01/07/2019
I feel compelled to tabulate the complete disaster foisted on the owner of an ME preamp that was submitted to the authorised ME repairer in Melbourne recently. The original, botched job was performed by a well-known modifier/repairer/builder in Canberra and serves as a salutary lesson for ME owners who allow their ME products to fall into the hands of non-authorised repair people. The preamp was an older style ME25 that has been factory upgraded with the later style internal and external power supplies.
The external power supply consists of three, independent power supplies and substantial filtering capacitance to ensure minimal ripple.
The internal power supply is quite complex, consisting of the following:
1) High capacity, low ESR, low ESL filter capacitors.
2) Two, high speed capacitance multipliers.
3) Two, low ripple, LM317/337, precision regulators, adjusted to better than 1% tolerance.
4) A large array of high speed, low ESR, low ESL filter capacitors.
5) Two, low ripple, LM317/337, precision regulators, adjusted to better than 1% tolerance, specifically isolating the phono stage from the main power supply.
6) An auxilliary supply, isolated from the audio power supply stages, specifically dedicated to digital and control systems.
Some additional points:
* All solder joints were performed by hand, with high silver content solder.
* All switches use hard gold plating on contacts. The toggle switches are hermetically sealed and faults (apart from mechanical damage) have never been noted in the more than 40 years that the same Japanese switches have been used. Distortion from the switches cannot be measured, as it is below the resolution of test equipment (and human hearing).
Below are photos of the shocking work done to this classic preamp. The poor workmanship and insane choice of re-design seriously compromised the performance of the preamp. Why such a crime was perpetrated is unknown.
#3 shows where the external power supply was modified to eliminate the house-keeping power supply.
#4 shows where cheap, crappy capacitors were used and more modifications were made. Regulators were added to the external power supply. The regulators used were the inferior, 78XX/79XX types. Regulators should always be placed close to the active circuitry and NEVER at the end of a long umbilical cable. Dumb, dumb, dumb.
#5 is an example of more poor workmanship and crazy design choices.
#6 is more poor quality soldering. No silver solder here.
#7 Just insane. I can't look at this.
#11 Here's where it just gets weird. The superb Alps, 'Blue Velvet' pot (Precision, laser trimmed, conductive plastic) has been removed and replaced with a cheap, nasty, Jaycar pot. Channel imbalance has been seriously compromised. Weirder still, the excellent Alps 'Blue Velvet' laser trimmed balance pot has been bypassed. This is seriously weird, because the Alps balance pot uses a pure metal to metal contact, when at the 12 o'clock position. Distortion, therefore, is non-existent, when at 12 o'clock. Insane.
#13 Another example of sheer incompetence. The modifier has decided to bypass the ME power switch and re-wire the system so it can be permanently powered. Trouble is: The ME25 is already configured so that power is applied to active circuits at all times.
#14 shows where the capacitance multipliers have been bypassed. Worse, the precision LM317/337 regulators have been removed.
#21 shows where the only isolation provided to the phono stages are a couple of resistors. The original ME design calls for dedicated regulators for the phono stages.
Although not shown by the photos, all the toggle switches have been bypassed. An insane and needless modification, given the nature of the switches used. The gold plated, hermetically sealed switches have never been known to fail, or cause distortion.
This is truly a 'Rogues Gallery'. This person should never be allowed near a quality product like an ME25. The work demonstrates a fundamental failure to understand not only how and why an ME is designed the way it is, but a failure to understand basic electronics.
Canberra ME owners, be warned! There is an alleged tech operating to damage the performance of your product in your midst.
