Ampex 440 varispeed oscillator suggestion

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dimebucker

Member
Joined
Aug 2, 2017
Messages
10
Hi all

I'm getting a 440 soon with the DC servo capstan installed. I wish to do some Beatles-type experimentation with varispeed around the 15ips setting.

(From what i've read it seems they would typically record around 5% slower or faster and then playback at normal speed.
This created an interesting subtle effect, particularly with vocals.)

From the manual it states that an external oscillator can be used to control the speed:





Can anyone suggest a set-up that I could use? 
I'm pretty much novice in terms of electronics, but have put together many kits, including preamps... I can solder well :)

I was thinking i'd need an Oscillator with at least:
-frequency control knob
-LCD display so that I can see when i'm back on 9600Hz (or is it 4800Hz?)
-maybe the potentiometer should have an indent, so I can easily 'click' back to  15ips.



Any suggestions would be much appriciated 

 

Attachments

  • Ampex Sync Lock Accessory for AG-440 and MM-1100.pdf
    1.1 MB · Views: 6
If you can write code, I'd go for an Arduino to generate the clock. The pdf says that it's quite a wide range servo (3 to 45ips) if I readit correctly. Repeatability would be excellent as the micro would be xtal controlled.
 
Yeah if you want an LCD and a "pot" with an indent, arduino is your best route. You can also use a cheapo function generator, or if you want want to play around with it, a simple LM555 timer. Plenty of calculators exist to calculate the circuit values you will need if you go for the LM555 route.
 
Thanks everyone, very interesting replies  :)


Martin Griffith said:
If you can write code, I'd go for an Arduino to generate the clock. The pdf says that it's quite a wide range servo (3 to 45ips) if I readit correctly. Repeatability would be excellent as the micro would be xtal controlled.
Very interesting.. but I'd have to get a lot of help with the coding, seems like an elegant solution though..

.. but just to clarify; i'd only need to adjust  max +-10% about the 15ips setting (which i'm assuming is 4800Hz).

Maybe I dont actually need an LCD screen and could just get a 'feel' for the speed change. This would be fine is the pot had an indent to return to 'home'... ( would need a trimpot to callibrate?)



squarewave said:
Just use a signal generator in your DAW and run it out of one of your DAC channels. It's just another track in the recording.

Can my DAW (+RME fireface) definitely generate the right kind of signal (voltage?)


Cheers guys
 
dimebucker said:
Can my DAW (+RME fireface) definitely generate the right kind of signal (voltage?)
I think it should. What is the RME output level? It sounds like it just has to be more than 3Vpp. I would be shocked if the RME could not make that. If not, maybe step up 1:2 with a transformer (but check input Z). You might want to test with a transformer anyway to make sure you're not getting any feed-through noise / ground hum.

Test it with a function generator just to get a feel for how it works (and series resistor to determine input Z) but it sure sounds like you could simply have square wave track and modulate the frequency to control speed. You could create that track using whatever software like Wavepad or some "function generator" plugin maybe. Mute for the normal speed tracks.
 
4800 Hz would be the required external frequency to run at 15 IPS  **if** the servo control card is strapped for 15/30 IPS operation.

On the servo control chassis box there is an eight pin Jones socket.  As delivered, a mating Jones "dummy plug" is installed which has a wire jumper to tie the internal 9600 Hz reference into the servo circuitry.  To use an external oscillator, that jumper has to be "opened" to allow the insertion of the external oscillator.

Bri
 

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