Moog Music Forum

The schematics for all the early Moog Modulars show power supplies of +12 / -6 and -10 volts. However, when in use and considering some systems with quite a lot of modules, what (has anyone ever measured?) are the actual running voltages?

I know most plug in power supplies (such as plug in battery replacment DC supplies) state 9v and 12v etc but when measured deliver
quite higher readings...same with Moogs???

Normally the ua723 (plus power transistor) based power supplies (like the one of the Moog Modular) should deliver exact voltages until the maximum of modules (meaning maximum of consuming current) is reached. No need to run voltages higher + or lower - to compensate higher current consumption.

Carsten

The voltages will be regulated up to a maximum current.

Once that current is exceed, the voltages are no longer regulated and will decrease.

Wal Wart type PSU (those that plug in a wall) usually are not regulated. For example, they sometimes show up to 15 volts for a 9 volts setting. But since they are generally of low power capacity, that voltage will drop down to about 9 volts quickly when power is consumed.

In modular synths, the PSU is regulated. Meaning that for a 12 volts setting, it outputs 12 volts exactly. And it will maintain that voltage stable until its maximum output current capability is reached (essential for VCO tuning stability).

So, if the specs indicate 12 volts, -10 volts or any other voltage in a modular system, you can be sure that's exactly what is actually being delivered to the modules. The PSU in modular synths casings are usually more powerful than the maximum number of modules that the casing can physically contain to prevent voltages from dropping due to over demand.

Just as a small note, the +12 and -6 volt supplies in Moogs are indeed regulated, but the -10 volt is not.
The only module that required -10 volts were the 901Bs (and perhaps the large 901- I really don't recall.)
But this voltage was used in waveform production, not in tuning.
Both the Moog 909 and 910 power supplies had unregulated -10 volt supplies.

Kevin Lightner wrote:Just as a small note, the +12 and -6 volt supplies in Moogs are indeed regulated, but the -10 volt is not.
The only module that required -10 volts were the 901Bs (and perhaps the large 901- I really don't recall.)
But this voltage was used in waveform production, not in tuning.
Both the Moog 909 and 910 power supplies had unregulated -10 volt supplies.

I didn't know about that. Good point. But if replacing an original PSU in an old Moog modular with a new one, it wouldn't hurt to have even that -10 volts regulated I guess...
Back in 1968, it wasn't as easy as today to build a regulated PSU.
In fact, I remember Herb Deutsch telling about the first live concert done with an early production modular which was powered by car batteries under a table because they were afraid the power from early PSU was going to cause problems with tuning and the overall performance of the synth ! Pretty funny and unbelievable today, but those were pioneering days back then... BTW, I was only 3 years old then!

thealien666 wrote:
I didn't know about that. Good point. But if replacing an original PSU in an old Moog modular with a new one, it wouldn't hurt to have even that -10 volts regulated I guess...

I agree. The 7910 fixed voltage regulator or LM337 are ideal.

Funny also- Moog's later 930 supply didn't provide this voltage.
I've seen people install 901s in later Moog modulars and couldn't understand why they made no sound.

Back in 1968, it wasn't as easy as today to build a regulated PSU.
In fact, I remember Herb Deutsch telling about the first live concert done with an early production modular which was powered by car batteries under a table because they were afraid the power from early PSU was going to cause problems with tuning and the overall performance of the synth ! Pretty funny and unbelievable today, but those were pioneering days back then... BTW, I was only 3 years old then!

Great story and I can completely see why Herb would do such a thing.
A well charged car battery has gobs of current and the early modulars required little.
Room temperature probably affected tuning more than that method of power for short or medium length shows.
Thanks for the anecdote.