What is this circuit section doing??

[Ronan]

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.

[armdnrdy]

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.

[Ronan]

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.

[tubegeek]

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."

[armdnrdy]

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.

[Digital Larry]

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.

[armdnrdy]

Thanks for the reply Larry (cool name by the way!)

Not a bad idea.

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!

[Govmnt_Lacky]

Thanks for the reply Larry (cool name by the way!)

Not a bad idea.

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  

[armdnrdy]

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.

[Govmnt_Lacky]

@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?

[digi2t]

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.

[Ronan]

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.

[armdnrdy]

@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!

[armdnrdy]

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




Heal down

[Ronan]

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).

[digi2t]

I received a MN3007 from jdub the other day, so I`ll be confectioning my little daughter board tonight.

Stay tuned folks.

[armdnrdy]

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.  
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)

[digi2t]

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.

[armdnrdy]

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! 

[digi2t]

Here are the voltages I recorded. It makes no difference if the unit is in pedal mode or not.



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.