Neovibe (power) wiring question

[manson]

I'm going to build a Neovibe soon, but some of the wiring isn't clear to me. I'll be using an 18v DC power supply (dunlop), isolated I/O jacks and an isolated power jack.
Please correct me where I'm wrong:

- Power jack positive and negative terminals connect to pads J and K, in either way thanks to the bridge rectifier
- Input and Output Jack negative, and chassis ground are connected together, and to pad B or pad O (both connect to pcb ground)
- LED positive connects directly to the power jack positive terminal
- LED negative (from 3pdt / resistor) connects to pad B or O? (or to the power jack negative?)
- Pads I and X (cancel switch) are not connected

Thanks for helping me out

[R.G.]

I'm going to build a Neovibe soon, but some of the wiring isn't clear to me. I'll be using an 18v DC power supply (dunlop), isolated I/O jacks and an isolated power jack.
Please correct me where I'm wrong:

- Power jack positive and negative terminals connect to pads J and K, in either way thanks to the bridge rectifier
- Input and Output Jack negative, and chassis ground are connected together, and to pad B or pad O (both connect to pcb ground)

Use pad B. It will offer some minor advantage in lower noise, being attached closer to the signal ground.

- LED positive connects directly to the power jack positive terminal

Depends. What circuit are you using for an LED? No LED in the Neovibe circuit as stock.

- LED negative (from 3pdt / resistor) connects to pad B or O? (or to the power jack negative?)

That will work if you want an LED indicator that's a bypass indicator. Preferably pad O, which is there for power connections.

- Pads I and X (cancel switch) are not connected

If you're not using a cancel switch and bypass instead, yes.

A quick note. If you will always use an 18V power supply for this thing, never any other power supply, you can simplify things on the board. The power supply on the board is a semi-replica of the original power supply which took in 120Vac and made the power inside the box. You can delete some things if you will always use 18VDC.

For that, you could leave out the bridge rectifier and one of the big filter caps, as well as the 7815 and the diode closest to it. You put on jumpers to conduct the DC from pads J and K through where the diode bridge used to be and across the place where the 7815 used to be. When you get to there, you can use a non-isolated DC power jack and not get the big hum issues that would otherwise be there with an AC power inlet.

To do this, put a wire jumper across the holes for the bridge rectifier in two places: one, from the hole nearest pad K to the hole that was pin 1 on the bridge rectifier, directly to the left of pad K; two, from the hole nearest J to directly across the bridge. Pad K becomes your DC + input pad, and J is your DC- pad. Also add a wire jumper across the two outside pads where the 7815 would be, being careful that your wire does not short to the middle pad, which is DC ground.

[manson]

Thanks for the reply R.G. The LED is meant to be an on/off indicator. Seems I pretty much got it right didn't I
Pad B for grounds it is, LED ground to pad O.
About the powersupply, the components are already ordered so it doesn't really matter. With the rectifier etc. in place it will only be more fool-proof!
I'll start building in 2 weeks, will post some pictures along the way

[manson]

Are the large 1000uF filter caps needed when using 18vDC? Can I use a smaller value like 2x 470uF to save some space/height?
Also, the dunlop 18v adapter can supply 150mA, this is enough isn'it? The bulb is 12v 40mA.

[proyal]

I'm getting ready to start a Neovibe build myself, but I have a few questions, and thought I'd post here rather than start a new thread.

I've seen a few people mention using a charge pump with a 9v power supply to power this.  I was wondering, specifically, if the 17 or 25 volt setup of this (click here) would work.  I've read a few things that seemed to fall on either side of the fence, or led me to believe it would work, but be noisier.  If this does work, I'll be using a One Spot wall wart, daisy chained with a few pedals, at least until I can get my hands on a good isolated PSU PCB (not ready to dive into etching).

Also, if I throw in a 3pdt with an LED in it's own circuit for on/off, would I need a heftier 24v LED, or would the standard LED with a bigger resistor be fine?  I've only dealt with 9v in previous builds.

Feedback would be greatly appreciated.  Thanks!

[R.G.]

Are the large 1000uF filter caps needed when using 18vDC? Can I use a smaller value like 2x 470uF to save some space/height?
Also, the dunlop 18v adapter can supply 150mA, this is enough isn'it? The bulb is 12v 40mA.

For a well filtered source, you can lower the size of the filter caps.

150ma is enough.

I've seen a few people mention using a charge pump with a 9v power supply to power this.  I was wondering, specifically, if the 17 or 25 volt setup of this (click here) would work.  I've read a few things that seemed to fall on either side of the fence, or led me to believe it would work, but be noisier.  If this does work, I'll be using a One Spot wall wart, daisy chained with a few pedals, at least until I can get my hands on a good isolated PSU PCB (not ready to dive into etching).

100+ ma is a lot of current for a charge pump. Some will, some won't, and the details of wiring, capacitor decoupling will matter where they would not with a lower current. This is why you're getting both answers.

Also, if I throw in a 3pdt with an LED in it's own circuit for on/off, would I need a heftier 24v LED, or would the standard LED with a bigger resistor be fine?  I've only dealt with 9v in previous builds.

There are no 24V LEDs. Only standard LEDs, and yes, you'll need a bigger resistor, and that will be fine.

Next question: how big a resistor. Answer, Ohm's law. A standard LED needs less than 20ma through it to live a long and prosperous life. Sometimes much less. Shoot for 10ma.

Standard LEDs have about 2V across them when they are active. If you have 24Vdc across a resistor and LED, and the LED has 2V across it, that only leaves 24V -2V = 22V for the resistor. The resistor has the same current as the LED, so you can simply say "I want 10ma" and then the resistor to do that is R = V/I =22V/0.01A = 2200 ohms. That may still be too bright for some LEDs. People often use 4.7K for LEDs on 9V (that is, 7V left over for the resistor), so you'd expect to see up to 12K for the resistor with a 22V dc supply.

Feedback would be greatly appreciated.  Thanks!

[proyal]

Thanks, R.G.

I guess I'll plan on getting a new wal wart, for now.  And that's what I thought on the LED, but I wasn't sure - I order a lot of stuff from Newark and they list Forward Voltage etc there... wasn't sure what to make of it.

Thanks, again.

[R.G.]

I guess I'll plan on getting a new wal wart, for now.  And that's what I thought on the LED, but I wasn't sure - I order a lot of stuff from Newark and they list Forward Voltage etc there... wasn't sure what to make of it.

Yep, "forward voltage" is the voltage across the LED when it's shining.

[manson]

It's done, and sounds great! Very Hendrixy indeed. Don't bash me for the Faux-Cornish look All I need now are some Dymo labels haha.

Preamp transistors (Q1 - Q3): 2N3904
Q4 - Q12: 2N5088
Q13: TIP122
Regulator: 7815
I had a pot in place of R50, as a simplified JC's offset mod. Ended up with 470k (!) there instead of 47k.
470uF 25V for the filter capacitors.
Volume pot is 250kA.
The metal lightshield is all mirrorlike on the inside, ldr's are flat on the pcb.

And here are a few pictures:

[joinpobob]

A quick note. If you will always use an 18V power supply for this thing, never any other power supply, you can simplify things on the board. The power supply on the board is a semi-replica of the original power supply which took in 120Vac and made the power inside the box. You can delete some things if you will always use 18VDC.

For that, you could leave out the bridge rectifier and one of the big filter caps, as well as the 7815 and the diode closest to it.

To be sure, did you mean the capacitor closest to 7815? If so that would be C26, right?

Thanks for all of the input, BTW!