Any fix on this 4343?

[pyonc]

Hi,

My audio gear is 4343, with Mcintosh C29 preamp and Marantz power amp.
Initially I didn't notice this, but as time went by, I suspected some sort of
difference in loudness of the right and left speakers. And only today I concluded that
the sound from the left speaker was a bit louder and clearer than the right one.
I heard the same difference when I played LPs from the 60s and 70s, or CD reissues from that era, and even modern CDs where stereo recording is almost perfect.
I reversed the speaker mode selector (left to right, right to left), and the result was the same.:banghead:
The right speaker was a bit weaker in loudness and clarity than the right one. What do you believe is the problem here?
Do I need to bring the pair to a JBL technician for thorough check? Or is there anyting I can do some check by myself?
Thanks a lot for your advice.

[rusty jefferson]

Try reversing the speaker wire connections on the amplifier. See if the condition stays or moves to the other side.

[Audiobeer]

Theres all kinds of things you can try first to see if it's an easy fix. I know you checked the reverse stereo mode on th C-29 but did you check the cable itself and the connections? The next thing I would try is rapidly rotating the L-pads on the weak speaker back and forth to see if that is the issue. If it's still weak then you may want to set your balance at the 12 o'clock on the preamp and use the tone controls on your C-29 to see if you can Isolate which driver is having the problem, start with de-emphasizing everything but the Low frequency band, then try the mids and then the high frequency. This should help you isolate which driver is the culprit if in fact it is a driver.

[pyonc]

Try reversing the speaker wire connections on the amplifier. See if the condition stays or moves to the other side.

Thanks, Jim. I tried this, and the condition stayed the same. Maybe I'm gong to use play the audio test CD.

[pyonc]

Theres all kinds of things you can try first to see if it's an easy fix. I know you checked the reverse stereo mode on th C-29 but did you check the cable itself and the connections? The next thing I would try is rapidly rotating the L-pads on the weak speaker back and forth to see if that is the issue. If it's still weak then you may want to set your balance at the 12 o'clock on the preamp and use the tone controls on your C-29 to see if you can Isolate which driver is having the problem, start with de-emphasizing everything but the Low frequency band, then try the mids and then the high frequency. This should help you isolate which driver is the culprit if in fact it is a driver.

Thanks for your advice. 'Rotating the L-pads'? That seems too technical to me, though.
C29 doesn't have the 'tone' controls to isolate the driver, though.
Looks like the problem comes from mids and highs, not the lows
because that's where I feel the difference when I played an instrumental jazz CD or LP with saxophone or trumpet player.

[Krunchy]

'Rotating the L-pads'? That seems too technical to me, though.

Its not really, just just rotate them back and forth (clockwise & counter clock wise) a few times & see if that impacts the sound emanating from the drivers.

[Robh3606]

Try turning the biamp switch on and off a couple of times. The contacts tend to oxidize just like the l-pads do. It is located on the back of the speaker where the terminals are.

Rob:)

[pyonc]

Its not really, just just rotate them back and forth (clockwise & counter clock wise) a few times & see if that impacts the sound emanating from the drivers.

Thanks. I've never done this before, though I assume my previous owner did so.
Do you have to take out the front lower baffle to do this?:blink:

[JeffW]

Thanks. I've never done this before, though I assume my previous owner did so.
Do you have to take out the front lower baffle to do this?:blink:

They're not talking about physically rotating the L-Pad in the cabinet, they are talking about adjusting the L-pad a few times through its adjustment limits. Like turning the volume knob up and down on a receiver a few times.

Does your 4343 have three little adjustments on the front of the baffle like in this pic? That's the adjustments.

http://www.lansingheritage.org/images/jbl/specs/pro-speakers/1977-4343/page1.jpg

[pyonc]

They're not talking about physically rotating the L-Pad in the cabinet, they are talking about adjusting the L-pad a few times through its adjustment limits. Like turning the volume knob up and down on a receiver a few times.

Does your 4343 have three little adjustments on the front of the baffle like in this pic? That's the adjustments.

http://www.lansingheritage.org/images/jbl/specs/pro-speakers/1977-4343/page1.jpg

Thanks a lot for enlightening me on this. :applaud:
Yes, definitely my 4343 has that adjustment levels on the front.
Currently, Ultra High, High, Mid volumes on left and right speakers are set at the same levels. What if I have the same weaker sound from the left speaker despite the matching level adjustments?

[grumpy]

Seriously. Find a large flat-bladed screwdriver. Turn the "level adjustment" L-pads up
and then down, several times... listening for scratchy sounds from the speaker (while
playing music) or for jumps in level... either indicates an eventual need for replacement
of the L-pad behind the front panel.

Sometimes you can get away with just finding a place where the L-pad is happy (not
oxidized, burned, or otherwise damaged in a particular area of its rotation. They wear out.
Same with the Bi-amp switch in the back, near the speaker wire terminals. Turn it back
and forth several times... it might scrape off some crud or oxidation that has built up
over time (just put it back when you're done).

Have you figured out which driver (or all of them?) is sounding less loud?

[JeffW]

The contacts inside the L-pad can become a little oxidized over time, affecting the level of the driver associated with it. That's why, with the L-pads on the 2 speakers set to the same level, the actual resistance across one L-pad might be considerably different than the other. By rotating the L-pad through its range of adjustment, you can often restore the contact area by breaking loose the oxidation/dirt. That's what's behind the suggestion to rotate the L-pads through their entire range a few times.

[pyonc]

Seriously. Find a large flat-bladed screwdriver. Turn the "level adjustment" L-pads up
and then down, several times... listening for scratchy sounds from the speaker (while
playing music) or for jumps in level... either indicates an eventual need for replacement
of the L-pad behind the front panel.

Sometimes you can get away with just finding a place where the L-pad is happy (not
oxidized, burned, or otherwise damaged in a particular area of its rotation. They wear out.
Same with the Bi-amp switch in the back, near the speaker wire terminals. Turn it back
and forth several times... it might scrape off some crud or oxidation that has built up
over time (just put it back when you're done).

Have you figured out which driver (or all of them?) is sounding less loud?

Thanks for your kind advice. I'll do so as advised this evening. By the way,
when I listened closer last night, mid-driver on the left speaker seemed to be the source of the less loud. Let me double check it this evening, and report back to you.

[pyonc]

The contacts inside the L-pad can become a little oxidized over time, affecting the level of the driver associated with it. That's why, with the L-pads on the 2 speakers set to the same level, the actual resistance across one L-pad might be considerably different than the other. By rotating the L-pad through its range of adjustment, you can often restore the contact area by breaking loose the oxidation/dirt. That's what's behind the suggestion to rotate the L-pads through their entire range a few times.

Thank you! I now understand more about all this talk about L-pad. Let me carry out your suggestion when I get back home this evening, and report back to you about the outcomes.:)

[badman]

Thank you! I now understand more about all this talk about L-pad. Let me carry out your suggestion when I get back home this evening, and report back to you about the outcomes.:)

It sounds like you're very non-technical. You can simply increase the clockwise rotation of the L-pad for the midrange to raise its loudness. You should rotate them per the other members, though, and remember to set them back to approximately where they were before you did this excercise. Check to see if they're set approximately the same place on both speakers. Wiggle the biamp switch.

[grumpy]

Wiggle the biamp switch.

"wiggle" meaning turn it the direction indicated on the rear input terminal panel, until
it clicks into position, then back, ... repeat several times.

Here are pictures (input terminal panel, crossover, switch, and L-pads) to help guide:
http://www.audioheritage.org/vbulletin/showthread.php?8919-JBL-4343-rebuild-and-configuration-project&p=119858&viewfull=1#post119858

It's OK for the L-pads to not be exactly the same on both speaker front panels (L vs R),
but an extreme mismatch -might- indicate other issues. Narrowing it down to a single
driver (possibly) does help define the problem, so you're headed in the right direction.

[pyonc]

"wiggle" meaning turn it the direction indicated on the rear input terminal panel, until
it clicks into position, then back, ... repeat several times.

Here are pictures (input terminal panel, crossover, switch, and L-pads) to help guide:
http://www.audioheritage.org/vbulletin/showthread.php?8919-JBL-4343-rebuild-and-configuration-project&p=119858&viewfull=1#post119858

It's OK for the L-pads to not be exactly the same on both speaker front panels (L vs R),
but an extreme mismatch -might- indicate other issues. Narrowing it down to a single
driver (possibly) does help define the problem, so you're headed in the right direction.

Thanks a lot, grumpy, for your kind guidance. I tried all the ways our forum members suggested to me, rotating the levels and wiggling the bi-amp switch. I heard some little scratchy sounds when rotating the left speaker's Mid toward +3 initially, and then it disappeared later after several rotations. My initial impressions are the sound from the left speaker got better. Yet, I have yet to test more for more accurate judgement. Instead of Mcintosh preamp, I'm going to try with an Adcom preamp this time, plus Adcom power amp. I suspect the current Mcintosh C29 might have something to do with the weak loudness of the left speaker, too. Or maybe I might be a little overly sensitive...

[grumpy]

glad to help (or at least hope it's of some help :))

can you put the C29 or adcom in mono mode? (a switch for that on the front panel)

It makes it easier to judge balance in mono with your head midline between the speakers...
close as you like... point them toward each other even. Turn the other L-pads all the way down
and concentrate on the drivers in question. FM inter-station noise makes a nice signal.

Note that speaker placement in a room can affect perceived L/R balance, but if this just
started and position of the speakers hasn't changed, then toss that idea.

[pyonc]

glad to help (or at least hope it's of some help :))

can you put the C29 or adcom in mono mode? (a switch for that on the front panel)

It makes it easier to judge balance in mono with your head midline between the speakers...
close as you like... point them toward each other even. Turn the other L-pads all the way down
and concentrate on the drivers in question. FM inter-station noise makes a nice signal.

Note that speaker placement in a room can affect perceived L/R balance, but if this just
started and position of the speakers hasn't changed, then toss that idea.

Thanks a lot, grumpy. Yes, it does have mono mode. I only tried using mode selector switch, namely STEREO or STEREO REVERSE. There're three MONO modes, namely MONO (L+R), L+R to L, L+R to R. You must refer to this modes, right? Let me try them tomorrow and give you some feedback, too. :)

[grumpy]

Yes, "MONO (L+R)" is what I would suggest.

[pyonc]

Yes, "MONO (L+R)" is what I would suggest.

Thank you, grumpy. I've found strange result on this after playing audio CD test. I played it to check PINK NOISE (-12db) for speaker balance. With the volume of my preamp at its lowest level, I played the test CD, and I found the ultra-high, high, and mid of the left speaker very weak in PINK NOISE, compared with the right speaker where I could a very strong PINK NOISE. :banghead: When I raised the volume a little bit, I started to hear a little bit stronger and louder PINK NOISE from the left speaker, but it was still way much lower in loundness, compared with the pink noise from the right speaker.

[grumpy]

1) many volume controls don't have good balance at their lowest position(s), so turning it
up a bit was a good idea.

2) did you ever try that other pre/amp set? or swapping the speaker cables L<->R?
... basically, anything that's in-line between the source (CD player) and the speaker
drivers themselves.

if so, it's probably worth having someone go over the internal wiring and crossover, as it's
very unlikely that multiple drivers would all lose sensitivity at the same time.

[grumpy]

Ah... I see you've "fixed" the speaker problem :applaud::

http://www.audioheritage.org/vbulletin/showthread.php?29209-How-to-fix-4343-speaker-unbalance&p=293243#post293243

Probably a good time to close this particular thread.

[pyonc]

Ah... I see you've "fixed" the speaker problem :applaud::

http://www.audioheritage.org/vbulletin/showthread.php?29209-How-to-fix-4343-speaker-unbalance&p=293243#post293243

Probably a good time to close this particular thread.

Thanks, grumpy. :) I think I have to settle for it for now, although the problem hasn't been solved complely.
I started a new thread on this, hoping someone in this forum mighth have similar experiences and share with me the solution...