different gain from each output channel [UPDATED - NEW PICS]

[Abraham]

Ok this is my first post. I've been around for a while reading your posts and comments and I've finally decided to take part of this. While registering process was a mess, staff people was kind enhough to help me out, so now, finally, Im a proud active member to this community.

Ok thats enhough... I own a 1976 Suitcase MKI 73, I'll post some pics later, with some issues I'd like to comment here, just hoping any of you to share your knowledge in the matter. Rhodes are really uncommon here in Spain so I couldnt find any tech around. So that fixing stuff myself is the only option. I have managed to work out some things myself, but sometimes I got stucked... my biggest problem right now is that Im getting different gain from each output channel, being the  trem...err.."vibrato" on or not. It might be around 2db+ from left to right channel of the amp. I wonder if the problem comes from the amp or else from the pre-amp. Its hardly noticeable while playing but it becomes obvious when recording. Any hints for fixing this?

thank you!

[Miguel Tuna]

Hi, welcome to the board.

I experienced this a while back on my suitcase. Check both your amplifiers (circuit boards) side by side and see if there is some unsimilarity. On my case it was a different resistor in one of them.

Hope it helped

[Abraham]

SOLVED!!?? ...or may I say DIAGNOSED

Thanks Miguel for the hints, I have inspected both power amps but there wasn't any noticeable modification there...

I had never opened my Suitcase bottom until today... then I realized the problem was so obvious, as it turns that only one of the original speakers was left inside

It seems that replaced ones have different specs which makes one channel louder, not just trough the speakers but also in the line outs & headphone out, whenever the speakers are connected.

"Problem" solves as soon as you get those disconnected, then panning is back to correct levels. Now the question is, might this setup harm my main amp or power amps? Should I replace all speakers so they will be the same? Should I left them disconnected meanwhile?

Thank you!!

[Abraham]

btw are those fender speakers still available? are them sooooo expensive? which ones are a good replacement? It seems that I couldn't identify replaced ones so I will have to get them all replaced

[bumpyrhode]

The speakers pop up on ebay from time to time. I've even seen a set of 4 NOS.

Vintage vibe makes a replacement.

http://cgi.ebay.com/Vintage-Fender-12-Special-Design-Speakers-Lot-4-/180666078369?pt=LH_DefaultDomain_0&hash=item2a108994a1

http://www.vintagevibe.com/p-47-fender-rhodes-piano-suitcase-speaker-32-ohm.aspx

[pianotuner steveo]

Someone may disagree with me, but as long as both speakers are working perfectly, I do not think you will damage anything, but you obviously want a matched pair at some point. It will damage the amp if you run it with the speakers disconnected for a period of time....how long is too risky to gamble. Keep them both connected until you can find a replacement.

[Abraham]

Thank you guys for your kind answers!

I guess Im replacing the whole set so that they all will be the same. Sadly, ebay is not an option here because of customs, also vintage vibe replacement is EXPENSIVE, so I'll have to find another option locally... Do you guys think if I just replace the fender one with another matching ohms, signal will level correctly between channels? Fender one is supposed to be 8ohms while others are 32ohms, may the impedance be the only reason?? I dont really understand how impedance of speakers could affect panning on line outs/headphone out

Hey, I was planning to let them disconnected while I got them replaced, so you couldn't imagine how grateful I am to your warning!!

thank you!!

[bumpyrhode]

To my understanding, solid state amps aren't as sensitive to mismatched impedance
as tube amps are. However, essentially you are putting different loads on each
of the amps which could cause the difference in output.

I think the Rhodes amps want a 16 ohm load to function at peak. If the 32 ohm
and 8 ohm are hooked series that is a 40 ohm load. If they're hooked in parallel
it's a 6.4 ohm load. I myself wouldn't use them together because you don't know
what affect this will have on the amp. You don't want to chance turning a speaker
repair/replacement into a speaker and amp repair.

If you can't locate another speaker see if there are any speaker reconing shops in
your area. They might be able to recone and recoil the speaker to match the others.

Can you post the numbers stamped on the speaker?

[bumpyrhode]

The second chart on this page shows you how to identify the speakers.

http://www.svvintageamps.com/dating.php

[sean]

oops.  Hey Bumpyrhode = can you go back and edit your post.  You accidentally got your series flipped with your parallel while you were typing at your calculator.


If the two speakers were in SERIES, then the total nominal impedance would be 40 Ohms (and the current through both speakers would be exactly the same).

If the two speakers were in PARALLEL, then the total nominal impedance would be 6.4 Ohms (and the majority of the current would flow through the 8 Ohm speaker).


If you did indeed have a mix of 32-Ohm original speakers and new 8-Ohm replacements, then you might have a bad situation on your hands. 

It will always be safer for the output transistors to run the two speakers in series.

If the speakers are in parallel, and the output transistors see only that nominal 6.4 Ohm load, there will be lots of opportunities for too much current flowing through the output transistors.  The excessive current in the output transistors can damage the transistor, can kill the transistor, and could damage other components in the amp.  (Remember, lots of current causes heat, and the heat melts and fries things.)

This is not good.  If two 8-Ohm speakers were installed with no major change to the wiring scheme, you could have two 8-Ohm speakers connected in parallel to one channel, and that would provide only a 4-Ohm nominal load on the amp.  If the amp is designed for a 16-Ohm load, then high volume music (high current) can damage the output transistors.

=================

Running a transistor amp that has no output transformer with no speakers attached should be perfectly safe for long periods of time.  (The output transistors are very happy that no current will be running through them.)

(Running a TUBE amp is NOT safe without speakers connected.)

=================

The original factory wiring with 32-Ohm speakers is smart.

The reason that it is smart to run a pair 32-Ohm speakers in parallel is this:  if one speaker dies, then the music continues, and the amplifier still sees a high impedance load, so does not have to supply lots of current.  The music continues, because there is still one working 32-Ohm speaker connected to the amp.

=================

If two speakers are connected in series, then when one speaker dies, the music usually stops.  The amp is safe, because:
     1.)  If the failed speaker's voicecoil melted and created an open circuit, then the amp sees an open circuit.  No current flows from the amp, so the output transistors are safe and happy.
     2.)  It is really unlikely for the failed speaker's voicecoil to melt and create a short-circuit.  However, it is possible, and sometimes the voicecoil rattles loose and touches the metal sides of the gap in the magnet structure.  Even if this created a short circuit in the speaker, you would have the load from the other speaker that is in series with this shorted-out speaker.  This is certainly not a great situation, but it is not the most common way for a speaker to fail.

===============

I would feel safe running a pair of 8-Ohm speakers in series on each channel in a suitcase.
This would provide the amp with the nominal 16-Ohm load for which it is designed.
But I would lose a channel if any one of those speakers failed.

[bumpyrhode]

oops.  Hey Bumpyrhode = can you go back and edit your post.  You accidentally got your series flipped with your parallel while you were typing at your calculator.

Done. Thanks Sean. I used a web based impedance calculator and must have
transposed the info. Should have caught it myself.

[Abraham]

THANKS!! thanks thanks thanks!!!

Ill check back my setup later and I'll post some pics.
There are 3 unidentified speakers marked as 32 ohm and one original fender which impedance I have no clue of (but someone here said original setup was 32 ohm paralell). I have no further info on watts or any other details, nor I remember if connections were serial or paralell, Im just thinking impedance might not be the problem but watts or anything else. Ill check later, thanx for your comments

[Abraham]

Sorry I've been busy lately so I couldnt take pictures yet... my new findings point out that unlabeled speakers look exactly like original eminence speakers from factory... looks like someone didnt find an exact replacement for a broken one, so they used the "fender labeled" one instead... then we have 3 original + one replacement. I was mistakenly assumming the fender one was the original instead.

That means I "only" need to find a healthy vintage 12" 32 ohm eminence for sale in Spain...

to be continued...

[Abraham]

Here we go...

First of all, introducing my Rhodes!



These are both speakers, the fender one (which impedance or any other info I don´t know) labeled blue on the left, and one of the 3 unlabeled, which pretty seems to be original eminence from factory, on the right.



now some closeups so you can observe details...







all speakers are connected parallel, the channel with the fender one provides the higher output
any further info appreciated, thank you guys!!

[Abraham]

I just found this old topic I posted a while ago... it was my first post on this board so it feels kinda nostalgic!

btw I have done some progress and I didn't take the care to post here for anyone who might find this useful...

Those unlabeled speakers turned out to be original EMINENCE 32 OHMS speakers, to my knowledge they're REALLY hard to find because most rhodes cabinets used to mount different ones, blue labeled and different shaped instead.

BUT believe me or not I managed to find a working and matching pair over the net and someone kind enough for shipping those internationally (for a price). It wasn't cheap but I got those replaced. This solved big part of the problem but... one channel stills output louder than the other...

So we cant consider this totally fixed...

Now one of the channels suddenly started to fail eventually, and it turns back working when I got the amp restarted... this might be part of the same problem, and at this point I think I will take this to be looked over, but if anyone could point to something I should look at before moving this heavy thing to the repairs, Ill be glad to know

thank you