Over the years, the EHX Deluxe Memory Man has undergone a number of changes, including the AC mains cable, internal transformer, and rectifier being swapped out for a 24 V DC input. Here‘s the latest version, and …
There are some pedals that have mojo parts in them. These parts have unique powers or provenance that give any pedal they are installed in somewhat mythological properties. A classic example of this are the transistors in fuzz pedals. The NKT275, a transistor found in classic, vintage fuzzes, are so desired that unscrupulous vendors will sell fake versions to those seeking to tap into whatever mystical capabilities the real deal possesses.
I’ve heard from one well-regarded builder who keeps his stash of fuzz transistors in the fridge, and carefully solders each transistor’s lead with heat sinking to keep any of the magic from being consumed by soldering-iron heat. Fuzz circuits are often so simple, that any remarkable ability they have is attributed to the constituent parts instead of their overall design. So, whether they have unobtainable transistors, carbon composition resistors, or tropical fish capacitors, the consumer can assume this pedal is imbued with magical properties. This can be in spite of the fact that the transistors are likely the last of a production run of devices that have been picked over for the last 60 years, the resistors are poor performers by almost every quantifiable measure, and the most special thing about the capacitors may be their paint job.
Sometimes particular makes and models of pedals are the holders of mojo. The Klon Centaur, Nobels ODR-1, and EHX Deluxe Memory Man all have vintage variants where it’s widely held that they have something special about them. Over the years, changes have been made to each of these designs. Some of these changes are literally superficial: Changes have been made to enclosure printing or paint. Some changes are technically superficial: Components were changed, but aren’t in circuit positions that contribute to audible differences. Lastly, some substantive changes genuinely alter the end product.
“If it sounds as though I’m suspicious of mojo parts and pedals, it’s probably because I am.”
As a case study, take the Deluxe Memory Man (DMM). The DMM has gone through some cosmetic changes over the years. None of these things contributes to the sonic delivery of the pedal. At one point, the AC mains cable, internal transformer, and rectifier were ditched for a 24V DC input. Both of these power arrangements fed regulators with the same voltage outputs to the DMM circuitry. It is difficult to say that the audio circuitry in the pedal could be “aware” of the changes to power supply elements pre-regulator, and dubious that any resultant change could contribute to an audible difference in the pedal’s performance. That said, at one point in history, the pedal’s delay-producing bucket-brigade chips were changed out for different types due to parts availability. This is a real change that a subset of players can readily detect.
Here's the vintage version.
If it sounds as though I’m suspicious of mojo parts and pedals, it’s probably because I am, and I think you should be suspicious, too. However, try not to be cynical, as I absolutely do not think that it can all be written off as fantasy. Sometimes the sum of the parts is really greater than the whole. The pedals we love are not often complicated, but they are always comprehensive. Every constituent part of a device can vary at both conception and over time, and these parts can often combine in unique and interesting ways. The guiding principle of evaluating whether a particular stompbox is special has to be listening to it. Its pedigree and provenance might increase the chance of it being something special, but, as is often true, the proof of the pudding is in the tasting.
In my estimation, the most powerful part of mojo-equipped gear is our own faith in it. When we are convinced that something is good, we enjoy it more and play better, and when we enjoy it more and play better, we actually do sound better! There is a great deal of inaccessible gear with a well-earned representation for unlocking the best in those who play it. You can also be certain there is something readily available that may speak to you in the same way. Good luck in finding your mojo, baby
Electro-Harmonix Nano Deluxe Memory Man Analog Delay/Chorus/Vibrato Pedal
Your amplifier's preamp and power tubes require a DC voltage to operate. The amplifier's power transformer converts the incoming AC line voltage to the levels required. The power supply rectifier, whether of the vacuum tube or silicon diode variety, converts the AC voltage to DC. That DC voltage is filtered and then sent along to the various amplifying stages to do their specific tasks.
The hard-working power supply must be able to deliver the amplifier's maximum continuous rated power for an extended period of time. Most well-engineered amplifiers can operate continuously at full power for hundreds of hours without generating sufficient heat to injure the operator or cause a component to fail. Even so, things do heat up.
A rectifier tube in a typical tube-rectified power supply: R1 and R2 represent the internal copper resistance in the transformer's primary winding, and R3 and R4 represent the same in the transformer's secondary winding. RA represents the tube's internal resistance between the anodes and the cathode. In a silicon-rectified power supply, RA is much lower and therefore produces less heat loss.
When you play at low volumes, you're not placing a great demand on your amplifier's power supply. At gig volume, however, you start drawing significant power from it. When you run the unit for several hours straight, the copper wire in the power transformer gets hot. Copper wire, being an imperfect conductor, exhibits resistance to current flow, and this inherent resistance causes the wire to heat up as the power demand increases. The resistance of a given length of wire is fixed, which means something has to give when the temperature goes up, and that something is voltage. As your power transformer heats up, the voltage it produces decreases. In a typical amp this decrease isn't large, but it's noticeable.
When we introduce a tube rectifier into the equation, the effect of heat-induced voltage loss is exaggerated. The reason is that the rectifier also has some internal resistance that contributes to a total drop of as much as 50 volts under full load. That's a lot. Silicon diodes overtook vacuum-tube rectifiers long ago because they were much less expensive and assembly was less labor intensive. But there was another reason: They're more efficient, due to low internal resistance. That difference in internal resistance means silicon and vacuum tube rectifiers are generally not directly interchangeable. Using a plug-in silicon device in place of a tube rectifier can cause excess DC to appear at the filter capacitors.
When you play at low volumes, you're not placing a great demand on your amplifier's power supply. At gig volume, however, you start drawing significant power from it.
A tube rectifier may make the cut when the goal is to produce a vintage-correct reproduction amp. Even though we can engineer a similar amount of voltage sag into the power transformer, purists may see the absence of the original part as a cop-out to save money, when, in fact, it may simply result in a more reliable, maintenance-free design. However, inducing sag into the transformer design can cause the temperature in the power transformer to increase more rapidly over time, in which case a larger, heavier, and more expensive part may be required to manage this drawback. In some cases, getting a power transformer design to conform to modern regulatory limitations can be simplified by using a tube rectifier to provide an easier path to safety compliance. We often see reissue amps that differ in performance from the originals simply because they have to clear regulatory hurdles that were non-existent at the time the originals were created. A crafty engineer can often find workarounds to such obstacles, and clever application of transformer technology and tube rectification are valuable tools in the kit.
In my experience, the most practical use of a tube rectifier is in dual-voltage power supplies, where a high- and low-power mode is required. For the high-power mode, a large, stable power transformer is necessary to meet maximum performance parameters. The downside? A high-capacity power transformer tends to yield stiffer performance when not running at or near maximum potential, such as in a low-power mode. This is where the tube rectifier really shines: It can be used to exaggerate the voltage sag in a power supply that would otherwise exhibit an unforgiving feel.
Whether the design objective is aesthetic, practical, or genuinely novel, it's good to have choices. Besides the satisfaction of seeing more glowing tubes humming away in our amplifiers, it's nice to know that players appreciate the extra effort involved in creating new designs around these familiar bottles.
[Updated 10/14/21]