Korg · Analog monosynth · Pre-MIDI classics
The Mono/Poly came out alongside the Polysix in the early 1980s, and the name tells you how it works. It has four VCOs, each with its own level, tuning and waveform control. Stack them in unison and you get a huge monophonic lead or bass. Switch to poly mode and each VCO takes its own note, so you can play four-note chords. All four still share one 24 dB low-pass filter and the same envelopes, which makes it paraphonic, and every note in a chord swells and fades together. If you want true polyphony, the Polysix is the Korg to buy. The Mono/Poly is the lead and bass machine. It adds two modulation generators, an arpeggiator, chord memory, and an effects section for oscillator sync and cross modulation. There's no patch memory and no MIDI from the factory, though it does take CV and gate. Tangerine Dream, The Orb, 808 State and the Chemical Brothers all used one, and that sync section is a big part of why.
Sound On Sound reports that the contact strip under the keyboard can become unreliable with age. It warns against cleaning those contacts with alcohol or solvent, which can corrode them and perish the rubber backing.
Buying guide
Our pick is the Mono/Poly titled tested and working with its original case at $1,997 delivered, and the cheapest tested one is $1,849. Only about 11 are for sale, most asking $2,000–2,525 delivered, and almost all ship from Japan, so check the voltage plate and plan on a step-down transformer for a 100V unit. Ask for a video playing all 44 keys, since the contact strip under the keyboard gets unreliable with age, and don't clean those contacts with alcohol or solvent when it arrives. The dealer's Pro-Refurbished unit asks $4,155 delivered, about $2,150 more than the tested ones from Japan.
$1,849.00delivered
The lowest confirmed delivered price on a Mono/Poly at $1,849, titled tested, about $150 under the band. Ask for a clip of each VCO soloed in turn and a four-note chord in poly mode.
KORG Mono/Poly Vintage Analog Synthesizer 4VCO Arpeggiator Tested from Japan
$1,997.00delivered
Titled tested and working, with its original case, for $1,997 delivered at the bottom of the band. A case is a real plus on a keyboard shipping from Japan.
KORG Mono/Poly MP-4 Analog Synthesizer - Tested & Working w/ Original Case Japan
$4,155.14est. delivered
Titled Pro-Refurbished by a US vintage synth dealer, so it should need the least work out of the box. At $4,155 delivered it's about $1,630 over the band, so you're paying for the refurb and a US seller.
Korg Mono/Poly synthesizer *Pro-Refurbished* monopoly mp-4 VINTAGE SYNTH DEALER
Delivered prices include shipping as eBay quoted it to a US address on Oct 5, 2026. Many sellers charge by distance, so your total may differ. eBay shows yours before you pay.
Snapshot
Checked . Some may have sold.
Delivered prices include shipping as eBay quoted it to a US address on Oct 5, 2026. Many sellers charge by distance, so your total may differ. eBay shows yours before you pay.
Used$1,849.00delivered
$1,849.00 · free shipping
Buy It Now$1,849.00
This seller takes offers, and many sellers accept less than the asking price.
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Good buy
Titled tested. Ships from Japan.
Seller: shopmin-japan
99.8% positive
Used$1,997.00delivered
$1,997.00 · free shipping
Buy It Now$1,997.00
Good buy
Titled tested and working, with its original case.
Seller: asterisk_llc
99.6% positive
Refurbished$4,155.14est. delivered
$3,999.99 + $155.15 shipping
Buy It Now$3,999.99
Good buy
Titled Pro-Refurbished by a US vintage synth dealer.
Seller: 123synthland
100% positive
Used$1,989.00delivered
$1,989.00 · free shipping
Buy It Now$1,989.00
This seller takes offers, and many sellers accept less than the asking price.
Fine if you might miss it? Send an offer first. Someone else can still buy it while you wait for a reply.
Want it for sure? Use Buy It Now.
Our take
Original case, no test claim.
Seller: shopmin-japan
99.8% positive
Used$2,099.00est. delivered
$1,699.00 + $400.00 shipping
Buy It Now$1,699.00
This seller takes offers, and many sellers accept less than the asking price.
Fine if you might miss it? Send an offer first. Someone else can still buy it while you wait for a reply.
Want it for sure? Use Buy It Now.
Our take
No test claim. $400 of it is shipping.
Seller: musical-0820jp
97.9% positive
Used$2,110.00est. delivered
$1,788.00 + $322.00 shipping
Buy It Now$1,788.00
Our take
No test claim. Ships from Japan.
Seller: tokyo_luxe_9
100% positive
Used$1,760.00+ shipping
$1,760.00 · shipping not stated
Buy It Now$1,760.00
This seller takes offers, and many sellers accept less than the asking price.
Fine if you might miss it? Send an offer first. Someone else can still buy it while you wait for a reply.
Want it for sure? Use Buy It Now.
Our take
Titled NM condition, with no test claim. US seller, shipping not stated.
Seller: blips-n-bleeps
100% positive
Used$3,000.00delivered
$3,000.00 · free shipping
Buy It Now$3,000.00
Priced high
Titled tested, about $475 over the band with no service claim.
Seller: jdmotorgear
99.6% positive
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