mods for MU-TRON III

[rx5]

Im happy with how the mutron III sounds..... after hearing an "AGENT 00FUNK" filter....wow.... i think i gonna build a LAG knob.... but im having a hard time getting it to work ..tried any possible experiment but to no avail... until ive read about R.G. KEEN's article about the tech of the filters... he said the 330 ohms serves as the -attack- resistor while the 47K acts as the -decay- resistor....well i tried to add a 500K pot in series with the 47K to get more decay...WELL it worked.... i get longer decay time.... then i changed the 330 ohm resistor with a 1K pot.... attack is fine if your in low resistance (<400ohms) but when i increase the resistance(1K) it seems it can hardly drive the rectifier....i had to struck the strings hard just to get an "OW" or "WAH" for that matter.... any ideas how this attack circuit would be??? maybe a signal delay line with MN3007 or a signal sequencer with CD4017 to delay the signal?? or better yet , any diagrams for that AGET 00FUNK filter?  :wink:  

hope to hear from all ya soon  ........... :roll:

[gez]

The more you increase the value of the attack resistor the more control voltage is dropped across it so you end up with less to drive your filter.  To compensate for this you can increase the gain in the envelope generator.  

You could try a little compression to stop the filter falling like a brick after initial attack.

[rx5]

ok ill try increasing the gain.. but i think the gain resistor is 1M allready...ill try a 2.2M or 3.3M........ :shock:

[Mark Hammer]

As the culprit in the suggested mods, what you have gotten is entirely normal.  That is the unfortunate side effect of altering the attack-time resistor in these simple half-wave rectifier circuits.  It ends up reducing the current driving the control element (which in this case is a photocell).

There are several suggestions for fixing this, some of which have been mentioned.  One is to increase the gain of the envelope follower itself, generally by increasing the feedback resistor to increase gain.  Another is to beef up the input signal, though given the design of the Mutron that is unfortunately yoked to the likelihood of overdriving the filter. A third is to conserve as much of the envelope signal as possible and you can do that by swapping the 1N914 series diode in the envelope follower path with a germanium type.  This should not impair the follower's capacity to function.

All in all, though, if feasible, the best alternative is to increase the gain of the envelope follower stage.  Unfortunately, this is one of those things where altering one parameter affects the stting of another.  When you use a chorus, turning up the speed generally means turning *down* the sweep width.  Similarly here, turning up the attack time (i.e., increasing the series resistance to slow it down) also means increasing the sensitivity.

Realistically, you may find little audible change between 500R and 1k so you might also consider either using a 500R pot or sticking a resistor in parallel with the pot.  Wider range of attack times can also be achieved by dropping the value of the 330R resistor too.  Whenever I use a 1k pot it is usually in series with a 47R or 68R resistor, so 330R+1k may be too much resistance.  Remember thatthe stock value is intended to provide a compromise one-size-fits-all attack time, and is higher than the minimum value that will still function well.

[rx5]

ok..

ill try them both..... ill change the gain (1M) of the envelop detector to 2.2M or 3.3M and not change the diodes... or just change the  (1N4148,thats what i used) to 1N60(voltage drop is .3V, pls someone verify))... or if still doesnt work , ill change the 1M AND 1N60 diodes....

thanks for the info   :wink:  :lol:      

[Mark Hammer]

Sorry, I spoke a little too soon.

The gain mods I suggested were for the rectifier circuit in the Dr Q, and might be problematic in the Mutron.  You can try increasing the 120k feedback resistor in the input/gain stage for more gain and more envelope signal.  Try 220k for starters.

Since this will not only produce more envelope signal but also more signal, period, you will probably need to stick an output volume control on the unit to be able to provide the level matching you want.

Sorry about the misunderstanding.

[gez]

Another possibility would be to wire up a resistor in SERIES with the 1M in the feedback loop of the envelope follower to give it more gain.  This would probably have a less dramatic outcome than changing the 1M for a value two or three times it's size, and it would be easier to fine tune the response of the follower (smaller value resistors mean more subtle changes).

[rx5]

sorry but LAG knob doesnt mean -attack- and -decay- control but more of a delayed replica of th signal triggering the envelop rectifier.....have tried changing the diodes to 1N60 and changed the 1M feedback res to 4.7M...still same result.... just changed my 1K pot to the original (330 ohms) ......  

any ideas for  a delay circuit ?? preferebly "input volage must be the same in amplitude with output voltage except it is delayed"....


tnx

[Rob Strand]

As everyone else said that is normal when you increase the attack.

I don't actually like how the sensitivity works on the Mutron.   I wouldn't go messing with the gain of the first stage it's already pretty high and you are likely to clip the first stage.

I reckon you should decrease the 12k and 22k on the input of the rectified (A5) by a factor of two (or maybe three but  no more) -  use the same factor for each.  If necessary, after that increase the 1M on A5 to say 2.2M.  This increases the gain of the envelope detector only, it doesn't boost the audio which risks clipping the audio.

[rx5]

thanks but i think ill stick to the original circuit but ill keep the the "decay" controls.... cheap trick for  the mutron and performance of the (deacy)control is good... try it ...

what i really wanted was the same effect (LAG) from agent 00funk filter... i think the only way is "delaying" the input signal and feeding it to the envelop rectifier...  i think that would be it... but still got no idea how to create a simple delay line.... think i need data sheet of MN3007 BBD chip... :wink:  

BR