While hunting for bargains on the net, I came across a pair of fairly old Ashly FET1500M power amp that was on sale for a reasonable price.
the above was the picture I saw on the net, and after a closer look, I got a feeling that they are using the "fabled" Hitachi J49/K134 family of MOSFET, because most TO-3 transistors/FETs do not have that "Dome" looking top, most are quite flat.
The seller was looking to sell 2 at the same time, and since the price was quite reasonable, I decided that, "Hey, why not get two and bridge them?" A few days later, I got the pair of amp in my home, the MOS used was 2SK135/2SJ50, which is the higher voltage version of 2SK149/2SJ49. For the first few weeks, I couldn't find a balanced source/pre to feed it, thus it was sitting idle there a lot. It was not until that I had acquired and modded a B&K CS-117 pre did I get the proper signal to the ashly amp.
As a side note, B&K CS-117 pre's volume pot sucks real bad, but it is a very interesting pre in the way that it actually have everything you need for a balanced output. Just add 2 dual OP and 2 XLR socket, and you automatically gain a balanced output. it even have all the resistor installed. (Next mod, the stupid volume pot)
Since I'm an avid modder, I requested the circuit of the amp from the manufacturer, they gave me their former top of the line FET2000's circuit, but they are quite close, no complains there.
Courtesy of Ashly, for reference only. Good luck for anyone trying to find those MOS in quantity tho
At first, I only hook up one Ashly amp, due to the other one is having some problem with the output protection fuse holder. The sound is neutral with a bit of "warmness", with a lot of control and power. The detail is excellent as well.
Instead of replacing the original fuse holder with something similar, I had elected to use the much bigger 10*38mm fuse instead. I feel that the larger contact area, sturdy construction of the fuse and fuseholder should work better than the original. due to the fact that I'm a "balanced" freak, I just had to update the already good unit with the new fuse and fuseholder too.
With both amp now in proper working condition (max DC output is 50mV at the speaker binding post), I decided to run them in bridged mode, which according to Ashly's manual, each unit is now capable of 550W @ 8 ohm with less than 0.01% THD. How did it listen? Well, one of disc we listened to is Paradiso, where it featured some hand beaten drumings in the first few seconds of the first track. Before it felted just "normal, nothing to be excited", now it felt like the drummer is having an adrenaline rush and is going all out on the drumming. This is now becoming quite an interesting experience. Everything seems to come alive again, with a lot more power controlling the speaker, it seems to be finally extracting most of what this speaker can do.
The newer fuse initially exhibited some extra "sharpness" and some undesirable sonic signatures, but it goes away rather quickly with some music running. Generally it sounds quite good.
A few days later, I got that modding craving again, this time it is to deal with the input capacitors, I dug out my store of high purity silver wires (single strand solid core) and cut 8 pieces of 3mm long silver wire as jumper, I basically soldered it onto the pins of the input capacitor, effectively bypassing the 47uF caps shown in the circuit above. Since there are 4 channels of 2 pins each, 8 pcs of caps were bypassed.
As I made sure that there are nothing wrong with my mod, I shoved it all back into the case and measure the output of the amp. Still around the zone of 50mV, the sound was a little thin in the beginning, but that was expected as the silver jumper is still new. Even then it is showing great promise, even better details, cleaner, more transparent highs. And within a few days, the thinness was all but gone. The detail had improved to the point that me and my girlfriend were able to hear a lot of faults in the recording, for example, Sally Harmon's Bravo! (Or was it "Brava!" ?) now have a very clear background hiss, and the first few second of second track, we now heard a distinct "soft sneeze" followed by a much louder one. That was something that we have never heard before, and we had play this disc for at least 50 times. Now that's resolving power! The sound is good to a point that it is starting to show flaws in the pre, and I do plan to mod the pre and put that 64 step attenuator into the CS-117 pre, possibly a pair of BB's OPA637 as well.
I have heard a lot of US$1000+ amps driving this pair of speaker, and they don't come even close, man this is one hell of a bargain! Don't toss aside those PA amps, some like this one is actually quite good, and can become amazing with a little tuning.
Everyone, good (bargain!) hunting.
Equiptment used:
Source: Sony CDP-X5000 analog out.
CD to Pre: Eichmann copper bullet with enamel coat wire, built it myself.
Pre: B&K CS-117 Modded Balance out.
Pre to Power amp: Monster professional line cable, forgot the model of the cable, capped it with Neutrik XLR connectors myself.
Power amp: Ashly FET1500M *2
Amp to speaker: 12gauge tin plated, stranded copper wire, with CMC's wavy type of banana plug.
Speaker: Acoustic Energy AE-120SE with Sound Care's Superspike feets.
