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Messages - Will

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1
Parts, Service, Maintenance & Repairs / PSU and amp module update
« on: January 14, 2022, 03:11:48 AM »
Hello,
A few months ago my piano amp was not working at all. I assumed the power supply was faulty. I ordered parts to restore the power supply and amp modules and made the change. It is working fine now. Here is a report of what I did, for the record.

My piano is a 73 suitcase Rhodes Mark I piano ref. 3077. No upgrades have been done on this power supply or on the amplifier modules so far. It was time to change all the electrolytic capacitors. I also changed the twisted wires to suitable 0.5ohm resistors. I did not change the transistors.

You will find a picture of the finished product here. Zoom in for details : https://photos.app.goo.gl/5TqvNPgFRDPxxpE1A

The part list. At the end of each line, what I ended up choosing.

Amp   capacitor   Electrolytic   C1   4,7uF / 25V NP       AXIAL    >>> Mundorf BG50 4.7uF 75V      
Amp   capacitor   Electrolytic   C2   1uF / 16V NP          AXIAL   >>> Mundorf BG50 1uF 75V   
Amp   resistor   Wirewound   R18-R19 R20-R21   0,47 ohm  -  5W      >>> Royal 0,47 ohm 5W
         
PSU   capacitor   Electrolytic   C1 C2   1000uF – 35V - 60 mm AXIAL   >>> Jamicon 2200uF 35V
PSU   capacitor   Electrolytic   C3 C4   500uF  -  15V - 40 mm AXIAL   >>> Vishay BC-021 470uF 25V
PSU   capacitor   Electrolytic   C1 C2   11000uF – 40V – diam 50 mm    >>> F+T GMB 33000uF 40V

It costed me 52 euros inc. VAT + 8 euros delivery = 60 euros in total ie. US$ 69 in jan 2022.

The Vishay 1000 uF were not available at the time of purchase so I ended up putting Jamicon spare cap I had from a PSU kit. Not the best choice. I will change them next time.
I left a gap between the resistors and the PCB when I soldered them. Those components are likely the get hot so they need space to dissipate heat.
I soldered an insulated terminal to the wires connected to the 33 000 uF capacitors. They have bolts.
I cleaned the PCB with 95% alcohol, a toothbrush and a tissue to remove flux.
The amp +/- rail shows 28.6V and the preamp rail shows +/- 14.6 V. Good !

Feel free to ask if you need more details.

Will










2
Hello !
Vintage Vibe has a reseller in Europe, ep-service.nl
Cheers !

3
Interesting topic. My second-hand suitcase Rhodes has new speakers, all 4. I've always wondered if those were the best match for the cabinet. They sound good to me but I never heard the original version to form an opinion.
Tell me if I'm wrong ...
The design of a cabinet depends on the characteristics of the speakers. Nowadays, special software is dedicated to their design. Replacing the original speakers with new speakers requires that their characteristics be close to the original, or suitable to the cabinet.
Is there a place where we can have the characteristics of the original speakers? To compare with speakers on the market? And especially to those mentionned by Frenchji (which I also found on the web as successors to the first)?
Or isn't it that important ?
There was a webpage about the speakers on the Rhodes website, but it has been removed...

4
Hello Sean,
Well spotted. Yes I should have mentionned that the right side of the PCD has not the original layout. You got the right link that explains why.
I did basic tests of the LDRs : 0.6V at led pins and resistance at opposite side, without unsoldering them. I saw nothing wrong here. They seem to work fine however, as the vibrato is working fine now, with front panel led disconnected.
I keep in mind your OpAmp advice for the next time I will put my hands into it. But not soon ; my next task is power supply and amp upgrade.
I will update this thread if I have further advance.


5
Hello Frenchji,
I am not the most experienced user here but here are my tips.

Quote from: Frenchji
Only one side of the speakers works [...] What is the best way to test the speakers to make sure they are fully operational? 
I usually use a 9V battery and connect it briefly to the poles of the loudspeaker. You can also connect it to the tip and sleeve of the jack connected to the speakers. You should hear a "pop" and see the membrane moving forward (or backward if reverse connection). This is very basic testing of course.

Quote from: Frenchji
...the amps needs some work.  There is a very obvious blown resistor ...
Your amp needs some electronics diagnostics to understand why the resistor has burnt. Replacing failed components would keep the circuit close to original and shouldn't be too costly.

Quote from: Frenchji
No Tremolo!  When Tremolo is engaged...
Same here. Some diagnostics are needed to find out what the problem is.
Here are two topics to start. Be aware that my Rhodes has Janus preamp (without bulb)
https://ep-forum.com/smf/index.php?topic=10265.msg57985#msg57985
https://ep-forum.com/smf/index.php?topic=10290.msg58076#msg58076

Last, your amp, preamp and power supply need to be recaped indeed. Electrolytic caps do not age well. You can find rebuild kits on specialized suppliers online shops which are well documented and inspiring. Here is a topic about my preamp upgrade :
https://ep-forum.com/smf/index.php?topic=10294.0








6
I did the upgrade last january, as described in the previous post. I kept the original polypropylic caps. I changed the ceramic caps to WIMA MKP types (except C2 120p which I forgot to order). I decided to change the resistors on the signal path but I am not sure it is that relevant (I tend to overdo it sometimes). I also thought of changing the cables but decided not to do it (yet). I cleaned the board carefully with acetone and put everything back in place.
How does it sound now ? Yes, it sounds good, clean and loud. I am satisfied.
Some pictures :

7
The Fender Rhodes Electric Piano / Re: Power down when vibrato switched on
« on: February 10, 2021, 07:17:59 AM »
Hello Sean,
It's a good idea I wish I had tried. I was focused on the led indicator as the oscillator works fine without it.
I may try this the next time the circuit will be on the lab bench but it won't be until... months. I keep my spare time to train my piano skills now... and enjoying my Rhodes. I will update this thread it this case. Many thanks Sean for your helpful replies.
Will

8
The Fender Rhodes Electric Piano / Re: Power down when vibrato switched on
« on: February 07, 2021, 10:55:12 AM »
I got back to my vibrato issue as I had few days off. I have spent quite some time to know more about the cause and eventually find the cure. To this day, the issue is not solved but bypassed. It is OK for me "as is". This is what I have done, just for the record.

I took the preamp out from the piano and I built a separate +/- 15 V lab power supply to see if I could reproduce the problem without the Rhodes power supply. Which I did. The Rhodes power supply is cleared.

I changed all the electrolytic caps which were all faulty. I also changed a non-polarised cap on the oscillator (C8). I removed the vibrato switch and put a shunt in place. I cleaned the board carefully. With no better result.

One interesting thing to notice : the voltage between the -15V rail and ground drops to few volts when the output of the oscillator (op-amp pin 7) is at low state. This is why the pilote indicator led (LED 4) gets dim. And this is why the sound gets distorted. The signal is clipping. This can be observed only when the oscillator is at a low rate as the the voltage has enough time to drop.

I have the feeling that the op-amp output at pin 7 is short-circuited to ground when at low state, draining the power supply. My guess was that the vibrato indication led or its transistor was the culprit. Disconnecting them from the oscillator did the trick indeed. However I did my best to find a failure there, without success. I even replaced the transistor to a new one... it did not do the trick.

I ended up leaving the vibrato indication disconnected from the oscillator output and left the led on : I removed R26 and the transistor. I added  a jumper from R28 to the led.

Back to the piano, the preamp and oscillator work fine now. Without vibrato indication however.

I also connected the third pole of the switch to ground.

Picture here : https://photos.app.goo.gl/Srw82URnJhFiVtXr9

9
I got back to my vibrato issue as I have few days off. I have spent quite some time to know more about the cause and eventually find the cure. To no avail but here is what I have done, just for the record.

I took the preamp out from the piano and I built a separate +/- 15 V lab power supply to see if I could reproduce the problem without the Rhodes power supply. Which I did. The Rhodes power supply is cleared.

I changed all the electrolytic caps which were all faulty. I also changed a non-polarised cap on the oscillator (C8). I removed the vibrato switch and put a shunt in place. With no better result.

One interesting thing to notice : the voltage between the -15V rail and ground drops to few volts when the output of the oscillator (op-amp pin 7) is at low state. This is why the pilote indicator led (LED 4) gets dim. And this is why the sound gets distorted. The signal is clipping. This can be observed only when the oscillator is at a low rate as the the voltage has enough time to drop.

I have the feeling that the op-amp output at pin 7 is short-circuited to ground when at low state, draining the power supply. My guess was that the vibrato indication led or its transistor was the culprit. Disconnecting them from the oscillator did the trick indeed. However I did my best to find a failure there, without success. I even replaced the transistor to a new one with no better result.

I ended up leaving the vibrato indication disconnected from the oscillator output and left the led on : R26 and transistor removed and jumper from R28 to led added. 

Back to the piano, the preamp and oscillator work fine now. Without vibrato indication however.

This initial design was changed to a later one, as Sean stated in Reply #1. More rational indeed. I also connected the third pole of the switch to ground as suggested by 1way2life, who borrows this concept from this later design.

Picture here : https://photos.app.goo.gl/Srw82URnJhFiVtXr9

The issue is bypassed, but not solved and remains a mystery to me.

10
Hi 1way2life,
Quote from: 1way2life
"shunt the base of Q1 to ground when the vibrato is off"
I drew two schematics to think about it. Which one is suitable to you ?
https://photos.app.goo.gl/n9P43wkdBMC9QpAg6
https://photos.app.goo.gl/c67NybXEV5G5EBRn6
The second one uses a DPDT switch.

11
Hi 1way2life,
Thanks for your reply.

Which wiring did you set up ? Out of phase (p.5)   or   in phase (p.3) as referred to in the vv document ?

I checked the rail without preamp (+14.58V  -14.58V) and with (+16V   -11V). Q1 tested (P>N 0.6V) and nothing wrong. A topic is opened at https://ep-forum.com/smf/index.php?topic=10290.0

"shunt the base of Q1 to ground when the vibrato is off" Which preamp version do you have, as referred to by sean ?


12
Hi,
I have the same vibrato issue. I checked my speakers and they have been changed too to some 8 ohm speakers by previous owner, obviously. The original parallel wiring was kept too giving 3.5 ohm for the PA output. I changed to series config, to no avail to my issue. Still investigating.

By the way, I found this vv document which is getting me confused. In page 4, I don't understand why Janus 8 ohm speakers should be kept in parallel. The page 5 series and phase invert config seems best to me. Which I chose.

13
Preamps, Modifications & Upgrades / Rhodes MK I Janus preamp upgrade
« on: June 29, 2020, 01:45:29 PM »
Hello

I have the early version of Janus preamp ref. PART NO.013487 which I intend to upgrade. You can find the schematic diagram here.
These are my thoughts and questions about its upgrade which I submit to your comments.
You can find the part list here to follow the subject.

The LM1458 OpAmp on signal path can be upgraded. I have a pair of Burr Brown OPA2134PA which I intend to use. They have the same pinout config. And add their package.

The electrolytic capacitors need replacement after more than 40 years of services.  I will choose Panasonic (FC series), Nichicon (KA, FG, KW), ELNA (not Silmic II)... The relevant capacitors are C8 C20 C12 C13 C14 C15 C3  and non-polarised C4 C6 C16.

Black and round shaped capacitors seem to be polypropylic. If that is the case, they are good quality caps and age well so they must be kept in place, right ? Those are C11 C1 C9 C5 C7 C10.

Small and flat caps are ceramic. From what I know, they are not suitable on audio signal path. On the schematic, they seem to help stabilise the OpAmp (C2) and to suppress unwanted high frequencies (C17 C18 C19). Am I right ? Are they worth to be changed ? For what type ?

I don't know the quality of the present resistors and I am wondering if a change to modern low noise metal oxyde resistors would be beneficial. I have an assortment of them.

The transistor and diodes are not in the signal path and don't need to be changed, unless faulty. Same for the vibrato speed pot.

Linear bass and treble pots and vibrato intensity pot are on the signal path. I don't plan to change them as they make no crack.





14
Hello,
Quote from: sean
With the preamp disconnected, what do the power feeds coming from the amp cab measure?
I get +14.58V and -14.58V. The drop in tension is coming from the preamp indeed. I also removed the A2 oscillator IC from its socket and I still have this -11V instead of -15V. So the OpAmp is not faulty.

Quote from: sean
check (...) continuity of the ground terminals
I checked all the bits with the multimeter and it is showing continuity.

Quote from: sean
Check that the 100%u03A9 current-limiting resistors are still in good shape (...) and close to 100%u03A9.
Yes to both, they are all fine.

Quote from: sean
take a good look at the PC board where the switch mounts.
I did and found nothing. However, I am suspicious about the switch, instinctively.

My to-do list :
- Draw up a components list to upgrade the preamp board (I will make a post very soon about this) and order the components
- Remove the components form the board. Remove the solder with a pump. Clean the board with care.
- Populate the board with new components and wires. Clean the flux from board. Look for any bridge between traces.
- Let you know...


15
Hi Sean,
I carefully read your post. I did few things this evening but I will do more this week-end. Some answers however :

A thick piece of plastic is already in place, stuck on the enclosure below the PCB. I don't know if it is from factory or if my friend put it in place but it is done very carefully.

The strips had some oxyde dust on them. They had some flux in some place too. So I cleaned them this evening. They need some more cleaning so I will start again this week-end. A leakage may occur here.

Switch case test still to be done.

The oscillator is actually running. I don't have a scope but at low frequency, my multimeter shows the voltage output swinging from + to - at OpAmp output pin 7. At top speed, the frequency-meter shows 15 Hz.

Removing the "vibrato indicator" LED causes the symptoms to occur, even if the switch is off.

I made further tests with interesting results :
When the vibrato is off :
...The positive power supply rail measurement is +16V (+15V expected from datasheet). The negative rail measurement is -11V (-15V expected from datasheet).

When the vibrato is on (at low frequency) :
...and when the oscillator output at OpAmp pin 7 is hight, the rails remain the same as above (+16V and -11V). The "vibrato indicator" led and the "pilote indicator" led are fully lit. The sound is normal.
...and when the oscillator output at OpAmp pin 7 is low, the power rails change to +26V and -0V. The sound becomes weak.  The "vibrato indicator" led is off which is normal. The "pilote indicator" led weakens too which is unusual. The reason is there is no more potential difference on its poles, between negative rail and ground.

There may be a ground reference issue because the + and - rail difference remain the same. Maybe an OpAmp failure...?

To be continued.

16
Hi Sean,
Thanks for your answer. The switch is connected to pin 7 of OpAmp IC A2 on one pole and to R26 resistor on the other pole so I deduce the Fig11-1 applies.
The board reference is
PART NO.013487
ASSY NO.013488
ECI-2
VO
so yes, 013...

17
Hello,
This is my first post.
I am the lucky owner of a 73 suitcase Rhodes Mark I piano ref. 3077 for two years now. I am a regular reader of this forum ever since and I would like to thank the members of this community for their contribution. I would like to pay tribute to my friend Pierre who offered me to be the second owner of his piano, and who passed away a few months ago. I have been confident enough to restore maintain and adjust my piano so far. But I now have an issue that I cannot fix by myself, which you may have gone through.
On the Janus preamp, I have a drop in power when I switch the vibrato on. The sound fades out and the LEDs light weakens. The switch seems to engage a short circuit. The power comes back to normal when the switch is turned back off. I don't make this test often as I would not like to cause a power supply failure.

I removed the preamp, opened the enclosure and I see nothing wrong. No smelly or burnt component. I tested the transistor and the diodes with a multimeter and they are fine. I sought a short circuit between +15V -15v GND and switch when the switch is on with no results.
One interesting fact is this phenomenon occurs also when I unplug the vibrato indicator led.

I could not find a topic about this. If you know of one please show me the link. Otherwise any advice or solution welcome.

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