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Mu-tron III

9/12/2000 7:03 PM
Mu-tron III
I'm trying to build a Mu-tron III schematic. I've heard a lot about this envelope filter. But I can't understand some pictures in the schematic. What is the "0805" ? What kinds of op-amps should I use? (I can't understand the bottom legend "A1-A2, ... *0802* type 4558 x.c." )  
And the drive and range switches, why do the have that point line putting a pair together? Is that supposed to be a DPDT ?  
I've heard about the R.G. Keen clone, The Neutron, but I couldn't find it anywhere. Have anyone built this? Does it sound similar to the Mu-tron? Is the schematic easier, smaller, or less complicated than the Mu-tron one??  
If anyone can help me where to find it (or send me), do it, please.  
9/12/2000 8:37 PM
John J
Did you try RG's home page. If it's his model clone it would probly be obtainable in that sight. Never the less, I've seen his his replies on this forum. If you red flag him you'll more than likely receive a competent reply.  
Some of his concepts lead to a further understanding of the FX Gallery. If you brief his arrangements as a silent listener on this forum and Ampege's. You'll eventually encounter another piece to the perplexing aspects of Electronic Circuitry Building and Troubleshooting.  
John J  
Starburst to aft Port,30 degrees Elevate.
9/12/2000 11:07 PM

The "0805" is a combination LED / dual LDR. The response of the LDRs seems to be fairly critical to the feel of the Mutron III, at least in my limited experience with building clones of it - all of the cheaper LDRs seemed to be too "slow", and don't give that "liquid" feel.  
Any dual opamps will work, so you can use 4558s, TL072s etc.  
The drive switch changes both the sensitivity of the envelope detector and the polarity of the LED-driving signal simultaneously, but you can just use a SPDT switch and substitute a pot (say 100k) in for the selectable sensitivity resistors instead.  
As you also guessed, the range switch is a DPDT that changes the two caps in the state variable filter .... of course, you can change this to a rotary switch to select more than two different cap values for the range  
This site has a schematic including these mods and others to work with NSL-32 LED/LDR packages:  
This site has the schematic and PCB layout for the Bassballs, which might be an easier to get working in an acceptable manner:  
No doubt RG's Neutron would be the way to go if you are looking for an easier building experience, and I seem to remember he said something about including discussion of a few options for getting the LED / LDR interaction just right.  
Good luck! Envelope filters rock ... errr ... funk. :)  
9/13/2000 12:17 AM
The Neutron - R.G. Keen
As it seems to be an easier way to get the Mu-tron sound, I would like to see comments about the Neutron.  
How much similar to the Mu-tron it sounds?  
Does it have any mod?  
would you like to help me building a Mu-tron clone? I'm not too experienced building effects. But I really would like to have this effect..  
I would appreciate a lot if you send me comments, and/or a copy of the Neutron schematic.  
Thanks a lot.
9/13/2000 2:36 AM
CJ Landry

Yes, I have built the Nuetron and it sounds just like the Mutron III. I should know because I posted the original schematic for the Mutron III. You can get the schematic at my web site:  
Click on the schematics link.  
Mike is right, the 0805 is a dual independant photconductive cell. I have about 15 in stock and you can order it from my web site also.  
The Neutron is easy to build and fits in a single 1590BB box. If you decide to build it and have questions feel free to contact me. Mine works great!  
CJ Landry
9/13/2000 3:07 AM

Thanks, CJ!  
For Funky - yes, it's an exact reproduction of the Mutron 3 circuit on an all-new circuit board layout. I did the board layout from C.J.'s schematic (us folks with only initials have to stick together ... *<8-)  
The only mods in the PCB are that I included an on-board means of generating a -9V supply from a single battery so you can run it from only one 9V battery if you like. You can also ignore that and run it from two batteries or a bipolar 9Vdc adapter just like the original if you like.  
The 0805 is a single-LED, two LDR opto device. I think C.J. may have some exact replacement devices left - he did at one time. The instructions for the Neutron do include several ways for making a replacement for the 0805, but C.J.'s replacement is easiest.
9/13/2000 3:43 AM
Ed Rembold

Wait a second...  
Mike, R.G. ,CJ,  
Would you guys spread a little more info out  
about "slowness-fastness" of Led/Ldrs,  
and what is most desirable?  
My own tinkering has led me to believe that  
"slowness" is very desirable, especially in the "decay"  
comments, please?  
Ed R.

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