EQP501 Passive Equalizer

EQP501 Passive Equalizer for the '500' Lunchbox - Kit

The EQP501 is a passive equalizer based on the classic PULTEC EQP 1A, adapted to the '500' format of API*.

It is made of an all passive section followed by a gain make up stage based on a Discrete Op-Amp (DOA).

The EQP501 retains all the controls from the original but adds some new frequencies to the low and high sections.

Just install it in your API* compatible LunchboxTM rack and start recording.

All passive, faithfull to the original,
Separate low end cut and boost allows achieving the "Low End Trick",
Coil based high end boost giving that famous airy, transparent high end,
Low frequency cut and boost: 15, 20, 30, 45, 60 and 100 cycles per second,
High frequency boost: 2.5, 3, 3.5, 4, 5, 6, 7, 8, 10, 12, 15 and 18 kilocycles per second,
High frequency cut: 10, 15 and 20 kilocycles per second,
Discrete Op-Amp, class A make-up gain,
Carnhill inductor,
Available assembled or as a full kit (everything included).

1 KCS Sets the high cut frequency in kilo-cycles (kHz). Three frequencies are available. The 3 in-between positions are bypass for the whole EQ.

2 ATTEN Sets the attenuation level from 0 to maximum.

3 B.WIDTH Sets the bandwidth of the high boost section. At 0 the bandwith is narrow, peaking high and at 10, the bandwith is wide

4 EQ ON LED indicating the on/off state of the EQ.

5 KCS Sets the high boost frequency in kilo-cycles (kHz). 12 frequencies are available from 2.5 to 18 kHz.

6 BOOST Sets the high frequency boost level from 0 to maximum.

7 ATTEN Sets the low frequency attenuation level from 0 to maximum.

8 CPS Sets the low cut/boost frequency in cycles per second (Hz). 6 frequencies are available from 15 to 100 kHz. There is a small difference between the cut and boost frequencies for each switch position allowing creative use of simultaneous cut and boost.

9 BOOST Sets the low frequency boost level from 0 to maximum.

What's in the kit?
Absolutely everything!

Passive components (resistors, capacitors),
Carnhill inductor
Output transformer
SK25 Discrete Op-Amp kit
Active components (diodes, transistors, LED, ...),
Front panel elements (switches, potentiometers, knobs),
Connectors, relay,
Front panel and side panel,
All hardware
You bring the solder (use good quality solder, 1mm diameter max) and the Lunchbox.

Difficulty level
The EQP501 kit is a medium difficulty build.


Available as an assembled Module and as a DIY project.

This Module is currently available.

$335 Price in €
1 HP Equalizer
submitted Oct 14th 2019, 13:24 by Kivig | last Change Oct 14th 2019, 13:32 by Kivig