Stupid gyrator question

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Bo Deadly

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stickjam said:
Planning on taking C506 to 0.047uF with the 68mH Murata. 
That won't work. The "Q" will change radially. Meaning instead of a narrow resonance, it will be broad and just boost everything around it.
 

abbey road d enfer

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PRR said:
And of course this is not "floating". One end is nailed solid to AC ground.
In the circuit in reference, the inductor is nailed to the +12 rail. I don't see why a "gyrator" referenced to this rail would not behave close enough,provided it is powered from a 24V rail.

A gyrator will not "kick" like a real coil.
If you mean the effects of changing magnetism, I agree. Is it what characterizes the sonic signature, I'm not sure...
Breadboarding it is easy enough...
 

PRR

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Yes, tying a simple gyrator to double the supply voltage will work on a steady-state system. This contraption is now popular in hi-fi tube amps. Instead of inductive kick we just throw twice the power at it. And here, that is not big power.

However the cowbell circuit changes gain from zero to big and back by changing transistor current radically and rapidly. Without a 2nd cup today, I feel that most will lag far behind the impulse.

And it is an any case less part-cost than the case and knobs will cost. May as well fire the high-price brains and just play the breadboard.
 

abbey road d enfer

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stickjam said:
Agreed that nothing kicks like real L. 
However, if you're still interested, I've done simulations that show possible feasability with the standard "gyrator". What is the resistance of tehe47mH inductor?
 

stickjam

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abbey road d enfer said:
However, if you're still interested, I've done simulations that show possible feasability with the standard "gyrator". What is the resistance of tehe47mH inductor?

That would be cool - especially for the voices that call for 700mH coils.  Mouser comes up dry in that range except maybe for common-mode chokes, which I'm not entirely uncurious as to whether those can be creatively used for that application.

Unfortunately I'm not sure of the resistance of the OEM inductors as I don't have access to an original Roland unit, so I'd just start with a guess  and tweak until it sounds right.   

Based on the odd "component salad" that those voice circuits are, I'd almost bet they were designed entirely by trial and error on a breadboard back in the 70's. 
 

stickjam

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Well, here is the shootout result of the simplest CR78 voice (the rim shot) three ways: 
  • A real CR-78 rimshot with OEM 700mH coil
  • The same component values except with a gyrator, exported from LTspice
  • The same component values except with a gyrator, on a breadboard
Which is which?    ;) Considering only the rimshot and clave use the big 700mH and everything else uses the 40mH that are easily purchased in the SMT format I'm building it in, I don't think it makes a difference. :)  ...and the 700mH ones go to ground, so the floating question is moot.
 

abbey road d enfer

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stickjam said:
Well, here is the shootout result of the simplest CR78 voice (the rim shot) three ways: 
  • A real CR-78 rimshot with OEM 700mH coil
  • The same component values except with a gyrator, exported from LTspice
  • The same component values except with a gyrator, on a breadboard
Which is which?   
Indeed they all sound close enough, but none sounds like a rimshot...more like a glitch.
 

stickjam

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abbey road d enfer said:
Indeed they all sound close enough, but none sounds like a rimshot...more like a glitch.

Yeah it does, but that glitch is part of the cheesy charm of the CR-78.  I think it's actually only used in the bossa nova preset too.

I think I've figured out the design I'm using now.  Thanks folks.  You guys are awesome.

-Bob
 
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