Universal Audio · Pro · Thunderbolt · 2019 on
Universal Audio released the Apollo x4 in October 2019, the same day as the Twin X, and called it the world's most advanced desktop audio interface. It takes the converters from the Apollo X racks and puts four Unison preamps, two front Hi-Z inputs and two headphone outputs on your desk, with Quad DSP built in. It also has a talkback mic, monitor controls and an optical input and output for eight more channels from an ADAT preamp. That's the right size for a band demo, a drum kit with a few mics, or two people tracking at once with a headphone output each. In October 2024 UA launched a grey Gen 2 with improved digital-to-analog conversion. A black first-generation x4 does the same job, and it's the version you'll see most.
In the photos
It's a wider version of the Twin X, about 23 cm across against the Twin's 16 cm, with four preamps on the back and two Hi-Z inputs and two headphone jacks on the front. The 2019 original is black, and the Gen 2 from October 2024 is pale grey. Every x4 is a Quad, so there's no DSP tier to check.
Mac and Windows
Current UAD software supports it on macOS 11 Big Sur through 26 Tahoe, Apple silicon included (with Reduced Security and kernel extensions allowed), and on 64-bit Windows 10 or 11 with a Thunderbolt 3, 4 or 5 port. UA says AMD PCs are untested and that a first-generation x4 needs UAD v10.0 or later, warning that earlier software can damage it. A Gen 2 needs v11.5.0 or later.
Power, cables and licences
Check the listing photos against this list, and ask the seller about anything you can’t see. A missing power supply or a licence that won’t transfer should come off the price.
UA warns that UAD software older than v10.0 can damage a first-generation x4, so install current software before anything else. The locking power plug must be twisted home or the unit can lose power. On Windows, UA's setup guide has you turn off Thunderbolt power management and check BIOS settings.
Buying your first one? How to pick a first used interface covers inputs, mic gain and drivers, and the power supply guide covers which ones need their adapter.
Buying guide
We'd buy the black first-generation x4 at $1,260 with free shipping from a 99.8% pawn shop, since its photo shows the box and the power supply. There are at least 31 for sale and most ask $1,450–2,000 delivered, but new and demo Gen 2 bundles from dealers like Sweetwater, Alto Music, Pro Audio Star and Vintage King set that band at $1,660–2,339, while used Gen 1 units ask about $1,000–1,500. Check the case colour in the photos against the title (Gen 1 is black, Gen 2 pale grey), and pick one with UA's 12 V, 4.2 A locking supply or budget for the matching one, plus a real Thunderbolt 3 or 4 cable. Essentials+, Studio+ or UAD Analog Classics plug-ins come with a new dealer unit but move on a used one only through UA's transfer form, and UA's warranty covers the original owner only. Skip the $1,000 Gen 1 whose title two other sellers share, and the $3,409 ask, about 1.9 times the median.
$1,259.99delivered
The lowest x4 here without a warning, $1,260 with free shipping from a 99.8% pawn shop. The photo shows a black Gen 1 with its box and power supply, though neither is in the title, so confirm both come with it.
Universal Audio APOLLO X4 Thunderbolt Audio Interface
$1,349.00delivered
Titled new, a Gen 1 Heritage Edition at $1,349 with free shipping from a 99.7% seller, under the band and only $89 more than the pawn-shop unit. Ask the seller to confirm it's never been registered before you count on the Heritage plug-ins.
*NEW* Universal Audio Apollo x4 Thunderbolt 3 Audio Interface - Heritage Edition
$1,799.10delivered
Sweetwater's refurbished Gen 2 at $1,799 with free shipping, the least guesswork for a working x4 here. The title names UAD Analog, so ask which plug-ins come with the refurb.
Universal Audio Apollo x4 Gen 2 Thunderbolt Audio Interface with UAD Analog
Delivered prices include shipping as eBay quoted it to a US address on Oct 14, 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 14, 2026. Many sellers charge by distance, so your total may differ. eBay shows yours before you pay.
Used$1,259.99delivered
$1,259.99 · free shipping
Buy It Now$1,259.99
Good buy
Black Gen 1 with box and power supply in the photo. Neither is in the title.
Seller: pawnamerica
99.8% positive
New$1,349.00delivered
$1,349.00 · free shipping
Buy It Now$1,349.00
Good buy
Titled new Gen 1 Heritage Edition, black in the photo.
Seller: eboy4sale
99.7% positive
Refurbished$1,799.10delivered
$1,799.10 · free shipping
Buy It Now$1,799.10
Good buy
Refurbished Gen 2 from Sweetwater, titled with UAD Analog.
Seller: sweetwatersound
99.8% positive
Used$1,399.99delivered
$1,399.99 · free shipping
Buy It Now$1,399.99
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
Heritage Edition from a 100% seller. No supply named; ask.
Seller: newsilva
100% positive
Open box$1,699.00delivered
$1,699.00 · free shipping
Buy It Now$1,699.00
Our take
Vintage King's Gen 2 Essentials+ Edition demo deal.
Seller: vintagekingaudio
99.9% positive
Used$1,799.00delivered
$1,799.00 · free shipping
Buy It Now$1,799.00
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
Used Gen 2 shown in UA's product photo, at Sweetwater's refurb price. Ask for photos of this unit.
Seller: 6stringsssss
100% positive
Used$999.99delivered
$999.99 · free shipping
Buy It Now$999.99
Check the seller
Well under other used Gen 1 asks, and two other sellers use the same title. Check feedback and photos.
Seller: ti424
99.8% positive
New$3,408.99delivered
$3,408.99 · free shipping
Buy It Now$3,408.99
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.
Priced high
New Gen 2 with UAD Analog Classics at about 1.9 times the median.
Seller: prestigesupplyllc9
99% positive
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