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PostPosted: Sun Sep 02, 2018 7:41 pm 
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NB: This thread is about the previous version of the analog vibrato.

I've finally got my old analog vibrato assembled, and it sounds really great. The problem is that the ramp toggle doesn't seem to do anything. If I understand the functionality, this toggle switch should bypass the effect unless/until the momentary footswitch is pressed. On my build, the effect is always on when the 3PDT is in the engaged position, regardless of the position of the ramp toggle. The momentary does nothing.

I've tested for the correct continuity on the toggle, and it seems fine: continuity with lug 2 switches from pin 1 to pin 3 as expected.

Here are some photos; let me know if you need to see anything not pictured. Thanks in advance, fellas.

PS: I sourced my own parts on this other than the following, which I got from BYOC: PCB, MN3102, MN3207, BA6110, 2SC945, and 2SA733.

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PostPosted: Mon Sep 03, 2018 1:37 pm 
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I would remove one of the wires from the momentary foot switch and test continuity across the foot switch poles (should o lay have continuity when pressed) and test continuity across the pcb pads where the FS wires connect. See if you can find a short there.

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PostPosted: Mon Sep 03, 2018 1:42 pm 
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Check out the ramp toggle and foot switch area of the schematic. You can see that the middle lug of the ramp toggle will be grounded when the ramp function is bypassed. Not bypassed, the ramp footswitch makes the ground connection. You’ll likely find that the center pole I’d grounded in both positions. You need to work out what is keeping it grounded.

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PostPosted: Mon Sep 03, 2018 3:31 pm 
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Thanks, Morgan.

Morgan wrote:
I would remove one of the wires from the momentary foot switch and test continuity across the foot switch poles (should o lay have continuity when pressed) and test continuity across the pcb pads where the FS wires connect. See if you can find a short there.

Footswitch tests as functional, and I do not have continuity across the PCB pads for it, except when I press the button on the switch. (I initially thought I had a short across those pads, but I rewired it—no change to how the pedal works.)

Morgan wrote:
Check out the ramp toggle and foot switch area of the schematic. You can see that the middle lug of the ramp toggle will be grounded when the ramp function is bypassed. Not bypassed, the ramp footswitch makes the ground connection. You’ll likely find that the center pole I’d grounded in both positions. You need to work out what is keeping it grounded.

Tested from the center pole to the chassis ground pad on the PCB. It only has continuity to ground in one position.

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PostPosted: Mon Sep 03, 2018 3:51 pm 
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Don't know that it would have anything to do with your problem, but the PCB silkscreen shows 18K for the spot where you have the carbon film resistor next to the 500K trimpot, but the banding seems to indicate that you have a 1K8 installed there (brown-gray-red-gold). The 4-band code should be brown-gray-orange-gold for an 18K.

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PostPosted: Mon Sep 03, 2018 4:22 pm 
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duhvoodooman wrote:
Don't know that it would have anything to do with your problem, but the PCB silkscreen shows 18K for the spot where you have the carbon film resistor next to the 500K trimpot, but the banding seems to indicate that you have a 1K8 installed there (brown-gray-red-gold). The 4-band code should be brown-gray-orange-gold for an 18K.

Your eagle eye for resistor color bands never ceases to amaze me. However…

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PostPosted: Mon Sep 03, 2018 5:46 pm 
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OK, this just got real weird.

I soldered the 1.8k resistor back in and proceeded to re-check a few things. Plugged it in to power, still sounds great, but still no ramp.

Unsoldered one wire to the momentary just to double check. It still tested as expected at the switch lugs.

Re-checked continuity on the pads for the momentary… and well, they were connected. WEIRD. No solder bridge or any other visible connection.

Then, as I'm continuing to check these pads to make absolutely sure I'm not accidentally touching the probes or something, I hear a pop and start to smell that awful smell. The .47u resistor (tantalum) is all brown and very hot. Now looking at it, I think perhaps I installed it backwards? Anyway, the pedal still works the same as it has.

I'm super confused. How's your long weekend going? :mrgreen:

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PostPosted: Mon Sep 03, 2018 6:42 pm 
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it does look like it might be backwards

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PostPosted: Mon Sep 03, 2018 7:20 pm 
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RiffRaff wrote:
it does look like it might be backwards

Yep, that 0.47uf tant is backwards. The "+" mark is on the side of the cap that is supposed to go in the square (+) hole.

Re: the 1K8 resistor, I must have an old set of instructions, 'cuz mine show an 18K resistor in the parts list, but no 1K8, and the PCB looks like so:

EDIT: Yep, just looked in the instructions archive, and the version there has the correct 1K8 resistor in the parts list and mentions that the 18K label on the PCB is wrong.

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PostPosted: Mon Sep 03, 2018 7:27 pm 
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Looking at the schematic, C27 (the .47u) definitely appears to be in the part of the circuit where the ramp toggle is. Let me replace that cap with a 1u as Keith suggested and see if that does the trick.

I'm curious about what happened with that resistor value now, too.

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PostPosted: Mon Sep 03, 2018 7:40 pm 
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Though there's no schematic in the BA6110 version of the old Vibrato instructions, there is one in the BA662A version, and it shows that 0.47uf tant is in the ramp switch circuitry. Replace it and see how the pedal acts. You can always use a 470nf film cap if you don't have another tant.

EDIT: OK, you're already on top of this, Scott!

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PostPosted: Mon Sep 03, 2018 8:49 pm 
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Swapped the cap. No change.

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PostPosted: Mon Sep 03, 2018 8:50 pm 
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PostPosted: Mon Sep 03, 2018 8:53 pm 
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Just to reset - even if you desolder one of the momentary FS wires, you are getting vibrato in both toggle positions?

And the center lug of the toggle is not grounded in one position?

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PostPosted: Mon Sep 03, 2018 8:55 pm 
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sjaustin wrote:
Re-checked continuity on the pads for the momentary… and well, they were connected. WEIRD. No solder bridge or any other visible connection.

Is this still the case?

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PostPosted: Tue Sep 04, 2018 4:53 am 
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Morgan wrote:
Just to reset - even if you desolder one of the momentary FS wires, you are getting vibrato in both toggle positions?

And the center lug of the toggle is not grounded in one position?

Yes and yes.

Morgan wrote:
sjaustin wrote:
Re-checked continuity on the pads for the momentary… and well, they were connected. WEIRD. No solder bridge or any other visible connection.

Is this still the case?

Also yes. So this has the be the issue, right? If there is continuity between those pads, it's exactly as if the momentary switch is always being pressed. I can't figure out why there would be continuity here. Close-up photos:

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PostPosted: Tue Sep 04, 2018 11:11 am 
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A high signal on Q1 kills the LFO. A low signal on Q1 turns the LFO on. If you look at the schematic, when you have the ramp "off", the toggle switch connects the base of Q1 to ground, taking the mom footswitch out of the circuit and allowing the LFO to always be on. When you have the ramp "on", R63 makes the base of Q1 high and turns the LFO "off" until you press the mom footswitch, which shorts the base of Q1 to ground and allows the LFO to turn on.

The "ramp" part of the circuit (Q9, VR3, D5, D6, R58, R25, and C26) is really no different from the "attack" control of a compressor or envelop filter. If you ignore the diodes, you should see the similarities between this and the envelope filter attack control.

Anyhow...a short anywhere could be causing your problem. I'd narrow it down by pulling the center wire from the toggle. If it ramps up when you touch it to ground and kills the LFO when you touch it to +9v, then your problem is probably somewhere in the switch(es). If it doesn't, then your problem is probably somewhere in attack circuit.

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PostPosted: Tue Sep 04, 2018 2:18 pm 
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byoc wrote:
Anyhow...a short anywhere could be causing your problem. I'd narrow it down by pulling the center wire from the toggle. If it ramps up when you touch it to ground and kills the LFO when you touch it to +9v, then your problem is probably somewhere in the switch(es). If it doesn't, then your problem is probably somewhere in attack circuit.

I performed this test, and jumping that middle solder pad to ground and +9V did not change the vibrato behavior at all.

Then I reconnected the toggle and re-checked continuity on the momentary switch pads. It's maddening. Sometimes it's there and sometimes it isn't. (I swear once it was there on top of the PCB but not on bottom.) I figured maybe the problem is that I have been testing it outside the enclosure; maybe a pot is touching a solder joint and creating a short. So I put it all back in the enclosure, and I do not seem to be getting continuity across those pads.

Then I tested the toggle switch connections to ground. Here is what I found. My brain is too fried to decide if this is correct or not. I may be approaching the Just set it aside for a couple days and settle down, Champ stage of troubleshooting. :wink:

(The black probe is standing up inside one of the screw bosses.)


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PostPosted: Wed Sep 05, 2018 4:02 pm 
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I'm thinking that your issue is likely between Q1 and the toggle switch. I think your tests have shown that the toggle or momentary switch is not the issue (despite your inconsistent continuity results). Check out the local components for shorts and polarity. Check that the polarity on C27 is correct - I see that you have another tantalum in there. And check for a solder bridge across the C27 pads. Reversing the polarity or having a short to ground could hold Q1 in the low state and just keep the LFO on no matter what the rest of the rise time circuit is doing.

If you cannot locate any shorts (make sure to reflow anyway), I would look at replacing Q1. Perhaps it's just not switching states.

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PostPosted: Wed Sep 05, 2018 5:22 pm 
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Morgan wrote:
I'm thinking that your issue is likely between Q1 and the toggle switch

I'm no schematic expert, but isn't pretty much the whole circuit between Q1 and the toggle switch? :mrgreen:

On the case with your suggestions. Will report back. Thanks as always for hanging with me.

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PostPosted: Wed Sep 05, 2018 6:08 pm 
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sjaustin wrote:
Morgan wrote:
I'm thinking that your issue is likely between Q1 and the toggle switch

I'm no schematic expert, but isn't pretty much the whole circuit between Q1 and the toggle switch?

Yeah, that's how I read it--everything from Q1 onward is related to the ramp switching and the rise time.

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PostPosted: Wed Sep 05, 2018 6:13 pm 
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Success!

It's amazing how many red herrings there can be in a troubleshooting process.

It took me a few minutes to figure this out, because C27 is not where my tantalum cap is—that's C26, which, as it turns out, you can remove from the circuit entirely and it will still produce vibrato. Once I figured out that C27 is the electro a little bit south of there, things got cooking.

I did in fact have a bridge across the poles of C27. But when I fixed that, nothing changed. Because yes, I had also installed it backward. I don't remember the last time I did that with a standard electrolytic cap. I've been building like mad for a few weeks now. Maybe I'm going too fast.

Morgan, thanks for another dose of genius. Now to try and compensate for my severely amateur-hour enclosure drilling job, and get this thing on my board. :)

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PostPosted: Wed Sep 05, 2018 6:32 pm 
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Ha! Awesome glad you got it!

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PostPosted: Thu Sep 06, 2018 10:11 am 
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Nice job, Scott!


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PostPosted: Thu Sep 06, 2018 10:16 am 
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I just wanted to say this is one support thread I truly enjoyed reading. Thanks for the verbose explanations and congrats on the successful solution. The little mystifying things that can happen in a build...


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