Neutron success!

[mdh]

After struggling with this circuit for months on a breadboard and about a week on RG's pcb, I finally got the Neutron working! This thing's a funk machine Thanks to RG for the great project, and to everyone who has posted on the Neutron, especially Mark Hammer. I'm gonna have to go take another ten passes through his auto-wah write-up one of these days.

For what it's worth, I used the Hamamatsu P873-13 optocoupler from Small Bear, and Rx is ~12k at the moment (higher than RG's upper bound of 4.7k, but with lower values I lost a lot of frequency content). I'll try to post a more complete build report later, after I've had it working for a while. A friend has an original Mutron III... can't wait to compare them.

[bdevlin]

Ha! I just got fed up with mine and traded it.  Did you try the LED/LDR option or the H11F3 option?
For me, the H11F3 was a complete failure.  The LED/LDR combo got some Mutron like sounds but the effect was not quite right. 

Anyhow, if the gentlemen the I traded the Neutron to has Neutron questions I hope you are willing to help.  I could never get a response to my 2 or 3 Neutron questions.

[Aharon]

I searched for a Hamamatsu P873-13 datasheet without success.
I wonder how it compares with the other opto choices for the project,just to see why some fail anyways.
That's one of the projects on my bench right now,I was going for the H11F3 but it seems not to work .
Aharon

[mdh]

Ha! I just got fed up with mine and traded it.  Did you try the LED/LDR option or the H11F3 option?
For me, the H11F3 was a complete failure.  The LED/LDR combo got some Mutron like sounds but the effect was not quite right. 

Anyhow, if the gentlemen the I traded the Neutron to has Neutron questions I hope you are willing to help.  I could never get a response to my 2 or 3 Neutron questions.

I used the Hamamatsu dual optocoupler, available from Small Bear, which has been said to be the part used in the original Mutron III. I don't know this first hand, but anyway, that's what people say. It's an LED with two LDRs in a single light-tight package. Originally I had breadboarded the Neutron with two single LED/LDR optocouplers that I bought from Electronic Goldmine. They were $1 each, so I figured they were a bargain, and bought 8. The tolerances were insanely bad, and out of those 8 I could only find 2 that matched relatively well, and they had very low dark resistances (~200k or so, if I recall correctly). Never got it working on the breadboard. So I lumped those and paid $0.75 less for the Hamamatsu. Maybe I'll be able to use them in something else...  From all the Neutron threads I've read (and I think I've read them all), it sounds like the H11F3 option is more often than not unsatisfactory. As for the Clairex/Silonex/Vactec 2 x single opto options, it seems like the cost is most often going to be about the same as the Hamamatsu, so as long as Steve's stock holds out, I think that's the way to go. It may be that the Hamamatsu requires a larger value of Rx than RG suggested in his doc, which is why I think it's a good idea to just wire up a fixed resistor + pot in place of Rx for preliminary tests.

[mdh]

I searched for a Hamamatsu P873-13 datasheet without success.
I wonder how it compares with the other opto choices for the project,just to see why some fail anyways.
That's one of the projects on my bench right now,I was going for the H11F3 but it seems not to work .
Aharon

I never managed to dig up the data sheet, either. For utterly practical purposes, the data sheet is unnecessary. The leads that look like LED leads are the LED leads, and the long one is the anode, by the normal convention. Beyond that, however, it would be interesting to see the graphs of LED current vs. LDR resistance and response times. I meant to take measurements of at least I_LED and R_LDR before I put the part in the circuit, but of course I didn't (and I would need 3 DMMs to do it efficiently, if I want to measure both LDRs). I think there's a pretty good chance that I'll be building another one for a friend, though, so if that happens I'll give his opto the guinea pig treatment I did this on a couple of the surplus single LED/LDR optos that I mentioned in my reply to bdevlin, but they proved so inconsistent from part to part that I pretty much gave up on them for this purpose. In my earliest Neutron attempts with those single optos, I spent a lot of time looking at data sheets, trying to figure out if my problems were because my surplus optos responded very differently from the CLM6000, NSL32, etc.

Maybe if we had a good current response curve for the Hamamatsu opto we could sit down and do some calculus, and figure out how to make the other options work better. It would be amusing to try, at least

[lowstar]

congrats, mdh. quite interesting.
i struggled with mine for some time too and finally got it working, but it´s not in a useable (that means gigable) state for me.
i used the silonex couplers and found i had to raise the value of Rx to 51K (!).
it sounds like the real deal, but what makes it ungigable for me is the bypass thingy.
i tried true-bypass with vol-pot first, but had to find out that in the useable settings for bass (when the filter barely opens with hard attacks), the vol was below unity, so with the volume-pot solution, i was stuck.
then i wired it up the original way, and i don´t like the low output that i get (now also in bypass of course).

to cut the long story short:
mdh, how did you solve that problem, or was it not a prob for you cause of the different optocouplers ?

(i know that as a last resort, i could rewire to true bypass and stick a booster behind it, but i would love to find a more elegant solution. and i really want to, because the sound of the effect is cool and it is 20% the size of my mcmeat, which is a real monster to carry to gigs and rehearsals...)

cheers,
lowstar

[waldo041]

i true bypassed my neutron with no problems. i jumpered the effect "always on" then ran the input and output to the 3pdt switch and and wired the jacks to the 3pdt switch. i added 1M metal film resistor's to ground on both input and output jacks and it worked like a charm.

there is some matching of resistors and capacitor's for the envelope detection. i matched and used metal film resistor's for the 220k resistors ran in parrallel with each ldr and also matched the 2200pf and 1800pf capacitor's.  i read this at R.G. site, but it was written by mark hammer. http://www.geofex.com/Article_Folders/ECFtech/ecftech.htm.
it is a good read!

to set the Rx resistor.
i used Winscope and ran a signal thru a mutron at the setting i liked, then tried to copy the trace with the neutron. i used a 100k potentiometer and i remember the final setting also being way over what R.G recommended for the neutron. i do remember that when i found what the value was i used metal film resistors for it.

i will email the spec sheet for the hamamatsu P873-13, which i got from Steve at small bear, to whoever wants to host it for all to see. steve also mentioned that these were the exact replacements for the mystery 0805 part on the mu-tron schematic.


peace,
waldo

[mdh]

congrats, mdh. quite interesting.
i struggled with mine for some time too and finally got it working, but it´s not in a useable (that means gigable) state for me.
i used the silonex couplers and found i had to raise the value of Rx to 51K (!).
it sounds like the real deal, but what makes it ungigable for me is the bypass thingy.
i tried true-bypass with vol-pot first, but had to find out that in the useable settings for bass (when the filter barely opens with hard attacks), the vol was below unity, so with the volume-pot solution, i was stuck.
then i wired it up the original way, and i don´t like the low output that i get (now also in bypass of course).

to cut the long story short:
mdh, how did you solve that problem, or was it not a prob for you cause of the different optocouplers ?

I true bypassed mine, and haven't noticed any volume drop, but then again I haven't really compared effect and bypass levels, because there's not much incentive to bypass it with all that funk pouring out I'll need to play with it some more before I know for sure that it's gig-ready. I will check on whether there is a volume drop, though, and try to get back to you.

[mdh]

i will email the spec sheet for the hamamatsu P873-13, which i got from Steve at small bear, to whoever wants to host it for all to see. steve also mentioned that these were the exact replacements for the mystery 0805 part on the mu-tron schematic.

That would be excellent! I could certainly host it. I'll pm you my email address.

Matt

[mdh]

Lowstar, I just A/B'd effect vs. bypass, and didn't detect any volume drop with the effect on. If you're using yours with bass, I wonder if maybe you need bigger caps in the feedback paths of U2. I don't have a bass, so I can't check my unit with a bass until my next band practice (which will be at least 2 weeks, as I'm going on a road trip in a few days). I find that in order to get the funky rhythm guitar sound that I'm looking for, I need to have the range switch in the low position, hi cuts too much bass. So maybe for actual bass frequencies you need to modify it a bit. I seem to recall lots of threads about modding various ECFs for bass, so you might want to search for those for ideas. Also, MH's article on GEO (linked by waldo041 upthread) may be useful as well.

BTW, waldo041 sent me a page of graphs from P873-13 data sheet, and I've put it up at http://two.ucdavis.edu/~holland/electronics/P873_13.gif. There's no index page in that directory yet. I'll put one up if I get a chance in the midst of trying to work and play.

[lowstar]

thanks for the answers, mdh and waldo !
since the gain control sets the overall output as well, it must be a coincidence that the sound you like for the guitar is just the right amount of gain to make the bypass and the effect same level, usually (like at pisotones), some vol control pot is put in between, but as i said, my output is already too for this trick (i like the filter to just open a little bit, muoop-muah, so probably my favorite gain settings are really low). i also use the low setting usually, the filter caps are fine, the sound is right, it´s just not loud enough ;-)
markusw sent me some ideas on how to incorporate a mod to make the gain independent from the sweep, i´ll look into it and also the other suggestions. if all fails, i´ll tack a booster stage at the end ;-)

cheers,
lowstar

[grapefruit]

I didn't have much joy using the H11F3 to control the cutoff frequency of a State variable filter either. It wasn't a Mutron, but a similar type filter. It distorted a lot with the H11F3, even with low levels. It sounded ok using CLM6000 optocouplers, sounding best if the CLM6000's were matched. To match them I put another resistor in series with the CLM6000 resistor, put 10 volts accross them and noted the voltage drop for different LED currents. I hope this helps anyone using CLM6000's for this kind of application.

Stew.