Mutron Micro V (+?) build guide

[GGBB]

I am getting ready for a build and revising my layout a bit, and I noticed that on the original schematic, the 10uF output cap is supposed to be non-polar.  Seems like everyone has been using polar without issues which is what all the layouts have shown - or has everyone been using non-polar without mentioning it?  Could that be related to styrene's popping issue?

[GGBB]

Here's some ideas for CV for a Micro V, just be careful not to put too much current into the control pin, 0.75mA usually gives full sweep for an LM13700 in my minimal experience. More than 1.5mA is pushing into the danger zone. For 2 input pins, as in this circuit in this thread, 2mA is a safe maximum. You can measure the current going into the control pins by measuring the voltage drop across R17 the 4k7 resistor connected to the emitter of Q3, that will get you ballpark figures.

A few questions about this - please excuse my ignorance here.  Why go to all that trouble instead of simply adding a variable resistor in front of the bias pins?  Does the voltage itself matter in addition to the current?  Also, since we are feeding two bias pins simultaneously, shouldn't we be shooting for double the current that is expected to be right for a single OTA?  This is why Jim used two 1M in parallel instead of the original single one, right?  And since we now have two bias pins to feed, doesn't that double the max current allowed to 4mA (current divider law).

And regarding the changing of the 1M to 500K, would that not have an impact on the 2N5087?  Do we need to be concerned about that?

As I am revising my layout, I want to be able to incorporate these things into it.  I have managed to leave the 1M as it is for the 2N5087 and am taking the OTA bias input from 9V direct through its own resistor and a trimmer.  I know I should just breadboard it, and eventually will, but it helps me to get the questions out of my head first.

[Perrow]

I'm debugging my reworked layout (don't think I've posted it). I get no filtering. Checked it multiple times against schematic and found no error. I've measured it and the only thing that stands out (more than a few tens of volts difference) against Mustachios build is that Q1 base and emitter are way low.

Q1 (mustachios)
8,96 (9.69)
3,40 (5.06)
2,84 (4.53)

This is after I upped the 10k resistor from the emitter to ground to an 18k, it was even lower before. The collector voltage is Vcc but even after scaling base and emitter values to account for that difference there's still 1.5 volts worth of difference. Does this give you guys any idea?

[Mustachio]

Hey Perro any chance you can post your new layout for me to look over? I'm building another couple of these now and double checking things over so I'll try to give yours a look over.

About the 1m to 500K and the current question. I can't answer very technical at the moment but I did try different values to get a different current at the bias when I was first doing this and using two 1m in parallel for 500K worked right for me. 1m gave nearly no effect.

[Perrow]

I've got two 1M too.

Found I had the npns the wrong way round. That fixed the voltages, but nothing else

I'll get the the layout to you, as soon as the kids sleep

[Perrow]

I've got two 1M too.

Actually tried a soldering bridge there as well but all that gave me was a burned 13700.

[Mustachio]

Ouch on the burned chip. I'll keep an eye out when ya post and try to help.

[Kipper4]

Please don't shoot me for resurrecting an old thread.
I'm having a run on envelope filters.
Who has built this. Which layout did you use.
Thanks

[Mustachio]

I've built 2 from the first posts layout.

[Perrow]

I've built my layout.

Haven't got it to work though

[deadastronaut]

^ watch out for fake 13700's...like i had. pissed me off no end with various projects..

[Kipper4]

I've built my layout.

Haven't got it to work though

I noticed your layout is differant in that pin 1 and 16 both go to the 500k where as moustashios is differant


thanks for the heads up guys.
Im thinking i'll build this tonight.

[Mustachio]

Check the jumper under the IC they are both connected. If you look down on page 1 I posted another board image showing the jumpers and then a little further down how to wire the switch.

Cheers, and good luck! It should go together easy.

[Kipper4]

thanks
just putting all the info from the thread in a word doc then i'll have a go when i've checked everything to be sure i know what im doing

I'm gonna need that luck. 

[Kipper4]

Dya think I could sub the 2n5087 with a 2n3906 anyone?

[Mustachio]

yes you can and I did originally because I didn't have any 2n5087's on hand. I ended up getting some of th 5087's and swapped out the 3906 and didnt hear any difference so you should be ok. I tried a bunch of transistors for this recently and none made to big of a difference.

I tried 5088's instead of the 89's as well. I think they have a little lower gain , if there was any audible difference I couldn't tell. You might want to socket the transistors and play around with diff npn's in Q1 and 2 but really I didn't find much of a difference if any.

let me know if you run into troubles ill try to help

[Perrow]

^ watch out for fake 13700's...like i had. pissed me off no end with various projects..

How would I test for that? Are those from Tayda "safe"?

[deadastronaut]

^ not sure on testing them as they never worked, but i tried various circuits with mine and even though i checked  the breadboard layout over and over...nopety nope...zilch...

i bought those on ebay...bad move.

i'm pretty sure tayda would be ok...

[Kipper4]

Just finished the offboard wiring and it works first time out.
Excellant job Mustachio.
the layout works a treat.
Right.
Question time.
Can it have a decay mod like the DrQ one?
Can it have an attack mod "     "     "       ?
In high mode is is supposed to sweep downwards too? can i change the rate at which it sweeps?
thanks
guys

[GGBB]

Just finished the offboard wiring and it works first time out.
Excellant job Mustachio.
the layout works a treat.
Right.
Question time.
Can it have a decay mod like the DrQ one?
Can it have an attack mod "     "     "       ?
In high mode is is supposed to sweep downwards too? can i change the rate at which it sweeps?
thanks
guys

R14 (680) controls attack - try a 1K-2K pot in series with a smaller resistor (220-100).  R15 (47K) controls decay - try a 50K-100K pot in series with a smaller resistor (22K-10K).  These are the two resistors that connect to Q3 base.  Sweep is the same (up?) in Hi or Lo mode.  The sweep rate is the combination of attack and decay.