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kenja58
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"Phantom Power" to control MidiBuddy
« Thread Started on Nov 22, 2010, 1:34pm »

Back in 2007 I started a thread in the "Zoom rfx2000 and Other Echoes" forum asking how I could get "phantom power" down the MIDI IN line out of a Quadraverb to power a Rolls MidiBuddy.
Apparently the MidiBuddy will accept 9 - 15VDC down pins 1 and 3 which saves the user having to use the unit's own power supply.

The discussion was useful as some people had done this by connecting the Quadraverb power supply through a splitter and introduced this power into the midi cable (also put through a splitter).

Its been a long time since then but I have just picked up the project again and have constructed a splitter box containing 4 female connectors (2 x 4-pin for power and 2 x 5-pin for MIDI). The power IN is wired to pins 1 and 3 of the 5-pin MIDI and only pins 2, 4 and 5 are connected between the Quad MIDI IN and the MidiBuddy OUT thus isolating the Quad just in case.

Still with me so far?......

Well... I just came across a potentially serious problem with this set up and it is this:

The MidiBuddy power input will accept AC or DC current as it has an integral converter. BUT - and here's the problem - will the MIDI out accept AC as well??? I can't tell by looking at the circuit board.

The manual mentions only DC but maybe because if phantom power were to be used then it would be DC and not AC.

The contributors of the forum discussion who had done this mod did not say whether they had used the original Quadraverb power supply which is 9VAC or whether they had substituted a 9VDC one.

The question remains then is: will I cause any damage by connecting 9VAC if indeed it will only accept DC current? Or will it just not work at all?

Sheendigs, if you see this post maybe you would tell me how you did this.

Does anyone else have an opinion on this situation?

Ken

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sheendigs
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Re: "Phantom Power" to control MidiBuddy
« Reply #1 on Nov 22, 2010, 4:21pm »

Hi Ken
Nice to hear again about this modification.
I am still using the same old box..Let me find a picture and a diagram and I will post it here.
The midi buddy comes with a Wall adapter that gives 9 volts DC.
I did not want to modify anything in the Q2 internally.

My little phantom power connection box is connected this way:
The midi cable coming from the midi input of the midibuddy, goes into my box..
The output of the box goes to the midi output connector of the Q2.
I have used the pins 1 and 3 connected to the wall adapter.
Just to be on the safe side..the connectors 1 and 3 are not connected internally in my box,
to the midi connector coming from the Q2.

Thus, I am sending 9 volts to the midi buddy as I have a 15 metres cable in length.
Here is the top of the box..schematic self-explanatory:

http://i545.photobucket.com/albums/hh400/ubijoux/Sheendigs_PWS.jpg
Sheendigs

« Last Edit: Nov 22, 2010, 6:56pm by sheendigs »

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kenja58
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Re: "Phantom Power" to control MidiBuddy
« Reply #2 on Nov 22, 2010, 11:48pm »

Hi Sheendigs, nice to hear from you.

Unfortunately you have not addressed my burning issue which is AC versus DC.

My MidiBuddy did not come with a power supply and I have used a spare 9VAC wall wart. The Quadraverb original power supply is similarly 9VAC.

I presume then that you do not use the Quadraverb original power supply but use the 9VDC MidiBuddy one to power both units?

Have I got that right?

Ken

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sheendigs
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Re: "Phantom Power" to control MidiBuddy
« Reply #3 on Nov 23, 2010, 12:21am »

Hi Ken
Sorry not to have answered that..
My alesis Q2 works with the original power supply 120VAC to 9V AC..
The Midibuddy has got its own powersupply being 120VAC to 12 V DC..
One would have to convert AC to DC and use the same power supply...
I do not have any mod in the Q2..to send 9VDC to the midi cable..
Perhaps someone has a better solution..
Sheendigs

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sheendigs
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Re: "Phantom Power" to control MidiBuddy
« Reply #4 on Nov 23, 2010, 2:56am »

Hi There
I am not a technician..but if one can use the 9AC output from the Q2 transformer through a Bridge rectifier..it should come out 9DC..like here:
[image]

And then it could be sent through the midi cable
Am I wrong?? (Any opinion from any fellow techie)
Sheendigs

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Charlie Hall
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Re: "Phantom Power" to control MidiBuddy
« Reply #5 on Nov 23, 2010, 9:32am »

Hi Sheendigs,
The circuit will work but is incomplete. There has to be a large value capacitor connected to earth (ground) at the output. The voltage will also not be 9 volts, it will in theory be 9 X 1.41 volts because the recitifier will convert the 9 volts RMS to the peak value. This would then provide an unregulated output. To regulate the output, a voltage regulator also has to be added, and the output voltage would be decided by the regulator type or circuit, it will always be less than the unregulated voltage. However, the MIDI pedal does not require a regulated voltage.
Regards,
Charlie

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kenja58
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Re: "Phantom Power" to control MidiBuddy
« Reply #6 on Nov 23, 2010, 11:41am »

Sheendigs
Last night after writing my post here a light came on - you must be using two power supplies! Your reply this morning confirms this.

So this is really just a way of operating the MidiBuddy from it's own power supply but from a distance, not quite what I am trying to achieve.

I suppose I could use a DC power supply to power both as I described earlier providing the Quadraverb will accept a DC supply. Charlie could you confirm whether this is correct or not?

The alternative is to follow a guy in the USA who had a similar requirement but went about it by installing a new MIDI female to the Midi controller chassis and wired the relevant pins to the AC input and to the correct three midi pins via the circuit board.

This scheme worked well but the only thing to be careful of is to wire the AC pins the correct way round to keep the polarity right just in case a DC adapter were to be used at any time.

If anyone is interested or wants to comment on this mod then I can try to find the link for it if is still exists.

I am not electronically minded but I assume, rightly or wrongly, that the AC to DC conversion within the MidiBuddy circuit board will not apply to any power input beyond this point and it will have to be DC.
Having said that, and from looking at the PCB the components just beyond the power input don't look very complex so it must be simple to replicate. Oh if only I knew what I was doing in this black art!

Any comments welcome.

Ken

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sheendigs
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Re: "Phantom Power" to control MidiBuddy
« Reply #7 on Nov 23, 2010, 2:26pm »

Hi Ken,
I was assuming that you remembered what I had done..
True, I am using two adapters.

As I said, one could perhaps use a bridge rectifier inside
the Q2..retrieving 9VAC inside, converting to 9VDC and making the connection to number 1 and 3 pins that goes to the midi out.
Will it make the midi buddy operate on 9 VDC and not as it says 12 VDC on the adapter?
I will have to test it.

The Q2 will still operate as it should since we are 'retrieving' and feeding the midi buddy.
I really do not like the adaptor scheme as it defeats the idea of supplying the necessary voltage internally from the Q2, but if one would like to do that..I say go for it.

Then if we ever use an external..there should be a switch of some kind...and a label advising the mod..

I will inquire with my technician here and see if it is doable..
Sheendigs

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kenja58
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Re: "Phantom Power" to control MidiBuddy
« Reply #8 on Nov 23, 2010, 6:24pm »

Hi Sheendigs
Actually the MidiBuddy input power spec is 7 - 15VAC/VDC, 80mA and it's "phantom power" spec is 7 - 25 VDC, 120mA, pin 1 neg, pin 3 pos.
The Q2 has to be 9VAC which presumably is converted to VDC inside the box.

So yes the MidiBuddy power supply would not suit the Q2 but vice versa it would be ok but only for the power input side, not the "phantom power".

The Q2 power supply has 1500 mA which should be enough for both units whereas the MidiBuddy's comes in at 120 mA which is tiny and would not support the Q2.

Ken

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Charlie Hall
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Re: "Phantom Power" to control MidiBuddy
« Reply #9 on Nov 23, 2010, 10:03pm »

The Quadraverb must have AC power. Clearly it isn't possible to power the pedal from that power supply.
Regards,
Charlie

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