I recently got hold of a andromeda II..
my only problem is that one of the channels seems to been blown (i have only plug it in once to test, and it gave a bad smell, smell of burned transistor and resistor, i took it apart an correct, a black resistor, but i was not able to find any broken transistors..
is it worth a try to fix it, and if i take some pics, is it possible to get some help..
i would also like to have a schematic or pbc.
the only thing i could get hold of it this:
http://www.davidsaudio.com/andromedaII.pdf
pretty poor res..
any ways in working order, how much is it worth ?..
my only problem is that one of the channels seems to been blown (i have only plug it in once to test, and it gave a bad smell, smell of burned transistor and resistor, i took it apart an correct, a black resistor, but i was not able to find any broken transistors..
is it worth a try to fix it, and if i take some pics, is it possible to get some help..
i would also like to have a schematic or pbc.
the only thing i could get hold of it this:
http://www.davidsaudio.com/andromedaII.pdf
pretty poor res..any ways in working order, how much is it worth ?..
Years ago I was given an Andromeda II, it was missing one complete channel, circuit board and output transistors. The one channel that was in it had many "afterthought" fixes and burned spots on the circuit board. This amp had been repaired at guess where........Sumo!!!!! I stripped the remains and am in the process of making it into a Pass A40. I've tracked down all of the original parts for the A40, including Signal xfmr and Lambda output transistors. Try doing that for the Sumo parts especially the mosfet output transistors, I say use the chassis and heatsinks for something else.
Craig
Craig
Most of the Sumo amplifiers were designed by Jim Bongiorno, a legendary power-amplifier designer from high-end audio's early days, who was responsible for the Dynaco 400 (an early high-power solid-state amplifier), a large portion of the SAE product line-up and the GAS (Great American Sound) Company's various Ampzilla designs (some of the first commercially-available, fully-balanced power-amplifiers). However, the Andromeda-II came along after Jim left Sumo. While the original Andromeda was a reasonably well-regarded MOSFET-based balanced power-amplifier, the Andromeda-II used a BJT-based output stage and was not considered to be as compelling as the original in delivering the musical goods.
MullardEL34 has that backwards, the first Andromeda was BJT output stage and the II was Mosfet. That's why I said good luck trying to find those Mosfets. I've also owned a couple of the first Andromedas, that's easy to repair since it IS a bipolar output stage. Andromeda II is a different animal that was NOT designed by James. The first Andromeda was almost like Ampzilla III, a kit from the the 80s. The whole design story was in an issue of Amateur Audio, 1984 I think.
Craig
Craig
I've looked for info on the II and all I've found is the schematic you found, not very much and not very good. There is a yahoo group called SAE Talk, it deals with SAE, of course, but GAS and Sumo as well. MAYBE you can get some info there. Right now I'm trying get in touch with my friend who knows(knew) all of the guys that were at Sumo and maybe find some more info. I think I know who was "in charge" but don't want to say anything just yet. This is the same friend that gave me my II cadaver. I've also been looking for more dead ones as it is a pretty decent platform on which to built A40s, etc.
Craig
Craig
I have an Andromeda II and I rather like it. In fact, I traded in my Andromeda I towards it.
Although they don't have too much in common, both are fully differential amps rated around 200WPC into 8 Ohms and are stable into 4 Ohms.
I managed to blow up my AII a while back (trying to drive a dead short out of one channel). Output devices are MTM20N10's and MTM20P10's - Motorola TMOS Mosfets. The N channels are hard to find and the P channels are much harder to find. I eventually ended up getting a set of them from one of those surplus parts companies that requires like $150 per part number per order minimum (Rayland Corp). I don't believe there are any suitable substitutes for these parts - originals are required.
I'd be surprised if both channels of your amp are blown and the problem is not the outputs. It might be only two or four devices in each channel that are blown, but I'd expect that some of them are.
Have you opened the amp yet? To open it you will need a couple of (English IIRC) Allen keys to remove all the screws that go through the heat sinks on the sides. Then you can lay the heat sink down and see what the internals look like.
If the amp has been driven into a short, the result will be shorted gates of the output transistors, shorted Zener diodes (which were supposed to protect the gates from being overdriven), burned resistors in series with the gates (75 Ohm IIRC), shorted drivers, and burned resistors feeding the drivers. That's what I had to replace in mine. I also had to get extra outputs so I could match them for transconductance. There are two devices per phase per rail that are in parallel, and should therefore be as close as possible to share current evenly.
Mine's been repaired and working fine now for about six months, and I'm very happy to have it back! It's driving the mids and highs of bi-amped Mangepan Tympani IV's.
A high-res photo of one of the boards and heatsink can be found here: http://residentialcolorado.com/images/100_1017.JPG
Cheers,
Paul
Although they don't have too much in common, both are fully differential amps rated around 200WPC into 8 Ohms and are stable into 4 Ohms.
I managed to blow up my AII a while back (trying to drive a dead short out of one channel). Output devices are MTM20N10's and MTM20P10's - Motorola TMOS Mosfets. The N channels are hard to find and the P channels are much harder to find. I eventually ended up getting a set of them from one of those surplus parts companies that requires like $150 per part number per order minimum (Rayland Corp). I don't believe there are any suitable substitutes for these parts - originals are required.
I'd be surprised if both channels of your amp are blown and the problem is not the outputs. It might be only two or four devices in each channel that are blown, but I'd expect that some of them are.
Have you opened the amp yet? To open it you will need a couple of (English IIRC) Allen keys to remove all the screws that go through the heat sinks on the sides. Then you can lay the heat sink down and see what the internals look like.
If the amp has been driven into a short, the result will be shorted gates of the output transistors, shorted Zener diodes (which were supposed to protect the gates from being overdriven), burned resistors in series with the gates (75 Ohm IIRC), shorted drivers, and burned resistors feeding the drivers. That's what I had to replace in mine. I also had to get extra outputs so I could match them for transconductance. There are two devices per phase per rail that are in parallel, and should therefore be as close as possible to share current evenly.
Mine's been repaired and working fine now for about six months, and I'm very happy to have it back! It's driving the mids and highs of bi-amped Mangepan Tympani IV's.
A high-res photo of one of the boards and heatsink can be found here: http://residentialcolorado.com/images/100_1017.JPG
Cheers,
Paul
Paul...
Hey.. thx for the reply..
yes i have taken the amp appart..
i'do not think that it has been driven in to a short, but i'm not sure.
but i know that one channel work, i hav not yet tried to test the other one, because it smelled at first opwerup (no speakers or anything connected), then i took it appart and gave it a look, i could se a bornd resistor...
if to any help i can take som photos of the circiut?..
Hey.. thx for the reply..
yes i have taken the amp appart..
i'do not think that it has been driven in to a short, but i'm not sure.
but i know that one channel work, i hav not yet tried to test the other one, because it smelled at first opwerup (no speakers or anything connected), then i took it appart and gave it a look, i could se a bornd resistor...
if to any help i can take som photos of the circiut?..
By the way, if you look at the picture I posted above, you'll see that the Zeners under the two MTM20P10s at the left aren't seated well, and that the board under the resistors next to them is darkened. You may also notice the darkened area of the board near C106. These are parts that burn up when the output section is overdriven or shorted.
The interesting thing is that this is the LEFT channel from my amp; I blew, and repaired, the RIGHT channel. This amp was a demo model from a local audio shop that I bought at a discount back when the Andromeda III came out. Apparently, they had managed to blow it and have it repaired at the factory before they sold it to me... or maybe it was a customer that blew it returned it to them. They had told me it was new, but apparently it wasn't enitirely new when I got it. In any case, I haven't had any trouble with that left channel.
On a side note, notice the dabs of paint on the outputs... I guess that's how they marked them for matching. Side note 2: I have since replaced the four bipolar caps in the middle of the board with film types - two are signal coupling and two are for the DC servo.
Cheers,
Paul
The interesting thing is that this is the LEFT channel from my amp; I blew, and repaired, the RIGHT channel. This amp was a demo model from a local audio shop that I bought at a discount back when the Andromeda III came out. Apparently, they had managed to blow it and have it repaired at the factory before they sold it to me... or maybe it was a customer that blew it returned it to them. They had told me it was new, but apparently it wasn't enitirely new when I got it. In any case, I haven't had any trouble with that left channel.
On a side note, notice the dabs of paint on the outputs... I guess that's how they marked them for matching. Side note 2: I have since replaced the four bipolar caps in the middle of the board with film types - two are signal coupling and two are for the DC servo.
Cheers,
Paul
reply
i sure do, a fluke 177..
also got scope and tone gen..
i know a bit about electronic but not much about amplifiers..
after a closer inpection of the amp, and your pic. i found A lot of different thinges, but also different thinges comparing the two channels..
looks like the boken channel have been repaired one time before..
the thinges in () is what i spotted...
R132 is newly burned.
R 232 is intact (or bothe) but seems like it had burned before and replaced
Pot marked is a new one, the original ones are different..
http://img166.imageshack.us/img166/6763/forstrkersideddwl9.jpg
i sure do, a fluke 177
..also got scope and tone gen..
i know a bit about electronic but not much about amplifiers..
after a closer inpection of the amp, and your pic. i found A lot of different thinges, but also different thinges comparing the two channels..
looks like the boken channel have been repaired one time before..
the thinges in () is what i spotted...
R132 is newly burned.
R 232 is intact (or bothe) but seems like it had burned before and replaced
Pot marked is a new one, the original ones are different..
http://img166.imageshack.us/img166/6763/forstrkersideddwl9.jpg
If R123 is burned, then Q119 and Q120 are probably blown, along with Q116, CR107 and CR108, and R150 and R153.
Good news is that these are the N channels, which are still sort of available for "only" $37 a piece: http://store.americanmicrosemiconductor.com/mtm20n10.html
If the P channels are OK, then you can relatively economically repair the amp. The problem is that that $37 a piece price is for unmatched devices, so it's a gamble as to whether the pair they'd send you would work OK.
Easiest next thing to check is whether CR107 and 108 are short, and also if CR103 and 104 are short. If the first pair is short, then the two N channels are almost definitely blown; if the second pair is short, then the P channels are likely out as well.
Good news is that these are the N channels, which are still sort of available for "only" $37 a piece: http://store.americanmicrosemiconductor.com/mtm20n10.html
If the P channels are OK, then you can relatively economically repair the amp. The problem is that that $37 a piece price is for unmatched devices, so it's a gamble as to whether the pair they'd send you would work OK.
Easiest next thing to check is whether CR107 and 108 are short, and also if CR103 and 104 are short. If the first pair is short, then the two N channels are almost definitely blown; if the second pair is short, then the P channels are likely out as well.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.