DIY’ing Circuits and Pedals – How I Approach It

[Big O]

I know all the rage on GPCB website are the new Nostalgia Tone circuits to get certain artists’ sounds.  I used to want to do that type of pedal building and I commend Barry for developing and producing the PCB’s for these circuits.  In the past, I used to try and build similar “artist” type pedals using GPCB boards.  A few years ago I built a Judas Priest pedal using a GBOF based NPN Ge Rangemaster into a Plexi Plus mated with a Tone Tweq (similar to and predating the Metal Godz Nostalgiatone Pedal).  However, nowadays I have gone on a different path and like to build new and possibly improved versions of old circuits, or try and figure out and build old circuits that are without much readily available documentation.  This is why I have sort have tended to more of a DIY pathway for pedal building.  I use GPCB boards for the most part, but will also use other boards or veroboard to build my pedals.  GPCB does offer a myriad of PCB’s that can be combined in many different ways for those who like to experiment and have their own ideas about what type of pedal might be an ideal build for them.

In order to guide those who may be more adventurous with regard to building and developing circuits on your own, I will commence with a short discussion about how I went about building a NPN Silicon MkI Tonebender.  First, I web searched the topic about MkI Tonebenders, a notoriously finicky circuit to build, and then looked to see if anyone tried to build a NPN Si version of the pedal.  After I waded through the available wealth of information, primarily on forums that had to do with pedal circuits and pedal building, I discovered a few threads and schematics to try.

The next step is very important, at least to me – building and tinkering with schematics I found on the internet on a breadboard.  I finally settled on building my own version of a Sonic VI Silicon MKI Tone Bender, as it was the circuit that was most easy to deal with and provided a great sound alike for the PNP Ge MkI.  I tried a couple of other schematics I found for a Si MkI, but these proved to be a bit more finicky to dial in and I went with my own slightly modified version of the Sonic VI as it has a proven track record as being a sound alike to the Ge MkI’s.  A video for a side by side comparison of a Ge MkI circuit with the NPN Si Sonic VI can be found here by copying and pasting the link inside the quotation marks:  “ https://www.youtube.com/watch?v=ASYRe93_1Uk “.  The Sonic VI sounds a lot like the pedal I built.

First, building MKI Tone Benders with PNP Ge Transistors is doable, but it is best to breadboard this circuit to tweak it to work and sound properly.  I found an excellent webpage regarding the MkI’s, found here by copying and pasting the link inside the quotation marks:  ” https://vero-p2p.blogspot.com/search/label/TONE%20BENDER%20MKI%20FAMILY “.  There is an excellent video about tuning a  MkI Tonebender properly on this page, which was extremely helpful to me and made me wish I had seen it before I built a couple of Ge MkI’s myself (Solasound and Gary Hurst versions).  I am probably going to go back and tweak one of the builds eventually when I get a chance to try and improve the pedal a bit.  The video on how to tune the MkI circuit can be found here by copying and pasting the link inside the quotation marks:   ” https://www.youtube.com/watch?v=sYg0V0_VdNE&t=4s “.

The above mentioned MkI page provides the basic schematic layout of the circuit and variations of component values in table form for some of the different versions.  These include the components for the Solasound and Gary Hurst versions that I previously built.

The Sonic VI Silicon MKI Tone Bender is closely based on the original Ge MkI schematic, with a couple of additions and some minor changes, primarily in resistor values.  Since the Sonic VI is silicon transistor based, the transistors do not self-bias like the Ge ones do, so additional resistors had to be added from power supply side to the bases of Q1 & Q3.  You can see in the schematic below showing a standard Ge MkI circuit with the changes and additions made for the Si version in RED.  The purpose of the extra resistors is to simulate the leakage of the Ge transistors that was responsible for the self-biasing.  Instead of the 8.2K resistor to ground after the capacitor that follows the Q2 transistor, a 50K bias pot is substituted, which allows the bias network of Q3 to be adjusted for optimal sound.

 

Lower gain Silicon transistors tend to sound a bit better in this circuit, as I discovered during breadboarding, than somewhat higher gain ones, which is probably has to do with the hfe of the chosen transistors.  I tried 2N2222A transistors with a gain of slightly greater than 200 hfe and the circuit sounded pretty good.  However, I experimented with other lower gain transistors on the breadboard, finally settling on 88 hfe for Q1, 131 hfe for Q2 and 215 hfe for Q3.  I also tweaked the Attack pot resistor on the breadboard so that it just cuts off with the pot near zero, as discussed in the “Tuning a MkI Video,” and I ended up using a 7.5K resistor.  Finally, I added some modern refinements to the final build, including power supply filtering and a 1.2M pull down resistor at the input to prevent a “pop” when the foot switch is engaged.  The final schematic is below.

 

I hope this gives people an insight of what you can accomplish doing some DIY R&D and breadboard building, and then translating it into a working pedal.  The GBOF is a good PCB to experiment with a simple circuit that has been tweaked on a breadboard changing component values – simple transistor boosters, fuzzes, etc.

Finished Silicon Mk1  Tonebender below (built on veroboard).  Note on the gutshot that there are a couple of empty sockets before Q2 and Q3 for filter caps, but these were not needed and the caps were left out.

 

 

 

[Barry]

I like this a lot. Thanks for sharing.

 

[Barry]

BUMP

[Big O]

Mick Ronson combo idea.  Fixed wah circuit + Si TB Mk1 + Marshall amp emulator.  Rono used the “Pig” aka a Marshall Major with his wah and Tonebender.  Reportedly he ran only two output tubes on his amp so it wasn’t so loud and clean.  I don’t now if there is any Marshall Major emulator circuit out there, though.

A couple of other combo ideas (i.e. Nostalgiatone):  Ritchie Blackmore/Deep Purple with a Hornby Skewes treble booster circuit into a Vox AC30 emulator, and a Michael Schenker circuit using a Fixed Wah into a Marshall Amp emulator.  An early GFR combo could be made with the Tone Messer circuit into a West Amp emulator.  The Tone Messer portion would have to have a voltage step down feature since it runs on a 1.5V source – I don’t know if you could mix the 1.5V fuzz with an amp emulator that runs on 9V.  I’m not an EE or expert circuit designer.  As far as I am concerned the HS treble booster and Tone Messer circuits are not proprietary so anyone can have at it.  I don’t care if anyone copies what I have done – and maybe the circuits can be improved upon.

 

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