Lindell Audio PEX-500 - 500 Series Pultec EQ

The Pultec Trick in a 500 Series Slot

The Pultec EQP-1A is one of the most revered pieces of outboard ever made, famous for a quirk of passive circuit design that no active EQ can replicate: boosting and cutting the same frequency simultaneously. The PEX-500 brings that same passive inductor-based design into the 500 series format, with transformer-coupled balanced inputs and outputs in an all-discrete signal path.

How the EQ Works

The low band boost and cut share a single three-position switch at 30Hz, 60Hz, or 100Hz. Boost the lows and simultaneously cut the same frequency and rather than cancelling, the passive circuit creates a natural resonant shelf that fattens the bottom end without adding boom. The high band offers three boost frequencies at 6kHz, 10kHz, or 16kHz, and a separate three-position attenuator at 10kHz, 15kHz, or 20kHz. Using the high attenuator alongside the boost shapes the top end into a smooth, shelved curve. MusicRadar found the PEX-500 has "that sweet but powerful top you would demand from anything claiming the revered Pultec heritage, while the lows are satisfyingly punchy and solid."

Passive, Transformer-Coupled, and All-Discrete

The PEX-500's passive EQ design uses inductors and transformers to shape the frequency response, with a make-up gain amplifier restoring the signal level afterwards. This approach is what gives Pultec-style EQs their characteristic sound: the inductors and transformers add a subtle transformer colouration to the signal even when the EQ controls are at zero. True bypass removes the circuit entirely from the signal path when not in use.

Lindell PEX-500 Features:

• 500 series passive Pultec-style parametric EQ
• Transformer-coupled balanced inputs and outputs
• All-discrete signal path, 990 amplifier stage
• Inductor-based passive EQ circuit
• Hybrid gain make-up amplifier
• Low band boost/cut: 30Hz, 60Hz, 100Hz
• High band boost: 6kHz, 10kHz, 16kHz
• High band attenuation: 10kHz, 15kHz, 20kHz
• Up to 15dB of high-end boost
• True hardwire EQ bypass
• Fits all 500 series compatible chassis