Neutron layout differences

Started by FarrisGoldstein, August 06, 2012, 12:41:48 PM

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Mustachio

Awesome your almost there! Check my pic there see how the led is in the first and last pins in the socket rows , and check the copper side of the board in that area for any bridges. Good luck!
"Hhhhhhhnnnnnnnnnnnnngggggggg"

FarrisGoldstein

For some reason, on my board that 1M pot for the gain is just too much. I replaced it with a 500k and now it's "perfect." But this led me to realize I'm a dumbass...

This whole time, I did not know that the volume on the test amp I was using had been bumped down considerably. By accident, I had my guitar plugged straight into it and noticed it was way too quiet. THAT is why I was getting too much gain: I WAS JUST PUTTING TOO MUCH GAIN ON IT TO COMPENSATE FOR THE LOW AMP VOLUME.

So, that problem is out of the way. Now I just have to figure out why my LED has stopped changing brightness. I'll break out the DMM later to find whatever short or other malady I've inflicted upon this thing.

FarrisGoldstein

Oh, and I'll still have to figure out why my circuit does nothing when the rotary switch is in the bandpass position.

FarrisGoldstein

Hmm... Checked my LED pins, checked (and replaced) U3, checked all the caps & resistors in the part of the circuit that drives the LED, checked the traces for bridges/shorts... Still can't figure out why my LED stopped sweeping with the signal.

Makes a really neat theremin, though, if I crank the gain and crank RX, then move my head around near the LDRs while I play.

Mustachio

hmm that's strange led stopped sweeping. Rx seems like what effects the leds sweep, but its connected there to r17 and u3(pin5) and r12 , and the other half the led is connected over the jumper there to pin one of U3. So hopefully you can find the problem in that area. I remember if Rx was i think too high the led stays on and doesn't really sweep, or maybe it was if its too low haha I cant remember.

That's a good idea about the 1m pot changing it out to 500K I think ill try it since my 1m seems to be to sensitive and less useable range because of it. My other idea is socketing the resistors after the ldr and seeing if I can compensate for the difference in LDR type that was used in the original. I'm thinking R8 and R9 but ill have to do some experimenting.

Really you fixed soo much so far well done , sure you will find the problem for the led soon. I will say with mine even tho it sounds amazing it does so mainly in LP mode, BP and HP are just overall to high pitched to me and I think others have said the same about all different builds of the Mutron III. Set your Peak pot around half way and adjust the gain untill you can get some womp in LP mode and your set, I personally only find the one direction from low to high sweep useful to me. Really nails that Jerry Garcia sound :D
"Hhhhhhhnnnnnnnnnnnnngggggggg"

FarrisGoldstein

I'm not making much headway. Trying to have this thing finished by friday as a gift to my brother.

I'm still pretty green with the theory behind this stuff, any idea which components actually cause the input signal to change the current through the LED dynamically?

Mustachio

I think this article has everything

http://www.geofex.com/article_folders/ecftech/ecftech.htm

i can post more pics of my board and wiring if it helps. I think I might tinker with mine today and change some values on components after reading this article a bit more.
"Hhhhhhhnnnnnnnnnnnnngggggggg"

FarrisGoldstein

Here's a list I've made of possible causes, and status of checking them.

Hypothesis: Something is wrong with my LED driver circuit, which centers around U3a & U3b.

Checked/Replaced:
C9 (checked it & replaced)
C4 (checked & replaced)
U3 (Tried with several 072s and 4558s)
D1 & D2 (Given their purpose as a rectifier, this seems like a contender for a root cause, but aside from direction, I'm not sure what to look for)

Not checked:
R12 through R19

Another out-of-my-ass idea is that one of the components in this part of the circuit isn't properly grounded, and thus the LED is getting constant current.

I would test voltages, but I'd have no idea whether they were correct or not. I saw a thread where a guy posted his measured voltages at several points, but there was no response.

FarrisGoldstein

Aaaand, it's almost definitely a bad solder pad somewhere. Accidentally bumped the board while I was testing it and the LED started sweeping. It's intermittent now.

It almost definitely has to be one of the pads at the top for the off-board components. I'll just resolder them all.

FarrisGoldstein

Found the source of my static LED brightness, but now I'm playing gain tug of war:

With the gain high enough to sweep the LED dynamically enough for sufficient quack, the signal is way too distorted.

With the gain set at a level for decent tone, the LED won't sweep much (or at all), so the LDRs don't get/give any dynamics.

How do I get less gain at the input circuit and more gain/dyanmics at the U3 LED driver circuit?

R.G.

Maybe use an LED with more light output per current. That has the effect of goosing up the gain of envelope-to-light.

What is the rated brightness (typically in millicandelas) of the LED you used?
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

FarrisGoldstein

I've tried tons of LEDs, between 23mcd & 2000mcd.

The grit/distortion at the higher end of my gain pot really sounds awful, so perhaps my problem is on the input/gain side of things rather than the opto part?


FarrisGoldstein

I'm getting the "best" results with awhite LED I yanked out of a very old keychain flashlight. I really like the quack I'm getting now, in all three modes, and both directions. I just can't stand the gain/distortion, and turning down the gain kills my filter because the LED is not getting enough juice to pulse.

However, I am now convinced that there is something wrong with the gain of my circuit somewhere. Once again, I had my non-bypassed board hooked up to my practice amp for so long that I had not noticed my master volume on the amp had been bumped down (probably because I was afraid of waking up the baby at some point). When I turned it up, and plugged straight in, I realized I had been playing with far too much gain. When I turned down the gain, however, even my bright white LED was not sweeping.

So, either the U1/U2  sections are boosting the signal path too much. Regardless of how far off-schematic I am, do any of you have any suggestions of where to start tinkering so that I can do one of the following:

a) Decrease the gain at the "to filter" leg of the input stage, but leave the "to envelope detector" leg alone.
b) Increase the gain at the "to envelope detector" leg of the input stage, but leave the "to filter" leg alone.
c) Anything else that will make my output cleaner & quieter, but the current through my LED higher.

R.G.

Are your parts values correct?  I'm slightly color blind and I forever confuse 4.7K and 47K resistors by eye; this is just an example. A wrong-value input or feedback resistor on an opamp can make the gain vastly different. There are few enough resistors to check them all by eye and by meter in a few minutes.
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

FarrisGoldstein

*DOH*

RG suggested I test all the parts. Could have sworn I'd done that, but why not try again?

I was fearing that everything was looking fine, until I got to R12 & R13. Color test was fine, but they both were reading .5Mohm instead if 1Mohm. There was a burr shorting them.

Filed that out, and VOI-FRIGGIN-LA I have a Neutron!

Thanks for all the help, y'all. My brother is going to brown himself when I give this to him. I'll post some photos when I finish the box and the art.

Mustachio

"Hhhhhhhnnnnnnnnnnnnngggggggg"

FarrisGoldstein

Here's a video of the thing in action:



I'll try to get some gut shots later. Pardon the name (and the classy cartoon turd). It's a gift for my brother. He is a sick bastard and will love this.

waltk

Nice work!  Your brother is lucky to have a brother like you.

FarrisGoldstein

Thanks, Walt.

It's all done, but... Apparently there is something loose or shorting in there. Every now and then, it cuts out and I have to slap it to get it back in line (no misogynistic jokes, please, I already thought of them all and giggled).

So... Spend the next 3 days fidgeting with wires and components to find the problem, or just give it to him and say "hey, it's my first real stompbox... deal with it or fix it"?