Monday, October 24, 2011

Modular equalizer with gyrator filter

Posting again about my modular gyrator-EQ project. This project not tested yet, but I made 5 channel EQ with gyrators and 10 channel active filters EQ formerly. Look at older pictures:

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.

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
The upper values are valid for all of the C(a) capacitors in this schematic:

For 10 band EQ:
  • All of the 50k adjustable resistors must be changed to 25k.
  • For capacitors and resistors look at the table below:
HzC3 and C1C4 and C2R3 and R1R4 and R2
316.8 uF100 nF470 Ohm100 kOhm
633.3 uF47 nF390 Ohm100 kOhm
1251.5 uF33 nF390 Ohm100 kOhm
250680 nF22 nF330 Ohm82 kOhm
500330 nF10 nF330 Ohm100 kOhm
1k150 nF4.7 nF330 Ohm100 kOhm
2k100 nF2.2 nF330 Ohm82 kOhm
4k56 nF1 nF390 Ohm82 kOhm
8k22 nF470 pF390 Ohm82 kOhm
16k10 nF220 pF390 Ohm100 kOhm

Here is the online gyrator calculator:

A little math:

Links for several method to get values of parts:
I think its enough if you want simple but very good quality gyrator EQ circuits.

See also:

PCB sales of this project
Module name Size
PDF SCH PCB image Tested Price (US$)
Des./3D Sim.1 Full2 Sim.1 Full2 Man3
Power filter V:1
51x22 11 Yes
Yes - - - 3 11 Yes
Power filter V:2 27x41 11 Yes Yes Yes
- 3 11 Yes
Power filter V:3 21x45
9 Yes Yes
Yes - - - 3 11 Yes
Power supply
212x57 69 Yes
Yes Yes - - 11 20 Yes
5 band gyrator EQ
161 Yes Yes Yes -
- - 23 33 Yes
Stereo gyrator EQ module
30x61 18 Yes
Yes Yes
- - - 4 12 Yes
Double mono gyrator EQ module
Yes Yes Yes - - - 5 12 Yes
5 band EQ mainboard
75x95 71
Yes Yes - - -
11 20 Yes
10 band EQ mainboard
Yes Yes - - - 15 24 Yes
How to order? Please read the rules carefully!

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