Square Waves on Combo's

[spacepatrollerlase]

I noticed something starting with the original Farfisa Professional. If you look at the voicing tabs, the green tabs are "Clarinet/sharp". This screams "Square Wave". The "Bright" waves on the Saturn and Yammies are also squares as is the whole "organ" on the Moog Opus 3, the "mellow"/"sharp" is done by a variable lowpass filter and the Moog's sawtooth waves are synthesized by stacking squares. In fact the only wave that is generated is a square that is filtered down and octiave-divided (although the Moog uses many IC's). This replaces the thin reed voices of the the older models like the Connies and "Compact"'s.

I don't know much about the FAST's but is there something about the silicon transister than makes it better for square waves than for thin reeds? This matters since it was the narrow-pulse or sawtooth that really defined the bright sound of the Combo organ.

[karl]

Hello Spacepatrol
The reason older combo organs use square waves is because of polyphony. You can get all the notes to sound at the same time ( if you can figure out how to hold them all down). To obtain this effect the highest twelve notes are generated square waves.
These notes are divided down to obtain each lower octave.
This allows all notes available at any time as opposed to the synthesizers at the time which had 5, 6 or 8 note limits.
Square waves easily allow this. Triangle, ramp or sine waves
are difficult to divide down.

Karl

[spacepatrollerlase]

It wasn't the older ones like the Voxen and Compacts that used them, it was the newer ones like the Professional, YC's and maybe the FAST's (although I'm not sure of that, I haven't looked at the voice selection. The Connies and Copacts used nammrow-pulse reeds and strings to grit up the sound.

The Opus 3 had a single tone generator that kicked out a square wave at some absurdly high frequencey that even a bionic bat on steroids couldn't hear and everyithing was divided down and synthesized

[karl]

Hey SPL,

I am sorry, I guess I don't understand the question. But generally I can say that silicon transistors drop or use up
a small voltage .6V from the voltage that is used to power it.
Older types of Germanium transistors use up more, and MOSFET
transistors drop almost nothing. If you make a square wave or narrow pulse generator out of any of these it will sound the same.
All I really want is an organ with a friggin laser strapped on it's
head.

Karl

[revtonynewnham]

Hi

The reason that most Combo organs use square waves is simple - economics. It's quite possible to design frequency dividers that produce sawtooth (or other) waveforms - but the simple "flip-flop" of "bistable" circuit is far less frequency conscious - hence there's no components that need tailoring to the specific note, needs no inductors or other specialised components, and uses cheap transistors simply as switches.

Incidentally, Germanium transistors (which pre-dated silicon by several years) have a lower voltage drop of 0.3v than the 0.6v of Silicon. The reason they have fallen out of favour is that they inherently have a higher leakage current, and in general are not so rugged as silicon versions. Germanium diodes are (or were until recently) still manufactured for specific applications where the low voltage drop was more important than other considerations.

With the introduction of IC's, the use of square waves became even simpler, with chips available that are, in effect, a whole chain of frequancy dividers (bistables) in one compact package.

Every Blessing

Tony

[Time Lord]

Hey,
Thanks Tony and Karl. That was very informative.

[karl]

Hello Tony,

Thanks for the techno save. I have never known much about germanium diodes. They were old when I was young, and school never really discussed them much. Guitar players have often swore that certain FX pedals were better because they used this component. Can you tell me if this characteristic would make a pulse wave oscillator sound different?
By the way, I notice you have a pipe organ. Does it work? I love the sound of these guys, but have not had the opportunity to play one for years.

Karl

[revtonynewnham]

Hi Karl

Just seen your post (I don't get time to look here very often!).

The higher leakage of Germanium transistors and diodes will have a very small effect on the waveform, and hence the sound, but other factors in circuit design are of far greater significance.

Valves were still in everyday use when I started getting into electronics, and Integrated Circuits were very rare and just coming into use.

As to my pipe organ, I rescued it from a church in Essex, and it's still in pieces - someone had "bodged" a lot of the construction at some time, so what should have been a relatively simple job has turned into a marathon, and because I don't currently have any workshop facilities or storage, it takes about an hour to clear things out of the way before I can get to work on it. I was thinking of trying to do some more today - but it's too hot already (and it's only just after 10 am)

I'm the President-elect of the Bradford Organists' Association - and I play the 1820 chamber organ in my church about 2 Sundays a month - as well as, sometimes, some much larger organs (including theatre organs).

Every Blessing

Tony

[wildkippy]

Mr. Newman, I'm a fortunate owner of one of the jennings-built vox continentals. his signature is written inside. in the vox continental website the original designers & builders told of building a portable organ to compete w/the electric guitars. they wanted a hammond type drawbar setup and they wanted a somewhat pipe organish/hammond sound. I think they achieved this in the vox continental. especially when i play it thru my leslie. there are many parts and designs that went into the original jennings organ that the later italian & us builders felt they can do without. like i said, i feel very lucky to have my english vox continental. it stood up well over the years probably from owner/s who knew what a good thing was and took genuine care as i shall do as long as i have it.