Pop goes a channel: SOLVED!

[jimbo7]

Until I get my other T24 built, I've been running a sub and top on one channel (2). From the amp it goes to the sub, then to the top. I run the other channel (1) with just the top. Both sub and top are 8ohm. There is a crossover in both.

I never push it hard at all since I know this is not recommended. If I wanna crank it up, I seperate it to the sub on one channel and a top on the other (both 8ohms). Now channel 2 only puts out very faint sound if amp is cranked up (only tried that once). I've tested with other cables/connectors/speakers and it seems to be dead.

Here's the path: music -> mixer -> Carvin DCM1000 channel 1 -> Carvin PM15 channel 2 (no sound) -> T24 -> Carvin PM15

Currently it's sitting unplugged to drain the caps some off before I open it up and kill myself. Any idea what could be wrong?

FYI - This will be my setup till I get some funds to build the second T24 and SLA's. Then I'll get a crossover, DSP, and another amp

[Grant Bunter]

Just making sure we're on the same page.

It doesn't matter which Carvin top you hook up to channel 2, there is pretty much no sound from that channel?

And you run in mono from your mixer, so you parallel the signal from the mixer to the amp to provide signal to both channels?

[jimbo7]

Just making sure we're on the same page.

It doesn't matter which Carvin top you hook up to channel 2, there is pretty much no sound from that channel?

And you run in mono from your mixer, so you parallel the signal from the mixer to the amp to provide signal to both channels?

Any speaker I use puts out no sound
Pre-recorded music (pc,ipod,ect.) input to mixer -> amp -> speakers. Both channels are recieving a stereo signal, but channel 2 was split between a top and sub and channel 1 was a top playing full-range

BTW, the bridge is working still, too.

[Grant Bunter]

Ok, so what happens if you swap sub and top to channel one (and solo top to channel 2)?

[Tom Smit]

Try this: disconnect channel two input, and engage the "parallel input" switch on the back so that both channels receive an identical signal. Report back.

[byacey]

Work the stereo / parallel mono switch back and forth a few times. These switch contacts can get oxidized and interrupt the signal.

[jimbo7]

UPDATE!

Ok, so what happens if you swap sub and top to channel one (and solo top to channel 2)?

If I swap them it sounds all muddy and bass-y with little to no mids or highs

Try this: disconnect channel two input, and engage the "parallel input" switch on the back so that both channels receive an identical signal. Report back.

sounded fine

Work the stereo / parallel mono switch back and forth a few times. These switch contacts can get oxidized and interrupt the signal.

I did this first and I may have knocked something loose. Now it works again, but if I run in stereo with just top (for simplicity) there's only muddy bass and no mids or highs on ch2. Same if I run sub+top on 2 and top only on 1.

So for some reason ch2 is pass only lower freqs and no mids or highs.

[Tom Smit]

Channel 2 sounds fine when the "parallel" switch is engaged and fed signal from channel 1, but is "bass only" when fed a signal from the mixer. Assuming that Ch 2 gets the R signal, try putting the L signal as the input instead. I'm wondering if the mixer is putting out a "bass only" signal, that, or the source to the mixer.

[jimbo7]

Last night I had a party at my house, so I just ran the amp bridged with just a t24 and a top in mono. Don't have a crossover or limiter yet, so the best I could do was measure the voltage as I turned up the mixer, then tape the sliders so you couldn't go past a certain voltage. I set it at 15v which was still plenty loud but never reached that. That was the first time I pushed my t24 for a long period of time and it performed flawlessly. It filled the whole house with good clean bass even with such low voltage. The top really wasn't pushed hard either, but the complimented each other well. Can't wait to get a real rig and find the real potential of these cabs.

Channel 2 sounds fine when the "parallel" switch is engaged and fed signal from channel 1, but is "bass only" when fed a signal from the mixer. Assuming that Ch 2 gets the R signal, try putting the L signal as the input instead. I'm wondering if the mixer is putting out a "bass only" signal, that, or the source to the mixer.

I tried another mixer and ch2 was still bass only. It has to be something in the amp causing this. I've tried everything.

[Grant Bunter]

Hmmm,
If one amp channel is no good, bridging certainly won't fix the problem, as bridging requires both channels of the amp to be working in order to bridge.

Since the amp running in bridge mode at the party worked fine, that almost eliminates the amp being the problem. (edit: other than as byacey says in the post below)

When you changed mixers, did you use the same cable connect from your source that you use every other time?
And if you use Ipod, or PC or CD, do you also use the same cable every time?

If you have PFL on your mixer, and use headphones to monitor left then right, you might pick up "muddy bass only" on one channel.
If you don't have PFL, and swap left to right and right to left at the mixer input for source, and the problem suddenly displays itself on the opposite channel of the amp, then it seems it would be your interconnect from source that's the issue.
Heck, even if it means spending $5 on a new cable, just to see, it's going to be a heap cheaper than sending your amp for surgery...

[byacey]

It sounds like something is wrong in the input stages of Channel 2. In bridge mode and parallel mono, the channel 2 input stage is bypassed. If it works fine in these modes but not stereo, it's something around the input.

It could be something as simple as a bad opamp or a shorted cap in the feedback loop of the channel 2 input..

[Hackomatic]

It sounds like something is wrong in the input stages of Channel 2. In bridge mode and parallel mono, the channel 2 input stage is bypassed. If it works fine in these modes but not stereo, it's something around the input.

It could be something as simple as a bad opamp or a shorted cap in the feedback loop of the channel 2 input..

+1

[jimbo7]

So this is really weird. Now it works fine. Of course it's after the N.Y.E. party. Even with the same mixer, cables, the exact way I had it set-up before, it work fine. This is after trying good 1/4" speaker cables and going from pc straight to amp then speakers. I then kept adding things one at a time like mixer then speak-on cables, ect. Channel separation is fine too.

The only issue now is that the output seems lower than it should be. I have the amp gain pegged, mixer at 50%, and channel slider at 50% and it's not loud at all. It should be deafening loud. I'm chasing gremlins here

[Bruce Weldy]

The only issue now is that the output seems lower than it should be. I have the amp gain pegged, mixer at 50%, and channel slider at 50% and it's not loud at all. It should be deafening loud. I'm chasing gremlins here

You didn't mention where the gain on the mixer channel is set. Also, what about the output of the playback device? Has it been changed? There are a lot of places along the line that have an effect on volume.

[byacey]

If the same signal is fed to the ch 1 input and the ch 2 input, and there is a difference in output, the problem is in the amp.

If you're running balanced line inputs, check the solder joints on the amplifier ch 2 input connector.

Loss of gain could also be caused by a shorted feedback loop cap as I mentioned, or a defective op amp, assuming the level control is good.