Morley Sync Attack Box

[FUZZZZzzzz]

I saw a second hand ad for one of these devices. Like a swell effect with a metallic pic. It looks really cool, but I could not find any videos online or information on this board. I found the schematic, but it didn't tell me what transistors to use. Looks like a fun build. I asked the seller and he told me that he could only read the transistor near the PIK point. He says its a 5087 transistor. Has anyone ever experimented with this? Also, VT811 doesnt show up on google.

you can find the morley schematics here:
https://www.schematicsunlimited.com/m/morley

[duck_arse]

MPSA06, MPSA06, MPSA12. easy subs for those, too.

[pacealot]

This thread about the Pik-A-Wah also discussed a SAB which was observed to have 5087s in it:

https://www.diystompboxes.com/smfforum/index.php?topic=71206.msg1124455#msg1124455

I have an interest in breadboarding one of these myself soon, but I haven't yet, so I can't speak to the merits/demerits of using PNPs vs. NPNs...

[RickL]

This is a great little circuit. If you can deal with having to use a metal pick attached to the box you will find that it tracks better than any other envelope controlled effect you have ever used. Because the envelope of the signal doesn't control the effect. Every time you touch the string with the pick it resets.

I think I just experimented with LED/LDRs I had on hand until I found one that worked. My guess is that just about anything will work with a bit of fiddling.

As mentioned in the linked thread, I think the trigger part of the circuit (or the one for the pik-a-wah - they work in opposite directions) would work great for controlling almost any parameter of an effect that is set by a resistance value. Imagine a distortion that faded in distortion amount on each note at the speed you set or a delay that shortened on each note (raising the pitch each time).

I have got to play around with this circuit more!

[pacealot]

Rick, your enthusiasm for the circuit is what piqued my interest in it to begin with! So thank you for that. 

Do you recall if you went with NPNs or PNPs in the positions of the two MPSA06s? I'd imagine any ordinary 3904/5088 etc. would probably work for NPNs, but was curious if you ran into any issues there...

[FUZZZZzzzz]

im building one soon. im drawing up a vero as well. just have to gather some parts. what kind of ldr range would be a good start? i would think id start with a 5mm red led. use 2n5087. they're easy to come by. any ideas?

[pacealot]

I suppose the question I still have (which, if I just cleared off a breadboard and tried it, might be quickly answered) is, if using 5087s or similar PNPs in those positions, do collectors and emitters need to be reversed from the schematic? MPSA06s are NPN, so one would think so...

[PRR]

That drawing top of thread looks wrong. Battery "+" is grounded when g-plug is inserted. So the "Hot" side is -Negative-, and about -8.4V due to the diode. The first two transistors' Collectors go to the "live" wire, which is negative of their Emitters, so PNP would be expected. Seen this way, Q1 defaults ON, forcing Q2 OFF, so the 0.5uFd is pulled to -8.6V through the 500k time-pot. With base of NPN Darlington Q3 near -8.4V, LED is OFF, audio is ON.

When PIK touches grounded string, everything goes the other way, sound stops. When PIK stops touching, it recovers at the 0.5uFd+500k rate.


Why such a brain-pain? I assume because jellybean Darlingtons only come in NPN, and all else followed.

With modern fad for common power supplies, you might re-think that ALL the way through.

[RickL]

I can't find my Sync Attack Box right now, but I used PN2222 and MPSA14 in my Pik-A-Wah, so it looks like NPN works in that one at least.

[pacealot]

Several months later, I've finally thrown this on a breadboard, but I'm afraid I can't get it to do its thing, so I have no answer for the NPN/PNP issue. I tried 5087s in the "right" way, 3904s in the "wrong" way, vice versa for both, even tried reversing the Darlington, but nothing I've done can get the LED to turn on, "pick" grounded or not (except turning it around, and then I can't get it to turn off). I could post voltages if anyone wants to look at them, but I don't want to waste anyone's time debugging something I can't quite wrap my brain around yet. I need to go back to the drawing board — I'm sure I'm making a stupid mistake, but I just can't see what it is. I'm not usually afraid of a positive ground circuit, but this one has got me stumped...

[pacealot]

In the interests of being thorough, here are the voltages I'm getting:

2N5087s in Q1 & 2, the "right way" (emitters to ground), "pick" ungrounded:
Power rail: -8.3V
Q1C/Q2B: -0.051V
Q1B: -0.632V
Q2C/Q3B: small neg. voltage drops immediately to 0V
Q3E: -0.16V
(Q1E, Q2E, and Q3C are all 0V connected to ground)

2N5087s in Q1 & 2, the "right way" (emitters to ground), "pick" grounded:
Power rail: -8.3V
Q1C/Q2B: -0.69V
Q1B: 0V
Q2C/Q3B: small neg. voltage drops immediately to 0V
Q3E: -0.16V
(Q1E, Q2E, and Q3C are all 0V connected to ground)

2N3904s in Q1 & 2, the "right way" (emitters to ground), "pick" ungrounded:
Power rail: -8.3V
Q1C/Q2B: -3.57V
Q1B: -2.93V
Q2C/Q3B: small neg. voltage drops immediately to 0V
Q3E: -0.16V
(Q1E, Q2E, and Q3C are all 0V connected to ground)

2N3904s in Q1 & 2, the "right way" (emitters to ground), "pick" grounded:
Power rail: -8.3V
Q1C/Q2B: -1.77V
Q1B: -1.15V
Q2C/Q3B: small neg. voltage drops immediately to 0V
Q3E: -0.16V
(Q1E, Q2E, and Q3C are all 0V connected to ground)

[pacealot]

I redrew the active portion of the circuit (excluding the LDR and signal path and simplifying switching for clarity) both to try to understand the circuit better and also to have something more readable to look at for analysing what's happening:



I'm still having no luck, and my brain hurts trying to follow the current path(s), in spite of Paul's very helpful explanation above...

[pacealot]

I know I'm probably flogging a dead horse at this point, but I happened to have a Mouser order going anyway, so in the interests of thoroughness I decided to get some of the (theoretical) original transistors to see what difference that might make. MPSA06s and an MPSA12, and I tried the MPSA06s both directions again. Still no LED joy, but the voltages were fairly different:

New Duracell 9V, measuring 9.42V
MPSA06s in the "right" way (emitters to ground), "pick" ungrounded, 25K trimpot at minimum resistance
Power rail: -8.77V
Q1C: -3.61V
Q1B: -3.01V
Q2C: -4.09V
Q2B: -3.61V
Q3B: -4.09V
Q3E: -0.195
LED cathode side: -8.76V
(Q1E, Q2E, and Q3C all 0V connected to ground)

MPSA06s in the "right" way (emitters to ground), "pick" grounded, 25K trimpot at minimum resistance
Power rail: -8.77V
Q1C: -1.725V
Q1B: -1.142V
Q2C: -2.21V
Q2B: -1.725V
Q3B: -2.21V
Q3E: -0.194V
LED cathode side: -8.75V
(Q1E, Q2E, and Q3C all 0V connected to ground)

MPSA06s in the "wrong" way (collectors to ground), "pick" ungrounded, 25K trimpot at minimum resistance
Power rail: -8.78V
Q1C: -2.20V
Q1B: -1.59V
Q2C: -2.70V
Q2B: -2.20V
Q3B: -2.69V
Q3E: -0.196V
LED cathode side: -8.76V
(Q1E, Q2E, and Q3C all 0V connected to ground)

MPSA06s in the "wrong" way (collectors to ground), "pick" grounded, 25K trimpot at minimum resistance
Power rail: -8.76V
Q1C: -0.641V
Q1B: -0.057V
Q2C: -1.142V
Q2B: -0.641V
Q3B: -1.143V
Q3E: -0.194V
LED cathode side: -8.74V
(Q1E, Q2E, and Q3C all 0V connected to ground)

I guess at this point if anyone feels like chiming in... 

[PRR]

Q3 or connections bad.

[pacealot]

Thanks for looking, Paul! I'll keep the A06s in the "right" way and focus on the Q3 area...

[pacealot]

Okay, so things are afoot (but still baffling). So the primary blunder I made was leaving the LED in the wrong way around. Keeping everything else known-(almost)-good, it results in a distinct voltage—and visible brightness—difference, and the time-constant pot also visibly results in a variable decay. But the LED never shuts completely off, even with the trimpot at maximum. New voltages:

Q1C/Q2B: -3.6V ungrounded/-1.7V grounded
Q1B: -3.0V ungrounded/-1.1V grounded
Q2C/Q3B: -4.1V ungrounded/-2.2V grounded
Q3E: -5.1V ungrounded/-3.7V grounded
LED cathode side (for realsies this time): -7.7V ungrounded/-5.9V grounded

Tomorrow I'll try messing around with a real LDR and/or vactrol to see if this is enough to make the effect work audibly. Thank you again Paul for pointing me towards my mistake!

I'm also beginning to wonder if the 5087s might have been paired with a PNP Darlington like an MPSA62/3 or similar in a negative-ground version in the real-world examples that they've been sighted in...

[nbenning25]

Hello pacealot,
New to the forum and been reading through these posts with interest.  Have you made any progress with this project?
Thanks!

[pacealot]

Welcome to the forum!

Sadly, I put the SAB on the back-burner right after my last post. But this might serve as a clarion call to pull it back out and see what I can do. My lingering concern is that the LED, as it last stood, doesn't dim enough to make the LDR change sufficiently to bring the "attack" down to audibly "off", at least not with the bog-standard vactrol-types that I have. Let me crack back into it and see what happens...

[pacealot]

So I just pulled this one out, fully populated it exactly as drawn in the Tel-Ray schematic (using a vactrol-type opto device I got from pre-SynthCube Small Bear which is similar to the specs of a VTL5C3), and it technically works, but not in a way that I can find useful. There's no setting of the trimpot which makes the level with "pick" grounded dip low enough to sound like it's "off"; it just drops maybe a few dbs at the most. The trimpot only seems to change the overall level of the "on" and "off" states, but not the ratio between them. When playing (I rigged up an alligator lead and used that as a pick for the purposes of the experiment) the swell was barely even noticeable or audible.

It also (unsurprisingly, given that the audio path is completely passive) results in a very dramatic overall level drop, which would require a significant boost to make up. That would be worth surmounting — and easily done — if the swell itself were able to be made more dramatic, but as it stands now, this circuit has thoroughly outfoxed me, which is tremendously dispiriting.

[Eb7+9]

It also (unsurprisingly, given that the audio path is completely passive) results in a very dramatic overall level drop, which would require a significant boost to make up ...

(i) it should be obvious that the only way there can be any signal losses upon recovery is IF the LED doesn't turn off completely

you need to re-think your thinking here, for a completely passive voltage divider won't incur any losses if the output resistance is infinite

(ii) you need to identify what's doing what "in global principle" here :

Q1 and Q2 are PNP TL (fast Transistor Logic) inverter stages ... the second one modified to slew
Q3/Q4 are NPN Darlington "voltage" follower going off the slewing cap ... Darlington'ized to minimize Base current loading on the said cap
LED current is set by difference between rail and follower output, and resistance in series with LED

(iii) you need to understand circuit state in rest position (recovered from last pick grounding)

at rest Q1 is maintained in "on" state via voltage input 47k/10k voltage divider
which means Vc1 "then" should be close to GND in voltage
which then means Q2 should be maintained in its "off" state ... if it is completely (well enough) off then Vc2 should be at RAIL voltage
if Vc2 is held at RAIL then obviously the 500nF slewing cap should be at RAIL potential as well
if the input to the Darlington follower is at RAIL potential then there is NO way it can be in any form of "on" state
which means there would be NO was for any current to flow thru the opto-LED
which means there would be NO way for the opto-resistor to have finite resistance
which means there would be NO way for any signal attenuation to take place as mentioned above

so, if you've go signal attenuation at rest then one or more of these conditions is not being observed

let's recap here:

at idle, signal should be wide open ... string sustain morphing into background noise, etc ...
simply put: Q1 ON, Q2 OFF, Qdarlington OFF, LED OFF, opto-R infinite

---

now, part-A of the dynamic part ... pick grounds input divider

(i)  Q1 goes "off" real fast ... why these stages where used in early TL logic gates

(ii) Q2 goes "on" not as fast but still fast enough ... slewing caps shorted to GND by Q2, again fastly enough

(ii) Darlington pair turns "on" and drives LED, again fastly enough ...

(iii) opto-resistor drops in resistance - from infinite (hopefully) to (hopefully) finite-low enough ...
maybe fast enough depending on opto specs

---

part-B of the dynamic part ... pick leaves string, input divider allowed to resume idling state rapidly

(iv) Q1 goes "on" again

(v) Q2 goes "off" again // essentially out of the circuit ...
slewing cap allowed to recharge to RAIL voltage thru variable resistance // setting cap slewing rate

(vi) opto-resistance starts to climb as LED gradually shuts off, signal gets faded back in

(vii) Slewing cap reaches RAIL potential


and the whole cycle starts again

---

from all this it should be clear what you need to do to get intended performance

ie., Q1, Q2 and Darlingtons need to do their thing "completely" first of all
then, at the end of all that, you need an opto-cell that's both fast enough and low enough in "on" resistance
since it is the slowest element in the whole control chain

I would try an NSL32-SR3 here ... (see smallbear)

---

obviously, there's no need for this to be a negative RAIL design

you could go positive RAIL and replace Q1 and Q2 by high gain NPN's (2n5089 say)
and Darlington pair by PNP x2 ... (2n3906's should do)
reversing slewing cap and opto-diode polarity ...

IMO, there's no real need for that rail diode and rail cap either ... leave 'em out for now

---

as for the grounded pick thing ...

well, there's no way I would go thru any of that crap
so the question then becomes (for me anyway) :

how to replace Q1 stage with something that creates an equivalent "sharp impulse" to drive Q2 ... ??!

I've got an idea or two from inventions of mine, but they both require dual RAILS
if I think of something simpler I'll chime in

also, there's the idea of replacing grounding pick by momentary footswitch and do a foot-controlled fade
obviously only good for slow speed playing ...

which reminds me, don't xpect really great performance compared to a digital unit doing the same work
like with any other time based effect ... gates, etc ...

but who knows ... let's hear what you get once you think you've the concept working right!