Clueless with HP Oscillator

coreytx

coreytx

New member
I enjoy this forum and it has helped me begin to understand how to calibrate and align my new Tascam 8 track. I haven't started yet, I'm still getting everything I need (MRL, demagnetizer, etc.). I'm coming from the digital world.

Anyway, I got this HP 204c sine wave oscillator the other day, I've read the manual 10 times, browsed online till my eyes were dry as rocks, and I just cannot understand the (proabably simple) task of connecting the thing to my Tascam or any kind of speaker via mixer.

The output is on the front and there are two knobs that tighten down on what I imagine would be some kind of speaker wire. It's 600 ohms.

Does balanced/unbalanced connections come in to play at all here? And would I use something like a [speaker wire] to [1/4" or RCA] cable?

This is a boring post that might belong on an entirely different site, but I thought most of you probably have some kind of similar setup to maintain your machines.

Thank you for your time.
 
Though the binding posts look like speaker wire connectors they are simply a connection terminal that accepts bare wire, spade lugs or banana plugs. But the wire should be a shielded wire, not speaker wire, that goes out of it and into your mixer and that can be a simple unbalanced line if the cable run is under 20 feet.

The output knob dial should be turned down though as at maximum, your oscillator will output a +5 volt signal which is way higher then an unbalanced line level that is normally closer to .316 volts for a -10 db unbalanced input.

If you have a voltage meter you can use that to dial in the exact voltage your mixer's line input is looking for. If you don't, set your mixer's trim control at 0, the channel strip's fader at 7 and then turn up the output gain on the 204C until the VU meter on the mixer reads 0 VU.

Hope that helps.

Cheers! :)
 
I had a quick look at the manual an spotted something that might be an issue--the oscillator is designed to work into a 600 ohm load.

This, plus the binding post connections, makes me wonder if the unit is designed more for phone companies than recording studios. I don't know about the USA but in the UK, the phone company there set their broadcast circuits to require 600 ohm equipment at both ends--and not doing so made any levels measured invalid.

Approach any alignment done with this with some caution.
 
Bobbsy said:
I had a quick look at the manual an spotted something that might be an issue--the oscillator is designed to work into a 600 ohm load.

This, plus the binding post connections, makes me wonder if the unit is designed more for phone companies than recording studios. I don't know about the USA but in the UK, the phone company there set their broadcast circuits to require 600 ohm equipment at both ends--and not doing so made any levels measured invalid.

Approach any alignment done with this with some caution.
Click to expand...
Impedance mis-matches are far more of a concern for full program usages, meaning music. But this is a simple tone generator, designed for outputting one frequency at a time. So as long as the level issue is addressed, which I did in my previous post, there should be no catastrophic issues in play here. Plus the 204C is designed to be a general purpose oscillator and there's nothing in the manual I found that warned of its usage to be only designed for telecommunications systems.

Also found this description from an ebay page where one of these were being offered for sale:

The 204C is described in the December 1968 issue of the Hewlett Packard Journal as a Low-Cost, General-Purpose Oscillator
Click to expand...

Hewlett Packard HP 204C Oscillator | eBay

Cheers! :)
 
Yeah, there ARE ways to compensate for the impedance mis-match (we just installed the appropriate resistors on the IDC Krone frame for out circuits to/from the Telco). However, the mismatch is enough to make a dB or two difference between indicated level and actual level. Since the main use I'd have for an oscillator is to be an accurate alignment tool, I thought it worth pointing out.

If the OP has the facility to measure the voltage output and adjust for that rather than believe the dials on the front, then all could be good--but impedance matched 600 ohm operation is a long way from standard in studio gear (and has been for several decades!).
 
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