musicforcities
Senior Member
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- Sep 18, 2021
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I just recapped my Marantz ma-500u monoblocks. I love the form factor, you can fit directionally in a 19” rack. they take up so little room for a 100-120w class AB amp and the sound is great—flat/neutral and zero hiss from my 84db speakers at max volume. The only thing they lack is a 12v trigger. The ma61000 are basically the same but with a trigger.
I did replace the power cords— and used the end of 3’ 2/ 14AWG cord instead of the 6ft long 16awg it comes with. not for snake oil reasons, I just wanted shorter cords and I had these extension cords laying around.
The bias voltage is rock steady and zero dc offset at binding posts. I mean zero. They don’t get hot in use either. Just warm.
They are elegantly laid out inside with plenty of room between pads for soldering. Not to many el caps to deal with and the pcb are of good quality. The only trick is the leads were all bent flat to the board at the factory. So you can lift a trace pad easily. I pumped the solder out and then clipped the caps leads on the other side of the board and that worked well.
The original caps are all Elna and most audio Elna. Nevertheless, they are all 85 degree caps and are a few are known to be prone to failure or to drift out of spec in the hotter spots. Including the filter caps. In one amp both Elna filter caps were bulging and had higher esr and lower capacity than the other. So I changed those. Of course one can’t find the exact caps anymore and the ones that do exist that fit are all 35mm rather than the original 30mm. So you have to drill new holes to accommodate. But the board is good, the filter pads are thankfully huge and a sharp drill bit did the job without any issue in minutes.
I refreshed all the thermal paste and pads while I was there as you have to detach the heat sink from the transistors to get to most things. A good preventative maintenance thing to do on any amp over 10 years old as thermal paste becomes less effective over time and sil pads can’t be reused anyway.
I did replace the power cords— and used the end of 3’ 2/ 14AWG cord instead of the 6ft long 16awg it comes with. not for snake oil reasons, I just wanted shorter cords and I had these extension cords laying around.
The bias voltage is rock steady and zero dc offset at binding posts. I mean zero. They don’t get hot in use either. Just warm.
They are elegantly laid out inside with plenty of room between pads for soldering. Not to many el caps to deal with and the pcb are of good quality. The only trick is the leads were all bent flat to the board at the factory. So you can lift a trace pad easily. I pumped the solder out and then clipped the caps leads on the other side of the board and that worked well.
The original caps are all Elna and most audio Elna. Nevertheless, they are all 85 degree caps and are a few are known to be prone to failure or to drift out of spec in the hotter spots. Including the filter caps. In one amp both Elna filter caps were bulging and had higher esr and lower capacity than the other. So I changed those. Of course one can’t find the exact caps anymore and the ones that do exist that fit are all 35mm rather than the original 30mm. So you have to drill new holes to accommodate. But the board is good, the filter pads are thankfully huge and a sharp drill bit did the job without any issue in minutes.
I refreshed all the thermal paste and pads while I was there as you have to detach the heat sink from the transistors to get to most things. A good preventative maintenance thing to do on any amp over 10 years old as thermal paste becomes less effective over time and sil pads can’t be reused anyway.