Abyss - vibrato disappears

[tinkertoneworks]

Hey all
This question has been asked before, but it seems like it's happening in a slightly different way?

The Abyss sounds great and exactly like I would expect it to, but at very slow speed and/or high intensity settings the vibrato will completely go away, even though the sound is clearly being effected by the preamp/eq. It will come back once intensity is backed off a little bit and when speed is turned all the way up to kinda "kickstart" the LED, then you can adjust it to a slower speed and it will usually stay if it isn't set too slow.

(to clarify high intensity at high speed is usually okay? It's mostly high intensity at low speed or just low speeds in general. The voice knob seems to have the least impact when all the way down)

This isn't a matter of bad solder joints or unseated IC/transistors or the back of the pots making contact with the solder joints, after asking someone and observing the LED while this happens it almost seems like there's a problem with how the LED is being driven

I'm aware taking the back off will impact how the LDRs detect light, but it almost seems like at these settings the variation in light is too subtle for the LDRs to detect that anything is changing. Someone suggested covering the LDR/LED arrangement with a small square of cardboard lined with tinfoil, but I'm wondering if there's any other solution I could be missing. It's an amazing sounding univibe and it went well for my first optical or modulation pedal build, but having the full sweep of controls is important to me if I want to build more complicated circuits.

Thank you

 

[Nostradoomus]

If you're in to experimenting, try the normal univibe mods. Lower R19/20 to 1.5k and bump C12 up to 2.2uf.

 

[tinkertoneworks]

If you're in to experimenting, try the normal univibe mods. Lower R19/20 to 1.5k and bump C12 up to 2.2uf.

I'm down for some modding, thank you

 

[Chuck D. Bones]

The type of LFO is notorious for failing at slow speed settings. It's EQD, 'nuff said.

The normal protocol in the Troubleshooting forum is you post detailed pix of your build. You tell us about any mods or parts subs.

If you are using aluminum electrolytics for C11-C13, try film. Aluminum caps are leaky and that alone will hinder the oscillator.

Use a higher HFE transistor for Q1. I like MPSA13. Or you can wired a pair of MPSA18s as a Darlington pair. If you do this, increase R21 to 4.7M so it will bias correctly.

 

[tinkertoneworks]

The type of LFO is notorious for failing at slow speed settings. It's EQD, 'nuff said.

The normal protocol in the Troubleshooting forum is you post detailed pix of your build. You tell us about any mods or parts subs.

If you are using aluminum electrolytics for C11-C13, try film. Aluminum caps are leaky and that alone will hinder the oscillator.

Use a higher HFE transistor for Q1. I like MPSA13. Or you can wired a pair of MPSA18s as a Darlington pair. If you do this, increase R21 to 4.7M so it will bias correctly.

I'll most likely do the suggested mods above this weekend and post pictures.

I've made the pedalPCB version of the monarch before and that was enough to make me curse Jamie Stillman's name (since I'm pretty sure it was a faithful recreation with no quality of life changes)

I'll have to see if I have a higher HFE equivalent transistor on hand. Thanks all, will update.

 

[Chuck D. Bones]

I've made the pedalPCB version of the monarch before and that was enough to make me curse Jamie Stillman's name (since I'm pretty sure it was a faithful recreation with no quality of life changes)

Not true. I personally corrected EQD's design flaws. You can read about it here. Just to be crystal clear: the Pedal PCB board contains all of the circuit design corrections/mods described in the article.

If you know how to set the bias on JFETs, it's a sweet pedal.

 

[tinkertoneworks]

Not true. I personally corrected EQD's design flaws. You can read about it here. Just to be crystal clear: the Pedal PCB board contains all of the circuit design corrections/mods described in the article.

If you know how to set the bias on JFETs, it's a sweet pedal.

Apologies, I tried building one a year and a half ago and it was just a personally frustrating experience at the time without having a lot of hands on testing/troubleshooting knowledge. I'm in an EE program now and I'd probably have a better shot in current day. No shade to your work at all.

 

[tinkertoneworks]

I will be
• attempting to do the MPSA18 darlington pair trick + 4.7m to R21
• replacing c11-c13 with box film caps (did not know you could just put a non polarized cap in place of an electrolytic in applications like this)
• R19 + R21 to 1.5k (I can't remember if I have 1/8w resistors in 1.5k so I might have to use a 1/4w and it'll look goofy)

I'm taking it apart after I get my next part shipment in but this is what the build looks like before all this (I know I'll clean up the flux too)

 

[Chuck D. Bones]

I would not change R19 & R20. They only affect the very top end of the RATE range and making those two resistors smaller runs the risk of stalling the LFO. Increasing C12 will slow the LFO down a little bit. Increasing C12 has a much stronger effect on the original UniVibe LFO circuit which has a pair of clipping diodes in parallel with C12. The Abyss does not have those diodes, and for good reason.

If you are into breadboarding, which is a great learning tool for an EE student, then I recommend breadboarding the LFO and LED driver. You can experiment away without touching a soldering iron to the Abyss PCB.

 

[ckendall924]

The type of LFO is notorious for failing at slow speed settings. It's EQD, 'nuff said.

The normal protocol in the Troubleshooting forum is you post detailed pix of your build. You tell us about any mods or parts subs.

If you are using aluminum electrolytics for C11-C13, try film. Aluminum caps are leaky and that alone will hinder the oscillator.

Use a higher HFE transistor for Q1. I like MPSA13. Or you can wired a pair of MPSA18s as a Darlington pair. If you do this, increase R21 to 4.7M so it will bias correctly.

Hey Chuck,

I see your expertise sprinkled on a few of these Abyss forums. I just finished my Abyss today and I am not getting any vibrato. The LFO just stays lit, and does get brighter with the voice control. I'm assuming you will suggest similar to your comments above.

So, it's ok to use film capacitors instead of electrolytic on C11-C14? I know in another Abyss forum you also mentioned the tantalum's. And I should swap out Q1 with a MPSA13?

I've added photos. (Pretty sure I need to revisit solder on IC2. Also, please disregard my mislabeling of the Voice/Intensity and Throb/Rate)

Many thanks!

 

[Chuck D. Bones]

Nice job on the artwork.
The RATE & THROB pots must have dust caps on them, otherwise the VOICE & INTENSITY pot leads can short against them. The pot bodies can also short to solder tits under them. Get that fixed and it might work. Use real dust caps, not tape. I have not seen dust caps made for dual pots, however a dust cap for a single-gang pot can be modified to fit by enlarging the cutout on the side. the Don't swap out any other parts until you take care of those two pots.

I am not a fan of using parts that don't fit, or hooking parts in series to get the right value. Too many opportunities for things to go wrong. You can use film for C11-C13 if you can find some that fit. I prefer tantalum there because they're not leaky and they fit.

 

[ckendall924]

Nice job on the artwork.
The RATE & THROB pots must have dust caps on them, otherwise the VOICE & INTENSITY pot leads can short against them. The pot bodies can also short to solder tits under them. Get that fixed and it might work. Use real dust caps, not tape. I have not seen dust caps made for dual pots, however a dust cap for a single-gang pot can be modified to fit by enlarging the cutout on the side. the Don't swap out any other parts until you take care of those two pots.

I am not a fan of using parts that don't fit, or hooking parts in series to get the right value. Too many opportunities for things to go wrong. You can use film for C11-C13 if you can find some that fit. I prefer tantalum there because they're not leaky and they fit.

Appreciate the quick response. I’ll give the caps a go and see what happens. I was using a piece of cardboard between the pot and the pcb, but removed that for the picture.

 

[Chuck D. Bones]

You also need an insulator between the pot body and the leads of the adjacent pot. If the INTENSITY pot's leads touch the body of the RATE pot, that could prevent the LFO from modulating the LED.


No need to requote me message