Filter
Top Products
1K2
1K8
27K
12K
8K2
5K6
3K9
2K7
1K8
1K2
820
560220
330
470
680
1K
1K5
2K2
3K3
4K7
6K8
10K
FREQUENCY FREQUENCY
2K7
FREQUENCY
3K9
820
560
390
270
180
120
82
FREQUENCY
680
1K
470
330
220
150
68
47
33
22
100 100
22
33
47
68
150
220
330
470
1K
680
FREQUENCY
82
120
180
270
390
560
820
3K9
FREQUENCY
2K7
FREQUENCYFREQUENCY
10K
6K8
4K7
3K3
2K2
1K5
1K
470
330
220 560
820
1K2
1K8
2K7
3K9
5K6
8K2
12K
27K
1K8
1K2
BANDWIDTH
20
0
20
0
BANDWIDTH
20
0
BANDWIDTH
20
0
BANDWIDTH
20
0
BANDWIDTH
20
0
BANDWIDTH
20
0
BANDWIDTH
20
0
16K 16K
DB
BANDWIDTH
DB DB DB DB DB DB DB
680
MASSIVE PASSIVE
STEREO EQUALIZER
12K
7K5
22
39
68
120
220
18K
0
0
POWER
9K
OFF
6K
7K5
OFF
9K
18K
12K
OFF
OFF
220
120
68
39
22
GAIN
6K
LOW
PASS
HIGH
PASS
IN
IN
+4
-6
-6 +4
BOOST
CUT
SHELF
BELL
220 ± 10K82 ± 3K922 ± 1K 560 ± 27K
BELL
SHELF
CUT
OUT
BOOST BOOST
OUT
CUT
SHELF
BELL BELL
SHELF
CUT
OUT
BOOST
OUT
BELLCUT
OUT
SHELF
BOOST
560 ± 27K
BELLCUT
OUT
BOOST
220 ± 10K
BELLCUT
OUT
BOOST
82 ± 3K9
CUT BELL
OUT
SHELF
22 - 1K
BOOST
SHELFSHELF
1) The Power Switch: First things first, turn it clockwise to power up the unit. There is no "power on LED", instead you can
use any of the Boost / Off / Cut switches in Boost or Cut and they light immediately with power on. There is a "warm-up" circuit
that forces the unit into "Bypass" for about 20 seconds, to prevent big thumps from hitting your speakers. This also prevents
the blue LEDs that indicate "EQ IN" from lighting up for that 20 seconds. This is not a total hardwire bypass - if power is not
on, the unit will not pass audio. At trade shows, we have seen a few people turn the "Power Switch" by accident, perhaps
thinking it was a tone control. Not knowing, there is a "warm-up" circuit, and seeing no blue light action, they thought they
may have broken the unit. The lack of a "power LED" is just one of the deliberate ideosyncracies. 4 reasons: there wasn't a
great place to put one, it was redundant with 16 boost/cut LEDs (we were laughing at other panels with dozens of lit LEDs
and a fast turn-on LCD screen also sporting a big power LED), and this unit is meant for professionals that we assume can plug
in a piece of gear, see (or feel) the switch and turn it on, and it may annoy those who want all gear to be just "normal" ;-)
2) EQ IN buttons: Push to activate the EQ circuits. The buttons glow blue when EQ is IN including the Filters and Gain Trims.
The "warm-up" circuit prevents both EQ to be IN and the buttons from lighting when it first gets powered up. In "bypass" (un-
lit) the tubes are not in circuit but the input amplifier and balanced output transformer are in circuit. Yes, real blue LEDs.
3) Gain Trims: Intended to help match levels between "Bypass" and "EQ IN" modes so that the EQ effect can be more
accurately judged. It is difficult to compare if the level jumps up or down and easy to prefer EQ when mostly it is just louder.
These trims only have a small range of -6 to +4 dB of gain. With drastic EQ there may not be enough range to match levels
but with drastic EQ this kind of comparison is of little use. The range is small to allow easier and finer adjustments.
4) Low Pass Filters: They pass lows and chop highs. There is a separate filter for each switch setting and they only share the
switch and one resistor. The filters are entirely passive and "inserted" between the boost sections and cut sections.
The 18kHz filter is probably most useful for warming up digital. It seems to remove some irritating super-sonic noise
associated with digital to analog converters. It is designed as a modified eliptical filter down 60dB one octave up (36kHz) on
paper but in real life "only" drops about 40 dB. It is flat within 0.5dB up to 16kHz then very steeply drops. It is sonically subtle.
12kHz position can be considered general purpose hiss killing. It is also very flat up to 11kHz and drops at 30 dB/octave.
9kHz, 7.5kHz & 6 kHz. These are intended for more creative sound sculpting than as utility filters. They have a 1.5 to 2 dB
bump or boost right before they cut at 18dB/octave. This helps compensate for the percieved loss of highs while still allowing
deep HF cuts. This gives them a little color and edge as opposed to just dullness. You may find they help remove some of that
buzzy super high distortion of cranked guitar rigs as well as help some synth and bass sounds. They are also intended to help
with "effects" such as "telephone sound" and vintage simulations and for some techno, rap and industrial style music.
5) High Pass Filters: They pass highs and chop lows. There is a separate filter for each switch setting and they only share the
switch and one resistor. The filters are entirely passive and "inserted" between the boost sections and cut sections. They are
all 18dB/octave (most modern filters are 12), with no bumps and no resonances. We use a large, low DCR, custom inductor.
The 22Hz is very subtle and is designed to remove sub-sonic frequencies that may have been boosted by previous EQ. Most
signal below 25Hz is only good for testing or messing up sub-woofers. You may not hear the effect in the studio, but often
you can see it on the meters. Now that sub-woofers are becoming common in autos and consumer systems, we are hearing more
complaints of excess lows and LF garbage. This filter is in response to these concerns and requests from mastering engineers.
The 39Hz filter can be used similarly, but may be audible with some material. This filter, as with the others, can be used with
the normal boost/cut sections for a more tailored low EQ. This can allow bigger and more effective LF boosts while minimising
the side-effects of excessive woofer excursions and unwanted audible LF noise like air conditioner or subway rumble.
The 68Hz filter is also general purpose and ideal for most vocals and pop removal. Also good in combination with shelves.
120 and 220Hz filters are intended for garbage removal, sonic sculpting, and effects. 120 is useful for some vocals. The 220
is for some close miked hi-hats and percussion instruments. Yup, 220Hz tends to be drastic and only occasionally valuable.
Check out the curves on page 16 for a little more detail on these filters.
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