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Mysterious Eagle Audio Generator - Any ideas?
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Author Mysterious Eagle Audio Generator - Any ideas?
alexbarbed

This was being thrown away at work so I rescued it. It works and sounds very beefy (but maybe I'm being tricked by the visuals...) I can't find much about it apart from someone on a forum saying Hawkwind used one live. It's an Eagle AG71. In bad need of calibration but otherwise sounds very nice... particularly when it powers up / powers down, it sounds like a UFO landing. Anyone had one?
cretaceousear
Sound samples needed of the UFO take off!
Perhaps Hawkwind had one after (was it Dikmik?) left with his VCS.
alexbarbed
I might have overplayed the UFO aspect but I'll record something tonight smile
sduck
Ah yes, an old oscillator without voltage control. Those used to be staples in radio stations and early electronic music studios. Not hard to still find them on eBay.
alexbarbed
Give it a few weeks and you might see this one on Ebay too...
calaveras
I had a much cruddier one of those for a while. There is something fun about being able to sweep continuously from 300hz down to 20hz, if your speakers can handle it. I used to like to ring the low frequency nodes in my old studio with a couple Community CSX57 3 ways and a 1600 watt amp.

But yeah, unless you can mod it to accept CV somehow, they get kind of boring unless you are doing drones/HNW.
alexbarbed
Funny you should mention 'ringing the nodes'. I was wheeling down the frequencies and suddenly it was like the room was going to explode... a beginner's mistake, obviously.
calaveras
My old studio was in a factory warehouse in West Oakland. It was pretty solidly built, probably from the 40's.
But certain frrequencies it sounded like the sheetrock was jumping off of the beams.
alexbarbed
Here it is powering up from cold... and off again

[s]https://soundcloud.com/loftelectronics/ag71-120hz-square[/s]
calaveras
well that has some harmonics!
Love to see that on a scope.
Never tried this, but I wonder what would happen if you put a variac on it?
alexbarbed
What a cool idea. If only I had one.
calaveras
You don't have a variac? How do you defrost things in the microwave?
alexbarbed
I wrap them in tin foil first
cretaceousear
Phat on/off sound! (phat was cool 20 years ago right?)
But if my UFO made that sound I'd not be in any hurry to ride home.

Hey just listening to your 'Hot in the loft' on Soundcloud - great !
(We know where you got that title.)
wackelpeter
hmm... the end sounds not much like an UFO starting, resembles more of an UFO farting... grin
But who knows, maybe the aliens are coming more likely from fart than far away....

When i started experimenting with electronics and was (well i am still) interested in experimental sounds and electronics, i had an old russian frequency generator which i used a lot. That beast was massive, weight of 10kg or so.

Also had an generator which looked like it was used for therapeutic treatment in physical therapy... hooked that one into an old tape deck and shortly after that some electrolytic rockets where starting from my tape deck and flying around in my room.
This was a very scary unit, i got several small electric shocks when i used it...
Dave Peck
Simple. Connect a DC Servo to a robotic armature that is attached to the outer edge of the large tuning dial so that the robot arm turns the wheel clockwise when it receives a higher DC control voltage and calibrate the arm and servo to make the generator track 1V/octave. Easy peasy. This is fun!
alexbarbed
That is a fantastic idea.
alexbarbed
wackelpeter wrote:

This was a very scary unit, i got several small electric shocks when i used it...

I once had to finish a mix to a deadline and my desk had an electrical fault. I finished on time but my eyelashes had all burned up. Later someone asked me why I didn't wear gloves, which seems obvious in retrospect.
Synthiq
calaveras wrote:
Love to see that on a scope.

Not on a scope, but sampled with Audacity. Is this supposed to be a squarewave?

alexbarbed
It is indeed supposed to be square wave.
MrNezumi
If you get eight or nine more of those big clunky oscillators and some telegraph keys, you can build your own Simeon. Then you could rock out Silver Apples style.
alexbarbed
That's a nice idea, but it's a bit like saying: hey that's a nice plectrum you got there. If you add a guitar and grow your hair you could be Jimi Hendrix.
MrNezumi
I had thought about adding a winky face to my above comment, but I thought it was absurd enough to go without.

As a side note: Nearly twenty years ago I met Simeon and got to play his rig for the second incarnation of Silver Apples. He used a Novation keyboard for the rhythm parts but still had a few big clunky oscillators. On the face of the "lead" oscillator he had crude lines in different colors drawn on the dial with markers. He used the lines to get notes relatively correct.
alexbarbed
Yeah I know. I was also winking invisibly. I guess deadpan doesn't work on the internet.

I saw Silver Apples in the 90s... was it at the Garage in Islington? I was most impressed by a joystick he seemed to be using... my memory might have embellished it but in my mind it looked like a fruit machine arm?
MrNezumi
alexbarbed wrote:
Yeah I know. I was also winking invisibly. I guess deadpan doesn't work on the internet.

I saw Silver Apples in the 90s... was it at the Garage in Islington? I was most impressed by a joystick he seemed to be using... my memory might have embellished it but in my mind it looked like a fruit machine arm?


Bugjar in Rochester, NY back in the late 90s (1998?). I don't specifically remember the joystick, but most things from that era are hazy.
ranix
Synthiq wrote:
calaveras wrote:
Love to see that on a scope.

Not on a scope, but sampled with Audacity. Is this supposed to be a squarewave?



this, in fact, is a square wave. It looks like it's been passed through a DC blocking filter.

Don't fuck with it if it's shocking you, gotta fix it first. Don't mess with equipment like this if it has ground faults. It's seriously dangerous.
alexbarbed
You got mixed up, it wasn't this that was shocking me, it was a Tascam desk, a long time ago.
Synthiq
ranix wrote:
this, in fact, is a square wave. It looks like it's been passed through a DC blocking filter.

Then, technically, it was a square wave before the highpass filter, sort of. Integrating the signal can more or less restore the original waveform but it is less than an ideal square wave. And as a side note, the frequency is 40 Hz and not 120 Hz. Would I spend time fixing it? Probably not.

ranix
alexbarbed wrote:
You got mixed up, it wasn't this that was shocking me, it was a Tascam desk, a long time ago.


aaah, ok. That's good news, this oscillator looks really cool thumbs up
alexbarbed
Synthiq wrote:
Integrating the signal can more or less restore the original waveform

What just happened? What did you do to 'restore the original waveform?'
Synthiq
alexbarbed wrote:
What just happened? What did you do to 'restore the original waveform?'

Maybe not a mathematically stringent explanation, but a highpass filter acts a little like a differentiator outputting a signal proportional to the change in the input signal and in your original example you can see a positive spike and half a period later a negative spike corresponding to the positive and negative edges of a square wave.

The inverse function to an differentiator is an integrator so if you integrate the differentiated signal you get the original signal back again and that's what I did. I put together a simple integrator in the LTSpice circuit simulator and it read your wave file as the input signal and wrote the output to another wave file.

A circuit simulator like LTSpice is a great tool to test design ideas quickly and without a lot of lab equipment, so it's worth learning how to use one if you do any circuit design.
alexbarbed
OK, thanks. I don't do circuit design and barely understand what you said, but I have had a look at LTSpice and it looks very interesting.

You said that the frequency was actually 40Hz, yet when I look at it in a frequency analyser the fundamental is at 120Hz. Would you mind telling me what I have got wrong there?
Synthiq
If you look at the time scale of the plots, it is clear the spacing between two periods is about 25ms which corresponds to 40Hz. I did analyze the distortion of your signal at time 6 seconds and the third (and seventh) harmonic is about the same strength as the fundamental, so that might have caused your frequency analyzer to report 120Hz. I only looked at the harmonics at one time and it may change over time so the third harmonic might very well have been stronger when you measured the frequency. Some counters measures the number of zero crossings (with some hysteresis) so it is possible it found 3 positive zero crossings per real period since there is quite a bit of activity going on all the time, not just where the edges are. With a complex signal like this, it is not unexpected if the wrong frequency is reported.

alexbarbed
You're a good wave doctor. When I have wave trouble in future, I'll know who to call thumbs up
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