Equalizer Q value

[caspercody]

Hello

I am building a 5 band EQ with same controls as a Mesa Mark amp. I am using the board I got from PedalPCB, and changing values using AMZ FX gyrator calculator.

My question is, for the Q value, does this need to be a small or large number? Or does it really not matter?

Thanks
Rob

[Rob Strand]

I am building a 5 band EQ with same controls as a Mesa Mark amp. I am using the board I got from PedalPCB, and changing values using AMZ FX gyrator calculator.

My question is, for the Q value, does this need to be a small or large number? Or does it really not matter?

I've posted a lot of stuff on these EQs.

The Q determines how narrow the bands are. For octave equalizers used for guitar and you might want to use between 1 and 3.
The choice of Q also affects how the band combine, which you can see in the second and last reference post.

For the Mesa Mark amp the Q is determined by the DC resistance of the coils and the series resistors.   However going to opamps you need to see the info in the third reference post.

Multiband EQs have a whole lot of details under the hood.   Those calculators will not give the correct results for amount of boost and Q.   What happens in a multband EQ is the bands interact and amount of boost/cut you actually get is much less than that indicated by the (single band) calculator.

Some Reference posts: (not all)

[1] 6 band eq question
Sept 2022
https://www.diystompboxes.com/smfforum/index.php?topic=129589.0
https://www.diystompboxes.com/smfforum/index.php?topic=129589.msg1252939#msg1252939

[2] Re: Choosing equalizer bandwidth
« Reply #2 on: August 24, 2019, 07:09:09 PM »
https://www.diystompboxes.com/smfforum/index.php?topic=122973.msg1161378#msg1161378

[3] Inductors vs gyrators in EQ filters
« Reply #10 on: September 03, 2019, 06:54:35 PM »
https://www.diystompboxes.com/smfforum/index.php?topic=123011.msg1161976#msg1161976

[4] An approach to designing Gyrator based EQ's
choosing pot values
Re: Eq Pedal Weird Response
January 03, 2024, 09:00:30 PM
https://www.diystompboxes.com/smfforum/index.php?topic=131587.msg1279085#msg1279085

[caspercody]

Thanks for the information Rob!

On the AMZfx calculator page Jack has a note that a typical 1/3 octave bandpass will have a Q of about 4.3. I entered values of resistors and capacitors until I got the frequency I was looking for and Q value close to the 4.3 recommendation.

[caspercody]

How does one determine how much it boosts? Example when a EQ says it will boost +/- 12db.

Thanks
Rob

[antonis]

[caspercody]

I used this website to determine the capacitor, and resistor values for the frequency and Q I was looking for. Is there anyway to determine based on the values I came up with what the db boost is?

http://tools.griffineffects.com/gyrator.php

[antonis]

I'm afraid you have to mess up with all those nasty formulas..  

[ElectricDruid]

Is there anyway to determine based on the values I came up with what the db boost is?

I use LTspice for jobs like this. Put the circuit in the sim, run it, look and see how much boost/cut you get. Basically, let the computer solve all those equations Antonis mentioned for you. I think that's probably the easiest way - certainly easier than crunching the numbers yourself.

[amz-fx]

I used this website to determine the capacitor, and resistor values for the frequency and Q I was looking for. Is there anyway to determine based on the values I came up with what the db boost is?

http://tools.griffineffects.com/gyrator.php

http://www.muzique.com/lab/gyrator.htm

The original has an additional calculator for determining Q of the bandpass filter. If you want 1 octave, then leave it as 1. A half-octave would be 0.5 and one-third octave is 0.33 for the bandwidth field.

regards, Jack

[caspercody]

I just created a circuit in LTspice, but I have two issues that I cannot find a working answer for.

One, to rotate an icon. the field is not even highlighted for me to choose the command for rotate, or mirror.

Two, where is a potentiometer icon? I tried some Youtube video ideas but nothing.

[ElectricDruid]

I just created a circuit in LTspice, but I have two issues that I cannot find a working answer for.

One, to rotate an icon. the field is not even highlighted for me to choose the command for rotate, or mirror.

LTSpice has the weirdest interface this side of the DOS era. "Quirky" is significantly too charitable.

If you use the Move or Drag tools to pick up an item, you can Rotate and/or Mirror it while you've got it picked up.

Two, where is a potentiometer icon? I tried some Youtube video ideas but nothing.

There is no proper potentiometer symbol in LTspice. It's a pretty daft ommission, but it's not there, which is why you can't find it. However, there *are* several good pot symbols flying around the web, but then you have to work out which folder to drop which bits into, which is *another* whole can of worms with LTspice. Not impossible, but just never as simple as it could be. Designed *by* geeks *for* geeks, maybe?!?
If you can't find one, email me, and I'll ping you one over.

[PRR]

there *are* several good pot symbols flying around...

In Guitar Amplifier Electronics: Circuit Simulation, Richard Kuehnel goes step-by-step through creation and installation of a POT. You have to follow the steps carefully, but you learn some about LTspice too. The model tutorial alone is NOT worth $50 (for most people); but the book is good meat on simulation of audio electronics. (Yes, the examples are all tube amplifiers but it applies to transistors too.)

Disclosure: I did some proofreading on the GAE:CS manuscript and remember the day I critiqued the POT model process with extra care.

While Kuehnel's site sends you to Amplified Parts to buy, because Amazon royally screwed the launch, and AP's price is 50 cents lower, Amazon's shipping is a better deal to my house.

[caspercody]

Thanks!

I think I got one created by following a Youtube video.

When I run Configure Analysis, I get "No analysis request found".

How do i set the parameters to check the boost +/-, or what Antonis wrote out?

[m4268588]

[caspercody]

M4268588

Do I need to enter those equations into LTspice?

[m4268588]

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TEXT 0 56 Left 2 !.AC Oct 100 100Hz 10kHz\n \n.Param Freq=1kHz A=0.25 B=0.98855 Q=sqrt(2)*A w0=Freq*2*pi\n+ EQ=0.5 R0=1k\n+ R1=R0*(A*B+B*Q*Q-Q*Q-A*A*B)/((1-A)*(1-A)*B)\n+ R2=R0*B/(1-B)\n+ C1=(1-A)/(R0*w0*Q)\n+ C2=Q*(1-A)*(1-B)/(R0*w0*(A*B+B*Q*Q-Q*Q-A*A*B))\n \n.Param VR_12=limit(1u,1-1u,EQ)*20k VR_23=20k-VR_12\n.STEP Param EQ 0.0 1.0 0.1https://www.google.com/search?q=LTspice+view+error+log
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