Korg Forums

evandepol · Joined: 28 Oct 2006 Posts: 15

I just bought an EMX (ebay) and it seems to be in fine condition.

I ran into a problem, would like to hear from the experts hear what you think of it. Thanks in advance for the responses.

The problem is that the right channel is much louder (4-5 dB) than the left channel. This is apparent in main L/R outputs, as well as in the headphone out. If I turn the master volume completely down, then the right channel is still audible (loud even). It does not really matter if the tube gain is all the way up or all the way down (although when it's up, the volume difference is less noticable). Left channel also appears somewhat distorted (while right is clean). When assigning parts to outputs 3/4 they sound clean.

What is you diagnosis? Is this likely a faulty unit, or could this be a tube problem?

Thanks,
Erik

Yatmandu · Full Member Joined: 18 May 2008 Posts: 162

Before I replaced my EMX tubes, both channels would leak even when master volume was zero (I would hear some sounds). After I changed my tubes to JJ's, there was no more sound at zero. (Also, the JJ's didn't distort the sound like the old tubes).

I think you have a bad right channel tube/and maybe the trim pot for the tube is off too. Try playing through the 3/4 outputs (which are not processed through the tubes). You should not hear 4-5 dB diff through those. If you swap the two tubes, you should probably hear the L-channel go 4-5dB louder.

Best solution (once youi determine that it is indeed the tubes at fault) is to pick up some JJ's (I was able to get some locally at $10 a pop).

evandepol · Joined: 28 Oct 2006 Posts: 15

Hello Yatmandu. Thanks for the reply.

No "leakage" indeed when playing through 3/4.

I tried swapping the tubes, and I get the same result (right channel still much louder than left channel, and even with master volume all the way down there is a lot of noise - more than what I would call crosstalk or crossover). So I'm not so sure just replacing tubes is going to make a difference. I'll give the pots a try though.

I heard there is a service manual floating around somewhere..

If other have suggestions to try or helpful pointers I'd be very grateful.

Ruso · Posted: Mon Dec 01, 2008 5:12 pm Post subject:

The electribes have two parts to calibrating tubes. There are the two pots next to the tubes but also the operating system itself has a setting which you can tweak. Obviously since it affects all channels I assume that it's the internal setting.

Also I will say that all three of my electribes had that problem, also both before and after swapping tubes. I actually didn't notice much of an audible difference and never bothered fixing it (because it's a pain in the ass and requires a special cable to be made) and that's if I'm right about the problem.

Search electribe-forum.com for the service manual, look at the end of it where they talk about tube calibration after main board replacement.
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evandepol · Joined: 28 Oct 2006 Posts: 15

Thanks for the observations. Note that 3/4 are NOT affected, it's just headphone out and L/R. And left channel definitely distorts, even with tubes off, so that's no good.

I just got the schematics and parts for the cable, so once I build the cable I'll give that a try next..

evandepol · Joined: 28 Oct 2006 Posts: 15

jerseykorg · Joined: 02 Oct 2008 Posts: 35

Oh, this is interesting. I just assumed I was losing the hearing in my left ear. Haha.

evandepol · Joined: 28 Oct 2006 Posts: 15

Hehe

.

Well, my problem returned, so I did some more troubleshooting.
Result: if I apply pressure on the main pot in a certain direction I can make the problems go away.

So it seems to be some mechanical problem: either a broken pot (my guess) or a bad solder job.

Time to look and see what's inside...

Tarekith · Posted: Mon Dec 08, 2008 4:02 pm Post subject:

Keep us informed of what you find. I've never been able to get my channels balanced dead on no matter what. I can get them to within 1-2dB, and that's fine for my uses, but no closer.
_________________
Erik M.
InnerPortalStudio.com - electronic music mastering

evandepol · Joined: 28 Oct 2006 Posts: 15

Got a replacement main volume pot (Alps RK12L12C0A0G, bought it a Mouser). It's a little different than the pot it replaces (A Bourns PTV112): it has a longer shaft that needs to be trimmed, and the curve is logarithmic instead linear (which is fine for a volume pot).

This is what I did:
To get access, remove all knobs (they pull right off). Undo the silver star screws. Lift of the aluminum panel. Remove the 4 silver screws around the tube window. Lift out the front panel (knobs and all) and flip it to the left side. On the underside of the front panel, remove the 20 or so black screws that hold the PCB to the ABS subframe. Slide off the white 'collar' that locks the flexible 'tape' from the ribbon controller. Now lift out the PCB and flip it to the right, and you'll have access to the pots.

Getting the old pot out was simple enough. Getting the new one in was a little fiddly but it worked out in the end. If you're not proficient with a soldering iron, get a friend well-versed in the art to do it for you, or take it in for service.

The unit works perfectly now. No more imbalance problems. Can be muted all the way. No more distortion on the left channel. Mission accomplished.

Ruso · Posted: Tue Dec 16, 2008 1:27 am Post subject:

great to hear, congrats on your fix Wink

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Douglas · Joined: 05 Mar 2009 Posts: 13 Location: China

maybe the volume register's problem.

Laxiton · Joined: 05 Sep 2011 Posts: 8

@evandepol In long term, was your fix solid and the problem stayed away? Am thinking of doing the same thing using the same potentiometer. They do charge a lot of money to send it. The thing itself is neglectable but the shipping is over 20€ (mouser). Interesting for bulk amounts but not so for single parts.

evandepol · Joined: 28 Oct 2006 Posts: 15

Hello Laxiton.

Since you use Euros as currency, I'm going out on a limb and assume you might be from Europe Smile

. Rather than ordering from Mouser in the US, why not locate an ALPS dealer in Europe? Alps has a distributor locator at http://www.alps.com/e/common/contact_us/wheretobuy/europe.html.

Check for instance RS (which operates worldwide, including most European countries). For instance for the UK: http://uk.rs-online.com/web/p/products/7293697/?searchTerm=Alps+RK12L12C0A0G

Hope this helps.

Laxiton · Joined: 05 Sep 2011 Posts: 8

Wow thanks a lot! I found a Belgian division of that same RS, in the checkout I didn't even see any charges?! And I was just at the last confirm page - I'm sure it's a lot better Smile

Just one more question, since you seem to know what you're doing, I can solder the potentio just fine,

but what if I ever just wanted to bypass the whole volume pot.. I imagine this should be possible, and a way to check if it's really the pot that gives the unequal volume. A matter of connecting the right pins, right? and you're at full volume (the only way I would use it anyway - it goes into a mixer).