Melos SHA Gold 2016 Project (Long Post)

I am still learning the ropes for the DIY audio realm but this has been a project that I’ve wanted to tackle for several years now and only recently have decided I would actually take the plunge and just go for it. My apologies that I am not committing to provide detailed sound impressions for the amp as this project for me is more for nostalgia than anything else. I am positive that most amps you can buy today are better built and probably better sounding. My purpose here really is to document what I am doing and hopefully to learn in the process so your input is greatly appreciated!

Melos SHA History, a lot of this is skimmed from web searching, since I don’t see it mentioned much here’s my notes on the matter. (Super cool reads http://www.head-fi.org/t/127867/an-interview-with-john-grado and http://www.head-fi.org/t/36656/melos-sha-x-modified-by-carlo-comments)

For those not familiar with the Melos SHA amps, the abridged lore goes something like this… back in the early 90’s before the headphone amp market was even a thing, Joe Grado (RIP) wanted a dedicated amplifier to power his HP-1000’s. Through some arrangement he contracted the then reputable Melos Audio to design said amp. Though I am not clear on the details, apparently he was not happy with the two prototypes they came up with (eventually dubbed the SHA-X) and eventually Joe created and sold his own Grado HPA-1 amp instead which is also quite a rare piece of history. The irony is that, based on what I’ve read, Joe actually kept an all Melos based gear chain for his own personal use.

I have no facts to back this up but Melos had a rocky history as an audio company, they sold many different iterations of the SHA amp (they also appear to have sold monoblocks, phono stage, R2R DAC, CDP) and like some amp builders something changed for the worse in the production quality standard along the way. The design of the SHA is pretty bad as far as I know, the PCB is a rats nest of traces, the higher end models add another rats nest of wires and jumped traces in addition, the parts selection was never top tier or even consistent. The Sha Gold added a Pho-Tentiometer which is a light dependent volume attenuator, on paper it sounds really cool but in reality it’s kind of a piece of junk. All of this resulted in poor reliability of the amp and probably by today standards mediocre sound. I can venture a guess that the reliability problems and skimping on parts were the beginning of the end for Melos as they closed their doors probably sometime around the early 2000's, there were even some failed promises to come back bigger and better but nothing ever panned out.

At Head-Fi there were some individuals who modded the hell out of these amps, carlo, nikongod, FallenAngel, nattonrice, they all certainly had better chops than I do. Even ECP Doug was in on the action! Sadly half of these guys are in retirement from the HF scene near as I can tell.

Melos SHA Gold
(Schematic here: http://www.eserviceinfo.com/downloadsm/21578/Melos_Melos Sha Gold.html)
(Questionable info for tube plate voltage adjustment here: http://www.head-fi.org/t/63652/compiled-melos-tube-impressions)



Before diving in I already had a rough idea of what I wanted to do with the amp, namely to see what exactly the hoopla back in the early HF days was all about with regards to the modding potential and its synergy with the HP-2. This particular unit was snagged on A’gon in stock form; many of these were upgraded (read: repaired and shoddily so) by Melos over the years to “reference” level. I actually had an after the fact non-officially modded reference in my heyday in superb condition which I remember fondly. I am not even clear on what the reference upgrade meant in terms of parts or modifications but it is very clear there are a slew of changes evident in the pics you can scour from the web. The faceplate is in decent condition and just slightly bronzing, kind of like the picture shown in the old fluffed Stereophile review. Sadly a lot of these suffered pretty gross anodizing failure. This one must have not seen a ton of use as the amp itself came to me fully functional and complete in the old beat up box with an owner’s manual and infrared remote.

The sound in stock form is not bad even when running some super common JJ 6922 gold pin tubes. The Melos has a reputation for eating tubes, I read up on adjusting the plate voltages but I don’t even know if adjustment will make a major difference. Maybe I got lucky with this one but hum or hiss is not a major issue (yet?) though it is certainly not the quietest or blackest background amp I have heard. The sound I would characterize as relaxed and warm and only decent in the details department. Bass is not well defined but bumped up just slightly so which works out great for HP-2’s and HD800. Soundstaging and placement is better than average which also makes for some engaging listening sessions.

Getting to Work Pt 1
(Rectifier Bridges here: http://www.superbestaudiofriends.or...schottky-sic-full-wave-rectifier-bridge.1625/)

The amp didn’t last long in stock form and I spent way too much time researching old threads, poring over the inadequate schematics, and ordering parts from pcx, sonic craft, and mouser. Worth noting is that this amp has soldered wires holding everything together; just to free the amp PCB requires almost 20 different wires to be de-soldered. Working on it really sucks but at least I am pretty handy with a de-soldering pump now!

I focused on the amp board first, simple drop-in replacements that seem to add up even when on a budget. Electrolytics are replaced with modern fancy Nichicon’s as the Black Gates that were once the standard are NLA and very expensive. I purchased a bunch of Sonicap Gen 1’s for bypasses and input. Not so much of a drop in replacement, the High Voltage and Low Voltage rectifier bridges in stock form are maybe enough to get the job done but probably run at their limits. In another post I replaced these with modern silicon carbide schottky diodes (about $3 each times 8) which are a popular audio tweak however they are still going to be constrained by a resistor capacitor snubber network. I am actually told these will be holding the schottky diodes’ performance back but I am a little afraid to simply remove them thanks to the convoluted pcb traces.

I swapped most of the caps over the course of a weekend and when I got the amp back up and running the sound was surprisingly much different. In my book the amp lost a lot of the warmth and instead moved noticeably closer towards neutrality, the bass loses a little on the impact and trades up for actual texture. The OK detail retrieval was a notch or two better which also further enhanced the soundstage and placement.

Some quirks about my amp I still need to figure out; on most pics I can find around the web there is a low value mylar cap tying the top tabs of two darlington transistors on the right side of the amp board, around the tube area I see jumper wires wrapping around the tubes that I can only guess are done to circumvent poorly laid out board traces (like the “left channel mod”), for reference models I also see a giant film cap acting as a shunt for the power supply. These small differences might add up to something so I want to wrap my head around them if I can. My particular board also has the HV TL783 voltage regulator pcb mounted with a heatsink whereas I am seeing most others remotely located to the chassis for better heat dissipation. I will relocate the TL783 later and add the cap on the darlingtons however the shunt cap and wire rerouting are to be determined.

Pt 2 Volume Board



My next step is to figure out a volume control solution which in stock form is pretty bad. The Pho-tentiometer is a weird beast, my board had 2 motorized Alpha pots for volume and balance; these pots fit super tight so upgrading them is likely not possible or even financially feasible. At 0 volume there is bleed through of audio which is documented in the user manual as normal operation. In turn Melos added a (stupid) mute component to the amp circuit triggered by the infrared remote (which is also required to kick it out of mute after power up). In operation you can see a light source on the underside of the volume board decrease as volume increases; what you get in reality is a frustratingly non-linear volume attenuation with limited range.

The popular solution is to remove the board and swap in a high quality attenuator or pot, however I have recently come across some light-dependent resistor (LDR) solutions that pointed me towards the Tortuga Audio LDR3x DIY controller. One user I have also been in contact with has some great pics up of his installation (https://www.flickr.com/photos/vintageglass/11017670143). If I can get this implemented then the idea of a light dependent volume control will at least remain as will a functional remote for volume control.

It doesn't look like much but a million man hours later and right now this is where I stand, the Tortuga volume board should arrive any day so I am excited to move forward but I still have a ton of unanswered questions, such as where I could tap the VU meter into and what other functionality I may end up losing to still figure out!

 

FWIW, I lusted after a Melos after hearing them at my local hi-fi dealer and reading the 1992 Stereophile review: http://www.stereophile.com/headphones/617/#wcyglOwjRpPKM12c.97

At the time, I settled for a Headroom Little and some SR80's I didn't manage to get my Melos for more than another decade, by which time Melos was long gone. However, in the early to mid 90's, Melos stuff was decidedly high end. As I recall, they had a 3 box preamp that sold for a lot and garnered great reviews, as did their big tube power amps. However, reliability was always an issue - not something that crept in late.

I think the tube eating is less of an issue than has been reported. Mine ran them quite lightly. However, the grid stoppers are too far from the tubes which means that they often oscillate and at best simply sound bad, and at worst, squeal. If yours is like mine, that is something to check for.

 

Pt 2 Continued




Made some progress over the weekend with the Tortuga board in-hand. Install proved to be a little tricky but it went alright. The Tortuga board is very compact and the screw-down posts are super tiny so it doesn't like the thick gauge stock wires, it is also two PCB's stacked so it needs about 1.5" of clearance in the chassis. The board indicators for the input and output are not as clear as they were with the v1 version so I actually hooked up these wires incorrectly on the first try.

I made a small change to the right hand DPDT "Monitor" switch by wiring the active pre- amp mute wires to it but I am not sure I will keep it that way. From the factory it serves as a tape input switch which is useless considering the sheer amount of inputs available, who the hell really needs that ONE more input in addition to the other 6 on the selector dial? With the unused tape input I added jumpers for a second set of loop outs.

The good news is it seems to be working OK. The passive pre- performance of the Tortuga LDR3x is actually pretty impressive, I can't understand how but it indeed made a very pleasing sonic difference with my old Yamaha CR-1020 receiver. The LDR3x draws 12v power from the Melos' amp board right off the secondaries, I've also attached additional grounds going to the chassis for power and Left and Right channels. The output then gets split for a passive output via rear RCA's and also into the Melos' amp board. There is additionally an alps encoder dial which acts as an interface/volume control and an IR module which receives inputs from an Apple remote.

While it is technically up and running I still have a laundry list of things I need to get hammered out. The most annoying at the moment is the Tortuga power on sequence. While the board gets power from the Melos' power switch, the LDR3x board must in addition be turned on by de-pressing in the encoder dial. If you turn the encoder knob right away without powering it on (like any normal human being would) it goes into an auto-calibration mode and behaves very obnoxiously if you happen to have headphones or speakers on. I also failed to get the Apple IR remote functional; I suspect I could have hooked it up wrong possible destroying the sensor and have already ordered a few new IR receievers from Mouser to try. The shape of the provided one is useless for the Melos anyways.

Another small annoyance is that the LDR3x does not completely mute at 0 volume just like the Photentiometer board, I intend to turn the tape monitor switch into functional a headphone mute of sorts but will have to see if it is possible.

I am now somewhat regretting not having plunged into the left- channel mod, it may be due to the lower 20k input impedence of the LDR3x (Photentiometer was 50k?) but I think the noise floor is a little more noticeable now. This can be adjusted to anything from 1 to 99k but requires a separate display module that I don't want to deal with mounting or purchasing at the moment.

Tearing it all back down again is going to suck that's for sure!

 

Happy to say, with some minor adjustments from my last update, both the amp and LDR3x is finally in a usable state! Thanks to some tips from a few internet pen pals and a call to Tortuga, the status LED, remote, and headphone mute switch are now sorted out.

The sound of the amp at this point is completely different from stock. It may no longer sound good with the HD800 (stock), but I do like what I am hearing with HP-2's, HD600's, and even TH-X00's. The soundstaging capability and detail retrieval of the amp, especially with the HP-2's, are definitely its strongest points. It has lost the original warmth and bass bump with the stock parts, but this is probably the tradeoff due to some bonus distortion to begin with. With any luck I will be trying out some cheapie reflektor 6h23-eb tubes to replace the gold pin jj 6922 to see if there are any more gains to be had.



Below are my notes to wrap up part 2:

The previously unmentioned status LED problem I was running into was due to the factory Melos LED which I overlooked. It is a "flashing" type so when it gets normal dcv it does not stay continuously lit but rather blinks all the damn time and is very flaky in operation. Needless to say with a half functional status LED and no remote it was very difficult to oeprate the volume board! I threw in a regular old 5mm red LED and it came to life as it was supposed to. Later I will swap in a closer color matched LED from clear red glass to opaque red, an easy fix.

The new IR receiver from Mouser also worked right away and fits perfectly into the stock holder with a dab of hot glue added. The Tortuga supplied part is Vishay TSOP31138 which will not fit the Melos bulb holder anyways so I ended up with TSOP32138 which matches the pinout. I must have hooked up the supplied part incorrectly or shorted it out somehow Worth noting is the plastic white Apple remote may pair but it definitely does not work correctly with the LDR3x v2.1; I would NOT recommend trying it! Without the display module(s) it is also of slight concern that the remote will allow a few operations that are difficult to operate with the status LED alone, IE source selection and input impedence (which thankfully doesn't stick unless you run auto cal after).

The headphone mute switch wiring took me a few tries but with some advice it is working great and does not seem to need additional resistors in the signal path to mitigate pop on/off noise. To do this I ended up extending the headphone out wires to feed to the middle poles of the DPDT switch and then sent the top poles (switch down) going to the jack itself. The bottom poles (switch up) are tied to earth/ground to mute, but in this case I opted to send them to an alternate ground point on the Melos pcb which shares a leg with a resistor. The active pre mute wires I then placed back onto the headphone jack like from the factory. Hopefully I made the right move as at 0 volume/ LDR3x mute the board still bleeds a little signal, again this behavior is normal operation for both the Melos and Tortuga volume boards.

While I was at it, I ripped the Melos board out once more to remove the traces for the left-channel mod. While the mod was not as difficult as I feared, I am not sure anything was really gained in my case, maybe just added peace of mind? After thinking on it late into the night, I believe the resulting noise I have at higher volumes (75%ish plus) is due to tube noise as what remains moves when swapping tubes around. I also looked into adjusting tube bias as per this thread (http://www.head-fi.org/t/63652/compiled-melos-tube-impressions) however the pots on my board seem to do nothing in terms of plate voltage! My plates are stuck at 56v-ish but that's not such a bad thing I think. If anyone has any tips here it would be greatly appreciated.

A final tweak, the 2.2uf capacitor across the top tabs of the position 106 and 108 - 2N6045 darlington transistors also proved to be fruitless. Soldering the tabs seemed to be incredibly difficult even with a temperature controlled solder station at my disposal. I don't believe to-220 tabs are meant to be soldered onto anyways. Even with my attempt, the cap seemed like it exacerbated background noises so I ripped it out right away.

To summarize what I've done up to now:

Silicon Carbide Schottky Rectifier bridges to replace the HV and LV bridges
Replaced all electrolytic caps with Nichicon's
Sonicap Gen 1's for inputs and the bypasses all over the amp
Big honking 100uf 400v Solen PB to replace the "last" power supply electrolytic
Left-Channel mod/reroute
Remote locate TL783 regulator from pcb to chassis
Swapped JRC NE5332N for a Signetics NE5332N
Jumpered Tape In to an additional Tape (loop) Out
Rewired Tape In monitor switch to a manual Headphone mute
Replace Photentiometer with Tortuga LDR3x v 2.1 board and wired output to passive pre-out and Melos input



What lies ahead?

For me this has been pretty exhausting work but at least I am happy to have picked up a few new tricks along the way. The amp in its current iteration sounds great to my ears and hopefully it will remain in service for the forseeable future; the Melos SHA may not win any amp measurement (or design) contests or offer world beating performance but it does indeed carry a nice sound with it that pairs nicely with the right headphones. It is a shame the Melos brand ended up in obscurity with such a poor reputation, many of today's headphone enthusiasts may never have any real idea where the whole idea of the commercial dedicated headphone amp came from nor will they care.

Still on my wishlist for this amp remain a few items which I may not be able to achieve without some outside help. Firstly, rigging up a timed relay to trigger the Tortuga board power, second determining if the Melos VU balance meter can be tapped in elsewhere without the Photentiometer board, and finally the above board wire trace re-route near the input caps and tubes. I almost forgot, I also have a 10R/5W resistor and .1uf X2 capacitor for a ground loop breaker that I may decide throw in at a later date.

If you have gotten this far, kudos for putting up with my long winded posts and thank you for having a look at my project! I hope that maybe it can help keep a few more of these old clunkers from the junk bin!

 

So this is interesting, I figured out that the 2.2uf mylar cap Melos used across the top tabs of two 2n6045 darlington transistors is a "miller cap" which seems to form a low pass filter:

http://www.aikenamps.com/index.php/what-is-miller-capacitance
https://en.wikipedia.org/wiki/Miller_effect

I don't know why they chose to solder it across the top tabs, it should equivalently be able to be soldered on the middle pins of each transistor as well. I also realized I could just use the mounting bolts holes to secure this capacitor too just to try it risk free.

 

I'm still restless on this one! Any feedback would be immensely helpful right now.

I currently plan to re-recap the amp board's electrolytics but this time using known quantity type low ESR caps instead of the sparse specs audio grade caps. Also grabbed an affordable set of Solen MKP caps for the 4 big silver can caps in the pre-amp section. I don't have high expectations for any real difference, but when it is dead quiet in the house I can still hear a tiny bit of hum through Grados while it seems Senns are always imperceptable.

Rigged up the DPDT switch temporarily to go between Active and Passive pre-amp output so that there is no splitting of the tortuga LDR output; it seems when the amp board sees no input however it will still play out white noise (evident on headphone and speaker out). I really like the passive performance of the tortuga but at the same time I need the active ability for headphone use. The gain of the amp board is ridiculously high so for temporary measure I am placing a shiit sys between the Melos and power amp. Would be nice if this switch did what I wanted as it would be both a headphone/pre-amp mute and allow uninhibited passive operation.

Did a little digging to get to the bottom of the trim pots on the amp board; one is attached to a resistor and pin 4 (vcc-) of the NE5332N opamp and the other is attached to another resistor and pin 6 (2IN-). It is clear now that these have nothing to do with tube bias but rather they are acting as a DC Servo. I feel like I am close to understanding what's going on with the trimpots but not quite there. It's possible I am measuring incorrectly, but I don't see any DC on the active outputs at least.

On another note, Tortuga has been releasing firmware updates on the regular as well so it was neat to rig up a DIY usb cable to re-flash the board. There is a way to change the input impedence of the Tortuga board but it requires a rather expensive set of optional display components which I can't realistically mount into the chassis.

 

Melos is definitely obscure like you said I never really hear about them.. did they precede Tyll's headroom headphone amps? or the Krell ksa5

 

I know that the Krell is pretty ancient as well as a bunch of obscure headroom amps, which came first I couldn't really say. I got into the hobby really around 2002ish so all this gear pre-dated my inception.

Today I swapped out the audio grade caps for boring but specced out caps. I then got my gears turning about resistor swapping and tracing the tube jumpers.

http://www.diyaudio.com/forums/tubes-valves/119683-where-low-noise-resistors-matter.html

I am hopelessly addicted and I'm definitely in WAY over my head!

 

Sorry for another long post! This one is big for me but likely small details that may not even add up to much.

I had a revelation tonight about something that has been chipping away at my soul for a while now... an explanation for the 4 jumper wires near the tubes and possibly for the miller cap tied to the transistors on the right hand side of the amp board. It appears these could be chalked up to running changes Melos made in the production and possibly servicing of the amps, did they produce meaningful results? Hoping I can find out soon!

It looks to me like the main goal of the jumper wires near the tubes serve to re-position four 1k ohm resistors closer to the tube pins, these 1k ohm resistors then get placed in series with four 18k ohm 2 watt resistors which are plate resistors for the tubes. I believe the idea is that resistors here at the plates are prone to noise pickup and hence you want them as close to the tube pins as possible.

It's a stretch but I believe the 2.2uf miller cap across the mosfet tabs is another running change that supplements four small "10 1kv" (not too sure on the uf value) film caps running parallel to the 18k plate resistors. When a small value cap like this is run in parallel to plate resistors it is said to act as high frequency roll-off, maybe there is benefit to having two forms of high frequency roll off?

There are some discrepancies between my board and what I noticed in low-res pics from yesteryear and the board stuffing/parts list document which helped put these things together, it's too bad NONE of this is documented anywhere else that I have found. Arguably I haven't determined a clear pattern to these revisions yet as some amps are simply DIY jobs and I could just be grasping for the explanations.

For a neat exercise, you can print out the board stuffing drawing front and back on two pieces of paper and line them up against a backlight to get an idea of the pcb traces running the bottom side of the board (top side you will still have to have look at the board itself). You can then drive yourself mad like I did following the traces.

As for resistor swap choices it's going to be a tough call and maybe not worth it, Melos used an assortment of pretty much all the resistor types outside of no carbon compositions are present. According to the old Carlo post, swapping resistors made a meaningful but small difference, but like everything else I've run into the really nice audiophile stuff like $5 per tantalum resistor + 10 shipping from PCX are also available only in oddball sizes and wattage.

The next limitation of knowledge for me right now is determining which sets of resistors for the 6922 correspond to input vs output but here is what I have gleaned so far based solely on regurgitation:

Cathode pins 3+8 - 475K + 2K
Grid pins 2+7 - 475K + 2K
Plate pins 1+6 - 18K w/ bypass cap + 1K
Heater supply - Pairs of 39 ohm

I've read that the plate resistors are the most important with regards to resistor noise and metal foils are not necessarily a great choice there.

Brain... melting.

 

The plate resistor jumpers are now done but I need to change the focus of this update onto grid stoppers!

I really have to thank Doug, as earlier he had mentioned how the grid stoppers for the tubes are poorly placed resulting in oscillation and potential for RF interference. The Melos with its reputation for noise, this then sent me down a dark path I would never come back from.

I did some digging and found some incredibly telling information:

"This resistor is the one that prevents oscillations and pickup of radio stations and other noise due to long or poorly-shielded cables. It is not usually a good idea to eliminate this resistor. Ideally, it should be soldered directly to the grid pins of the socket, with very short leads."
http://www.aikenamps.com/index.php/grid-resistors-why-are-they-used

So here's what NOT to do…



Shown above was my first attempt at shortening the traces for the grid stoppers, 4 cut traces from the 2nd and 7th pins of each tube and 4 relocated resistors along the underside of the PCB, 4 jumper wires make up the difference where they need to. Note that the PCB traces, especially with these sets of resistors, run both top and bottom of the board and that the set of drawings publicly available do not tell the whole story.

While this attempt was ultimately a big failure, it at least got me part of the way where I needed to be and is hopefully illustrative enough to get the idea across. I'm kicking myself now because I didn't grab a pic of the finished result, but will try to post up a drawing for this when I get the chance. For each grid stopper there is a 2K + 475K + 1uf film cap, the 475K in series (actually a 470K Takman carbon film now) must stay put in the stock location and it is just the 2K resistors that can then be soldered directly to the tube sockets. I believe that the swapping in better resistors for the grid stoppers and getting the resistor as close as possible to the tube socket has had a greater impact on the noise floor than even the left channel mod or the jumper wires for the plate resistors.

All other resistor swaps went fairly smoothly and I would report they also help in ways that are absolutely noticeable, I attempted to swap as many of these as reasonably financially possible with a mix of popular carbon composition, carbon film, and metal film.

The amp is finally approaching inky black background territory, the bass is authoritative and reaches down deep, the amp still excels in detail and the soundstage and decay are very believable.

I noticed pre-grid stoppers that when swapping from JJ 6922's to Genalex 6922's that the amp sounded much clearer in most areas except for a top end harshness, to that extent the JJ's were simply more forgiving and tolerant of most music. After the resistor changeover, the top end harshness is much less an issue so the benefits of the more expensive tubes still remain.

Another point of note that may help some owners, I screwed something up with my relays and the wiring for the HP/Active pre- mute circuit. Basically I tried to relocated the red/green LED and broke one of the three leads on the lamp, the amp would remain stuck with the active pre-amp muted even after replacing the bulb. In frustration I removed both relays (they are socketed) and swapped in a standard LED for the red/green one. Removing the relays defeats the 3 minute timer and circumvents the headphone/active pre- switching behavior.

Here's where it is now, I am working on making a passive attenuating cable next to combat the extreme gain of the active pre-amp. If you care to know, the giant white caps for the active pre-amp outs are Sonicap Gen I at 11uf (value adjusted up from 6uf and part chosen based mostly on cost), the leads need a lot of work to get to fit for the original snap-in holes and I ended up having to hot glue them in place.

 

I haven't thrown in the towel just yet!

Had a major scare a week or so back and thought I had completely lost the right channel of the amp (many thanks to those who provided emotional support and bashing!!). After several late nights of troubleshooting, found out it was due to a short courtesy of a bent leg of one of the plate resistors' tiny ass film cap bypasses. I found it when I measured the plate load on the right tube, it was seeing only 1k resistance (supposed to be 19k) resulting in about 100v going to pin 1 with power applied. Stock bias seems to run between 55-65v, luckily I didn't keep the amp running in that state for very long and also have cheap tubes to spare.

None too happy about any of this, I decided I could live with the stock plate resistor arrangement if it means eliminating the chances of this ever happening again. This time I opted to change out the Koa Speer SPR2 (aka Kiwame) 2 watt carbon film resistors for the plates and used 3 watt IRC GS3 metal films instead. Another motive for the swap, the carbon films I had in previously were not matched as tightly as I would have liked. I relocated the bypass caps on the bottom of the board with some teflon sleeving for good measure, this is what I should have done from the start!

A side commentary on resistor choice, I think the carbon film resistors provided a more raw and upfront sound while the metal film are actually smoother and more even toned, this doesn't quite match with what I've read about resistor choice but I ultimately can't say which I preferred. With genalex gold lion tubes however, the smoother tone metal film probably works better in the long run.

Along the way I experimented a bit of trial and error using a pi attenuator calculator to add a resistor network on the pre out to lop off about 22db for a low-output pre out. In my particular case I used 20k input impedance for the Tortuga board and measured a hair less than 10k output impedance at the jacks.

Thanks to all of this resistor swapping I learned the importance of over-ordering by at least double on resistors and matching the values as closely as possible. The plate resistors obviously had a large effect on the voltage of the tubes and at higher impedance values it's much harder to get a tighter tolerance.

The last thing I did was to re-examine the input traces and quickly learned that the old melos left channel mod is only half the story. The input wire for the left channel is obscenely long when compared to the right channel. It's pretty bad and makes my head hurt trying to figure out why they would do it that way. The trace goes from one end of the board to the other going from the bottom and top of the pcb. The fix was easy and worth it, just follow the input trace back and then re-wire it directly to the 1uf cap (or the pad right above it). I made sure to cut the trace topside as well for good measure. The 1uf input film caps can easily be relocated off-board for larger and more boutique options but I will stick with the Sonicaps I have for now, the factory solder pad locations for these caps is unfathomably bad.

I am not ready to try it yet but I also had a thought about a way to get the Tortuga board functional as a passive pre without sacrificing the amp section. The loop out jack is fed off of the source selector switch and currently goes unused, either the Tortuga board or a physical volume pot/attenuator may be able to be fed from the loop out wiring without interfering with the other. If it can work in this way without impedance issues, since the LDR uses a remote it does not necessitate the presence of the rotary encoder then a traditional pot could go back in and allow physical control of the amp while the remote then dictates the Tortuga.

In the current state, there is STILL the teeniest bit of noise present when looking for it but I am overall quite satisfied with the performance of the amp right now. Even more, I am thankful I haven't quite blown it up yet.

Some pics. The last of this set shows the final resistor arrangement for the grid stoppers and jumper wires. If you look closely you can see where I made trace cuts on the pcb bottom, there are two cuts on the top of the board as well. Yikes, I just noticed all the splotchies are from my isopropyl alcohol swabbing.

 

The best part is, as horrible as this amp should be it has had its share of praise and adulation from its heyday. At some point in history, an ex-employee or group of them, maybe even Mark Porzilli had talks of bringing the brand back and or at least offering upgrades and service.

Excited that you replied, I recollect these old threads about cloning the SHA board and then something about a SHA-2 for April fools, obviously nothing ever materialized!

I think the guy that bought all the leftover paperwork and inventory ended up selling some of it to Carlo who then became a myth.

http://www.head-fi.org/t/6239/clone-the-melos-dammit
http://www.head-fi.org/t/9381/introducing-the-melos-sha-2

 

Hello Mr. Sneis,
I joined this group because of your posts on the Melos. I recently bought a Melos sha gold, it has many of the well known Melos problems. It sounds nice when it works. My unit's main problem is that one channel drops off after about an hour or so of playing. I have taken it to the local electrical repairing shop and they can't figure out what is the problem. I am desperately searching for some advice, suggestion,HELP! Any info on how and where I can turn to for help will be immensely appreciated. Regards.

 

Very cool to find another owner!

You're job is probably going to be a bit tough. There's no real schematic for the Melos as far as I know. I also won't pretend to be a well informed and seasoned tech either lol.

If it is not bad tubes and it occurs after getting warm, a cracked solder joint would be my first guess. The places that get the hottest are around the tubes and then near the rectifier bridges just after the transformer wiring. The active devices with heatsinks on them also can get quite hot.

It's really not too bad to reflow all the joints on the amp board, the hardest part is getting it out of the amp.

 

Thanks a bunch. I will inform the tech what you mentioned. Much appreciated.

 

Hi,

I hope you see this.

Found your thread and read it. Clearly I don't know as much as you do about these things thus I am asking for help.

I just picked up one of these pre-amps for $80. I read how great and expensive they are...blah blah.

It came with the remote and box. All the switches work via the remote too.

When I plugged it in I get very faint sound in both channels even at full volume. Previous owner told me one channel was not working 100%.

Everything looks fine inside. It has 4 large caps....2 on each side of the board, they are nice cpas made in france. One of them has a slight indent on the side (Grey color) like a soldering iron touched it. Not leaking or anything else.

What do I need to do to fix it and is it worth fixing or should I give it back to the previous owner.

To be honest, I am disappointed of the poor build quality of this so called "High end" pre amp.

HELP please.

Thank you.

 

When you turn it on it is muted by default. After the timer clicks you have to use the remote to un mute.

Design is not great build quality is not great. This company went under over 15 years ago and you bought a needs repair amp for 80 bucks. Not sure what more you would expect

 

New here decided to join because of this thread. I own 2 Sha1 and a 202st triode amp I do have the problem with my 1 sha where it cuts out on one side after about a half hour or so. I was told though that the earlier models didn't have the reliability issues which seams to me at least thats true the one with the problem is a later model with the removable power cord my other has a fixed cord. My amp is also the first run of that model which is the most stable and i have not had any problems with it knock on wood. As far as sound i own several different preamp's including several Audio Research tube and solid state ones the Sha1 puts them all to shame on sound. Reliability might be an issue but i haven't heard anything as smooth and detailed as the Sha1 period especially at there price point. With that being said I am trying to buy as much Melos gear as I can find at reasonable prices so if anyone want to unload anything let me know