Guitars - BrixIT Blog

Harley Benton (Thomann) Power Attenuator test and teardown

Martijn Braam — Fri, 26 Feb 2016 23:00:00 -0000

Thomann just started shipping their new Harley Benton Power Attenuator. It can handle an input power of
80 watts (it contains an 100 watt L-pad, so they added some margin). It is a simple device containing
only passive components. It has a control for cabinet volume and line-out volume but they are not fully
seperated. The line-out level is a signel tapped of after the main cabinet volume knob so you can't
turn the cabinet completely off and use the line out for recording / headset usage.

Measurement

To measure the performance of the attenuator I connected it to a USB DAC/ADC and ran a frequency sweep with the
tool QLoud. QLoud is a tool normally used to measure the frequency response of a speaker using a measurement microphone.

I connected the line out signal of the DAC to the 16 Ohm speaker input of the attenuator and connected the
speaker output of the attenuator to the line in of the USB DAC. I also did a reference measurement by
connecting the input and output of my DAC/ADC directly together. The last set of measurements is connecting
the line signal to the input of my guitar tube amp (a Defender 5H 15 watt all-tube amp) and connecting the
line-out of the attenuator to the USB ADC.

Taking it apart

I'm also curious what is inside a fully passive device for ~100 euro so I took it apart. The case is
very easy to open, 4 screws on the front and 4 on the back and you can just lift the side and top part off.

The answer to my question: there is not a lot in it.

The main part of the attenuator is the 100 watt L-pad (The huge potentiometer behind the cabinet volume knob).
The signal from the amp is put almost directly accross the two outer pins of the potmeter so it will dissipate
most of the energy. The other large part of the circuit is a bunch of 50 watt resistors (The resistors with
orange cooling fins). They are there to match the impedance for the amp. The signal coming from the L-pad pot
and the small potmeter for line-out is put straight into the line-out and speaker-out jack on the PCB. The rest
of the circuit on the PCB is for the MicMod circuit that is supposed to simulate a cabinet and provide a balanced
microphone signal. I haven't tested the MicMod output yet.

Yeah, I'm not so great with CAD software

Modding a Behringer VT911

Martijn Braam — Sun, 03 May 2015 22:00:00 -0000

A few weeks ago I replaced my Line6 Podxt live multieffect pedal with a guitar amp, cabinet and 2 pedals.
The amp is a Kustom Defender 5H head and I use a Kustom 1x12 cab with it.

To replace the multieffect pedal I bought a Behringer VT911 overdrive pedal and a
Digitech Digital Reverb pedal. I chose for the VT911 because it contains a tube for the distortion and it
only cost me € 14,90 at Thomann.

The pedal sounds fine. Not great but it's a great pedal for the price. I searched on the internet
for easy mods to do on the pedal to improve the sound quality and found various suggestions on a few forums.

The first thing I did was adding a resistor and capacitor to the tube board to give the tube some extra
headroom. One of the major problems I had was that it doesn't really have a setting to only distort a little.
In the 0-1 range on the overdrive the pedal is usable but is very quiet even with the volume all the way to 10.
On the 1-10 range the pedal distorts so much that I wouldn't call this a overdrive pedal anymore.

The mod on the tube board increases the headroom so the tube distorts later and has a lot less compression
but the drive knob doesn't have a very large usable range. On the high distortion range the pedal also
starts to sound very muddy. The second mod adds another resistor and capacitor parallel to the drive potmeter
to change it's range and frequency response.

Here is a list of the exact values used in the mod:

Tube board:
  4.7 nF capacitor between pin 1 and 7 on the tube (marked 472)
  470 ohm resistor between pin 7 and ground (yellow purple black black brown)

Main board:
  1.0 nF capacitor connected to the outer pins of the drive pot (marked 102)
  100 Kohm resistor parallel to the same pot (brown black black orange brown)

I've recorded a sample before the mod and after the mod. Judge for yourself:

Some guitar refinishing

Martijn Braam — Sun, 28 Dec 2014 23:00:00 -0000

In the previous post about guitars I told you about building my own guitar. This one is about the finishing
of that guitar and 2 other guitars

The AtlasCaster

I've forgot to take some pictures from the first guitar (The AtlasCaster). The plan was to leave the guitar natural and only apply some glossy finishing. The first thing I did (without reading the manual) is applying some grain filler to the guitar. This obviously made it too white.

The AtlasCaster with grain filler

After actually reading some manuals on the internet I sanded off most of the filler and applied 1 layer of danish oil to the guitar. This really brings out the colour of the wood itself. The manual of the danish oil states that I need a minimum of 3 layers to have it permanently sealed but since I'm applying a high gloss finish after this I've decided that more layers is unnecessary.

The AtlasCaster with danish oil

After letting the danish oil dry I've applied 4 layers of nitrocellulose high gloss lacquer from an aerosol can. This is then sanded down with some 800 grit sanding paper and then polished with some car wax.

The red Stratocaster

The next guitar to receive a finishing upgrade is my brothers stratocaster. This stratocaster is made from a brandless guitar kit and actually the first built. After building this guitar was stained mahogany red.

The guitar kit used for the red Stratocaster

The stained guitar

After finishing the AtlasCaster with a glossy finish my brother decided the guitar should be candy apple metallic red. My brother sanded almost all the stain of and applied the grain filled (this time I was right) and after that some candy apple red metallic nitrocellulose aerosol paint.

The Les Paul model

At the same time as the red Stratocaster I've also refinished my Les Paul guitar kit This guitar was also stained with the mahoney red stain but I've only applied one layer.

I've sanded down this guitar only a little bit and applied some grain filler after. After the filler I've applied a whole can of nitrocellulose black paint and sanded all the texture down.

Since the guitar is completely black and I've painted over the white binding I thought it would be cool to add some gold lines around the edge. To add these lines I've used some gold gel pens. I drew 2 lines around the whole edge of the guitar (excluding the neck) and added some extra lines at the knobs and the switch on the guitar.

After drawing the lines I sprayed on a whole can of high gloss lacquer again and sanded that down with 800 grit sandpaper. After polishing I found that the lacquer looked scratchy so I ordered some 2000 grit sandpaper and sanded and polished it again. Now it only looks slightly scratchy under bright lighting but that seems unavoidable with a black nitro finish.

What's left to do...

The only problem left with the Les Paul model guitar is that it sounds crappy (because it has 2 for 5 dollar grade pickups, it sounds fine acoustic) so I ordered the Seymour Duncan hot rodded set. While browsing the website I also ordered a Fender custom 69
and a Seymour Duncan SSL-5 pickup for my AtlasCaster. Those should arrive in a few days so then I will upload some sound samples from both guitars.

From Atlas Cedar to rocking ear bleeder

Martijn Braam — Tue, 16 Sep 2014 22:00:00 -0000

Because of the urgent need for satellite reception of a friend of mine my brother needed to cut down an Atlas Cedar tree. The wood from this tree was just lying around so my brother and I decided to build a guitar with it.

The first guitar I've got is a Fender Squier Strat (made in India). After opening up the back cavity I found out that its completely made of plywood so the plan was to use all the parts from the Squier (including the neck) and to create a new body to fit it all

My brother owns a chainsaw jig to cut planks from the tree trunks. I've set the jig to the thickness of the guitar (43 mm) and cut out a part big enough for the guitar body. Online I found the design for a 53' model Fender Stratocaster as full-size PDF. I've used this to cut out the basic shape of the guitar.

After cutting out the basic shape I decided that I didn't want it some colour + white parts but instead I want it the original wood colour and everything else black or chrome. It would also be nice if it had some better pickups than the original china-made crap that was in the Squier so I ordered a new black pickguard, pickups, volume/tone knobs and 5-way switch (the old one was crackling and noisy).

While milling the holes for all the parts in the body I made a measurement error for the bridge. The hole was too big and a centimeter off in position. After having the hole filled up with another part of wood I ordered a new bridge (black of course) that was top-loading. That means I don't need to create a new hole for the bridge, its completely mounted on top of the body and doesn't require springs in the back of the guitar.

This is the new bridge, fully toploading

After putting together the parts i soldered the electronics. I reused the old pots and output jack from the Squier guitar. To connect it all I needed to solder 6 grounding wires to the housing of the volume pot (I don't use the tone pots) I found out that I burned the old pot. Also the new 5-way switch was crackling worse than the original one from the Squier guitar. I've decided to order original Fender ones from a local webshop (for a whopping 2 euro more than the knock-offs I got from ebay) and used those. The official Fender one is actually a logarithmic pot instead of the cheap linear ones thus making volume control much more precise in the low volume range.

After building the guitar and using it for a while I decided I would like to know how it sounds with an actual a-grade pickup so I ordered a DiMarzio DP187BK Cruiser Bridge(a rail humbucker) and put that in the bridge position. I've also replaced the tone knobs with two switches. One switches the polarity of the middle pickup and the other one connects the neck pickup to the volume pot so I can enable all three pickups at the same time.

Now the only thing that's left is the output jack and the neck of the guitar. Here are some audio samples recorded through a Line 6 PodXT Live emulating a Fender Reverb Deluxe Blackface