Questions and notes on the Neutron Filter - mostly the optos

[Kevin Mitchell]

Finally got mine together after designing the template months ago.


Some quick notes on my build
-Homemade PCB with the GGG project files (most recent Neutron Documentation)
-Current wiring is a little different than the photo.
-Hand rolled optos with 3mm green defused LEDs. LDRs are either GL5516 or KE-10720, can't remember which I used.
-The 7660 caused some serious whine. I swapped it with a LT1054 - no trouble at all now.
-DP3T (on,on,on) toggle instead of the Mode rotary switch
-1MC for Gain
-1MB with a 180K resistor wired between lugs 1 & 2 for Peak, gives ~150K audio taper. Works well from what I can tell.
   -Geofex PDF shows both pots wired backwards
   -GGG shows only Peak wired backwards

Now for the trouble. For a about a day I thought I had a wire issue but everything checked out. At that point only the down sweep kind of worked and the other controls were not so pleasing and seemingly didn't function correctly - would get nasty distorted garble. So I subbed the RX resistor for a 1MB pot. I was able to dial it in to get the up sweep to work with the peak and gain as well. For the hell of it I put a 2.2m in place of RX. Now only the down sweep works. I can't find the sweet spot for this setup. I can dial in RX to get either up or down but I can't keep both. Since RX shouldn't be more than 4.7k though I've seen many folks test otherwise I am lost and can only blame the range of the LDRs.

Any tips on dialing this thing in? I'm going to make a couple of small boards as a homemade opto using both of the LDRs I have and matched this time. But that shouldn't make a big difference since all of the resistors used are 5% so matching will only do so much.


-One thought I had was to lower the 220k resistors that are in series with the LDRs. That should lower the dark resistance a bit - hopefully put them in a more usable range so both the up and down sweep are good.

-Also read the 4.7uF can be raised if the LDR's response is too fast. I'll worry about matching it with the original once it's actually working okay.


-KM

[idy]

you mean 220k in parallel with the LDR.

Rx is current limiting for LED. 2.2M things aren't working as intended at all.
Are you sure the on/on/on switch is switching modes the same way the rotary would?

Did you use an "external indicator" LED? does it do what you would expect? (dark to light and back on up range, vice versa on down)?

With the meatballs I have made I sometimes had to sub out the envelope opamp. For me the recommended did not work right for the envelope... I think neutron uses 072.  I sometimes used in place of lm1458 lm358.

Yes, matching LDRs can make a difference.

[Kevin Mitchell]

I've built a couple of meatballs. This is certainly a different beast.

Sorry, 220k resistors are in parallel.

I did not use an indicator LED. But I should probably put my oscilloscope to use here.

RX at about 820k brings the up sweep to life. I put 2.2M there out of curiosity because the pedal was behaving better with higher values. Anything less than about 500k would kill the up sweep (no sound at all), the down sweep would be very distorted and the gain knob can't really tame whatever's going on.

Everything works as it should except the drive switch due to the LDRs I've used. Or so I believe.

-KM

[Kevin Mitchell]

I'm going to remove and measure my rolled optos.

I'm comparing the GL5516 and KE-10720 datasheets to the P873-13 optocoupler (the Musitronics 0805 in the original). The 0805 seems to spec ~ 1k on, 10M off. So I'm thinking I actually used KE-10720 which is 10k on, 500k off. The GL5516 are rated 1k on, 10M off - identical to the 0805.

Will need to verify as I had not tested the optos I've used - prepped them months ago.

I also have some NOS VTL5C3 optos to try.

-KM

[Kevin Mitchell]

I put a couple VTL5C3 optos in with a 10k trimpot for rx (no matching). It works well now! I'm a little puzzled because my hand made optos used GL5516 and should be reasonably close in spec. Perhaps the LEDs I used respond differently compared to the 5C3s.

-KM

[Papaya59]

Hey Kevin !

Nice build here. I just ordered the PCB, components + the VTL5C3 in order to build the beast.

About the optos, I have seen on tagboardseffect website that a lot of DIY builders are using 2*GL5539 optos with LEDs, they are available very cheap on ebay or aliexpress, maybe it is worth a try ! I bought a batch of 25 for testing purpose.
For the whine induced by the 7660, it is maybe because you didn't bought the 7660S version of it, I have seen some builders jump pins 1 and 8 and it seems reducing the whining.

I'm really a beginner in DIY pedals and I have a question concerning the DPDT ON/ON/ON that you use instead of the rotary switch, I would like to do the same thing but I don't know how to adapt the wiring... Could you explain me how to do that using this drawing please ?



Also, I'm struggling to find the 15uF N.P. electrolytic capacitor, do you think it would be ok to put a 10uF N.P or a 22uF N.P ?

Finally, I was firstly interested to build the VFE MiniMu (Madbean's 2020 version) and he included an intermediary value for the RANGE switch (HIGH/MID/LOW), would it be possible for you to check the schematics and see if it is possible to introduce this in the Neutron ?

https://www.madbeanpedals.com/projects/_folders/VFE/pdf/VFE_MiniMu.pdf

Thanks in advance 

- AS

[Kevin Mitchell]

Hello! I had tried 2 different types of 7660 chips - one was the S variety. I think you mean using inductors to reduce the whine - not jumpers. Honestly the LT1054 just makes it easy and I have plenty as they are my go-to voltage chips (for voltage doubler or inverter). They haven't disappointed me yet.

I'll be back later with more details for you and also a wiring diagram to do what you're asking.

-KM

[Kevin Mitchell]

You had ordered one spaghetti monster? 
The range is matched to the MiniMu simply by using an on/on/on switch instead of an on/on. Just make sure you wire the correct sides as demonstrated in my layout.


Also, your choices for the bipolar capacitor should be fine. Or just bypass it.

-KM

[Papaya59]

Hi !

Wow, nice man I didn't expect that much ! What a nice spaghetti monster by the way xD
No, seriously thank you ! As soon as I receive the component I will follow your wiring !

The GGG (http://www.generalguitargadgets.com/effects-projects/filters-envelope/neutron/) website recommand to connect pin 1 to 8 with 7660 IC, it may stop the whine ! But yeah you are right, the .PDF also talk about a 680uH inductor. If I have any problem with the 7660S I'll try the one you used but I'll have to order some.

Looking to your drawing it seems that VFE MiniMu didn't introduce a new caps value but just blend the two pre-existing one to have a "middle" value, is that right ?
Also, I now understand what you mean when you said the peak pot was wired backward on GGG's wiring drawing.

Oh and also it seems that you wired the 3PDT trueBypass + DC jack a bit differently, do I have to follow your wiring or GGG's one ?

Thank you for your help ! 

-AS

[Kevin Mitchell]

My pleasure! Wiring can be a nightmare so I figured it's best to draw it out for you.

You should always bridge the boost pin on the 7660 chips when using for voltage tricks. But that didn't help me.

I had excluded the battery snap as I never use them - especially in builds I can't fit a 9V battery in!! That's why the power routing is different.

The range switch doesn't use any extra parts. You can see in the MiniMu it's just a DPDT switch - just half of the switching happens in center position. Thought it was strange but I've never tried it. The B position moves first, then the A position (or vice-versa). You can make sense of it looking at the Mode switch drawing in that schematic.

The bypass wiring is true bypass just like the GGG diagram but I do the dumb-down method. Following the GGG one should reduce bypass clicking. But that never seems to be a problem if you have pulldown resistors - which most stuff does nowadays. Or I'm just lucky? 
edit; the Geofex wiring or "A Neutron Wiring Diagram for the Schematic-Impaired" is just like mine, but he did it sideways so folks would wire it wrong

-KM

[digi2t]

Hey Kev...

Is it my eyes, or does the Type 1 switch you show on the side not work with the wiring scheme shown in the diagram? I follow it around, and the low or band pass doesn't seem to connect.

On the other hand, if I throw a Type 2 scenario at it, it works. Or... if you simply mirror the wiring and jumper on the switch, then Type 1 works?

Or, I'm I seeing things?

[Kevin Mitchell]

Ehh you're right I goofed something up. I'll look at my Neutron and refresh myself on the switching gymnastics. It'll look good later tonight! Could just be the diagram on the side being mirrored vertically.

3 hours of sleep and playing with DIYLC before work picked up.... I think I did okay 

[Papaya59]

Yeah ahah, wiring is a nightmare especially when you are a noob like me, I'm slowly learning but the slope of my learning curve is not as steep as I would like ! 
I won't use the battery clip either, that's good to skip it.

Thank you Dino to join us here !

What will be the solution of this wiring problem of the DPDT ON/ON/ON switch ?
I checked the datasheet of my switch and I don't know which type it is unfortunately, it is not referenced, but as soon as I receive it I'll let you know.

Again I apologize as my understanding of schematics and overall electronics is really small.

Thank you for your help.

Cheers,

-AS

[Kevin Mitchell]

I just need to make sure the diagram on the right is correct - which it likely isn't. The rest (as in the entire layout) should be good as I had used my own photos here as a reference.

The implication is what side of the switch changes in center position. I wanted to elaborate with the snippet on the right but messed that up 

I'll check first and then use good ole' MS paint.

-KM

[Papaya59]

Ah ok ! So the wiring diagram is right but depending on the switch type it's likely that I would have to mirror the wiring to match the pin-connexion layout !

cool, I'm new here, this website is a gold-mine and I truly think the guitar pedal DIY community is one of the best existing, so much sharing and learning here, thank you !!

-AS