Pontus turn on “thump”

[Wolf11Man]

Ok, that may isolate the problem.
Anway, I know of no normal quality power amp that has no mute cirquit.

I had a close look at the Denapripsr products. They build stuff like we had it at the end of the last milenium, only using new Chinese parts, and lots of them.
They are really fast, too. From the web page: "The HESTIA and HYPERION are fully developed in-house, the entire R&D process took a good 1 year duration to complete." That is a record for a world best power-amp and (!) pre-amp.
People like Burmester, Nelson Pass or Peter walker needed years to refine their amps.
If you are so fast, you may miss something secondary, like a mute thingy.

Serious: If they call it a defect, what options do you have to get it repaired? Do they have any service partner near you?

 

[Sokel]

Normal power amp that do not have a mute relay usually thump, right?

No, go to Amir's reviews, at the end of the reviews it shows how gear behave at turn ON/OFF.
They all measure mere, single mV spikes, a little over normal noise floor, have a look here for example.

Close to 3mV at turn off and 15microV at turn on.
That's about normal.

 

[gjpmho]

The voltage spike was measured on the DAC was disconnected from the amp with the amp powered off.

I might habs found a bread crumb

Ok, that may isolate the problem.
Anway, I know of no normal quality power amp that has no mute cirquit.

I had a close look at the Denapripsr products. They build stuff like we had it at the end of the last milenium, only using new Chinese parts, and lots of them.
They are really fast, too. From the web page: "The HESTIA and HYPERION are fully developed in-house, the entire R&D process took a good 1 year duration to complete." That is a record for a world best power-amp and (!) pre-amp.
People like Burmester, Nelson Pass or Peter walker needed years to refine their amps.
If you are so fast, you may miss something secondary, like a mute thingy.

Serious: If they call it a defect, what options do you have to get it repaired? Do they have any service partner near you?

oh thanks for your perspective. It’s not under warranty, the cost to ship it to and from the service center will be $200. And then the cost of repair could be hundreds. I know another Pontus owner who says they’re hearing the same thump. I
I might have found a bread crumb. Pushing the stanby switch engages TWO buttons. These push button style buttons (circled in red) can go bad. I’ll try and see if pushing the standby button harder clears the issue. Right now I can’t do anything since it is dissambled. I am planning to add heatsinks to several mosfets.

 

[gjpmho]

No, go to Amir's reviews, at the end of the reviews it shows how gear behave at turn ON/OFF.
They all measure mere, single mV spikes, a little over normal noise floor, have a look here for example.

View attachment 504587


Close to 3mV at turn off and 15microV at turn on.
That's about normal.

Can you please send me a link to Amir’s review?

 

[Sokel]

Can you please send me a link to Amir’s review?

boXem A 4216/E2 Stereo Amplifier Review

This is a review and detailed measurements of the boXem A 4216/E2 stereo balanced amplifier based on Purifi 1ET6525SA class D module. It was sent to me by the company and costs €1,160 (USD $1,350). While not built out of billet of aluminum and such, the 4216/E2 still manages to look unique and...

www.audiosciencereview.com

Most gear reviews here have it, towards the end of the first post.

 

[gjpmho]

boXem A 4216/E2 Stereo Amplifier Review

This is a review and detailed measurements of the boXem A 4216/E2 stereo balanced amplifier based on Purifi 1ET6525SA class D module. It was sent to me by the company and costs €1,160 (USD $1,350). While not built out of billet of aluminum and such, the 4216/E2 still manages to look unique and...

www.audiosciencereview.com

Most gear reviews here have it, towards the end of the first post.

this is one example out of thousands if not tens of thousands of different amp circuits. By design, some amps will produce a thump, and some will not. 1VDC is not that much out of this DAC that outputs 2Volts.

 

[Sokel]

this is one example out of thousands if not tens of thousands of different amp circuits. By design, some amps will produce a thump, and some will not.

There are many more examples, from a point on Amir measures that normally as it's a sign of good health.
If an amp thumbs by design, it's a bad design (edit) or badly chained.

(OK, I exclude corner cases like amps chained to 105dB sensitivity speakers. Some single digit mV there can produce a mild thumb)

 

[Sokel]

1VDC is not that much out of this DAC that outputs 2Volts.

It doesn't sound much but think of the amplification it will get.

Also note that at line-level nicely recorded music's combined spectrum voltage rarely exceeds 500mV.

And another, if something in there lurks slowly (like a voltage's bad joint going worst for example) this 1VDC can easily end up equaling to PSU's full voltage.
You definitely don't want that.

 

[gjpmho]

There are many more examples, from a point on Amir measures that normally as it's a sign of good health.
If an amp thumbs by design, it's a bad design (edit) or badly chained.

(OK, I exclude corner cases like amps chained to 105dB sensitivity speakers. Some single digit mV there can produce a mild thumb)

boXem A 4216/E2 Stereo Amplifier Review

This is a review and detailed measurements of the boXem A 4216/E2 stereo balanced amplifier based on Purifi 1ET6525SA class D module. It was sent to me by the company and costs €1,160 (USD $1,350). While not built out of billet of aluminum and such, the 4216/E2 still manages to look unique and...

www.audiosciencereview.com

Most gear reviews here have it, towards the end of the first post.

It doesn't sound much but think of the amplification it will get.

Also note that at line-level nicely recorded music's combined spectrum voltage rarely exceeds 500mV.

And another, if something in there lurks slowly (like a voltage's bad joint going worst for example) this 1VDC can easily end up equaling to PSU's full voltage.
You definitely

let’s say my volume control goes from 0 to 10. I usually have my volume set near 2 or 3. I heard a thump at 3. The thump isn’t that loud. If I set volume to 10 that would be a complete different story, and likely blow my speakers. CD players and DAC output 2Vrms though single ended output, but the amp volume control attenuates that signal.

 

[Sokel]

let’s say my volume control goes from 0 to 10. I usually have my volume set near 2 or 3. I heard a thump at 3. The thump isn’t that loud. If I set volume to 10 that would be a complete different story, and likely blow my speakers. CD players and DAC output 2Vrms though single ended output, but the amp volume control attenuates that signal.

You can measure that at speakers binding posts the same way you measure the outputs.
It's always a good idea to measure there, all states, on,off, idle, etc. It shows the combined system's health.

And remember, analog pots don't like DC very much.

 

[HenrikEnquist]

I measured a voltage spike at the Pontus RCA outputs.

How did you measure this? Oscilloscope or multimeter?

 

[gjpmho]

How did you measure this? Oscilloscope or multimeter?

multimeter. Here’s the video.I measured around 0.9VDC across RCA (at the DAC) signal to ground several times. My amp is turned off and the only connections to the DAC are the power and RCA cords. The multimeter is connected to the RCA cord from the DACs analog out in the video.

 

[HenrikEnquist]

Ok, I would not trust a multimeter to catch the real amplitude of short spikes. It likely does some low-pass filtering before measuring. So the real peak may be quite a bit higher, if it's very short.

 

[Wolf11Man]

Personaly I do not think your DAC has an actual defect if other owners can reproduce the fault.

In theory, if the op-amps feeding the output are using a dual power supply, like maybe +-15 Volt, in case of one voltage missing there could be DC voltage at it's output.
Now, your DAC will not be DC coupled, but have a capacitor between OP-amp output and the line out to your amp as a safety measure. This capacitor has to be loaded to full DC potential, then it can work as normal. The loading process will produce a huge voltage spike at the output.
This could explain why both stereo channels show the "thump".
Many HIFI amps are driven to full output with less than 1 Volt, usually around 800mV. So 1V at the output is hardly tollerable when amplified. Quite a small spike can blow a tweeter, the larger drivers are not in danger, even if you hear it very loud.

If you have very large capacitor banks and a torrodial transformer, things can go wrong after some time. Maybe check the voltages, before and behind the regulator.
Please, if you are not practiced in electronics, measureing inside a running circuit is the number one ticket to a deadly short. Never measure Amps or Ohms!
Even with the mains plug removed, the capacitors can keep a lot of energy, sometimes for hours.

 

[HenrikEnquist]

This is by design and a 1VDC spike is okay in the scope of things:

I do not think this is ok at all. A proper mute circuit is very simple and part of the absolute basic requirements for any circuit that isn't inherently silent at power on and off (which is possible but unusual).

 

[gjpmho]

Personaly I do not think your DAC has an actual defect if other owners can reproduce the fault.

In theory, if the op-amps feeding the output are using a dual power supply, like maybe +-15 Volt, in case of one voltage missing there could be DC voltage at it's output.
Now, your DAC will not be DC coupled, but have a capacitor between OP-amp output and the line out to your amp as a safety measure. This capacitor has to be loaded to full DC potential, then it can work as normal. The loading process will produce a huge voltage spike at the output.
This could explain why both stereo channels show the "thump".
Many HIFI amps are driven to full output with less than 1 Volt, usually around 800mV. So 1V at the output is hardly tollerable when amplified. Quite a small spike can blow a tweeter, the larger drivers are not in danger, even if you hear it very loud.

If you have very large capacitor banks and a torrodial transformer, things can go wrong after some time. Maybe check the voltages, before and behind the regulator.
Please, if you are not practiced in electronics, measureing inside a running circuit is the number one ticket to a deadly short. Never measure Amps or Ohms!
Even with the mains plug removed, the capacitors can keep a lot of energy, sometimes for hours.

1. The 1VDC spike is attenuated by volume control. The thump measures less than 100mV at the speaker terminals when I have the volume set to regular listening levels.
2. Thank you for the tips. I have repaired a few integrated amplifiers and receivers with service manuals. I don’t have the service manual but can deduce quite a bit from the difference IC datasheets. It’s grunt work so far I can trace the signal from the mute button to DSP module. Still I think this is by design and don’t see it causing issues in the DAC.

 

[gjpmho]

It appears the FPGA chip mutes the signal when I press the mute button. If that is the case, then would it make sense that a mute relay or separate muting circuit is needed in the analog audio section to mute voltage spikes in the analog output while powering up?

 

[MAB]

It appears the FPGA chip mutes the signal when I press the mute button. If that is the case, then would it make sense that a mute relay or separate muting circuit is needed in the analog audio section to mute voltage spikes in the analog output while powering up?

Yes, muting the outputs is best practice. Rod Elliott has a good discussion.

Project 104 - Preamp/ crossover muting circuit

ESP Audio Projects - Project 104 Preamp or crossover muting circuit using a common hex Schmitt trigger IC

sound-au.com

A relay can either short the outputs to ground, or disconnect them. Shorted to ground has some advantages so long as it's implemented properly.
I have a 30 year old R2R DAC from Adcom that has proper muting. To bad we have lost our way on this. Possibly due to various opinions about relays degrading the sound.

The downside, many of the vintage gear I have has relay issues at some point. But they are all three or more decades old, and also typically have switch and control issues too.

I get it that people are paranoid about this stuff, but if we get rid of relays shouldn't we also get rid of volume knobs?

In reality, the volume knob and any other contacts and switches are likely introducing more noise and distortion than the DAC itself. If done right, the impact is inaudible for decades. I do think some companies struggle with best practices though.

 

[gjpmho]

In some cases that’s true, Schiit Audio has mute relays in their DACs. They even talk about them in the FAQs. Some folks don’t know what the clicking was all about. We’re a fussy bunch lol. Thanks for the link it is educational.

 

[JeffS7444]

I don't have a solution, but I see what appears to be 4 sealed relays on that Denafrips DAC and wonder if those have anything to do with muting. Reliable switching of low voltages and currents can be tricky.

For what it's worth, as shipped my not-cheap Benchmark DAC2HGC had a terrible turn on/off thump, which would be unthinkable in a more mainstream piece of equipment. OTOH, my Marantz AVR is a model of civility, and surprisingly, so is an inexpensive Behringer DEQ2496. A series of firmware updates mostly fixed the Benchmark's problems, though I got charged $50 each time. For reasons I don't understand, bad behavior is tolerated more in pricier, higher-end components.