Tuesday, April 22, 2014

Final pictures of amp

I added labels using a paint pen to the front of the amp, so others can know what each switch or knob does. It felt so good to finally put screws into the amp, and seal it up for the last time.

Sunday, April 20, 2014

Footswitch Install

I drilled a hole for a 1/4" mono input jack, which has two terminals. After many attempts testing the input, I discovered which terminals should go where. One terminal is wired to the ground of the volume pot, and the other is soldered to the JP1 jumper switch. I tried multiple locations of where the second solder should be, included on both sides of R6 and R8. Across R6, it eliminated the push-pull option for the tone pot. Across one terminal of R8 created a mute button, which just silenced the sound output when pressing the foot switch. On the other side, the button created a metronome style click, which is useless.

The foot switch is a single button, SPST Johnson foot switch. The cheapest one on Amazon. I like the way the switch is wired up now. When the JP1 switch is off, the foot switch barely notches up the volume. If JP1 is up, then the foot switch toggles a louder, cleaner volume output. This easy volume boost is useful for playing solos live.

Tuesday, April 15, 2014

Paint it Black

I painted the front of the amp chassis black. The black is a special black, GM black. That means it is the same exact black as my Cadillac. People write songs about black Cadillacs, and now I have an amp that is as black as a Cadillac. I will use this amp to write songs about how black this amp is.
Anyways, since this is car touch up paint, the painting took forever and is very uneven. This gives it a unique textured look.

Tuesday, April 8, 2014

BitMo Push-Pull Tone Installed

Today, I installed the Push-Pull Tone control to the Valve Jr. This mod, which I bought from BitMo, uses a DPDT attached to a potentiometer, a resistor and a few capacitors. The potentiometer is wired up similar to the volume knob potentiometer, with the left-most terminal being power, middle being the wiper (variable), and the right being ground. The tone of the amp is affected by the bottom two terminals of the DPDT when the pot is in the "down" position. This is just one small capacitor (once again, I'm not supposed to disclose values. I think). When the pot is in the "up" position, the upper terminals of the DPDT is used, which is using three capacitors and a resistor. The external wires for the pot were soldered to two resistors already on the Valve Jr board, R6 and R8. Capacitor C4 was cut off of the board, to be overridden by the new pot components.

The result: This tone knob adds a great more tone options (of course) to the amp. When turned all the way left, or counter clockwise, the bass is super high. The resulting sound is mellow and jazzy. Towards the right, the treble is picked up, and it sounds incredible paired with a distortion pedal. Using the push-pull option gives you even more diversity with the tonal range. There are so many different styles of sounds I can get from the amp now, especially paired with my pedal board. I don't know what else I can want from an amp. Pictures below!

Starting soldering caps to the DPDT.

Soldering pot across two resistors on top of the board.

Current inside of amp. 

All mods visible.

Rear of recent mods.

Trio mod (far left), volume pot (left), tone pot (right), and bright switch (below, with green wires).

Saturday, April 5, 2014

Amp Tested with Pedalboard

I tested the amp tonight with my pedal board, so I got to run distortion through the amp for the first time. It sounds great, and surprisingly has no hum anymore. Either the pedals eliminated the feedback, or it just went away during the hours I wasn't in lab. This might have been because of interference from things that were on in Broun Hall.

Tuesday, April 1, 2014

BitMo Trio Mod Install

I got the BitMo Trio Mod in today, and I started working on installing it. It has a a scary copyright notice on the front saying I can't say what it does, blah blah blah, so I will only describe what it does and how, rather than describe the components it comes with and the direct connections.

This mod consists of two parts: a DPDT switch and a push/pull potentiometer with a DPDT switch attached to the back. If the pot is in the down position, it uses one set of the DPDT's poles, and if the pot is in the up position, the other set of the DPDT's poles are active.

The first mod only uses the DPDT switch, and works as follows.

First of all, DO NOT BREAK THE DPDT SWITCH. I have done this twice already. Make sure not to overheat the switch, and only solder it when in the "Off", or middle position. There is an option for both a Version 2 and Version 3 Valve Jr. Mine is the Model 2, but I have changed R1 to 1 Mega ohm, so it has the same affected component as the Model 3 amp. However, I chose to use the Model 2 schematic. To do this, cut R1 off from the main board and make two connections on to the end of R1, and to the place on the board where R1 previously was. If you did the Model 3 mod, you would keep R1 soldered in and solder these connections in parallel.
  • Option 1: "Bright." Straps a small "bright" capacitor in parallel with the volume pot output. Fender imitation sound. This setting has great gain. When you hit the strings hard enough, you've got a good classic rock tone already. 
  • Option 2: "Brit." British style sound, increases impedance for great mids. My favorite setting as of now, super clean and mellow, no matter how hard you pluck. 
  • Option 3: "Brat." Straps an extremely small capacitor with the volume pot output. Cuts the lows. So much treble. 
At first, I couldn't notice any difference, and just more hum. After playing a few chords on each setting, I noticed a major difference in each channel. I think the hum could be cut by using some insulation for the two long wires I used, shown below.

I covered the two long thin, orange wires with yellow electrical tape, and pulled two wires from the insulated wire that came with the kit that I did not use. So now, all wires should be insulated, and there are no unused wires floating around. Result? No less hum. It might be interference, since the DPDT switch is right next to the volume pot. That was advised against. I might build some sort of smallmouth Faraday cage to isolate the issue.

Notice the long orange wire to R1 from the DPDT.
Current front of the amp. New DPDT switch is far right, and new push-pull pot will be above the input (hole already drilled).

Tuesday, March 25, 2014

Updated Components Continued

The amp was way too quiet for my tastes, so I made two more changes. First, I took out R7. This value was originally 1 Mega ohm, but I changed it to 100 kilo ohm. Now it is nonexistent.

Originally, R2 was 68 kilo ohm, but I lowered it to 47 kilo ohm originally. Next, I lowered the value of R2 down to 10 kilo ohm.

Below is a schematic of the Valve Jr, Version 2. Ignore those arrows, that isn't my work. As you can see R7 was used to bring the signal down, as it goes straight to ground. This is useless for what I want, so it is gone.

R1 and R2 are in parallel on the guitar input jack. Since I changed R1 from 68 kilo ohm up to 1 Mega ohm yesterday (HUGE INCREASE), I decreased R2 much more. Since R2 is actually before R1 in the circuit, it creates a voltage divider which decreases the signal right when you plug in your guitar. Making R2 smaller will give less signal loss. One modification option I have in the future is to move R1 in front of R2 in the circuit, which would decrease the voltage divider even more. 

Un-modded Valve Jr Version 2.

The results? Sounds incredible. The amp can get loud again, which is what I wanted, and the mellow sounds when you turn the tone pot down on the guitar and use a neck pickup is incredible. I love this amp and the way it sounds so far. I have been working on my pedal board at home, and I'll bring that in next week to play some pedal through the amp. I haven't played anything but clean on it so far.