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I think my Dahlquist setup killed my amp!!!

bored184

bored184

AK Subscriber
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Just recently I bought a a pair of DQ-10s, DQ-1W woofer, and DQ-MX1 crossover. I hooked up everything up and I had no sound out of my right speaker, just a buzz. I had the the DQ-10s running just by themselves on the amp prior to all this so I know the amp and both speakers were working. I took the amp out and tried it in another setup and sure enough no sound out of the right channel. I checked all the fuses, all were fine. With the top off I actually saw sparks when I tried to power it on again! The amp is dead until it goes into the shop. Not real happy because its a Tannoy SR-840, great amp but not much info out there about these.

The only thing I can could see being the culprit is the crossover. Everything was working just fine before its introduction and the DQ-10s with a different amp are still working great after this incident.

Any ideas of how to test this crossover to see what culprit is responsible for killing my favorite amp?
 
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There is nothing in the xover to indicate that is at fault. I don't have a diag on sub woofer end of the deal so maybe a phase issue? I do know the brand has been around a long time and reputable with nice gear and powerful gear.

The other thing is perhaps this is just a coincidence.

Where did you see the sparks? (pic would help where you saw it wider view of chassis and near close up.)
 
A common mistake people make is to not properly terminate the speaker wire ends. They should be trimmed to only about 1/2" of bare wire at the ends, with the strands neatly twisted together or soldered, then inserted into the speaker connectors so that no frayed strands stick out. People leave the ends a mess with strands that can short out, and blow the amp up. This is why a lot of people blow their amps up when they are connecting / disconnecting the speakers. That or they don't turn the power off.
 
dr*audio said:
A common mistake people make is to not properly terminate the speaker wire ends. They should be trimmed to only about 1/2" of bare wire at the ends, with the strands neatly twisted together or soldered, then inserted into the speaker connectors so that no frayed strands stick out. People leave the ends a mess with strands that can short out, and blow the amp up. This is why a lot of people blow their amps up when they are connecting / disconnecting the speakers. That or they don't turn the power off.
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I am pretty good and making sure this is not an issue with my equipment. But I am not perfect by any means.

Binkman said:
There is nothing in the xover to indicate that is at fault. I don't have a diag on sub woofer end of the deal so maybe a phase issue? I do know the brand has been around a long time and reputable with nice gear and powerful gear.

The other thing is perhaps this is just a coincidence.

Where did you see the sparks? (pic would help where you saw it wider view of chassis and near close up.)
Click to expand...

As requested a few photos below. Spark occurred in the bottom left corner. I checked the main fuse and its fine but there is some carbon build up on it and the holder as well.
Close up:

Using the crossover I did a simple and experiment. Using my ohm meter I took a ohm reading from positive in to positive out for the left and right speakers, photos below. I figured the ohm reading should be the same or pretty darn close it, tuns out they are not. In the right section I got 3.156 ohms and the left 33.83 ohms. The right section is the suspected issue.
 
Here is a photo of the inside of the crossover. Are the black 150uf caps NPEs or Poly caps?


I am not to worried about the amp, it will go to the tech. I am more worried about getting this crossover working so it doesn't blow anything else up.
 
bored184 said:
I am pretty good and making sure this is not an issue with my equipment. But I am not perfect by any means.


Using the crossover I did a simple and experiment. Using my ohm meter I took a ohm reading from positive in to positive out for the left and right speakers, photos below. I figured the ohm reading should be the same or pretty darn close it, tuns out they are not. In the right section I got 3.156 ohms and the left 33.83 ohms.
Click to expand...

I would expect those readings to be closer together, but am not familiar with the item

That said, I'm struggling with how a lower or higher resistance from (+) to (+) respective to a channel (as you measured) would damage your amp. I'd think a short or very low resistance (+) to (-) would be much more likely to damage the amp, which is why I think some have proffered up a connection issue as the more plausible situatiom.
 
bored184 said:
I am pretty good and making sure this is not an issue with my equipment. But I am not perfect by any means.



As requested a few photos below. Spark occurred in the bottom left corner. I checked the main fuse and its fine but there is some carbon build up on it and the holder as well.
Close up:

Using the crossover I did a simple and experiment. Using my ohm meter I took a ohm reading from positive in to positive out for the left and right speakers, photos below. I figured the ohm reading should be the same or pretty darn close it, tuns out they are not. In the right section I got 3.156 ohms and the left 33.83 ohms. The right section is the suspected issue.
Click to expand...

There is definitely something wrong with one of the crossovers, but having 3 Ohms from input to output or 30 Ohms from input to output would not damage your amp. I will see if I can dig up a schematic of the crossover so I can see what it should read, but to find out if the crossover damaged the amp you have to measure from the + to - input connectors on the crossover. If it reads less the 4 Ohms, you've got a problem. Those are film caps.
 
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Can't find a schematic for free. You will have to purchase one and post it or give it to your tech to fix. One of them is bad for sure, I am pretty sure the one with 30 Ohms from in to out is bad; you can't drive speakers with a 30 Ohm impedance.
 
bored184 said:
If I did + and - would I need to use a piece of wire as a jumper across the other side?
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I would for sure do the test without (then maybe with some 8 ohm resistors just for curiosity) but a dead short isn't appropriate. The test without should be all you need to know whether the crossover itself is presenting any unusual resistance at its input.
 
bored184 said:
If I did + and - would I need to use a piece of wire as a jumper across the other side?
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We are only concerned that the crossover itself has some internal shorted component that presents a short or low impedance load to the amp. Just check the resistance from the + to - inputs on both channels. It is also important to check the impedance but that would require at minimum an audio generator and a meter with flat frequency response from 20Hz to 20 KHz, and an 8 Ohm resistor.
 
When measuring impedance with a DVM does it not use a reference frequency of 1khz which means yes the suspect side has a fault as it will be passing a short as frequency rises.
I assume the measurements were in the low-pass or subwoofer connection.

This would indicate a bad capacitor and if those caps are what I think they are and due to age they would be going bad.

Matt...tubeornotube
 
tubeornotube said:
When measuring impedance with a DVM does it not use a reference frequency of 1khz which means yes the suspect side has a fault as it will be passing a short as frequency rises.
I assume the measurements were in the low-pass or subwoofer connection.

This would indicate a bad capacitor and if those caps are what I think they are and due to age they would be going bad.

Matt...tubeornotube
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DMM's use a DC current to measure resistance, they don't measure AC impedance. You would need an impedance meter for that.
 
Using my multimeter I measured + and - on the input, I got 0 ohms on the left channel and 3.4 ohms on the right channel. I then check for continuity which I have in the right channel but not in the left.
 
bored184 said:
Using my multimeter I measured + and - on the input, I got 0 ohms on the left channel and 3.4 ohms on the right channel. I then check for continuity which I have in the right channel but not in the left.
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Now we know what blew up your amp, the left channel is bad.
 
I used the "beep" function on my meter to see if I had a complete circuit. On the left channel I got no beep to indicate a complete circuit, if there was a short wouldn't I have gotten a beep?
 
bored184 said:
I used the "beep" function on my meter to see if I had a complete circuit. On the left channel I got no beep to indicate a complete circuit, if there was a short wouldn't I have gotten a beep?
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You said you measured 0 Ohms from the + to - on the input on the left channel. that's a short. If you try the beeper there you should get a beep. If not, your meter is suspect.
 
dr*audio said:
You said you measured 0 Ohms from the + to - on the input on the left channel. that's a short. If you try the beeper there you should get a beep. If not, your meter is suspect.
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There is one thing I looked over and I feel stupid that I did it. I need to make sure the meter is reading 0 ohms vs reading anything at all. I did not put the two leads together before I did my readings. This I will correct tonight. I will probably go back to my older analog meter, I prefer those over the newer digital.
 
I have all new caps ordered for the DQ-10s, and the external crossover. I hope to tackle this over Christmas break. I will update with photos as I tackle these.
 
bored184 said:
I have all new caps ordered for the DQ-10s, and the external crossover. I hope to tackle this over Christmas break. I will update with photos as I tackle these.
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Make the same resistance measurements: in + to - when you are done.
 
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