[shawn_low]

Hi all,

I did yet another silly thing: accidentally pumped 240V into a 110V Melos Maestro amp. GAH!

The amp was heavily modded by Fallen Angel on HF and his mods are detailed here: http://www.head-fi.org/forum/thread/...8-large-photos

The pictures on day 5 & 6 posts is the final configuration I am left with. Fallen Angel has schematics and also further technical details on the mod.

There was a pop sound. The fuse burnt out. I forgot to put the power through a step-down convertor.

 

I replaced the 250V fuse and put the power through a step-down convertor. It powers up. However, there is a low hum. I replaced the tubes and the hum is still there.

I sent pictures to Fallen Angel and he says that no caps or resistors look burnt out. The transformer seems OK (no sound nor is it overheating).

There are 4 LEDs that should light up (on the right side of the board). However, only the top three briefly come on before dying out. The fourth one doesn't even come on.

Fallen Angel said that that could be the cause of the problem and suggested I find someone local to look at it. He is in Canada and unable to look at it for a few months. He said it could be a burnt-out transistor and that this is probably the cause of the problem.

It works...music plays above the hum (and I can't hear the hum once the music is cranked up), but there certainly is something wrong with it.

Can anyone help look at it or direct me to a store which might look at it?

Also, would it be possible to replace the transformer to a 240V one? Fallen Angel says this "If you find a transformer that has the same secondaries, sure, but I doubt it's easy to find though and I'm not even sure of what secondaries it even has."

 

Should I still be using the amp?

 

Pics of the Melos after the damage are here:

http://picasaweb.google.com/whooping.cough/Melos#

LEDs in question are these ones:

http://lh5.ggpht.com/_sAadCLmQiA8/TGIC1D7WSUI/AAAAAAAAD0k/5qoSmW85Qag/s800/P8118186.JPG

 

I'm located in Australia but will accept all help.

Thanks in advance!

 

[nikongod]

Just to clarify: are you still running the amp on 240v? If so stop. Now. Please. 
 
All

LED's should be lit equally.
 
There are so many things on that amp that running too much voltage (running a 120v transformer on 240v mains certainly qualifies) could blow up. I would start with looking at the regulators for B+ and both low voltage supplies but that is just a guess.

 

[shawn_low]

Quote:

Just to clarify: are you still running the amp on 240v? If so stop. Now. Please. 
 
All

LED's should be lit equally.
 
There are so many things on that amp that running too much voltage (running a 120v transformer on 240v mains certainly qualifies) could blow up. I would start with looking at the regulators for B+ and both low voltage supplies but that is just a guess.

 
Hey Nikongod.
 
Thanks. I am not running on 240V at all. I put my power through a step-down voltage convertor. The mistake happened when I forgot. 
 
Nikongod, if I can't find someone local to look at it, would you be happy to look it over? Thanks.
 

 

[pcf]

Hi Shawn,
 
Where are you located?
 
I got my Melos Sha Gold fixed and modded by Benny here:
 
http://www.aminaaudio.com/
 
Paul

 

[jjinh]

Quote:

Hi Shawn,
 
Where are you located?
 
I got my Melos Sha Gold fixed and modded by Benny here:
 
http://www.aminaaudio.com/
 
Paul

He's in Melbourne, Australia if that helps.

 

[qusp]

well I dont know that he will be able to heklp you directly by doing the work, but Natonrice (a member here) is about to start modding (upgrading) a melos SHA GOLD in sydney; so I assume he has had a good look at the amp internals and has schematics. he has already received the parts, the pics sure look to detail a pretty decent overvoltage before the fuse cut in and I would probably cease using it till you sort it out. with the power supply not working correctly, there could be all manner of evil going on even if it still makes sound. you could be subjecting your headphones or speakers with severe amounts of DC, you could be (pretty much definitely) running it with short circuits, further risking damage.
 
replacing the transformer with pone rated for OZ would be reasonably sikmple task. who knows, the amp may already have transformers with dual primaries, an easy mod to change for OZ. any reasonable DIYER would be able to find out what rating you need

 

[Uncle Erik]

If you're getting hum, my guess is that a bit of AC is getting through.  You might have fried some of the caps and regulation devices in the power supply.
 
I wouldn't use it until it's checked out.  I'm not too much up on solid state devices, but I'd be concerned about cooking off a transistor.  They're pretty sensitive about voltages and I don't know whether replacements are available.
 
Replacing the transformer for 240V might be tricky.  There might not be one with the same voltages, so you'd either need to have one custom wound or use two or three to cover everything.

 

[pcf]

Quote:

He's in Melbourne, Australia if that helps.

Thanks.
That's a bit too far.

 

[nattonrice]

I do indeed have a (decidedly hard to read, i.e. very small) schematic. You can get the same one from fallenangel's thread afaik.

 

[qusp]

Quote:

If you're getting hum, my guess is that a bit of AC is getting through.  You might have fried some of the caps and regulation devices in the power supply.
 
I wouldn't use it until it's checked out.  I'm not too much up on solid state devices, but I'd be concerned about cooking off a transistor.  They're pretty sensitive about voltages and I don't know whether replacements are available.
 
Replacing the transformer for 240V might be tricky.  There might not be one with the same voltages, so you'd either need to have one custom wound or use two or three to cover everything.

 
yeah I suppose it depends on how much regulation is done by the transformer. getting a custom bit of iron is not the cheapest thing from OZ, thats correct (not sure who you would see to get it locally actually) I can recommend richard sumner in canada though if it comes to that. of course its cheaper than a good stepdown convertor, but yeah I think you have a bit more work to do than that. The Melos is a hybrid amp though right? rather than a pure tube or pure solid state design
 

 

[Uncle Erik]

Quote:

yeah I suppose it depends on how much regulation is done by the transformer. getting a custom bit of iron is not the cheapest thing from OZ, thats correct (not sure who you would see to get it locally actually) I can recommend richard sumner in canada though if it comes to that. of course its cheaper than a good stepdown convertor, but yeah I think you have a bit more work to do than that. The Melos is a hybrid amp though right? rather than a pure tube or pure solid state design.

Yes, the Melos is a hybrid.  Just took a look around and found the SHA-Gold schematics.  Should help a little when taking it in for repairs.

 

[shawn_low]

Thanks everyone from chiming in.
 
I'm not a DIYer by any means so would prefer if someone would be keen to have a look at it for me. I have STOPPED using it until it is fixed.
 
I did some digging and found that the transformer has Dual Primaries and according to Minivan, can be rewired to 220V. It's a Parnell Electronic Components Model AT D4011. Sticker on it says:
 
 
Blu (.)            (.)Blk

Gry                   Red

2 x 120V          12V + 12V

Vio (.)            (.)Ora

Brn                Yel

 

 

Minivan said: "in this case it look like the secondary is 2x 12v output and the input is 2x120v wired in parallel for 110v operation.Iin some transfomer it allow you to wire the 2x120 in series mean 120+120=240. so it's a possibility it can wire for 240v. but you have to check the datasheet of the transformer to confirm."

 

I have emailed Parnell but haven't heard back.

 

Any further thoughts?

 

Any Aussies care to help with taking a look at this beast?

 

[qusp]

yep, connect the violet and grey wire together to put the primaries in series and use the brown (live/end) and blue (neutral/beginning) . 
 
sorry mate, repairing tube gear isnt really my thing, as i'm pretty unfamiliar with it (although the problem looks to be in the regulator section which is solid state) and i'm far too busy at the moment to consider looking at it. I wont put natonrice forward either, as hes got some rather important papers due at uni. You might post in the local audio clubs newsletter or on DIYAUDIO to see if someone can help you there without charging you a bomb.

 

[shawn_low]

@ Qusp.
 
Thanks. I'll gather all information for whoever will eventually look at it...

 

[qusp]

no problem mate, sorry I couldnt be of more direct help. i'll see if I can find contact info for the melbourne chapter of the audio club for you, but yeah check DIYAUDIO.