evm1024
New member
First results Hiss comes from headphone amp.
First results back tonight indicate that the headphone amp hiss in intrinsic to the IC power amp. Shorting the summing input to ground does not change the hiss level. Plus the hiss is much the same in both channels.
I suspect that the IC amp has always been this hissy as a design "feature". Rather than as an aging of the device. (I have one more test to do on this amp so all is not lost yet)
For me the next step is to take a look at replacing the headphone amp. Possably with a CMoy amp or other headphone amp. Target headphones would be Koss pro4aat (150 ohm headphones)
As a side note in the process of tracking down the hiss I have noted that the record and playback circuits are quite quiet. This is limited to the headphone amp.
Regards
First results back tonight indicate that the headphone amp hiss in intrinsic to the IC power amp. Shorting the summing input to ground does not change the hiss level. Plus the hiss is much the same in both channels.
I suspect that the IC amp has always been this hissy as a design "feature". Rather than as an aging of the device. (I have one more test to do on this amp so all is not lost yet)
For me the next step is to take a look at replacing the headphone amp. Possably with a CMoy amp or other headphone amp. Target headphones would be Koss pro4aat (150 ohm headphones)
As a side note in the process of tracking down the hiss I have noted that the record and playback circuits are quite quiet. This is limited to the headphone amp.
Regards