Dammit not again..

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lilviper
Posts: 270
Joined: Tue Nov 06, 2012 9:30 pm

Dammit not again..

Post by lilviper »

Got an odd one pull the car out for the summer driving and I re-set the levels on the amps, and i have very little bass. Last summer it would knock the rearview mirror off, now you cant hear it.

head unit is a Nakamichi CD45Z, Feeding a TBA-1 front to rear TBA-1, From that it goes in to a Audio control EQL, then 24xs, then the fronts go down to a 400.2 set to bypass on both, over to a 500.4. Subline splits out of the 24xs to a Bass Cube and down to my MS2250 feeding a set of X-Max 12's.

If i unplug either of the RCA's from the bass cube i get full system bass. plug the L or R back in and almost nothing, bypass the bass cube by plugging either right or left into the 24xs and i get full sound. So Im guessing that its the crossover, if i have a normal output on one and an inverted on the other i could be getting cancellation. I cant find 24xs's anywhere that aren't beat to hell, but what could be causing that drastic of a cut in input signal.. and what do i look for inside the crossover?

The AMP and subs are fine, direct lined to them from the head unit and they reproduce sound. The 400 and 500's make mostly normal noises at the expected volumes. Occasionally the 500.4 has static on the rear Right channel which drives a triple set in the front of the car, I suspect the crossover is wonky.. most of them are at this point. No idea where to start troubleshooting the crossover inside the 500.4.

Also, the 400.2's LP crossover hum/thumps if i engage that. But it works fine in bypass.
lilviper
Posts: 270
Joined: Tue Nov 06, 2012 9:30 pm

Re: Dammit not again..

Post by lilviper »

Some time and testing.. The RCA to the sub amp is bad, I get zero volts through the red side it and that zero rotates between L and R when I move the source, its shorted.

I used a 1khz test tone and an oscilloscope to test the output of the system processors and crossovers, they all work and I set their outputs to 6V with no input clipping.
The 400.2
LP/HP has no output on the right channel and 54V on the left. 1khz
BY/BY has 54V on the right channel and 54V on the left. 1khz
The waveform of the left channel is not totally sinusoidal. The right is.

The 500.4 is hard wired to use the front inputs for all 4 channels Same 6V input, 1khz. The blue lights on top of the amp flicker and pulse
Right front shows 10hz at about 8V until I turn the front gain off of 6V about 1/4 of a turn then the frequency comes on to 1khz and i get 54V i can drive it to clipping at 56V.
Left front is the same
Right and left rear do not show this behavior and come to 54V just off the max.

Any direction on the crossovers would be great.
ttocs
the Floor Sweeping Hack with Golden Ears
Posts: 14783
Joined: Fri Dec 19, 2008 9:53 pm

Re: Dammit not again..

Post by ttocs »

if it rotates when you switch the source l & R then isn't it the cable or the source that has a problem?
what else can I say I am a grumpy asshole most of the time.
lilviper
Posts: 270
Joined: Tue Nov 06, 2012 9:30 pm

Re: Dammit not again..

Post by lilviper »

Sources are ok, i was initially worried about the xover being bad but it sorts the high and low signals appropriately. There is signal at the xover, one side is missing at the amp, switching the rca left to right doesnt change the signal that arrives at the amp. Left is always good, right is always no signal. the only thing thats between them is a set of RCAs thats buried in the install, that i have to get out and replace.
ttocs
the Floor Sweeping Hack with Golden Ears
Posts: 14783
Joined: Fri Dec 19, 2008 9:53 pm

Re: Dammit not again..

Post by ttocs »

sounds like the amp. It sounds like you have had your hands on all the knobs on the amps but if by chance you have not touched one or just want to try, just try sweeping them back/forth through their entire sweep a few times. Sometimes some corrosion develops or some dust gets in just the right place to keep it from making contact and sweeping them can clean them off.
what else can I say I am a grumpy asshole most of the time.
lilviper
Posts: 270
Joined: Tue Nov 06, 2012 9:30 pm

Re: Dammit not again..

Post by lilviper »

Changed the amp, had the same problem. Which made me dig out the scope to start troubleshooting the signal path with an actual signal.
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