Author Topic: Rhodes 54 preamp level very low compared to harp level  (Read 3247 times)

Offline musomarc

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Rhodes 54 preamp level very low compared to harp level
« on: June 13, 2014, 01:42:53 AM »
Hi all Rhodes lovers,
Working on restoring a Rhodes 54 stage and have just about finished BUT am getting a very low signal from the jack out on the preamp rail compared to from the harp ( via RCA).
It's probably X3 the level from the harp compared to from the jack out on the piano preamp rail. I've looked everywhere but can't seem to find a schematic circuit diagram for a Rhodes 54 preamp amp ( the one with 2 slider pots one is volume the other is tone).
Does anyone have a schematic for this preamp?  Possibly there may be a problem from the preamp wiring or components!
Or any suggestions to boost the output level from the jack out rather than use the rca Harp output. I know some people use external preamps e.g VV Tone bomb, but am wondering if there is a simple alternative to check my preamp and level or to boost it.
Great forum and always helpful advice Thanks!!!!

Offline Cormac Long

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Re: Rhodes 54 preamp level very low compared to harp level
« Reply #1 on: June 13, 2014, 04:43:45 PM »
Stage passive controls..



There's no actual preamp here as its unpowered. I'm not familiar with the 54 in person but its the same passive wiring used in other stage models. Aside from sliders/versus circular pots, there may be fluctuations in actual resistance values used given the shorter set of pickups and wiring variations of the 54 harp.

Also attached to this post is a simplfied image someone posted way back on how the circular pots for the stage models were wired. Its the same wiring as shown above.

See if you can following the wiring and confirm its as shown. We can go from there then in troubleshooting the signal drain.

Offline David Aubke

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Re: Rhodes 54 preamp level very low compared to harp level
« Reply #2 on: June 13, 2014, 04:48:40 PM »
I just pulled the Tine Bomb out of my Fifty Four. It works fine but doesn't do anything for my tin ear.

I referred to a drawing I made when I first installed the preamp to restore things to their original state but now it doesn't seem to work properly. My volume increases slowly then swells drastically during the last ten percent of the fader's range. Also, my tone seems to be non-functional. I'm feeling quite certain I've put it back the way it was but if anyone has any thoughts, please chime in.

Anyway Mark, here's a drawing of what I believe to be the correct wiring. Does anyone know the values of the two faders?

Dave Aubke
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Offline Cormac Long

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Re: Rhodes 54 preamp level very low compared to harp level
« Reply #3 on: June 13, 2014, 05:26:25 PM »
David,
   in your wiring, the capacitor needs to be shorted out on the tone/bass boost when its up full. So the pickup hot runs serial through the capacitor onto the volume pot and the tone is merely shorting out that capacitor, negating the bass filtering. Based on your image there, I suspect you're getting no bass.

As for the non-linear volume, it could be an aged pot, but equally a facet of the amplifier. There's a balancing game being played with a volume pot in that its 2-way setup to add resistance between the jack tip and RCA signal while you reduce volume while at the same time reducing resistance between the ground and jack tip. The logic with that is that it tries to maintain a continual resistance over the ground and signal out. That helps avoid buzz if the impedance goes too high... otherwise you'd get a buzz increasing as you turned volume down.

The original resistance rating should be on the sliders and I'd start with trying to source a modern equivalent from an electronic parts shop.

You can also get one readymade from VV...
http://www.vintagevibe.com/shop/rhodes-54-note-passive-electronics/

Offline musomarc

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Re: Rhodes 54 preamp level very low compared to harp level
« Reply #4 on: June 13, 2014, 06:50:54 PM »
Hi Cormac and Dave,
Thanks so much for your speedy response and great help with the wiring details, diagrams etc!
Dave, when you used your 54 without the VV tone bomb preamp did you also only get a very low level of output from the piano?
Regards :) ;)

Offline David Aubke

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Re: Rhodes 54 preamp level very low compared to harp level
« Reply #5 on: June 15, 2014, 09:07:49 AM »
The output at the name rail jack was comparable to that of the harp's RCA. No, the tone and volume controls did not reduce the output level.
Dave Aubke
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Offline voltergeist

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Re: Rhodes 54 preamp level very low compared to harp level
« Reply #6 on: July 28, 2014, 11:59:05 AM »
David, the VV Tine Bomb page has the following:

"Note: This product will not work for a Mark II without modification to your piano. Also for 54 note models, name rail mod and rewiring pick ups will be necessary. "

(emphasis mine)

I don't know the nature of the rewiring, but were you aware of that 'rewiring pickups' caveat when you installed the TB in your 54?
Restored or Overhauled: '65 A-model Sparkletop, '78 Suitcase 73, early-'75 Satellite 88, '81 MkII Stage 73, two '77 Mk1 Stage 73's, '74 Mk1 Stage 73
In Progress: 1 '78 Suitcase (2nd one), '70 KMC - Customized w/ Peterson 4x12, '77 Wurli 270

Offline David Aubke

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Re: Rhodes 54 preamp level very low compared to harp level
« Reply #7 on: July 28, 2014, 12:05:17 PM »
Well, I didn't at first. But in my defense, neither did Vintage Vibe... or at least they forgot.

I did rewire my Fifty Four to work properly with the Tine Bomb but still can only hear a volume difference.
Dave Aubke
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Offline voltergeist

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Re: Rhodes 54 preamp level very low compared to harp level
« Reply #8 on: July 28, 2014, 12:11:25 PM »
Did you get your problem with the original passive electronics straightened out?
Restored or Overhauled: '65 A-model Sparkletop, '78 Suitcase 73, early-'75 Satellite 88, '81 MkII Stage 73, two '77 Mk1 Stage 73's, '74 Mk1 Stage 73
In Progress: 1 '78 Suitcase (2nd one), '70 KMC - Customized w/ Peterson 4x12, '77 Wurli 270

Offline David Aubke

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Re: Rhodes 54 preamp level very low compared to harp level
« Reply #9 on: July 28, 2014, 12:15:29 PM »
No. I haven't looked at it since I posted those earlier comments.
Dave Aubke
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Offline vintagekeyboards

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Re: Rhodes 54 preamp level very low compared to harp level
« Reply #10 on: July 29, 2018, 06:26:44 PM »
... the capacitor needs to be shorted out on the tone/bass boost when its up full. So the pickup hot runs serial through the capacitor onto the volume pot and the tone is merely shorting out that capacitor, negating the bass filtering. Based on your image there, I suspect you're getting no bass.

As for the non-linear volume, it could be an aged pot, but equally a facet of the amplifier. There's a balancing game being played with a volume pot in that its 2-way setup to add resistance between the jack tip and RCA signal while you reduce volume while at the same time reducing resistance between the ground and jack tip. The logic with that is that it tries to maintain a continual resistance over the ground and signal out. That helps avoid buzz if the impedance goes too high... otherwise you'd get a buzz increasing as you turned volume down.

The original resistance rating should be on the sliders and I'd start with trying to source a modern equivalent from an electronic parts shop.


Hello everyone.... I unfortunately rarely read or post on here, as I have bee busy learning the basics with repairing a Rhodes 54 for a friend. 

I have rewired the pickups per VV’s suggestion as a series-paralleli configuration, however I did not touch the passive electronics on the name rail, and after putting the piano back together, I was not able to get any sound at all from the piano (where, prior to my tedious pickup coil repair—that I was very careful to do correctly, each pickup tested great—the piano produced sound except for the few pickups with issues).

I took the name rail off from the piano again, and noticed the main RCA output wire from the harp to the passive electronics, had broken from one terminal point on the passive electronics.

Problem is, I am uncertain from which terminal the spliced wire was originally connected to.

I realize that these passive electronics controls may not be in original wiring format, and it is possible (though doesn’t look likely) that someone had modified it prior to my working on it.

Can anyone help me determine where the lead/wire from the RCA output on the harp, needs to be properly connected onto the passive electronics on the name rail?

Thank you in advance for any time/effort with this!

(I may need to have this explained in layman’s terms, as I am learning and fairly new to Rhodes repair)

1973 Fender Rhodes Suitcase Piano - 73 key
Hammond M3 organ (blonde)
Vox Jaguar
Hammond C2 organ
Rheem combo organ
Hammond chord organ
Yamaha S90
Roland JX-1

Offline vintagekeyboards

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Re: Rhodes 54 preamp level very low compared to harp level
« Reply #11 on: July 29, 2018, 11:14:56 PM »
I also have photos to provide, to better explain my problem, however my photos are too large in resolution, making for a file size that exceeds the limit of this chat group.

anyone able to direct me to a method of resizing photos to be able to post within this chat group?

(I realize how ‘kindergarten’ my issues may seem, that being said, I very much appreciate any help with this... thank you in advance)

1973 Fender Rhodes Suitcase Piano - 73 key
Hammond M3 organ (blonde)
Vox Jaguar
Hammond C2 organ
Rheem combo organ
Hammond chord organ
Yamaha S90
Roland JX-1

Offline sean

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Broke the wire off the pot...
« Reply #12 on: July 30, 2018, 03:02:02 PM »


Your namerail wiring should look like the schematic, drawing, and photo in this post:

https://ep-forum.com/smf/index.php?topic=4650.msg22605#msg22605


We are not afraid of Kindergarden questions - we are happy to help. 
Many of the simple questions are covered in the service manual: http://www.fenderrhodes.com/service/manual.html
Some good stuff in the technotes:  http://www.fenderrhodes.com/service/technotes.html
Lots of good stuff on Vintage Vibe's website, and their youtube channel.
Lots of good stuff on RetroLinear's website, and their youtube channel.

Sean

Offline vintagekeyboards

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Re: Rhodes 54 preamp level very low compared to harp level
« Reply #13 on: July 30, 2018, 04:41:12 PM »
thank you for the response, Sean... much appreciated!

I looked at the link you shared, and it looks like it’s for a Stage piano 73 key electronics schematic.

The piano I am working on is a 1980 Rhodes 54 key with the two slider variable pots (volume and tone) passive electronics.... do you happen to know of any photos or links to that type of schematic?
1973 Fender Rhodes Suitcase Piano - 73 key
Hammond M3 organ (blonde)
Vox Jaguar
Hammond C2 organ
Rheem combo organ
Hammond chord organ
Yamaha S90
Roland JX-1