EQ with gyrator filter is noiseless, simple, and cheap. Because the first version made for guitars or instruments, the adjustment was too fine for me, the "Q" of separated bands was not permanent, one of the EQ band adjusted another frequencies too. Therefore this method is better for home stereo hi-fi instead of instrument amplifications.
After my first gyrator EQ project I made 10 band active filter EQ by RANE. This EQ have permanent Q, the result is much better for instrument amplification. But 10 channel was too much for me, very hard to set the best sound, because I got too much possibilities. Otherwise the noise of this method is much higher than simplest EQ with gyrator filter, but for instruments was much better for me.
Now I have new (untested at this time) equalizer-projects, with 3 different versions. The first is the modular EQ with gyrator, maybe just for home hi-fi. The second is an UREI545 clone parametric EQ, the 3rd is the new modular RANE based permanent Q equalizer. Now I posting about the first type of EQ with noiseless gyrator filers. With current version, I have module with adjustable gyrator circuit only. I made two versions of PCB: the first mounted with one stereo adjustable resistor for home stereo systems, the second is mounted with two mono adjustable resistors for instrument amplification systems to separate left and right channels.
Images:
Stereo gyrator module:
Dual mono gyrator module, the channels (Left, Right) can be adjust separately:
One of the upper modules have to be insert to one of the mainboards.
For 10 bands:
For 5 bands:
To the upper mainboards required one of the gyrator module (stereo or double mono), and module called "power filter" for less noise, and certainly power supply. I have three versions of "power filer" PCB, portrait, landscape, and something between fat and thin :). Look at all pictures about modules.
In this project, very important to able to count out the values of capacitors and resistors. Look at examples, links, and expressions:
5 band EQ:
- 100Hz - 330nF
- 300Hz - 100nF
- 1kHz - 33nF
- 3kHz - 10nF
- 10kHz - 3.3nF
For 10 band EQ:
- All of the 50k adjustable resistors must be changed to 25k.
- For capacitors and resistors look at the table below:
| Hz | C3 and C1 | C4 and C2 | R3 and R1 | R4 and R2 |
| 31 | 6.8 uF | 100 nF | 470 Ohm | 100 kOhm |
| 63 | 3.3 uF | 47 nF | 390 Ohm | 100 kOhm |
| 125 | 1.5 uF | 33 nF | 390 Ohm | 100 kOhm |
| 250 | 680 nF | 22 nF | 330 Ohm | 82 kOhm |
| 500 | 330 nF | 10 nF | 330 Ohm | 100 kOhm |
| 1k | 150 nF | 4.7 nF | 330 Ohm | 100 kOhm |
| 2k | 100 nF | 2.2 nF | 330 Ohm | 82 kOhm |
| 4k | 56 nF | 1 nF | 390 Ohm | 82 kOhm |
| 8k | 22 nF | 470 pF | 390 Ohm | 82 kOhm |
| 16k | 10 nF | 220 pF | 390 Ohm | 100 kOhm |
Here is the online gyrator calculator:
http://awasteofsalt.com/gyrator/
A little math:
Links for several method to get values of parts:
- About EQ by RANE
- Expressions for active EQ designs
- About EQ design
- Windows software to count MFB EQ values
- Very good PDF with expressions and examples
- Another very good PDF with expressions
See also:
- Simulation of UREI LP/HP filter module
- Modular, expandable parametric equalizer based on UREI546
- Simulation of 8 band parametric equalizer
- Simulation and software analysis of UREI 546
- UREI546 parametric EQ like URS VST EQ bundle
- 6 and 10 bands for UREI 546 parametric equalizer
- Math expression for UREI546 parametric EQ design
- Parametric EQ Project - Modular UREI545 and 546
- PDF manual of modular gyrator EQ
- PDF manual of UREI 545 and 546 EQ clone
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