Thanks for the explanation. I have a mytek stereo 192 dsd dac, I was just told over on CA that it does has caps on the output but it also has jumpers to bypass them, i'm going to check to see if they came bypassed or are set wrong?
Thanks, i'll try that to see if that is what the voltage is around.
Same technique for measuring the voltage coming from the dac, xlr pin 2 to pin1?
Yes, see page 36 of the manual (downloadable from http://www.mytekdigital.com/download_library/stereo192-dsd-dac_manual_v1.4.2.pdf.
No, between 2 and 3 on the XLR. But your multimeter is probably not sensitive enough. better to test with a pair of caps.
This is messed up, my dac has no jumpers on so it is in default mode where is should go through the caps not bypass it.
I just experienced something even worse, just doing some testing, if I shut the dac off before the amp the voltage spikes up HUGE. My meter shows 11-12VDC and then it slowly starts dropping down. Turning the dac back on resets it back down to 0.5VDC but off again and it spikes HUGE. I had my speakers plugged in while testing
Didn't think shutting the dac off would cause that kind of spike.
I just experienced something even worse, just doing some testing, if I shut the dac off before the amp the voltage spikes up HUGE. My meter shows 11-12VDC and then it slowly starts dropping down. Turning the dac back on resets it back down to 0.5VDC but off again and it spikes HUGE. I had my speakers plugged in while testing
Didn't think shutting the dac off would cause that kind of spike.And ChrisPa you are exact on those numbers. Measured output at the DAC/PRE and it is 0.026VDC so that works out to the 0.5VDC with the 26dB gain you listed.
The huge spike when powering down is really scaring me though.
I know this is no longer a hypex issue and everything is good on the amp side now but i'd appreciate any input from you guys, you've all been a lot of help and I am very thankful.
The huge spike when powering down is really scaring me though.
I know this is no longer a hypex issue and everything is good on the amp side now but i'd appreciate any input from you guys, you've all been a lot of help and I am very thankful.
I agree. But... I also realized that nowhere in the DAC documentation does it say that the caps are the last thing on the output. They only state that bypassing them extends frequency response to 0 Hz. So even with caps not bypassed, there *could* be some stage *after* the caps that adds a small DC bias - you only need 25 mV to produce 0.5 V at the speaker output.
I just experienced something even worse, just doing some testing, if I shut the dac off before the amp the voltage spikes up HUGE. My meter shows 11-12VDC and then it slowly starts dropping down. Turning the dac back on resets it back down to 0.5VDC but off again and it spikes HUGE. I had my speakers plugged in while testing
That sounds like typical behaviour of a DAC that has a single-ended power suppy, and a *large* capacitor on the output. Isn't the DAC designed to drive a headphone? So it might be designed to deal with a very low impedance on the output, requiring a large cap. But you are only loading it with the extremely high input impedance of the nc400 - about 100 kohm. So it takes a long time to charge/discharge that cap.
Have you tried to measure the output of the DAC directly?
This could very well be due to the DAC having a large transient on it's output when you switch it off. Wouldn't surprise me, I have seen lot's of audio components that do this.. The only way to get around this if this is the case is to use a defined power up / down sequence. That is when powering up the amps should be the last component and when powering down the first component to switch.
You posted this while I was responding to the previous message, so ignore the thing about measuring the DAC output
Do you see the spike on the DAC output when you turn on/off the DAC?
Well, the crude solution is to make sure you always turn on the DAC before the power amp, and turn off the amp before the DAC. Not ideal.
Adding caps at the amp input will take care of the constant 0.5 V on the output issue, but not the spike. You didn't have the spike with the Cambridge amp?
Ok just spoke with the designer of my DAC, it appears that the 25mV on the output is totally normal, he is saying the amp i'm using should have some sort of cap to offset the DC. They even tested the dac on their bench and it had higher voltage then mine.
And the jumpers for the DC bypass on my dac are for the inputs into the dac, not the outputs.
So looks like my dac is fine, and my amp is fine, but because the way both are designed they don't play nice.
And the jumpers for the DC bypass on my dac are for the inputs into the dac, not the outputs.
So looks like my dac is fine, and my amp is fine, but because the way both are designed they don't play nice.
I always turn the amp off first, just in my testing and not being 100% on the ball i shut the dac off first with my speakers still plugged in, didn't even realize it, big moment of stupidity.
This is messed up, my dac has no jumpers on so it is in default mode where is should go through the caps not bypass it.
I just experienced something even worse, just doing some testing, if I shut the dac off before the amp the voltage spikes up HUGE. My meter shows 11-12VDC and then it slowly starts dropping down. Turning the dac back on resets it back down to 0.5VDC but off again and it spikes HUGE. I had my speakers plugged in while testing
Robbbby.....
Always switch on smallest signals first and power amps last..!!! So the sequence of switch on should be DAC-PreAMP-Poweramps and always with volume to minimum then.... switch off in reverse order. Volume down, Poweramps off then PreAMP then DAC.
This should apply to every sound system even if you haven't got a DC problem.
Cheers
I always do that but like I said I had a dumb moment while hastily trying to test what was going on, I didn't realize the speakers were still plugged in, I usually disconnect them when poking around in the amp with my meter.
Speakers still working so hopefully my moment of stupidity didn't cause any damage.
Speakers still working so hopefully my moment of stupidity didn't cause any damage.
What I don't understand though, the guy I spoke to who designed my dac said it is totally normal for lots of gear to have such small voltages on the outputs, if this is the case how come nobody else with ncores is having this same issue of that small input voltage being bumped up 20x because of the amps voltage gain?
Curious problem
Hi, I have been enjoying my Ncores enormously, these are very good amps.
I however have a curious problem. Once the Ncores have been turned on for approx 5-6 hours one channel starts to turn off (0.5-1 sec) and on intermittently at irregular intervals (c.a. 5-30sec.). I have tried to turn off my preamp (Leben rs28cx), switch inputs and use e.g. dac through a passive amp (Slagle autoformers) to no avail, so this is probably inherent to the nc400 unit.
Once off for some time, they are ok for a while (something must be gettin hot or something). Nothing however seems or smells hot.
I use one smps600 for two nc400, unbalanced as in figure 4 in chapter 12.3.2 Hardbonded RCAs and no mains earth.
I thougt this was something in the environment at first, but regardless of time of day, once on (used or not used) for 5-6hours this starts again and only in one channel.
Any ideas?
Regards
Kjartan
Hi, I have been enjoying my Ncores enormously, these are very good amps.
I however have a curious problem. Once the Ncores have been turned on for approx 5-6 hours one channel starts to turn off (0.5-1 sec) and on intermittently at irregular intervals (c.a. 5-30sec.). I have tried to turn off my preamp (Leben rs28cx), switch inputs and use e.g. dac through a passive amp (Slagle autoformers) to no avail, so this is probably inherent to the nc400 unit.
Once off for some time, they are ok for a while (something must be gettin hot or something). Nothing however seems or smells hot.
I use one smps600 for two nc400, unbalanced as in figure 4 in chapter 12.3.2 Hardbonded RCAs and no mains earth.
I thougt this was something in the environment at first, but regardless of time of day, once on (used or not used) for 5-6hours this starts again and only in one channel.
Any ideas?
Regards
Kjartan
I would assume many of us put caps on the inputs - and despite what the guy says, it is not that common. Most preamps and DACs have caps on their outputs.
I suggest you get 4 0.47 uF caps, and connect them between the XLR connector and the nc400's.
Sounds like a thermal problem. Have you felt how warm the amps feel when the turning off starts? Do you have an IR thermometer? What kind of enclosure do you have?
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