I have too many questions Re: Rustbucket, ne OG Vintage EHX Attack Decay pedal!

[Scruffie]

The signal is heavily divided at that junction hence the weak signal, you need to adjust your scope, but sounds like that stage is actually working.

So, once biased, on to IC11 pin 6 which is the VCA (voltage controlled amplifier) controlled by all that 4013/4066 business, so attack & decay will impact it.

[Carlsoti]

Any suggestions as to where I should have the various pots set at this point?

[Scruffie]

Sens, Decay & Attack about 1/3rd the way up.

[Carlsoti]

    I had to go back to square one.  It seems I have at least one bad cap upstream. I get solid signal at the input, pin 3 and pin 1 of the first 4558, and can see it shorting to ground on the wiper of the sense pot when turned to that extreme.

   Pin 5 of the 4558 has NO signal on it. But I do get a signal at the output pin 7. It seems the coupling cap is DEAD.(C2 on the RB schem) I verified the crappy new DMM with some other known good caps which read in spec. I guess more parts need to be ordered. I really miss having old-school RadioShack and Fry's Electronics stores to go to.

What signal am I seeing downstream from the 4558? Amplified noise? An OOP signal from the differential amplifier?

[Scruffie]

Have you checked for broken/intermittent traces? The board mounted pots do lead to failure and sometimes need a jumper or re-flowing. Also check for broken leads on the cap, not saying a dead film cap isn't possible, but it's rare, but if you're going that route, the 39k biasing resistor being dead would also cause issues.

But IC1 pin 1 is your input signal at twice gain, IC1 pin 7 is a compressed output with a little tone shaping.

Scopes are great, but I do still suggest you build an audio probe, can't beat being able to actually hear what is happening and they only take 15-30 minutes to whip together.

Edit: Sorry, I misread your post, see you've taken the cap out and tested it to verify your hypothesis. Hopefully that's all that's wrong now.

[Carlsoti]

    Little by little, I seem to be eliminating unexpected problems. Scruffie was right in regards to changing my scope settings. Previously, I was trying to bias the 3007 from what I think is the timer noise from the 4047. I had thought that the low output from pin 7 of the 4885 was just a quirk of a circuit I still don't fully understand. Now that the coupling cap between the A/B sides of the 4558 has been replaced, I'm seeing that timer noise riding something that more resembles the waveform going into the 3007.

    It seems my signal at the 28/29/30 junction is low, or I've killed another 3080. Pics show the signal on pin 3 of the MN3007, junction of 28/29/30, (input)pin2 of the 3080, and (output) pin6 of the 3080. Obviously, the signal isn't coning out of IC11. I probed pin 3, seeing as this is a differential input, but there was nothing there. R55, R56, and C17 measure appropriately.

   After lunch, I'll try a different 3080 in the IC11 position.

Any input on what sort of signal strength I should be seeing at various parts of the circuit would be appreciated.

[Scruffie]

The signal at the 28/29/30 junction is meant to be very low, OTA's can only accept 25mV (IIRC, low anyway) signals before distorting and you'll get nothing on the output of the OTA @ pin 6 if it's not turned on via current at pin 5 from the attack/decay circuitry.

Have you tried playing through the pedal again?

[Carlsoti]

   I'm not sure if it's fixed just yet, but it is doing SOMETHING! I wonder how much of the way this is working is part-and-parcel of the triggering circuit and how much of it is other things that have yet to be repaired. Is it possible that "hot" pickups would mess up the triggering? Sloppy playing messing up the trigger? Is it just a matter of setting all the knobs correctly?

   Around the 35sec mark of this first video, you can hear there is still quite a bit of hum in the background of the effect that is not at all present on the "clean side" of the blend pot.
https://www.facebook.com/100074733483188/videos/pcb.185448067289642/1071094436871915

The second video is essentially more of the same string slapping and knob twirling.
https://www.facebook.com/100074733483188/videos/pcb.185448067289642/765317831370852

I feel like there's more to do, but my expectations may be greater than the reality of what this pedal does. What do you think?

[Scruffie]

It was designed at a time of low output single coils, it is monophonic so playing is important and it's not the quietest circuit, plus the transformer adds hum.

Operating Instructions:

Plug the unit into an AC-outlet and turn it ON. Connect your
instrument to the input jack, amplifier to the output. Unmodified
signal is available at the DIRECT output and at the effect output
alternating with the processed signal when the footswitch is
thrown. Operation is most reliable when only the rhythm pick-up
is used and the guitar volume is at or near maximum.

Set SENSITIVITY about 1/3 of the way up, HARMONICS all the way
down, BLEND fully clockwise (proceeded signal only), and ATTACK
and DECAY about 1/3 up. Play a single note and if no effect is
heard, throw the footswitch. The attack-decay should be heard,
and the infinite variety of effects possible by varying the
controls can be explored.

The best setting for the SENSITIVITY control is where it triggers
Reliably for notes on the high strings but doesn't multiple-trigger
When playing the lowest string. Once found this setting should
not be changed. This unit works best for single notes and some
basic two-string chords; complex or discordant chords will cause
multiple triggering. The EDGE switch adds bite to the effect of the HARMONICS control.

EFFECT                                       CONTROL SETTINGS

                        Attack             Decay            Harmonics            Blend

Tape               medium or         minimum        as desired            processed signal
  reverse            long                                                                 only
Slap echo        minimum          short or med   as desired             midway
Modulated       short or med      min  to med    as desired            as desired
   envelope
Sustain*         minimum           maximum        as desired            processed sig only
Chops            min or short       short or min     as desired            processed sig only
Violin,            medium             med or long     as desired            processed sig only
  Cello
Acoustic         min or short       medium          as desired            as desired
  bass
Bowed bass    medium             medium          as desired            processed sig only
Toy Piano       minimum            short             med or high           processed sig only
Piano              minimum           medium         medium                processed sig only
Banjo              minimum           short              maximum             processed sig only
Horns              min or short        maximum      med or high          processed sig only
                                                                    (EDGE on)
* Set SENSITIVITY at or near maximum

[Carlsoti]

    I guess I'll have to box it back up and see if I can get to a point where it feels like it's "done."
  Thank you so much, Scruffie. I would've NEVER suspected that coupling cap was bad and I would never have gotten to the point of suspecting it had you not talked me through the rest of the stuff.

[Carlsoti]

A kind person in Japan sent me a private link of their working Attack Decay and it confirms that this one still needs some work. I think I'm going to have to build an audio probe to figure the rest of it out. I suspect it'll be easiest to just hack an old multimeter probe with an appropriate capacitor, but if anyone knows of some tricks for the "ultimate audio probe", I'm all ears. I'm considering building a +1000V probe as I've recently been given an AIMS VT-100 all tube PA amp, and I think voltages are over 600V in that beast.

[Scruffie]

Possibly something to do with Q2 emitter, was okay on your first set of voltages but not on your second.

[Carlsoti]

Thank you, Scruffie. Plans for today changed when my GF said she won tickets to the first band she saw live, so I'm working on making that happen as smoothly as possible. I'll look at the AD tomorrow, hopefully for the last time.

[Carlsoti]

Yeah, I'm still struggling with this. The hass-alfed audio probe I made is far too noisy just from handling to be any good to me. It doesn't help that the amp itself is noisy and frequency limited. Regardless, I took new voltages with sense, blend, and attack around 30%, everything else at zero, and a 1k signal of .25v p-p on the input. I can't seem to do much with the info today. Too many superglue fumes, maybe? Q2 emitter V is way low. I pulled the part and tested it as good; replaced it with another with similar results. Hopefully tomorrow I'll be able to look at these voltages and my brain will do stuff.

[Scruffie]

Noisy audio probe sounds like a ground issue.

So what exactly is wrong with it now that makes you sure it needs work?