SSL (Or Similar) Console Saturator/Distortion

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cpsmusic

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Hi All,

SSL very kindly got back to me and I now have the patent. I haven't had a chance to look at it but it's probably a bit beyond my electronics knowledge anyway. For those interested here it is. Maybe someone can have a look at it and explain how it works?
 

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abbey road d enfer

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Q: Did Gibson ever get a patent for their PAF pickups ? :unsure:
Yes, in 1959. But they feared being copied by competitors, so they used another patent # on the stickers that replaced the P.A.F. stickers. Which led a number of people to think they didn't get a patent on humbuckers.
 
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abbey road d enfer

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Maybe someone can have a look at it and explain how it works?
I had a brief look, and that's all I'm gonna do, because I don't advocate the idea of deliberately introducing distortion in the signal path.
The NFB, which is traditionally applied to the emitters of the input devices, is now brought to FET's that are in series with said emitters, actually modulating the effective resistance seen by the emitters.
Doing so on one leg introduces dominant 2nd harmonic, on both legs results in 3rd.
 

Michael Tibes

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Maybe we should change perspective and look from a different angle. I assume we all want to achieve the 'big console sound' - without the big console.
I had a brief look, and that's all I'm gonna do, because I don't advocate the idea of deliberately introducing distortion in the signal path.
The NFB, which is traditionally applied to the emitters of the input devices, is now brought to FET's that are in series with said emitters, actually modulating the effective resistance seen by the emitters.
Doing so on one leg introduces dominant 2nd harmonic, on both legs results in 3rd.
Wow, thanx for the summary, I didn't expect SSL to get back to cpsmusic on that. That'll need some reading. I do definitely like to deliberately introduce some distortion in my signal paths every once in a while :cool:

What is the sonic experience with the circuit, can it be fun? I haven't worked with it yet.
 

Whoops

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I'd like to make a simple saturator/distortion processor for use in my small home studio. I recently came across this one:

HITMAKER 4000 80's E-Series Console Colour

which is supposed to emulate the sound of an SSL E Series console. This is the sort of thing I'm after - some gentle 2nd/3rd-order harmonic generation, but not too much.

The best SSL saturator/distortion processor is the mic preamp itself.
It's an amazing piece of gear for saturation or distortion, you crank the gain and lower the output volume.

I would advise you to do any of the SSL mic pre's from this thread:


My favorite is the SL4K-G91, but you can also go for the SL4K-E01 or SL4K-E49

Best regards
 

bowanderror

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The patent is pretty hard to track with all of the number labels, so I edited in the functions of each block instead:
SSL VHD v1.2 Cropping 96DPI.png
A basic summary of the patent text:
  1. Initially I1 & I2 are equal.
  2. As differential signal applied to circuit input, the voltage difference at V1 & V2 (voltages across diff amp inputs) will cause diff amp to produce negative feedback in order to make these voltage equal.
  3. Differential input voltages at BJT base result in modifications to each transistors emitter current - EX: For diff voltage, Q1 emitter current may increase, while Q2 emitter current decreases.
  4. In the above case, current I3 will shunt between emitters of Q1 & Q2, through Rs
  5. As shunting of current starts to take place (I3), the feedback loop will attempt to rebalance the circuit. Feedback signal is applied to gate of F1 & F2. As negative feedback, the current from the Drain of F1 will increase, while current from Drain of F2 will decrease, resulting in shunting of current I4 through resistor Rd.
  6. Due to the non-linear characteristics of FETs, the flow of current I4 will not behave in the same way as the flow of current I3, such that the feedback characteristics are distorted with respect to the input signal thereby ensuring that the distorted characteristic is imposed up circuit output in a controllable fashion
  7. Constant current sources are made variable such that a reduction in the level of current flowing through the FETs increases the non-linear characteristics
Overall gain is related to the ration of the resistance of R/Vr:
  • Resistance of R is made larger than Vr to provide gain
  • Vr acts as a gain control as it's a variable resistor
Any ideas what the Constant Current Source is? I'm only familiar with current mirrors in this application.
 

cpsmusic

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The patent is pretty hard to track with all of the number labels, so I edited in the functions of each block instead:
View attachment 81896
A basic summary of the patent text:
  1. Initially I1 & I2 are equal.
  2. As differential signal applied to circuit input, the voltage difference at V1 & V2 (voltages across diff amp inputs) will cause diff amp to produce negative feedback in order to make these voltage equal.
  3. Differential input voltages at BJT base result in modifications to each transistors emitter current - EX: For diff voltage, Q1 emitter current may increase, while Q2 emitter current decreases.
  4. In the above case, current I3 will shunt between emitters of Q1 & Q2, through Rs
  5. As shunting of current starts to take place (I3), the feedback loop will attempt to rebalance the circuit. Feedback signal is applied to gate of F1 & F2. As negative feedback, the current from the Drain of F1 will increase, while current from Drain of F2 will decrease, resulting in shunting of current I4 through resistor Rd.
  6. Due to the non-linear characteristics of FETs, the flow of current I4 will not behave in the same way as the flow of current I3, such that the feedback characteristics are distorted with respect to the input signal thereby ensuring that the distorted characteristic is imposed up circuit output in a controllable fashion
  7. Constant current sources are made variable such that a reduction in the level of current flowing through the FETs increases the non-linear characteristics
Overall gain is related to the ration of the resistance of R/Vr:
  • Resistance of R is made larger than Vr to provide gain
  • Vr acts as a gain control as it's a variable resistor
Any ideas what the Constant Current Source is? I'm only familiar with current mirrors in this application.

I was wondering if some kind person could draw a schematic of this so that I could test it out?
 

zvukofor

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Oct 31, 2012
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My guess would be that one of the most important nonlinear effects for kind of SSL sound is basically done by overdriving VCA input... theoretically, VCA input distorts with tanh(x) curve, which is very pleasing and has nice harmonics balance (mainly odd, with a good amount of even). Set the constant current for control input - and that's all.
After all, even Moog used this trick in some of it's synths - driving VCA to nonlinearity.
 
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