# DIYstompboxes.com

## DIY Stompboxes => Building your own stompbox => Topic started by: armdnrdy on August 08, 2013, 02:00:15 PM

Title: What is this circuit section doing??
Post by: armdnrdy on August 08, 2013, 02:00:15 PM
This is the pedal control section from the Mutron Flanger.

(https://dl.dropboxusercontent.com/u/53299166/DIYstompboxes/Mutron%20Flanger%20pedal%20circuit.jpg)

Dino, (digi2t) yours truly, and an assorted cast of characters have been communicating back and forth, throwing ideas around, and gathering information for a Mutron Flanger build.

The above circuit looks to me to be a voltage comparator with an adjustable voltage divider on the non inverting input of IC10A and an adjustable (controlled by the reflection of the silver pedal shutter) voltage divider on the inverting input.

Can anyone give a description of what this circuit is doing? I'm a little lost!  ???
Title: Re: What is this circuit section doing??
Post by: slacker on August 08, 2013, 02:38:13 PM
Where is LDR1 placed in relation to the LED, what controls whether it's in the dark or in light?

On the face of it it's some odd feedback loop that makes no sense to me, the resistance of LDR1 determines whether the voltage on the inverting input is higher or lower than the non-inverting input, which in turn determines whether the LED is on or off, which sets the resistance of LDR1................................
Title: Re: What is this circuit section doing??
Post by: gritz on August 08, 2013, 02:45:42 PM
I don't suppose you guys actually have one of these hen's teeth and can supply a sketch / photo showing the orientation of the LED, LDRs and shutter? That would be cool, simply from a "wow, look at that!" point of view. :)

It looks to me like the LED, LDR1, IC10A and that mysterious shutter might form a servo (negative feedback) loop that causes the resistance of LDR2 to accurately (or repeatably) follow the position of the shutter (and thus the pedal). Or something. It's possible that Mutron chose this method to generate a quiet, smooth control voltage, rather than resort to noisy, don't-last-for-ever pots. That's my guess anyway.

Edit: slacker beat me to it on the "how does it all fit together?" front.
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 08, 2013, 02:55:18 PM
I don't suppose you guys actually have one of these hen's teeth and can supply a sketch / photo showing the orientation of the LED, LDRs and shutter?

Courtesy of Dino:

(https://dl.dropboxusercontent.com/u/53299166/DIYstompboxes/LED_LDRARRANGEMENT_zpsd4a345c0.jpg)
Title: Re: What is this circuit section doing??
Post by: slacker on August 08, 2013, 02:57:55 PM
Interesting, which one of the LDRs is LDR1? From the schematic it's presumably the one next to the LED.
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 08, 2013, 03:03:53 PM
Interesting, which one of the LDRs is LDR1? From the schematic it's presumably the one next to the LED.

Correct!
Title: Re: What is this circuit section doing??
Post by: slacker on August 08, 2013, 03:13:38 PM
I'm totally stumped then, it appears that a high resistance on the LDR is likely to turn the LED on, which will lower the resistance of the LDR which will likely turn it off. Is it supposed to cause the LED to flash? The expected light and dark values for the LDR might help.
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 08, 2013, 03:26:09 PM
The thing that I don't understand is what the comparator section is doing if the LDR (controlled by the pedal) connected to IC10B is controlling the output voltage going to the VCO input of the 4046. (not shown in the above image)

Maybe the comparator section "softens" the abrupt attack of the pedal shutter moving up and down, turning on and off the light to LDR2.

The capacitor C51 might add a slight delay while it charges and discharges through R67 before the voltage makes it's way to the base of Q3. (just a theory!)
Title: Re: What is this circuit section doing??
Post by: digi2t on August 08, 2013, 03:52:59 PM
From what I know, T4 is the trimmer that sets the sweep range of the pedal. That is the two ends of the sweep move up/down together. The pedal is independant of the START/STOP pots. Could it be that it`s just set up to do this as linearly (is that a word?) as possible?

(Notice the «OMG the guy`s got one, but is a total noob» question at the end. :icon_mrgreen:)

Actually, Larry brought up a good point in our PM exchange. Since that LED/LDR1 combo is inside the same tube, could the shutter also affect the intensity of the LED? As the shutter moves out of the way, light bleeds out to LDR2, and LDR1 on the LED side reads this variation, adjusting the LED intensity slightly? Keep things really super linear?

Please tell me if my cheese has gone off it`s cracker again... :icon_rolleyes:
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 08, 2013, 04:03:44 PM

(Notice the «OMG the guy`s got one, but is a total noob» question at the end. :icon_mrgreen:)

If I had a Ferrari, that wouldn't mean that I would know everything about the motor!  :icon_wink:

Actually, Larry brought up a good point in our PM exchange. Since that LED/LDR1 combo is inside the same tube, could the shutter also affect the intensity of the LED? As the shutter moves out of the way, light bleeds out to LDR2, and LDR1 on the LED side reads this variation, adjusting the LED intensity slightly? Keep things really super linear?

Please tell me if my cheese has gone off it`s cracker again... :icon_rolleyes:

As in our communication, I think that the LED/LDR1 combo will react to the silver reflective shutter. Remember that there are bi-convex lenses that will amplify the light as well!
Title: Re: What is this circuit section doing??
Post by: slacker on August 08, 2013, 04:04:29 PM
The comparator can only do two things, it can either turn the LED on or turn it off, if it just did either of those it doesn't seem to serve any purpose, it has no controls so it's not being used as a fancy switch. Thinking it through the, the only thing that makes sense to me is that it causes the LED to flash on an off. Maybe it's like a PWM light dimmer circuit and flashes the LED on and off faster than you can see, creating a constant brightness that doesn't vary with supply voltage, this would in turn keep the range of control voltages to the VCO constant.
That seems far too complicated though.

EDIT: wrote that before I read Dino's post, sort of fits with what he said, twiddling the trimmer sets the brighness and therefore the sweeps. Still sounds too complicated though. Maybe there is something in Larry's idea.
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 08, 2013, 04:08:43 PM
Dino.....we need measurements of the base of Q3 with the pedal in the toe down position and the heel down.

Title: Re: What is this circuit section doing??
Post by: slacker on August 08, 2013, 04:17:32 PM
Good call, or even better if you've got a scope get that on there.
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 08, 2013, 04:20:58 PM
Very similar circuit:

http://electronut.in/ambient-light-sensor-using-an-op-amp-comparator/
Title: Re: What is this circuit section doing??
Post by: Digital Larry on August 08, 2013, 04:21:31 PM
I'll tell you what I THINK is going on.   This often results in much hilarity when I'm proven wrong.  Let's see what happens.

If the left side of the circuit is just a range adjustment, then I would not expect the comparator to be switching after the trimmer settles down.  I think the LDR in the comparator circuit attempts to linearize the response of the right hand LDR to the trimmer's range adjustment.  Without that it probably would do nothing for most of its range and then all of a sudden go over the entire range.

I didn't do any math and I'm not at all familiar with this circuit.  However, way back when, I did design an LDR which had a split (center tapped) element into a voltage controlled midrange notch (think of the bottom resistor in a Fender tone stack).  The center tap of the LDR went to ground.  One end went to the notch circuit and the other end went to the op-amp circuit.  This way, regardless of the non linearities of the LDR itself, the resistance presented to the notch circuit would be linearly related to the voltage coming into the op-amp.  There are enough differences between that and this circuit that my confidence is about 50%.

Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 08, 2013, 04:34:54 PM
So Larry,

Let me get this straight. What you are saying is that you are 100% sure that you're 50% confident?  :icon_wink:

Come on guys....this circuit only has a few components! Surely we can figure this out. (he mumbles as his brain begins to swell)
Title: Re: What is this circuit section doing??
Post by: Digital Larry on August 08, 2013, 04:37:24 PM
Let me get this straight. What you are saying is that you are 100% sure that you're 50% confident?  :icon_wink:
It might be the other way around.
Title: Re: What is this circuit section doing??
Post by: Gurner on August 08, 2013, 04:38:19 PM
Dunno...I'm as perplexed as the next guy ....my punt (& it's an outside one!) is that LDR1 might some form of ambient light cancellation? (cos I reckon when the shutter is open a degree of ambient light will reach both LDRs .....if it's daytime, then that light spill-in could be significantly more than on a dark stage .... therefore perhaps such an arrangement is to cater (help cancel out) for extremities?
Title: Re: What is this circuit section doing??
Post by: Digital Larry on August 08, 2013, 05:34:38 PM
It may be for temperature compensation - but probably not.

See:

http://www.silonex.com/audiohm/levelcontrol.html figure 14.

Figure 15 shows what is pretty close to the Mutron circuit used for linearization.  I stick by my original guess.
Title: Re: What is this circuit section doing??
Post by: Lurco on August 08, 2013, 05:49:12 PM
linearization: optical feedback from output to inverting input.
Title: Re: Re: What is this circuit section doing??
Post by: slacker on August 08, 2013, 06:07:38 PM
Can you elaborate? What's it linearising and how?
Title: Re: What is this circuit section doing??
Post by: Gus on August 08, 2013, 06:27:23 PM
I posted what it is doing in the other thread

It is a servo control to control the LED light output
Title: Re: What is this circuit section doing??
Post by: Digital Larry on August 08, 2013, 07:23:27 PM
The op-amp and trimmer circuit form a light-bias circuit for the right hand LDR.  Pretty sure that the LED current does not change except in response to the trimmer.  Even though the circuit looks somewhat like a comparator, think of it as a really high gain amplifier (which it is).

As the trimmer increases the (+) input voltage, the output voltage goes up and more current goes through the transistor and LED.  This reduces the resistance of the LDR on the left and the (-) input goes up.  How far does the (-) input go up?  It goes up until it matches the (+) input, if it can.  If it goes a little higher than the (+) input, then the transistor base voltage starts to drop, reducing the collector current, etc. so it balances out.   This is the servo circuit in action.  It adjusts the current to whatever it needs to be, within the limits, to get the (-) voltage to match the (+) voltage.  It automatically creates a non linear current/illumination curve in order to get a linear resistance curve.  The same illumination is used for the audio control LDR.  Fortunately you adjust it by ear so that you can accommodate any differences in their sensitivity or illumination.

There are limits to (1) how much current you can pull through the LED and (2) how low the LDR resistance will go.  The op-amp's output voltage is (when the circuit is working properly) not slammed high or low as it would be for a comparator.  Once you hit one of those limits, the output voltage can't move far enough to reduce the error voltage to zero and so the op-amp output WILL be slammed into the rails.

I think figure 15 in the link I posted awhile back is instructive.  In that example there are two separate LDR/LED assemblies, but the LEDs are connected in series and the nonlinearity of the LED current to LDR resistance relationship are assumed to be identical for both devices (which might not be true, but it's as close as we're going to get).  In this example there is one LED shining on two LDRs and most likely the intensity is not the same, but that is just a matter of a gain correction factor (er... or it might explain why the left hand LDR is looking at the LED from the side).
Title: Re: What is this circuit section doing??
Post by: PRR on August 09, 2013, 01:39:06 AM
> the LED current does not change except in response to the trimmer.

Exactly so for a hacker's guide.

It keeps the LED's *brightness* CONSTANT.

Secondarily it corrects LED and LDR temperature drift, age drift, and perhaps battery voltage drop.

Imagine you want to keep a 100fc lamp at 85fc, despite wall-voltage surge/sag or lamp glass darkening with age. You put a light meter on it. You compare the meter to the desired 85fc. If you read 80fc, you dump more power to the light; if 90fc you put less power in. This is a dummy job. If the light-meter output and the desired light level are both voltage signals, any (DC) amplifier can do it. Depending on the lamp, it may be necessary or convenient to buffer the lamp, hence Q3.

Sadly it does not linearize the LDR's curvature. (However a fair fit can be had by "bending" the shutter, either with a curve-taper slot or in the linkage to your shoe.)

What the trimmer probably does here is correct for the flanger's JFETs turn-on/off voltage or voltage-range. If you have alignment instructions(?) this will probably make sense: you trim for best response when the shutter is not blocking.

Title: Re: What is this circuit section doing??
Post by: Lurco on August 09, 2013, 03:30:33 AM
somehow I had fig.3 in mind, which by accident just had crossed me earlier yesterday: http://www.keith-snook.info/Wireless-World-Stuff/Wireless-World-1976/Wideband%20compander%20design.pdf . Call it optical feedback or servo, ymmv.
Title: Re: Re: What is this circuit section doing??
Post by: slacker on August 09, 2013, 07:32:53 AM
Slaps head, I was being a complete buffoon, got too carried away with looking at what happened at the extremes of the LDR's resistance and forgot about all the points in between.
Thanks to Larry's explanation it now makes sense to me. Can I have some points for getting the right answer even though my working was wrong?
Title: Re: Re: What is this circuit section doing??
Post by: Digital Larry on August 09, 2013, 09:02:13 AM
Can I have some points for getting the right answer even though my working was wrong?

This circuit, a non inverting op-amp stage, and an inverting op-amp stage all can be understood on a few fundamental principals.
1) There is a feedback path from the output to the (-) input.  The difference between the (+) and (-) inputs is considered the "error" voltage.
2) The circuit, due to its extremely high gain, moves the output voltage to "whatever is necessary" to keep the voltage at the (+) and (-) inputs the same, reducing the "error" to zero.
3) The op-amp's input impedance is infinite (no current flows into either input) - this is an oversimplification.
4) The op-amp's output impedance is zero (another oversimplification).

A comparator lacks negative feedback, so (1) and (2) do not hold in that case.  (3) and (4) are still valid.
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 09, 2013, 09:55:51 AM
We've got a winner!!

Thanks Larry for the explanation!

I was completely wrong in my assumption that this circuit had something to do with a cheese grating attachment!  :icon_wink:

I'm working on a prototype of the LDR/LED tubes with dimensions provided by Dino. The idea is to fabricate them from easily obtainable plumbing/sprinkler parts.

So Larry, when are you or Mick going to post one of those cool sounding FV-1 projects?
Title: Re: What is this circuit section doing??
Post by: Digital Larry on August 09, 2013, 10:16:26 AM
So Larry, when are you or Mick going to post one of those cool sounding FV-1 projects?
Hi Larry,

Glad to have helped.  Part of my enjoyment hanging out here is dusting off my ancient analog skilz.

If you MUST know, I have a couple top-secret possibly revolutionary designs in progress.  These leverage the FV-1 in a way that I have not seen done and also tie into some things which are very commonly discussed here.  Interested yet?   ;D  By the way I sure hope it works!

I was at first motivated by the contest but I started a new job a few months back and so I don't think I'll be able to make the deadline and still give it enough time.  Hopefully by the end of the year.
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 09, 2013, 11:16:38 AM
If you MUST know, I have a couple top-secret possibly revolutionary designs in progress.  These leverage the FV-1 in a way that I have not seen done and also tie into some things which are very commonly discussed here.  Interested yet?   ;D

Does this design have anything to do with easily obtainable plumbing/sprinkler parts?  ;D

You threw out just enough to make me curious! Let me see....Octave divider perhaps?

Title: Re: What is this circuit section doing??
Post by: digi2t on August 09, 2013, 03:43:41 PM
If you MUST know, I have a couple top-secret possibly revolutionary designs in progress.  These leverage the FV-1 in a way that I have not seen done and also tie into some things which are very commonly discussed here.  Interested yet?   ;D

Does this design have anything to do with easily obtainable plumbing/sprinkler parts?  ;D

You threw out just enough to make me curious! Let me see....Octave divider perhaps?

The octave divider might be something to consider, but I`m definately in for the cheese grater attachment.  :icon_wink:

Thanks for the explination. Especially in terms that I can understand.
Title: Re: What is this circuit section doing??
Post by: Digital Larry on August 09, 2013, 06:35:17 PM
Does this design have anything to do with easily obtainable plumbing/sprinkler parts?  ;D
The octave divider might be something to consider, but I`m definately in for the cheese grater attachment.  :icon_wink:
Thanks for the explination. Especially in terms that I can understand.

(furiously scribbling notes on old In-n-Out Burger wrappers)...

Hmmm, an Octave Divider is one thing this WON'T do, although it will support pitch shifting.

Now I'm wondering why you want "easily obtainable" plumbing/sprinkler parts, when I just so happen to have some NOS RainBird timers over here... pre-RoHS for sure... well, I don't want to give TOO much away... cheese grater... flat or one of those hand crank dealybobs?
Title: Re: What is this circuit section doing??
Post by: tubegeek on August 09, 2013, 07:58:56 PM
Let me get this straight. What you are saying is that you are 100% sure that you're 50% confident?  :icon_wink:
It might be the other way around.

But how can you be sure?

"60% of the time, it works every time."
Title: Re: What is this circuit section doing??
Post by: digi2t on August 09, 2013, 08:12:19 PM
Quote
cheese grater... flat or one of those hand crank dealybobs?

Flat... definitely flat. Nothing beats that old school elbow grease. Makes the cheese taste better. :icon_mrgreen:
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 10, 2013, 01:46:01 AM
Okay,

Here's the "tube" I fabricated that houses LDR1 and D18.

(https://dl.dropboxusercontent.com/u/53299166/DIYstompboxes/LED_LDR%20tube.jpg)
Title: Re: What is this circuit section doing??
Post by: digi2t on August 10, 2013, 08:24:20 AM
LAIR!!!! You actually salvaged that from a scrapped Mutron Flanger.

:icon_lol:

Beautiful work Larry. :icon_biggrin: What materials did you use?
Title: Re: What is this circuit section doing??
Post by: Digital Larry on August 10, 2013, 09:12:40 AM
Let me get this straight. What you are saying is that you are 100% sure that you're 50% confident?  :icon_wink:
It might be the other way around.
But how can you be sure?
"60% of the time, it works every time."

I checked with my cat, but he doesn't appear to be feeling well.
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 10, 2013, 09:48:42 AM
LAIR!!!! You actually salvaged that from a scrapped Mutron Flanger.

:icon_lol:

Beautiful work Larry. :icon_biggrin: What materials did you use?

I wasn't joking about the sprinkler parts!  :icon_wink:

A 1/2" X 12" cut-off riser from Home Depot, a 3/4"plug, party favor (plastic) magnifying glass for the lens from Party City, red, diffused LED, and a 10K-1M 20ms-30ms LDR that I had some stock of.

I'll take some construction photos for the next tube.

Title: Re: What is this circuit section doing??
Post by: digi2t on August 10, 2013, 07:26:17 PM
Brilliant!!
Title: Re: What is this circuit section doing??
Post by: R.G. on August 10, 2013, 08:23:17 PM
But how can you be sure?
"60% of the time, it works every time."
There is a serious saying in programming that "almost always is almost always as good as always".
Title: Re: What is this circuit section doing??
Post by: Ronan on August 12, 2013, 02:45:41 AM
Hmmm, I thought that circuit was simply to keep the LED at a constant brightness to compensate for what I don't know. The trimmer adjusts the brightness. Way overkill IMO. The simple Morley approach should work fine, I almost would always think.
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 12, 2013, 12:44:03 PM
I have a Morley EVO optical volume pedal arriving today so I'll mess with that circuit a bit to see what it's all about.

When the first prototype of the Mutron Flanger is built I plan to socket certain sections to experiment.
I think it's a good idea to build it as close to the original to start so that there will be a point of reference.
Title: Re: What is this circuit section doing??
Post by: Ronan on August 13, 2013, 03:26:08 AM
Sadly I somehow missed PRR's post on page 2. If I had read that I wouldn't have posted.

Anyway, build it close to the original and see what happens, certainly won't hurt.
Title: Re: What is this circuit section doing??
Post by: tubegeek on August 13, 2013, 11:29:11 AM
I checked with my cat, but he doesn't appear to be feeling well.

You could always ask Werner Heisenberg but I have a feeling he won't be much help. As an example, when he was pulled over for speeding, the cop asked him, "Do you know how fast you were going?"
His reply: "No, but I knew exactly where I was."

Also: a quote that seems apropos.

"The man with one watch always knows what time it is. The man with two watches is never sure."

Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 13, 2013, 12:08:10 PM
Got a little problem here!

I received the Morley Optical Volume pedal that I was going to use for the enclosure for the Mutron Flanger.

The problem is the pedal shutter arrangement. The shutter is located toward the rear of the enclosure. The shutter moves down (blacks out the LED light to the LDR) in the heel down position. This is the opposite of the Mutron Flanger which "blacks out" the light in the toe down position.

It would take some major reconstructive surgery to make this enclosure work!

I think at this point I might use a Dunlop type foot pedal, fabricate brackets, find a suitable size enclose to mount the foot pedal on, cut a slot on the top of the enclosure and be good to go.

Another bad thing about the Morley enclosure is the shallow size which is kind of limiting for a build like the Mutron.
Title: Re: What is this circuit section doing??
Post by: Digital Larry on August 13, 2013, 12:16:08 PM
Well if all you need is a control voltage that goes up instead of down (or vice versa, I'm not really following the details), consider adding an inverting op-amp stage.
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 13, 2013, 12:34:26 PM
Thanks for the reply Larry (cool name by the way!)

There's another issue with this enclosure....the shutter slot is less than 3/4" from the rear of the enclosure. If we do in fact need to use the two LED/LDR "tubes" they would be situated in this area. This is also where the effect on/off switch and the effect/pedal switch need to go. This won't work!
Title: Re: What is this circuit section doing??
Post by: Govmnt_Lacky on August 13, 2013, 12:45:54 PM
Thanks for the reply Larry (cool name by the way!)

There's another issue with this enclosure....the shutter slot is less than 3/4" from the rear of the enclosure. If we do in fact need to use the two LED/LDR "tubes" they would be situated in this area. This is also where the effect on/off switch and the effect/pedal switch need to go. This won't work!

Larry,

Didn't you say that the optical tube thingamabobby that you built was 1/2 inch wide? I have an old Morley Alligator pedal and it looked to me like there is enough room for that. Am I wrong?

Also, as for the pots. Couldn't they be relocated somewhere else in the enclosure. There is a lot of real estate on the flat portion of the enclosure.

Finally, is the shutter "screwed" onto the foot pedal? If so, then possibly a solution would be to use some black painted plexi or thin aluminum and custom-cut the proper holes so it would work then, bolt it back on.

Just throwing out some suggestions. Its been a while since I have looked at mine  :-\
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 13, 2013, 01:09:38 PM
The inner diameter of the tubes is 1/2". The O.D. of the tubes that I fabricated is 3/4"...... and since the tubes are located 1/4" from the shutter there's not much room left for footswitches.

The shutter on the Morley is attached via a clip to a "L" bracket that is tack welded on the foot pedal. Moving the l bracket would involve some intensive surgery.

I PM'd Dino to verify the shudder travel.

(https://dl.dropboxusercontent.com/u/53299166/DIYstompboxes/morley%20enclosure%20tube%20layout.jpg)
Title: Re: What is this circuit section doing??
Post by: Govmnt_Lacky on August 13, 2013, 10:56:39 PM
@Larry

I realize that you are working off of the original but...

Is that tube assembly crucial to the circuit? I am asking because I am wondering if the LEDs and LDRs could be exposed and get the same results a-la the Morleys and Lovetone pedals.

Essentially... Could you explain the reason why they would have used that black tube and lens contraption?
Title: Re: What is this circuit section doing??
Post by: digi2t on August 14, 2013, 12:32:13 AM
OK, I've checked the Mutron, and the shutter comes between the tubes in the toe down position.

Also, looking at a Bad Horsie that G_L sent me, it refreshed my memory that the shutter on the Morley's actually moves more at a 45 degree angle from vertical, when looking at the side of the unit. I think if the tubes were mounted back far enough, then toe down would send the shutter between them.

I have to echo G_L's question here. Why do we need the damn tubes? What's wrong with an LED with the servo LDR looking at it on one side of the shutter, and the other LDR on the other? Cut a pie slice in the card, and be done with it. Ronan's Talking Pedal layout might easily accept this layout. No? If ambient light being emitted into the unit from the LED is a problem, then some black heatshrink around it, with just a small peephole might do the trick. This is what I did to both LED's in the Talking Pedal, to avoid light from one LED interfering with the others LDR, and vice versa.
Title: Re: What is this circuit section doing??
Post by: Ronan on August 14, 2013, 01:54:05 AM
I attached wires across the Talking Pedal LDR's in the Morley enclosure and did resistance measurements with the pedal upright, and the base attached, there was no significant light leakage that I could measure. If I was doing this build there is no way I would be using those tubes, I can't see any advantage, and building the tubes is unnecessary IMO. The shutter can easily be modified to work in reverse. Just my 2c.

To put it another way, if there were ambient light problems with Morley pedals it would be well and truly documented by now.
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 14, 2013, 02:04:45 AM
@Larry

I realize that you are working off of the original but...

Is that tube assembly crucial to the circuit? I am asking because I am wondering if the LEDs and LDRs could be exposed and get the same results a-la the Morleys and Lovetone pedals.

Essentially... Could you explain the reason why they would have used that black tube and lens contraption?

I had the idea to build the first "prototype" as close to the original as possible so I would have a point of reference to any changes/modifications that might deviate from the original sound and function.

The original tubes are made from a black, shiny plastic. The tubes that I made are the same shiny plastic. I've found when looking down the tube at a light source, the inside of the tube acts as a reflective source. When the end of the tube is partially covered, a full beam of light still exists, though not as bright. (full coverage of the LDR Face)

The plastic double convex lens on the original tubes magnifies the light. I used a plastic magnifying glass to fashion a similar lens.
(This could be achieved with a brighter LED....but how bright does it need to be?)

What effect all this has....I'm not sure.
Does it have any effect on the function of the pedal.....I would think so.

If I had an original pedal in front of me for reference, modifications to the pedal circuit would be much easier to realize.
Thank heaven that Dino has one and we can play the question/answer game!
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 14, 2013, 02:39:29 AM
I finally (it just arrived yesterday) found the time to open the Morley up and take a look at the shutter configuration.

Two LED and two LDRs. In the heel down position the front LED is blocked by the shutter and the rear LED is shining on the rear LDR through a hole in the shutter.

In the toe down position, just the opposite.

Conclusion? this pedal does do "toe down" LED blocked.

Here's some pics:

Toe down

(https://dl.dropboxusercontent.com/u/53299166/DIYstompboxes/Toe%20down.jpg)

Heal down

(https://dl.dropboxusercontent.com/u/53299166/DIYstompboxes/Heal%20down.jpg)
Title: Re: What is this circuit section doing??
Post by: Ronan on August 14, 2013, 03:24:44 AM
Larry L. you have made some good points in post 52, but, the bottom line is that all the LED/LDR circuitry is doing is generating a DC voltage to substitute for the LFO, and the only requirement for the circuit to function is a DC voltage proportional to pedal position. This DC voltage will not affect the sound quality or characteristics of the effect if it has the required sweep range and response to pedal position.

These days, due to improved LED brightness and higher sensitivity LDR's with a wider spread of light/dark resistance, tubes and lenses are no longer needed (IMO). If however, you were going to use original LED's and original LDR's, then the tubes and lense might be essential.

Where some tinkering will be required, is in the linearity or non-linearity of the DC voltage with pedal position, but unless you had the original genuine LED's, LDR's and shutter shape and material, you would still have this tinkering requirement anyway.

Dino and I and others have spent considerable time modifying Morley shutters to get required responses, so I don't think this will be a show-stopper. Also, with the pedal in LFO mode, the LED/LDR combo will be out of the equation completely and a direct comparison with the original could be made (for sound quality etc).
Title: Re: What is this circuit section doing??
Post by: digi2t on August 14, 2013, 08:36:16 AM
I received a MN3007 from jdub the other day, so I`ll be confectioning my little daughter board tonight.

Stay tuned folks.
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 14, 2013, 09:13:06 AM
Ian,
You've made some good points as well.

Believe it or not....I don't have a love affair going on with these tubes! I can lose them in a heartbeat. They are a pain to make, are huge compared to a LED/LDR combo, and the way that they are mounted evenly between the top and bottom of the circuit board makes attachment a challenge.

I think at this point the most useful information I can have is the voltage at the output of IC10 with the heal down and the toe down.

I can build a small proto board of the foot pedal circuit and experiment with it in the Morley enclosure.

@ Dino,
These voltages can be taken at E12 of the component overlay that I drew up or at the pedal switch.  :icon_wink:
Also, the voltages of both LDRs pedal up and pedal down (after voltage divider calculations) will help determine more accurately our LDR on/off range. (Each side of LDR lead to ground)

(https://dl.dropboxusercontent.com/u/53299166/DIYstompboxes/Mutron%20Flanger%20voltage%20points.jpg)

Title: Re: What is this circuit section doing??
Post by: digi2t on August 14, 2013, 11:44:30 AM
OK, I`ll jot those down before I disassemble the pedal. I have to re-verify the clock frequencies as well.

This is going to be interesting. :icon_cool:
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 14, 2013, 11:55:46 AM
Thanks Dino,

Good luck with the 3007 board! I am confident that it will work....well I'm 50% sure that I'm 100% confident!  ;)
Title: Re: What is this circuit section doing??
Post by: digi2t on August 14, 2013, 05:49:41 PM
Here are the voltages I recorded. It makes no difference if the unit is in pedal mode or not.

(http://i214.photobucket.com/albums/cc196/digi2t/Mutron%20Flanger/Ldrtestpointvoltages_zps67d7673a.jpg) (http://s214.photobucket.com/user/digi2t/media/Mutron%20Flanger/Ldrtestpointvoltages_zps67d7673a.jpg.html)

UPDATE - I made the daughterboard, and plugged it in. Folks, we have flanging. The only problem right now is that I'm getting oscillation when the sweep is at the low end with the resonance cranked. If I back it off a bit, it's OK. I'm not quite sure what the Balance trimmer before the 2N5088 is doing. I've cranked it from one end to the other, but I can hear any difference. Adjusting the Bias helped a bit, but I noticed that on the 3007 redraw that two 4.7K resistors were added on either side of the trimmer. I'm wondering if this would help cut down the oscillation.

On a lark, I pulled the 2N5088, and jumpered the E and B. The output level was much lower, but the oscillation disappeared.
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 14, 2013, 10:25:23 PM
Good news indeed!

The problems you are encountering are all fixable.

The balance trimmer before the 5088 is the BBD output trimmer. You really won't hear much of a difference when you adjust it.

The BBD output trimmer needs to be adjusted with a scope. You put the scope lead on the trimmers wiper and move the trimmer until the two BBD output signals perfectly overlap into one signal. There are other easier ways to achieve this output mixing with resistors....but IMO this is the best way.

Did you add the BBD output level trimmer at the emitter of the 5088? Right now the signal is being boosted too much for the surrounding circuitry. The signal is making it's way to the output of the NE571 then going two different directions. The signals going to the output and to the feedback circuit. That's why it's oscillating. The trimmer (it's on the Mutron Flanger 3007 drawing that I did) will allow you to roll back the signal.

Oh...and thanks for the voltages Dino!
Title: Re: What is this circuit section doing??
Post by: digi2t on August 14, 2013, 10:41:22 PM
Quote
Did you add the BBD output level trimmer at the emitter of the 5088?

There already is a 10K trimmer (R21) on the original, so I'm using that one.
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 14, 2013, 11:05:49 PM
Quote
Did you add the BBD output level trimmer at the emitter of the 5088?

There already is a 10K trimmer (R21) on the original, so I'm using that one.

Do you mean R80? The trimmer that's connected to the second SAD section output?
If that's the trimmer your referring to, that is the output pull down trimmer. That won't affect level. Notice how the BBDs output pins 5 & 6 are connected, uninterrupted to the filter, 571, then output.

You need a trimmer connected to the emitter, the other side of the trimmer connected to ground, and the wiper to the remaining output signal path.

Update  :icon_eek:

I just looked at the other thread and I see that I gave you the advise the original trimmer would work.
Well it will.....if configured the right way.
The original trimmer has lug 3 left floating (not connected) you need to tack a jumper to the unused lug and attach that to the 5088 emitter. You can't use the SAD's socket pins 5 & 6 for the BBDs output because they are connected to the trimmer. You need to get the 3007s outputs (with pull up resistors) to the base of the 5088.

Have you ever noticed that sometimes everything seems to be a big PITA!  :icon_wink:
Title: Re: What is this circuit section doing??
Post by: digi2t on August 15, 2013, 06:34:54 AM
Damn, I didn't notice the configuration. My bad. I'll reconfigure it tonight, and try it again.

Do you think that I'll need the two 4.7K resistors on T1?
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 15, 2013, 09:33:26 AM
Do you think that I'll need the two 4.7K resistors on T1?

No....The two 4.7K resistors are there as a voltage divider just to "zero" in on the useful bias voltage. Without them the trimmer can go all the way from 0 volts (GND) to 15 volts.
With the resistors you have around 7.5 volts centered with a swing from 3.63 to 11.36 volts. Much more useful for bias voltage.

I hate to ask....but do you think you can take the LDR voltages again?
I should have been more clear on the subject.
If you look at the schematic, you'll see that all of the components in the foot pedal control circuit go back to "power" ground.

After reviewing the voltages you took, it seems as if you took them from the points I specified to signal ground.
Signal ground is actually a reference voltage so the voltage points to signal ground will give different readings. (negative, 1/2 voltage for +V, 1/2 voltage to ground)

A couple of the voltages I can transpose, but the negative voltages kind of got me.
When these voltage points are taken to power ground there won't be any negative voltages.

(https://dl.dropboxusercontent.com/u/53299166/DIYstompboxes/power%20ground%20points.jpg)
Title: Re: What is this circuit section doing??
Post by: digi2t on August 15, 2013, 12:45:49 PM
You`re absolutely correct, I did connect to the signal ground (output jack ground). I`ll take the readings again tonight.

Noob question running through my mind here; Even with the negative voltage readings I gave, considering the signal ground sits in the middle of +/-7.5v, would it be logical to assume that we can add the recorded voltages to the + reference voltages to get the real voltages? Guess I`ll get my answer to that tonight. :icon_mrgreen:
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 15, 2013, 12:54:19 PM

Noob question running through my mind here; Even with the negative voltage readings I gave, considering the signal ground sits in the middle of +/-7.5v, would it be logical to assume that we can add the recorded voltages to the + reference voltages to get the real voltages? Guess I`ll get my answer to that tonight. :icon_mrgreen:

Definitely,
but for some reason between work and all of the other projects that I'm working on...my brain seems to be exhibiting a loss in the forward/backward/negative/positive region!
Read as: can't wrap my mind around it!  ;D
Title: Re: What is this circuit section doing??
Post by: Ronan on August 15, 2013, 08:00:45 PM
Here you go:
0V to signal ground is 7.58V
toe up 7.58 - 5.35 = 2.23V
toe down 7.58 + 4.31 = 11.89V
Resistance of LDR 2 at toe down position approx 5.3 Megohms.

If the voltage across LDR 1 (PC1) does not change with treadle position, then that confirms that PC1's only purpose in life is to help maintain the light output from the LED CR18 at a constant brightness.
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 15, 2013, 10:08:46 PM
Thanks for the brain power Ian!

I have to recharge my mental batteries!

I first saw those numbers this morning before my first sip of coffee and my brain said, "Sorry....I don't think so!"
Title: Re: What is this circuit section doing??
Post by: digi2t on August 15, 2013, 11:43:27 PM
Here you go:
0V to signal ground is 7.58V
toe up 7.58 - 5.35 = 2.23V
toe down 7.58 + 4.31 = 11.89V
Resistance of LDR 2 at toe down position approx 5.3 Megohms.

If the voltage across LDR 1 (PC1) does not change with treadle position, then that confirms that PC1's only purpose in life is to help maintain the light output from the LED CR18 at a constant brightness.

Confirmation on the numbers. Just as Ian has stated. No change on the numbers for the other LDR (facing the LED), a steady 5.50 volts on one lead, and 15 volts on the other.

Also, I modded the daughterboard, by lifting the number 6 pin of the SAD1024 adapter, and connecting the existing 10K trimmers free leg to the 2N5088 emitter.

SUCCESS!!!!

I readjusted the bias and output, and it sounds pretty much like it does with the SAD1024. I pulled the daughterboard out, popped the SAD1024 back in, and readjusted... yup, same sound. Absolutely smashing, I say! :icon_cool: We're good to go with the MN3007, as drawn, minus the 4.7K resistors around T1. (Cue the marching band.)

Sorry, no video proof. The wife is gone on vacation, and she's got the camera. :icon_cry:
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 16, 2013, 12:04:53 AM
I just don't have the words!  :icon_cry:

I am overcome with joy!

Okay, I have regained composure.

Great work! Now we can forge ahead!
Title: Re: What is this circuit section doing??
Post by: digi2t on August 16, 2013, 12:38:12 AM
Thanks. It just impressed the hell out of me that it worked. I can't put into words how humbling it is to be working with some great brain power here. I just wish I had been a bit smarter back in the day, and stayed in school longer. Oh well... a late start is better than no start at all.

When I get the camera back, I'll shoot some pics of the daughterboard, after a make a small mod for connecting to the output trimmer. It's low enough to plug into the socket of the SAD, and fit between the board and the enclosure. Could be a nice retrofit for a Mutron with an SAD that's kaput.
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 16, 2013, 12:50:41 AM
Yes....this is good!

Sketch up a schematic and I'll draw it up all nice like if you don't have the time.
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 16, 2013, 04:06:55 PM
I worked up some calculations from the voltages taken at the LDR (PC2) and IC10 test points. From that info and the known resistance values and voltage, I was able to calculate the specs of the LDR's dark resistance and light resistance.

(https://dl.dropboxusercontent.com/u/53299166/DIYstompboxes/Mutron%20Flanger%20pedal%20calcs.jpg)
Title: Re: What is this circuit section doing??
Post by: digi2t on August 17, 2013, 08:14:48 PM
Finally got a couple of pics of the daughterboard. Here ya go...

(http://i214.photobucket.com/albums/cc196/digi2t/Mutron%20Flanger/DSCF3813_zpse0e99396.jpg) (http://s214.photobucket.com/user/digi2t/media/Mutron%20Flanger/DSCF3813_zpse0e99396.jpg.html)

(http://i214.photobucket.com/albums/cc196/digi2t/Mutron%20Flanger/DSCF3812_zpsd08ba62d.jpg) (http://s214.photobucket.com/user/digi2t/media/Mutron%20Flanger/DSCF3812_zpsd08ba62d.jpg.html)
Title: Re: What is this circuit section doing??
Post by: armdnrdy on August 17, 2013, 08:40:38 PM
It's ALIVE!  ;D

Great job Dino!
Title: Re: What is this circuit section doing??
Post by: digi2t on August 19, 2013, 08:54:21 PM
Here's the final layout of the daughterboard;