I just acquired an Adcom GFA-5400. It is in very good shape and very clean inside and out. I don't know the use history but it looks like the previous owner had not used it very much. It is a Version 2 (i.e., made in China with Jamecon caps and contains a protection board).
I don't want to recap it if it is not necessary, and I don't want to pull the caps out to measure them. Instead I measured the ripple and wanted to see if the results would tell me whether the caps are good or not. The results are attached, but I don't have a reference so I don't know if they're good or not. Note that I'm not trying to assess the amp design. I'm just trying to see if the kind of ripple observed is normal or not for this amp, and hope from this info I can decide if the caps need to be replaced or not.
At 20Hz 40Vp-p (into 5 ohm load), I got a ripple of 2.7Vp-p in one rail. That works out to 2.5% sag in the upper rail. I think that is not too bad but what is more concerning is that the other channel sagged 20% less. Also, when I cranked up the power (forgot how high but definitely not at full power) the amp suddenly shut down which also caused my scope to shut down and reboot. The last time my scope shut down and reboot happened when I connected the negative output of a Class D amp to the ground (forgot it was a full bridge), which caused big sparks to fly. There was no damage and everything started up fine again, but I did not attempt to measure at higher power at 20 Hz.
The scope captures are attached. Can we tell if the supply caps are in good shape or not from these measurements?
I don't want to recap it if it is not necessary, and I don't want to pull the caps out to measure them. Instead I measured the ripple and wanted to see if the results would tell me whether the caps are good or not. The results are attached, but I don't have a reference so I don't know if they're good or not. Note that I'm not trying to assess the amp design. I'm just trying to see if the kind of ripple observed is normal or not for this amp, and hope from this info I can decide if the caps need to be replaced or not.
At 20Hz 40Vp-p (into 5 ohm load), I got a ripple of 2.7Vp-p in one rail. That works out to 2.5% sag in the upper rail. I think that is not too bad but what is more concerning is that the other channel sagged 20% less. Also, when I cranked up the power (forgot how high but definitely not at full power) the amp suddenly shut down which also caused my scope to shut down and reboot. The last time my scope shut down and reboot happened when I connected the negative output of a Class D amp to the ground (forgot it was a full bridge), which caused big sparks to fly. There was no damage and everything started up fine again, but I did not attempt to measure at higher power at 20 Hz.
The scope captures are attached. Can we tell if the supply caps are in good shape or not from these measurements?
