Help - amplifier shuts off when I connect my x10 cable

owdi · 16th February 2007, 03:58 AM

My equipment:

Niles Audio SI-275 amplifier
M-Audio Audiophile 2496 sound card
DIY x10 cable using a 16 ohm and a 1.5 ohm Dayton non-inductive resistor.

If I connect only the output from my sound card to the amplifier using an standard RCA cable, no problems.

If I connect only the x10 cable from the speaker outputs on my amplifier to the sound card, no problems.

If I connect both, the amplifier clicks and shuts off. Half a second later it turns on, clicks again, and shuts off. It repeats this until I unplug any of the cables. I have no idea why this is happening. Here are some more tests I did:

Measured the resistance at the speaker end of the x10 cable, it was 16 ohms. Measured the RCA end, it was 1.5 ohms.

If I connect everything to my receiver, it works fine, and I can take measurements. I used RMAA to measure the FR and harmonic distortion with great results (-1db at 10hz and 30khz), -75db THD.

If I connect the output from my sound card to my receiver, then connect the speaker outputs of the receiver to the amplifier with the x10 cable, it works fine. This is my normal everyday setup, and it sounds great.

My only guess is the amplifier has some protection circuitry which is detecting a feedback loop, as if I had plugged the speaker outputs into the RCA inputs. I don't know how this could be happening because my sound card is configured to not output whatever comes in on the inputs.

Any ideas? I was thinking about trying a ground loop isolation circuit (basically a pair of transformers), but I'm afraid it will add distortion to my measurements.

Dan

eclectic2k · 16th February 2007, 05:27 AM

So by "x10" I assume you mean 10:1 (or /10) so you have a 10 to 1 voltage divider cable.
(or ~11.5:1)

only thing I can think of is the ground loop. You've tried most of the basic configurations to eliminate some of the other possibilites. I think the amp doesn't like having it's negative speaker terminal shorted to the input/chassis? ground (not surprisingly)

If you try the transformers should tell you if it is the problem. You could also ohm things out and try a few experiments to confirm this as well. Then maybe find out a bit more of the amplifier circuit to determine why, if you're curious.

As far as your measurements, use the receiver to test with and without the transformers. This will give you an idea of how much they affect your measurements. Good transformers are quite linear, so whatever effect they have should be manageable.

good luck...

owdi · 16th February 2007, 07:06 PM

Instead of using the transformers, I was thinking about adding a 10Kohm series resistor to my x11.7 cable, after the voltage dividier. The input impedance on the amplifier is 56Kohm, so the series resistor will attenuate the final signal less than 1db. Maybe that will be enough to prevent the amp from turning off.

If it's not, I'll test the transformers by doing a loopback test with my sound card. The Audiophile 2496 is very clean, so any distortion will quickly show up in the tests.

Dan

AndrewT · 16th February 2007, 07:40 PM

Hi,
could the divide by 10 cable be connected return to input and input to return?

Is the amplifier double insulated?

Try connecting just the amplifier input and output returns to each other.
Try connecting these same returns to the in/out returns of the sound card.

Maybe some of those answers will guide you to a conclusion.

owdi · 17th February 2007, 03:38 PM

I made another x10 cable, this time using a 10kohm and 1kohm resistor. Using the new cable the amplifier did not shut off, and I was able to take some measurements.

Dan

AndrewT · 17th February 2007, 04:18 PM

Hi,
is divide by 10 important to your measurements?
10k & 1k0 do not give 10%
You also need to take account of the loading in parallel with the 1k0, a change here also changes that % reading fed back to your sound card input.

As an example, assume that the loading is a 10k input stage.

The effective resistor in the ladder after the 10k is 1k0//10k = 909r1
the divide ratio then becomes 909.1/[10k+909.1]=0.0803
the 10k/1k0 will send 8.03% of the sampled signal back instead of 10%

owdi · 18th February 2007, 03:26 AM

The 10% does not matter to me, the signal just needs to be attenuated so it does not blow up my sound cards inputs.

Dan

16th February 2007, 03:58 AM	#1
owdi diyAudio Member Join Date: Sep 2003 Location: Bellevue, WA	Help - amplifier shuts off when I connect my x10 cable My equipment: Niles Audio SI-275 amplifier M-Audio Audiophile 2496 sound card DIY x10 cable using a 16 ohm and a 1.5 ohm Dayton non-inductive resistor. If I connect only the output from my sound card to the amplifier using an standard RCA cable, no problems. If I connect only the x10 cable from the speaker outputs on my amplifier to the sound card, no problems. If I connect both, the amplifier clicks and shuts off. Half a second later it turns on, clicks again, and shuts off. It repeats this until I unplug any of the cables. I have no idea why this is happening. Here are some more tests I did: Measured the resistance at the speaker end of the x10 cable, it was 16 ohms. Measured the RCA end, it was 1.5 ohms. If I connect everything to my receiver, it works fine, and I can take measurements. I used RMAA to measure the FR and harmonic distortion with great results (-1db at 10hz and 30khz), -75db THD. If I connect the output from my sound card to my receiver, then connect the speaker outputs of the receiver to the amplifier with the x10 cable, it works fine. This is my normal everyday setup, and it sounds great. My only guess is the amplifier has some protection circuitry which is detecting a feedback loop, as if I had plugged the speaker outputs into the RCA inputs. I don't know how this could be happening because my sound card is configured to not output whatever comes in on the inputs. Any ideas? I was thinking about trying a ground loop isolation circuit (basically a pair of transformers), but I'm afraid it will add distortion to my measurements. Dan

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16th February 2007, 05:27 AM	#2
eclectic2k diyAudio Member Join Date: Nov 2005 Location: Silicon Valley	So by "x10" I assume you mean 10:1 (or /10) so you have a 10 to 1 voltage divider cable. (or ~11.5:1) only thing I can think of is the ground loop. You've tried most of the basic configurations to eliminate some of the other possibilites. I think the amp doesn't like having it's negative speaker terminal shorted to the input/chassis? ground (not surprisingly) If you try the transformers should tell you if it is the problem. You could also ohm things out and try a few experiments to confirm this as well. Then maybe find out a bit more of the amplifier circuit to determine why, if you're curious. As far as your measurements, use the receiver to test with and without the transformers. This will give you an idea of how much they affect your measurements. Good transformers are quite linear, so whatever effect they have should be manageable. good luck...

16th February 2007, 07:06 PM	#3
owdi diyAudio Member Join Date: Sep 2003 Location: Bellevue, WA	Instead of using the transformers, I was thinking about adding a 10Kohm series resistor to my x11.7 cable, after the voltage dividier. The input impedance on the amplifier is 56Kohm, so the series resistor will attenuate the final signal less than 1db. Maybe that will be enough to prevent the amp from turning off. If it's not, I'll test the transformers by doing a loopback test with my sound card. The Audiophile 2496 is very clean, so any distortion will quickly show up in the tests. Dan

16th February 2007, 07:40 PM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, could the divide by 10 cable be connected return to input and input to return? Is the amplifier double insulated? Try connecting just the amplifier input and output returns to each other. Try connecting these same returns to the in/out returns of the sound card. Maybe some of those answers will guide you to a conclusion.

17th February 2007, 03:38 PM	#5
owdi diyAudio Member Join Date: Sep 2003 Location: Bellevue, WA	I made another x10 cable, this time using a 10kohm and 1kohm resistor. Using the new cable the amplifier did not shut off, and I was able to take some measurements. Dan

17th February 2007, 04:18 PM	#6
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, is divide by 10 important to your measurements? 10k & 1k0 do not give 10% You also need to take account of the loading in parallel with the 1k0, a change here also changes that % reading fed back to your sound card input. As an example, assume that the loading is a 10k input stage. The effective resistor in the ladder after the 10k is 1k0//10k = 909r1 the divide ratio then becomes 909.1/[10k+909.1]=0.0803 the 10k/1k0 will send 8.03% of the sampled signal back instead of 10%

18th February 2007, 03:26 AM	#7
owdi diyAudio Member Join Date: Sep 2003 Location: Bellevue, WA	The 10% does not matter to me, the signal just needs to be attenuated so it does not blow up my sound cards inputs. Dan