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Topic: DAC-amp volume goes up by itself under certain circumstance (Read 1850 times) previous topic - next topic
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DAC-amp volume goes up by itself under certain circumstance

Hi,

I'm playing with a new DAC-amp Denon PMA-50 (25 W + 25 W at 8 Ω/ohm, 1 kHz, THD 0,1 %, 50 W + 50 W at 4 Ω/ohm, 1 kHz, THD 1,0 %, Speaker: 4-16 Ω/ohm) and noticed an issue for which I could not find on Google a clear explanation of the root cause.

I've connected it through USB and use Windows 10 with foobar2000 and its Advanced Limiter plugin. Foobar2000 volume is put a 0.00dB and I do not use ReplayGain. Output is set to 192kHz 24 bits.

I've hooked up bookshelf Wharfedale Valdus 100 speakers: Nominal impedance 4-8 Ohm, Sensitivity 88dB and Power handling 100 Watts. These are at least 15 years old.

The volume knob can go from -90 to 0dB. When I pass about -25dB uptil 0dB the volume doesn't get louder although flatter. At maximum volume the speakers don't sound really distorted, but just sound flatter and not crystal clear.

Now the issue: when turning the volume knob down again from max volume to about -25dB the volume gets lowered, but inmediately after this the volume slowly goes up by itself! dBs of volume knob on display stays unaltered. When turning volume below about -30dB, the volume gets lowered and doesn't go up anymore by itself.

Is this a kind of speaker or amp protection?
Has this to do with speakers not able to handle the power?
Would speakers of higher quality have better behaviour at (almost) maximum volume? (not that I go often beyond -40dB)

On headphone I didn't notice this issue.

Thanks all.
Alexxander

Re: DAC-amp volume goes up by itself under certain circumstance

Reply #1 –
Quote from: Alexxander on
I'm playing with a new DAC-amp Denon PMA-50 (25 W + 25 W at 8 Ω/ohm, 1 kHz, THD 0,1 %, 50 W + 50 W at 4 Ω/ohm, 1 kHz, THD 1,0 %, Speaker: 4-16 Ω/ohm) and noticed an issue for which I could not find on Google a clear explanation of the root cause.

I've connected it through USB and use Windows 10 with foobar2000 and its Advanced Limiter plugin. Foobar2000 volume is put a 0.00dB and I do not use ReplayGain. Output is set to 192kHz 24 bits.

I've hooked up bookshelf Wharfedale Valdus 100 speakers: Nominal impedance 4-8 Ohm, Sensitivity 88dB and Power handling 100 Watts. These are at least 15 years old.

The volume knob can go from -90 to 0dB. When I pass about -25dB uptil 0dB the volume doesn't get louder although flatter. At maximum volume the speakers don't sound really distorted, but just sound flatter and not crystal clear.

This kind of performance is commonly seen in automotive sound. There is a protective circuit in the amplifier that keeps the amplifier from ever seeming to be distorted. If you turn up the volume to the point where the amp would clip, the protection circuit simply automagically turns the volume down electronically until there is no distortion.

Quote
Now the issue: when turning the volume knob down again from max volume to about -25dB the volume gets lowered, but inmediately after this the volume slowly goes up by itself! dBs of volume knob on display stays unaltered.

That's the protective circuit slowly resetting itself.

Quote
When turning volume below about -30dB, the volume gets lowered and doesn't go up anymore by itself.

The protective circuit has nothing to do and it is inactive.

Quote
Is this a kind of speaker or amp protection?

Yes.

Quote
Has this to do with speakers not able to handle the power?

No, the amp has hardly a clue what the speakers are doing unless they are already damaged by too much power which can lead to voice coil rubbing which may temporarily short out the amp and cause distortion.

Quote
Would speakers of higher quality have better behaviour at (almost) maximum volume? (not that I go often beyond -40dB)

There's a pretty obvious problem with this combination of speakers, amp, and your thirst for loudness.    One or more of those things will have to change.

From thousands of miles away and sitting behind a computer, I can't tell because of all of the possible permutations.

Quote
On headphone I didn't notice this issue.

Using headphones completely changes the power levels in your amp.
 

Re: DAC-amp volume goes up by itself under certain circumstance

Reply #2 –
Thirst of loudness?  ::)   :)) I'm only testing.

So, I understand that the protective circuit jumps in when the power source isn't able to deliver all the needed current.
If I play the music with ReplayGain applied, the protective circuit doesn't act, so input level is important.

Overall, I'm pretty happy with this DAC+amp. And it has enough loudness for me  ;)

Thanks for all the answers.

Cheers!