Comparing Plugs of Center-Negative 9V Adapters for Guitar Pedals

Recently, we received an inquiry about an adapter plug that couldn’t be fully inserted into an effect pedal’s jack because it was recessed too deeply. This issue, where the plug shape doesn’t match the adapter jack, preventing proper power connection, has been common with some pedals for years. For example, the classic wah pedal, the GCB-95 CryBaby, has a thick casing and a small hole, making it difficult to fully insert some plugs. Occasionally, you might even find modified units with widened holes on the used market.

While I’m aware that adapter plugs come in various shapes, I’ve never compared them in detail. This time, I’ll measure and compare the ‘length of the plug terminal’ and the ‘size of the grip’ using calipers. Keep in mind that such plugs may undergo minor changes in design, so the measurements are based on the current situation as of July 2024.

Key points to consider are the length of the terminal tip and the size of the grip’s end.

The adapter hole of the GCB-95 CryBaby looks like this:

When you look closely, you’ll notice that the center of the jack is not at the center of the hole. Thus, the hole’s diameter is about 9.5 mm, but the adapter plug must be around 9.2 mm to fit all the way in.

I am using digital calipers, but there may be a margin of error of about ±0.5 mm. These measurements are approximate.
I’ll also measure the body size of some adapters that don’t have listed dimensions. These sizes do not include protrusions.

Contents

1. BOSS / PSA-100 Power Adapter
2. Providence / PAP-509DCJ-2
3. NUX / ACD-006A
4. Visual Sound / 1 Spot 9V AC-Adapter
5. Zoom / AD-16 AC Adapter
6. Korg / KA181
7. Jim Dunlop / ECB-003M
8. One Control / EPA-2000 High Capacity Adapter
9. Moridaira / Silent Power DC-009SP
10. CLASSIC PRO / DC9V 0.5A 2.1 mm Center-Negative Power Adapter

BOSS / PSA-100 Power Adapter

Body Size: (W) 30 mm × (D) 68 mm × (H) 67 mm

First is the classic BOSS PSA-100S. The plug length is 9.5 mm, and the grip end measures about 9.65 mm. I’ve been using this for many years. Though I always thought the plug was short and thick, the measurements confirm it. Among those compared here, it had the thickest grip.

Providence / PAP-509DCJ-2

Body Size: (W) 48 mm × (D) 77 mm × (H) 40 mm

The Providence PAP-509DCJ-2 plug length is 9.2 mm, with a grip end of 8.00 mm.
With an output of 200 mA, it might not be suitable for power-hungry digital devices but should work well with distortion pedals.

NUX / ACD-006A

Body Size: (W) 38mm × (D) 62mm × (H) 42mm

The NUX ACD-006A has an L-shaped plug, measuring 9.8 mm in length and 8.5 mm at the grip end.
The grip’s end is small, which is the part measured.

Visual Sound / 1 Spot 9V AC-Adapter

Body Size: (W) 27 mm × (D) 74 mm × (H) 45 mm

The Visual Sound 1 Spot is now a standard. The plug length is 10 mm, and the grip end is 9.1 mm.
The grip’s end is slightly smaller.

Zoom / AD-16 AC Adapter

Body Size: (W) 35mm × (D) 23mm × (H) 49mm

The Zoom AD-16 is also a common one. The plug length is 9.3 mm, and the grip end is about 9 mm.
Note that Zoom adapters might not work with non-Zoom products due to compatibility issues.

Korg / KA181

Body Size: (W) 28 mm × (D) 64 mm × (H) 41 mm

The Korg KA181 has a plug length of 10 mm and a grip end of about 8.5 mm.

Jim Dunlop / ECB-003M

Body Size: (W) 34 mm × (D) 55 mm × (H) 48 mm

The Jim Dunlop ECB-003M has a plug length of 10 mm and a grip end of about 8.6 mm. The casing has an interesting shape, likely designed to fit the GCB-95.

When inserted into the GCB-95,

it fits perfectly.

One Control / EPA-2000 High Capacity Adapter

Body Size: (W) 40 mm × (D) 65 mm × (H) 28 mm

The One Control EPA-2000 has a plug length of 9.5 mm and a grip end of about 9 mm.

This plug can be used with the GCB-95 but might come loose because the L-bend is shorter.

Moridaira / Silent Power DC-009SP

Body Size: (W) 29 mm × (D) 26 mm × (H) 50 mm

Moridaira’s original adapter, with a plug length of 9.5 mm and a grip end of about 9 mm.

CLASSIC PRO / DC9V 0.5A 2.1 mm Center-Negative Power Adapter

Lastly, the CLASSIC PRO has a plug length of 10 mm and a grip end of about 8 mm.

Comparing these, did you notice any differences? There might be some inaccuracies, so please consider these as rough guides.

Even other pedals with recessed adapter jacks might not accept plugs fully.
While longer terminals and smaller grips may fit various pedals, short and thick ones feel more robust. Additionally, if the terminal is too long, it might protrude slightly even when fully inserted, causing an unstable fit. When fitting pedals into a pedalboard, shorter ones might be easier to manage.
The specific reasons behind each manufacturer’s plug design choices are unknown, but each likely has its rationale.
It’s unlikely that pedal manufacturers have their own adapter factories; they probably order from another factory, which could also influence design.

I also measured the adapter bodies, but shapes vary greatly, making it hard to decide what’s the width or depth. Please consider the longest dimensions provided in the accompanying pictures.

About 20 years ago, when I started playing guitar, the only center-negative 9V adapter readily available was the old BOSS PSA-100 at music stores (or I just don’t remember other adapters).
Now, there are numerous pedals and adapters, each with its fans. The adapters mentioned here are just a few examples.
While there may be compatibility issues between adapters and pedals, it’s hard to pinpoint the specifics. It’s more than just the power consumption.

For basic knowledge about adapters, refer to the article below:

⇒ Mastering How to Choose an AC Adapter

I might also cover power supply cables in future articles.