Music Mart, United Kingdom, by Kevin Morgan - All Rights Reserved 08/01

The U5 from Avalon Design proves that there can be more to Direct Injection than you might have thought. Kevin Morgan checks it out.

The U5 DI box from Avalon costs a shade under 500 quid, a lot of money for a DI box, but if you were to invest your money in one you really would be getting a fair deal. First, it’s not just a DI box, but a DI and pre-amp. Second, it comes from Avalon Design, a company renowned for top quality audio gear whom, with the U5, have probably realized the world's most versatile DI and pre-amp unit.

Let's get down to business

Avalon has been producing non-compromised top quality audio equipment out of their San Clemente, California base since the mid 80's. Like all Avalon products, the U5 features pure Class A audio amplifiers and is of sturdy, attractive, and functional appearance. It also incorporates the following features:

- Instrument and speaker level inputs
- Six bank "Tone" selector curves for tone shaping
- Variable "Boost" for level matching and gain control
- High cut filter
- Headphone output
- Twin XLR BALANCE Mic and Line level outputs
- Earth isolation ground lift


The U5 is built to last. Two rack spaces tall and one-half rack spaces wide the internal working of the U5 are housed in a heavy-duty steel case with a brushed-aluminum face plate. All jacks and XLR sockets are attached to the circuit board by means of flying leads, and the front panel features two control knobs for BOOST and TONE settings that are machined from solid aluminum. The BOOST gain ranges from +2dB to +32dB in ten 3dB increments and the TONE control offers six different settings that aim to improve the sonic character of individual instruments.

As well as two beautiful blue LED's that indicate power and signal presence (triggered at -2 dB), the front panel also features four clear plastic push-buttons that glow a deep warm orange when activated and correspond to the following functions: High-Cut filter, Speaker to Input, Active to Thru, Tone, High-Cut filter is used to cut unwanted hiss that may be present in the signals high end. Speaker to Input initiates the U5's speaker input jack - more on this later. Active to Thru sends a post/EQ signal to the external outputs. Tone adds the selected contour shaping setting of the TONE knob - again more on this later.

A quick look at the U5's back panel finds the following: AC mains input socket, Ground lift switch, Headphone socket, Balanced Mic and Line level XLR outputs, and 400-watt speaker input jack. The mains input is for that of ICE or if you like kettle lead type. The ground lift switch, as featured on all good DI boxes, safely eliminates any mains hum from the incoming signal. The XLR outputs are self-explanatory and the 400-watt speaker input jack enables connection from an amplifiers speaker output.

Zero Load Effect

A major important feature of the U5 is its high input impedance of 3,000,000 Ohms. This is because that in the main, safety concerns aside, a DI boxes prime purpose is to convert a low level signal, generated by magnetic or electro-piezo pick-ups, to a Mic or Line level signal that's balanced. Now don't get me wrong as their are many good reasons for DI'ing synthesizers and other higher level signals but low level pick-up signals can be somewhere in the region of -50dB and need to be treated with a lot of respect. It is therefore important that a DI box, when amplifying a signal, dose not overload it by drawing too much current from it, and this is achieved by presenting the signal with a high or "zero load effect" input impedance like the U5 does.

Pure Class A

The U5 can match input signals to desired output levels by use of its BOOST control on the front panel. As stated, the BOOST offers variable gain of +30 dB in ten 3 dB increments. Also stated is the fact that the U5 does this through the use of pure Class A amplifiers. This is a non-compromise approach to signal amplification as pure Class A amplifiers use expensive discrete components rather than IC's. The reason for this is simple as it is the only way to go if you want a faithful linear amplification of the signal across all frequencies.

Studio Equipment for Musicians

It really does seem that Avalon understands the needs of the musician when it comes to DI'ing instruments. This relates to the fact that the U5 offers six different tone curves and a 400w speaker input socket. In the ideal world I would think that most musicians would prefer to Mic up their instruments in a live or recording situation. However, in the real world this is not always possible as issues like feedback and location may mean that your only option is to DI your instrument. The problem with DI'ing instruments is that you can never capture the real acoustics of the instrument like you can with a Mic. Also if you are a bass player or guitarist, then part of your sound has as much to do with your amp as it does your guitar.

However all is not lost. In this latter case the U5 enables you to feed the speaker output from your amp into it's speaker input socket. This means the amp's sound can be captured without having to stick a Mic in front of it. In the former case relating to acoustic instruments that feature some form of pick-up - the U5 offers 6 different pre-set EQ curves for guitar, string, electric and acoustic instruments in order to help compensate for any loss of character that these instruments may experience.


In use the U5 is simply wonderful. Any signal sent through is done a justice with added warmth and clarity and it's input sensitivity is quite outstanding. The six tone bank settings, of which at first I was quite dubious of, offer seriously thought out equalization curve's that work. Three of the curves are subtle variations of a flat response and could be applied to most instruments. Setting two is for bass guitar which acts like a notch filter around 1 kHz and settings 5 and 6 feature bass roll off where 6 also offers a bit of roll off at the top end.


My only criticism of the U5 relates to the fact that it uses DC coupling in its circuitry. Now my problem is not with DC coupling as I understands that using this helps retain signal depth, but the fact that it can cause the emission of cracks and pops on the output when alterations are made to it's setting. Therefore a nice feature would be that of a mute button as this could save many a journey to the console or amplifier.

In Conclusion

The U5 is pure Class A and this is reflected in its price. For the audio professional it is surely one of those essential pieces of kit that can make all the difference in certain situations. Those of you who seriously care about the sound you produce when you DI your equipment, you may want to consider the possibility of making the U5 a worthwhile investment.

DI Facts

Maximum Input Level: +24dBu unbalanced, 400w speaker input
Maximum Output Level: +30dBu DC coupled, balanced 600 ohms
Headphone Output: 0.5w into 600 ohms
Noise: -100dBu
High Cut Filter: -3dB at 8kHz
Dimensions: 8.5 x 3.5 x 12 in (216 x 88 x 305mm)
Weight: 7 lbs (3.2kg)

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