The Source Audio ZIO Analog Bass Preamp + DI is a compact, easy-to-dial-in pedal that shapes a bass tone and sends it wherever it needs to go. Source Audio describes it as an "ultra-low noise, all-analog tone shaping tool" that "works equally well in front of your amplifier or as a preamp/direct box via its balanced XLR output"1. In other words, it does two jobs at once: it is a preamp that conditions and voices your bass signal, and it is a DI (direct injection) box that feeds a balanced, low-noise signal straight to a mixing desk or interface.
The circuit is built around a Burr Brown OPA1656 op-amp, which Source Audio says it selected after bench-testing about half a dozen popular op-amp chips spanning back to the 1970s, choosing this one "for its pure tonality, dynamic range, frequency response, and overall feel"1. The pedal sits in a brushed anodized aluminum housing, measures 4 in. long by 3 in. wide by 2.25 in. high including the knobs, and weighs 0.75 lb.1
Source Audio's product page lists the ZIO Analog Bass Preamp + DI as sold out as of October 2026, so availability is limited to remaining dealer stock or the used market.
The controls and outputs
The front of the pedal is deliberately simple. Two controls and a toggle do the tonal work, and the switching handles the rest.
| Control | What it does |
|---|---|
| BASS knob | Provides what Source Audio calls "colossal low-end boost at around 100Hz," while gently reducing muddy low-mids to keep the low end clear1 |
| GRIT toggle | Captures transformer-style breakup, the tone of a vintage tube amp pushed toward overdrive1 |
| DIRECT OUT | Balanced XLR output with a ground LIFT switch, delivering a low-noise, amp-like signal to the desk1 |
| 1/4 inch output | Standard output that allows a parallel signal to a pedalboard or bass amp1 |
The BASS control is the heart of the pedal for bass players. Rather than a simple shelving bass boost, it pushes energy around 100Hz while trimming the low-mids that can make a bass sound muddy, so the bottom gets bigger without losing definition1. The GRIT toggle sits on top of that as a character switch rather than a full overdrive control.
The two outputs are what make the ZIO a DI as well as a preamp. The XLR DIRECT OUT with its ground lift switch handles the desk feed, while the 1/4 inch output feeds your amp or pedalboard in parallel, so you can run both at once1.
Power: 9V, 200mA
The ZIO Analog Bass Preamp + DI runs on a 9V power supply and draws 200mA1. That figure matters for pedalboard planning: 200mA is a substantial draw for an analog pedal, well beyond what a small daisy-chain supply typically allocates per output, so a dedicated 9V output with adequate current is the practical choice.
For comparison, the guitar-focused ZIO Analog Front End + Boost draws only 20mA at 9V DC center negative2, a tenth of the bass version's consumption.
The ZIO family
The ZIO Analog Bass Preamp + DI is the bass member of a small family. Its sibling, the ZIO Analog Front End + Boost, is a guitar preamp/boost pedal and Source Audio's first all-analog effects pedal2. Where the bass ZIO is built around the BASS control, GRIT toggle, and XLR direct out, the Front End + Boost offers four selectable preamp circuits: JFET, Low-Cut, Studio, and E-Plex, each an all-original circuit design2.
| ZIO Analog Bass Preamp + DI | ZIO Analog Front End + Boost | |
|---|---|---|
| Voicing circuits | BASS control plus GRIT toggle1 | Four circuits: JFET, Low-Cut, Studio, E-Plex2 |
| Boost | Not specified as a boost pedal | Up to +20dB of signal boost2 |
| Outputs | Balanced XLR direct out with ground lift, plus 1/4 inch1 | Main and Tuner/Line outputs3 |
| Power draw | 200mA at 9V1 | 20mA at 9V DC center negative2 |
| Bypass | True bypass1 | True bypass2 |
| Status (Oct 2026) | Sold out1 | Sold out, listed at $199.00 sale price2 |
The E-Plex circuit on the guitar version "captures the focused and subtle grit of the preamps found in vintage Echoplex Tape Delay units," and the Low-Cut circuit reduces "tubby" bottom-end for a tighter sound with added headroom2. Both pedals use high-fidelity Burr-Brown op-amps, which Source Audio says give the ZIO line "extreme clarity and responsive pick dynamics"2.
Delicious Audio described the guitar ZIO's design goal as simple but ambitious: "Make Everything Sound Better!" The pedal takes a guitar's high impedance signal, sweetens it through one of its four preamp circuits, and outputs a strong low impedance signal unaffected by the buffered dry tones of other pedals4.
What reviewers said
Guitar World's Trevor Curwen reviewed the ZIO Analog Front End + Boost, finding that its four preamp options are a plus, and describing it as "capable of up to 20dB of boost via a choice of four different preamp circuits to colour the sound"3. MusicRadar's Jonathan Horsley similarly noted it "offers a healthy +20dB of boost per preamp voicing"5, and gearnews.com characterized it as functioning almost like "a Buffer / Preamp / Booster all in one," helping condition the signal6. These reviews cover the guitar version rather than the bass ZIO, but they describe the shared analog approach of the family.
"In essence, it helps condition your signal, almost like a kind of Buffer / Preamp / Booster all in one."
Videos
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Nate Navarro
The Bass Channel
Questions
Is the Source Audio ZIO Bass Preamp + DI true bypass?
Yes. Source Audio lists the ZIO Analog Bass Preamp + DI as true bypass, so with the pedal disengaged the bass signal passes through without the circuit in the path. The same is true of the guitar-focused ZIO Analog Front End + Boost.
Does the ZIO bass preamp have an XLR output?
Yes. The DIRECT OUT is a balanced XLR output with a ground LIFT switch, delivering what Source Audio describes as a low-noise, amp-like signal. A standard 1/4 inch output runs in parallel, so you can feed a pedalboard or bass amp at the same time as the mixing desk.
What does the Grit toggle do on the ZIO?
The GRIT toggle captures transformer-style breakup, the tone Source Audio describes as what occurs when a vintage tube amp gets pushed toward overdrive. It is a voicing switch rather than a full drive control, adding character on top of the preamp's clean analog signal path.
What power supply does the ZIO bass preamp need?
The ZIO Analog Bass Preamp + DI runs on a 9V power supply and draws 200mA, which is far more than a typical analog boost pedal. A dedicated 9V supply with enough current headroom is the safe choice; the guitar ZIO, by comparison, draws only 20mA.
Is the ZIO Bass Preamp + DI still available?
As of late October 2026, Source Audio's product page lists the ZIO Analog Bass Preamp + DI as sold out, and the ZIO Analog Front End + Boost is listed as sold out too. Check the maker's page for current availability.
What is the difference between the ZIO bass preamp and the ZIO front end and boost?
The ZIO Analog Front End + Boost is a guitar preamp/boost pedal with four selectable preamp circuits (JFET, Low-Cut, Studio, and E-Plex) and up to +20dB of boost. The ZIO Analog Bass Preamp + DI is the bass-focused version, built around a BASS tone control, a GRIT toggle, and a balanced XLR direct output for the desk.
Sources (6)
- ZIO Analog Bass Preamp + DI, Source Audio
- ZIO Analog Front End + Boost, Source Audio
- Source Audio ZIO Analog Front End + Boost, Guitar World, 2022-06-10
- Source Audio ZIO Analog Preamp/Boost, Delicious Audio, 2024-01-09
- Source Audio's ZIO Analog Front End + Boost packs four preamp circuits into one powerful tone-sweetening stompbox, MusicRadar, 2022-01-14
- Zio Analog Front End + Booster, gearnews.com, 2022-01-13
