The Noise Receiver?


Squire Champ 15 amplifier

  This cute, unassuming looking little amplifier was sitting in Guitar Center with a tag on it for $25. Sounded great I thought, but there were two or three other people checking out amps nearby at the time. Real amps, like Marshalls and stuff. So I wasn't able to hear too well, but what the heck, $25 for a channel-switching amp you can carry with two fingers? Very handy, especially since its 15 mighty watts could blow away my friends with their fancy 5 watt amps!

  I bought it and brought it into the studio and really listened to it for the first time. I plugged in my Strat, and with its single-coil pickups it is known to buzz a little, but this thing was crazy! I tried the usual tricks of turning this way and that, and moved the amp around, but the buzz was still way louder than anything else I use here. Here's a sample:

Hum with nothing plugged in

  Yes, it made that much noise sitting on my workbench with nothing plugged in to it. You should have heard it when I turned on my fluorescent work light! Oh wait, you can hear it...

Hum with nothing plugged in and the light on

  Because it hummed like this with nothing plugged into it I figured that something had come loose inside- a ground wire had come off or something. I never heard a solid-state, modern amp buzz like this. Tube amps with bad power supplies, yes, but not a fairly new solid state amp. So I knew I was going inside it to try to fix it, and I decided to try to get some sort of objective measurement of any improvement I could make. I set up a mic and recorded the hums.

Squire Champ 15 amplifier test setup

  All very scientifically, with the mic exactly 3" from the grillcloth and all the settings at known positions.

  The solid back comes off with a few screws, and as you can see by the light shining through the ports, I had the back off when I recorded my buzz.

Inside a Squire Champ 15 amplifier


  Here's the inside. Very neatly built, in my opinion, just like the rest of the amp. I mean, it has real Tolex, and big-boy metal corners, and even the sparkly-grey grill cloth like real Fender amps! And a decent handle, too! The only thing I wasn't so crazy about was that the power cord is permanently attached, so it doesn't travel as well as it might, but no big deal.

  I couldn't find any loose or broken wires inside. This could be a harder fix than I hoped for. I turned the amp back on and started moving my hand around behind the amp section to inject some nice AC into my new noise receiver.

  The buzz level got really high when I moved near the input section, there to the right in the rear view. This is to be expected, because this is where the most amplification happens. You can see that there is a piece of silver shielding along the inside of the case on that side- I checked to be sure it was in contact with the chassis of the amp- it was. But there was nothing below or behind that section of chassis to shield it, meaning that any RF signal coming at this from the point of view of the camera could go unimpeded into the input section!

input 
section of a Squire Champ 15 amplifier

  Here's a closer look at the input section. The two black squares to the right are the input jacks, and I tried wiggling them a bit to see if some connection was loose. Things got real noisy when I touched them! Surely they wouldn't design an amp and make it this neat and then allow an unshielded input section to ruin the whole thing? But so it seemed.

  In a bit of undocumented work, I took a piece of aluminum foil and shaped it to fit around the input section. Nothing too tight, mind- I didn't want to short anything out. I just built a shell around that area. Lo and behole, when that aluminum foil shield made good contact with the chassis, the buzz disappeared. I decided to build a permenant shield and mount it.

raw shield  
for the input section of a Squire Champ 15 amplifier

  Here's phase one. I found some lightweight aluminum sheet in my scrap pile that was perfect! You might also make a shield out of a beer can. I cut it to make a tab for mounting, because you need a good connection with the chassis.

bent shield
 for the input section of a Squire Champ 15 amplifier

  Phase two. A little trimming, a little bending and another mounting hole...

shield
 mounted inside a Squire Champ 15 amplifier

  Phase three. The completed thing in place. The shield does not touch the circuit board, just the chassis. I set the amp up as before and recorded the buzz levels.

Hum with nothing plugged in and new shield

Hum with nothing plugged in and new shield and the light on

  I know it's working now, because there is no difference between the noise level with the light on and off. But what I find very interesting is that the level of hiss has seemingly increased. I attribute this to the possibility that the buzz was masking those higher frequencies before- or maybe the buzz was sucking power that is now free to amplify the hiss. It's unclear, but the hiss sounds much worse in this recording than it is in reality.

  Turns out that this amp is very cool. The tone section (bass, mid, high, presence) is made such that if you turn them all down to zero, no sound passes through! In practice, this makes the tone settings very effective. You can dial in a lot of wacky sounds on this beast. The overdrive is typical solid-state nastiness, but by rolling off the highs at the guitar I found some sweet sustained distortion at very low levels.

  So if you see a deal on these, grab one and do the mod if you get buzz! Just be aware that there are a lot of Squire Champ versions out there- I don't know when this one was made, but it's fairly new. Look carefully at the front panel- this is the only one I've seen with channel switching and external speaker and headphone jacks.

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