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How much DC offset is coming out of your amp?

Vladimir

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Dec 26, 2013
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Question for insider09 primarily, since he uses an active setup where no DC offset coming out of the amp is further filtered by a passive crossover.

Lets do a health check. Amps warmed up, playing no sound, everything set to default, volume down, measure each channel L/R at the speaker terminals with a multimeter set for mV DC.

Simple tutorial

 

insider9

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Sep 20, 2016
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However I'm back to passives at the minute. My active Jamos are not being used right now.

Have a look at my current setup in a recent thread below.

https://www.whathifi.com/forum/hi-fi/red-rose-and-densen-long-post-warning
 

insider9

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Sep 20, 2016
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insider9 said:
However I'm back to passives at the minute. My active Jamos are not being used right now.

Have a look at my current setup in a recent thread below.

https://www.whathifi.com/forum/hi-fi/red-rose-and-densen-long-post-warning
 

Vladimir

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Dec 26, 2013
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Hmm, it shouldn't measure absolute zero, unless its capacitor coupled amp or the speaker relays aren't switched on.
 

insider9

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Vladimir said:
Hmm, it shouldn't measure absolute zero, unless its capacitor coupled amp or the speaker relays aren't switched on.
It fluctuates for a second or two but goes down to zero.

I first measured it with speakers connected and it was giving me around 6mV from left terminal and 3mV from right terminal.

I shall try it again to double check.
 

Vladimir

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Dec 26, 2013
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Even 3mV and 6mV is superb. As good as zero. Anything under 20mV is a health check PASS.


I'm measuring 0.5mV and 4.5mV on the old geezer Technics SU-7700. I do this check twice a year.
 

insider9

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Sep 20, 2016
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Double checked and it's zero on both. I've never done this before but glad it's all good. If it wasn't I could always complain to the dealer they did give me warranty eventhough the amp wasn't new.
 

insider9

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Sep 20, 2016
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Densen seem to be quite sure of their build quality. I'd love to have one from new as they come with lifetime warranty. That's either good engineering or smart marketing and quite likely both.

On a similar note this is the first amp I've measured acoustically that outputs the same volume from both left and right terminal. The closest I've seen before was within 0.3 dB.
 

Vladimir

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The thin slab factor is certainly deceiving. And no analogue volume pot. Brilliant!

It has the Electrocompaniet appeal.
 

insider9

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You know far more than I do about these things but thought that the whole design concept was rather interesting. Form factor and the looks really nice and then the specs which I though were rather good also.
 

Andrewjvt

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Jun 18, 2014
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Interesting
Love the tech

Never gave densen another look before

0.3db difference on a second hand amp is very very good.
How old insider?
 

insider9

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Andrewjvt said:
Interesting
Love the tech

Never gave densen another look before

0.3db difference on a second hand amp is very very good.
How old insider?
0.3dB measured (channel imbalance) was an 18 year old Sony STR-DB930 :)

I've checked a number of amps that could be closing on 2dB channel imbalance. It's incredibly annoying when there isn't a balance knob.

Densen measures virtually same on both channels. I notice these things straight away as with my setup listening distance is low and everything is measured out so image shifts.

Oh and the one I'm using is about 5-6 years old from what I've seen on the Internet. It's one of my newer components. I usually go for much older gear.
 

nopiano

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Feb 15, 2009
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insider9 said:
Densen seem to be quite sure of their build quality. I'd love to have one from new as they come with lifetime warranty. That's either good engineering or smart marketing and quite likely both.

On a similar note this is the first amp I've measured acoustically that outputs the same volume from both left and right terminal. The closest I've seen before was within 0.3 dB.
I've mentioned my positive encounter with Densen previously, but one of the disappointments was that the warranty is back to base, and that means shippping abroad for those of us in the UK. Had the importer honoured this, or even a five year warranty, it would be far more attractive. As it stands, I'm afraid it is no more than marketing puff outside its homeland.
 

insider9

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Sep 20, 2016
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nopiano said:
insider9 said:
Densen seem to be quite sure of their build quality. I'd love to have one from new as they come with lifetime warranty. That's either good engineering or smart marketing and quite likely both.

On a similar note this is the first amp I've measured acoustically that outputs the same volume from both left and right terminal. The closest I've seen before was within 0.3 dB.
I've mentioned my positive encounter with Densen previously, but one of the disappointments was that the warranty is back to base, and that means shippping abroad for those of us in the UK. Had the importer honoured this, or even a five year warranty, it would be far more attractive. As it stands, I'm afraid it is no more than marketing puff outside its homeland.
Good to know, thanks Nopiano.
 

Al ears

Moderator
Vladimir said:
Question for insider09 primarily, since he uses an active setup where no DC offset coming out of the amp is further filtered by a passive crossover.

Lets do a health check. Amps warmed up, playing no sound, everything set to default, volume down, measure each channel L/R at the speaker terminals with a multimeter set for mV DC.

Simple tutorial
First locate a multimeter...... :)
 

Vladimir

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Dec 26, 2013
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I'd measure every amp in the house, especially AVRs. They sometimes come from the factory with horrible DC offset, which translates as distortion during listening sessions. I'm not saying this is inherent to AVRs, but considering they are more mass produced, there's a higher chance to get a dud.

0-25mV is excellent

25mV-50mV is OK, but not great. Might have audible distortion with certain speakers and discernable listeners.

50mV+ something is acting up. Time to open the bonnet.

For amplifiers that will be used in active setup, DC offset must be under 10mV considering there are no more capacitors in the signal path to the drivers to filter DC (no passive crossovers).
 

DocG

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May 1, 2012
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I'm a little late to the party, but thanks for pointing me to this issue, Vlad. I use an active set-up, and my power amps are DIY: two good reasons to check this DC thing ASAP.

And it's not as good as I had hoped...

I've built two stereo units. One unit gives 7,2 and 9,4 mV respectively, but the other one reads 19,6 and 20,0 mV.

When building the units, I used one case, one power supply and two NC-400 amplifier modules for each; I split the wiring from PS to amps (artisanal cutting and soldering together, connection protected with a heat shrink).

I never noticed any sound quality issues when listening these past few months -- all crystal clear and tight...

Any suggestions for solving this issue? What to look for when opening the case?
 

Vladimir

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Dec 26, 2013
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DocG said:
I'm a little late to the party, but thanks for pointing me to this issue, Vlad. I use an active set-up, and my power amps are DIY: two good reasons to check this DC thing ASAP.

And it's not as good as I had hoped...

I've built two stereo units. One unit gives 7,2 and 9,4 mV respectively, but the other one reads 19,6 and 20,0 mV.

When building the units, I used one case, one power supply and two NC-400 amplifier modules for each; I split the wiring from PS to amps (artisanal cutting and soldering together, connection protected with a heat shrink).

I never noticed any sound quality issues when listening these past few months -- all crystal clear and tight...

Any suggestions for solving this issue? What to look for when opening the case?
If the amplifier has DC offset setting on the PCB (small turn pot), you simply hook up your multimeter as before and adjust the pots to get close to 0mV DC reading. I see three blue trim pots on pics of the Hypex NC-400. Can you find out which one is for biasing and which for DC offset?

 
Q

QuestForThe13thNote

Guest
Is this a problem that can happen a lot or is this surely something that just fails, as I’m sure you’d hear it if so.
 

Vladimir

New member
Dec 26, 2013
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QuestForThe13thNote said:
Is this a problem that can happen a lot or is this surely something that just fails, as I’m sure you’d hear it if so.
It's a draw of the luck where and how much the DC leak from the amp displaces the speaker cone. It could be inaudible distortion, or could be even lower distortion than factory if the offset moved opposite of an ill centered cone (no driver is perfectly centered). In this case it might be less than a mm. But if you can get it perfect with just a turn of a pot, why ignore it.
 
Q

QuestForThe13thNote

Guest
I’d invalidate all warranties if I started doing that, haven’t had any issues I don’t think, so sensibly I’d have to leave it.
 

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