Mojave Coyote schematics

[Gilles Maltais]

Hi,

I am curious about the design of the Mojave Coyote amp but this beast seems to be quite discrete. Does anybody have a schematic or advicethat would help me understand how its controls work ?

Thanks !

[Cathode Ray]

Try asking on the MetroAmp forum.

Seems like there were several guys there into those amps a while back.

[Gilles Maltais]

Thanks Ray !



I was reading Rob Robinette's pages about amp modifications and saw that he tweaked his to give it a broader tonal palette. His efforts yielded a british voiced Bassman, a different flavoured Deluxe and tons of ideas. I was really impressed with the versatility features he added to an already good amp. Then I browsed on the internet and for an unknown reason, I was intrigued to go a little further, hence my quest for the Coyote, even if Mojave's site is down.

Long story short, while pursuing the idea of a better understand of this beast, I started to compare its overall characteristics to other amps, in theory, since I have not seen one for real. It reminded me of the 5E3 Fender Tweed Deluxe with its 2 « intertwined » channels. Some informations from Dave Hunter's book, gave me an approximation of the overall topology of the amp but not much more besides a picture nearly good enough to read components values.

Besides specific components such as aluminium chassis vs steel, transformers, rectifiers and tubes, I believe the biggest difference between both amps lies in their « volumes ». I suspect a kind of either crossover or a divided filtered- with a certain degree of overlapping frequencies- signal that feed independantly each volume-gain section.

One solution would be to have a kind of A-B switch with voiced signals, before getting through the preamp tube. Another option would be to feed, in parallel, as in the Coyote, 2 preamp tubes (in this case, to keep the second set of inputs). Third, would be to add filters past the first tube, but before tone section.

There is also, at the end, a kind of attenuator, or a power brake, or an impedance-matching-extra-energy-dump-controlled-by-a-potentiometer (any hint ?) that replaces a master volume.

In orange, you see the blocks of a Fender Deluxe. On the bottom, the modification. Please note that each channel in green feeds half of the tube. I know this is overly simplified.

What are your insights about all this ?

Do you also have any knowledge of transformer specs, rectifier and other specific components related to the Coyote ?

[John_G]

Gillies,
Tried to PM you.......didn't work ??
John

[Cathode Ray]

Thanks Ray !



I was reading Rob Robinette's pages about amp modifications and saw that he tweaked his to give it a broader tonal palette. His efforts yielded a british voiced Bassman, a different flavoured Deluxe and tons of ideas. I was really impressed with the versatility features he added to an already good amp. Then I browsed on the internet and for an unknown reason, I was intrigued to go a little further, hence my quest for the Coyote, even if Mojave's site is down.

Long story short, while pursuing the idea of a better understand of this beast, I started to compare its overall characteristics to other amps, in theory, since I have not seen one for real. It reminded me of the 5E3 Fender Tweed Deluxe with its 2 « intertwined » channels. Some informations from Dave Hunter's book, gave me an approximation of the overall topology of the amp but not much more besides a picture nearly good enough to read components values.

Besides specific components such as aluminium chassis vs steel, transformers, rectifiers and tubes, I believe the biggest difference between both amps lies in their « volumes ». I suspect a kind of either crossover or a divided filtered- with a certain degree of overlapping frequencies- signal that feed independantly each volume-gain section.

One solution would be to have a kind of A-B switch with voiced signals, before getting through the preamp tube. Another option would be to feed, in parallel, as in the Coyote, 2 preamp tubes (in this case, to keep the second set of inputs). Third, would be to add filters past the first tube, but before tone section.

There is also, at the end, a kind of attenuator, or a power brake, or an impedance-matching-extra-energy-dump-controlled-by-a-potentiometer (any hint ?) that replaces a master volume.

In orange, you see the blocks of a Fender Deluxe. On the bottom, the modification. Please note that each channel in green feeds half of the tube. I know this is overly simplified.

What are your insights about all this ?

Do you also have any knowledge of transformer specs, rectifier and other specific components related to the Coyote ?

As I understand it, Mojave Ampworks is out of business and Victor is now selling real estate.

Try contacting him here, as this email addy is supposedly still working: victor@mojaveampworks.com

[Gilles Maltais]

Hi,

Got your PM regarding the attenuator. According to various sources, for which I have not checked in details their reliability, it was possible that a different device than an attenuator circuits you sent me was at the end of a Coyote. That's why I left this as an option in case it was a twisty-esoteric device. Occam's razor: I would probably go the attenuator way since it is well known and easy to build.

And thanks for the email too !

[Gilles Maltais]

Hi

I have started to populate a Coyote board from a photograph trying to "reverse engineering" this amp to better understand how its tone control works. Here is so far the idea. Please note I will post an updated-translated pic later. Feel free to add your insights, especially regarding color coding for wiring.

[Gilles Maltais]

Hi,

While I was thinking about the layout of the Coyote, my mind started to wander. I do not have any access to the real stuff so I departed from orthodoxy, to focus on results.

This diagram was inspired by Dave Hunter's writings at first but it is not an attempt to recreate a Coyote but to think about different means to « get to the sound ».

One of the main goal is to voice the amp properly to get the right tonal control. First, let's look at the characteristics of the instrument.

Fundamentals of electric guitar go from roughly 82Hz to 1318Hz (a little lower if you have 20 or 21 frets)

Harmonics are found between 1000 and 15000Hz but they are rarely heard past 3500Hz directly from an amp.

Presence is found between 2000 and 3000Hz.

This amp has 2 channels in parallel and they are mixed together.

First option would be to split signal between fundamentals and harmonics.

Second option would be to split at another point, either below or above presence frequencies to differentiate the tone. Soloing start generally between 330Hz (E4) and 440Hz (A4) and go up to the top so a mid-point would be around 494Hz (B). For basses, 147 (D3) to 220Hz (A3) would be a reasonable mid-point.

This means, there would be 2 combined channels, having individual gain control that would be mixed together. One would have a low pass filter and the other, a high pass. One problem rises, EQs induce phase shifting and if you go beyond a certain point, it becomes unpleasing for the ear.

So let's have 2 Fender Champ (a simple as we can go) linked at the mixing point, sharing a common PI and output transformer. Another option would be to combine them into a souped up 5E3 Deluxe with or without master volume. In that latter case, an attenuator can be used, as long as frequency response has been taken care. Limited output would minimize drawbacks of too much attenuation.

I'll start building on these bases. Here is the block overall layout. I have not figured yet the details but here are the main goals :

1) An amp that has a broad tonal palette. It does not require a lot of power but I want crisp response.
2) A simple design that can be tailorized to specific needs. I think about mods described on Rob Robinette's website.
3) Something reliable and serviceable.
4) A modular scalable approach. For example, if I want to add an effect loop, a line out, an headphone jack, get a better response from plugged in effects at the beginning of the chain, add presets, using a single channel, etc.

In this perspective, Mojave's approach seems quite interesting. Now becomes time to understand its basics.

A key point from Mojave is to use the unused part of each preamp tube for independant cascading gain. This is different from having a crossover, splitting single channel that split signal in 2 because you have a frequency overlap in the middle. If you take into account Fletcher-Munson effect, you need to boost lows around 100Hz and highs over 4000Hz to compensate for non-linear human hearing perception. Best response for the human hearing is around 1000Hz.