[FallenAngel]

Hey guys,

I've got a story to tell. Once upon a time, about a week ago, a certain FallenAngel saw a for-sale ad for a Melos SHA-Gold and snatched it for an incredibly low price. What arrived in the mail was actually the Melos Maestro and it damn rocked with the Grado RS-1.

Of course, I couldn't help but to rip it open and see what I can do with it. So here comes the my modification log as a work-in-progress which will likely take a few weeks to complete.

Modding Day 1:
1) Remove "Pho-tentiometer" with cheap volume and balance controls
2) Remove monitor switch and "Tape In" inputs, there are enough as is
3) Install stepped attenuator

Modding Day 2:
1) Replace low-voltage bridge rectifier with FREDs
2) Reroute left channel using wire instead of PCB trace
3) Replace IEC inlet with higher quality IEC with integrated line filter and install proper ground-loop breaker.
4) Replace power switch and reroute "standby" to use the "Monitor" switch
5) Install two quality 1/4" headphone jacks (the other in place of "Balance")

Modding Day 3:
1) Replace input caps with 1.0uF Vitamin Q
2) Wire input caps to exactly where they need to go on the board instead of very long PCB trace for left channel (complete left channel mod)

Modding Day 4:

1) Low voltage PSU caps : Nichicon UHE / Panasonic FM
2) High voltage PSU caps : Panasonic TS-HA
3) High voltage 100uF/200V : AEON (Solen) 100uF!

4) Replaced High Voltage rectifier bridge with HEXFREDs
5) Re-routed Headphone jack wiring

Modding Day 5:

1) BIG UPDATE, likely the FINAL for a while.

Taking nikongod's advice about moving the cap huge film cap, I have rearranged the caps a bit.

1000uF TSHA is now 100uF Solen
470uF TSHA is now 1000uF TSHA
100uF Solen is now 470uf TSHA

I figured that would increase capacitance by quite a bit, but no 10x in one place.

Since I got the Sonicap 1uF, they were also installed. 4x for inter-stage coupling and 2x for Grid to Ground (opposite side of signal).

Well, I if I might say so myself, it sounds absolutely incredible! The bass is through the roof with the RS-1 and the detail is incredible. By far the best I've ever heard the RS-1 sound. I prefer this to the Beta22, screw neutrality, RS-1 is mean to be FUN!

Next up, I don't even know yet.

Probably will swap out some RCA to nicer ones and perhaps rewire the amp. I like this amp so much as a headphone amp, I'm seriously considering removing the source selector and rewiring it as single-input, skip the source-selector and optimize the wiring. That's for another day though, this amp is getting closed for another day, it's been through enough that I will just enjoy it.

Modding Day 6:

Well, this thing didn't stay closed for too long.

I noticed some background hum, like a ground-loop and since I really didn't like the ground scheme of this amp anyway, I got to work. I isolated the headphone output, RCA input and PCB from the case and routed a ground-loop breaker from the "center" ground on the PCB to the case. The case is now earth-grounded. There is no more hum.

I also removed ALL of the RCA inputs/outputs of the amp and made it into a single-input headphone amp. No selector switch, no extra wiring, and no pre-amp outputs (at least not yet, I can add them later if I decide to use it as such). The RCA input is a copper Vampire RCA and input wiring has been replaced with solid-core Cardas. The rest of the wiring is high quality mil-spec SPC. I also took the time to hot-glue the unused knobs back on, just for show.

----

Previous posts I've read and found most helpful:
http://www.head-fi.org/forums/f5/mel...thread-197603/
http://www.head-fi.org/forums/f5/mae...art-3-a-44134/

Schematic for SHA-Gold
RapidShare: 1-CLICK Web hosting - Easy Filehosting

 

[Pars]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif <snip> 2) Low voltage PSU caps : Elna Silmic II / Nichicon KZ (perhaps other low-ESR), open to suggestions, will not consider blindly using BlackGate, must be a reason for choice. 3) High voltage PSU caps : Open to suggestions <more snip>

Panasonic TSHA are very good and go up to 450Vdc. They are snap-in; you didn't indicate form factor and looking at the picture those appear to be snap-in.

 

[Killercrush]

I found this page to be really helpful :

Carlo's old page :

http://www.melosmods.netfirms.com/

 

[nikongod]

The gold and the maestro had the same PCB. The difference is that the gold ALWAYS came with the photentiometer and remote control, where the maestro did not.

fwiw, the 2 potentiometers are not in the signal path AT ALL on the photentiometer. it is a photo-cell based attenuator, and was the upgrade to replace the cheap alps RK-40. I still prefer a stepped attenuator to the photentiometer or RK-40, although mostly because the photentiometer can *only* provide about 50db of attenuation as configured which is not enough for this amp (IMHO) and my RK-40 is not balanced chan-chan at the levels where I like to listen.

It IS worth your effort to replace both of the rectifiers with ones made from fast switching & low-noise diodes (fred, hexfred, etc). The HV regulator used on the maestro/gold is AWESOME, but mosfets have trouble dealing with the HF "hash" from clicky diodes: in my amps this reduced a LOT of the background hiss without touching any of the HV power supply caps. I would do this BEFORE replacing any of the electrolytic caps. You will probably need to build a little daughter-board for these.

The SIZE of the coupling caps between the tubes (physical location on the board) is important, DO NOT go less than about 1.5uf, maybe 1uf. the input caps CAN NOT be removed from the circuit, but should be upgraded too.

do the left-channel mod.

For the LV caps, I have heard that the "lone cap" off to the back right of the board (very close to a relay) has a big effect on the sound. I have not tried this, and it makes no sense according to the schematics I have, but I have received this info from a source I trust (he dosnt post here much) and it will only cost like $2 more to swap that cap too if your not using black-gates. Im not a fan of bypassing electrolytic caps with film, so I have removed most of the film bypass caps from my melos's. I am not 100% convinced that black gates are the end-all-be all choice for these caps, but whatever you get should be of very good quality.

A choke in the HV supply (replace the 100 to 200 ohm resistor - depends when the board was populated) and a film cap to replace the last (largest) electrolytic round out the mods if you want to go totally ridiculous. I used a 100uf solen here, and it sounds like sex.

 

[FallenAngel]

Very cool, thanks for the info guys.

nikongod: A little help on 2 fronts.
1) I'm a little lost on the FREDs here, I've still got some UF4004 left from the SOHA2 build, would these work or is there something better?

2) Left channel mod? I've read it routes the signal away from the PSU, but I haven't checked under my PCB yet so I'm really not sure what this is going to look like at the end.

Thanks for the link Killercrush and thanks for the cap tip Pars, I've always been a huge fan of Panasonic FM caps, I'll look at how the TSHA look on paper.

 

[FallenAngel]

A little update. Both questions above still standing, I wasn't able to get a clear answer in my search yet.

1) I was looking around and saw there are a pair of input caps on this amp. I am thinking that these will definitely be thrown out!

2) After much searching I found the "left channel" mod. Just wanted to clarify: essentially, the 2K resistor above the inter-stage caps needs to be re-soldered to the underside of the board and the trace replaced with a direct wire.

 

[dsavitsk]

Quote:

Originally Posted by nikongod /img/forum/go_quote.gif the input caps CAN NOT be removed from the circuit, but should be upgraded too.

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif 1) I was looking around and saw there are a pair of input caps on this amp. I am thinking that these will definitely be thrown out!

.

 

[nikongod]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif Very cool, thanks for the info guys. nikongod: A little help on 2 fronts. 1) I'm a little lost on the FREDs here, I've still got some UF4004 left from the SOHA2 build, would these work or is there something better?

they are pretty nice, but you can get MUCH lower recovery times than they have. This helps QUITE a bit.
Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif A little update. Both questions above still standing, I wasn't able to get a clear answer in my search yet. 1) I was looking around and saw there are a pair of input caps on this amp. I am thinking that these will definitely be thrown out!

The stock caps are pretty much junk, but you MUST HAVE caps in these spots. Replace=OK, remove=no! I tried to run the melos without these caps, and nothing good came of it.

If anyone cares (it has been asked before, and I didnt know the answer) the melos uses a combination of 2 things to bias the tube and split the phase for the balanced output.

The input stage is a long-tail pair BUT with a transistor configured as a constant current sink. The grid of the tube is tied to the bottom of a resistor but BETWEEN the resistor and the transistor. The grid of the tube is actually a few volts above ground, which dosnt matter because it is less than the cathode voltage. The fact that the grid of the tube is NOT at ground is what makes the caps mandatory.

this photo illustrates it, although it shows a pentode where the melos uses a transistor, and the voltages are allllllll different. It does not show that the voltage on the cathodes of the signal tube is about 102V in this photo.

full site, good reading
Quote:

2) After much searching I found the "left channel" mod. Just wanted to clarify: essentially, the 2K resistor above the inter-stage caps needs to be re-soldered to the underside of the board and the trace replaced with a direct wire.

For my left-channel mod, I broke the trace under the board (it makes a big s-shaped sweeping path around all of the power lines, which is how it picks up noise) near both the resistor and the mosfet. Then I soldered a wire on the TOP of the board, away from all of the power-lines.

 

[FallenAngel]

Thanks guys,

I went with 8x MUR1520PBF for the diodes.
EDIT: Oh ****! These are only 200V, guess I'll be buying something else for the HV bridge. But than again, the caps after the bridge are 200V, so I don't see any reason why these diodes won't work. Any hints?

I'm bidding on 6x 1.0uF Vitamin Q caps on eBay (which are REALLY hard to find in 1.0uF values for some reason), hopefully to replace the 2 input caps and 4 inter-stage coupling caps. If I don't win those, I'll just go with Sonicap Gen 1 as I've had good results with them in the past and they're a great bargain.

Thanks again for the hint on wiring the left-channel mod, I'll look at it tonight.

 

[FallenAngel]

Little update. I replaced the IEC socket with a nicer one that has a built-in line filter and implemented a proper ground-loop breaker from earth ground to the case.

I also replaced the LV bridge with 4x MUR1520 diodes.

Since I had a little trouble with the other set of diodes, I will be ordering another set of FREDs.

 

[Blutarsky]

I've had my Melos SHA Gold for about a week and already love it.

I plan to upgrade it to full maestrobator status at some point and have been looking through the old threads. Better to have an active discussion among other knowledgeable headfiers who are loving this very versatile piece of gear!

Thanks for posting this discussion and the fantastic hands-on info you're sharing.

 

[FallenAngel]

Any thoughts on how to get rid of the "Mute" function? The switch wiring looks very funky and I can't understand what the little white wires are for.

 

[FallenAngel]

Ok, another update.

1) I have replaced the power switch with a nicer one which also means I removed the weird wiring associated with it.

2) Now there is a switch (placed where the "monitor" switch used to be) that selects whether pre-output is enabled or not (before it was done by whether headphones are plugged in).

3) Since I don't use the balance control, I added another 1/4" headphone output.

4) You can also see the little green jumper wire of the "Left Channel mod" wired on top as per nikongod recommendation.

Latest photo:

 

[HiFi FOR METAL]

You may want to consider intsalling a nuetrik powercon to replace the IEC, It helps with power phase and factor a great deal and also is non current limiting.

 

[FallenAngel]

Quote:

Originally Posted by HiFi FOR METAL /img/forum/go_quote.gif You may want to consider intsalling a nuetrik powercon to replace the IEC, It helps with power phase and factor a great deal and also is non current limiting.

Uhm... come again? How does it help "power phase and factor"? I just installed a nicer IEC socket with integrated line filter just because I wanted an easy way to have a line-filter installed.

I think replacing this would be a distant concern whereas the signal stuff should come somewhat before. Still, I would definitely like to know why you think PowerCon is the way to go.