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Feedback - La2a?
Old 19th January 2004
  #1
Gear Head
 
Ribbledox's Avatar
 

Cool Feedback - La2a?

Good afternoon Fellows=)

Nice day isn't it?

I'm sitting here with a block diagram and some schematics for the La2a. THe only thing that confuses me is that it says written: "La2a is a feedback style compressor. This is due to that the signal that is used to drive the side chain circuit is affected by the reduced signal". But on the block diagram the Feedback signal goes from the Cathode Follower to the Voltage Amplifier, and is not even close to the side chain.

Also, what's the reason behind the Feedback? And what is the Cathode Follower for? Someone told me that the feedack feature helps keeping down the THD...but how???

I would really appreciate if someone could clear it out...

Have a great day=)!!!

/Tom
Old 8th February 2004
  #2
Gear Nut
 
Bo Hansén's Avatar
 

Hi Tom,

You talk about two different feed back, one of the "feedback" mean that the side-chain, as you say all ready have say, take the signal after the reduced signal and if it take the signal before it call "feed forward"

The other "feed back" it´s a amplifier negative feed back loop that it´s use for take down the "open loop gain" in a amp circuit with a number of gain step in same amp circuit.
This result also in lower distortion and lower output impedance.

The cathode follower is a 1:1 unity gain amp (with no gain) and it have also low output impedance, so it can feed cables and a output transformer as in LA-2 case. (not a 600 to 600 ohms transformer but aprox. a 10 kohm to 600 ohm )

--Bo
Old 8th February 2004
  #3
Gear Head
 
Ribbledox's Avatar
 

Cool Thanks for your reply Bo=)

It all made sense, and I now realise how I mixed up the two things. But I don't really understand why you feed the already reduced signal into the side chain. I mean, isn't the amount of signal going to the side chain what is controlling the compression in the first place. So by feeding back the reduced (already compressed) signal, how can that help to determine the amount of compression needed? Isn't that giving the compression stage the wrong information?

Thanks again for your reply...
Have a great day!=)

/Tom
Old 8th February 2004
  #4
Gear Nut
 
Bo Hansén's Avatar
 

Hi Tom,

If you want to go more deep in this matter, you can find a very nice reading here:
http://www.tangible-technology.com/dynamics_index.html

--Bo
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