Weird problem here......

[djem]

I have a JCM 800 4-12. The top left speaker is noticeably louder than the rest of the speakers.

Does anyone have an idea why this is happening?

All answers are appreciated. Thanks in advance!

dj

[RevelationAmps]

are they all the same model/make of speaker? date range? any other reason why one speaker might be different?

otherwise maybe it's a wiring issue.

[djem]

are they all the same model/make of speaker? date range? any other reason why one speaker might be different?

otherwise maybe it's a wiring issue.

yup, all the speakers are the same and i believe it's wired correctly in series-parallel config.

can the way it's wired in the cab affect the output?

[Roccaforte Amps]

yup, all the speakers are the same and i believe it's wired correctly in series-parallel config.

can the way it's wired in the cab affect the output?





If it's wired correctly, and one speaker is louder than the others,
chances are the other three have cooked voice coils (larger impedence).
The one with the lowest impedence will take all the juice and be louder.

[djem]

Good point I will check the impedance of each speaker as well as the wiring. Man, I hope the voicecoils aren't blown. Sheesh!

[djem]

If it's wired correctly, and one speaker is louder than the others,
chances are the other three have cooked voice coils (larger impedence).
The one with the lowest impedence will take all the juice and be louder.

Finally got around to checking speaker impedences. My findings as follows:

Note: cab is a Silver Tolex 4-12 Jubilee (JCM 800) loaded with G12T-75's. All speakers were disconnected from the circuit and registered exactly 7.3 ohms. I was surprised to get such consistent readings.

Anyone have any ideas why the top left speaker is louder than the rest? I'm completely stumped. :confused:

An aside - I was disguted at the poor workmanship in the cab interior. tolex not trimmed evenly, glue marks on the plywood and what squeezed out of the wood joints, grill cloth not trimmed back properly and shitty light gauge hobby wire. Like, would it really kill them to use a heavier wire. What, like it may increase the cabinet's cost by a buck or two.

Anyway, if anyone has a clue to the 'loud speaker issue' please let me know.

Thanks man,

dj

[djem]

Comments?

[stevieray]

Describe exactly how it's wired. Sometimes talking it through will tip you off, or we'll see something wrong. Not suprised by the workmanship at all, or the wire gauge. It's a short run, so it's not a huge deal, but a better wire would certainly make an audible difference. Take this opportunity to clean it up yourself. You'll be a proud poppa and the next guy will thank you for it.

[Gumby]

Even though it "appears" to be wired correctly, there is a possibility that one of the runs of wire is defective. New wiring is cheap, but before you re-wire, check all connections and solder.

[djem]

Describe exactly how it's wired. Sometimes talking it through will tip you off, or we'll see something wrong. Not suprised by the workmanship at all, or the wire gauge. It's a short run, so it's not a huge deal, but a better wire would certainly make an audible difference. Take this opportunity to clean it up yourself. You'll be a proud poppa and the next guy will thank you for it.

Damn! And I screwed the back on again. Good tip. I'll check the wiring and perhaps make a new harness with 16 ga keeping the original for collectability purposes.

You're right, I'll be a proud poppa, but I won't be letting go of this cab since it's a Silver Jubilee Series that has the matching 50w head.

dj

[John Phillips]

Does it have push-connects on the speaker wiring? If so, get rid of them and solder the wires to the terminals properly. They often add extra resistance when they get a bit old and corroded - actually the connection between the crimp and the wire, rather than between the connector and the speaker terminal, usually.

While you're at it, strip back some of that 'hobby gauge' wire and have a look what's inside :).

You'll find the wire is almost as thick as the outer plastic - which is incredibly thin. In fact, it's very slightly (16 strand vs 14, of the same gauge) thicker than the 'proper' red and black wiring in the vintage cabs that everyone loves :eek:.

Thanks to Doug for this revelation - years ago I use to just junk the pink and grey stuff completely as well as the push-connectors, and never checked what it really was inside - now, I just cut off the connectors and re-use the same wire. It is plenty good enough.


You also need to check that the cab really is wired correctly - a year or two ago I bought an old Hiwatt cab, which had been 'creatively rewired' - at a quick glance it looked sort-of right, but on checking I found: two speakers in series with each other, out of phase; one speaker in parallel with those two; and the fourth speaker in series with that lot! Of course, the fourth speaker was taking most of the power for the whole cab, and sounded way louder than the others... so much so that it completely masked the out-of-phase problem.

[RevelationAmps]

Has this cabinet always sounded this way, or is this a new problem?

I guess it's possible for one speaker to just be notably more efficient than the others due to construction variances and tolerances. Speaker efficiency has to be +/- a dB or so so if three were -1dB and one was +1dB you'd notice... But I kind of doubt it.

About the wiring, I kind of disagree about soldering. I think you're more likely to do damage to the speaker through overheating the voice coil or the wires leading to the terminals by soldering directly to the speaker. With the correct tool (which pretty much nobody has except for production line), a fast-on connector can be crimped air-tight and get somewhat of a cold-weld with the wire and has lower resistance than a soldered joint and is also less apt to contamination and oxidization. Always conductor-to-conductor contact is going to be lower resistance than interleaving the interface with solder but we're talking probably milliohms here, hardly makes a difference.

Anyway, one way to test to see if it could be related to wiring is to reverse the wiring harness so that the upper speakers are connected where the lower ones were or something like that, then see if the "louder" speaker changes rows.

[John Phillips]

About the wiring, I kind of disagree about soldering. I think you're more likely to do damage to the speaker through overheating the voice coil or the wires leading to the terminals by soldering directly to the speaker.I can't believe that's possible... could you really supply 25W or more to the voice coil down the flexible braid - which itself is pure copper or some alloy of it, and so immune from damage at soldering temperatures? I don't think so.

With the correct tool (which pretty much nobody has except for production line), a fast-on connector can be crimped air-tight and get somewhat of a cold-weld with the wire and has lower resistance than a soldered joint and is also less apt to contamination and oxidization. Always conductor-to-conductor contact is going to be lower resistance than interleaving the interface with solder but we're talking probably milliohms here, hardly makes a difference.I've come across many examples of crimp connector corrosion causing enough extra resistance to be easily measurable (several ohms), and in at least one case, actually breaking the circuit completely.

Push-connectors are top of my list of Bad Ideas in speaker wiring for several reasons... I also think they can affect the tone far more seriously than any difference between wire types or gauges, assuming you're not talking about really thin stuff.

Anyway, one way to test to see if it could be related to wiring is to reverse the wiring harness so that the upper speakers are connected where the lower ones were or something like that, then see if the "louder" speaker changes rows.That's about the one advantage of push-connectors, it's quite easy to do that :).

[djem]

While you're at it, strip back some of that 'hobby gauge' wire and have a look what's inside :).

You'll find the wire is almost as thick as the outer plastic - which is incredibly thin. In fact, it's very slightly (16 strand vs 14, of the same gauge) thicker than the 'proper' red and black wiring in the vintage cabs that everyone loves :eek:.

Thanks to Doug for this revelation - years ago I use to just junk the pink and grey stuff completely as well as the push-connectors, and never checked what it really was inside - now, I just cut off the connectors and re-use the same wire. It is plenty good enough.

I'm a little confused. I was getting the impression that you agreed that the thin wire was less desireable, but then you say to just cut off the connectors and re-use it.

What I intend to do is to properly rewire the cab using 16 ga. speaker wire soldered to the terminals. I will keep the old wiring harness just to preserve the original components of this Silver Jubilee 4-12. Who knows, one day I may sell the head and cab so I want to save all the original parts.

Anyway, please explain since I find it a little confusing/contradictory.

You also need to check that the cab really is wired correctly

Good point. I assumed that a series-parallel config. is simple enough and I didn't even bother because I thought, "who'd be dumb enough not to......", but I know the cab was opened up before and someone may have switched connections without knowing the implications.

'Leave no stone unturned'

Thanks for the input everyone. Will report back.

Doug

[djem]

Finally got around to fixing a bunch of gear this weekend.

Fixed my MXR Distorion +
Fixed my Ibanez Analog chorus

Most importantly, my Jubilee cabinet is now working properly.

Pulled all the wires off and just plugged them all back in a proper series-parallel scheme. Plugged her in to a 50 watter and behold....even sound distribution from all 4 cones! Before I did that, I isolated each speaker and played through it to make sure it was fine. And they all were.

To all who suggested that it was wired improperly, you were 100% correct. Guess the guy who had it before me messed with the wiring.

Thanks for all your suggestions.

dj

[Whiskeyroad]

shitty light gauge hobby wire. Like, would it really kill them to use a heavier wire.


Hmm.. whats the age? If no speakers are cooked it would have to be the *#!@ wire....

[dbx]

Finally got around to fixing a bunch of gear this weekend.

Fixed my MXR Distorion +
Fixed my Ibanez Analog chorus

Most importantly, my Jubilee cabinet is now working properly.

Pulled all the wires off and just plugged them all back in a proper series-parallel scheme. Plugged her in to a 50 watter and behold....even sound distribution from all 4 cones! Before I did that, I isolated each speaker and played through it to make sure it was fine. And they all were.

To all who suggested that it was wired improperly, you were 100% correct. Guess the guy who had it before me messed with the wiring.

Thanks for all your suggestions.

dj

I get alot out of reading these types of threads with a positive resolution...sometimes the solution is not to throw more $$$ at the problem. First step is always a thorough check out, checking connections and whatnot, revalidating assumptions along the way. Good to see you got it sorted out...

[djem]

I get alot out of reading these types of threads with a positive resolution...sometimes the solution is not to throw more $$$ at the problem. First step is always a thorough check out, checking connections and whatnot, revalidating assumptions along the way. Good to see you got it sorted out...

Exactly. Take a step back and assess the situation.

"out here we is stoned - immaculate..."

[John Phillips]

I'm a little confused. I was getting the impression that you agreed that the thin wire was less desireable, but then you say to just cut off the connectors and re-use it.

What I intend to do is to properly rewire the cab using 16 ga. speaker wire soldered to the terminals. I will keep the old wiring harness just to preserve the original components of this Silver Jubilee 4-12. Who knows, one day I may sell the head and cab so I want to save all the original parts.

Anyway, please explain since I find it a little confusing/contradictoryWhat I said was that the 'thin' wire appears less desirable because it looks thin, but that if you actually check the wire - not just the plastic coating - it's actually marginally thicker than the 'desirable' vintage wire. It's only that the plastic covering is incredibly thin on the new stuff that gives the impression of poor quality. There is no need to rewire the cab with heavier stuff.

I fully admit that it was only after Doug Roccaforte pointed this out that I checked it properly too - the optical illusion of the thinner wire is so strong that it's hard to believe the core is actually larger.

I assumed that a series-parallel config. is simple enough and I didn't even bother because I thought, "who'd be dumb enough not to......", but I know the cab was opened up before and someone may have switched connections without knowing the implications.Either that, or it was due to a poor connection at one of the push-tags, which by disconnecting and reconnecting to check the impedances, you cured without knowing it. It is worth getting rid of these little pieces of junk and soldering the wires on. (I don't believe it would affect the value of the cab in any way.)

It's entirely likely that it was wired incorrectly though - it's quite common. A couple of years ago I bought an old Hiwatt cab which had two replacement speakers fitted (at different times I think) and a combination of 'interesting' wiring - the two original speakers were wired in series but out of phase; one replacement was in parallel with those two, and the second (the weakest speaker in the cab) was in series with all three! It's a miracle the last speaker didn't blow again, since it was taking 60% of the total power for the cab. Amazingly, the cab didn't even sound that unbalanced like that either, although the last speaker was louder. I suspect you may have had something like that.

[teleamp]

Either that, or it was due to a poor connection at one of the push-tags, which by disconnecting and reconnecting to check the impedances, you cured without knowing it. It is worth getting rid of these little pieces of junk and soldering the wires on. (I don't believe it would affect the value of the cab in any way.)




+1

Mike

[djem]

What I said was that the 'thin' wire appears less desirable because it looks thin, but that if you actually check the wire - not just the plastic coating - it's actually marginally thicker than the 'desirable' vintage wire. It's only that the plastic covering is incredibly thin on the new stuff that gives the impression of poor quality. There is no need to rewire the cab with heavier stuff.


John & all others who are interested......

Agree on soldering the connections. I have done that to all my combos. Other than the extra cost, why not use heavier cable within the cabinet? The only reason why I ask is that I have a 16 ga. speaker cable connecting the cab to the head. Why not carry that inside in order to decrease resistance associated with a smaller wire?

From your experience, will there be an perceptable difference using heavier ga. wiring within the cabinet?

Good discussion.....

[John Phillips]

Apart from cost, and (minor) hassle, no reason at all not to.

I don't think it's necessary, but not that it would be in any way a bad idea. It might improve the tone too, although my personal experience is that it's marginal at best, and possibly not audible... some people hear it otherwise though. I do think it makes a difference for high-power applications, but at the currents in a guitar cab - a maximum of about 2A for a 50W amp into 16 ohms - I think the standard wiring is plenty.

Personally I would replace the 75s with better speakers before worrying about the quality of the wire ;).


(I must get around to properly testing some different gauges of cable with a switching rig and see if I find any difference...)

[djem]

Apart from cost, and (minor) hassle, no reason at all not to.

I don't think it's necessary, but not that it would be in any way a bad idea. It might improve the tone too, although my personal experience is that it's marginal at best, and possibly not audible... some people hear it otherwise though. I do think it makes a difference for high-power applications, but at the currents in a guitar cab - a maximum of about 2A for a 50W amp into 16 ohms - I think the standard wiring is plenty.

Personally I would replace the 75s with better speakers before worrying about the quality of the wire ;).


(I must get around to properly testing some different gauges of cable with a switching rig and see if I find any difference...)

Yes, it would be nice to switch the 75s with nicer speakers, but there is a financial issue to consider - my wife.

Not sure if you saw my post in the Amps & Cabs forum, but I recently came across some old Celestions that I bought a few years back from a stusio friend. He just wanted to get rid of them and all he wanted was $50 - $75. I couldn't get anyone to tell me exactly what these speakers were on this forum, but found the answer out at Weber's Speakers BBS. Definately not going to power these up with a 50 watter.

Here's the link:

http://www.thegearpage.net/board/showthread.php?t=226526

I'm considering finding an empty 2x12 or making one this summer.