparison,

The only bias control I have in my Tonebender is a 20k multiturn trimpot on the third transistor's collector,works well for me,instead of 470 ohms for the resistor going from the 20k trimpot to the supply,and with the output capacitor(.01uf) going to the level control,I use a 4k7 resistor to give loads of output,might change it though.

I might see if I can upload a pic of my pedal's insides so you can see what it looks like...

I'll just get busy with my digital camera...

DrNomis · Post by **DrNomis** » 27 Jul 2010, 17:42

Okay,here we go,here's a pic of the insides of my Tonebender...

kaycee · Post by **kaycee** » 27 Jul 2010, 23:11

Yeah, I've got some of those fat green caps, love using them.

2N651 in Q1, CV7355 2&3 - the board on the side is a polarity converter with trim for voltage sag - I don't use batteries in my builds, but include the option for selling on later most of the time.

Should have added that the clip was on a tele with vintage noiseless pups, pedal into Marshall JCM600 on the clean through a condensor mic and in partnership with two bottles of Speckled Hen...hic!

DrNomis · Post by **DrNomis** » 28 Jul 2010, 08:03

Lol....that would do it,the Heineken that is,actually it was a good clip to listen to,my pedal seems to sound roughly like yours,but I think mine has a bit more gain,my Tonebender is at Billy Hyde Music here in Darwin NT at the moment,they wanted to give it a demo,so I'll have to wait till I get it back off them to do a clip that I can upload....

I like your pedal build,looks cool,love the graphics on it too...

devastator · Post by **devastator** » 28 Jul 2010, 19:57

Nice ! did you use the Maxx1044 for the power converter ? I've the same idea for my next tonebender loaded with AC128 .

DrNomis · Post by **DrNomis** » 29 Jul 2010, 10:11

I've never tried using those Maxx power converters in my pedals,they all operate off 9V batteries,even my Germanium transistor based pedals,this way I don't have to deal with needing a separate -9V supply,wall warts tend to generate low level mains hum,and I suspect that those Maxx power converters probably inject a small amount of noise into the supply,switchmode power supply units are very notorious for injecting the switching frequency into the supply,this switching frequency can be as high as 200kHz,and a real bugger to filter out completely,found this out by first hand experience,200kHz isn't something you'd want as part of your guitar signal since it can cause your sound to sound bad for no apparent reason,I only found this out with the help of my trusty oscilloscope,I saw a nice 200kHz sine wave superimposed on my guitar's signal after passing through an effect powered by a switchmode power supply.

This is why I went back to just using batteries,yes they do have a limited life span,but my signal chain is alot cleaner sounding now...

DrNomis · Post by **DrNomis** » 29 Jul 2010, 10:14

My 4 Knob Tube Driver pedal,is the only fx that I run off a wall wart since it requires both a +V supply and a -V supply,it took me quite alot of work and head scratching to get it mostly noise free,there is still a very slight amount of mains hum present,but it seems to be loudest when my guitar is plugged in...

kaycee · Post by **kaycee** » 30 Jul 2010, 17:29

devastator wrote:Nice ! did you use the Maxx1044 for the power converter ? I've the same idea for my next tonebender loaded with AC128 .

Hi,

no I use the ICL7660S for this purpose, I've found it a better alternative. You just need the chip and two electro caps and you have a polarity converter - can also be rigged as a voltage doubler. Make sure you use the one with the 'S' suffix, or you'll get whine ine the audio signal and you'll be fine

DrNomis · Post by **DrNomis** » 14 Aug 2010, 11:44

Hi all,just thought I'd upload a pic of a re-draw of the Super Pagebender schematic that I did with some mods to the original schematic,hope this is useful to you in helping getting your builds going and sounding good,I've included some expected collector voltages as a guide,note that these voltages are as measured with your multimeter's common (black) lead to ground with a positive ground system for PNP Ge transistors....

SPeter · Post by **SPeter** » 14 Aug 2010, 21:26

A bit more clear!
Can you make the schematic more readable?
Thanks!