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PostPosted: Thu May 10, 2018 1:49 pm 
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I was just looking at the new two-toggle switch Large Beaver pedals, and was trying to work out if it was possible to add the toggles as mods to the opamp Lil Beaver.

I think I've got it, but if anyone can confirm it would be greatly appreciated. Looking at the schematic I think I need to put the switch around C7, and I think I'm ok to use the same .047 and .0082 caps as all the Large Beavers have on switches?

New Ram's Head schematic here: http://byocelectronics.com/largebeaverramschematic.pdf

Can anyone let me know either way whether I've got this right or not? Thanks in advance.


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PostPosted: Thu May 10, 2018 4:15 pm 
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The op amp version won't work like that. The 8.2k and 1.2k resistors are just too small. Also, it would never be flat. You'd have to change that 1.2k to something similar or exactly the same as 8.2k. But because those resistors are so low, it shifts the center frequency down, so you'd really be changing the low mids, not the mids. And you'd be using much different capacitor values that what you have suggested. I'd recommend converting the tone stack values to ram's and going from there.

Edit: I had originally suggested removing C8, but later realized that it is a necessary decoupling cap.

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PostPosted: Tue Jan 21, 2020 11:29 am 
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Did you ever end up doing this mod? Can you guide me?

oncewewererobots wrote:
I was just looking at the new two-toggle switch Large Beaver pedals, and was trying to work out if it was possible to add the toggles as mods to the opamp Lil Beaver.

I think I've got it, but if anyone can confirm it would be greatly appreciated. Looking at the schematic I think I need to put the switch around C7, and I think I'm ok to use the same .047 and .0082 caps as all the Large Beavers have on switches?

New Ram's Head schematic here: http://byocelectronics.com/largebeaverramschematic.pdf

Can anyone let me know either way whether I've got this right or not? Thanks in advance.


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PostPosted: Fri Nov 20, 2020 9:34 am 
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I was contemplating this same mod and stumbled onto this thread. I had worked out I should probably change the resistors and caps in the tone section to transistor Muff values, but I was puzzled by the “extra” capacitor (C8).
I believe C9/R11 and C7/R12 constitute the Low and High Pass filters, respectively. But what is C8 doing in the stock Op-amp Muff?

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PostPosted: Fri Nov 20, 2020 11:46 am 
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C8 isn't doing anything, with regards to the tone control. It's necessary decoupling cap. The output of the op amp needs to have the DC voltage blocked. This isn't necessary with the typical transistor output of the other BMP versions. When modifying the tone stack, just pretend is isn't there.

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PostPosted: Fri Nov 20, 2020 12:03 pm 
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Awesome! Thanks for the reply.
I shall ignore C8 and proceed:)

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PostPosted: Wed Feb 24, 2021 12:27 pm 
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Got sidetracked away from this project for a bit by the holidays and some other nonsense, but I’m back at work on it now.

Looked at the Ram’s Head schematic, if I’m reading it right, it looks like the Mids toggle switch switches between three cut-off frequencies (142Hz, 1.85kHz, 597Hz) for the high-pass filter, while the low-pass filter stays at 482Hz.

But looking at the low-pass filter on the Op-Amp schematic, it’s at 194Hz. Quite a difference.

Has anyone added another toggle to switch between different low-pass values, and found it useful?

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PostPosted: Thu Feb 25, 2021 2:29 pm 
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prickly-robot wrote:
Got sidetracked away from this project for a bit by the holidays and some other nonsense, but I’m back at work on it now.

Looked at the Ram’s Head schematic, if I’m reading it right, it looks like the Mids toggle switch switches between three cut-off frequencies (142Hz, 1.85kHz, 597Hz) for the high-pass filter, while the low-pass filter stays at 482Hz.

But looking at the low-pass filter on the Op-Amp schematic, it’s at 194Hz. Quite a difference.

Has anyone added another toggle to switch between different low-pass values, and found it useful?



I have not, but it would make it possible to shift the center frequency and/or adjust the Q with a switch to change the low pass cut-off. That's probably of some use. Although, at that point, I'd just amputate the passive tone knob and add an active EQ, but that's just my opinion.

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PostPosted: Thu Feb 25, 2021 5:33 pm 
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I also just came across this: http://www.muzique.com/lab/tone3.htm
If you took that idea, of adding a pot to make a continuously variable high-pass filter, and extended it to the low-pass filter as well (I calculated that a 27k resistor in series with a 100K pot should give you a 125-589 Hz, on the low-pass side), and retained the standard Tone knob to morph between them, seems like it would be pretty versatile.

Although, as you say, at that point (when you’re already at 3 knobs) an active EQ might make more sense.

I think what I’ll do is build up the PCB, except for the Tone section, have some wires coming off the board, and breadboard a few different tone set-ups.

I’m trying to transition from my past paint-by-numbers approach to kits, to actually trying to understand some of what’s going on technical-wise. This seems like a good learning opportunity.

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PostPosted: Fri Feb 26, 2021 11:39 am 
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Experimenting with the AMZ muff tone control is a right of passage for all who become obsessed with the BMP circuit. If you're planning on doing some heavy tinkering, definitely look into the passive Baxandall EQ. A prime example of this in action is the Colorsound Power boost. On the BYOC Colorbooster, it would be the section of circuit between C4 and C7/9. It's particularly relevant here, because you can see how it connects to an LPB boost tacked on the end, which the BMP as has.

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PostPosted: Fri Feb 26, 2021 11:40 am 
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Ah, but wait....if you're doing this on the ICBM, then there won't be an LPB tacked on at the end.

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PostPosted: Fri Feb 26, 2021 2:32 pm 
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byoc wrote:
Experimenting with the AMZ muff tone control is a right of passage for all who become obsessed with the BMP circuit. If you're planning on doing some heavy tinkering, definitely look into the passive Baxandall EQ. A prime example of this in action is the Colorsound Power boost. On the BYOC Colorbooster, it would be the section of circuit between C4 and C7/9. It's particularly relevant here, because you can see how it connects to an LPB boost tacked on the end, which the BMP as has.


I was always very fond of the eq in the Colorsound...that explains it. :)

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