[sdiy] Euro Synth Spec

[rsdio at audiobanshee.com]

Certainly, gear could be designed to run on anything, ac or dc. It could even be designed to run on any voltage, provided that there is enough current to support a boost regulator that would increase the voltage to the necessary internal levels. However, each of these flexible options requires more parts, is more expense, and sometimes - in the case of the boost regulator - produces much more noise!

It’s fine when a reasonably large piece of gear has a single supply. I love that my MobileIO interface can run on just about any DC or AC voltage within a reasonable and convenient range, provided that the total power is sufficient. But that’s a full rack enclosure where all the boards run from a single power input (even if there are multiple voltages from the main internal supply).

The most significant aspect of Euro rack Synth gear is the cost savings from sharing the enclosure across several modules, while also sharing the power supply across all of the modules. If each individual module were designed to handle anything you plug in power-wise, dc or ac, any voltage (even without a narrow range), then the cost of the modules as well as their size and heat dissipation would go up. It’s also far more likely that there would be more unwanted noise in the audio with that many flexible power supplies in the same cabinet.

Another aspect is efficiency. Every conversion between AC and DC, DC to AC, or from one voltage to another is not 100% efficient. The best I’ve seen is 80% to 90% efficient, maybe 92% with the latest technology. Each stage is burning at least 8% or maybe even 20% or more in wattage. Those handy diode bridges might only lose 0.4 V on each leg, but as more current is pulled through the power supply, more wattage is burned off as excess heat. For anyone running on batteries, or even just with an almost underpowered supply, that means your modular rig stops working reliably.

In other words, there’s a huge advantage to standardizing on a single set of bipolar DC Voltages instead of trying to support anything that might be plugged in. Regrettably, this significant advantage is almost completely sabotaged by the lack of reliably keyed cables and headers.

Brian Willoughby


On Oct 21, 2017, at 6:46 PM, Mike HEQX <mike at heqx.com> wrote:
> Why can't gear run on anything you plug in either polarity dc or ac. Using a diode bridge as protection should allow you to do this. Some of my gear will run on anything you plug in. I love that. 
> 
> On 10/21/2017 5:59 PM, axisair at comcast.net wrote:
>> Two parallel diodes reverse biased won't short out the supply, they just wont allow current to get to the circuit.
>> For the price of about $0.015, I just use four 1N914 small signal diodes in a full wave bridge configuration. That just supplies the correct power to the rest of the circuit regardless of if the polarity is reversed. The voltage drop from the mains is 0.6V to 0.7V per leg. Minimal drop considering the existing overhead.
>> Since they're small signal diodes, they can handle around 1/3A and have less reverse bias leakage (and cost less) than 1N40XX series. They also double as a fusible link if the circuitry faults.
>> Obviously, if they connect everything correctly, two diodes just sit there.
>> 
>> -----Original Message-----
>> From: pete.hartman at gmail.com
>> 
>> And in that latter case usually we put ptc fuses in line as well so we DON'T actually damage the supply or other modules.
>> 
>> I do diy, not commercial modules, but the same logic applies.
>> 
>> On Oct 21, 2017 3:24 PM, <mskala at ansuz.sooke.bc.ca> wrote:
>> On Sat, 21 Oct 2017, Ben Bradley wrote:
>> > Do many or any Euro modules have reverse-polarity protection? It seems
>> > easy enough to add a series Schottky rectifier in series with each
>> > power line, but it adds parts cost and drops a little voltage where
>> > people are already thinking the 12V supplies should be 15V.
>> 
>> Many; not all.  Some do it in other ways, such as with parallel diodes
>> that will be reverse-biased in normal operation and effectively short out
>> the power supply when the connection is backwards.