How It Was Recorded

Chicago · Album, 1970

Chicago

This is an album-level record: the sources describe how the album as a whole was recorded, not one song. Where a detail belongs to a single song, the row says so.

Songs this record stands for: 25 or 6 to 4, Colour My World, Make Me Smile. We found nothing specific to these songs, so this album record is the closest account we have.

Background vocalsGuitar riff and solosBassDrums (two passes)PianoHorns and mixReported13

What the sources do and do not say

One Mix Classic Tracks article (originally July 2019) covering the July 1969 CBS Hollywood sessions and the New York mix, with quotes from Guercio, Seraphine, Lamm and Puluse. Most gear statements are journalist narrative, so they are reported rather than verified. Microphones are given only as U67 or U87 for the album, not per instrument. The article mentions an unidentified pedal or outboard fuzz on the third guitar part and a list of Pultec, Kepex, 1176 and LA-2A units in the mix rooms with no stated use, so these are omitted.

Background vocals

Terry Kath, Robert Lamm and Peter Cetera

Mix effects

UREI 1176

Reported

The mix engineer believes he probably used an 1176 on the background vocals when mixing the album.

Source: Mix, accessed 15 Nov 2026

Emulation of this unit

Universal Audio 1176 Classic Limiter Collection

compressor

Models several revisions of the 1176, including the blackface units.

Get the plugin ↗What else it stands in for

Also worth a look: Waves CLA-76 Compressor / Limiter (Models two 1176 revisions (blacky and bluey)).

Guitar riff and solos

Terry Kath

Amplifier

Fender Concert

ReportedOne song

Amplifier Kath played through for the main guitar riff, modified in a way the producer attributes to Kath himself.

Source: Mix, accessed 15 Nov 2026

Approximate

IK Multimedia AmpliTube 5

amp and cabinet simulator

An amp and cabinet simulator covering this style of amplifier. Whether this exact model is included was not checked.

Get the plugin ↗What else it stands in for

Also worth a look: Native Instruments Guitar Rig 7 Pro (An amp and cabinet simulator covering this style of amplifier. Whether this exact model is included was not checked).

Mix effects

EMT Plate reverb (model not stated)

Reported

At the mix, Puluse sent Kath's guitar parts through the EMT plates to get delay effects.

Source: Mix, accessed 15 Nov 2026

Close match

Universal Audio EMT 140 Classic Plate Reverberator

reverb

The 140 is the EMT plate most studios have; the source does not name the model.

Get the plugin ↗What else it stands in for

Also worth a look: Waves Abbey Road Reverb Plates (Models the EMT 140 plates at Abbey Road).

Bass

Peter Cetera

Instrument

Fender Precision Bass

Reported

Cetera played the producer's own Precision rather than his usual Fender bass on these sessions.

Source: Mix, accessed 15 Nov 2026

No plugin suggested. A bass guitar is the source of the sound, not a process applied to it. No plugin stands in for it.

Amplifier

Fender Bassman

Reported

The bass amplifier was either a Fender Bassman or a Showman; the article does not say which. (recalled with uncertainty)

Source: Mix, accessed 15 Nov 2026

Emulation of this unit

Native Instruments Guitar Rig 7 Pro

amp and cabinet simulator

Its Tweedman amp is modelled on the Fender Bassman.

Get the plugin ↗What else it stands in for

Also worth a look: IK Multimedia AmpliTube 5 (Includes Fender-style tweed amp models; an official Bassman model is sold as an add-on collection).

Microphone

Neumann U 67

Reported

Like the other instruments, the bass was miked with one of Guercio's preferred Neumanns, either a U67 or a U87. (recalled with uncertainty)

Source: Mix, accessed 15 Nov 2026

No plugin suggested. Microphone-modelling plugins only work with their own matched hardware microphone, so there is no plugin to link. Placement and the room matter more than the model.

Drums (two passes)

Danny Seraphine

Instrument

Rogers Drum kit (model not stated)

ReportedOne song

Seraphine's kit at the time was a white marine pearl Rogers set with a 24-inch kick drum.

Source: Mix, accessed 15 Nov 2026

Approximate

Toontrack Superior Drummer 3

drum instrument

A sampled drum instrument. It does not claim to be this kit or drum.

Get the plugin ↗What else it stands in for

Rogers Dynasonic snare

ReportedOne song

Seraphine's kit at the time included a wood Dynasonic snare.

Source: Mix, accessed 15 Nov 2026

Approximate

Toontrack Superior Drummer 3

drum instrument

A sampled drum instrument. It does not claim to be this kit or drum.

Get the plugin ↗What else it stands in for

Piano

Robert Lamm

Instrument

Steinway Piano (model not stated)

ReportedOne song

Lamm played the studio's Steinway piano during basic tracking.

Source: Mix, accessed 15 Nov 2026

No plugin suggested. The source does not name the model, so no specific plugin can be suggested.

Horns and mix

Microphone

Neumann U 67

Reported

The horn section was recorded with Guercio's favourite U67s and U87s.

Source: Mix, accessed 15 Nov 2026

No plugin suggested. Microphone-modelling plugins only work with their own matched hardware microphone, so there is no plugin to link. Placement and the room matter more than the model.

Neumann U 87

Reported

The horn section was recorded with Guercio's favourite U67s and U87s.

Source: Mix, accessed 15 Nov 2026

No plugin suggested. Microphone-modelling plugins only work with their own matched hardware microphone, so there is no plugin to link. Placement and the room matter more than the model.

Mix effects

Ampex 350

Reported

The mix rooms mixed down to an Ampex 350 two-track quarter-inch machine.

Source: Mix, accessed 15 Nov 2026

Approximate

Slate Digital Virtual Tape Machines

tape

Models two Studer machines, not this recorder. It gives the general behaviour of analogue multitrack tape.

Get the plugin ↗What else it stands in for

Also worth a look: Universal Audio Studer A800 Tape Recorder (Models a Studer A800, not this recorder. It gives the general behaviour of analogue multitrack tape).

Unidentified Console (model not stated)

Reported

The mix was done on a console made in-house for each of CBS's mix rooms.

Source: Mix, accessed 15 Nov 2026

No plugin suggested. The source does not name the model, so no specific plugin can be suggested.

Sources

  1. Classic Tracks: Chicago’s “25 or 6 to 4”, Mix, 2019-07. Accessed 15 Nov 2026.
Verified

Stated by the engineer, producer or artist, or by the manufacturer.

Reported

Stated by a reputable secondary source.

Inferred

An educated suggestion, not a documented fact.

Disclosure: plugin links currently go straight to the maker and earn us nothing. If that changes, affiliate links will be marked here. Suggestions are chosen on fit, never on commission, and are kept separate from the recording facts. More.