Great news, it's not my tweeters!
Jesus gave me the idea this morning
I use iphone and istreamer, so logically I should not be able to adjust volume on the phone since it sends digital signal.
But strange thing, I was always able to with this DAC (never searched about this).
So far I always used the max volume, just with the idea to maximize voltage output. Old habit from when I didn't have external DAC when the phone was plugged directly on ms8.
This morning I tried to lower it a bit, and the crackles disappeared!!!!! Yalaaaaa
Even just one step, like 90% did the trick!
Of course I lost few db in the total chain, but I still could increase the ms8 volume to insane level without anything disturbing.
Happy man here
I also tried the AUX input setting in ms8, min or max > no effect
I alsways assumed that with iPhone, ms8 and ms amps I would not have to deal with gain etc
I guess I was wrong.
I'll try another DAC soon, the audio engine d1 (with a knob)
this one I know that the phone volume is bypassed.
Just found this about the istreamer:
"The iPod volume control does affect the volume coming out of the iStreamer. By default, it's at the top, so the iStreamer puts out a 2.25 volt signal. But if you need a weaker signal going into your amp, it's great that you can reduce the volume.
At work, my current headphone amp is a portable and the 2.25 volt signal is too strong, causing distortion. Turning down the iStreamer volume a touch eliminates the distortion and the sound is great.
At home, in the bedroom, my integrated amp is 50 watts and my speakers are sensitive (92 dB). If I'm listening very quietly at night, the only way to get the sound quiet enough is to turn down the iStreamer volume.
The iPod is probably just sending a signal to the iStreamer to attenuate the analog output signal. Since the iPod is sending the iStreamer raw data, you can't reduce the "volume" of that data. But you can send extra info along with the data to control the volume once it's been converted into analog sound. It must work that way somehow.