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API 512 vs. 312: Does anyone know the difference?
Old 16th August 2005
  #1
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API 512 vs. 312: Does anyone know the difference?

Other than the fact that the 512 is modular and the 312 isn't, is there a difference in the circuit itself?

I know the 312 was the preamp in many of the orginal consoles.

I have a 3124+ and a pair of 512Cs in a lunchbox. They DO sound a little different to me, but could that be because of their different power supplies?

Who's an API guru in this forum?

Paul Wolf around?
Old 16th August 2005
  #2
Quote:
Originally Posted by GearHunter

I have a 3124+ and a pair of 512Cs in a lunchbox. They DO sound a little different to me, but could that be because of their different power supplies?


I posted about this before.

Try strapping a 1200 ohm resistor to the output of the 512C's of your lunchbox.

See if its closer in the sound.
Old 16th August 2005
  #3
Gear Nut
 

Didn't Paul say somewhere that the 512C has a dc servo on the output?
Old 16th August 2005
  #4
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Does it make sense that the 312 sounds a little rounder, bolder, punchier? And the 512 is a little sweeter or airier? Again, I'm talking about ultra-subtle shades of difference. When I garb an API it's because I always know what to expect and I always get it, so I haven't really a/b'd them. I use them interchangeably. But yes, they are a little different. But why?
Old 18th August 2005
  #5
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Quote:
Originally Posted by LRRec
Didn't Paul say somewhere that the 512C has a dc servo on the output?
No DC servo on the 512c., or 312...
Old 18th August 2005
  #6
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Quote:
Originally Posted by GearHunter
Does it make sense that the 312 sounds a little rounder, bolder, punchier? And the 512 is a little sweeter or airier? Again, I'm talking about ultra-subtle shades of difference. When I garb an API it's because I always know what to expect and I always get it, so I haven't really a/b'd them. I use them interchangeably. But yes, they are a little different. But why?
The input trans is different, the output trans is suppose to be the same, and as for the Op Amp; if its the older taller one it is also a little different, if the caps are older that could make a bigger difference than the other components.
Old 18th August 2005
  #7
Gear Nut
 

I found this:


Quote:
Originally Posted by Paul Wolff
512C was a 512B with a phase switch and a DC servo to minimize DC offset at the transformer input. DC on a transformer changes the tone and lowers the headroom. The servo made them all sound closer to each other.

.
Old 19th August 2005
  #8
Dot
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According to Paul Wolff:

Differences between 312 and 512:

The similarities are that they use one 2520 op amp and one 2503 transformer each, which is the larger transformer. The differences are that of course, the 512B/C brings out all of the knobs and functions to the front panel, so X that, the differences are that the 312 has no coupling capacitor between the output transformer and the op amp, which means that if the op amp has any offset, it may cook the transformer. The 512C has a very large coupling cap, in parallel with a high frequency cap, in parallel with a resistor for transformer damping. The op amp has a servo to eliminate offset, resulting in two things, increased headroom and the elimination of popping when the phase switch is used.

The 512B and C were the next generation of the original 512 mic pre, which was the first modular mic pre and was used for mics, line amps, summing, and booster/distribution. Different models had meters, banana jacks, input selectors, and pots, in just about every combination, in the original consoles that API made in the early 70's. It is most similar to that instead of a 312 card, which has no features.
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