I hooked up a pair of stereo integrated amps in bridge mode recently. Sonic nirvana.
After a couple months both developed a hiss after playing for an hour or two. But only on the input connected to a source. Both amps close to the same. The open inputs are totally silent on high efficiency horn speakers.
How this was identified.
A week ago after playing for several hours got close to the mid and tweeter horns. Heard an annoying hiss when head was close to the speaker. Could not hear 2’ away but easy to hear at 1’ away. Mainly from tweeter, 4K crossover. Some from mid.
Blamed dac. Selected another analog input and no noise. Swapped back and forth. Had to be dac. Had another of these dacs, hooked it up and got the same hiss. Replaced the iPower switcher with a linear supply. Same hiss.
Turned off and ran a shorter balanced cable. No noise. Built a true Star Quad cable and connected. No hiss. Played for several hours and hiss was back.
Next day same thing deathly quiet on power up. Play music and hiss returns. Played with power cords and wall outlets. Move second dac to equipment rock to allow using 1/2 meter analog input cables. Same quiet at first and hiss after an hour of playing. Unused analog inputs (open) were silent.
Finally redid system and hooked up a single stereo amp with single ended RCA input. Problem gone. Silent on power up and after hours of playing.
Can only guess temperature drift somewhere in amplifier created this low level high frequency noise when the channels are bridged. And only when input sees low impedance from a powered source. Open inputs are silent when selected.
Amps have a single resonant mode supply shared between channels. So one supply for both +/- rails when bridged. But silent until music is played and amp warms up a little. And only if amp seeing the low impedance of a powered up dac’s output stage.
For now going to just use a single amplifier in stereo mode. Normal output is 100 mW or less. But hope to identify issues and try to address to allow going back to bridged amplifiers.
Cannot accept any hiss even with 105 dB efficient horns because it is not unavoidable. Other amps I have are silent with ear in tweeter. The fact that it is not audible in listening position does not make it acceptable.
After a couple months both developed a hiss after playing for an hour or two. But only on the input connected to a source. Both amps close to the same. The open inputs are totally silent on high efficiency horn speakers.
How this was identified.
A week ago after playing for several hours got close to the mid and tweeter horns. Heard an annoying hiss when head was close to the speaker. Could not hear 2’ away but easy to hear at 1’ away. Mainly from tweeter, 4K crossover. Some from mid.
Blamed dac. Selected another analog input and no noise. Swapped back and forth. Had to be dac. Had another of these dacs, hooked it up and got the same hiss. Replaced the iPower switcher with a linear supply. Same hiss.
Turned off and ran a shorter balanced cable. No noise. Built a true Star Quad cable and connected. No hiss. Played for several hours and hiss was back.
Next day same thing deathly quiet on power up. Play music and hiss returns. Played with power cords and wall outlets. Move second dac to equipment rock to allow using 1/2 meter analog input cables. Same quiet at first and hiss after an hour of playing. Unused analog inputs (open) were silent.
Finally redid system and hooked up a single stereo amp with single ended RCA input. Problem gone. Silent on power up and after hours of playing.
Can only guess temperature drift somewhere in amplifier created this low level high frequency noise when the channels are bridged. And only when input sees low impedance from a powered source. Open inputs are silent when selected.
Amps have a single resonant mode supply shared between channels. So one supply for both +/- rails when bridged. But silent until music is played and amp warms up a little. And only if amp seeing the low impedance of a powered up dac’s output stage.
For now going to just use a single amplifier in stereo mode. Normal output is 100 mW or less. But hope to identify issues and try to address to allow going back to bridged amplifiers.
Cannot accept any hiss even with 105 dB efficient horns because it is not unavoidable. Other amps I have are silent with ear in tweeter. The fact that it is not audible in listening position does not make it acceptable.
