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Mk2 Suitcase Tremolo Issue

Started by Noah Peterson, June 09, 2024, 06:25:08 PM

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Noah Peterson

Ever since I got my Rhodes there has been an intermittent issue where the output of the headphone jack constantly has the tremolo on, even if it is switched off. If I turn on the tremolo, weirdly, it is *almost* normal with a slightly dip in volume when it would normally cycle. I thought it was a preamp issue so I recapped it and replaced the transistor, unfortunately this didn't really do anything about the weird tremolo. Has anyone had this issue before? A majority of my Rhodes usage is through the headphone jack whether it's just recreational playing or recording.

I remember this happening a few months ago but the problem seemingly resolved itself until recently. I opened up the power amp section to see if there was anything that looked out of place, I did find two black wires that weren't connected to anything but they looked like they had never been soldered to anything. Hoping someone on this forum has encountered this issue before so I can get back to playing like normal.

In case it's relevant to the particular model it's a 1980 MK2 Suitcase 88.
1980 Rhodes Mk2 88 Suitcase

Will

Hello Noah,
No response to your message so I'll give it a try. I am not a professional ; just the happy owner of a 1977 Rhodes suitcase that I maintain. However, I have some knowledge of electronics.
I had a tremolo problem on my piano a few years ago. I was able to resolve it by refurbishing the electrolytic capacitors, especially those on the power supply board and amplifier boards. You can find the report of this operation on the following link.

https://ep-forum.com/smf/index.php?topic=10556.0

For your problem, my instinct leads me to suspect these components. If they have never been changed, they are probably out of order and may be the cause.
I hope this will help you. Please let us know.

Noah Peterson

I ended up replacing the capacitors on the preamp since that seemed to be advisable even if I didn't have the issue I do, while it did make it sound a fair bit cleaner the problem still remained (even replacing the transistor didn't change this.) I currently am just taking the output from the accessory jack directly into my audio interface, which does work perfectly for me. I wish I knew why it had that problem but for now I am happy to just DI it.
1980 Rhodes Mk2 88 Suitcase

Jenzz

Hi :-)

Since your Suitcase is from 1980, chances are that you have the preamp version that produces some kind of 'faint tremolo' even when tremolo is switches off.

In the former preamp version, the switch disconnects the LEDs in the photocouplers from the oscillator and cuts off the LED at the panel.

In the 2nd version (like yours), the switch only cuts off the 'intensity' pot and the LED on the panel, but the  photocoupler LEDS are still runing. Due to the circuit itself, this will produce a faint tremolo, which is more prominent over headphone than the cabinet (hence that both speaker channels work in the same box).

Jenzz
Rhodes tech in Germany
www.tasteundtechnik.de
www.spontaneousstorytelling.net

VintageVibe 64 ACL + Type 120 (DIY MXR MX-120 clone) Env. Filter, EHX SmallStone, EHX NeoClone

Adams Solist 3.1 Vibraphone

In the Past:
Stage 73 Mk1 (1977)
Stage 88 Mk1 (1975)
Stage 73 Mk2 (1980)
Stage 73 Mk2 (1981 - plastic)
Suitcase 73 Mk1 (1973)
Suitcase 73 Mk1 (1978)

HappyTinkerer

@Noah Peterson: You state your model is a "1980 MK2 Suitcase 88", does that have the five knobs or the sliders?
@Jenzz: It is not quite clear what the "2nd version" is supposed to mean. Do you refer to the "late mark II preamp" w 5 knobs? (https://www.fenderrhodes.com/pdf/late-mark2-suitcase.pdf)
Or are you referring to the Janus I with sliders?
(https://www.fenderrhodes.com/pdf/late-mark1-suitcase-janus1.pdf)

If "2nd version" means the 5 knob Janus, then I would like to add my findings:
Indeed, the double pole push button switch turns off the LED and grounds the signal (from the oscillator) at the non-inverting input of U1B. This definitely shuts off any signal at U1B's output and therefore at the input of the comparators/LED drivers U4A and U4B and therefore the LED current is not modulated. I simulated the circuit in ltspice and also did measurements on my implementation of the "late Mark II preamp".

I assume you meant the "late mark 1 janus 1"? Here, the one pole Vibrato on/off switch does a bad job and does not fully suppress the signal from reaching the two LEDs in the Vactrols.

HappyTinkerer