What the Hell is a Gyrator for?

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ScreamingDaveScreamingDave Frets: 845
My father-in-law was a meteorologist in the RAF back in the 50s.  One day they were all sat around drinking tea because the RADAR equipment was out of action.  An NCO got uppity with them and demanded to know what was wrong with it, and they told him they were waiting for a new magnetotron.  He didn't believe there was such a thing, got angry with them for trying to make him look stupid and went off to report them to the CO.  The CO told him that, no, there was a component called a magnetotron, and they were, indeed, waiting for a new one and he'd told the men to stand down until it arrived.  After that they could tell him what they bloody well liked, because he wasn't about to make an idiot of himself by checking up on them again.

This is how I feel about the Gyrator.  

I was playing my DSL40CR at home today, at low volume, and as I bent down to fiddle with the knobs, I heard a low rushing sound which sounded like the wind.  I got on the floor and listened closely and it was, indeed, coming out of the amp.  I hadn't heard this before so I decided to contact Marshall.

First of all, it's not as easy as it used to be.  You used to call the switchboard and they'd put you through to the technical help guys, good solid guys with names like Mike and Gerry, who were only too happy to advise you about your amp, chat about the design philosopy and tell you yarns of rock star Marshall users of long ago.

Now you get a chat bot on the website.

Who promises to put you through to someone in technical support.  Probably even if you ask it for an egg sandwich.

Me being me, I had the Marshall switchboard number saved in my phone, so I called them.  They seemed confused that there was an actual person on the phone wanting to actually talk to someone and said I should email.  I said that was sad, as I used to phone up and talk to the technical support line.  I was told, "Oh, yes, he retired".  After some more chat they did put me through to a guy in the service dpartment, who was very helpful and sent me an email to give him all the details, and I did get an email response quite quickly, to be fair.  This is what it said (I've cut and pasted it out of the email, so any spelling mistakes are theirs, especially as I suspect they mean, "Gyrator," not, "Gryator.")

"Thank you for reaching out to us, with regards to your DSL40CR, the amplifier has a built in gryator to give a better bass response, this creates the low wind noise you can hear when the amplifier is sat idle, as long as it cannot be heard whilst playing then the unit isn`t faulty."

Now I feel like that RAF NCO.  I feel like I'm being told there's something in my amp that I've never heard of and it sounds made up.

So, what is a gyrator (gryator?) please?  And why is it a good thing?

Thanks, chaps
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Comments

  • SporkySporky Frets: 32599
    That sounds hokey to me, but probably wait for the amp people.

    https://en.m.wikipedia.org/wiki/Gyrator
    Never forget that you are wearing your invisible tiara. 
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  • ecc83ecc83 Frets: 1825
    Yes the Gyrator is a circuit realized with an op amp that can simulate a capacitance or an inductance, mainly the latter as such "inductors" can be made of a precise value, very small and do not suffer the limitations of Iron and Copper ones. e.g. no hum pickup.

    Several Blackstar amp and pedal circuits use them.

    Dave.
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  • So in this case, what does it actually do?  How does it improve the bass response, and why does it make a noise?
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  • KittyfriskKittyfrisk Frets: 22268
    Are you sure that they weren't referring to an internal Atmospheric Vortex Gyrator?
    Often referred to as a 'Fan'...
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  • ecc83ecc83 Frets: 1825
    So in this case, what does it actually do?  How does it improve the bass response, and why does it make a noise?

    Well, Gyrators are used in EQ circuits so it is probably used to make an "inductor" based LF boost circuit (a real inductor for a bass boost circuit would be huge and expensive!) After boosting the bass they might not have thought of or could have been arsed to put in a high pass filter to stop the boost descending into the mud!

    Dave.
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  • thermionicthermionic Frets: 10343
    Interesting stuff. It seems to be used to generate a resonant peak (much like a wah circuit), and is found in many pedals.

    https://youtu.be/L4MGG3kt5pY?si=OlTBf6qlGTCWZf0h

    I wonder if the Marshall Guv’nor II’s famed Deep control uses a gyrator to simulate that 4x12 thump?
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  • Dave_McDave_Mc Frets: 2537
    That's very interesting. My DSL has a bit of a windy noise at times too (it's had it since I got it), if it's nothing to actually worry about that'd be great!

    Didn't some overdrive/distortion pedals use a gyrator for an active bass control? Some of the Digitech ones, maybe the Hardwire OD/Distortion? Or the MXR Super Badass OD?
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  • JayGeeJayGee Frets: 1410
    ecc83 said:
    Yes the Gyrator is a circuit realized with an op amp that can simulate a capacitance or an inductance, mainly the latter as such "inductors" can be made of a precise value, very small and do not suffer the limitations of Iron and Copper ones. e.g. no hum pickup.

    Several Blackstar amp and pedal circuits use them.

    Dave.
    Also found in low cost graphic equalisers to form the precise, narrow band filters required I believe. Not sure how/why one would make a physical noise though if that’s what’s happening!
    Don't ask me, I just play the damned thing...
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  • thermionicthermionic Frets: 10343
    Dave_Mc said:

    Didn't some overdrive/distortion pedals use a gyrator for an active bass control? Some of the Digitech ones, maybe the Hardwire OD/Distortion? Or the MXR Super Badass OD?
    The Bad Monkey, according to the video I found above.
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  • ecc83ecc83 Frets: 1825
    Bit paradoxically laughable really! The guitar electronics industry shuns the active, "Baxandal" type of EQ circuit, "Ooo no! Them's don't SOUND right!"

    But then it seems go even higher tech on yer A and use Gyrators! B's even use what looks like the even more sophisticate "state variable filter" EQ circuitry!

    'tis a very silly industry sometimes. (but I loved it)

    Dave.
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  • impmannimpmann Frets: 12908
    Dave_Mc said:
    That's very interesting. My DSL has a bit of a windy noise at times too (it's had it since I got it), if it's nothing to actually worry about that'd be great!


    Unlikely the cause of 'windy noise' - thats normally associated with contaminants inside the (usually preamp) valves.

    There was a batch of Chinese-made ECC83s about two/three years ago that were incredibly noisy because of poor manufacturing and zero audio QC checking at the factory. Whilst they were returned for destruction/credit by most of the major wholesalers/manufacturers, its highly likely that at least some will end up with the sales channel through another route. They'd probably be fine in a non-audio application, to be fair, but were unacceptably noisy in a guitar pre-amp.
    Never Ever Bloody Anything Ever.

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  • Dave_Mc said:
    That's very interesting. My DSL has a bit of a windy noise at times too (it's had it since I got it), if it's nothing to actually worry about that'd be great!
    Really interesting to know this. Mine also has a very faint intermittent whooshing/rustling breezy noise, I’d previously put it down to a valve somewhere getting a bit tired. 
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  • ThorpyFXThorpyFX Frets: 6382
    tFB Trader
    we use a mix of active baxandall (treble and bass) and a Gyrator for the mids part of the EQ. This setup is used on the team medic. SO yes... a Gyrator is a thing and it can be used in  guitar equipment.  Other notable uses of the Gyrator in guitar pedals is.... Boss HM-2. Boss are always first.
    Adrian Thorpe MBE | Owner of ThorpyFx Ltd | Email: thorpy@thorpyfx.com | Twitter: @ThorpyFx | Facebook: ThorpyFx Ltd | Website: www.thorpyfx.com
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  • So, next thing, were they lying about the Nonexistotron?
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  • ecc83ecc83 Frets: 1825
    So, next thing, were they lying about the Nonexistotr
    Certainly not. Next we need to investigate the parameters of the Flux Capacitor!

    Dave.

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  • So, next thing, were they lying about the Nonexistotron?
    That got replaced by the DFA Circuit. 
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  • Dave_McDave_Mc Frets: 2537
    Dave_Mc said:

    Didn't some overdrive/distortion pedals use a gyrator for an active bass control? Some of the Digitech ones, maybe the Hardwire OD/Distortion? Or the MXR Super Badass OD?
    The Bad Monkey, according to the video I found above.
    Ah yes that would make sense, thanks. :) I think they maybe brought that across to the Hardwire OD as well.

    impmann said:
    Dave_Mc said:
    That's very interesting. My DSL has a bit of a windy noise at times too (it's had it since I got it), if it's nothing to actually worry about that'd be great!


    Unlikely the cause of 'windy noise' - thats normally associated with contaminants inside the (usually preamp) valves.

    There was a batch of Chinese-made ECC83s about two/three years ago that were incredibly noisy because of poor manufacturing and zero audio QC checking at the factory. Whilst they were returned for destruction/credit by most of the major wholesalers/manufacturers, its highly likely that at least some will end up with the sales channel through another route. They'd probably be fine in a non-audio application, to be fair, but were unacceptably noisy in a guitar pre-amp.
    Thanks :) I suspect that is more likely- I made a thread about it at the time and I also had another amp more recently which had similar noises and I fixed it with contact cleaner and changing the valves. Never got round to it yet with the Marshall!

    Dave_Mc said:
    That's very interesting. My DSL has a bit of a windy noise at times too (it's had it since I got it), if it's nothing to actually worry about that'd be great!
    Really interesting to know this. Mine also has a very faint intermittent whooshing/rustling breezy noise, I’d previously put it down to a valve somewhere getting a bit tired. 
    I suspect it probably is a dodgy valve, as @impmann said. Bit annoying as mine was brand new!
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