Mark 1 rewiring

[Badoumba]

Hello

This is my first post in this forum.

Renovating a Mark 1 (1976), I am now at the pickups rewiring phase. As most of us are using guitar pedals, I was wondering if it could be useful to rewire everything in serial like an old 54 keys so the impedance will be closer to a guitar pickup one. Why Rhodes decided to wire with 6 pickups in serial and then down to 3 with later on when replaced with shorter magnets to reduce decay? I have the choice now so I wonder what could be the optimized solution.

Thanks !

[David Aubke]

If you wire a Seventy Three entirely in series, you'll end up with a 13K circuit. Pretty hot even by overwound humbucker standards.

I don't think your piano will sound very good wired entirely in series. Of course that's subjective but it will lose too much from the higher frequencies and sound muddy.

I think if you want to strengthen the signal, you should be looking at some Rhodes-specific preamps that are out there.

[David Aubke]

There was a recent discussion where the subject of series/parallel wiring came up.
http://ep-forum.com/smf/index.php?topic=9473.0

Here are some recordings comparing the sounds of a Fifty Four wired two different ways.
All series
Series/Parallel

[sean]

I strongly recommend that you wire the harp in groups of threes.  (Well, the lowest group is a group of four, but....)  Threes.

If you wire all the pickups in series, you might get a slightly louder piano, and it will almost certainly sound different.

In groups of threes wiring, each pickup creates a little voltage that is shorted out by the other pickups in the immediate group.  Well, not really shorted out, because the don't have zero resistance, but the other pickups in the group greatly reduce the output from each pickup.  If there were five other pickups in the group (as there was in the older groups-of-six wiring) then the individual notes would be even quieter.

I think that if the pickups were wired in series, then each individual note might be 9.5dB louder.  That isn't much considering the gain available from any preamp, guitar amp, or stomp box.  I have never found a guitar effect pedal that was unhappy with the existing low output from a Rhodes Stage piano.  They all seem to work fine.


Okay, so what would happen if you wired them all in series?

Well, you get the 1970's Christmas light problem... lose one light, lose them all.  If one pickup goes open circuit, the Rhodes is dead for the rest of the gig.  That's enough for me to not even try it.

But if you did wire all 73 pickups in series, then you get the additional resistance of all the other pickups in series fighting each note, but more importantly, you get the additional INDUCTANCE of all the other pickup coils in series with each note.  The pickups are wrapped around an iron core, so it is possible for the core to become saturated if there is enough current in the coil.  (I don't know if this normally happens in a Rhodes pickup, because the current is tiny; but I have no experience nor anecdotal evidence to compare with, and no way to test or measure this.)

So anyway, what I do know and have evidence of is that the inductance in the harp will cause louder notes to ring or buck... causing distortion.  Well, I guess we have come to know this distortion as a characteristic of the Rhodes piano sound.  However, if the inductance was significantly increased, the distortion might become objectionably pronounced.

Below are two oscilloscope shapshots of the E56 note, 659Hz, first played softly, and then poked a little harder.  The louder, slightly-higher-voltage note shows a wrinkle in the output.  The little bump is caused by the inductive kickback from the other coils in the harp (I think).

If you put all 73 pickups in series, the total series inductance is a little more than nine times of the group-of-threes harp.  I don't know how this would sound, it might sound fine, it might sound tanky on some loud notes.  But still, we do have a hint of what it would sound like:  since there are 54-note pianos that work reasonably well when wired in series, the 73 might sound okay this way too. 

In the example recordings that Dave posted, I think the group-of-threes harp sounds better than the series harp.  I really see no benefit at all in wiring the whole harp in series.

Sean

[Badoumba]

Thanks all of you for your comments, additional links and oscillo screenshot!

I never said that I intended to connect everything in serial, far from this. Just asking the motivation behind the 6 or 3 parallel choice. But from Sean's reply, I guess everything is related to the final sound color.
Initially wired with group of 3 (total impedance of 1400 ohm approximately), I finally gave a trial to groups of 2, giving me impedance of 3200, which is slightly below my stratocaster pickups' one.
Sounds good with my gear, still too much high frequencies for my taste that my MesaBoogie 5band corrects perfectly