Stereo question- lost in the 70's

[JLR]

Well, it appears that I may have a stereo issue. Talking about a a Clarion CMD4 on the bridge connected to a Clarion amp driving four speakers plus a sub woofer. Unfortunately, the last time I knew anything about stereos was in the '70's. Here is the issue. I have a discernible hiss/static that comes through on one set of speakers ( rear channel) and the sub woofer speaker. The other channel of two speakers is crystal clear. As best as I can surmise, I might have an output problem from the pre amp on the head unit, and output problem on the powered leg coming from the amplifier that only drives the three affected speakers, or, the gain on the amplifier is set too high/low. The cost to replace the head unit and the amplifier is under $500 so I do not want to spend a great deal of time finding out what the problem is unless, of course, unless it is a simple gain adjustment or something equally as easy. Any ideas what might be causing the audible static on this channel? By the way, it happens no matter what input source is selected and is not a noise interference that needs a noise filter like in the old car stereos. As always, any ideas are welcomed.

 

[Genesis]

It is probably the head unit if it is not impacting all four channels (only two of them) but IS impacting the sub.

You have (I presume) the CMD4 (same unit I have on my little 23 center console, incidentally) driving a POWERED sub and one 4-channel amp. I also assume the sub is taking signal from a separate feed -- if it's taking its feed from the same channel that has the noise on it, then it could be the preamp output there.

Assuming the sub and speakers are driven off separate RCA cables I'd change those FIRST. There may be a bad ground in the feed cables but for it to hit two cables at once is unlikely -- albeit possible.

If not, the odds are it's the head unit. Easiest test is to grab a MP3 player and a stereo-to-RCA cable and jack it into the power amp and see if the static/hiss disappears and you get clean audio. If so you know where the problem lies.

(I'm assuming you visually inspected the speakers, especially if they're outside! I generally get two years, maybe three out of the ones that I have in my center-console before the surrounds turn into dust and need replacement.)

 

[JLR]

Thanks Karl. I do need to investigate further. Yes, it is the CDM4. I need to determine whether the separate amp is only driving the subwoofer or the subwoofer and the rear channel. If the latter, I would suspect the amp. I will swap cables and check speakers as well. Unfortunately, it is not that easy to access which is why I am a little reluctant to spend too much time chasing the problem. Any possibility that the gain on the amp may be too high (or low)?

 

[Genesis]

Probably not.

One common setup if you don't have a separate sub output (I will go check my CMD4 later this morning and see what's on the back of it -- mine is easily accessible on my CC) is to drive the sub off one of the sets of SPEAKER outputs. It should be the fronts although it doesn't matter all that much if you don't have time alignment (and the CMD4 does not.)

Hiss that is associated with a channel's input attenuation being turned up too far would also result in that channel (E.g. the front's) being grossly out of balance in terms of volume and they would clip earlier as well. If you have the noise but not the overly loud output that's probably not the issue.

It's possible your power amp has lost part of an output stage which will produce noise and distortion on that channel. Depends on the design of the amp; a push-pull design that loses one of the paired output transistors open will produce both noise and a "scratchy" sound along with a materially lower sound level because only half the waveform is being driven.

 

[JLR]

Cleared many a dirty pot (which frankly is what is sounds like) in the 70's by just rotating the dial a few times. I long for the days of tube amps.

 

[season]

JLR,
I would check to see how many channels your amplifier has. Most marine subwoofers are not amplified internally and require a sub amp. 5 channel amps are the most used for a four speaker plus sub setup. Or it could be a four channel amp plus mono sub channel amp. This requires that either the head unit, which would have to have a "sub output" to feed the sub amp channel plus two pairs of RCA outputs to go to the four speaker channels on an amp. If the amp is a 5 channel amp there will be an internal crossover to separate the bass info to the sub channel and the high pass info to the four speaker channels. If you have this setup, your problem could also be in that crossover. There will be a crossover on/off switch which you can turn off. Your sub will try to play all of the music like the rest of the speakers but if the hiss and distortion goes away; it was the amp's crossover causing the issue. Genesis is right when he says bypassing the head unit with a signal fed directly into the amplifier will prove that the problem is either in the head unit or the amp. If the problem goes away it is the head unit, if it remains it is the amp.
Genesis if you would like to PM me I have a suggestion to fix your longevity issues with your CC speaker setup.
Thanks
Randy

 

[JLR]

Thank you. I will check to amp crossover and see if that is the problem.

 

[JLR]

Turns out that the input selector slide on the amp which controls the rear channel speakers and the subwoofer was dirty. Once set to mono for all three speaks, problem solved. Major popping sound when slide is touched or set properly but once set all the way over, all seems well. I am not inclined to fiddle with it any more as the speakers do not appear to like it when the slide is touched/moved.

 

[season]

JLR<
I checked with one of my tech support guys to see if he agreed with me on this and he does. Pick up a spray can from Radio Shack of TV Tuner cleaner with the little straw. Turn off the system and spray into the opening around the switch and then slide the switch back and forth a good 20 times or so. Give it about 15 minutes to completely dry out and turn on the system and see if your "contact problem" is solved. If not it could be in the circuit that the switch feeds into. Of course, you could just listen to old Beatles and Elvis in Mono. LOL

 

[Genesis]

That'll almost-certainly work, or just moving it back and forth a number of times may clean it as well. Modern (e.g. built last 20 years or so) contacts are intended to be self-wiping, provided they're used.....

 

[JLR]

Thanks. Will do. All is working fine now but exercising the switch is probably a good idea. Believe it or not, I just figured out how to turn off the amp (do not turn on the pre amp--duh) in order to be able to do it. Missed that simple step before.