Moid's Random Tremolo

[Transistor-Transistor]

I wonder if there would be a way for phototransistors to act as a replacement for LDR's as they're much easier to find and don't have the Cadmium that Europe doesn't like. I have a 3d printer and I'm planning on making my own vactrols with that (just to be less janky than shrink wrap and duct tape)
Phototransistors and LDR's are not really interchangeable but I'm sure things can be done circuitry wise to make it more similar

Thanks Transistor-Transistor - I also looked into phototransistors but they seem to be for modulating current? Can that be used to modulate resistance? They don't have any banned materials in them which sounds good.

Phototransistors can be used to modulate resistance, and they're very sensitive which you said you wanted. The cons is that they're active components and need to be biased in order to get an output. HOWEVER
They're lower noise 

I haven't used them too much but they essentially feel like active LDR's that can do more stuff.

[moid]

A few ideas:


2. Play around wiht the value of your R2. It should affect the depth of the effect, especially if you put a buffer or another effect in front of the Moidulator. With a passive guitar straight in to the R2 it might not make as big difference.

Just tried changing R2 - 100k resistor kills all sound, a 1k makes everything much louder and clearer! Thanks for that, I have changed to 1k. You were right about passive guitar - I couldn't hear much difference between the original 10k and the new 1k, but if I stick a boos pedal in front of the circuit there is a huge volume difference - same thing happens if I use a boost pedal.

[duck_arse]

we are told, when leds cycle, they have "circuitry" inside, and they are inherently noisy. it might be that you can't get them noise free.

sing.

I laughed when I saw your finger. I'm off to listen to Jnr's playing.

[Matthew Sanford]

Loving Moid Jr.'s playing! Early one the second he slides up before switching to the next chord, great to mix a little lead into the rhythm!

Opto/phototransistos, like LDR but npn's base is light dependant. As Transistor said, very sensitive-but don't flicker.


SeePC817 data sheet.

Paralleling a resistor with the LDR will lower the value to 1/inverse of sum, I believe. Digi-key's calculator. So 2 10k resistors give 5k (1/10k+1/10k=2/10k=1/5k). With an LDR having high dark resistance the drop on the other value is small but gives you your new max resistance.

You might ditch the 78L05 and just use 9 volts with big enough CLR. Keep the power decoupling caps though.Looking for flicker LED datasheets it seems 30mA and 2-4volt drop is common-ish. A green led is normally 20mA, 2.1 forward voltage drop.
LEDs use current, so Ohm's Law is your friend there. This calculator is good to see the arrangements either way (parallel/series) with current usage etc and CLR value.

On the volume out thing forget it, just realized your kind of already doing that with LDRs to ground. You could put a small series resistor before them which could make it more pronounced.

[moid]

sing.

I laughed when I saw your finger. I'm off to listen to Jnr's playing.

I always knew I had it in me to be an all round family entertainer! I can do witty repartée, cutting one liners and slapstick. I should get a raise.

Jnr's playing is a lot better than mine - although the few mistakes were due to the room being very dark so that the LDRs wouldn't pick up any stray light, which meant that he couldn't see the fretboard that well.

Loving Moid Jr.'s playing! Early one the second he slides up before switching to the next chord, great to mix a little lead into the rhythm!

Opto/phototransistos, like LDR but npn's base is light dependant. As Transistor said, very sensitive-but don't flicker.


SeePC817 data sheet.

Paralleling a resistor with the LDR will lower the value to 1/inverse of sum, I believe. Digi-key's calculator. So 2 10k resistors give 5k (1/10k+1/10k=2/10k=1/5k). With an LDR having high dark resistance the drop on the other value is small but gives you your new max resistance.

You might ditch the 78L05 and just use 9 volts with big enough CLR. Keep the power decoupling caps though.Looking for flicker LED datasheets it seems 30mA and 2-4volt drop is common-ish. A green led is normally 20mA, 2.1 forward voltage drop.
LEDs use current, so Ohm's Law is your friend there. This calculator is good to see the arrangements either way (parallel/series) with current usage etc and CLR value.

On the volume out thing forget it, just realized your kind of already doing that with LDRs to ground. You could put a small series resistor before them which could make it more pronounced.

Thanks Matthew! Jnr was really happy about your comments I honestly don;t know how he does it - he just comes up with things all the time and it's effortless for him. I struggle to remember two chords at a time and a selection of notes that might work with them. And I'm resolved to the fact that my music is more 'abstract' than rhythm based

Thanks for the information about phototransistors. As you say - they don't flicker - I had a look at some examples on Mouser, and they seem to be like vactrols (which explains your diagram), so possibly if they were broken apart (split the LED part off) the phototransistor part could be used as an LDR if attached to one of my flickering LEDs? Or they might just break; the packages look very tightly combined and I haven't found a phototransistor separate to an LED yet. They look like they might work as substitutes for LED/LDR combinations that are controlled by a 555 circuit (squarewave or triangle) type LFOs?

I'm going to keep the 78L05 as it seems happy now and everything works around it! What did you mean by "Keep the power decoupling caps though" I didn't have any capacitors in that previous build?



 

[moid]

New changes to the circuit. I added a DOD 210 preamp as a booster to the front of the audio. This makes the audio louder (but without adding the fuzz that an LPB1 does) and seems to work with the tremolo happily - sounds similar to the versions I posted previously when I played through a booster pedal first. Does adding this circuit mean I still need a buffer?



The next thing to work on is to try to figure out how to add switches to each LED section so that I can take one or more LED/LDRs out of the circuit when I want to vary which tremolo is functioning. Should the switches be positioned on the little vertical spurs that fall down from the 5 volt power line that goes to each potentiometer, so that each spur can be switched on and off, or should I place the switches on the LDRs somehow to break the connection there? I can't work out what would be best from an audio point of view / least likely to cause issues when I do it.

I definitely need to get more sensitive LDRs as well; even with all the changes the effect of the LEDs is not strong enough - most of the time I hear one LED particularly, and the others kind of blur together. It seems odd to me that I can have 4 of them working on the audio at the same time and still a lot of music carries through - I would've thought there would be moments when 4 LDRs would remove so much audio that it must cut out completely, but I guess that's because they are not sensitive enough.

[Matthew Sanford]

They have separate phototransistors that look like LEDs like this one. It seems green is best wavelength to turn it on, but not sure how it'd improve your situation...might be more sensitive.

Put switches before led pots, that way LDRs go max resistance and mess with the others less. You might want to tie the led's pot's pin 3 to 2, they look floating so may catch noise on the breadboard.

Doesn't that FET kind of buffer it too? I'm not sure so asking...

[duck_arse]

discrete photo transistors - FPT100. also, MEL12 and 2N5777, both photo darlingtons. old parts all, good luck finding.

[moid]

They have separate phototransistors that look like LEDs like this one. It seems green is best wavelength to turn it on, but not sure how it'd improve your situation...might be more sensitive.

Put switches before led pots, that way LDRs go max resistance and mess with the others less. You might want to tie the led's pot's pin 3 to 2, they look floating so may catch noise on the breadboard.

Doesn't that FET kind of buffer it too? I'm not sure so asking...

Thanks! Switches before pots makes sense now that you explain it. I've made some changes to the circuit (see below) but have only just read your comments. I will tie the floating lugs to pin 2 on hte next iteration.

Interesting thing about the buffer or lack of - with the changes I've made to the power line (see below) the circuit is fairly quiet with a guitar plugged in directly and not playing, but even quieter still when I stick my Boss RC1 in there... so I think the boost circuit works, but a Boss buffer is even better, because without it there is this weird hiss warble sound at around 1.5Khz - when you play it can't be heard, but when you stop playing it is audible on headphones (not sure about speakers; it's late here so I had to turn the amplifier off).

Does this mean I should build a buffer in as well? I wonder if the hiss might be because the new powerline changes affect the tremolo but not the booster circuit. IF I should build a buffer circuit, is there a particular one you would recommend?


If neither Boss pedal or guitar is plugged into the circuit, but the circuit is attached to the amplifier there is quite a loud hum... it disappears as soon as the guitar is plugged in. I'm not worried about that!

[moid]

discrete photo transistors - FPT100. also, MEL12 and 2N5777, both photo darlingtons. old parts all, good luck finding.

Well I found a chap on ebay who has the FPT100 for sale at a mere £7 each! Couldn't find any MEL12, but 2N5777 are available on ebay for a paltry £14.95! So obviously I ordered his entire stock, I mean for peanuts prices like that I'd be silly not to invest eh? I'll just explain to my family that we don't need to eat this month, but in ten years time we'll be millionaires...

ahem, after a brief consultation with the stakeholders of moid PLC, I think those parts will need to remain in the hands of others for now! Thanks for the suggestion Duck. I'll go back to being a peasant and will make do with what I've got!

[Matthew Sanford]

Ebay, well, never know what you get! But the link I'd posted for Digi-Key, those were under $1 a piece (US, not sure how they go in UK).

For a buffer, read our wonderful Jack's amazing page about different buffers. I'd say scroll past the FET and play with the opamp ones - you'll see a cap either side and a big resistor to bring bias voltage in, make sure you bias it. I think one either end would do you well (after input, before output), you wouldn't need other pedals before but hey it might change it up so keep doing it!

[moid]

All change ladles and jellyspoons, all change!



Now let it be said that that Electric Druid chap is not just a pretty (or even not just a ruggedly handsome) face; I won't judge... I completely stole the power section from his FilterFX circuit, because Matthew said something about decoupling capacitors and I thought maybe he meant those? Anyway, if you stick that mass of diodes and capacitors into the circuit, guess what? Three of the LEDs stop singing! And I can revert them back to 220ohm resistors for brighter brights and they stay silent The fourth LED remained stubborn making a pulsing hiss noise that I hadn't noticed before (but the other noises were louder so it was probably always there)... so I increased its resistor to 1K (I tried every value between 220R and 1K that I had), but even 820R doesn't stop the hiss - however it goes at 1K. The downside is that particular LED is considerably less bright now and doesn't have much brightness range difference between when the pot is full on or full off. So I guess only a more sensitive LDR can save me on that one?

At the moment the new power caps and diode are only affecting the tremolo and not the boost circuit. Should they affect both circuits? In which case I should presumably only use D5, R13, C3 and C4 and conncet them to the 22K resistor on the boost?

[moid]

Ebay, well, never know what you get! But the link I'd posted for Digi-Key, those were under $1 a piece (US, not sure how they go in UK).

For a buffer, read our wonderful Jack's amazing page about different buffers. I'd say scroll past the FET and play with the opamp ones - you'll see a cap either side and a big resistor to bring bias voltage in, make sure you bias it. I think one either end would do you well (after input, before output), you wouldn't need other pedals before but hey it might change it up so keep doing it!

Whoops, I didn't notice the link in your post! Sorry! OK luckily Mouser sell them in the UK and they only cost £0.56 so are perfectly affordable. I might buy a few when I buy the LDRs for future experimentation.

Thanks for the buffer info. If I was to put a buffer before and after, could I use a TL072 so I could use both op-amps in that chip (one for the before buffer and one for the after) or is that considered a bad idea? I can use 2 TL071s if required, but that's a lot of extra space used up if I don't need to! Should the buffer go in front of the boost circuit (I think so?) or between the boost circuit and the tremolo?

Yet another question (what else?) what do you mean by 'Make sure you bias it'? Do you mean try different value resistors there? And what sort of change would I be looking for? EDIT after reading Jack's page again, I think you mean try different resistors between 1M and 10M and see if the audio sounds cleaner / brighter and there isn't any new source of noise.

[Transistor-Transistor]

What I'm about to say may be sacrilege.
You may wanna sit down for this

...

Sometimes if parts are expensive on digikey and mouser you can find them really cheap on Amazon-

(Sometimes I use parts bought from amazon and I haven't noticed a quality difference)

That's my controversy of the day

(Quick edit)
Okay I just looked for phototransistors on amazon and I was way wrong. disregard me

[Matthew Sanford]

Moreover just make sure a midpoint voltage (4.5 for 9 Vcc) is present on the + in. I don't think resistor values matter much if you set it like Jack's example, however... I like to set up the divider with a couple 10ks, one to V+, one to ground, then where they meet (giving 4.5 volts as half the power supply) use a 1 Meg resistor to bring it to the op amp. You should also put a cap, say 10uF from that midpoint to ground to keep it stable-don't use the cap if it's going to an LFO generator (thanks to Duck for that). Reason for lower bias divider resistors and big ones to bring it in is that big one essentially is parallel to the one going to ground, so making it decades larger doesn't change the divider resistor value (much...)

Use a dual, it won't mess with it, so save space!

Digi-key has loads of calculators for most things. If you feel you need a lower voltage you can plug in values to see what you get, has the formulas too.

I hope the actual smart peeps are checking me, don't want to lead you astray.

[duck_arse]

I knew if I gave you some numbers, you'd find them. you're good like that.


LPT80A Side Viewing Silicon Phototransistor $1.33

LTR-4206 3mm NPN Silicon Phototransistor $1.87
https://au.mouser.com/ProductDetail/Lite-On/LTR-4206E?qs=GHV6gLndNKlNoc%252Btn97dSA==
https://www.digikey.com.au/en/products/detail/liteon/LTR-4206E/121710

SFH325G Side LED SMD NPN Sensor Phototransistor $0.61
https://au.mouser.com/c/?q=SFH325

I found three obsolete parts at my nearest surplus joint, Rockby. plenty cheep options at digikey and mouser. dunno why you want them, tho.

[moid]

What I'm about to say may be sacrilege.
You may wanna sit down for this

...

Sometimes if parts are expensive on digikey and mouser you can find them really cheap on Amazon-

(Sometimes I use parts bought from amazon and I haven't noticed a quality difference)

That's my controversy of the day

(Quick edit)
Okay I just looked for phototransistors on amazon and I was way wrong. disregard me

No need to apologise, I'm happy for any tips - so thanks for saying so. I've usually found Amazon to be more expensive unless I'm buying one of those bundled kits of components (or I run out of a certain part and it will take a few days for something to arrive from an electronics specialist and I really want it now, so I just buy a lot of one part and I know it will arrive the next day... don't ask me how I've got too many resistors of very obscure values that I doubt I will ever use in this lifetime!

[moid]

Moreover just make sure a midpoint voltage (4.5 for 9 Vcc) is present on the + in. I don't think resistor values matter much if you set it like Jack's example, however... I like to set up the divider with a couple 10ks, one to V+, one to ground, then where they meet (giving 4.5 volts as half the power supply) use a 1 Meg resistor to bring it to the op amp. You should also put a cap, say 10uF from that midpoint to ground to keep it stable-don't use the cap if it's going to an LFO generator (thanks to Duck for that). Reason for lower bias divider resistors and big ones to bring it in is that big one essentially is parallel to the one going to ground, so making it decades larger doesn't change the divider resistor value (much...)

Use a dual, it won't mess with it, so save space!

Digi-key has loads of calculators for most things. If you feel you need a lower voltage you can plug in values to see what you get, has the formulas too.

I hope the actual smart peeps are checking me, don't want to lead you astray.

Thanks Matthew. I'm going to have to draw this out in schematic first before I start ripping the breadboard apart to get the buffer in (I've run out of space on that breadboard)... Hmmm I wonder if you can get bigger breadboard; I bet it's possible... I'm going to look

[Matthew Sanford]

Post your drawings! Good for a spot check...

And bigger! I'd bought those six pack of littles, they all have stuff living on them now so had to get a big board, like 4 tall stuck together...which now has stuff living on it too

[moid]

I knew if I gave you some numbers, you'd find them. you're good like that.


LPT80A Side Viewing Silicon Phototransistor $1.33

LTR-4206 3mm NPN Silicon Phototransistor $1.87
https://au.mouser.com/ProductDetail/Lite-On/LTR-4206E?qs=GHV6gLndNKlNoc%252Btn97dSA==
https://www.digikey.com.au/en/products/detail/liteon/LTR-4206E/121710

SFH325G Side LED SMD NPN Sensor Phototransistor $0.61
https://au.mouser.com/c/?q=SFH325

I found three obsolete parts at my nearest surplus joint, Rockby. plenty cheep options at digikey and mouser. dunno why you want them, tho.

Thanks Duck. The UK doesn't seem to have cheap surplus electronic component stores at all. I've searched and there are plenty of surplus stores, but they all seem to be of the 'we know what we've got, no low ball offers' and the prices are quite silly... Maybe surplus stores are more of an Australian / North American thing? Or if they are actually cheap, you have to buy the components in huge quantity...  I saw one had CD4046 and CD4049 ICs for really cheap... but you had to buy 50 - 100 minimum order.

Thanks for the mouser tips though!