Hi again - weird one this, but I'm sure someone will know why 😊
I have been experimenting with using the ICEPower 125axs2 amplifier kit I made with both a pre-amplifier and also direct from my DAC (Pontus II) with my streamer (Lumin) dealing with volume control via LeedH processing. When connected directly to the DAC via RCA out every time the sample rate changes I get a little pop, also when I turn the Lumin streamer to standby (via remote app) I get a couple of little pops as well. When using the amp with a Fosi P3 pre-amp (for a bit of fun😊) in-between there are no pops or noises at all. Only problem is I pretty much prefer the raw amp direct, its quite astonishingly revealing.
The location of components has not changed, the only thing that is different is the DAC goes into the pre-amp and the pre-amp then goes into the ICEPower amp. So I am sort of thinking it might be a grounding issue, I can feel the 'liveness' of the Fosi pre-amp by sliding my finger along the casework so I m pretty sure it just has a two pin connection to the mains block via its wall wart plug. Whereas the ICEPower is properly wired into a three pin plug with earth (and the case is earthed and the board is earthed to the case in two places via tinned holes to the case - funnily enough one of the tinned holes did not line up with a bare tinned hole in the case so I scraped away the paint to ensure it did earth... di I do wrong?
I'm a total newbie at this so I only have 50 years of hi-fi fanatic level of info, although this project as certainly fired my enthusiasm for more self builds in the future... 😊
I have been experimenting with using the ICEPower 125axs2 amplifier kit I made with both a pre-amplifier and also direct from my DAC (Pontus II) with my streamer (Lumin) dealing with volume control via LeedH processing. When connected directly to the DAC via RCA out every time the sample rate changes I get a little pop, also when I turn the Lumin streamer to standby (via remote app) I get a couple of little pops as well. When using the amp with a Fosi P3 pre-amp (for a bit of fun😊) in-between there are no pops or noises at all. Only problem is I pretty much prefer the raw amp direct, its quite astonishingly revealing.
The location of components has not changed, the only thing that is different is the DAC goes into the pre-amp and the pre-amp then goes into the ICEPower amp. So I am sort of thinking it might be a grounding issue, I can feel the 'liveness' of the Fosi pre-amp by sliding my finger along the casework so I m pretty sure it just has a two pin connection to the mains block via its wall wart plug. Whereas the ICEPower is properly wired into a three pin plug with earth (and the case is earthed and the board is earthed to the case in two places via tinned holes to the case - funnily enough one of the tinned holes did not line up with a bare tinned hole in the case so I scraped away the paint to ensure it did earth... di I do wrong?
I'm a total newbie at this so I only have 50 years of hi-fi fanatic level of info, although this project as certainly fired my enthusiasm for more self builds in the future... 😊
So I've changed where the amp is plugged in to the mains, but no effect. I've had DAC's that pop as sample rate changed before, but for my Pontus II the latest firmware seemed to stop that issue - just think its strange that with a pre-amp in between DAC and amp there was no pop but now there is?
It may be a common-mode disturbance pop that your preamp rejects, or something like that going on.
Regarding the "liveness" its probably a leakage current that may be within legal limits. It can be caused by a capacitor from AC line hot to common (the chassis) to reduce noise, or for other reasons. Some guitar amps have a switch in the back with two on positions. One position has a cap connected to the chassis, the other on position doesn't. Its can be set to whichever on position produces the least hum and buzz. If set to the cap on position, it can also give the guitarist an unpleasant tingle if they touch a ground and the guitar at the same time.
In your case, my inclination probably would be to try grounding it.
Regarding the "liveness" its probably a leakage current that may be within legal limits. It can be caused by a capacitor from AC line hot to common (the chassis) to reduce noise, or for other reasons. Some guitar amps have a switch in the back with two on positions. One position has a cap connected to the chassis, the other on position doesn't. Its can be set to whichever on position produces the least hum and buzz. If set to the cap on position, it can also give the guitarist an unpleasant tingle if they touch a ground and the guitar at the same time.
In your case, my inclination probably would be to try grounding it.
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I'm learning so much here, so like a diligent helpful person I'm going to waffle on about how this issue was cured should anyone else come across something similar (why I'll leave to you folk to explain!)
So as a logical sort of chap I started working backwards form the 'pop' situation...
Back one step: using the little Fosi P3 as a pre-amp with the ICEPower power amp there was no pop
Back two steps: using the Fosi P3 pre-amp with the Fosi V3 amp together (before the ICEPower arrived) there was no pop
Back three steps: using my Line Magnetic tube integrated amp (prior to it developing a fault and getting the V3 as a bit of fun) there was no pop
So... what had changed?
Well obviously the ICEPower amp is the culprit, but why only when used directly to the DAC with nothing in-between?
Then I remembered a problem with earlier firmware versions that some people had with the Pontus II DAC, it made a pop when it changed sampling rates! I never had this issue and my firmware is the latest anyway. But that made me recall a review from GoldenSound and I quote "However the Pontus 2 does not clip, but instead when a sample value reaches above the maximum, it ‘wraps around’ to the minimum negative value, causing a huge sudden transient which will be very audible and may appear as crackling/popping. If you hear crackling/popping from your Pontus 2 now and then, this is likely why. Hopefully Denafrips can resolve this in a firmware update, but failing that, add -3dB of headroom/volume attenuation in your media player to resolve the issue."
Ah! I now realised the only other variable that had changed! I could never turn the Line Magnetic volume control above about 7 o'clock before it blew my ears away, so years ago I bought some in line attenuators to reduce the volume by 10dB. When I took the Line Magnetic out of the rack I removed the attenuators as I thought this was an amp input issue not a DAC output issue - and of course using the Fosi amp I had no problem so this confirmed the idea.
Then as I have read just about everything on the ICEPower modules before buying the 125asx2 I remembered something about input impedance to the board and output impedance from the source, and I quote from this group... "'...it turns out that the input impedance of these ICEPower amps drops significantly with rising frequency. At DC, the input impedance is 270K, at low frequencies, it drops to about 27K, and at 20KHz it's below 6K. This means that the amp needs a low output impedance source to drive it."
I don't have the tech knowledge to know why, well only a basic idea, but all this talk of output impedance and lowering the headroom/volume attenuation seemed to be encouraging me to put those attenuators back into the mix - and the result is no more pops! Result!! 🙂
Now, the exact reason why this might be I'll leave to someone who has more understanding of input/output matching than me... 😊
So as a logical sort of chap I started working backwards form the 'pop' situation...
Back one step: using the little Fosi P3 as a pre-amp with the ICEPower power amp there was no pop
Back two steps: using the Fosi P3 pre-amp with the Fosi V3 amp together (before the ICEPower arrived) there was no pop
Back three steps: using my Line Magnetic tube integrated amp (prior to it developing a fault and getting the V3 as a bit of fun) there was no pop
So... what had changed?
Well obviously the ICEPower amp is the culprit, but why only when used directly to the DAC with nothing in-between?
Then I remembered a problem with earlier firmware versions that some people had with the Pontus II DAC, it made a pop when it changed sampling rates! I never had this issue and my firmware is the latest anyway. But that made me recall a review from GoldenSound and I quote "However the Pontus 2 does not clip, but instead when a sample value reaches above the maximum, it ‘wraps around’ to the minimum negative value, causing a huge sudden transient which will be very audible and may appear as crackling/popping. If you hear crackling/popping from your Pontus 2 now and then, this is likely why. Hopefully Denafrips can resolve this in a firmware update, but failing that, add -3dB of headroom/volume attenuation in your media player to resolve the issue."
Ah! I now realised the only other variable that had changed! I could never turn the Line Magnetic volume control above about 7 o'clock before it blew my ears away, so years ago I bought some in line attenuators to reduce the volume by 10dB. When I took the Line Magnetic out of the rack I removed the attenuators as I thought this was an amp input issue not a DAC output issue - and of course using the Fosi amp I had no problem so this confirmed the idea.
Then as I have read just about everything on the ICEPower modules before buying the 125asx2 I remembered something about input impedance to the board and output impedance from the source, and I quote from this group... "'...it turns out that the input impedance of these ICEPower amps drops significantly with rising frequency. At DC, the input impedance is 270K, at low frequencies, it drops to about 27K, and at 20KHz it's below 6K. This means that the amp needs a low output impedance source to drive it."
I don't have the tech knowledge to know why, well only a basic idea, but all this talk of output impedance and lowering the headroom/volume attenuation seemed to be encouraging me to put those attenuators back into the mix - and the result is no more pops! Result!! 🙂
Now, the exact reason why this might be I'll leave to someone who has more understanding of input/output matching than me... 😊