MKII Suitcase 88 weird noise - please help!

[chris2886]

I was lucky enough to have been given my Dad's 1980 MKII Suitcase 88 after he'd stored in the garage for about 10 years. I managed to ressurect it myself by swapping out some of the dead white label pickups, but it had problems with intermittent noise, tuning, pick-up spacing and all that stuff.

After moving it from house to house with me for about 15 years I finally thought I'd bite the bullet and have it restored properly, so I found a great technician about 4 hours from me who did a great job sorting out all of the issues. I went to pick it up from his workshop and it sounded amazing! I was super excited to get it home and try it out.

When I got home, I set it all up, but when I turned it on there was a really weird kind of swirling noise. I contacted the technician, but he was as stumped I was! He thinks it might be RFI getting picked up by the pick-up array, but if use the accessory 2 out to connect it to one of my old guitar tube amps, it doesn't have the same noise! I've tried lots of different plug sockets, I don't have any other keyboards or equipment sat on top of it. I don't have too many issues with RFI in my house when playing and recording guitars. I've tried turning off other appliances in the house when the rhodes is on, putting ferrite clips on cables for the computer and things, but it hasn't made any difference.

I'm hoping someone might be able to listen to the recordings and see if they can identify the cause of the sound or have any ideas on how to fix it? I thought it was RFI then I should still be able to hear the problem when I connect the rhodes to a guitar amp? The technician has offered for me to take it back to him to have another look, but it's so big and heavy to move and it's an 8 hour round trip, so I'd hate to get there to discover that it is just RFI!

I've attached some audio clips taking a DI out of the headphones jack, but also the preamp out in case anyone has heard anything like it before!

https://soundcloud.com/chris-callaghan-music/sets/fender-rhodes-weird-noise-issue (putting a link instead because the mp3s are too big to attach)

[OZDOC]

Hi Chris, while I don't have my circuits for this here at the office, if you're able to get a clean signal from the accessory insert point, that suggests that it's not RF. The sort of noise you're hearing is much more likely to be a failing or loose component in the pre-amp or main amplifier. The noise you're hearing has a cyclic nature - something charging and discharging. Perhaps to do with the vibrato circuit. If it's a failing component it may be a capacitor. However, it could be a loose or failing component (like a valve or transistor) that is simply creating noise pulsed by the vibrato circuit.

This is going to be unrelated to the work that your previous tech has done - and possibly something that vibrated free during transport. There should be a local home organ repairer near you who makes house calls who can solve this problem quite quickly. It will almost certainly be a generic amplification problem and not a Rhodes specific problem.

[piano1071]

Did you try to pick up the signal directly from the harp?

[vanceinatlance]

It might be worth it to re-flow the solder on the 6 and 8 pin connectors mounted to each of the two amplifier boards of the power amp. These are notorious for causing issues like you are experiencing. This would also be in line with OZDOC's suggestion of possible loose components. You might want a tech to do it, bad soldering jobs can cause more damage if you are not familiar with soldering circuits.

[Tim Hodges]

It might be worth it to re-flow the solder on the 6 and 8 pin connectors mounted to each of the two amplifier boards of the power amp. These are notorious for causing issues like you are experiencing. This would also be in line with OZDOC's suggestion of possible loose components. You might want a tech to do it, bad soldering jobs can cause more damage if you are not familiar with soldering circuits.

Agreed, also some hot glue applied to the base of the connector and the PCB can give it some rigidity to reduce the risk of it happening again.

Speaking from experience in my early days I made a terrible mess of some of my gear by lifting tracks using a cheap soldering iron and lack of knowledge. A temperature controlled soldering iron is definitely the best investment and some 60/40 solder. Draper's 61478 40W soldering station is a very good model if you need one.

[vanceinatlance]

Great info Tim! I forgot about the hot glue support on those. That is really good practice. if you are already in there, you might as well make it so that it is less likely to occur again.
I don't like to admit it, but I have destroyed probably more than my fair share of traces due to lack of experience and use of cheap/incorrect irons and solder types. Way back when, of course, haha! Point is, you dont want to learn the hard way on your good, and or, hard to replace equipment!

[chris2886]

Thanks so much to everyone for their advice! I've been through some more troubleshooting for this, speaking to the guys that did the service recently, they did re-flow the solder and they still think it sounds more like an RFI or grounding issue. Weirdly, if I power the cab on without the harp unit plugged in (trying the cable disconnected at both the cab and then also the piano) the signal is clean, which I guess suggests that the issue isn't in the cab? But if I take the accessory out, the signal into another amp is clean - so I'm still stumped!

To take the signal directly from the harp unit - is that just unplugging the grey RCA cable and taking a signal from there into a DI?

I think I will definitely steer away from trying to solve anything myself and bring in a professional! Does anyone know someone local to Cambridge who might be able to help me troubleshoot? The guys who did the original service have offered to look at this again, but the round trip time is a lot - and I figure a local repair is probably cheaper than the fuel to get there and back!

[vanceinatlance]

One last thing you can try before dropping more money/effort into it is the two 1/4" aux input jack's on the power amplifier. They sometimes develop continuity issues and can cause wierd things.

My simplistic understanding of them is as follows:
When plugged in, they bypass the harp input and pass the signal from your 1/4 line.
When unplugged, the two metal contacts in the plug are supposed to reconnect and pass the harp signal again.
Simple thing you can try is just plug and unplug a 1/4 plug into each one and see if the sound changes or, more desirable, goes away.

[sean]

Good call Vance!

Plug a guitar cable from one jack to the other, and the problem might go away.  If it does, then you must either clean the jacks (works for a few months), or replace the jacks.

The problem is shown here:



Sean

[chris2886]

Thanks Vance/Sean

I tried patching the pre-amp out to in (on both L and R channels) and sadly no luck - still the same issue. I'm going to try taking the power amp out and just checking that all of the connections are in firmly. Other than that, I'm still stumped!

[OZDOC]

Going back through the things you seem to have eliminated:
1/ The signal from the harp (this is identical to the signal out on the name-rail) is clean.
So it is not the harp picking up radiated noise.
2/ The main Rhodes amplifier, separated from the Rhodes name-rail preamp, is clean and can amplify cleanly a signal from some other device.
So the power-amp is not faulty.
3/ This leaves the pre-amp circuitry in the name-rail pre-amp. The noise you are hearing is apparently being pulsed or modulated by the vibrato part of the pre-amp circuit.
So somewhere along the amplification chain in this pre-amp is a faulty device.
Examining the signal of a single note on an oscilloscope as it is passed from transistor to transistor should track down where the noise initiates.
If the noise is equally on the right and left channels of the stereo reverb then it should be in the mono section prior to this.
If the noise is only on one of the stereo outputs then that also narrows it down.

If the problem is isolated to the name-rail pre-amp, then this is the only part of the keyboard that you need to deliver to an electronics workshop to have this problem solved.