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Radial Pro DI Passive Direct Box

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Product Details

The Radial ProDIs are high-quality, full-range passive direct boxes equipped with custom-made audio transformers for exceptional signal handling without saturation and with extremely low phase distortion in the critical bass and mid regions. The result is exceptional clarity and definition at an attractive price point. Ultra-compact and made of 14-gauge steel, both ProDI models feature internal I-beam construction with a 'book-end' outer shell for extreme durability in the most demanding environments. The ProDI and ProD2 share the same feature set. Available in single-channel (ProDI) or dual-channel (ProD2) stereo, these exceptional direct boxes offer performance superior to any other DIs in their price range and are ideally suited for use with acoustic guitar, bass and keyboards.


- Full range passive direct boxes
- Isolation transformer eliminates noise
- Very low harmonic and phase distortion
- Compact and rugged design
- Ideal for live sound and studio

ProDI/ProD2 Development

When the Radial JDI was introduced in 1996, it revolutionized many preconceived concepts of what a direct box is and how a passive DI can, in many instances, be a better choice than it's active counterpart.The central task of a direct box is to convert an instrument's signal from high impedance to balanced low impedance. This enables the signal to travel long distances without adding noise and provides a proper load to the mixing console input for improved audio performance.Active direct boxes employ electronic circuits to change the impedance from hi-Z to lo-Z and balance the signal. Passive DIs employ a simple passive transformer to do the work. Active DIs require batteries, 48V phantom-power or external power supplies to power their circuits. Passive transformer-equipped direct boxes do not require any power to perform their task. The advantage of a transformer over typical active circuits can be summarized as 'a great device to reduce system noise' in a sound system.A transformer is an ingenious device that works by converting an electronic impulse, generally referred to as a current, into a magnetic field and then back again into a current. This 'magnetic bridge' has the distinct advantage of decoupling the source instrument from the receiving mixing console or mic preamp. When you hear a hum or buzz in the sound system, this is usually caused by stray voltages traveling through the wire causing havoc at the receiving end. This effect is commonly referred to as a ground loop. The most effective solution to this common malady is to place a transformer between the two offending devices.If the solution is so easy, why aren't all direct boxes passive? The trick lies in the quality of the transformer. The Radial JDI, the Duplex, and the JD6 all employ the world's finest audio transformer, Jensen, to manage the task. The problem lies in the fact that high quality transformers are expensive. These employ hand-stacked and laminated nickel core materials, precise winding schemes and expensive mu-metal Faraday shielding, all of which adds up to big bucks. Cheap transformers employ iron core materials and as a result, tend to saturate quickly, causing harmonic distortion and phase shift resulting in groups of frequencies exiting the transformer at different intervals or out of phase. Bottom line -
- cheap transformers sound bad.The quick solution is to employ an active circuit to balance and convert the impedance. Although this works and active DIs have their advantages, they do not provide any isolation and therefore are ill-equipped to eliminate ground loops.The Radial ProDI and ProD2 direct boxes employ a custom-made transformer that is fashioned around the Jensen transformer they use in the more expensive Radial JDI. No, the ProDI is not quite as good as the industry standard JDI (see comparison below), but considering it is half the price, the performance is nothing short of impressive.

Using the ProDI and ProD2

The best feature of the ProDI (and ProD2) is 'plug & play' ease of use. All you do is connect the instrument to the 1/4 in. input(s), the 1/4 in. through jack(s) to the stage amplifier(s) or mixer and the XLR output(s) to the mixing console and you are done. Any distortion? Hit the -10dB pad. Any noise? Just depress the ground lift switch.You will find that with acoustic guitars and basses, the natural tone of the instrument will shine through with a smooth and musical rendering. For electrically powered devices such as keyboards, the ProDI will immediately eliminate troublesome ground loops while delivering solid dynamics with a full rich sound.Look inside a ProDI or ProD2 and you will find the build quality and components to be of only the highest professional standards. Radial's proven construction methods and materials ensure years of trouble-free service. The ProDI and ProD2 feature audio transformers custom made to exacting standards to achieve the highest possible audio quality while maintaining an affordable price. The ProDI and ProD2 easily outperform all other direct boxes in their price range in both signal integrity and features

Inside the ProDI and ProD2

- Isolated XLR connectors to eliminate chassis ground potential.
- Custom audio transformer on input provides 100% isolation to eliminate hum and noise causing ground loops while maintaining signal integrity.
- Military spec PC board with full surface ground plane to reduce susceptibility to RF noise.
- High grade switches -
- long life, high cycle for reliable performance.
- 14-gauge steel welded I-beam construction makes it virtually impossible to torque the PC board.

ProD2 Input and Output Panels

- Pad -
- 15dB pad for left channel reduces the level going in from loud sources that could overload the circuit and cause distortion.
- Left input and thru -
- instrument 1/4" input and thru-put to amplifier.
- Right input and thru -
- instrument 1/4" input and thru-put to amplifier.
- Pad -
- 15dB pad for right channel reduces the level going in from loud sources that could overload the circuit and cause distortion.
- Book-end design creates a protective zone around the switches & connectors, indestructible 14-gauge steel construction.
- Full no-slip rubber bottom pad provides mechanical isolation, electrical insulation and prevents unit from sliding around.
- Left -
- balanced male XLR output connector, AES standard with pin-1 ground and pin-2 hot.
- Lift ground pin-1 -
- switch lifts the ground to pin-1 on both channels.
- Right
- balanced male XLR output connector, AES standard with pin-1 ground and pin-2 hot.
- Heavy-duty baked enamel finish for excellent durability and great looks for years!


The ProDI and ProD2 are designed to withstand the rigors of the most demanding high-use professional environments. Radial pioneered the use of it's innovative 'book cover' design, which provides a protective zone around the switches and connectors that keeps these components safe.Stress on circuitboards causes broken and intermittent solder joints, a common cause of failure in commercial rental and other high-use environments. Radial's 14-gauge welded I-beam inner chassis and 14-gauge outer shell greatly reduce the possibility of torque stresses being applied to the PC board.A full-bottom no-slip rubber pad works double-duty by providing protection from electrical shock and making sure these DIs stay put.

ProDI/ProD2 FAQs

Q: Why do some people feel active direct boxes are better than passive DIsA: Comparing active DIs to passive ones is akin to comparing condenser mics to dynamics.Condensers tend to have more 'reach' and upper end clarity, while dynamics tend to be bolder and better suited to handling transients without distortion. Active direct boxes are signal preamplifiers that draw very little current from the instrument and because of their higher input impedance, tend to have more reach and sparkle. The high input impedance results in less loading on the pickup, an effect that can cause passive pickups, as found on vintage basses and electric guitars, to sound thinner. Today, most basses and acoustic guitars employ battery-powered preamps that buffer the signal and are not affected by loading. Most pros have some of each depending on the tone they are looking for or the problem they are trying to solve.Q: If the Radial DI is the best, should I spend more money to buy it?A: This depends entirely on the sound system you are using. Most PA systems are not capable of producing the bandwidth that comes out of the Radial JDI and therefore, the Radial ProDI is a good solution.Q: What causes ground loops?A: When manufacturers build their products, the internal circuit and outer shells are teaming with electrical currents traveling all over the place and returning to the safety ground. This ground reference voltage varies between manufacturers and when two devices are connected together, these 'stray' voltages can often combine to create 60 cycle hum commonly known as a ground loop. A good transformer provides an effective solution in reducing this 'common mode' noise and is the reason why passive direct boxes are often preferred for live concert touring.Q: Is the ProD2 two separate DIs in one?A: Yes. Each channel inside a ProD2 is completely isolated from the other and is the same as having two ProDIs in a single box. The ProD2 was designed for stereo keyboards and devices (such as CD players) that need to be balanced.Q: Can I rack-mount the ProDI or ProD2A: The ProDI is not rack-mountable while the ProD2 is. In fact, with the J-Rak, you can jam in 16 separate channels (8 x ProD2) in two rack spaces, making it ideal for large keyboard rigs on tour.Q: Can I use a headphone out into the ProDIA: Yes. Keep volume low and use the pad. Listen for distortion as overly high levels can saturate the transformer.Q: Can I use a ProDI backwards for reamping?A: Yes. Careful on the level as it should be very low: mic level -
- not line level!Q: Will phantom-power hurt the ProDIA: No, phantom-power is DC and very low current. The ProDI will ignore it.Q: Can I run a guitar into effects and then into the ProDI for direct recording?A: Yes! The ProDI will eliminate noise caused by stray voltages and provide a smooth, natural response.
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- Frequency response: 20Hz to 20kHz (+/- 2.5dB)
- Harmonic distortion: 0.01% (20Hz to 20kHz)
- Phase distortion: 1 degree at 1kHz, 8 degrees at 20Hz
- Common mode rejection: -90dB @ 60Hz
- ProD1 input impedance: 140 kilohms
- Output impedance: 600 ohms
- Input pad: -15dB
- ProD1 size (W x H x D): 2.75 in. x 4.25 in. x 1.75 in. (70mm x 108mm x 44mm)
- ProD1 weight: 1.2lbs / .54kg
- Construction: 14-gauge steel chassis & shell, baked enamel finish
- ProD1 options: none
- Warranty: 3 year limited warranty

When will I receive my shipment?

We ship on business days (Saturday, Sunday, and holidays are not business days). Packages ship from Mississippi, Nevada, New Jersey, or Ohio -- we cannot guarantee that any product will ship from a specific warehouse. Expedited Shipping (1-Day Air and 2-Day Air) is the only way to guarantee that you will receive an item within a certain time frame. Delivery estimates for expedited shipping options are listed on the product page for the item in question. All expedited shipments are delivered Monday-Friday.

Ground Shipping typically takes 1-4 business days from the date of shipment (for orders within the 48 contiguous United States). Residential ground and Free 2-Day shipments are delivered Tuesday-Saturday. Commercial ground and Free 2-Day shipments are delivered Monday-Friday. Make sure to select the proper address type for your address in checkout, as delays may occur if your selection is incorrect.

For APO/FPO customers, all orders ship via USPS. Expedited shipping is not available. Tracking for these orders is not available.

For customers shipping to a PO Box, the order may need to be shipped via USPS. For this reason, expected delivery dates cannot be guaranteed.

Do you ship to my location?

For most products shipping to the continental United States, customers may choose Ground, 2-Day Air, or 1-Day Air delivery. We also ship to Alaska and Hawaii; however, due to carrier restrictions, we cannot ground-ship to those states.

In addition, we ships to the following destinations, though some restrictions apply:

  • Canada
  • Puerto Rico
  • U.S. Territories

See instructions below for how to search the site by our eligible shipping destinations.

Note: We cannot change a shipping address on an order after it has shipped. If an order is returned because it couldn't be received at the listed shipping address, we will accept the return but will not refund the shipping charges.


We ship a lot of our most popular gear to Canada! To determine if item(s) ship to Canada, add the item(s) to your cart and enter your shipping postal code. Items that ship to Canada are sent via International Air, and delivery is typically 2-5 business days from the date of shipment.

Canadian orders are charged in U.S. dollars. Actual charges are dependent on your bank's conversion rate. Your bank may assess additional fees for international orders.

Although items shipped to Canada receive their full factory warranty, they must be returned to a United States service center for repairs. We're not responsible for any shipping or customs fees incurred in such a case.

Puerto Rico

We ship many items to Puerto Rico. To determine if item(s) ship to Puerto Rico, add the item(s) to your cart and enter your shipping zip code. Eligible items ship via International Air, and typically arrive 2-5 business days from the date of shipment.


We ship to APO/FPO addresses for free, though over-sized items may be ineligible. To determine if item(s) ship to your APO/FPO address, add the item(s) to your cart and enter your shipping zip code.

U.S. Territories

We ship eligible products to American Samoa, the Federated States of Micronesia, Guam, the Marshall Islands, the Northern Mariana Islands, Palau, and the Virgin Islands. Eligible items typically arrive 2-7 business days from the date of shipment.

What about customs fees?

Please be aware of customs fees such as taxes and duties, which are not included in our shipping charges. Customs fees vary from location to location. Please check with your local customs office for more information on the fees in your area. If you refuse to pay these fees, your order will not be delivered. We cannot refund shipping charges if an item is returned due to refusal to pay fees, and a restocking fee may be applied to cover the cost of return shipping. Customs fees are non-refundable.

Which items ship immediately?

Most orders ship the same business day your order is placed when you place a valid order before the shipping deadline.

Immediate shipment is available Monday-Friday. A valid order placed before 5 p.m. EST will ship the same day when using Ground or Free 2-Day shipping. Ground and Free 2-Day shipping orders placed after 5 p.m. EST will ship the next business day. Many orders using an expedited shipping method (2 Day Air or Next Day Air), and placed before 10 p.m. EST, will ship the same day.

Shipment and availability information updates from our warehouse to our website almost in real time. We are highly confident of the status of each item when you view a page. However, we do not reserve inventory being viewed or even placed in shopping carts, so we cannot guarantee an item's availability until you have placed your order. In particular, if you have been in the checkout area for more than about 10 minutes, we do recommend that you refresh the page to get the most current inventory prior to checking out.

What is a valid order?

A valid order is for a valid item at a valid price, placed with a credit card with complete and verifiable address and other information. Details.

Does immediate shipment mean immediate delivery?

Once an order is shipped, our carriers (Federal Express and UPS) typically guarantee a service time for when the order will be delivered to you. Our carriers have a very good record of delivering at their promised service time. We will ship immediately, and on all items, we will refund expedited shipping charges if the carrier's service levels for your chosen shipping method are not met.

If a product is in stock, is there any reason it will not ship immediately?

Exceptions are very unusual, but here are some examples of reasons that might prevent us from shipping immediately:

  • Warehouse, call center, or web operations lose power or telecom connectivity.
  • Warehouse, call center, or web operations lose capability due to adverse weather (blizzard), safety threat, or other factors.

What can I do if I don't feel you've lived up to your guarantees?

If you ever feel we have not lived up to any of our guarantees, we want to know about it -- and we want a chance to do right if we agree. Contact Us.

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