Please help me to add a Pre-distortion Mid Control to a Rockman X100

[Vivek]

Part of the scope of the project to make a modernised clone of the ROCKMAN X100 is to add some new features

I am very interested in adding a pre-distortion Mid Boost/Scoop

Please help me to decide

A) Would fixed Q and F and pot for amount of boost/cut be sufficient ?
If yes, what Q at Max boost and F would you recommend ?

B) How about the semi parametric MT2 Mid control (explained so well by Tom / Electric Druid)




C) What about the Gyrator Mid control as explained on Tom's HARD BARGAIN page ?





D) Respected Mr. Hammer had a 3 band EQ circuit which I remember seeing long ago. It had an Active mid control

E) There was a recent post here with 100mH inductor for Mid control
https://www.diystompboxes.com/smfforum/index.php?topic=126694.msg1212436#msg1212436


F) STM non-interacting 3 band EQ has a mid with a Q of 1.4 at max boost at 700 Hz

https://www.aronnelson.com/gallery/main.php/v/STMs-Circuit-Ideas/Three_band_Eq_non_interacting_bands.png.html?g2_imageViewsIndex=1


G) A Baxandall type Mid control can have a rather low Q around 0.57 at max boost at around 750 Hz

Any other options I should look at ? Which approach is best (Sufficient functionality without being overdesigned)

Looking forward to your guidance on best way to go with a pre-distortion Mid boost/cut to be added to Rockman X100

[iainpunk]

how about a bridge tee filter in the feedback loop of an opamp?


the opamp in this dist/fuzz does some aggressive mid pushing, might be nice. it doesn't scoop tho.

cheers, Iain

[marcelomd]

I'd go the Baxandall route.

The Sansamp Character Series call it the "character" knob. Every one is a bit different. I have a Joyo clone of the Blonde (Fender Tweed). Sounds pretty good.

[Vivek]

how about a bridge tee filter in the feedback loop of an opamp?
the opamp in this dist/fuzz does some aggressive mid pushing, might be nice. it doesn't scoop tho.

cheers, Iain

Dear Iain,

I feel a scoop is also necessary, to be able to do "Frown EQ". Am I on the correct track ?

I'd go the Baxandall route.

The Sansamp Character Series call it the "character" knob. Every one is a bit different. I have a Joyo clone of the Blonde (Fender Tweed). Sounds pretty good.

I do not have enough information on the Sansamp

There is Teemu K's excellent analysis from long ago

Then some frequency response graphs measured by someone.
https://www.tdpri.com/threads/joyo-american-vs-tech21-blonde-comparison-many-graphs.786013/
https://www.tdpri.com/threads/different-voice-settings-on-joyo-american-sound.821457/

and two sites in Russian with schematic and some explanations.

Could you point me to best schematic and best frequency response graphs ?

Is this Baxandall placed pre-distortion ? Would you know the Q of the Mid band ? I saw on some of my SPICE models, that the mid band Q can be 0.57 at max boost at around 750 Hz, which is miserably low. I have a gut feel I need around 1.7 to 2.5 Q for mid band Pre-distortion control


I will most probably have a post distortion tone control at the end of the mono part and most probably that would be a Baxandall.

But now I am looking at pre-distortion controls.



Thank you for your inputs

[marcelomd]

I'd go the Baxandall route.

The Sansamp Character Series call it the "character" knob. Every one is a bit different. I have a Joyo clone of the Blonde (Fender Tweed). Sounds pretty good.

I do not have enough information on the Sansamp

There is Teemu K's excellent analysis from long ago

Then some frequency response graphs measured by someone.
https://www.tdpri.com/threads/joyo-american-vs-tech21-blonde-comparison-many-graphs.786013/
https://www.tdpri.com/threads/different-voice-settings-on-joyo-american-sound.821457/

and two sites in Russian with schematic and some explanations.

Could you point me to best schematic and best frequency response graphs ?

Is this Baxandall placed pre-distortion ? Would you know the Q of the Mid band ? I saw on some of my SPICE models, that the mid band Q can be 0.57 at max boost at around 750 Hz, which is miserably low. I have a gut feel I need around 1.7 to 2.5 Q for mid band Pre-distortion control


I will most probably have a post distortion tone control at the end of the mono part and most probably that would be a Baxandall.

But now I am looking at pre-distortion controls.



Thank you for your inputs

I saw the schematics in the other forum (Can we name that forum here? Can I post something from there here?). They are in PDF, so here is a screenshot.

The general idea of those circuits is input buffer -> Baxandall mid -> distortion -> some filters, maybe cab simulation -> Bax mid control -> Bax bass+treble -> output buffer. The difference between the models are mostly the pre distortion mids and some eq later.

[FiveseveN]

Am I on the correct track ?

I feel like you're still missing an important aspect: you can't design an effect by looking at graphs. A guitar signal will need to go through it at some point, and not a prerecorded one.
For example:

I saw on some of my SPICE models, that the mid band Q can be 0.57 at max boost at around 750 Hz, which is miserably low. I have a gut feel I need around 1.7 to 2.5 Q

A Q any higher than miserably low will noticeably affect the "character" of the guitar, which is great if you're making an MT-2 but not if you're going for "transparent" tone. Neither is "better", it's an aesthetic choice. How do you decide which one you prefer without hearing it?

Second example:

I feel a scoop is also necessary

You could spend a lifetime trying to characterize the vast landscape of guitar signals, study intermodulation and count harmonics 'till the cows come home. Or you could strum a chord through it and realize in one second why that's rarely musically useful.

[iainpunk]

a scoop is super nice... if playing clean...
if you like distortion, i don't think a scoop is all that useful, only when you can compensate with a mid push in another area, and order of operations is super important as well:
[boost mids > clipping > scoop mids]
for instance, scoop at 500Hz with 6dB and boost at 1k with 18dB for a ''BROOOOTAL'' death metal tone, if you switch those around you get the ''desert rock'' kind of vibes. if you place both at 750 Hz you have the metal zone sound

i strongly recommend you experiment with a bunch of filters to ''test your taste'' as to which frequencies you like to boost or scoop.

if you want to copy a real unit, you might want to just clone its numerical character. but if you want to do a ''based on but improved'' you have to bread board a bunch of filters and just experiment until your finger tips are sore of changing components (or playing the strings for hours on end)

cheers

edit: warning!!!
don't scoop before clipping, this makes things muddy and inconsistent. i had build a dirt pedal for bass once, and when playing guitar through it above about the 5th fret on the low E string or higher, it became almost clean, but really muddy in character. its one of the few perfboards i actually threw away after putting something better in the enclosure.

[Vivek]

Pre-distortion mid control "Character" in a Joyo clone of a TECH21 BLONDE Character series pedal

It has boost and scoop.




https://youtube.com/watch?v=G6XK6khLaxM&feature=share

Demo of Character knob around 01:40

[iainpunk]

Pre-distortion mid control "Character" in a Joyo clone of a TECH21 BLONDE Character series pedal

It has boost and scoop.




https://youtube.com/watch?v=G6XK6khLaxM&feature=share

Demo of Character knob around 01:40

yeah, but the only point where he shows the scoop below center with the drive up is at 4:42, and it sounds kinda muddy and... not so great in my opinion, i bet it farts out when you crank the gain and scoop all the mids. it also kinda takes down the drive when scooping, but i doubt you want to use the distortion channel for cleans?

cheers

[Vivek]

Thank you for your comments and advice, Iain , FiveseveN, marcelomd

[marcelomd]

yeah, but the only point where he shows the scoop below center with the drive up is at 4:42, and it sounds kinda muddy and... not so great in my opinion, i bet it farts out when you crank the gain and scoop all the mids. it also kinda takes down the drive when scooping, but i doubt you want to use the distortion channel for cleans?

cheers

It farts a little. I don't remember it being too much tough. Supposedly this emulates the early tweed series which farted out because of oversized coupling caps passing to much bass.

[ElectricDruid]

If you want a mid that boosts and cuts to put ahead of the distortion, and with the relatively high Q you were after, then the gyrator is probably the best bet. If you can manage with lower Q, the baxandall is simpler, and gives a better knob response. The gyrator does nothing until the extremes of the pot, which is a bit annoying (see my graph that you posted, and my comments on the Hard Bargain page). The control response was the reason I went with the Baxandall for the Hard Bargain, ultimately. The gyrator is a bit "all or nothing", and the feel isn't so good.

If you were looking for a mid boost only before the distortion, you might have a few more options. Well, you have a few more options anyway, but they all get more complicated for no massive benefit. I mean, you *could* use a state-variable filter EQ to provide this function, but it'd cost you a ton of op-amps and mucking about for something that could be done more easily. Unless you decide you need something semi-parametric or fully-parametric, those more complex designs (like the MT-2 mid) aren't really worth it. But they're great if you want all the options!!

Tom