Gyrator circuit

fastonebaz

I sent my Marshall back for inspection to check whether it was normal noisy or broken noisy (just a bit too hissy when at gig volume with 3/4 gain) and their engineers tested it advising it was normal noisy,  it was the gyrator circuit that causes the noise. 

Question 1: wtf is this and what does it do?

Question 2: is there any common solution a decent amp tech cld do to improve these kind of issues (e.g. replace a certain cap/filter etc)?

Question 3: what is the average wing velocity of a swallow? 

I appreciate this is a bit vague but I was interested in a generic response rather than an amp specific debate. 

Cheers

ecc83

A  gyrator is an active circuit that inverts the function of a component. Most often seen to mimic an inductor with a capacitor, especially in "graphic" EQ circuits.

Dave.

fastonebaz

ecc83 said:

A  gyrator is an active circuit that inverts the function of a component. Most often seen to mimic an inductor with a capacitor, especially in "graphic" EQ circuits.

Dave

Are these commonly noisy then? 

ecc83

fastonebaz said:

ecc83 said:

A  gyrator is an active circuit that inverts the function of a component. Most often seen to mimic an inductor with a capacitor, especially in "graphic" EQ circuits.

Dave

Are these commonly noisy then? 

No not likely any noisier than the op amp it is built around and for say an NE5532 or TL072 that will be very low, certainly not a problem in the gitamp world! (IIRC there is one in the B'star EQ stack)

Dave.

robinbowes

fastonebaz said:

Question 3: what is the average wing velocity of a swallow? 

Is that an African or European swallow?

fastonebaz

robinbowes said:

fastonebaz said:

Question 3: what is the average wing velocity of a swallow? 

Is that an African or European swallow?

Well I don't know.   Arrgghhggg

DJH83004

Dave’s description is bang on the money, gyrators are generally used by manufacturers to emulate costly inductors  in filter circuits, or in our world the EQ or tone stack. Would be interested to to know which Marshall you have?

jpfamps

As ever, IT'S REALLY USEFUL TO KNOW THE MODEL OF THE AMP!!!!!!!!!!!!!

Noise can be a problem in gyrator circuits as they use an active device.

BOSS graphic eq pedals are particularly noisy as the opamp used in GE7 for example, TL022, was chosen, I assume, for low current draw to prolong battery life.

The noise performance of the TL022 is abysmal, about 9 db worse than a TL072, which is hardly the last word in low noise op-amps.

It could be that the active device in the gyrator circuit is defective, or simply that it was not designed for low noise performance.

Noise performance could improved by using a lower noise op-amp such as the OPA2134; however this is an expensive part, and MUST be purchased from a reputable source to make sure you get a genuine part. There are many fakes out there.