nivk
New Member
Posts: 1
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Post by nivk on Feb 17, 2022 17:01:07 GMT
Hi everyone, I found the "Mojo Maestro" project and seams to be exactly what i'm searching for a long time (no fancy outboard gear or pedal mystic stuff). I would like to make one by my own, but make few mods. I have some questions about the schematic. In the schematic R1 is 1k resistor at the input, what is the purpose of that and why 1k? Can i substitute it (with a 10k Lin pot, for exemple) to vary the impedance (input volume?) or just remove it? Also, i would like to replace SW1, R2 and R3 by a Lin 10K pot too, to vary the amount of distortion, is it a good idea? Is there a relationship between the value of R1 and R2, do they need to have the same maximum value? If i want to vary the Low pass filter, a log 10k, would be nice? I would like to add transformers in the input, if i want to push them "hard" for them pleasing "behavior", do i need a volume pot after to control the volume before clipping stage? I'm a real noob in electronic world. Thanks in advance Original circuit here:  |
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Post by Ethan Winer on Feb 17, 2022 17:12:42 GMT
The input resistor is needed to avoid forcing too much current into the clipping diodes. The circuit will probably work well enough with a higher value, though you'll probably need to increase R2 and R3 as well. This is a simple circuit, so there's no chance you'll electrocute yourself experimenting.  Though without R1 it's possible to blow up the diodes. Yes, you can certainly replace the switch and fixed resistors with a pot to vary the distortion continuously. I picked those values by trial and error, and that's what you should do too. Either by building the circuit and listening as you experiment, or start first with LTspice as I did. |
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Post by Hexspa on Feb 19, 2022 10:55:43 GMT
I just watched a video with Tom Oberheim and that's how he voiced his SEMs as well. youtu.be/mAdapwLeXgs |
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Post by rock on Feb 19, 2022 16:31:59 GMT
Hey Hex,
Wow, talk about going down the rabbit hole! Absolutely a great story but the trial and error method was hardly the take-away (at least for me).
Sorry to sound negative about your contribution but on the contrary, thanks SO MUCH for posting the link!!! I really never knew the story behind the man and his company. So much of his early life and education is relatable to mine even though he's probably 20 years older! I never owned any Oberheim products but a bandmate/roommate around 1980 owned a 4-Voice which I played quite a bit. The very cool thing about it was not only the polyphony but the ability to play four DIFFERENT voices together! One of the more subtle thing I liked to do was to set it up for a horn ensemble patch by tweaking filters and envelopes of each of the four voices to get a texture that even most later (if not all at the time) poly-synths could not yet get!
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Post by rock on Feb 19, 2022 16:39:27 GMT
Oh and Hexspa,
I meant to suggest that regarding your electronic project building: Ethan's Mojo might be a good little project to build. I was thinking about building one for myself. Maybe just a mono channel version to put inline with my interface to use in an analog channel FX loop with my DAW.
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Post by Ethan Winer on Feb 19, 2022 16:50:25 GMT
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Post by rock on Feb 19, 2022 16:55:54 GMT
Hi Ethan,
Yeah, I saw that before but I forgot:( Thanks for reminding us!
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Post by Ethan Winer on Feb 19, 2022 17:11:34 GMT
To be clear, I gave them permission for free. I don't make any money when someone buys a kit! |
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Post by Hexspa on Feb 20, 2022 10:33:15 GMT
Hey Rock. I'm glad you liked the video. 'Trial-and-error' wasn't the takeaway for me either but it's a good hook line. I've definitely got DIYRE bookmarked but let me first attach an LED to a 9-volt battery before I take on anything more complex  . |
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Post by rock on Feb 20, 2022 20:22:06 GMT
OK, just remember, most regular solid state diodes including LEDs need a current limiting resistor to prevent the diode from drawing too much current which will cause instant self-destruction  (of the diode, not you  ) Here's an LED calculator ledcalculator.net/ to easily get a resistor value that will limit the current to a level that won't destroy your LED. BTW, I have found that some LEDs are way to bright with these calculators so using a larger resistance value than calculated will allow you to get the LED down to a desired brightness. (Using the trial and error method; again, it's a good way to tweak circuits). A bonus to reducing the brightness of an indicator LED, is that with less current draw, you can somewhat extend your battery life  |
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Post by Hexspa on Feb 21, 2022 10:53:12 GMT
I'm with you that far. The whole voltage, current, resistance thing seems pretty straightforward. The rest of it is a lot like How to Draw An Owl.  [ripped from knowyourmeme.com because their entry on it is nsfw] |
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Post by rock on Feb 21, 2022 14:34:50 GMT
Yep, it's just that easy . |
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Though without R1 it's possible to blow up the diodes.
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(of the diode, not you 
)
