Why no feed forward Vari-mu?

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Hi Guys, (and especially PRR)


   As always, I am absolutely thrilled by all the responses I have received on this subject, and vari-mu in general. I cannot thank you guys enough. I actually feel that I have LEARNT some fascinating stuff.
  With my u74/fb76's,  it seems I have the basis for some experimentation sitting on my bench, without having to build anything. Excellent! Basically, I want to try to end up with something with a gentler slope.
   PRR suggested that FF would probably give a "soft-knee and an erratic limiting level". I am guessing that the u73 must have some clever stuff goin' on. The u73 goes from linear to limiting in approx 6dB. is this because of the "The large G2 resistor semi-linearize(ing) the V/I curve"? Would running the tubes with a smaller G2 resistor make it into more of a compressor? How about if we run the E99F's in triode? would that reduce the slope? I will definitely be trying out all of the above, but would welcome any input before I start!

    Kindest regards,


        ANdyP
 
strangeandbouncy said:
PRR suggested that FF would probably give a "soft-knee and an erratic limiting level". I am guessing that the u73 must have some clever stuff goin' on. The u73 goes from linear to limiting in approx 6dB. is this because of the "The large G2 resistor semi-linearize(ing) the V/I curve"?
Not really. The main reason is because the side chain has a very well defined threshold, thanks to the bias voltage coming from the 1k trimpot. The relatively narrow knee is the result of a sufficiently large loop gain in the side-chain.
Would running the tubes with a smaller G2 resistor make it into more of a compressor?
I don't think it would do that. It would probably make the transfer curve a little less linear. I think their VCA is as optimized as can be (you can count on IRT designers to go to extremes to extract the last drop of performance from a given circuit). When you have a linear VCA, you don't want to mess with it to twist the curve; you work on the side-chain, using the non-linearities of low-level rectification to shape the response.
How about if we run the E99F's in triode? would that reduce the slope? I will definitely be trying out all of the above, but would welcome any input before I start!
Kindest regards,
ANdyP
I think this should be a good opportunity for you to do a sim. Get LTspice for free from the Linear Technology site and take a plunge. They have an excellent forum there, they will help you doing that, and then you'll let us know your conclusions. ;)
 
SSLtech said:
Why no feed forward Vari-mu?

I appreciate that I'm late to the party, but I believe that the Gyraf Variable-mu compressor is Feed-Forward.

-My 'belief' however, is not worth as much as a comment from Jakob of course! ;)

Keith

You're late and you didn't bring any beer!  See my link on the previous page of this thread to a thread where Jacob clarifies this (your belief was right!).

Cheers,
Ruairi
 
Hi Abbey Road D enfer,


    Thank you for replies. I am very interested in the idea of sim-ming. Unfortunately, I am a Mac user. Guess I'll have to use my ears, unless you can recommend something that'll run on an Apple.



      Kindest regards,


        ANdyP
 
I may not be a real man, but I am a real producer/engineer/mixer, and I personally have NEVER had a session on a PC that wasn't full of problems!


  I am very very tired of this Mac/PC argument. . . . . I know what works for me, and has done successfully for the last 10 years. I actually don't know a single artist, writer, producer or mix engineer who DOES use PC's for music, and I know a hell of a lot of artists, writers, producers and engineers - Just a considered observation, no more!


Having said that, I am actually "BootCamping" my Mac this evening, so that I can  out the free software you suggested, but I am expecting a steep learning curve since I don't know the OS at all


    Is my Manhood restored? :D


      ANdyP
 
real men use bench presses and test gear, rather than simulators and FPE.  ;D
 
strangeandbouncy said:
I am very very tired of this Mac/PC argument. . . .
It certainly wasn't my intention to re-launch it. Sorry if I hurt you. It was just a way of saying that if you want to use some softwares that are, if not essential, very useful for DIY, they are massively for PC only.
Having said that, I am actually "BootCamping" my Mac this evening, so that I can  out the free software you suggested, but I am expecting a steep learning curve since I don't know the OS at all
If you're not familiar at all with Windows, you can expect some frustrating moments, but there's help everywhere, and I think you can download from your OSX and just run the installation in Windows. After that, using LTspice is easy, but you'll have to go to the forum to download the triodes and pentodes. The LTspice forum is very friendly and helpful, I have no doubt they will help you all along.
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