Author Topic: Loads of Pickup Capacitors  (Read 529 times)

Offline leander

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Loads of Pickup Capacitors
« on: June 25, 2021, 06:21:24 AM »
Heyhello everyone,

glad to be on board. A few years back I bought a Rhodes which I did a lot of repair work on. Mostly mechanics and pickup replacements. It was in a very weird condition tho.

Somebody made a mod to split the pickup areas into different sections to have different outputs (not sure why anybody would do that, how common is that btw?).

I assume in this process about 24 capacitors have been added (see Pictures). I really don't understand the electrics of the Rhodes too good. Now I wonder why those have been added. Also because my Signal to noise level even after preamping with an "ART Tube MP Studio V3" is quite bad.

Since I don't need the additional outs and don't plan on using them should I remove all the capacitors?
Why are they there?
Is there any good video or read on understanding the rhodes electronics better. I really feel too stupid to e.g. understand why there is pickup groups.


Best Regards from Bremen, Germany, Leander

Offline sean

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Re: Loads of Pickup Capacitors
« Reply #1 on: June 25, 2021, 02:10:09 PM »
Hmmm... The old Unordentliche Masse von Kondensatoren mod!

Wow.  I have never seen the capacitors added to every group-of-three pickups.
I wonder if this was an attempt to make the attack on each note less percussive, or if it was an attempt to bypass the inductive load that every pickup group represents to every other pickup group.  Sadly, the capacitors bypass the local three pickups as they try to generate voltage and current to make the notes heard in the first place.

Maybe the capacitors were an attempt to minimize EMI.  Maybe the Rhodes lived in a place with lots of radio interference, and the owner tried to reduce the buzz.

Oh goodness, maybe the capacitors were an attempt to make the piano still generate sound when a complete group-of-three pickups are all dead.  The capacitor would bypass the dead group-of-three.

A prominent question would be:  What value capacitors are used?  I would expect that a very low value (a few picofarads) would be imperceptible and ineffective, and a very large value (say 100nF) may reduce the volume of the piano and make it sound muffled.  (Of course, I am totally guessing at these values, I have not tested this at all.)

If I were you, I would take a pair of sharp diagonal cutters, and clip every capacitor out of there.
____________________________

Splitting the harp into two sections is common.  Splitting the harp into more than two sections is uncommon.

See the split mod explanation here:  https://ep-forum.com/smf/index.php?topic=4730.msg52770#msg52770

This drawing shows the "groups-of-three" pickups more clearly:  https://ep-forum.com/smf/index.php?topic=10079.msg56091#msg56091


The wiring on your piano at the split point (three cables) shown in the photo implies that there is an additional split point higher up to the right.  Looks like they used coax cables, not twisted-pair microphone cable.

I have two pianos that have the harp split at E32/F33.  There are two output jacks on the faceplate, and a switch to choose if I want the harp split or not.  Works very well, and is musically useful.

The faceplate of my split-modded pianos looks like this:


Sean

« Last Edit: June 25, 2021, 02:17:32 PM by sean »

Offline sean

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Re: Loads of Pickup Capacitors
« Reply #2 on: June 25, 2021, 02:21:08 PM »


Please note that I made that reply without even once mentioning the Town Musicians of Bremen.

DOH!  Now I ruined it.  Sorry.

Offline Jenzz

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Re: Loads of Pickup Capacitors
« Reply #3 on: June 27, 2021, 09:03:33 AM »
Hi .-)

The cap mod was published in german music magazine 'Fachblatt' back in the 70s (attachment)...

Adding the cap forms a resonant circuit, which enhances a certain frequency. If the cap value is propperly chosen, it can enhance the 'bell' attack tone or add some bite to the mids.

Jenzz

« Last Edit: June 28, 2021, 01:58:04 AM by Jenzz »
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Offline leander

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Re: Loads of Pickup Capacitors
« Reply #4 on: June 28, 2021, 06:14:27 AM »
Thank you so much for your answers so far!

Since Signal to Noise is low on my Piano I wonder if the capacitors are to blame.

Since it is 24 caps I also think they might introduce certain electric properties which lead to lower output gain?

20 of the used caps used are Wima MKS-4
0.047
100-B
T2

Offline sean

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Re: Loads of Pickup Capacitors
« Reply #5 on: July 03, 2021, 02:30:39 AM »
Here is my brother's translation of the German Music Fachblatt (trade magazine) article:


BELL SOUNDS FROM A FENDER RHODES

It has always been a difficult problem for pianists to get a good bell sound from a Fender Rhodes.  Either you had to strongly increase the highs (and/or presence) in the amplifier, so that the tones in the two top octaves sounded loud and shrill (and the amplifier noise was also more or less audible); or you had to turn off the lows to achieve a dry sound, but then did not get enough bass.  However, using a simple trick, you can create bell sounds surprisingly well in the piano itself, without preamplifiers, batteries, etc.
 
Just a soldering iron and some capacitors are needed.  If you remove the black cover from the piano, you can see the reeds and the individual coils under the golden resonators [tonebars].  The coils are connected as follows: coils are connected in parallel as units of three each (except on the far left, the first coils for the lowest notes (E, F, F#, and G) are connected in a group of four).  These units of three coils are connected again in series, and so forth. 

If you simply solder a capacitor parallel to each group of three, so-called "oscillating circuits" will result, which generates the bell sound, but does not make the overall sound shrill.  The capacitors must have specific values, but these items can be obtained in any electronics shop. 

Here are the values: 47nF for the lowest group of four as well as each of the subsequent ten groups of three; 0.1uF for the five groups of three from D to E; 27nF for the next four groups of three; 4.7nF for the highest four groups of three.  (nF means "nanofarad"; uF means "microfarad".) This produces the following order list for the electronics shop: 11 pieces 47nF, 5 each 0.1uF, 4 each 27nF, 4 each 4.7nF [plus one 6.8nF added in the last paragraph].

Make sure that you get the smallest possible models of each capacitor; these depend on the voltage load capacity: it is sufficient to tell the dealer that small voltage values would be especially good.  (Note: The 47nF capacitors may instead be labeled 0.047uF, and for 4.7nF you may see 4700pF, so don't panic.  If necessary, ask a fellow hobbyist among your friends). 

The capacitors should now be soldered to the coils (make sure to use a hot soldering iron, otherwise there will be "cold" joints, meaning ineffective solder connections).  The capacitors are best held on the coils with tweezers or needle-nose pliers, so that you do not come into contact with the tonebars. 

Two small corrections are then needed:
1.  By slightly lifting or lowering the gold tonebars, determine the position where the bell sound and the metal tongue sound are particularly audible.  For this purpose, use a Phillips screwdriver to turn the front Phillips screws a little.  Before doing this, of course, connect the piano to an amplifier (and increase the highs). 

2.  The coils for the last two octaves should be moved a little away from the reeds.  For this, you need a hammer and a small piece of wood.  The wood is held against the edge of the pickup mounting tab, and with light hammer strikes, the tab and pickup coil can be moved back.  As a result, the high tones lose their aggressiveness, and the bell sound is clearly audible, without distortions and clipping, even for the upper tones!  It is important that after the corrections, all of the notes in the entire keyboard have the same volume. 

Volume re-adjustments can be made on all notes according to the procedure described under (2).  The further the coil is moved backwards (away from the resonator/tine), the quieter the key will sound.  You can give a finishing touch to the whole thing by making a small adjustment to the bass control: disconnect the capacitor on the bass control, and replace it with a new one with the value 6.8nF.  As a result, you can reduce the bass very strongly (the bass boost control now has a stronger effect).  For example, if you turn the bass completely down, you can even connect the Fender Rhodes to a microphone or tuner input of a normal hi-fi amplifier, without any muddy or distorted sound.  This is very pleasant for practicing, such as when using headphones in the evening.




So, like, uhm... don't do this.

Sean

« Last Edit: July 03, 2021, 07:46:19 PM by sean »

Offline sean

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Re: Loads of Pickup Capacitors
« Reply #6 on: July 03, 2021, 07:43:57 PM »


Spulenschiene - could be translated directly as "Pickup Rail," but the diagram makes it clear that the author intends it to mean Pickup Mounting Bracket... I think I like "Mounting Tab" better.  The aluminum tail on the pickup assembly is called the "pickup arm" in the description following figure 6-1 in chapter six the service manual. 

I have corrected the translation above, and it sounds less crazy to bang the pickup mounting tab than the pickup rail, but still....

Don't do this.

Sean

Offline sean

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Re: Loads of Pickup Capacitors
« Reply #7 on: July 03, 2021, 08:03:24 PM »

And Furthermore...

In the first paragraph , the author gripes about having to cut all the bass from the signal... and then in the final paragraph specifically recommends that you modify the bass boost control to enable you to cut all the bass from the signal.

Personally, I accept none of the statements made in the first paragraphs as truths.

However, I am still interested to hear sound samples of the piano modified with all the caps across the pickup groups. 

Leander - Please can you post a few recordings before you remove the capacitors?

Sean

Offline Tines&Reeds

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Re: Loads of Pickup Capacitors
« Reply #8 on: July 04, 2021, 06:54:46 AM »
In my opinion such a recording doesn't make sense without a comparison since overtone has a lot to do with voicing as well. For a convincing comparison you'd need an (almost) perfectly serviced Rhodes piano which you record without the caps and then with.
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Offline Tines&Reeds

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Re: Loads of Pickup Capacitors
« Reply #9 on: July 04, 2021, 06:58:05 AM »
But what is interesting to me is I've seen such modified instrument a few times already. And the funny part is, that the capacitors on all models looked the same which would be uncommon if this was only a DIY-solution and not a professional. There are tons of such caps on the market and they all look different. So it seems there were a guy (or a company) who did this modification as a professional I guess...
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Offline gacki

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Re: Loads of Pickup Capacitors
« Reply #10 on: July 04, 2021, 01:11:36 PM »
But what is interesting to me is I've seen such modified instrument a few times already. And the funny part is, that the capacitors on all models looked the same which would be uncommon if this was only a DIY-solution and not a professional. There are tons of such caps on the market and they all look different. So it seems there were a guy (or a company) who did this modification as a professional I guess...

I've seen such a mod so far only once; about 15 or so pickups were dead in this particular Rhodes. So this would point more towards an individually done modification. Not sure if I kept the dead pickups and caps; it was a couple of years ago.
As far as your theory goes: perhaps one of the retailers did this to all models he sold?

Offline gacki

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Re: Loads of Pickup Capacitors
« Reply #11 on: July 04, 2021, 01:21:59 PM »
Found them. Here's a couple: WIMA and EROMET.