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A few 660 questions for Tim
Old 4th March 2003
Lives for gear
paterno's Avatar
🎧 15 years
A few 660 questions for Tim

Hey Tim --

I've owned a 660 for a few years now, and it is one of my favorite pieces of gear. It always ends up on something while I'm tracking, and it's almost always my vocal compressor when I mix. I've always wondered a few things about it, so I figure this is a good time for a few answers!

- I was wondering why the tone and gain structure changes so much as you go from limiting to compression? How many aspects of the circuit is that switch affecting? Is there a position on that switch that is the same limiting ratio as the Fairchild? The switch usually ends up between 12 o'clock and 3 o'clock for my uses.

- Have you ever experimented with varying the output impedance? A while back I put a 680 ohm resistor wired across pins 2 and 3 of a barrel connector, and plugged this connector on the outputs (one at a time, or course) of all my 600 ohm output gear to hear what, if any, tonal difference there would be if I lowered the output impedance. It made a difference on a few things -- LA-3a's sounded different, maybe even more full range, but then it didn't sound like an LA-3a anymore. I liked what it did on the 660. Any comments?

- How long will the tubes last? They don't seem like they run very hot, so i would imagine the lifespan would be pretty good.

-Where would you consider the unity gain point to be on the input? I usually start around 9 o'clock...

Thanks in advance for your answers!

Old 5th March 2003
Gear Head
🎧 15 years

Thanks for your comments. The DC threshold for most job should be around the 12 o clock. No it does not change the circuit just the slope ie soft compression to more true limiting and that is what you are hearing. the ratio of loud to soft bits. The input is usually about 9 o clock for unity. I normally for mastering set for 4 dBs of gain then what I send can easily be limited with about 3 to 5 dbs of compression just to tighten up the leveling without it being obvious.
Tube life should excede 10 years. I have not retubed any any other the units in The Exchange a mastering facility in London. Did things like The Propellor Heads and Bojk.
Your loading of another 680 Ohms on the output will not effect the frequency response. but will just lower the output by about 3 dB. Output impeadance is about 250 Ohm

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