RAM 512 power amplifier
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Shinano
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So I finished listening to the RAM for about two hours. I first let the amp play on low volume for 2-3 hours to reform the caps as I don’t know the last time it was used. The preamp used was a Rotel RSP-1572, and speakers were B&W CM9. I had listened to a Rotel RMB-1555 with this preamp before, so that was my reference. The RAM sounds slightly warmer than neutral, but not as warm as the Rotel. It has a punchier sound overall, but still maintains a smoothness to it. It never felt fatiguing or harsh, even at slightly higher than normal listening levels (somewhere between 80-85db). The bass on the Rotel was thicker, but the RAM was a little more controlled and punchier, where the Rotel was a little slower. The other frequency ranges weren’t super different, but the RAM felt more energetic than the Rotel. Overall, the RAM, which I paid $260 for, sounded like the better amp in the finer details. The differences were minimal in some areas, but at worst, the RAM equaled the Rotel. At best, the RAM was slightly ahead, which considering the price difference between the two, is quite amazing. I’ll get pictures tomorrow morning, but unfortunately some of the screws for the top cover are pretty much stuck, and I don’t want to strip them out, but I’ll try to get pictures through the vents.
Shinano
Shinano
Shinano
Member
I just listened for about another hour. I did a A to B test first, and here are my thoughts. The RAM conveyed stringed instruments a bit softer and more delicate than the Rotel. Pianos and the like were similar. General listening was about the same as yesterday. The RAM has definitely seen a noticeable improvement after I had it sit at low volume for a few hours yesterday to reform the capacitors. Compared to the first time (which was before yesterday’s test), it has definitely improved in all areas, and is no longer as harsh and thin sounding.
Shinano
Member
Final thoughts: I did a final bit of listening, this time paying attention to separation between instruments, vocals etc. The separation was good, about on par or slightly worse than the Rotel (first time I didn’t feel the RAM was better). The soundstage was as good as the Rotel, but at times felt a little behind where the Rotel’s soundstage was, but not significant enough to dock the RAM (I’d have to say it sounded maybe 6-12in behind at those times). For reference, seating position was 13.5ft away from the speakers, and speakers are 48in away from the central line of the listening position. So all in all, if you manage to come across a RAM 512, I feel it’s worth picking up and giving it a listen. For the price I paid, I doubt I could do any better. I may have more to add or do another review when I get the RAM recapped, but I don’t know when that will be (at least a few months). I’m excited to hear it afterwards though, since it sounds so good already, I can’t wait to hear what it’s like afterwards.
Shinano
Member
I was able to obtain more information about the power amp through Peter Ledermann at Soundsmith New York. He was able to answer the few questions I had about it, so thanks again to him. It was produced in the early 70’s, marketed towards the high end segment, received good reviews, and about 100-120 were handmade. After hearing that the production was that low, it feels crazy that it still had the manual, inspection sheet, and a warning about A/B testing amplifiers all this time later. It’s sure to be a core component of my system for years to come. I’ll get proper scans of the manual sent to the AK manual database sometime soon.
Shinano
Member
Left yes, right not really. The right kind of wakes up at way above normal listening volumes, but still lags behind the left by a good bit. The left seems good because it corresponds with the light for 1 watt of power output at -20 on the meter which is 1 watt (ironic because the adjustment screw is gone on the left). The right I’ve tried to adjust, but can never get it perfect. I have it set to be in line with the left at normal volume (where they barely move).
Shinano
Member
I have to write this again due to page refresh! 
. I noticed through the top panel of the amp when looking at the heatsinks (which to me look similar to the ones on a McIntosh MC-2105 due to the three fins, then space for transistor to mount, then three fins design of them), that the transistors used on the left are different from the right. On the left front, you have MJ15003. On the left rear, you have MJ15004. On the right front, you have 2N3773. On the right rear, you have 2N6609. Is this arrangement normal. It seems strange using 2N devices on one side, but using MJ devices on another. I don’t know much, so this could be the norm for all I know. But they do seem original to the amp? They are all stamped with a Motorola logo without a ring around it, and aren’t stamped with Mexico like many I’ve seen. Any input is a big help.
. I noticed through the top panel of the amp when looking at the heatsinks (which to me look similar to the ones on a McIntosh MC-2105 due to the three fins, then space for transistor to mount, then three fins design of them), that the transistors used on the left are different from the right. On the left front, you have MJ15003. On the left rear, you have MJ15004. On the right front, you have 2N3773. On the right rear, you have 2N6609. Is this arrangement normal. It seems strange using 2N devices on one side, but using MJ devices on another. I don’t know much, so this could be the norm for all I know. But they do seem original to the amp? They are all stamped with a Motorola logo without a ring around it, and aren’t stamped with Mexico like many I’ve seen. Any input is a big help.
Picture would help....but odds are good some aren't original.I have to write this again due to page refresh!
Shinano
Member
I can get pictures of the inside possibly next week. What is funny is I checked the one side before and saw the 2N output transistors, and was looking into the possibility of replacing them with MJ series ones if required (I think a replacement option I saw was MJ15054? Could be wrong in the exact part number.)
Based on the 2N devices, I think MJ15003/4 would be best.
No doubt you could use MJ15023/4 or MJ21193/4 also, but I don’t have the knowledge to make that call.
Shinano
Member
I finally got moved and had tools again, so with the use of a drill, the stuck screws came right out, revealing the inside. I was having an issue with the right channel where when I'd connect an RCA cable to the input, it would create this hum, and along with it a few volts of AC. That confused me for a while, as since I'm not super technically inclined, I was thinking I'd just have to take it somewhere. After I got the cover off, I decided to poke around a little, checking for the usual things, like if anything looked burnt, etc. I didn't see anything at the time, so I just closed it up, and left it. Then today, I thought I'd take another look at it. So I took the cover off once more, and started working my way back into the amp from the input jack. I didn't get far, as the issue was to do with one of the wires from the input jack had broken loose from where it was soldered. How, I have no clue, as I hadn't been able to get into it before, so what caused it to come off is a mystery. So I just put a drop of solder on it, and the issue is gone! That was actually the first repair I've done where I had to solder, so that was fun (in the minimal capacity/difficulty that I did). And here are the pictures I took of the inside (I took them yesterday, so I'll circle what was causing the issue):
(Note the different output transistors)
(Note the different output transistors)