Neovibe power confusion

[aishabag23]

Greetings,

I'm almost done with building a GGG Neovibe (ver. J 10/07). I plan to power it with a 24V DC adapter. I've read all the documentation over and over, I'm still confused about how to wire it properly.

Currently, I have the bridge rectifier installed. From what I'm reading, it seems this is un-necessary if I'm powering it via 24V DC adapter... Can anyone shed some light on how I should properly wire this?

I've read that some folks blew up those big caps by wiring it up incorrectly. I would rather avoid that! Thanks in advance to anyone who can help.

[GGBB]

In the future, you can really help yourself out in getting assistance by including links to pertinent info like schematics. Makes it a lot easier for someone wanting to help.

I believe this one is here: http://www.generalguitargadgets.com/pdf/univibeupdate.pdf

From the looks of that doc, building the pedal as described allows you to use either AC or DC power. So you don't need to do anything special to use DC. You don't even need to worry about jack or supply polarity as the bridge will handle both positive and negative DC supplies in addition to AC. Have a look at this bridge diagram and think through what happens when you feed it DC instead of AC, positive or negative:

[R.G.]

The Neovibe will run from a DC power supply as is, with no possibility of reverse polarity, because of the bridge rectifier, as GGBB correctly notes.

However, when it's set up this way, with a DC power supply as an input, you can not also use the same DC power supply to run other pedals. This is because the bridge rectifier makes the DC supply "inside" the pedal be two diode drops smaller than the applied AC peaks or DC. The negative side of the "inside" DC is connected to signal ground, so the (-) side of the incoming DC is then one diode drop lower than the signal ground. If you connect the external DC supply to other pedals, they will connect either the (+) or (-) side to signal ground, shorting out one side of the rectifier bridge. This can cause both noise and smoke problems.

[aishabag23]

Thanks for the explanations, fellas. Now I understand how the rectifier works.

I wired pad K to the positive terminal of my power jack, and wired pad J to the negative terminal of my power jack. The part of the enclosure that houses the power jack is made of bakelite, so it's not touching the metal top plate of the chassis at all. The grounding is what is confusing me. I have my input jack sleeve wired to pad B. The output jack sleeve is wired to volume pot lug 3, as well as to the top metal plate of chassis. Am I missing anything?

[antonis]

I have my input jack sleeve wired to pad B. The output jack sleeve is wired to volume pot lug 3, as well as to the top metal plate of chassis. Am I missing anything?

Nothing at all..
(except of wrong distinction between pad B & C) 

Pad C ic connected (via Input sleeve) to GND "common" for Power Supply and PCB circuit.. Pad C is also connected (via circuit) to Pad L which is wired to Volume's Pot lug 3 as well as to the Output sleeve to "transfer" the GND to Output Jack (and whatelse comes next..). It's also connected to metal enclosure for shielding purposes..

Pad B is an alternative for pad A (selection of different Input resistors..)

[GGBB]

The output jack sleeve is wired to volume pot lug 3, as well as to the top metal plate of chassis. Am I missing anything?

The output jack sleeve should go to volume pot lug 1. Volume pot lug 3 should go to the common lug of the SPDT switch. But the only problem that would cause is a volume control that works backwards. Pedal wiring diagrams typically show the underside of pots and switches etc. although there's no specific rule. In this case it's just a very common volume setup with the pot before the output where lug 1 always goes to ground, lug 3 to effect out, and lug 2 to output. Check that you've got the other pots the right way as well.

[aishabag23]

Thanks again, GGBB. I think I'm almost ready to plug this in and test it. I ordered an Electro-Harmonix Power supply rated at output 24v DC 100mA. It needs 200mA or better, no? Maybe I need to look around for a different power supply. Do you folks know of a suitable power supply?

[aishabag23]

According to the wiring diagram here:
http://www.geofex.com/Article_Folders/univibe/vibeupdate.pdf

Pad C connects to the speed pot. That's how I have it wired.

I have my input jack sleeve wired to pad B. The output jack sleeve is wired to volume pot lug 3, as well as to the top metal plate of chassis. Am I missing anything?

Nothing at all..
(except of wrong distinction between pad B & C) 

[GGBB]

Thanks again, GGBB. I think I'm almost ready to plug this in and test it. I ordered an Electro-Harmonix Power supply rated at output 24v DC 100mA. It needs 200mA or better, no? Maybe I need to look around for a different power supply. Do you folks know of a suitable power supply?

I don't know the circuit well enough to say for certain, but 100mA is plenty for most analog pedals.

[aishabag23]

Awesome. Just to clarify, my power supply is center positive (Electro-Harmonix model MKD-352400100). If I understand correctly, it doesn't matter because of the bridge rectifier. Is that correct?

I plugged it in and I'm definitely getting power. My lamp is not lighting when I have the Q13 2N3904 in correctly (EBC). However, I originally had mistakenly put the 2N3904 into the TO-220 slot... Which has a pinout of ECB. The lamp lit steadily with no dimming when I had the transistor in incorrectly. When I put it in with the correct orientation into the TO-92 slot, the lamp doesn't light at all. I also tried bending the legs into an ECB configuration in the TO-220 slot, with the same results.

I should point out that I am passing clean sound both in bypass as well as when the effect is switched on. The volume knob is fully functional. I think the speed (or rate) pot may be the culprit. I have it wired like this:

(A refers to the top row of lugs while pot is front facing, B refers to the bottom row of lugs)
A1- wired to A2, as well as to B1 and B2, and to pad C
A3- wired to pad D
B3- wired to pad E

Do I have that wired incorrectly?

[GGBB]

You've connected the speed pot correctly according to how I read the build doc. Make sure Q13 is in the position for your 2N3904's pinout. That probably means leaving the upper square pad empty and mounting it:

   C
B
   E

when looking down at it from the component side so that the pins are underneath and the bulb and LDRs are to the right.

You probably just need to adjust TR1 - see the doc for details.

[aishabag23]

Ok! Getting somewhere now. I got the bulb to flash, all the pots are working perfectly. However, even with the trim pot maxed, the brightest flash of the bulb is still extremely dim. I'm definitely getting a lush effect, just the slower speeds have very little effect audible. I'm sure with a few minor adjustments, it will be amazing.

I previously built the Madbean Harbinger running at 9v and I very much prefer the sound of this Neovibe.

GGBB, I can't thank you enough for helping me. 

... And nothing blew up... Always a plus 

[GGBB]

R50 will also affect bulb brightness and may need to be adjusted. The doc has more info about it.