If the pop is heard only by putting your ear to the speaker, then it is just a symptom of the amplifier’s age, but if it can be heard from the listening position then it’s not normal. The pop is caused by a potential difference in the output voltage rails on startup, bleeding out a small amount of dc. What I would do is check to see the dc offset at startup and then after warm up. If the dc offset on startup jumps to no more than 50 millivolts and then drops to a few millivolts, then the amp is most likely ok. But ML amps usually show a dead zero dc offset and I wouldn’t buy it if it shows more than 10 millivolts of offset after a 20 minute warm up.
Another thing to check would be the rail voltages. Simply measure across an output resistor from the metal case (the collector) to the ground lug or speaker negative. The voltages on all resistors should be exact. If any voltages are off by a even couple of hundred millivolts then it could be a bad trimmer resistor or the trimmer may have to be adjusted. Then that may be all that’s needed to cure the popping and/or dc offset.
The ML amplifiers have a series of speaker protection: thermal, dc offset, high input voltage, overvoltage and short circuit trips. They do not use output relays. The clicking relays on startup are surge protection and input stage isolation. All clicking sounds are normal.
Keep in mind you are looking at a 25 year old amplifier. It costs $1500 just to replace the filter caps — the sucky Phillips made in China caps that are practically guaranteed to fail.
But then again, for $2500 asking price you are getting performance that would require an outlay of 25 grand or more to buy new.
Another thing to check would be the rail voltages. Simply measure across an output resistor from the metal case (the collector) to the ground lug or speaker negative. The voltages on all resistors should be exact. If any voltages are off by a even couple of hundred millivolts then it could be a bad trimmer resistor or the trimmer may have to be adjusted. Then that may be all that’s needed to cure the popping and/or dc offset.
The ML amplifiers have a series of speaker protection: thermal, dc offset, high input voltage, overvoltage and short circuit trips. They do not use output relays. The clicking relays on startup are surge protection and input stage isolation. All clicking sounds are normal.
Keep in mind you are looking at a 25 year old amplifier. It costs $1500 just to replace the filter caps — the sucky Phillips made in China caps that are practically guaranteed to fail.
But then again, for $2500 asking price you are getting performance that would require an outlay of 25 grand or more to buy new.