NeoVibe users- who is running 18+vDC

[DiamondDog]

To all Neovibe users out there-

I am considering changing my beloved 'vibe to run of  18+VDC  instead of its current 17vAC. I am conslidating my pedalboard power requirements, and see this change as being viable according to R.G.'s docs. I have a couple of other 18VDC pedals, so this makes sense.

Those of you running it on DC- are you happy with it?

Has anyone else swapped over from AC to DC, and are you happy with the results (ie no loss of quality)?

Thanks, DD

[Auke Haarsma]

I am currently using two LT1054 in parallel to provide 100mA @18V from a 9V source.

The vibe itself is running on DC anyway, so why would 18V+ DC (after the bridge rectifier) differ from 17V AC converted to DC via the bridge rectifier sound any different?

[R.G.]

The only quirk in switching a 'vibe from AC to DC is that you have to worry about ground.

In the stock uni- or neo-vibe, the power coming in is AC and neither side of the power jack can be grounded. The AC is full wave rectified to pulsing DC and filtered to real DC on the PCB, the negative side of the created DC being tied to signal ground.

You *can* put DC into the power jack on an unmodified -vibe and the full wave rectifier diodes will obligingly convert it to the proper polarity. In doing this, you lose 1.4V of the DC to the diodes. Compared to the signal ground at the jacks, one side of the incoming DC is always at -0.7V and the other at Vdc-0.7V. This means you cannot connect up the same DC power supply to other pedals and have the minus side connected to ground. The -vibe is trying to hold it at -0.7V and the other pedals are trying to hold it at 0V; they fight it out, with bad audio results. But it works fine to connect an external DC supply to an unmodified -vibe as long as you do not try to connect that same DC adapter to power other pedals.

If you simply must run other pedals from the same external DC power supply adapter, then you also must modify the vibe. The mods are simple - you just remove the rectifier diodes and use wires to connect the incoming DC to the filter caps inside the 'vibe. This removes the -0.7V offset on the incoming DC and lets you use the same power supply in parallel to other pedals.

Done correctly, there is no possible loss of quality. The vibe doesn't know whether the electrons were once AC or DC. Neither do the electrons.

[DiamondDog]

Thanks to both R.G. and Auke.

Yes, the bridge recitifier was the area of greatest concern for me, and I'm loathe to apply a hot soldering iron to a circuit that is working properly unless I  know exactly why I'm doing it. I've screwed up too many projects doing that.

Thanks especially to R.G. for your usual thorough explanation. Much appreciated as always, Sir, and I look forward to building your treadle-vibe (non-TM    ) when it's released.

DD

[chi_boy]

Just for reference, I built mine without the bridge and run on 18vdc. The thing is fantastic (thanks to R.G.'s troubleshooting).  I can't imagine how it could be made to sound better.

[R.G.]

Ah. If the board is already built, you have a couple of options. One is to strip the ends of a couple of wires, and bend a tiny hook in the stripped wire on each one. Hook one under the lead of the diode/bridge pin that goes to the + side of the filter caps, and solder. Do likewise with the other wire, but on the pin from the diodes/bridge that goes to the (-) side of the filter caps. Now take those two wires off to your power input plug. You can leave the bridge/diodes there. They're always reverse biased.

[DiamondDog]

Yes, R.G., it's a built one- it's been in AC-powered service for over a year from memory. In retrospect I could have made that clearer. My bad.  

Thanks again for the additional info, and thanks for the great design. It has been put to good use.

DD