I've been struggling with a MXR Envelope Filter built from the old Tonepad layout (A-gua2, Rev 1: http://tonepad.com/getFileInfo.asp?id=5 (http://tonepad.com/getFileInfo.asp?id=5)), and I'd like to try to make some headway by breaking the circuit down into functional blocks that I can breadboard and test individually. The main reason I want to do this is that I'm stubborn, and I'd like to see if I can make the circuit work with the TI 4069UBEs that I have, even though build reports seem to indicate that they don't work in this circuit. If I play around with it on the breadboard, maybe I can figure out what needs to be tweaked to make it work. I also have some 4049s that I'd like to try out on the breadboard. These considerations, along with Occam's Razor, make me want to break it down to the essential bits.
So... looking at the schematic, I'm thinking that after the input cap, R7 leads to the filter portion of the circuit, and R8 leads to the envelope follower. Within the filter portion, IC1c is a gain stage to drive the filters; IC1a and IC1f, with associated capacitors and resistors, comprise the filters, which are swept by the switches in IC3. I'm a little unclear on how that works, though. Could I just stick a dual-gang pot (wired as variable resistors) in place of the in/out terminals of IC3 for the purpose of manually sweeping the filter? Again, this is just for playing around with the circuit on the breadboard, I'm not trying to come up with a manual sweep mod or anything like that.
The envelope follower leaves me very confused. I'd rather not speculate too much on what's going on in there. Unfortunately, that's where I suspect the problem will be, so it's the part I'll need to make an effort to understand. Any hints would be most welcome!
If anyone is willing to help walk me through this thing, I would be most grateful. I'm very willing to study specifications and graphs in data sheets, but I need some guidance to get started. Thanks!
I had the same question some time ago and was really lucky :)
http://www.diystompboxes.com/smfforum/index.php?topic=20811.0 (http://www.diystompboxes.com/smfforum/index.php?topic=20811.0)
Markus
wrong post
Quote from: mdh on March 29, 2007, 03:23:19 AM
I've been struggling with a MXR Envelope Filter built from the old Tonepad layout (A-gua2, Rev 1: http://tonepad.com/getFileInfo.asp?id=5 (http://tonepad.com/getFileInfo.asp?id=5)), and I'd like to try to make some headway by breaking the circuit down into functional blocks that I can breadboard and test individually.
:icon_biggrin: :icon_biggrin: :icon_biggrin:
The switches are turning on and off the resistors in series with them (think of it this way, if you connect a 10K resistor fo only 50% of the time, it looks like a 20K resistor!) so, replace the switches by a dual pot, maybe 500K.
Quote from: markusw on March 29, 2007, 04:13:09 AM
I had the same question some time ago and was really lucky :)
http://www.diystompboxes.com/smfforum/index.php?topic=20811.0 (http://www.diystompboxes.com/smfforum/index.php?topic=20811.0)
Markus
Excellent, I must have just missed that thread. Thanks!
Quote from: StephenGiles on March 29, 2007, 04:25:08 AM
Quote from: mdh on March 29, 2007, 03:23:19 AM
I've been struggling with a MXR Envelope Filter built from the old Tonepad layout (A-gua2, Rev 1: http://tonepad.com/getFileInfo.asp?id=5 (http://tonepad.com/getFileInfo.asp?id=5)), and I'd like to try to make some headway by breaking the circuit down into functional blocks that I can breadboard and test individually.
:icon_biggrin: :icon_biggrin: :icon_biggrin:
I could interpret this as, "Way to go, have at it!" or, "Jeebus, man, you're a fool! Go back to playing with your tinker toys!" I'm sort of curious whether you meant one or both of those sentiments :icon_wink:
Quote from: Paul Perry (Frostwave) on March 29, 2007, 09:19:11 AM
The switches are turning on and off the resistors in series with them (think of it this way, if you connect a 10K resistor fo only 50% of the time, it looks like a 20K resistor!) so, replace the switches by a dual pot, maybe 500K.
Perfect, that's what I thought (except I didn't get the rapid switching angle... makes a lot of sense now). Thanks!
Quote from: mdh on March 29, 2007, 12:21:56 PM
Quote from: StephenGiles on March 29, 2007, 04:25:08 AM
Quote from: mdh on March 29, 2007, 03:23:19 AM
I've been struggling with a MXR Envelope Filter built from the old Tonepad layout (A-gua2, Rev 1: http://tonepad.com/getFileInfo.asp?id=5 (http://tonepad.com/getFileInfo.asp?id=5)), and I'd like to try to make some headway by breaking the circuit down into functional blocks that I can breadboard and test individually.
:icon_biggrin: :icon_biggrin: :icon_biggrin:
I could interpret this as, "Way to go, have at it!" or, "Jeebus, man, you're a fool! Go back to playing with your tinker toys!" I'm sort of curious whether you meant one or both of those sentiments :icon_wink:
Mr Giles often suggests breaking large circuits down into blocks for building and testing, so I assume he meant it in a good way.
I can't believe the timing of this thread, I was just about to ask exactly the same questions :)
I'm thinking of building something based on this but couldn't figure out the whole schematic, mainly the bit that I now know is the "clock".
Quote from: mdh on March 29, 2007, 12:21:56 PM
Quote from: StephenGiles on March 29, 2007, 04:25:08 AM
Quote from: mdh on March 29, 2007, 03:23:19 AM
I've been struggling with a MXR Envelope Filter built from the old Tonepad layout (A-gua2, Rev 1: http://tonepad.com/getFileInfo.asp?id=5 (http://tonepad.com/getFileInfo.asp?id=5)), and I'd like to try to make some headway by breaking the circuit down into functional blocks that I can breadboard and test individually.
:icon_biggrin: :icon_biggrin: :icon_biggrin:
I could interpret this as, "Way to go, have at it!" or, "Jeebus, man, you're a fool! Go back to playing with your tinker toys!" I'm sort of curious whether you meant one or both of those sentiments :icon_wink:
Way to go, have at it!
I received an off-line query from someone about the MXR EF clone at Tonepad recently. As usual, it was an "I built it but it doesn't work, did I get the wrong chips?" sort of query. That's something that comes up often enough that I started to cogitate about it, and it dawned on me that maybe the culprit is not the brand of invertor chips, but rather the specific CMOS switch chip in tandem with the components that result in the amplitude of the clock pulse. Is it possible that the "on" pulse going from the clock to the switch is simply not enough to turn the switch on for some brands? If so, then that might mean that one could use virtually ANY brand of CMOS chips if we knew how to change certain component values and adjust the properties of that clock pulse to do its job.
Does that make sense, and does anyone know what to zero in on in the circuit to accomplish that?
Quote from: Mark Hammer on March 29, 2007, 05:14:38 PM
I received an off-line query from someone about the MXR EF clone at Tonepad recently. As usual, it was an "I built it but it doesn't work, did I get the wrong chips?" sort of query. That's something that comes up often enough that I started to cogitate about it, and it dawned on me that maybe the culprit is not the brand of invertor chips, but rather the specific CMOS switch chip in tandem with the components that result in the amplitude of the clock pulse. Is it possible that the "on" pulse going from the clock to the switch is simply not enough to turn the switch on for some brands? If so, then that might mean that one could use virtually ANY brand of CMOS chips if we knew how to change certain component values and adjust the properties of that clock pulse to do its job.
Does that make sense, and does anyone know what to zero in on in the circuit to accomplish that?
That was me... but then I decided to try to "learn to fish," so to speak, rather than to post a debugging thread with voltages. I freed up a largish breadboard by finally committing my GEO test oscillator and GEO FET matcher to perf, so I should be good to go.
FWIW, with respect to the interaction of the 4066 with the 4069s, I originally had TI 4069s and a TI 4066 in there, but I've also tried a Motorola 4066, which resulted in the same behavior that I described in the PM I sent you. I'm guessing that the problem is in that clock pulse generator. This would be consistent with the Tonepad build reports, in that it seems like swapping IC2 out for a non-TI brand improves the behavior of the circuit. So I think that what I've done here is volunteered to try to become an expert on this portion of the circuit, and work out whether we can make it work consistently with chips from different manufacturers. I have a long way to go, but I'm willing to try :icon_redface: Maybe I'm naively optimistic, but I think if I can break it down into simple enough blocks, I have a chance of figuring it out.
Quote from: slacker on March 29, 2007, 12:32:19 PM
I can't believe the timing of this thread, I was just about to ask exactly the same questions :)
I'm thinking of building something based on this but couldn't figure out the whole schematic, mainly the bit that I now know is the "clock".
Cool. I've been meaning to play around with your Slack Trem, and I seem to remember seeing something else you did with inverters.
If the problem is that the pulse isn't high enough to switch the 4066 then it might be possible to increase it by putting a large value resistor across pins 8 and 9 of IC2 turning it in to an amplifier. There's an example oscillator circuit using this method in the Philips 4069 datasheet. I guess that could affect the sensitivity of the envelope follower though so that might need some tweaking as well.
Could the problem be that the oscillator isn't even oscillating?
Quote from: mdh on March 29, 2007, 06:23:21 PM
and I seem to remember seeing something else you did with inverters.
I think the only other thing I've done using invertors was the LFO from the slackfilter (http://www.diystompboxes.com/smfforum/index.php?topic=45148.0). I'm hoping I can mod the Envelope Filter into a simpler, better version of this. Pretty much like Mark and Markusw talked about in the other thread.
Quote from: slacker on March 29, 2007, 06:44:11 PM
If the problem is that the pulse isn't high enough to switch the 4066 then it might be possible to increase it by putting a large value resistor across pins 8 and 9 of IC2 turning it in to an amplifier. There's an example oscillator circuit using this method in the Philips 4069 datasheet. I guess that could affect the sensitivity of the envelope follower though so that might need some tweaking as well.
Could the problem be that the oscillator isn't even oscillating?
Could be anything... I haven't actually had a chance to implement my master plan of breadboarding this stuff, and the last time I probed around my PCB build, I didn't really know what I was looking for. Thanks for the data sheet reference... I think I'll be looking at all the CMOS inverter data sheets I can get my hands on.
Could be a further example of cutting a circuit to the bone, so that it just worked using the parts on which MXR got a good discount on - sound marketing sense of course, but doesn't help you.
I was wondering whether anyone might be able to clarify for me what kind of behavior I should expect from the oscillator comprised of IC2a,b,c,d. I gather that it should be oscillating all of the time, so that if I build it in isolation (which I have, on the breadboard) it should oscillate. The trouble is that I don't know what the frequency should be, and I'm not sure that I have any instrument capable of detecting ultrasonic oscillations. My DMM has a frequency setting, but I have misplaced the manual, so I don't know the range over which it can measure. I don't have a scope either, just a high-impedance buffer for my soundcard, so I assume I won't be able to detect anything above audio range.
If I'm not equipped to study the oscillator directly, maybe I can study its effect on a 4066 switch. If I put a voltage across the switch (with a current-limiting resistor in series, I assume... I'll look at the data sheet), then I should be able to measure the effect of changes in the oscillator circuit on the current passing through the switch, right?
Finally, am I correct in thinking that introducing a signal (from, e.g., an LFO) somewhere around IC2d pin 8 will allow me to look at the transient behavior of the current through the 4066 switch, or should I introduce the signal just after the attack pot (R28)?
I've got this on the breadboard now so hopefully I can help. The oscillator should be working all the time, mine seems to be running somewhere between 10-20KHz, so you should be able to measure it with your DMM. Probe around either side of c10 and you should get some readings. The other thing you could try is change c8 (the 100pf) for something like a 1n or larger cap. That drops the speed and if the oscillator signal is switching the 4066 you'll be able to hear it as a whine on the output of the filter.
Quote from: mdh on March 31, 2007, 10:54:24 PM
If I'm not equipped to study the oscillator directly, maybe I can study its effect on a 4066 switch. If I put a voltage across the switch (with a current-limiting resistor in series, I assume... I'll look at the data sheet), then I should be able to measure the effect of changes in the oscillator circuit on the current passing through the switch, right?
Yes, exactly. This is one of the first things that I would try. I didn't go to read the other thread about the theory of how this filter works, so I don't know what has already been explained about how this works, so I'll repeat it here for the sake of everyone who did not follow the link to the other thread (simple convenience):
The oscillator should be approximately triangle wave . IC2d theoretically will switch when the voltage is near 1/2 Vdd (these typical numbers are quoted in the datasheet). The envelope follower circuit provides a DC voltage to shift the "0" point on the triangle oscillator center. When the triangle oscillator center is low, IC2d only turns on for a short pulse, since the triangle wave crosses over the switching threshold and back for a very brief period of time. When you dig into your guitar, the dynamic increases, thus the DC voltage shift at the gate of IC2d increases, thus pushing the triangle wave '0" reference more positive, which cases the switch to be on for a longer period of time. R22,23,26,14,16 all will effect where this "0" point resides in the "off" state. You can also twiddle R14,16,20 to change the amplitude of the oscillator. All the changes in this part of the circuit are pretty interactive, so you may find it most useful to mess with R23 and R26 the most if it appears to be not working. I really think that the ratios of the resistors there are theoretically optimal for the type of circuit this is. The only reason you would need to change these is if the turn-on threshold of IC2 is much higher than that of a different brand.
Finally, C10 is an interesting circuit part that had me scratching my head for a few minutes. It's a small-valued capacitor that feeds signal from the square wave output of the oscillator. It is small enough that all it allows through is a short pulse to pop IC2d open once for a short time every oscillation period. What this does is it makes sure the switch is on for at least a very short duration each clock cycle. If both switches were turned off altogether for a long period of time, it would screw up the bias on the filter section so it would sound pretty weird when you started to play up until the filter was able to reach bias conditions. It would be distorted sounding on the attack.
So...I would recommend that you do as you said, by hooking up a resistor and a switch together. I would also suggest putting a capacitor in parallel with the resistor to even out the DC. Breadboard the oscillator section with IC2, and apply a voltage from a pot buffered by an op amp to R23 on the IC2a side. Watch what happens to the voltage at the switch/resistor setup you made as you twiddle the pot.
FYI, This "test setup" would make an interesting distortion pedal. At the junction of your pot you could add an amplified guitar signal through a capacitor and then take the output from the switch. It could also work as a somewhat clean amplifier for lower amplitude signals--in this case the triangle wave oscillator amplitude controls the gain. I got off topic.... :icon_wink:
Wow, thanks for that post, Transmogrifox. I breadboarded it twice yesterday, and I finally got the oscillator running at about 30-80kHz, depending on the chip (according to my DMM). I found that one of the TI 4069s oscillated closer to 1-3kHz, so I wonder if that one has suffered some static damage or something. I still haven't been able to measure the amplitude of the oscillation, and haven't yet had success measuring the oscillator's effect on the 4066. Alas, I've run out of weekend, and probably won't have much time to work on it this week :(
One thing I have noticed consistently, however, is that about half of the supply voltage is getting dropped across that 3k resistor between +9V and Vs (R4 on the Tonepad schem). I had asked Mark about this when I PM'd him a couple of weeks ago, and he thought that resistor should just be limiting current, and shouldn't drop a significant voltage. I figured maybe there was a solder bridge or bad resistor value somewhere on my PCB, but since I've breadboarded this circuit (and variations) twice with the same result, I don't think that's it. The thing is, if the 3k resistor is dropping 4.5V, then the whole circuit is drawing 1.5mA, which seems on the low side for all that appears to be going on in this effect. But if that resistor was dropping 0.5V, giving a Vs that's still close to 9V, then the circuit would only be consuming 167uA, which would be lovely, but I don't believe it. So all of this makes me wonder what would happen if I replaced R4 with a smaller value, or jumpered it altogether, but I'd like to know beforehand if I'm likely to let out the magic smoke. Or am I missing something here? If the designer wanted a supply voltage around 4.5-5V, why not just use a zener diode or voltage regulator?
Slacker, what voltage are you seeing at Vs?
And thanks for your patience, everyone. I'm determined to get this, but I am groping around sort of half blind here.
Quote from: mdh on April 02, 2007, 01:29:45 PM
Slacker, what voltage are you seeing at Vs?
And thanks for your patience, everyone. I'm determined to get this, but I am groping around sort of half blind here.
I get about 4.5 volts for Vs. I think it's correct, if you jumper it so the chips are running off 9 volts then the filter looses all its "quack". It is a bad way to get 4.5 volts as it relies on the current draw of the chips, like Stephens Giles pointed out though it's probably the cheapest way. I suppose the current limiting could be deliberate though.
What exactly was the problem you had when you built this before, did the filter not pass any sound at all or was it just that there was no sweep from the envelope follower.
Have you got any 40106 or other schmitt trigger chips? If you have you can make a simple clock out of one of those, which would let you test the switches and envelope follower. Let me know if you have and I'll do a quick schematic.
It's definately worth getting it working because it sounds amazing :)
Couple more things you might like to try.
To test just the envelope follower disconnect the clock by removing R26 and C10. Then get an LED and a current limiting resistor, 5-10k should work, and connect them between point G and ground. The LED should flash as you play. On mine if you remove the LED and attach Point G to the 4066 control pins the filter will sweep even with the clock disconnected. It gates horribly but it does sweep.
If you connect the control pins of the 4066 to Vs through a resistor you should get sound through the filter. If you connect the control pins to ground you'll get no sound at all.
QuoteWhat exactly was the problem you had when you built this before, did the filter not pass any sound at all or was it just that there was no sweep from the envelope follower.
Have you got any 40106 or other schmitt trigger chips? If you have you can make a simple clock out of one of those, which would let you test the switches and envelope follower. Let me know if you have and I'll do a quick schematic.
The exact problem was that the effect basically behaved like a bad noise gate. With the threshold pot turned fully one way (don't remember which direction), it passed little or no signal. As I turned it in the other direction, it started acting like a gate, but there was a big spike (pop!) when the gate opened and closed. I ended up building the whole circuit twice on different breadboards, and the first one behaved like I described, but I didn't bother to twiddle the threshold pot on the second attempt. It's still on the board, though, so maybe I'll get to it tonight. I'll also check the original build and see if the clock is oscillating. Maybe I'm barking up the wrong tree by concentrating on the oscillator, but then again, maybe not. It seems that if the amplitude is off, it could screw up the switching.
I don't have any Schmitt trigger chips, but I can make a Schmitt trigger out of two inverters, right? I saw this in one or more of the 4069 data sheets.
Thanks for the confirmation on the voltage. I guess I must have just missed Mr. Giles' comment, even though I thought I scoured the various threads for information about voltages for this circuit.
... and you posted more while I was replying... this place is the gift that just keeps giving. I'll try those things, too, but like I said, I probably won't have much time to work on it this week. Thanks again!
Quote from: mdh on April 02, 2007, 03:10:33 PM
The exact problem was that the effect basically behaved like a bad noise gate. With the threshold pot turned fully one way (don't remember which direction), it passed little or no signal.
Maybe I'm barking up the wrong tree by concentrating on the oscillator, but then again, maybe not. It seems that if the amplitude is off, it could screw up the switching.
Thats basically what mine does with the clock disconnected, so it does sound like the clock isn't oscillating or the pulses aren't strong enough.
Quote
I don't have any Schmitt trigger chips, but I can make a Schmitt trigger out of two inverters, right?
Not sure, if you haven't got the right chips you might as well carry on with the original clock. It's just that you can make an oscillator out of 1 gate of a 40106, which works as well as the original clock and would be simpler to debug.
Quote
Thanks for the confirmation on the voltage. I guess I must have just missed Mr. Giles' comment, even though I thought I scoured the various threads for information about voltages for this circuit.
I just meant his post about MXR stripping things down to the bone for maximum profit, not specifically about the voltages, sorry for any confusion.
Quote
Thats basically what mine does with the clock disconnected, so it does sound like the clock isn't oscillating or the pulses aren't strong enough.
That's really useful to know. If you try to measure an AC voltage at the output of the clock, do you get anything? My DMM will report a frequency there, but it doesn't seem to be able to measure the voltage. I don't know if this is because of the high frequency, or just because the meter is loading the circuit. I guess I really need a scope for this kind of stuff.
Quote from: mdh on April 02, 2007, 04:51:32 PM
Quote
Thats basically what mine does with the clock disconnected, so it does sound like the clock isn't oscillating or the pulses aren't strong enough.
That's really useful to know. If you try to measure an AC voltage at the output of the clock, do you get anything? My DMM will report a frequency there, but it doesn't seem to be able to measure the voltage. I don't know if this is because of the high frequency, or just because the meter is loading the circuit. I guess I really need a scope for this kind of stuff.
It may be as simple to solve as making C10 larger (like 22pF, or 33pF). As far as testing the AC amplitude, you can make a peak detector out of a pair of op amps. This would be like what you see in Harry Bissell's envelope follower, except you manually reset the peak with a switch or jumper wire. You could measure the peak AC voltage by measuring the DC on the peak detector output. You could then reverse the peak detector diodes and measure a negative peak. You wouldn't be able to see the waveform, but you could tell how far it was deviating either way.
As for making an oscillator with variable pulse-width control, this can be done with a single opamp, a capacitor, diode, a handful of resistors and a pot.
That way you could at least test the filter section. You may also simply want to use a dual-ganged 500k pot to replace the switch in the filter section just to test that part. Then tackle the clock.
I had a chance to play with this a little bit tonight. I built a peak detector on the breadboard (http://www.uoguelph.ca/~antoon/gadgets/741/741.html (http://www.uoguelph.ca/~antoon/gadgets/741/741.html), a little more than halfway down), and checked the amplitude at pin 9 of IC2. With the diode oriented as shown in the schematic, I measured about 2.5V. Increasing the value of C10 to 20pF seemed to increase the peak voltage at first, but after a little twiddling of the attack and threshold pots, the change seemed to go away. I'm not sure if this should be the case, but in any case it seemed like a little more signal was passing with the larger cap, and I was getting a kind of (faint) misbiased fuzz sound.
I guess this is really just a little progress update. I'm having a surprisingly good time debugging this thing, and I'm learning a lot. Thanks for holding my hand through this.
Just for starters, I'm curious if the filter works at all. Replace the switches (IC3) with 22k resistors (try a few different values in the 1k-50k range) and see if it sounds like a stuck wah. If it doesn't work with resistors like a stuck wah, then you may as well quit worrying about the envelope follower and clock section until you can get the filter to work.
I'm glad you're enjoying this. It's much more fun when you can enjoy the process as much as the outcome. Obviously if you were only interested in the end result, you'd have bought the IC's that work with the filter a long time ago :) Kudos on taking up the challenge
Thanks for the continued support, Transmogrifox. I didn't see your last post until just now, when I came to post a little bit of an update. I did manage to get ahold of some Toshiba 4069s, and the PCB build works now. But I am still interested in figuring out whether I can make the circuit work with the TI ICs (I actually picked up a big pile of TIs when I got the Toshibas). Now that I have a working version of the circuit that I can make measurements on, it should be a little easier.
I've done too many little experiments to describe here, but I think I'm making progress. I think I'll rig up a way to sweep the filters with an LFO so that I can easily test different chips in the filter section. Hopefully in the end I'll be able to provide some answers. I have quite the assortment of 4069s and 4066s now, so I should be able to establish which chips play well together, and hopefully I'll be able to figure out why.
Guys,
I search and found this thread. Currently also i'm on this project with the same problem. The sound is too low need to crank my amp just to hear the sound and what i could hear is like tremolo sound and not sweeping also with popping sound which when attack knob is turn the pop sound become slow? My VR is 4.78v. I did change R16 into 62k already. R1 = 1k C2 = 1uf tantalum with neg going to output is this correct? I don't have mkt cap can I use NP electrolytic cap? One strange is even the circuit has no power the I still get fair amount or little bypass sound!! Bypassed is ok. I already change all the out board wiring and DPDT and switch craft still strange!!
Anyone guys :'(
mdh, hi what was your project outcome?
Transmogrifox,
QuoteJust for starters, I'm curious if the filter works at all. Replace the switches (IC3) with 22k resistors (try a few different values in the 1k-50k range) and see if it sounds like a stuck wah.
R18 and R25 resistor is the one I should replace with 22k? (i'm using Tonepad Schem)
Thanks guys,
Roger
I just took a look at the original MXR EF schematic....... if my analysis is correct, no wonder people are having trouble!!
Because it seems that the detected envelope voltage AND the ultrasonic triangle voltage are both being fed to an inverter pin, so that they are being combined (as in a passive mixer - but a passive mixer that is depending an various characteristics of the oscillator inverter) - and if the result is above whatever the threshold of the inverter is (this can vary quite a bit, and changes with battery voltage as well) then the output changes & the frequency determining resistors are switched.
Now there is quite a lot to go wrong there, it's just plain dodgy to my mind!
> the ultrasonic triangle voltage are both being fed to an inverter pin,
Paul, I analysed this ages ago and it's not dodgy. As I recall it's is actual how the PWM works!
In many PWM circuits the voltage control varies the threshold where the tri-wave is sliced and this varies the PWM.
In the MXR ckt the detecting inverter has a fixed threshold and you vary the DC offset of the tri-wave so the (fixed threshold) inverter slices the tri-wave at different points (as the control voltage is varied). If you see that (?) you will see that it works and that there is nothing dodgy going on - but yes it's a bit harder to see/understand.
I had no problems at all breadboarding this a few years back and even used 4049 for the 4069 :icon_biggrin:
George, I agree with your analysis, but I can't help feeling that to have to depend on the detecting threshold of the inverter is a bit rough, because 1, the threshold varies between units (especially between manufacturers) and 2. the threshold varies with Vcc.
And the ultrasonic triangle oscillator probably DOES have 'issues', because - from posts - people have had trouble when they used different manufacturer's inverters.
Personally, I think the MXR envelope filter is a very creative design & gives very good results - the thing that concerns me here though, is whether it is an easy design to get going. I don't believe it is. If I wanted to make a hundred of them, I would have no trouble, once I secured the 'right' inverters & tweaked the circuit to suit. It's like a lot of the early EH designs, where the primary design aim appears to have been, how few parts can we use? (note in manufacturing, you pay for the parts twice - once when you buy them, and once when you pay to have them soldered in place.)
If I were designing a PWM envelope filter to build for myself, I'd be thinking a couple of 555s instead. (mind you, I could be wrong - wouldn't be the first time). But if I were wanting to manufacture a PWM envelope filter, everything would be happening inside a PIC.
> Personally, I think the MXR envelope filter is a very creative design & gives very good results
It's a great design from an innovative perspective.
> people have had trouble when they used different manufacturer's inverters
Some people are obviously having problems but I'm not sure what is going on here.
As far as stability and repeatability goes take the following extremes: regulate everything and make everything precise in *absolute* terms, or, make the circuit self scaling in that it is independent of supply voltage. (In the second case can only make the frequency independent of supply, not the output level).
From what I remember the thresholds of CMOS gates were a fairly predictable from unit to unit for a given supply voltage - that excludes Schmitt triggers which are extraordinarily variable! The threshold was a relatively constant percentage of the supply. That should make the MXR EF behaviour relatively independent of supply.
With oscillators like the LFO in flangers and phasers the opamps have constant staturation voltages on the output stage which make their behaviour deviate from self scaling. The same goes for CMOS oscillators where the input clipping diodes are used to discharge the timing caps. If you double the supply the saturation voltages and diode voltages don't double. If MXR EF design doesn't have any traits like that.
On the MXR EF, if the supply voltage varies the behaviour seems like it should be relatively constant. For example if the supply voltage varies the PWM inverter threshold will vary, however, the bias point of the prior envelope gain stages should also shift down in proportion and all should be well.
That's why I can't explain why people would have a lot of trouble with this circuit!
As a side note if you look a the 555 it's threshold are derived from the power rails and will vary with the supply voltage. However, because the capacitor charge circuit is derived from the supply rail the thresholds vary in the same proportions and that's why 555 is stable with voltage variations. *if* the threshold on CMOS inverters is relatively constant fraction of the supply voltage then it should be resonably stable with the supply in the same way.
If you wire up a 555 with the a resistor from the output back to pins 2 and 6 and a cap to ground it will operate as a Schmitt oscillator. As usualy the threshold points will move up and down in proportion to the supply but this circuit has nowhere near the robustness to supply variations. The reason is the 555's bipolar transistor outputs now feed timing resistor and the saturation voltages don't scale up and down with the supply voltage.
(Sorry for the long winded drivel.)
Ed: The 40106 mentioned above is a CMOS schmitt trigger which are known to have widely variable thresholds. Also it *won't work* properly in the PWM threshold inverter positions or any of the positions where the inverters are operating as amplifiers. The 40106, or any other schmitts, should not be used in this circuit!!!!
George, I appreciate your response. It is exactly the kind of reply I was hoping to see when I switched the computer on tonight!
Quote from: George Giblet on January 05, 2008, 11:56:46 PM
Ed: The 40106 mentioned above is a CMOS schmitt trigger which are known to have widely variable thresholds. Also it *won't work* properly in the PWM threshold inverter positions or any of the positions where the inverters are operating as amplifiers. The 40106, or any other schmitts, should not be used in this circuit!!!!
You're right it shouldn't be used to replace any of the 4069s in the circuit. The only reason I suggested it is because you can make an oscillator using 1 gate of a 40106, 1 cap and 1 resistor that works just as well as the more complicated oscillator used in the original. This could be used to debug the circuit to try and identify whether the issue was with the "clock" or the switching.
Like Paul pointed out this circuit seems to be a bit touchy as to whether it works or not but no one ever seems to have got to the bottom of it. The only solution that seems to work is switching to different manufacturer's 4069s, but that's not solving the underlying problem.
Quote from: rogeryu_ph on January 04, 2008, 08:07:13 PM
One strange is even the circuit has no power the I still get fair amount or little bypass sound!! Bypassed is ok. I already change all the out board wiring and DPDT and switch craft still strange!!
That's normal with no power to the circuit the signal can still pass through C3, R7, R12, C2, and R1 so you will get some sound.
QuoteJust for starters, I'm curious if the filter works at all. Replace the switches (IC3) with 22k resistors (try a few different values in the 1k-50k range) and see if it sounds like a stuck wah.
R18 and R25 resistor is the one I should replace with 22k? (i'm using Tonepad Schem)
[/quote]
No what you need to do is remove IC3 and put the 22k resistors between pins 10-11 and 8-9 of where IC3 was. If you've used a socket just plug the resistors into the socket. IC3 basically acts a a variable resistor so replacing it with normal resistors will make the filter work. If this solves you volume problem then you've got the same problem as mdh had and the only fix might be to try some different 4069s.
Mine worked perfectly well once I ran out and got 4069s and a 4066 from manufacturers other than TI. I believe the 4069s are from ST Micro and the 4066 is a Motorola. I've been meaning to break the circuit down into its constituent parts and test them with chips from different manufacturers, but I haven't had the time, and it went down on the list of priorities after I got it working. So far, I think this thread has the best information on what the problem might be.
Are you using TI chips, Roger?
My 4049 was a CMOS :icon_biggrin: I also experimented with inverting the CV, using 2 filters in parallel and using an LFO. But where all the posted notes on this are I don't remember. I recall that Mark Hammer did something, but it may have been over at Ampage.
Slacker,
Copy that. I thought was the resistor :icon_lol: I did audio probe the sound like tremolo. I'll try your instruction and many thanks. Also I see that why the sound is there even without power. I'm using 105 tantalim for 1uf is that okey? the neg side is going to output.
Mdh,
I'm using HEF4069 maybe it's from Philip. Once I tried slacker's instruction and it's okey maybe I only have to shop for several brand. Many thanks also.
Roger
> oscillator using 1 gate of a 40106, 1 cap and 1 resistor that works just as well as the more complicated oscillator used in the original. This could be used to debug the circuit to try and identify whether the issue was with the "clock"
Yes that's an easy one to whip up. It could be used for debug but I wouldn't go modding the original to incorporate it.
I have some notes on the oscillator section. They say 35kHz, 2.3Vp-p with 2.3V DC offset; presumably at the triangle waye output, the inveter that goes to the 47k. A square-wave output would be present at the inverter output that connects to the small cap (10p).
I suppose all you need to do is check the oscillator is working. A multimeter set to Frequency connected to the *square-wave* output would do. You could also measure the DC voltage at the square wave output. If it's 0V or 4 to 5V then there the oscillator might not the oscillating if it's around 2.3V +/- 0.5V then it's probably working.
A CRO would make life easier.
> Like Paul pointed out this circuit seems to be a bit touchy as to whether it works or not but no one ever seems to have got to the bottom of it. The only solution that seems to work is switching to different manufacturer's 4069s, but that's not solving the underlying problem.
I would not expect that circuit to be too badly behaved.
There are many inverters operating in linear (amplifier) mode. The original circuit used 4069UB, the unbuffered version. If some people are unknowingly sub'ing the buffered version that might be a problem.
Another thing to try would be to inject into the junction point of the 1M and 22M resistors, near the envelope detector output. Perhaps by connecting a 470k resistor (experiment) from there to ground. That should force the filters to change frequency and let more highs through. Play a signal through the unit and switch slowly between resistor and no resistor. You should be able to hear the filters working (or not working if something is wrong). If it works then everything is working (to some extent) - the only thing unchecked is the inverters (amplifiers) around the threshold control.
When we say oscillating it whine high pitch is'nt it? That what I hear on the audio probe on IC1 and IC2 and also IC3 but when attack is full sound like a pump boat and there is a beat and when the attack is reduce it becomes faster. And the sound fairly low you need to crunk the amp just to hear but the guitar sound is like little bit tremolo..
Thanks
Roger
There diferent types of oscillation!
There is intentional and unintenional oscillation. The oscillation you mentioned is unintentional high frequency oscillation. You get often get this in high gain circuits the frequency may be so high that you cannot even hear a whine. The motor boating you are experienced is also unintenional this is low frequency oscillation.
The oscillation I was talking about is intentional oscillation. The circuit needs an oscillator to function, the PWM generator that feeds filters. This oscillation frequency shouldn't get into the audio, and it is not intended to do so, it's kind a behind the scenes block of the circuit. For the MXR circuit you probably won't hear much on the audio probe, the 35kHz is beyond your hearing.
Early in the thread slacker gave a good suggestion. If you increase the capacitor on the oscillator by factor of 10 to 100 it should put the oscillation into the audilbe range. The intention here is not to make the circuit work, it's not a mod. It's just a way you could confirm the oscillator is working using the tools you have. If you had an oscilloscope you would just probe the circuit with out having the change the part values because a cross can display the high frequencies.
A couple of other things:
- Do you have a multimeter?
- It is normal for this circuit to produce and output when the power is off, don't worry about that behaviour.
Guys,
Finally RCA CD4069UB made it! I shop for National, ST micro, Harris but to no avail. Strange why only RCA. I did change only the IC2. The IC1 is Philips and IC3 is Harris. Everytime I change ic the VR varies RCA vr become only 3.14V I don't know if this is ideal but the sound is huge. I did the emphasis mod and the filter range mod it's ok next week i'll try the reverse. Thank you so much Slacker, mdh and George for this. BTW I changed back r16 into 100k
Roger
The good thing is everything is working. The bad this is we still don't know what the problem is! I looks like it is related to IC2, but is it? Did the change in Vr fix something else?
The chip voltage on the original I measured was 4V.
The only "bad" thing about the original circuit I could see is that IC1 pin 8 is left floating. This is a no no for CMOS so it probably should be grounded. The original circuit actually left this input floating but that doesn't make it right.
No I think. co'z when i debug this before, I have for 4069 chips which when i measure the VR i got also 3.15v but not working. This make me suspect that the vr is lower so I stick to 4.5 pair of chips but still to no avail. So I run out to buy 4 more brand. For awhile I suspect maybe that I have problem on my built circuit and need to build another one. The vr with different combination has different voltage. I got one measure 5.6V some 4.9v other 4.1v but as i said stick to combination with 4.5v which has sound like motor boating sound and some whining or whistle when full the emphasis knob and attack. So I change back it into 100k and tried the new 4 chips again which RCA comes alive.
The big question now is what can I do with the rest of 4069 :icon_biggrin:
Thanks again,
Roger
Guys, out of curiousity I swap IC1 to IC2 it does'n't work!!! I measured the vr it's 4.3V!!!! Before is 3.14v. I immediately return after this co'z i'm alarm it may damage the ICs well it works again, strange ???
Roger
Glad you got it working. I haven't got much time at the moment but when I do I'll try and get some 4069s that don't work and see if I can figure it out what the problem is.
> Guys, out of curiousity I swap IC1 to IC2 it does'n't work!!!
Thanks for doing that test, very interesting. Seems like a biasing or gain issue - are you sure these are unbuffered (4069UB)?
One thing you can try is to tie a resistor from the output of the inverter back to the input, use say 1MEG. Power the inverter from 4V and/or 9V and measure the voltage at the output of the inverter. Tie unused inputs to ground. (If you like, repeat on a few gate or ICs).
What that tells you is the self biasing point for the inverter. It's usually just under half the supply voltage, say 45%. If a CMOS gate biases to around that figure it should work with reasonably high gain. If it's way off there's something weird going on with the devices.
Going beyond that, use the above circuit but this time add a 10MEG to the input of the inverter. Connect the free end of the 10MEG to Vr and measure the output voltage, now connect the free end to gnd and measure again. From those two voltages you can see the gain of the CMOS gate and the symmetry of the swing.
I'm not sure if these are unbuffered George. Definitely these chips are not defective maybe it's the manufacturer output variation to their standard co'z I put the same PhilipsHEF4069 on IC1 but the difference was one with no sounds at all the other has fairly low sound both don't wah.
BTW I don't expect this kind of good sound i'm getting for this project but really i'm impressed with the outcome of the wah sound!!! Great project.
Roger
Quote from: slacker on January 06, 2008, 07:46:16 AM
Quote from: rogeryu_ph on January 04, 2008, 08:07:13 PM
One strange is even the circuit has no power the I still get fair amount or little bypass sound!! Bypassed is ok. I already change all the out board wiring and DPDT and switch craft still strange!!
That's normal with no power to the circuit the signal can still pass through C3, R7, R12, C2, and R1 so you will get some sound.
QuoteJust for starters, I'm curious if the filter works at all. Replace the switches (IC3) with 22k resistors (try a few different values in the 1k-50k range) and see if it sounds like a stuck wah.
R18 and R25 resistor is the one I should replace with 22k? (i'm using Tonepad Schem)
No what you need to do is remove IC3 and put the 22k resistors between pins 10-11 and 8-9 of where IC3 was. If you've used a socket just plug the resistors into the socket. IC3 basically acts a a variable resistor so replacing it with normal resistors will make the filter work. If this solves you volume problem then you've got the same problem as mdh had and the only fix might be to try some different 4069s.
[/quote]
When I put 22k Resistors into 8-9 & 10-11, I got the stuck-wah sound. So the whole issue with these is definitely just the TI chips. My 4066 is a Fairchild chip, but my 4069s are TI. I'm ordering replacements for them now. I'll post when they come in to confirm. Good thing I socketed these.
Quote from: mdh on March 29, 2007, 06:19:39 PM
Quote from: Mark Hammer on March 29, 2007, 05:14:38 PM
I received an off-line query from someone about the MXR EF clone at Tonepad recently. As usual, it was an "I built it but it doesn't work, did I get the wrong chips?" sort of query. That's something that comes up often enough that I started to cogitate about it, and it dawned on me that maybe the culprit is not the brand of invertor chips, but rather the specific CMOS switch chip in tandem with the components that result in the amplitude of the clock pulse. Is it possible that the "on" pulse going from the clock to the switch is simply not enough to turn the switch on for some brands? If so, then that might mean that one could use virtually ANY brand of CMOS chips if we knew how to change certain component values and adjust the properties of that clock pulse to do its job.
Does that make sense, and does anyone know what to zero in on in the circuit to accomplish that?
That was me... but then I decided to try to "learn to fish," so to speak, rather than to post a debugging thread with voltages. I freed up a largish breadboard by finally committing my GEO test oscillator and GEO FET matcher to perf, so I should be good to go.
FWIW, with respect to the interaction of the 4066 with the 4069s, I originally had TI 4069s and a TI 4066 in there, but I've also tried a Motorola 4066, which resulted in the same behavior that I described in the PM I sent you. I'm guessing that the problem is in that clock pulse generator. This would be consistent with the Tonepad build reports, in that it seems like swapping IC2 out for a non-TI brand improves the behavior of the circuit. So I think that what I've done here is volunteered to try to become an expert on this portion of the circuit, and work out whether we can make it work consistently with chips from different manufacturers. I have a long way to go, but I'm willing to try :icon_redface: Maybe I'm naively optimistic, but I think if I can break it down into simple enough blocks, I have a chance of figuring it out.
I've built this project from tonepad with sockets, and I can say that the TI chips do not work at all, the Motorola ones introduce some distortion, and the Fairchild ones work PERFECTLY. So do yourself a favor and order fairchild ones from your parts supplier.
Quote from: thedefog on April 02, 2009, 09:26:13 PM
I've built this project from tonepad with sockets, and I can say that the TI chips do not work at all, the Motorola ones introduce some distortion, and the Fairchild ones work PERFECTLY. So do yourself a favor and order fairchild ones from your parts supplier.
Question... What Fairchild chips are you using? I am having the same problem with the Fairchilds...
Thanks
Bob
If I remember correctly, there is a 62k/100k voltage divider pair, that sets a bias voltage in the free-running clock circuit. The collective suspicions of several of us here are that whatever bias voltage is required by that sub-circuit for THAT chip may occasionally (and more frequently for some brands) fall outside of what is produced by that divider pair, given their typical 5% tolerance. The punch line is that some brands will work for some people but not for others.
Just for the heck of it, replace the 100k fixed resistor in that pair with a 68-82k resistor and a 50k trimpot, and fiddle with it to see if you can nail the required bias voltage. My hunch is that this mod will make it amenable to essentially any brand of 4069.
YES!!! Put a 100k trimpot in place of the 100k resistor and adjusted down until the sound stopped. Turned it back up a hair, sound kicked back in with a wicked WAH!!!
Voltage at divider is 1.62v...
Works on both TI and Fairchild. I have a clone MXR Envelope filter with 2 TI 4069 and 1 TI 4066 and it sings!!!!
I am going to do a layout to include the trimpt tonite. Once I verify it by building it, I will post.
Thanks for the help!!!!!!
peace
BobP
Excellent!! Thanks for taking the chance and reporting back. I'm sure there are others who will appreciate this info.
I was gearing up to build this soon. Thanks a lot for posting this info!
Don't forget the double or even triple filter mod - well worth it!
Quote from: StephenGiles on July 02, 2009, 05:19:24 AM
Don't forget the double or even triple filter mod - well worth it!
Oh hell, I need to look that one up!! Thanks. :icon_biggrin:
Also need to find out how to make a switchable LFO circuit for it like Charlie Moosapotamus mentioned somewhere... I still have some studying to do.