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Controlling A Neo Instruments Ventilator II From A Stage Organ

DIY Cable Solution By Hugh Robjohns
Published April 2023

Rotary Club

This DIY adaptor cable will fool your organ into thinking a real Leslie is attached.

The Neo Instruments Ventilator II Leslie emulator pedal (reviewed in SOS November 2014) is widely regarded as a one of the very best hardware Leslie cabinet simulators currently available, with many experienced organ players preferring it to the simulators built into their stage organs. There are several versions of the Ventilator of different sizes and capabilities, and many users are quite happy to tread on the pedal’s own stomp buttons to change Leslie speeds. However, the large Ventilator II model includes a remote‑control connection which allows speed switching via a separate foot pedal, a classic ‘half‑moon’ (Hammond CU‑1) switch mounted on the organ itself, or even an expression pedal for fully variable speed control.

Socket To Me

Despite all this versatility, some players prefer to use the dedicated fast/slow speed buttons on the organ console itself, which normally control the internal Leslie emulator. Fortunately, most stage organs have a special socket for connecting a real Leslie speaker and, when plugged in, the onboard emulator is automatically disabled and the fast/slow controls routed to the external Leslie instead. But wouldn’t it be great if there were a way of fooling the organ into believing the Ventilator II pedal is a real Leslie, thereby disabling the internal emulator and routing the fast/slow controls directly to the pedal? Well, there is! And it just requires a custom adaptor cable to plug into the organ’s Leslie socket.

There have been a lot of different Leslie speaker models over the years, and they’ve used a variety of similar‑looking but incompatible connection formats. But thankfully, modern stage organs and Leslies really only use two connection formats: an 8‑pin DIN socket or an 11‑pin Amphenol socket; the latter is far and away the most common.

Since neither connector carries mains power (unlike most of the vintage Leslie interfaces) it’s relatively straightforward and safe to construct an adaptor cable. Only modest soldering experience and DIY skills are required and all the parts are available from specialist retailers or online marketplaces. Please note, though, that this is not intended as a step‑by‑step constructional guide, and while the information in this article has been carefully researched it is used entirely at your own risk — neither SOS Publications Ltd nor the author can accept any responsibility whatsoever for misprints, void warranties, or any harm to equipment or persons!

Although it’s virtually the modern standard Leslie interface, I’ve been unable to find a ready‑made adaptor cable for the 11‑pin format used on models such as Suzuki‑Hammond’s old XK3, the new XK5, the SKX and the SK‑Pro models, as well as almost all of the popular clone organs including Viscount’s Legend organ range, Nord’s C‑series organs, Crumar’s Mojos, and many more. So this article will concentrate on the requirements for this adaptor. Hammond already offer a ready‑made adaptor cable to connect a Ventilator II pedal to the 8‑pin DIN Leslie connector found on the popular (but no longer available) Suzuki‑Hammond SK1, SK2 and XK1‑c stage organs, but if you’d like to make your own I’ve included the wiring details in the ‘8‑Pin DIN Leslie Interface’ box.

Leslie Connection Overview

As I said earlier, an organ with a built‑in Leslie emulation needs to know if an external Leslie speaker system has been connected so that it can: (a) disable and bypass its internal Leslie simulator; (b) route the organ’s Leslie speed switching to control the external Leslie; and (c) in most cases also route the organ sounds via the Leslie connector instead of the normal line‑out connectors. This ‘Leslie present’ information is conveyed in different ways for the 8‑pin DIN and 11‑pin Amphenol connections, but it’s obviously critical that we replicate this feature for correct operation with the Ventilator II pedal.

While all Leslies accept a mono organ input signal to the Rotary speaker channel, many models also accept one or two extra line inputs to feed Stationary channels — fixed speakers typically used to reproduce non‑organ sounds. For example, many stage Hammond organs include extra voices like electric pianos, choirs, strings and so on, and those aren’t normally routed through the rotary speakers. So most stage organs provide two options for these extra voices: (a) send them to the Leslie’s Stationary channels, if provided; or (b) route them as usual to the organ’s own line outputs. The latter is normally the default condition, of course. Separating the organ and extra voices in this way is potentially helpful, too, improving mixing flexibility on stage.

Obviously, the Ventilator II only emulates a Rotary channel, so it’s important that the organ is configured to send only the organ sounds via the Leslie connector. In Suzuki‑Hammond models that is done via the configuration menu, under sub‑menus along the lines of: Leslie Parameters / External Leslie Speaker / Leslie Channels. The critical value is ‘1ch’ (usually the default), and this parameter is stored with all patches. In this configuration, pipe organ patches and extra voices on organs that include them will continue to play (in stereo) through the instrument’s rear‑panel line outputs as normal. The alternative setting in Hammond models is ‘3ch’, whereby pipe organ patches and extra voices are also routed through the Leslie connector to feed a real Leslie’s Stationary channels. However, using the adaptor cable would render them inaudible, as they are removed from the organ’s line outputs but won’t reach the Ventilator II either!

Having sorted out the audio path, we need to consider the speed control functions. The speed of all modern Leslies is set using two control lines which simply need to be grounded to activate and sustain the required mode. One line selects the slow (Chorale) speed, while the other selects fast (Tremolo) speed. If neither are grounded the Leslie stops (Brake).

Neo Instruments have provided several different remote‑control options in the Ventilator II which are selected using the Remote function. This is a secondary mode of the unit’s variable knobs, accessed simply by pressing the Bypass and Slow/Fast stomp switches simultaneously. The Speed LEDs blink twice per second to indicate secondary mode is active and, once the parameters are set, pressing both switches again saves settings and exits the secondary mode.

To work correctly with the Leslie adaptor cable the Ventilator II’s Remote option needs to be set to Switch 2, which is with the control knob in the 9 o’clock position. This configures the unit to expect the latching grounded speed control signals which the organ generates.

Most stage organs now use an 11‑pin Amphenol connector to connect to rotary speakers.Most stage organs now use an 11‑pin Amphenol connector to connect to rotary speakers.

11‑pin Amphenol Interface

For the 11‑pin Amphenol Leslie connector, the system used to inform the organ that a Leslie is connected relies on detecting a DC voltage (of at least 12V) on pin 11. Obviously, when a real Leslie is connected that 12V is obtained from the Leslie’s internal power supply, but the Ventilator II can’t do that directly. We could use a spare 12V DC wall‑wart power supply for the purpose, but I think it’s more convenient to use the Ventilator’s own PSU since it has to be there anyway and the organ doesn’t draw any significant current from this sensing voltage.

The diagram shows the wiring for the 11‑pin Amphenol connector, viewed from wiring side.The diagram shows the wiring for the 11‑pin Amphenol connector, viewed from wiring side.Consequently, this design of adaptor cable terminates in the 11‑pin Amphenol plug at one end, with four tails at the other: a quarter‑inch TRS jack plug for the speed control functions, a quarter‑inch TS jack plug for the monaural organ audio signal, a 5.5 x 2.1mm coaxial socket to accept the Ventilator’s 12V DC supply, and a 5.5 x 2.1mm coaxial plug to pass that 12V DC supply through to the Neo Ventilator II. Both coaxial connectors are wired centre‑positive.

The 11‑pin Amphenol plug is available from specialist Hammond/Leslie spares retailers, but I’ve also seen them on popular online market sites quite regularly. Beware: the rear covers are often sold separately (and in different styles), and you need to make sure you get both parts! The plug typically comes with a large crinkly washer, which is intended to hold the plug into a chassis hole (such as in a Leslie amp); it’s not needed when using a rear cover, so don’t worry that you have a spare part and nowhere to put it! Pin numbers are normally embossed on the Bakelite plug body, and while some versions have solder tags to connect the wires, others just have hollow pins. For this older type, the wires have to be poked right down through the middle of the pin and soldered at the tip instead — so make sure you have plenty of terminating wire available, and a powerful soldering iron!

As well as passing audio and control signals, the 11‑pin Amphenol adaptor cable makes use of the Ventilator II’s PSU.As well as passing audio and control signals, the 11‑pin Amphenol adaptor cable makes use of the Ventilator II’s PSU.For the power connections the easiest option is to purchase a ready‑made extension cable with 5.5 x 2.1mm plug and socket. You could use a pair of very long extensions to run down to the Amphenol plug and back, but I prefer to keep the main current‑carrying part of the cabling as short as possible and so I spliced a ‘sensing’ cable into the middle of a short extension instead, with suitable insulation and heat‑shrink sleeving to isolate and reinforce the join. In my adaptor cable, this connection was hidden under more heat‑shrink sleeving where the control and audio tails break out of the main cable.

This powering arrangement means only three cables are needed from the Amphenol plug, rather than four, and I used Canford MSJ three‑pair miniature jacketed multi‑pair cable for the purpose ( This is available at around £6.70 (about $8) per metre, with 1m being the minimum length, so it’s quite affordable. Obviously, the required cable length depends on where you intend to place the Ventilator II and where the Leslie socket is on the organ, but 1.8m to 2m seems about right. In my cable, pair one carried the unbalanced audio (with the black core wired in parallel with the screen), pair two delivered the control signals terminating in a TRS plug, and the third pair carried the power sensing (using the black and red inner cores only).

Given the presence of a 12V DC supply with a reasonable current capability, it is obviously wise to test the adaptor cable connections very carefully after construction.

Given the presence of a 12V DC supply with a reasonable current capability, it is obviously wise to test the adaptor cable connections very carefully after construction, using a multimeter to check for continuity and shorts between each break‑out connector’s terminals and the appropriate Amphenol pins. Then double‑check all the power connections again to make absolutely sure there are no shorts or reversals. The required wiring is indicated in the table on the previous page. Note that several pins are unused in the adaptor cable and, for reference, that pins 2+3 are Stationary channel audio inputs. Also, pin 6 is grounded when the organ is working, to inform a real Leslie speaker to power up, while pins 9+10 are unused.  

Ventilator II Connection

Amphenol Plug


Audio TS Tip


Single Channel Organ Audio

Audio TS Sleeve


Audio Ground


Control TRS Sleeve


Control Ground

Control TRS Ring


Leslie Fast (when grounded to pin‑5)

Control TRS Tip


Leslie Slow (when grounded to pin‑5)

(If neither Pin‑7 or 8 are grounded the Leslie Stops)


Power In/Out Gnd


Control Ground

Power In/Out +ve


+12VDC provides Leslie Detection

8‑pin DIN Leslie Interface

The simpler 8-pin DIN version of the adaptor cableThe simpler 8-pin DIN version of the adaptor cable......and its wiring connection diagram, viewed from the wiring side....and its wiring connection diagram, viewed from the wiring side.The 8‑pin DIN version of the adaptor cable is much simpler, breaking out to a quarter‑inch TS plug for the unbalanced organ signal input, and a TRS plug for the remote speed control. The 8‑pin DIN plug (standard, not mini!) is widely available from most electronic component suppliers. Here in the UK, for example, the Deltron metal‑bodied version is available for under £3 ($3.60) from CPC (

The cable entry hole in the Deltron strain relief is only 6mm in diameter, but it’s possible to squeeze two very slim cables into the DIN plug. However, I opted to use a more robust single multicore cable, partly because I have a lot of it lying around (I use it for wiring stereo mic arrays all the time!).

So in my version I used Van Damme Blue Series pre‑jacketed 2‑pair cable ( The overall diameter of this cable is 7.5mm, so I had to remove the rubber strain‑relief sleeve from the plug and replace that function with generous heatshrink sleeving over the whole plug and cable. The two inner pairs in the multicore have their own jackets and are robust enough to be wired straight into the TS and TRS plugs.

The wiring arrangements are listed in the table below. The link between pin 5 and the control ground on pin 2 informs the organ that an external Leslie is connected — no external power supply is required in this case. If neither pin 7 nor 8 are grounded, the Leslie stops. Pins 4 and 6 are not connected.

Ventilator II Connection

DIN Plug


Audio TS Plug Tip


Single Channel Organ Audio

Audio TS Plug Sleeve


Audio Ground



‘Leslie Present’ (connect to Pin‑2)

Control TRS Plug Sleeve


Control Ground

Control TRS Plug Ring


Leslie Fast (when grounded)

Control TRS Plug Tip


Leslie Slow (when grounded)