Melos SHA-Gold Headphone Amp On The Bench

SCompRacerSCompRacer Posts: 6,952
edited October 20 in DIY, Mods & Tweaks
While recovering from some minor surgery, I took this project on for a good friend. A Melos SHA-Gold Headphone amp and pre amp (1996). It has some issues. There are plenty of reviews and opinions about the SHA-Gold if you are not familiar with it.

Snagged these from the web to show assembled.

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While it powered up, the remote did not work. The remote is important for volume control but essential for the un-mute function and balance control. There is no mute/un-mute switch or balance knob on front panel. When you power up, it is in mute and the remote is the only way to un-mute it. The balance pot is behind the front panel meter.

A cell phone verified the remote IR transmitting. I had 5v power to the IR receiver, and voltage dropped when remote buttons pressed. I got a remote signal to IC chip, but no command action took place. Fortunately, a disassembly and cleaning on the remote buttons repaired that. The buttons that contact the remote board are a stippled black metal. After remove corrosion with rag and cleaner, life was good. Note black stuff on rag. My guess is the remote sent a corrupted signal.

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While the mute/un-mute worked now, the remote volume and balance controls did not. The motors spun but the pots did not move. I disassembled them and found the thin plastic on one end of the gears that acted as spacer had broken, allowing the gears to drop out of alignment.

The volume control was easy to remove, but the balance control was soldered to the board. I drilled a robust aerosol straw to press fit on the gear shafts and cut to length for a spacer. Now the gears stay in alignment and I have volume and balance control. The meter on front panel indicates channel balance.

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The volume of the Melos Gold is photo optical. An incandescent bulb illuminates below photo cells to vary resistance and change the volume. The idea here was to eliminate any mechanical wiper noise or inconsistent wiper pressure/inaccuracy. There are folks that can’t/won’t repair it. The owner prefers to keep it as designed but working. A popular remote volume board used to convert these runs $300.

The volume bulb is actually a fuse bulb originally made by BUSS. It illuminates under two photocells, one for right and one for left channel volume. The original bulb was blown. Bright is minimum volume, dim is max volume.

There were no specs on the bulb or published that I could find. After measuring voltage and current, I purchased a few 6 volt fuse bulbs in various amperages. So far the 6v .25 amp looks the best based on video I watched of one in action.

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More problems lurk as the scope shows. Those sine waves connected to the outputs don’t look like what is coming out of the signal generator. More to come.


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Here is a good shot (snagged from web) of the volume control board with balance control at left. The remote pictured is not the one we have.

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Make yourself necessary to someone. Ralph Waldo Emerson

Salk SoundScape 8's * Audio Research Reference 3 * Bottlehead Eros Phono * Park's Audio Budgie SUT * Krell KSA-250 * Harmonic Technology Pro 9+ & Pro 11+ * Signature Series Sonore Music Server w/Deux PS* Twisted Pear Buffalo III Dual Mono ESS Sabre32 DAC * Heavy Plinth Lenco L75 Idler Drive * AA MG-1 Linear Air Bearing Arm * AT33PTG/II & Denon 103R * Richard Gray 600S * NHT B-12d subs * GIK Acoustic Treatments * Sennheiser HD650 *

Post edited by SCompRacer on

Comments

  • EndersShadowEndersShadow Posts: 16,131
    Rich, as always your work is top shelf!
    "....not everything that can be counted counts, and not everything that counts can be counted." William Bruce Cameron, Informal Sociology: A Casual Introduction to Sociological Thinking (1963)
  • pitdogg2pitdogg2 Posts: 11,479
    You need a hobby Rich....

    Nice ;)
  • kharp1kharp1 Posts: 2,586
    Ah, heck, anybody could do it the easy way.
    :)
    I admire your troubleshooting skills.
    Main System:
    Joule-Electra LA 100 MKIII
    Pass Labs Aleph 30, McCormack DNA-125, Parasound A21
    Marantz SA-14S1
    Usher CP-6311/Tyler Acoustics Taylo Reference Monitor, LSA-1
    Dual SVS SB2000
    Wireworld Equinox 7 bi-wire, Wireworld Silver Eclipse 7 IC

    Secondary Rig:
    Parasound P5, Audio Electronics by Cary Constellation
    Marsh a200s, Audio Elecrtonics by Cary Hercules
    Pioneer Elite DV-45a, Denon DVD-2910
    Klipsch Epic CF-1, Vandersteen 3CE sig
    Analysus Plus Oval

  • machonemachone Posts: 1,018
    Nice work!
    Mojo Audio Joule v5>>Quantum Byte w/JRiver 24 and Fidelizer>> Starlight 7 USB >> Mojo Audio Mystique v2 SE>>ModWright SWL 9.0 SE Signature>>Hafler DH-500 Amp+ (Musical Concepts PA-6 Elite Mod)>>
    SRS 2.3TL (Fully Modified)...SDA-1A (Fully Modified with Dimensional Tweeter Delete)
    1KVA Dreadnought
    Marantz SA 8005
    Pioneer PLX-1000 Turntable - Shure SC35C/N35X - V15III/VN35HE
    Yamaha TX-540 Tuner...Sony BDP-S570

    Separate subpanel with four dedicated 20 amp circuits.
    1. Amplification 2. Analog 3. Digital 4. Video

    "All THAT IS LOST FROM THE SOURCE IS LOST FOREVER"
  • schwarcwschwarcw Posts: 7,164
    Rock on Rockman! Nice work.
    Carl

  • delkaldelkal Posts: 345
    For its original price I wouldn't have expected that many different things to break in 12 years!

    What happened to it? In the basement during a recent hurricane?
  • schwarcwschwarcw Posts: 7,164
    edited October 21
    How about 22 years :D ? This Melos model has a reputation for sounding great but has reliability issues.
    Carl

  • delkaldelkal Posts: 345
    schwarcw wrote: »
    How about 22 years :D ?

    Sorry but I ran out of fingers! You are correct.

  • agfrostagfrost Posts: 2,180
    If you knock it off the bench, you can drive over to Holm Audio to pick up their used one as a replacement... :D
    Jay
    SDA 2BTL * Musical Fidelity A5cr amp * Marantz DV-9500 * Modded Adcom GDA-600 DAC * Rythmik F8
    Micro Seiki DQ-50 * A hodgepodge of cabling * Belkin PF60
    Preamp rotation: Krell KSL (SCompRacer recapped) * Manley Shrimp * PS Audio 5.0
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