Need troubleshooting help

[Dunlavyphile]

I've got techs at S.M.S.L and Hypex looking into this, but I'd like to understand this on my own:

S.M.S.L D400ES DAC.
Nilai 500 monoblocks.
USB, optical and coaxial inputs.

There are two problems. The first occurs when I use the DAC's remote to cycle through the inputs. When I reach I2S (unused) often there is a loud pop from the right speaker and the right amp shuts down. This happens to that particular amp regardless of whether I connect the Right or Left channel to it.

The second occurs when the system is sitting idle, set to coaxial (TV) with the TV off. A soft click sometimes comes out of the right speaker, spaced about a 1 1/2 seconds apart. I can stop it by making a selection on the DAC, but I'm nearly positive it continued once even after I unplugged the DAC.

To confuse matters further, over the months I've discovered the offending amp shut down for reasons I couldn't explain, without any pops or clicks, and before I installed this DAC. This was rare.

DC output from the normally functioning amp is a steady 12.5V. From the amp that's blowing it fluctuates a bit around 7.2V.

The question I don't think S.M.S.L or Hypex might answer independently is whether the DAC has damaged the amp. I don't see why there should be a spike with I2S selected, even if only one of the amps is overloading. I'd hate to replace the amp, only to have this DAC damage the new one. Do I have a legitimate case with S.M.S.L?

 

[MaxwellsEq]

DC output from the normally functioning amp is a steady 12.5V. From the amp that's blowing it fluctuates a bit around 7.2V

Can you check this? Those levels are way too high!

 

[Sokel]

12.5VDC by the amp alone?
With nothing connected?

Disconnect your speakers from this thing immediately or else you may have to replace those too except from the DAC and amp.

I would suggest to test the DAC alone with your DMM doing exactly what you do when this pop happens and check what it sends,both DC and AC.
I said it again and again,that is a test anyone must do prior to connect with other stuff,right out of the box.

Hope it ends well for you but 12.5VDC are not reassuring,if I recall well that's the limit that Hypex amps pass through before they shut so it's maybe more.

 

[Dunlavyphile]

Yeah, I didn't know what I was doing: my meter switches automatically between V and mV, and I had no idea what reading to expect. The amps are actually reading around 14-18 mV at the speaker terminals, which Hypex says is normal.

However, Hypex did have me return the amps for repair. They said that earlier revisions sometimes had problems with low impedance speakers, which I have, so they're going to modify mine.

I'm still concerned whether the DAC is sending a spike when set to I2S and nothing is connected to that port. Something, after all, kept setting off the amp with that input. However, the left mono amp never complained, and now I'm using my Nilai stereo amp from my other system and it seems to be fine. SMSL has not been responsive, but I can't really prove there's anything wrong with the DAC.

 

[MaxwellsEq]

amps are actually reading around 14-18 mV

That's a relief!

I'm still concerned whether the DAC is sending a spike when set to I2S and nothing is connected to that port.

Stick the multimeter on the outputs and measure the spike it outputs.

When you feed a DAC directly into a power amplifier you are taking a risk (one that I admittedly took for years). A DAC's default setting is 100%. So it's quite possible that it will produce peak input into the power amplifier. Good practice is to use a preamplifier or passive attenuator between the two.

 

[Sokel]

SMSL has not been responsive, but I can't really prove there's anything wrong with the DAC.

Just disconnect it from the amp,stick your meter in it's right output and cycle through it's inputs to see what it sends,both AC and DC.

Edit: @MaxwellsEq was faster.

 

[Dunlavyphile]

With the I2S input set on the DAC's remote I get 4.24V DC (not mV) for both channels and both pins on each channel. With the other inputs at idle I get nothing. There is nothing connected to the I2S input. Of my three Nilai amps so far only the right mono amp has complained.

S.M.S.L seems to have stopped talking to me.

 

[Sokel]

With the I2S input set on the DAC's remote I get 4.24V DC (not mV) for both channels and both pins on each channel. With the other inputs at idle I get nothing. There is nothing connected to the I2S input. Of my three Nilai amps so far only the right mono amp has complained.

S.M.S.L seems to have stopped talking to me.

To make it clear,cause "pins" can be debatable.
You mean the outputs,right?XLR's,RCA's,etc.


If so return it if it's still on warranty,4.25VDC amplified by your amp's gain can cause mayhem.

 

[MaxwellsEq]

With the I2S input set on the DAC's remote I get 4.24V DC (not mV) for both channels and both pins on each channel.

that's scary! I wouldn't accept that.

 

[Dunlavyphile]

To make it clear,cause "pins" can be debatable.
You mean the outputs,right?XLR's,RCA's,etc.


If so return it if it's still on warranty,4.25VDC amplified by your amp's gain can cause mayhem.

I measured at the XLR outputs from the DAC. The pins aren't numbered. This DAC has the middle XLR pins on top. I think that means Pin 1 is on the right, Pin 2 on the left and Pin 3 on the top. Correct? Left-Right (2-1?) and Top-Right (3-1?) measure 4.24V.

 

[Sokel]

I measured at the XLR outputs from the DAC. The pins aren't numbered. This DAC has the middle XLR pins on top. I think that means Pin 1 is on the right, Pin 2 on the left and Pin 3 on the top. Correct? Left-Right (2-1?) and Top-Right (3-1?) measure 4.24V.

That's how it should be:

1-Groung
2-Hot
3-Cold

You must measure 1-2 and 1-3,correct.

 

[Dunlavyphile]

S.M.S.L says that the voltage is normal and that XLR+ and XLR- minus offset. Does that make sense? Why would I2S be different than the other sources?

 

[Salt]

+- 4V means no attenuation. But what is the input signal that is not attenuated??