The EQP501 is a passive equalizer based on the classic PULTEC EQP 1A, adapted to the 500 series 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 Lunchbox^TM rack and start recording.

Highlights

• 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).

Controls

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

4: 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

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
• Active components (diodes, transistors, LED, ...),
• Front panel elements (switches, potentiometers, knobs),
• Connectors, relay,
• PCB's,
• 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.