"Line up Oscillator"

[iomegaman]

Ok I am trudging through this Amerimex Console...its fun and not fun because I have no manual no schematic and my best guess is usually just to push a button and see what happens...(which in this case was a quite painful blast from the button I pushed)


The Cue channel has a "Line up Oscillator" ...under the weathered metal channel down where the components live is a small bulb and a vertical plastic trim pot that adjusts something...seems related to the frequency volume...turning it counter clockwise does 2 things...the bulb begins to glow and the frequency seems to drop...turning it CC seems to raise the freq a bit and then it fades to a quieter sound and the lite goes out...

What am I adjusting here?

Full disclosure I pushed the "Line up Oscillator"  with my Mackie HR824's plugged in and the painful level of the siren it imposed upon my ears sent me into another room cursing...(the Mackies are self powered with no volume level control)...I immediately disconnected my speakers and have opted to using the headphone cue channel alone with the headphones sitting on the bench...

Is this some way to set the meter levels or "line level" as it supposes...checking voltage on the outputs has yielded nothing compelling...I can adjust the voltage to .075 AC...which seems like a faint memory of what line level was supposed to be on my Tascam Recorder years ago...refresh my tinnitus induced coma...

 

[pucho812]

+4dBu = 1.228V/1.23V = 0VU.        .775V= 0dBu

 

[Brian Roth]

The light bulb makes me think it is a Wein bridge oscillator:

https://en.wikipedia.org/wiki/Wien_bridge_oscillator

Bill Hewlett (as in Hewlett-Packard) came up with the light bulb idea and it is discussed in the above article.  The bulb helps stabilize the oscillator. 

Bri

 

[iomegaman]

+4dBu = 1.228V/1.23V = 0VU.        .775V= 0dBu

yea thats what my head remembers now...but there's no way to get to .775 here (I'm taking measurement from the XLR Main Output pins)...the most I can get is .100v AC

I'm thinking this is how to calibrate the VU bridge (which I have disconnected at the moment)...I'll plug it in and turn knobs...

 

[PRR]

> Bill Hewlett (as in Hewlett-Packard) came up with the light bulb idea

The lamp was around before Terman suggested Bill look at it. (Meacham)

The light should NOT light!!

Starting from "dead", turn up slowly until it *just* starts to oscillate. Cycle power a few times, use a weak battery if applicable, be sure it starts reliably with consistent level. That's good enough for "line-up".

A "Low THD" Wein wants more elaborate testing for lowest THD. Still, the level is the level, set by lamp constants; you adjust output level elsewhere. (Is it the original lamp or ??)

 

[iomegaman]

Original lamp

 

[iomegaman]

> Bill Hewlett (as in Hewlett-Packard) came up with the light bulb idea

The lamp was around before Terman suggested Bill look at it. (Meacham)

The light should NOT light!!

Starting from "dead", turn up slowly until it *just* starts to oscillate. Cycle power a few times, use a weak battery if applicable, be sure it starts reliably with consistent level. That's good enough for "line-up".

A "Low THD" Wein wants more elaborate testing for lowest THD. Still, the level is the level, set by lamp constants; you adjust output level elsewhere. (Is it the original lamp or ??)

and this seems the idea...it oscillates at the "dead" end glows bright and then levels out once turned up to "no light"...

 

[JohnRoberts]

Ok I am trudging through this Amerimex Console...its fun and not fun because I have no manual no schematic and my best guess is usually just to push a button and see what happens...(which in this case was a quite painful blast from the button I pushed)


The Cue channel has a "Line up Oscillator" ...under the weathered metal channel down where the components live is a small bulb and a vertical plastic trim pot that adjusts something...seems related to the frequency volume...turning it counter clockwise does 2 things...the bulb begins to glow and the frequency seems to drop...turning it CC seems to raise the freq a bit and then it fades to a quieter sound and the lite goes out...

What am I adjusting here?

Full disclosure I pushed the "Line up Oscillator"  with my Mackie HR824's plugged in and the painful level of the siren it imposed upon my ears sent me into another room cursing...(the Mackies are self powered with no volume level control)...I immediately disconnected my speakers and have opted to using the headphone cue channel alone with the headphones sitting on the bench...

Is this some way to set the meter levels or "line level" as it supposes...checking voltage on the outputs has yielded nothing compelling...I can adjust the voltage to .075 AC...which seems like a faint memory of what line level was supposed to be on my Tascam Recorder years ago...refresh my tinnitus induced coma...

Line up oscillators were general purpose signal sources designed to cover sundry applications.

#1... It was common to print tones to the leader of master tapes with say 10kHz and 100Hz so the mastering engineer could confirm/verify head alignment and response between the two tape machines.

#2 when you want all the VU meters to read 0.00 dB, the line up oscillator could usually bang all the buses at the same time for quick zeroing.

#3 slate tones... When accumulating multiple sessions on a single tape reel it could be convenient to print a LF slate tone on the tape leader between songs so when you fast forward through a tape, the LF tone gets shifted up higher to become an identifiable beep... 

etc...  Generally line up oscillators are not very low distortion, but needed to deliver stable level so cheap function generator chips were popular.

JR

 

[iomegaman]

Thanks JR always helpful to get the point of the technology...makes complete sense now.

Asking questions > pushing buttons...

 

[Brian Roth]

One good thing about Ye Olde  available function generator chips were very flat frequency response and very fast settling times.  A half percent of THD made no problems when setting levels.  Other designs took many seconds to settle down on levels, especially when moving down into the sub 100 Hz area.

I still use a Heathkit function generator when aligning levels/EQ on analog recorders.  A bit of THD is a non issue.

Bri

 

[PRR]

> it oscillates at the "dead" end

How do you get "oscillation"="dead"?

If it oscillates, it is alive! Alive!

At the other extreme it is dead=NoOscillation. Sneak up from *that* condition.

Your Choir Master wants a small *clean* song-note from you. You put a Kilo of breath pressure and it comes out SCREAM. Put a gram of breath pressure and the vocal cords don't work. Say at 2 grams  of breath pressure they start to work, usually. Then aim for 2.1 grams to get the cleanest song-note with the least harshness and sure-starting.