Neutron Filter problem (anyone?)

[mat]

Hello,

I got my Neutron Filter finished couple of days ago and it is not working as it should be so here it comes:


1.What does it do, not do, and sound like?

Notes fade ugly, loud peaks in sound.
http://koti.welho.com/mtiilama/sound/neutron.mp3

2.Name of the circuit =

Neutron Filter

3.Source of the circuit (URL of schematic or project) =

http://www.geofex.com/PCB_layouts/Layouts/neutronpub.pdf

4.Any modifications to the circuit? Y or N

N

5.Any parts substitutions? If yes, list them.

-R9 is 250k instead of 220k
-C14 is 10u and 4u7 polyesters in parallel instead of a 15u non polar
-peak pot is 220kA
-gain po is 1MB not reverse
-RX is 4k7 pot
-variable resistors section has option 4. components. Two LDR (matched) + ultra bright green led. They are covered with a piece of tape for now

6.Positive ground to negative ground conversion? Y or N

N

7.Turn your meter on, set it to the 10V or 20V scale. Remove the battery from the battery clip. Probe the battery terminals with the meter leads before putting it in the clip. What is the out of circuit battery voltage? =>

unconnected batteries 9.89V and 9.8V
connected batteries and the terminal are  -9V , 0 , +8.9V

PCB done by drawing with permanent marker and after etching carefully measured every trace (I've done this alot).

After soldering checked with magnifying glass for all traces\connections

C9 electrolytic +side is -70mV and -side is 0V.

C1 4u7 tantalum was first wrong way (did not knew they have polarity ?!)

Forum searched and read about three hours of the subject. Did not find direct solution (noob). I have to try Mark Hammers tip for using the 10u cap and someone elses tip for using bigger pot for the RX.

IC voltages:

U1

1 0,8mV
2 1,3mV
3 1,6mV
4 -9,58V
5 0
6 1,7mV
7 1,7mV
8 9,45V


U2

1 2,1mV
2 -2,2mV
3 0
4 -9,53V
5 0
6 0,8mV
7 -2,2mV
8 9,4V


U3

1 -2,64V (or 8,65V when sweep switch flipped)
2 -75,4mV
3 -76,2mV
4 -9,49V
5 0
6 -1,5mV
7 0,5V
8 9,37V



Here is how I wired it.

http://tinypic.com/5ebvh5

It was a little difficult for me to understand it correctly (still is). There is one wire unconnected (the red-dot wire) and the indication led has no power yet (with ? mark). I think it shoul be connected to +9 terminal.

I was very glad to at least have a sound out of the effect so I might not be very far to have a working Neutron.

I would be most grateful for the help on this one.

Thanks,
mat

[Mark Hammer]

First, thanks for the sound sample.  That helped a lot.

Second, mine is a mostly populated board, and I haven't gone farther than that (hmm, maybe too damn many autowah's lying around to be motivated?).  I salute your diligence.

Your part substitutions do not seem to be important to the problem I heard.

The sample (funky riffing, incidentally) uses a downward drive setting, and I think that is where the problem lies.  What to do about it, I'm not entirely sure, but we'll consider a few things here.

In the upward drive mode, U3a puts out an AC voltage that ought to be going positive before it falls back down again to zero.  In the downward drive mode, a bias voltage is applied to pin 3 of U3a, via the dividing down of +9v by R18 and R19, and the envelope signal is essentially "subtracted" from that, before it begins to drift upward to that bias point again.

For me, the clue to an error at this point is the fact that your "starting point" in the filter sweep seems very low, in fact too low.  What this means is that the envelope follower (U3b) will essentially try to subtract more voltage from the bias point than is physically possible.  Again, the clue is in the way it starts out the sweep in a reasonable fashion but sounds awful as it hits the bottom of the sweep.  I'm assuming that it isn't a result of distortion in the sound card itself.

So, I don't think the problem lies in the LED or LDRs you've chosen, the pot values/tapers, or the remote possibility that your filter caps are too large (lower range if that was true).  My first instinct would be to see if setting the bias a little higher in U3a might do the trick.  R19 is 120k.  Why don't you try sticking a 50k trimpot between R19 and ground.  Set it to zero ohms, and gradually increase the resistance to see if a) your start point for the downward sweep moves upward, and b) it craps out less often or not as much at the "bottom" of the sweep.

Others here will surely have some good advice too, but if you can do the suggested test and get back to us with the outcome, I think other future builders would appreciate it.

Hmmm, does this make you my brother-in-wah? :lol:

Best of luck,
Mark

[gorohon]

How many values did you try for Rx?  I had to meddle around to get mine to behave.  I actually put in a toggle to select three different Rx's so I could get some weird sweeps.  I used a dual vactrol type optocoupler, so my Rx might be different than what might be suitable for other setups.
BTW, it took me a long time to work out all the bugs in mine, mostly due to the PCB turning out much smaller than it was supposed to be (I didn't adjust the print out to the proper scale). My IC sockets look like they're on stilts!  I also had some broken traces and lifted pads.   I used my POD XT's version of the MutronIII to make comparisons of the "up" sweep to determine when it was close.  I really haven't been able to settle on a single Rx that suited both the "up" sweep mode and the "down" sweep mode, that's one of the reasons why I used an "on/off/on" spdt switch to select different sweeps.  I still think that the "down" mode is a little weird--it sweeps either too fast or stays at it's peak too long.

[mat]

deleted OT post

mat

[mat]

Hi Mark,

First, thanks for the sound sample.  That helped a lot.

I thought so, the warbling(?) tone is quite hard to describe (with my far from perfect english)

Your part substitutions do not seem to be important to the problem I heard.

Ok, btw the C6 and C8 are 1n5 not 1n8.

The sample (funky riffing, incidentally) uses a downward drive setting, and I think that is where the problem lies.  What to do about it, I'm not entirely sure, but we'll consider a few things here.

The other setting does not change the sound (does not light up the led). Not eaven with the 50k pot installed between the R19 and ground.

The sweepin happends only with the RX AT 0OHMS or with a very little of resistance (with downward setting).

In the upward drive mode, U3a puts out an AC voltage that ought to be going positive before it falls back down again to zero.  In the downward drive mode, a bias voltage is applied to pin 3 of U3a, via the dividing down of +9v by R18 and R19, and the envelope signal is essentially "subtracted" from that, before it begins to drift upward to that bias point again.

For me, the clue to an error at this point is the fact that your "starting point" in the filter sweep seems very low, in fact too low.  What this means is that the envelope follower (U3b) will essentially try to subtract more voltage from the bias point than is physically possible.  Again, the clue is in the way it starts out the sweep in a reasonable fashion but sounds awful as it hits the bottom of the sweep.  I'm assuming that it isn't a result of distortion in the sound card itself.

It is the effect that is broducing the distorted peaks.

So, I don't think the problem lies in the LED or LDRs you've chosen, the pot values/tapers, or the remote possibility that your filter caps are too large (lower range if that was true).  My first instinct would be to see if setting the bias a little higher in U3a might do the trick.  R19 is 120k.  Why don't you try sticking a 50k trimpot between R19 and ground.  Set it to zero ohms, and gradually increase the resistance to see if a) your start point for the downward sweep moves upward, and b) it craps out less often or not as much at the "bottom" of the sweep.

I tried with the 50k pot in series with the R19 to ground but did not noticed any difference on the sound either down or upwards settings.

I also changed the C9 from 4u7 to 10u and the RX to 220k pot but the nasty death of the notes still remain.

Hmmm, does this make you my brother-in-wah? :lol:

 Yes, I think so. Me being a recruit  :wink:

I'm big noob about knowing what part does what but is there some cap that could be faulty. When the note dies ugly the led is blinking very fast. What could be the reason for that ?

Here is sound sample recorded after changing the parts. First the effect bypassed.
http://koti.welho.com/mtiilama/sound/n3.mp3

mat

[mat]

Hi gorohon,

How many values did you try for Rx?  I had to meddle around to get mine to behave.  I actually put in a toggle to select three different Rx's so I could get some weird sweeps.  I used a dual vactrol type optocoupler, so my Rx might be different than what might be suitable for other setups.

As I noted I used a 4k7 pot for the RX but just changed it to 220k - no help in this case.

BTW, it took me a long time to work out all the bugs in mine, mostly due to the PCB turning out much smaller than it was supposed to be (I didn't adjust the print out to the proper scale). My IC sockets look like they're on stilts!

   

I also had some broken traces and lifted pads.   I used my POD XT's version of the MutronIII to make comparisons of the "up" sweep to determine when it was close.  I really haven't been able to settle on a single Rx that suited both the "up" sweep mode and the "down" sweep mode, that's one of the reasons why I used an "on/off/on" spdt switch to select different sweeps.  I still think that the "down" mode is a little weird--it sweeps either too fast or stays at it's peak too long.

Maybe You could tweak the downmode to it to behave properly ? Sorry I can not give any help because as You see I'm quite helpless with this one already  :roll:

mat

[gorohon]

I'm glad that I got mine to where it's at right now.  It's always a huge challenge to debug these pedals and it seems that I never have any work right off the bat.  Maybe, in another five years, I'll have a better technical understanding of what is going on with these things.  I am more gifted with mechanical aptitude and just have the right amount of ignorance that keeps me building stuff that should be beyond my electronic capabilities :lol:

Anyways, it sounds like you got yourself quite a challenge debugging your neutron.  Good luck, it will be worth the trouble.  I just wish I could help you out more.

[moisho]

Hi guys. This is my firs post... and I'm sorry it has to be just here... :roll:
Let me introduce myself... I'm from Spain... (I've seen some people also from span here   ) and I'm really enjoying DIY. I have build a lot of stompboxes... Big Muff, LPB, SmallClone, SmallStone, a piece of a Rebote, another fuzz, a crash synth (f* optocoupler!!!), you know....

First of all, congratulations for this amazing place.
Second... mat, perhaps we are going to be brothers-in-wha also....  

I've got a clear envelope filter in one position (lets say A position...) of the up-down switch, but not for the other (let's say B).
I've put the 50k trim pot and I've tried diferent sets of values with no result (for the B position, very sensitive in the A pos.)

My voltages are:

U1

1 2.4 mV
2 5 mV
3 2.9 mV
4 -11.5 V
5 -0.2 mV
6 2.9 mV
7 2.7 mV
8 12.19 V

U2

1 7.5 mV
2 3 mV
3 0 V
4 -11.8 V
5 0 V
6 2.4 mV
7 3 mV
8 12.19 V

U3 A position

1 11.8 V
2 0.15 V
3 4.5 V
4 -11.5 V
5 0 mV
6 -0.7 mV
7 0.4 mV
8 -0.2 V

U3 position B (I have almost no effect here)

1 7.4 mV
2 3 mV
3 0 V
4 -11.8 V
5  0 V
6 2.4 mV
7 3 mV
8 12.5 V

Any Idea?

By the way... I'm using a MAX charge pump, GGG PCB and schematic, and I have made no modifications except the trimpot.
The optocouplers are VTL's

Thanks in advance.

[mat]

Hi moisho and welcome  

We have a wonderful forum here, full of gentlemen. I'm sure You will enjoy it very much.

For Your problem, as You might have guessed, _I_ have no solution. I think I'm goig to read again everything I can find with the search option here about the Neutron and the relating problems.

Tervetuloa  :!:  (welcome in Finnish),
mat

[mat]

Hi again,

I've read most of the forum about the Neuton Filter but can't find my way out of the problem.

Could someone have some kind of idea about the following:

I wrote:
When the note dies ugly the led is blinking very fast. What could be the reason for that ?

- that is just when the ugly distortion happends.

mat

[mat]

Hello,

Well this circuits seems to be too much for me. Don't know eaven where to start to debug it  :cry:

To medicate my wounds i built my first Fuzz Face and GGG Modable Wah, they both work wonderfully - they ROCK  :twisted:      Soundclips to come..

If someone could give me a hint for the Neutron Filter's 'led blinking fast/nasty distortion' at note fade - problem, I would be most thankful.

mat

[gorohon]

Just curious, have you tried using different optocouplers for the LED/Dual LDR.  I'd wonder if there might be something funky going on (not the good funky) with your setup there.  I used the dual optocoupler from Smallbear that is recommended for the Neutron.  Of course, there are a whole bunch of good options to use.
I don't know what else you could do except build it again, but real slow and zen-like, hoping that it won't break your heart again.

BTW: My pedal that gives me fits is my Craig Anderton Compressor.  It ate CLM6000's like candy, and now it only wants to be an overdrive.  It's a pity, because that is a great compressor when it works right.

[mat]

Hi gorohon,

Just curious, have you tried using different optocouplers for the LED/Dual LDR. I don't know what else you could do except build it again, but real slow and zen-like, hoping that it won't break your heart again.

BTW: My pedal that gives me fits is my Craig Anderton Compressor.  It ate CLM6000's like candy, and now it only wants to be an overdrive.  It's a pity, because that is a great compressor when it works right.

All right, I'll try another ldr's - thanks for the tip. When I measured them with the normal light and dim light they were exactly same but the value was quite high if I remember it right.

I think I'm not going to build this from zero again. I'll try to swap components to the death  :?

The Craig Anderton Compressor seems to be a real nice unit. (http://diystompboxes.com/sboxforum/viewtopic.php?t=26218&postdays=0&postorder=asc&highlight=craig+anderton+compressor&start=15)
I've built the Orange Squeezer so far and have made PCB for the ross/dyna comp. After the dyna I might try the Anderton one (if that is not too much for me also.. :oops: )

I had similar issues with my Orange Squeezer also, and while it to stop the compression it just suddenly came alive again - go figure  :roll:

Thanks again for Your tip,

mat

[Mark Hammer]

Very often, what people call "distortion" in envelope-controlled devices (filters, compressors, noise gates) is actually envelope ripple in the audio range.  What I mean is that the envelope signal is not smooth.  Imagine a tachometer on your dashboard that showed and updated your exact RPM every 100msec.  It would be unreadable because it doesn't stay still.  You want the envelope signal to be as smooth as possible.  Otherwise, it sounds like your pedal is speaking Scottish or Hebrew very badly.

One of the things that LED/LDR combinations do is help that.  In my Technology of Auto-Wah pedals article, I present a table showing the  advantages and disadvantages of different "control elements".  LDRs have the advantage of being slow enough in their return to a high-resistance state (although, yes, you CAN buy some which are pretty fast, though never as fast as transistors or OTAs), that they act like extra filtering during the decay phase of a sweep.  Normally, it is during the decay phase that you REALLY notice the small ripple remaining in the envelope.  Since the LDR is slower to react than a transistor, it doesn't change resistance fast enough for that ripple to be heard.

The envelope follower and LDR cooperate so that a slightly faster decay from the rectifier (i.e., a smaller capacitor to ground) is offset or compensated for by a slightly slower LDR response time.  If it should happen that the LDR is a fast one (i.e., it easily responds to small illumination changes, across its entire resistance range), then the rectifier cap may not be large enough in value to produce a nice smooth sweep without audible ripple.  The practical solution is to increase the cap value, but of course that also means that after you strum a chord the filter may take longer to settle down and recover than you would like.  My advice is to get the Hamamatsu dual photocell that Small Bear sells, if only to be able to rule out optoisolators as a source of the problem.

[gorohon]

Yep, Hamamatsu dual photocell is the one that I used.  I forgot the name.

[moisho]

OK I will try the hamamatsu dual photocell.

Right now my Neutron has become unusable, the gain pot acts like a kind of switch... no signal o hiper-high distorted one (with a small intermediate position).
Is there any modification to compensate the usability range of the pot??

[mat]

Hi Mark,

Very often, what people call "distortion" in envelope-controlled devices (filters, compressors, noise gates) is actually envelope ripple in the audio range.  What I mean is that the envelope signal is not smooth.  Imagine a tachometer on your dashboard that showed and updated your exact RPM every 100msec.  It would be unreadable because it doesn't stay still.  You want the envelope signal to be as smooth as possible.  Otherwise, it sounds like your pedal is speaking Scottish or Hebrew very badly.

Good description, I learned a new thing. Also very hilarious presentation of the sound  :lol: My family had a good laugh when I showed them how daddys new effect sound  :lol:  :lol:  :?  :oops:  :roll:

One of the things that LED/LDR combinations do is help that.  In my Technology of Auto-Wah pedals article, I present a table showing the  advantages and disadvantages of different "control elements".  LDRs have the advantage of being slow enough in their return to a high-resistance state (although, yes, you CAN buy some which are pretty fast, though never as fast as transistors or OTAs), that they act like extra filtering during the decay phase of a sweep.  Normally, it is during the decay phase that you REALLY notice the small ripple remaining in the envelope.  Since the LDR is slower to react than a transistor, it doesn't change resistance fast enough for that ripple to be heard.

I downloaded the autowah.pdf. I will read it and try to learn more.

The envelope follower and LDR cooperate so that a slightly faster decay from the rectifier (i.e., a smaller capacitor to ground) is offset or compensated for by a slightly slower LDR response time.  If it should happen that the LDR is a fast one (i.e., it easily responds to small illumination changes, across its entire resistance range), then the rectifier cap may not be large enough in value to produce a nice smooth sweep without audible ripple.  The practical solution is to increase the cap value, but of course that also means that after you strum a chord the filter may take longer to settle down and recover than you would like.  My advice is to get the Hamamatsu dual photocell that Small Bear sells, if only to be able to rule out optoisolators as a source of the problem.

Ok, I'll try different ldr/led combinations. If those will not work I try to find the Hamamatsu optoisolator here in Finland, if not I'll shop Small Bear.

I subbed the C9 from 4u7 to 10u without hearing much improvement to the sound - if that is the cap You are referring to.

Thank You for Your help and patience,
mat

[Mark Hammer]

Yes, C9 is the one.  I'm not suggesting that you should go on subbing capacitors indefinitely, but try 22uf and see if it starts to sound more acceptable at that point.  10uf may not be enough to make a huge difference.

Also, just to be clear, when I say about LDRs that "... they act like extra filtering during the decay phase of a sweep...", what I mean is filtering of the envelope, not the audio signal.  R14 and C9 act like a simple lowpass filter on the rectified/envelope signal.  

Think of envelope ripple as being like "fizz" on a distortion unit, except at a much much lower frequency.  The same way one might stick an extra capacitor in an op-amp feedback loop to kill unwanted hiss or upper harmonics, increasing the value of C9 essentially lowers the "rolloff" of that lowpass filter so that any ripple in the envelope signal is attenuated a bit.  With R14=330R and C9=4.7uf, that gives a lowpass rolloff starting around 102hz, which obviously leaves plenty of room for any ripple to be audible (imagine you were sweeping the filter with an LFO at 100hz).  A 22uf cap for C9 starts to roll off at 21hz.  If the LDR can't respond to voltage changes faster than 20hz (i.e., it takes at least 50msec to react/change/settle), then that reduces the audibility of any remaining ripple in the 15-25hz zone even more.

Starting to fit together now?

[mat]

Hi Mark,

Starting to fit together now?

Thanks Mark, I really hope so ! Thanks for the further clear up.

I have to drive almost 2000km on the next three days (and the mooses are very active on this time of the year) so I'll get back to the Neutron matter after our trip.

mat

[ambusch]

I just finished building one and it sounds awesome.  Used the h-bomb photocoupler from small bear electronics, almost too big for my case.  In addition to the stock model i put in a mix pot, and a single transistor booster circuit and a volume pot.  The only bad thing is the notes fade ugly.   I'm going to try replacing that cap as mark suggests... I will report back soon to see if it clears anything up.