# OctaMayer (Octavia II) Tone Mod



## Chuck D. Bones

I posted a modded Octavia in Build Reports, here are the details of the TONE mod.

I pulled a schematic for the Octavia 2 from the 'net and redrew it.  There are no Build Docs yet for the OctaMayer, but I am 99.9% sure this is how the OctaMayer board is designed just based on the parts.  The schematic below shows the Tone Mod.  I added VR3 and C22, that's all.  Take those off and you have a stock Octavia II.  I don't know how Roger Mayer implemented the Tone control in his Vision Octavia.  I could not find any schematics for it.  If you listen to the demos, the Octavia II and the Vision Octavia sound the same when the Tone control is dimed.  I suspect that the circuitry is the same, except the Vision has a Tone control and buffered bypass.  On his webpage, Mayer describes the location and purpose of the Tone control as reducing the treble content before the octave stage, similar to rolling back the guitar's tone control.  This was a simple way to accomplish that on the OctaMayer board.  Be aware that this Tone control does not behave at all like the Tone control on the Foxx Tone Machine and it's not supposed to.  It's pretty subtle and works best at low to moderate DRIVE settings.  C22 was a guess and I think it could be larger, something like 10nF to 15nF.





With TONE dimed, the freq response is flat from 100Hz on up.  With TONE at noon, the response is down 3dB at 600Hz, drops by 11dB at 2KHz and flattens out.  With TONE at zero, the response is down 3dB at 600Hz, drops by 20dB at 10KHz and flattens out.  Increasing C22 moves those break-points down proportionately.  This is true for drive settings below 4:00.  When DRIVE is dimed, the TONE control has less effect, which is fine because when we max out DRIVE, we're going for a much nastier tone anyway.

I had one other version of this mod in mind.  It behaves the same and is a little cleaner to install.  The advantage is you can wire VR3 to the holes in the circuit board that would have been occupied by R8.  Use an A50K pot for TONE, remove R8 and wire it like this:


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## Robert

Chuck D. Bones said:


> There are no Build Docs yet for the OctaMayer



Yep, there is. It was posted Monday. 
https://docs.pedalpcb.com/project/OctaMayer.pdf


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## Chuck D. Bones

Robert said:


> Yep, there is. It was posted Monday.
> https://docs.pedalpcb.com/project/OctaMayer.pdf



*Well Alrighty then!*


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## Chuck D. Bones

Based on the official Build Docs, the Tone Mod goes in parallel with 47K resistor R9.  

I did a few part subs, mostly based on availability.  I was out of 22uF tantalums, so I used 27uF.  The 220R resistors are 226R. The 39K resistors are 40.2K. Q1 is 2N5087 because they are quieter than 2N3906.  Q2-Q4 are MPSA14.  Those are the same as MPSA13, except the MPSA14's have higher gain.  Doesn't matter in this circuit, it's just what I had.  I used FDH400's in place of the 1N4148's; very similar and I have a ton of 'em. Do not use Ge diodes because leakage will unbalance the octave generator.  I lowered the LED ballast resistor to 1.2K because I used a UV LED.


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## cooder

Awesome, thanks again for sharing and explaining this! Another one on my list now...


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## BurntFingers

Noob question but is this using the resistor and c22 to create a low pass filter?


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## Chuck D. Bones

Yes. It creates a shelving low-pass filter with (using ref des from the top schematic, above) C22, VR3 and R8.  All three parts are in the negative feedback loop for Q1 & Q2.  When DRIVE is dimed, it works a little differently because in that situation, there is no negative feedback.  In that case, C22, VR3 and R8 shunt some of the signal on Q2's collector to ground thru C5.


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## BurntFingers

Chuck D. Bones said:


> Yes. It creates a shelving low-pass filter with (using ref des from the top schematic, above) C22, VR3 and R8.  All three parts are in the negative feedback loop for Q1 & Q2.  When DRIVE is dimed, it works a little differently because in that situation, there is no negative feedback.  In that case, C22, VR3 and R8 shunt some of the signal on Q2's collector to ground thru C5.



Cheers Chuck, I appreciate you taking the time to flesh it out.


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## music6000

BurntFingers said:


> Noob question but is this using the resistor and c22 to create a low pass filter?


Google It!!!


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## BurntFingers

music6000 said:


> Google It!!!



First thing I did actually, but none of the diagrams seemed to be what Chuck mentioned.


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## Chuck D. Bones

My stuff is so innovative that Google doesn't even know about it!  

What I did was shape the freq response in the feedback path. It's pretty much equivalent to putting capacitor between the output and - input of an opamp.  We see that all the time in pedals.  It's not usually called a low-pass filter, although it behaves like one.


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## BurntFingers

Chuck D. Bones said:


> My stuff is so innovative that Google doesn't even know about it!
> 
> What I did was shape the freq response in the feedback path. It's pretty much equivalent to putting capacitor between the output and - input of an opamp.  We see that all the time in pedals.  It's not usually called a low-pass filter, although it behaves like one.



Indeedy, hence the question 

I've been toying with adding a high pass filter (cap into a VR to ground) into a fuzz pedal but am struggling with lots of volume loss as resistance increases, which is why I was intrigued about your post(s).

Cheers Chuck.


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## taxfree

Could you make a video demonstrating how the pedal sounds with these mods? Thanks


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## Chuck D. Bones

Have you listened to the Mayer Octavia Vision demos on YouTube?  It sounds like that.  NB the tone of any Octave pedal is strongly dependent on the guitar & playing style.  Short answer: I'm not going to, but someone else here might.


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## taxfree

Eu construí um, sem controle de tom. Realmente, pude ver que usando o controle de tom da guitarra, tenho um resultado muito interessante. Outro Octave muito legal é o Octaland.


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## harmaes

Hey @Chuck D. Bones 

Did you see this post? https://www.freestompboxes.org/viewtopic.php?p=287288&hilit=Octavia#p287288

There are some slight differences to your tone control like removing the 10nf and moving it to a veroboard with a 100nf.
Could you describe the differences to your tone control?

I just build the Octa Mayer and I’d be interested in a tone control on a small veroboard as the circuit can be quite bright. On it’s own it can almost be used as a ringmod and for gain I put it in front of the corduroy fuzz.


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## harmaes

I noticed that Musikding delivered KSP13 (108) or are these just re-labeled MSPA13?


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## Chuck D. Bones

That's the conversion to a Vision Octavia, based on an _allegedly _correct trace.  I have my doubts because it has two redundant parts, a cap of dubious value and the phase compensation network is missing.  Sure, this _might _be how Roger Mayer designed it, but his designs are usually cleaner and more intelligent.

My tone control is a shelving type.  The rolloff freq is constant and the amount of attenuation at high freq is variable.  The tone control here has a variable rolloff freq.  Either one will do what you want.  Is one better than the other?  IDK.  

Referring to the OctaMeyer schematic, the only parts needed to add the tone control shown in the FSB post are the C47K (C50K) tone pot and the 10nF to ground.  You can put both after C6 and increase C6 to 1uF.  The cap between the tone control and Q3 is unnecessary.  I recommend putting a 1K resistor in series with C6

The purpose of the tone control on the Vision Octavia is it takes the place of rolling the tone back on the guitar.  The purer the tone (fewer harmonics) going into the octave circuit, the cleaner octave-up coming out.  That's why octave-up works better with the neck pickup and playing on the higher frets.

The other changes in the FSB post are about removing two redundant parts (R16 & C9) and changing the transistors from MPSA13 to BC550C.  You can do that if you want but it won't alter the tone.  I do not recommend removing C3 & R5.


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## Chuck D. Bones

harmaes said:


> I noticed that Musikding delivered KSP13 (108) or are these just re-labeled MSPA13?


Looks like they are similar to MPSA13. 
Check your kit carefully because Musikding has been know to substitute parts or put in the wrong parts.  Don't be surprised if some of the parts don't fit the board.


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## harmaes

Chuck D. Bones said:


> Looks like they are similar to MPSA13.
> Check your kit carefully because Musikding has been know to substitute parts or put in the wrong parts.  Don't be surprised if some of the parts don't fit the board.


I will order some MSPA13 and a 2n5087 from a dealer here in the Netherlands. I socketed them so easy to compare.
The OctaMayer worked pretty well with the KSP13 though.


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## Chuck D. Bones

I think those KSP13s will be fine.  Do they have the ON Semiconductor logo on them?


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## harmaes

Chuck D. Bones said:


> I think those KSP13s will be fine.  Do they have the ON Semiconductor logo on them?


Only KSP13 108 mentioned on them


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## harmaes

I’m used to rolling down and playing with the tone control on my neck pickup and the octave up works great already on the pedal. It even works quite well on a bridge pickup with the tone rolled down completely. I favor fuzz and octave pedals with strats. 
So not sure if a tone control would be that necessary? Maybe your version is better then a simple tone control like on the guitar?


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