AL3 Problem

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sea
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AL3 Problem

Post by sea » Sun Oct 23, 2016 3:40 pm

I am having a strange problem with a pair of AL3's. At moderate to loud volume the amp goes into protection and cuts out only to kick back in a few seconds later. I acquired this pair of speakers a few months ago. Other than clean then up a bit I have not done any work to them.

Initially I was biamping them with a M1.0t MKII Opt 2 on the woofers and a TFM55 on the ribbons. I listened to them off and on like ths with no issues. Recently I connected the M1.0t to both high and low frequencies. This is when the trouble started, At first I thought I had a bad speaker cable. I finally decided that the M1.0t was the problem. As I type this it is on a UPS truck on its way to Greg. I now belive the amp to be fine. My TFM55 is with Keven for LED repair so I hooked them up today with a TFM35. Same problem. Through process of elimination I am certain that the amp is struggling to drive the woofers. I have a line level input connected directly to the amp (no preamp).

If I remove the jumpers and drive just the ribbons all is fine. I switch and drive just the woofer then the amp goes into protection. I even went so far as to connect them to my TFM75. No problem driving ribbons and woofers at high volume. I have been successfully with a 2 Channels of Sunfire 200x5.

The woofers are original.

Thoughts or questions?



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sea
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Re: AL3 Problem

Post by sea » Sun Oct 23, 2016 3:51 pm

One strange this is that both speakers act the same. EIther one when connected alone will exhibit the problem.

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kingman
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Re: AL3 Problem

Post by kingman » Sun Oct 23, 2016 6:36 pm

sea wrote:One strange this is that both speakers act the same. EIther one when connected alone will exhibit the problem.
Did Jerry call you???
In reality, it only matters what it sounds like to YOU!!!

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sea
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Re: AL3 Problem

Post by sea » Mon Oct 24, 2016 5:10 pm

kingman wrote:
sea wrote:One strange this is that both speakers act the same. EIther one when connected alone will exhibit the problem.
Did Jerry call you???
Yes. Jerry called and offered this theory. Perhaps the woofers were pushed hard and the voicecoil is partially burned so that when you get to moderate volume and extend the cone it could be shorting. Unclemeat had also offered up this theory. Well I am not exactly sure how to test this. Jerry suggested that I connect a DVM to the woofer and measure the DCR while gently moving the cone up and down. When I do this I have a nice steady 3.4 ohms until I start messing with the cone. As soon as I touch the cone the number gets very erratic even going negative. I have no idea what this means. I checked a polk driver I have laying around and it pretty much behaves the same.

If it the woofers, is there a reasonable cost replacement? Help!!

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Magnaryder
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Re: AL3 Problem

Post by Magnaryder » Mon Oct 24, 2016 7:45 pm

sea wrote:If it the woofers, is there a reasonable cost replacement? Help!!
Ed, when I get home let me look, IIRC I have at least one original woofer for the ALIIIs. I get back home late Friday afternoon. You can have it, if I can locate it it. Ping me your snail mail addy

ray
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radioeng2
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Re: AL3 Problem

Post by radioeng2 » Mon Oct 24, 2016 8:37 pm

An ohm meter uses DC for determining resistance.

When you move a cone, it's a AC generator.

So you will get enough voltage while moving to disturb the resistance value. If you could hold it still enough for the reading to settle, it'd be reasonably real value. But only while the cone is not moving.

I'd agree a fried coil is a possibility. Either that or look for the crossover to be bypassed or highly incorrectly modified. Since they seem to work when driven seperately, but a too stiff impedance seems likely from the single amp result, I'd be looking for a reason to lean one of those two directions.

Mark
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sea
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Re: AL3 Problem

Post by sea » Mon Oct 24, 2016 9:04 pm

radioeng2 wrote:Since they seem to work when driven seperately
Mark, this is not the case. Either speaker when driven alone will cause the problem. Obviosuley when both are driven it also kicks the amp into protection.

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sea
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Re: AL3 Problem

Post by sea » Wed Oct 26, 2016 6:26 pm

Today I unsoldered one of the woofers and connected directly to the outputs of the TFM35. I turned the volume up to about 75%. No problem. This is much past the point that has been sending the amp into protection mode. What does this mean? A problem with both crossovers?

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Miko1971
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Re: AL3 Problem

Post by Miko1971 » Thu Oct 27, 2016 7:51 am

If the crossovers are original and have not been updated I say yes. The woofers are very robust, you'd be hard pressed or on a mission to hurt them. I ran a pair of Sunfire 300's into my Amazings and after a few times of concert level fun, I had a plate of freshly roasted crossovers to pass around.

Rebuild them and your speakers will sound and preform better then new. The quality of components available today far exceed the best of yesterday. Plus, it's well known the bean counters at Carver specified the minimum specs on those parts.

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UncleMeat
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Re: AL3 Problem

Post by UncleMeat » Thu Oct 27, 2016 4:44 pm

What got roasted Miko? Was it the Caps or the Incuctors (or Both)?

I'd suspect the 300uF cap first; it seems to be the likely suspect causing a bridge across the woofer's impedance. If he inductors on the low pass filter had failed by shorting across windings, it should not cause a low impedance circuit.

EDIT: A shorted inductor WILL lower the impedance also.
Last edited by UncleMeat on Thu Oct 27, 2016 8:13 pm, edited 1 time in total.

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sea
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Re: AL3 Problem

Post by sea » Thu Oct 27, 2016 5:44 pm

UncleMeat wrote:What got roasted Miko? Was it the Caps or the Incuctors (or Both)?

I'd suspect the 300uF cap first; it seems to be the likely suspect causing a bridge across the woofer's impedance. If he inductors on the low pass filter had failed by shorting across windings, it should not cause a low impedance circuit.

Today I did several things in an effort to run this to ground. First I cut the 300uf cap out of the circuit and just jumped it. This caused the amp to go into protection at an even lower output. After replacing the cap I jumped the rheostat out. No change. I replaced the rheostat and then cut the 300uf cap out and replaced with an identical cap from a spare platinum crossover. The damn thing still sends the TFM35 into protection at moderate volume.

I was talking to Bob today about another issue and I ask him about this. He seems to think it is the amp. I did not really understand his theory but if only the TFM35 was doing it I would think it just does not have enough ass to drive them but it does not make sense that the M1.0t MKII would do the same thing. Right now the TFM35 is playing at about 70% through a pair of Silvers . No problem.

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UncleMeat
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Re: AL3 Problem

Post by UncleMeat » Thu Oct 27, 2016 6:03 pm

OK, here's something we have not taken into account. The 300uF is to allow high frequency signal to pass to ground instead of going through the woofer. If you are passively bi-amping and running the amp full range, a large percentage of the signal is going to be sent across the capacitor, with little resistance, to ground. The amp will 'see' a lower overall impedance than if you were sending full range signal to the woofer's voice coil.

When the woofer gets a sound input that makes it's impedance minimal; the result might be that it causes the amp to clip. I'm wondering if a resistor in series with that cap might be needed; or attenuate the high frequency before the amplifier.

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Miko1971
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Re: AL3 Problem

Post by Miko1971 » Thu Oct 27, 2016 6:28 pm

I figured out my crossovers were fried by bypassing them and trying the woofers and ribbons separately straight to my amp.
I never found out exactly what went south on them. I gave up since you can't get the ribbons rebuilt anymore. I dumped them on eBay.

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UncleMeat
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Re: AL3 Problem

Post by UncleMeat » Thu Oct 27, 2016 7:55 pm

Ed (SEA) has had replacement kapton made; he can now repair these ribbons if needed. I suspect the design of the crossover when used for passive bi-amping, not the crossover itself.

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Re: AL3 Problem

Post by UncleMeat » Thu Oct 27, 2016 8:12 pm

sea wrote:Today I did several things in an effort to run this to ground. First I cut the 300uf cap out of the circuit and just jumped it. This caused the amp to go into protection at an even lower output.

I was talking to Bob today about another issue and I ask him about this. He seems to think it is the amp. I did not really understand his theory but if only the TFM35 was doing it I would think it just does not have enough ass to drive them but it does not make sense that the M1.0t MKII would do the same thing. Right now the TFM35 is playing at about 70% through a pair of Silvers . No problem.
Making the 300uF a straight wire is only going to bypass the woofer entirely. I'm surprised the amp didn't protect immediately or the cause the 4Ohm fuse to pop. Did you check that fuse to be sure it has not been bypassed?

The L5 inductor acts as a resistor to HF so maybe that's what saved the fuse and the amp. But maybe the L5 isn't doing it's job well enough to protect the amp at high volumes. The TFM-35 should have plenty of power to drive a 10" woofer.

Try running the TFM-35 to drive both the woofer and ribbon. What happens then?

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