Most valve amps need to be run loud to get a good tone out of them, which often makes it difficult when performing in intimate settings, playing late at night or if you have picky neighbours. An attenuator is an electronics device that reduces the amplitude of a signal without appreciably distorting its waveform - perfect for getting that cranked amp sound, at a lower, more manageable volume level.

This simple attenuator box will allow lower wattage (less than 30 watt) amp users to push their amps that little bit more and maintain a reasonable volume level, with little tonal effect at low attenuation levels. The best thing is that it costs around $40 to build, so why not give it a shot?

Introduction

I stumbled upon this device when looking into attenuators for my amp. I wanted to push the amp a little harder, but could not justify the cost of the high end attenuators. This is not enough to tame a 100 watt Marshall on Warp 9, but enough to push a 15 watter than little bit harder and bring the volume back a notch, which is exactly what I was after.

This little attenuation box is good for low attenuation levels. As you start to attenuate your signal heavily you will, like most attenuators, notice some tone suck. If you stay below around 6dB of attenuation though, you should have very little, if any, effect on your tone.

You can modify this circuit more and add in some capacitors across the wipers of the L-Pad, to bring some treble back into your signal if you decide to attenuate heavily, as this is usually the first thing that gets sucked from your tone.

This circuit also has a DPDT switch built in so it can be true-bypassed, allowing you to leave it permanently connected in the back of your amp and bypassed when not needed. Technically the DPDT is not really needed as the attenuator does not really affect the signal when set on zero, but some people like having a circuit bypassed completely if it is not needed.

Although the L-Pad used is rated at 50 watt RMS, that doesn’t mean you can use a 50 watt amp with it. A tube amp dimed will put out more than it’s rated power, so I would stay under 30 watts if possible. It all does depend on how hard you drive the amp, and the level of attenuation. If you are not running your amp full pelt and not attenuating to heavily, you may be okay pushing the boundaries a little in terms of amp wattage. If you do decide to push the boundary a little, please keep a check on the L-Pad temperature. If it is getting too hot, stop immediately, as it can fail.

Parts

Parts needed to build this attenuator are listed below. I source all my electronics parts from Jaycar Electronics so I have included the Jaycar part numbers too.

• 1 x 50 watt RMS Fader Mono - CAT. NO. AC1672 (Also known as a L-Pad)
• 2 x 6.5mm Mono Chassis Socket - CAT. NO. PS0162
• 1 x DPDT Miniature Toggle Switch - CAT. NO. ST0572
• 1 x Sealed Diecast Aluminum Enclosure - CAT. NO. HB5064

Schematic

Here is the schematic diagram for the attenuator:

Assembly

Assembling this attenuator is not too difficult and involves drilling a few holes into the aluminum box and soldering a few connections.

If you look closely at the front of the L-Pad you’ll notice that the legs are numbered 1, 2 and 3.

A picture showing the 6.5mm jack is shown, with the ‘Tip’ and ‘Ring’ connectors labeled.

If you are not going to use a switch then:

1. Solder the tip of the input jack to leg 3 of the L-pad.
2. Solder the tip of the output jack to leg 2 of the L-pad.
3. Solder the ring of the input and output jack to leg 1 of the L-pad.

If you are using a switch:

1. Solder the top two lugs of the switch together to ‘jumper’ them.
2. Solder the tip of the input jack to the 1st middle lug of the switch.
3. Solder the 2nd middle lug of the switch to the tip of the output jack.
4. Solder the 1st bottom lug of the switch to Leg-3 of the L-pad.
5. Solder the 2nd bottom lug of the switch to Leg-2 of the L-pad.
6. Solder the ring of the input and output jack to leg 3 of the L-pad.

To mount the 6.5mm sockets and the L-Pad you will need a 10mm drill bit. Drilling through aluminum is easy, but one tip when drilling metal is to go slowly and work up to your final hole size. Start with a small size drill bit and go up in a few increments to reach your final hole size. I used a 1/8″, then a 3/16″, then a 1/4″, then finally drilled out the 10mm hole.

In the end I decided to drop the DPDT switch, as I needed a 12mm drill bit to mount it and didn’t have one on hand. I may fit it later on if I get my hands on a 12mm drill bit.

Using The Attenuator.

The attenuator is very simple to use. The jack on the left is the “input” jack, which connects to your amp and the other jack is the “output” to the speaker. The knob controls how loud the speaker is, it basically acts as a volume control. All the way to the right is “maximum”, which is maximum volume, or zero attenuation. All the way to the left is minimum volume ,or maximum attenuation.

Start with the knob all the way to right, on maximum, and then bring it down to achieve the level of attenuation you desire.

How Does It Sound?

I tried out this attenuator on my own amp, a Vox AC15cc. I found immediately that once you reach the 12 o’clock position, you start to notice a bit of tone suck creeping in. As you go further and further towards maximum attenuation, turning the knob to the left, the tone becomes more ‘lifeless’ as the guitar sound loses a lot of it’s attack, as well as the top end dropping off.

I leave knob set on about the 2-3 o’clock position, before any noticeable tone suck occurs, and dial my amp in from there when I’m using it. This way I’m getting the best compromise between attenuation and maintaining my tone, while being able to push my amp a little bit harder.

Conclusion

Given the price of this attenuator, it’s something worth trying out if you wish to bring the volume of your amp down a little. If you are attenuating heavily, do expect there to be some impact on your tone, although some people say you can compensate by dialing your amp in differently.

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