I wanted to duplicate the mutron sound with a simpler circuit, more control of the bandpass peaking and single supply. I came up with this and I am really pleased with the sound.
(http://circuitsaladdotcom.files.wordpress.com/2014/05/mutro_mini_-envelope-filter2.gif)
The only drawbacks are: It needs three LDR's (I just made mine in about ten minutes with some heat shrink and super-glue) and I couldn't get a TL072 to work well. I had to use a higher bandwidth op amp. I offer a few suggestions on the schematic.
Here is a board for a 1590b enclosure...not much to it. It took about thirty minutes to build.
(http://circuitsaladdotcom.files.wordpress.com/2014/05/minimu-board.jpg?w=560&h=600)
The design has adjustment for resonance peaking, sensititvity and attack. The attack control is extremely useful.
here are some sound samples:
http://circuitsaladdotcom.files.wordpress.com/2014/05/very-slow-attack_high-resonance_demo.mp3
http://circuitsaladdotcom.files.wordpress.com/2014/05/fast-attack-_high-resonance_demo.mp3
http://circuitsaladdotcom.files.wordpress.com/2014/05/low-resonance_-attack_slower_demo.mp3
Sounds absolutely great!
Oh yes, love it, nice work man, the filter sounds excellent, 8 :icon_cool:)
I have avoided LDR's in the past just because they are hard to find but if you suck it up and just make yur own - its worth it for envelope effects like this. The smoothing of the slow response time and wide range of R is hard to beat.
Sounds good.
Did you consider contolling LDR1 and 2 with a single LED?
yes I did that on the breadboard and of course it works well - it saves a little current, but the circuit only draws 5mA when operating and 1mA of that is the bypass/effect LED pumping. I just figured it was easier to make or get commercial single ones. You would probably want to adjust R5 up some if you did that.
Very nice, RRing!! I'm impressed. You managed to give it 'what it needs', but kept the parts count down quite a bit.
Sweet. Good work.
I like the low counts part too.
Sounds great. Time for me to do some data sheet comparaisons on those oppys against the Tl072.
What is the purpose of D2 please.
Is R1 a boot strapping stabaliser?
Thanks
PS - hey, was there any reason for choosing an LM358 for IC 1? Looks like just about anything would be OK there, huh?
How D2 functions is hard to visualize but it allows the negative cycle of the audio swing to charge the cap thereby making a voltage doubler output of the diode integrator. R1 is just bias because there is no feedback....the collector is just tied to V+ - just think of R1 tied to V+ and not the collector. Bipolar Transistors bias up very consistently, unlike JFETS. I tried 3 or 4 and they all biased up to 4.2 to 4.5 volts at the emitter node.
Another good possibility for an op amp choice is: the TL972 it is available in DIP or SOIC from digikey for less than a buck
there is more info on this circuit at my blog: www.circuitsalad.com
^PS - hey, was there any reason for choosing an LM358 for IC 1?
Looks like it needs to be single supply as the input of 1B is tied to ground.
Ray - I like the way Q1 is set up to supply a DC bias, but was wondering how variable it would be. How/why did you pick the value of R2?
Yes you are correct - good point.. I need to address that. Numerous op amps will work. The only problem is the actual led driver portion needs to work near 0 volts, so again a TL072 is not a good choice. To your point, any of the filter op amps I suggest will work for the envelope detection portion. I just used the LM358 because I had a bunch. On the breadboard I used two OPA1652's, then tried two TS922..etc, same goes for the TL972 I just suggested - it will work for both amps.
I think I just answered that above(mostly). It won't be that variable. Most bipolars have high DC gain and the base/emitter diode behavior is very uniform - so the feedback behavior dominates operating point. The basic design procedure was: decide my operating point(1/2 supply), decide the highest value of emitter resistor I could use(achieve close to unity gain but still have fairly low drive impedance) and then select the bias resistor to turn on the transistor such that the operating point is obtained. I did this in SPICE and then verified with 3 or 4 junk box 2N2222A's and 2N3904's.
Alrighty, I threw together a through-hole layout for this thing if anyone wants to give it a shot
I haven't built it myself (I only have 1 LDR in my parts drawer :() but at a glance it look OK, maybe someone else can spot something before starting with the acid. I added space for an optional 1Meg anti-switch-pop resistor at the input. I kind of eyeballed the size for the LDR+LED combos but I think it should work....
<look on the next page because this layout had errors!>
edit: wooooo, post #2000, time for celebration :icon_mrgreen: :icon_mrgreen: :icon_mrgreen:
I think you have the - and + inputs of the LM358 reversed on the layout because pin 5(+input) should not be connected to current feedback resistor(3.3k)?
Quote from: rring on May 09, 2014, 08:47:37 AM
I think you have the - and + inputs of the LM358 reversed on the layout because pin 5(+input) should not be connected to current feedback resistor(3.3k)?
Hah, good spot! your schematic appears to to have the same issue and I blindly copied it over.
Probably won't do much without the negative feedback :P
edit: so on your original schematic both + and - and IC1 are flipped around, I assume IC2A is good which leaves IC2B. Is everything in order there? I'm searching through the Lancaster filter book and google to find such a topology to verify it.
ouch- thank need to fix that!
^...I did this in SPICE and then verified with 3 or 4 junk box 2N2222A's and 2N3904's.
Thanks Ray. The resistance is a little higher than I was expecting, but that makes sense.
Sounds really nice.
I was pondering whipping up a simple 2-pole lowpass with a pair of LDRs. I think it could be done with a quad op-amp: one op-amp for the input stage, one for the filter, one for the envelope extractor, and one to spare for whatever.
Yes that extra op amp could be used for up/down reversal of the envelope following maybe.
I just changed the schematic ....it correct now on the LM358 input reversal. the correct rev so far is rev1.1 (as shown on the current schematic)
here is my surface mount layout and the silkscreen:
http://circuitsaladdotcom.files.wordpress.com/2014/05/minimur.pdf (http://circuitsaladdotcom.files.wordpress.com/2014/05/minimur.pdf)
http://circuitsaladdotcom.files.wordpress.com/2014/05/minimussilkscreen.pdf (http://circuitsaladdotcom.files.wordpress.com/2014/05/minimussilkscreen.pdf)
Quote from: rring on May 09, 2014, 09:09:26 AM
I just changed the schematic ....it correct now on the LM358 input reversal. the correct rev so far is rev1.1 (as shown on the current schematic)
IC1A is also at fault :icon_razz:
well here comes rev 1.2..... duh!
Its fixed...sorry about that. For what its worth the filter op amp is correct -I swear it! The new rev is 1.2
To answer an earlier question, the filter topology is a Fliege filter (the low pass form). It is a second order filter with control of Q and filter knee. The interesting thing is the pass band always has a gain of two no matter what the Q is (the peak at the knee goes higher if the resonance is set high). I used it because its relatively simple and easily adapted to single supply operation.
Quote from: rring on May 09, 2014, 09:51:35 AM
Its fixed...sorry about that. For what its worth the filter op amp is correct -I swear it! The new rev is 1.2
Haha :D
I checked the filter in SPICE and it filters correctly .
Thats a nice filter if I ever saw one :)
(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=51006&g2_serialNumber=1)
But as they say: "the proof is in the pudding", I'm going to have the build this to find out!
Heres my layout fixed of the aformentioned issues, I even managed to get rid of one jumper :) . Board size is 4.5 x 6.5cm .
(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=51003&g2_serialNumber=3)
link to transfer http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=51000&g2_serialNumber=2 (300dpi)
Yay, a new CS design! :D
A few inevitable questions:
Do you think TLC2272 (http://www.ti.com/lit/ds/symlink/tlc2272.pdf) will work for the op amp? It's rail-to-rail with more bandwidth than the TL072. How important is the rail-to-rail output -- would the OP275 perhaps work? It's got really great bandwidth characteristics, but not the rail-to-rail output. What I'm focusing on is finding usable op amps in DIP through-hole packages.
Do any of the concerns with the TL072 go away with a higher supply voltage? After all, the original Mutron ran on split rail. I assume it would help with the headroom problem, but not sure about the bandwidth or oscillation. If we're talking about using $4 op amps, I wonder if it's not just easier on some people to power it on 18V.
Thanks for linking to the LDRs used. It looks like their turn-off time is a bit slow, but there's also no Decay control in this design. Since the Silonex 7532 and Smallbear's 9203 have similar on/off resistance, I'm going to try those (though they're a bit faster). But I was wondering if you had some insight into the switching range really needed to get a working effect, since you also have the vactrols limited with 470K. Would it simplify the design to use, say, the NSL-32 (1K on/500K off, about $2-$4 each, but uses a superbright LED inside) or even the cheap ones at Tayda (~1-5K on/1M off) and omit the limits, or are you using the high dark resistance and parallel limiting resistors to set a sort of "taper" to to the sweep?
I figured the RC time constant of C5 and R10 would dominate the time response. Honestly, I just chose those photocells because they were small and not too expensive. Their R range was pretty good. Also C4 limits attack somewhat- if you made that bigger it will respond faster.
The main thing I needed to achieve electronically was a fairly linear change in R over change in current. This is so the peaking control ratio stays the same over the range of the filter. To your point, I think just about any LDR combo will work as long as you get the sent point current correct with R5. In this circuit your at about 10k frequency knee when the photocell is @ 1K. The way I have it set the best you can get to is about 1.5 to 2k ohms when you slam the output of IC1 to the rail. You may find a better performing LDR combo so if you do let me know! The general theme was- can I grab any ol' photcell and get it to work. I was hoping the op amp wouldn't be so critical but I am sure there is a more common junk box type that will work- just got to find it.
With regard to the op amp choice. You may be right about the TLC2272 - I don't have one to test and I have not done a detail analysis to determine exactly what is going wrong with the TL072. It must be related to loop gain and phase shift and if you look at that filter topology, it pretty scary because you to op amps driving each other in a loop. Maybe someone can breadboard just the filter portion and use a POT to shift the LDRs to test the TLC2272?
As I mentioned before: the TL972 comes in DIP is a buck and should work great
Quote from: rring on May 09, 2014, 09:04:51 AM
Yes that extra op amp could be used for up/down reversal of the envelope following maybe.
cool, 8)
Quote from: rring on May 09, 2014, 09:04:51 AM
Yes that extra op amp could be used for up/down reversal of the envelope following maybe.
If we rig up a version with only a single LED and three discrete LDRs, I think you can just switch R6 to +9v instead of ground.
You can't do that because the peaking control needs independant control of current to be shifted as desired from the other two frequency sweep LDRs- this means it needs it's own LED(for LDR3)
Very nice, consider a second filter in parallel using say 0.047 or even 0.068 capacitors, which may add a vocal feel to the sound.
Quote from: rring on May 09, 2014, 01:13:57 PM
You can't do that because the peaking control needs independant control of current to be shifted as desired from the other two frequency sweep LDRs- this means it needs it's own LED(for LDR3)
Oh, bugger. Okay. :)
This Looks and sounds awesome rring! Gonna give this a try when I get some time. I love envelope filters! 8)
Nice playing in the demo's too!
The smd version looks fun! I just got a bunch of 0805 resistors and caps to play around with. I've only done smd IC's by hand prior, for the Pearl Octaver from Gaussmarkov . I noticed you included a stencil for doing the solder paste and bake method! That's Awesome , I've never tried it that way but it looks great. Do you use a regular toaster oven for that ?
In the past when experimenting rolling my own vactrols I found using 4mm green LEDs with built in fresnel lens worked great , I believe the ones I used had a slightly different forward voltage and a wide viewing angle which I think helps even out the light distribution across the LDR. On the LDR side I used the common KE10720.
Are you confusing my "liquid tin" coating for a solder wash. I soldered the board by hand - I just get liquid tin (from amazon in a little bottle) to plate the copper boards with a thin tin coat- you just wipe a little bit on..it takes about ten seconds. It protects the copper from corrosion and makes for easy soldering.
This layout has lots of open space - a good choice someone who dosent work with SMT much to give it a try. Also, I intentionally used as few a variety of and the most standard values for parts possible. There are only thirty some parts - it goes quick by hand.
The main reason I did not use leaded parts was - I just didn't want to drill all the holes! Otherwise leaded parts would have fit just fine on that board.
As for the toaster oven yes I have used that before with leadless packages - it works well - you just have to be careful taking the board out.
Yes the DIY vactrols are very workable. My choice of LED was based on the nice flat face to bond the photocell. I noticed the amount of light required is not very much in my testing. I made about ten of the things and all were within 5% of each other over a range of current, except one which was way off and an outlier. So just as your expereience with making them conveys, I think its a very practical solution.
VERY nice! I would like to make one using standard Vactrols.
Good work, it sounds amazing!
Earlier in this thread there was a question about the purpose of D2. I just would like to add that with C4, D2 forms a commonly known Clamper circuit. When the diode is placed with that polarity it makes a positive clamper and opposite polarity makes a negative clamper. If there exist a very high resistance path to ground for C4, then in this case the negative swing of the output of IC1A quickly reverse-charges C4. This creates a voltage across the C4 terminals and due to high resistance path to ground this voltage stays as a bias for the output of IC1A. Hence, the signal at the junction of D2 and D3 is always above ~ 4.5 V and the maximum signal voltage at this junction can momentarily be 9 V + 4.5 V. This voltage is also the base voltage for D3, which does not conduct when the voltage of C5 exceeds the voltage at D2. What puzzles me though is, does IC1B go to saturation if the voltage over C5 is over 9 V ...
edit: Ah, the clamper base level is a diode drop below 0 V and not 4.5 V as I claimed. C4 first takes the average signal level to 0 V and only after that the clamping takes affect and rises the bottom level around 0 V. Small details, but just wanted to understand what is happening here.
Quote from: jatalahd on May 10, 2014, 09:56:41 AM
Good work, it sounds amazing!
Earlier in this thread there was a question about the purpose of D2. I just would like to add that with C4, D2 forms a commonly known Clamper circuit. When the diode is placed with that polarity it makes a positive clamper and opposite polarity makes a negative clamper. If there exist a very high resistance path to ground for C4, then in this case the negative swing of the output of IC1A quickly reverse-charges C4. This creates a voltage across the C4 terminals and due to high resistance path to ground this voltage stays as a bias for the output of IC1A. Hence, the signal at the junction of D2 and D3 is always above ~ 4.5 V and the maximum signal voltage at this junction can momentarily be 9 V + 4.5 V. This voltage is also the base voltage for D3, which does not conduct when the voltage of C5 exceeds the voltage at D2. What puzzles me though is, does IC1B go to saturation if the voltage over C5 is over 9 V ...
I'm very interested in the front end of this circuit up to R4, and bearing in mind what you are saying jatalahd, how would you make the voltage at the junction of D3 and R4 only go high on the leading edge of the note played - or does it do this already? Would a sample and hold circuit be needed perhaps?
Because of the varying signal, the op amp not able to make it to the rails all the way, the finite Z of the op amp, bleeding of the charge on the caps through R4 and the attack POT, slow charging of C5 via the attack pot and of course diode voltage drops...I don't really observe the behavior described in the last couple of posts.
The simulated behavior and observed behavior on the scope is: the clamper circuit, combined with the half wave rectifier, forming a half wave voltage double with diode voltage drops. It has a slow rise time and it
bleeds away static charge relatively quickly with no signal. So you never see actual true voltage doubling and never any voltage level exceeding little more than 4 to 6 volts when you are beating your guitar like a gorilla with the sensitivity all the way up.
All in all its not very exciting but it works. A BAT46 schottky or similar will work better(lower voltage drop) and then you can lower the gain of IC1A by increasing R3 some.
The IC1B can only source up to approx: +l9V at the output, but the current mode feedback requires that (I Output*R5) = Voltage In (at IC1B's positive input).
This maximum current is (V+supp - LED V Drop)/R5. So the output of IC1B will always be the (LED V drop) greater than the voltage at the + input of the op amp. The maximun output will be reached when the + input of IC1B is somwhere between 6 to 7 volts.
is the OPA1652 only available in SMD?...
probably...its meant for super Hi Fi audio. I had a bunch leftover from another project and I just soldered on little legs so I could put in a breadboard when I did initial testing. The TS922 is in DIP also the TL972 and the OP213
I found a TLC2274 to try ....this evening I'll see if I can get that to work?
Quotethe clamper circuit, combined with the half wave rectifier, forming a half wave voltage double with diode voltage drops. It has a slow rise time and it
bleeds away static charge relatively quickly with no signal.
Ok, I think I need to re-analyse the behaviour of D2. I see that there is a possibility that it does not function as a proper clamper in this context.
QuoteAll in all its not very exciting but it works
Actually it is very exciting :)
StephenGilles:
Quotehow would you make the voltage at the junction of D3 and R4 only go high on the leading edge of the note played - or does it do this already? Would a sample and hold circuit be needed perhaps?
The time constant for charging C5 is C5*Rattack and for discharging C5*(Rattack+R4). As long as the discharge time is longer, the voltage over C5 will grow along with the current coming through D3. The voltage at the junction of D3 and R4 fluctuates until voltage at C5 has grown enough to stop D3 from conducting.
FYI the TLC22 series of op amp does not work ... I see the same problems as before with TL072. Someday I'll figure out why.
Quote from: rring on May 10, 2014, 03:55:30 PM
FYI the TLC22 series of op amp does not work ... I see the same problems as before with TL072. Someday I'll figure out why.
I've had bad issues with stability with TLC2272 on multiple occasions, even in very simple circuits where you think there never would be a problem :P
Used a BA15218 for U2, which works fine. Had to change c6 to 100n though, to get a noticeable sweep. Also replaced Led 3 (the one on the intensity) to a blue led - the green one did not seem to have enough effect in this spot (I used transparant green leds which give a kind of yellowish green light. Nice and easy build, thanks rring!
maarten
Now that Chip BA15218 is available in dip8 and is much cheaper than i could find all the others suggested especially in the uk.
Unless anyone knows differant.
Can you post an audio sample fo your working circuit please Maarten
Thanks
Yes looked at the data sheet - this op amp is much like the others that I have gotten to work. I think this is a great choice and others will work well also. Not sure what the issue is with needing to use a different LED for the resonance adjustment? The choice of .01 uf was based on the sweep range of the photcell I used- if you have a phototcell with a range that is shifted lower - you would need a larger value -so could make sense. You get much more bandpass peeking when the photcell R (for LDR3) is higher than the other two so you should be able to achieve this without critical or special choice of the LDR setup for LDR3. This seems a little odd?
Maybe the values for R5 and R6 need to be adjusted higher? Also if with no signal you see volatge across R5- there is offset error- which would also expalain some of what you describe. Are you able to get a nice bandpass sound with the intensity turned all the way up? It sounds like you got it working.... but I am concerned that you had to fuss with it. I built three of them with very repeatable results. Perhaps it has to do with your LDR's vs mine?
Chips on back order.
Another one for the list.
I just love filters.
I'm about to redraw the schemo in Eagle and would like to know what the B+ is for?
thanks
B+ connects to the battery, the 9 volts connect through the diode to the 9 v indicated in the circuit.
Haven had a chance to record a sample (audacity is giving me some problems on my new PC) yet, but as you are going to build this yourself probably you won need this.
Later in the weekend I will have a look at my LDR's to see whether I can find out what is different in my built.
Maarten
Thanks Maarten
I've been scouting out the data sheets and it looks like a LM6132 might do for IC2 and is half the price of the OPA1652 in the uk
and its available in DIP8
Data sheet here
http://www.ti.com/lit/ds/symlink/lm6132.pdf
Here is a schematic with a much clearer function of B+ which is simply the battery connection that would go to the jack switch. Sorry about that - I seemed to be a little sloppy with this schematic - which understandably would annoying to other builders.
(http://circuitsaladdotcom.files.wordpress.com/2014/05/mutro_mini_-envelope-filter3.gif)
The LM6132 looks like a good choice.. again the cheapest one I found that looked good(in a DIP) was the TL972 which I found on mouser and digikey for about $.97 generand in stock. In fact the specs and price were so good I plan on getting some of these to use for general tinkering.
Thanks
My chips arrived today.
I'm doing a perf layout ready before i heat up the iron.
I am very interested to find out how it works for you - especially with a different op amp and I assume different LDR's?
I'm thinking of using GL5549 ldrs and I got some green 5mm diffused leds approx 100mcd on ebay, I'm nearly ready to go on this.
If anyone sees a problem with these please let me know.
GL5549=
@10lux 100-200k
10 dark
Link to the GL55 series photoresistors
http://akizukidenshi.com/download/ds/senba/GL55%20Series%20Photoresistor.pdf
Thanks
Rich
I think ten lux is pretty close to dark? if so you should be good. Regardless, The led has to be able to get you down to 1K at high brightness to work with my cap values(.01) if you can get that low just make the caps smaller.
Thanks mate I'll do some testing maybe before I make a final decision on the ldrs.
Can someone please post some voltages. I'm losing signal after d3.
You won't be able to hear any signal after D3 as the signal is rectified at this point.
The audio path is Q1 -> IC2A -> out
yes after D3 you should a DC voltage that goes up and down (with the sensitivity all the way) up when you strum. If you don't see that ... there is a problem with the side chain. If that works, then measure the R of your LDR's and make sure that is changing with the voltage described above ....etc. What op amp are you using for the filter?
There's the hitch I've yet to put the vactrols in.
I'll do it now. There's another socetted 3k3 to put in too.
I'm using the ba15218 for the filter op amp
Ill check out what you said rring too.
the vactrols are in and im getting a change in resistance on the one i just put the dmm on.
im getting signal on the output but no wah
i guess this is the time i need to experiment with the 4k7 and 3k3?
by the way i use a diffused blue 5mm led for vactrol 3 as stated by the builder with the same op amp as i used.
i can easily build another green one though.
i'll check the resistances on the vactrols mean time too and post those up
got it.
it was a missing trace on vactrol 1 ldr to the 470k
impressive thanks dude
i'll have some more dumb ass questions when ive had a play.
I guess the reason it doesnt tick is the 10k /10uf to ground on pin5 of 1c2?
I'm also guessing that c6 is the cap that charges and discharges for the sweep? from Maartens comment.
I tried a 10k in the place of the 4k7 off the intensity pot and it works well also.
"I guess the reason it doesnt tick is the 10k /10uf to ground on pin5 of 1c2?"... not sure what you mean here.
C6 and C9 are a matched pair and both must be shifted as required.
I wasn't trying to cause offence or suggest it ticks.
It's just a lot of times envelope filters with homemade vactrols tick.
This one doesn't so I was just trying to work out what does what in the circuit.
Never having used the type of filter before. It's a bit of a mystery.
It sounds great. I have no issues with the design or sound.
Good job well done.
Nice work mate.
Thanks
One more question
What effect would a transistor with greater hfe have on the rest of the circuit ?
Oh no I just didn't understand what you meant by ticking. Now I get it. I have not done a whole lot LDR's before so I that issue is not something I had ever come across. The cap and the resistor just provide the 1/2 supply bias from the other stage and feedback to provide the loop gain for the filter. The design only works correctly when that divider is at half. The cap ensures that it is only AC referenced to ground.
The transistor stage has a gain of hfe/(1+hfe) so as the hfe goes towards infinity the gain approaches unity. The voltage at the emitter will also increase toward the supply rail( which would be bad). Normally 2n2222a's and 3904's have a hfe between 100 and 200 and this will put you between 4 and 5 volts. You can always add a resistor to ground to make a divider to limit the max dc voltage set point.
Thanks for that. I understand a little better now.
IIRC my emmitter voltage is around 5.5v..
It's a really cool easy to make low parts envelope filter and as you say yourself it uses everyday stock parts which is always a bonus.
Not that it matters, but you can always lower your emitter resistor to 4.7 k or so to get the voltage at 1/2 supply. I am glad you got it working though.
The NJM2068D op amp works great in this circuit. You can get it for 60 cents from Mouser and Tayda.
Great news thanks
I'm wondering if H11F1M could be used as octos
some reading, rich. not sure if it's exactly the answer, but all the big names are there.
http://www.diystompboxes.com/smfforum/index.php?topic=103749.0
http://www.diystompboxes.com/smfforum/index.php?topic=99516.0
Couple problems.
The optofet is much faster then the LDRs so this will require a slower decay and slower attack to avoid the growl of modulation of the signal ripple getting through the control voltage. The LDRs are slow and smooth this out. You would have to change the the filter some on the side chan.
The bigger problem is that the optofets work well as linear resistors only over a small range of voltage across them. If the signal is over 100mV or so it will start to distort. I have designed a number of popcorn compressors with the H11F1M and you have to use attenuation or shunt feedback to reduce the voltage across the device from the signal source.
I also used this part as a product mixer in a ring modulator device - it works great but I had to limit the voltage across it as described above.
In this filter design, I think the signal voltage across them will and be to high and distort.
Thanks R and Duck Arse.
It was worth a punt.
I didnt look at the spec sheets however when I looked at the links I already built the optofet and I like it too. which I believe you had a hand in the development RR. So thanks for that too
This sounds awesome with my active bass too.
build no2 with a differant oppy
this time an opa2604 for ic2 and it sounds as good as the first and it's a cheaper chip
The opa2604 looks like a really nice part but @ 9V it is at the lower specified limit of supply voltage(+-4.5V).....notice any issues with this?
Seem like a good candidate for a charge pump :)
Did anyone had success making one own's vactrols from 5539/5549 photoresistors and LEDs for this pedal? I have some VTL5C1, could I use those?
I finally made it:
(https://s26.postimg.cc/5st3e9l7t/20180501_063118_0004_Mini_Mu.jpg)
(https://s26.postimg.cc/8mw8rpv3t/20180430_175726_0001_Mini_Mu.jpg)
How you like that?
Great is'nt it.
Good job
Yes, it's great! I used some kind of Chinese VTL optos. I believe my unit works fine, however, it seems that it is not so easy to use - hitting strings too strong doesn't trigger the effect, so I have to strum carefully. Or maybe I need to master controls a little bit more :)
That's funny cause my sens knob takes care of that.
But then again. I Mostly play with fingers,
I'll try to experiment with Sens a little bit more.
wow that looks cool...not sure what your sensitivity issue could be...should be very adjustable over quite a range of input...if you still have trouble let me know.
Hello!
I'm very interested in building one of these. is the LED at the far right (connected to R14) the indicator led for the effect?
Also could someone please break down how this circuit works? I would like to try and understand :)
Thanks!
Yes, it is indicator LED for effect (shows what is going on inside LDRs), not on/off LED. You can see it mounted under sensitivity pot on my enclosure.
If I wanted to have send/return feature in this circuit, where would I put it? I want to be able to control the envelope with something like this: http://www.geofex.com/Article_Folders/LFOs/psuedorandom.htm
You would need some extra componants to bias the op amp but right before pin5 ic1b would be one suggestion.
Then it's a case of is the sudo lfo compatible.
there may be other issues but.
sorry for all the dumb questiosn but would I be able to use 3mm LEDs instead of 5mm?
In general, what is the difference between the two?
Aside from size, the bigger ones might (or might not) be able to take more current without burning-out, and/or be brighter at the same current. Or, they might be literally the exact same thing in different size packages.
Either way, they should both work just as well... you still might have to fiddle-around with diffferent values for R5 and R6, same as you would if you were using ready-made vactrols.
The only problem I could imagine is that it'll be easier to make a light-tight seal if the LED has the same diameter as the LDR, but that shouldn't be a deal-breaker.