schematic reading help... what is this component?

[pacific]

Greetings, all.

Please forgive me for being a newb to both electrical schematics, and to this forum.

I would like to build a copy of the Ibanez CP-830 compressor, but I can't figure out what the MOD-735 component is that looks like a resistor and a buffer (?) inside an oval at the three o'clock position on this layout:



From the picture below (I think it's a similar circuit, if not the same, as the CP-830), it looks like some sort of optocoupler... maybe?



Several Google searches for that component / part number, as well as search at mouser's website for "MOD-735" have yielded nothin'.


Thanks a million in advance for any help!

[iq01221]

It's an optocoupler, use anyone or a taped led and ldr. I suggest 3mm red leds and 5mm ldrs.

[pacific]

Hey Juan! Thanks for your help. Less than ten minutes after I posted, my question has been answered. This forum is chock-full of solid brainpower and good vibes. Thanks again, man!

[LucifersTrip]

http://www.ebay.com/itm/Vactrol-LED-Photocell-EG-G-VTL5C2-/270591343718?pt=LH_DefaultDomain_0&hash=item3f00803c66

[pacific]

http://www.ebay.com/itm/Vactrol-LED-Photocell-EG-G-VTL5C2-/270591343718?pt=LH_DefaultDomain_0&hash=item3f00803c66

Thank you, good sir. I did find the same part at Small Bear, and was wondering if it would be a suitable replacement. In all the scouring I did of postings in various places on the internet I found out the optocoupler used by Ibanez / Maxon was a MCD-735 made by Moririca and has (conveniently) long since been discontinued.

I would just try either swapping some other photo coupler (e.g., the VTL5C2) or making my own from an LDR and a yellow LED joined with some heat shrink tubing, but I am growing convinced that this circuit is tuned specifically for the MCD-735, and anything else might not sound quite right unless some of the other resistors (and who knows  what else) were swapped for ones with different values. At this point, we're dealing with a level of nerdiness which is WAAAAAY beyond my grasp.

Unless, of course, someone here is willing to help me out by dropping hints or suggestions re: vactrol and/or LDR values...

Thanks again to iq01221 and LucifersTrip for helping steer me in the right direction.

[oskar]

...but I am growing convinced that this circuit is tuned specifically for the MCD-735

No.

and anything else might not sound quite right unless some of the other resistors (and who knows  what else) were swapped for ones with different values.

The optocoupler is setting the gain of the op-amp but so is the resistor net r3, vr2 and r4. An optocoupler generally has a high dark/off resistance and this net clipped in parallell will set the maximum gain. Just throw whatever you've got in there and see what happens. If you think the response is wrong you can change the value of these resistors.

At this point, we're dealing with a level of nerdiness which is WAAAAAY beyond my grasp.

I think it's well within your grasp...   

ps. r2/r3 is in series. Substitute with one 10k instead.

[pacific]

The optocoupler is setting the gain of the op-amp but so is the resistor net r3, vr2 and r4. An optocoupler generally has a high dark/off resistance and this net clipped in parallell will set the maximum gain. Just throw whatever you've got in there and see what happens. If you think the response is wrong you can change the value of these resistors.

You know what? I think I have been worrying too much, and I should just give this build a try. If the resistor net is only those three components, then I'm probably not dealing with something so complicated that I can't troubleshoot my way out of it. LDR / LED, a snippet of heat shrink tubing, and a couple drops of flat black paint for a light-tight seal should do the trick, yes?

I think it's well within your grasp...   

Thank you for the vote of confidence!

ps. r2/r3 is in series. Substitute with one 10k instead.

Solid suggestion. I would also be happy to forego the internal trimpot! Thanks, Oskar.

I'm going to place a parts order soon, and in a month or so when this build is completed I'll post some photos and/or clips.
For now, I'm eagerly awaiting a package from Pedal Parts Plus containing the parts for my SHO clone!

[oskar]

That trimpot also sets the gain. Leave it in or breadboard the circuit first (which you off course should do anyway) and find a good substitute value.
Look up non-inverting opamp amplifier for more info on what's going on in that circuit. A similar opamp circuit is the gain stage in MXR Distortion+.

Good luck!