duhvoodooman
Addicted to solder....
The 5W Epiphone Valve Junior has certainly gotten its share of press here at TheFret.net, being the subject of the longest single thread in this forum's brief history (212 posts and counting as of today, 6/20/06), and deservedly so. This little gem has quickly established a cult following, since it offers genuine class A tube amp vibe for a ridiculously low price ($140 for the combo, $100 for the head). And you can pick up used examples of the combo version in good condition on eBay for well under $100 (I got mine for $92).
But rather than further effuse over its goodness, which Nelskie, Tone2thebone and others have already done in the aforementioned thread, I thought I'd post my experiences, both completed and in progress, with modifying this amp to improve its tone and performance further. Nelksie talked about swapping tubes and changing the stock speaker, but I want to get into some more fundamental changes here, involving making additions and substitutions in the amp's electrical chassis componentry. These modifications are covered in much more detail on some other websites, and I won't endeavor to go into the technical depth they do. But these are the websites where I found all of the information that I base my following comments upon, so check them out if you want more detail:
Erik Miller's VJr Mods at Euthymia Electronics
Dennis Cronin's VJr Mod Site
Svokke's VJr Mod Page
Brian Oddi's VJr. Mod thread at Kluge Music
VJr Mod Thread at Hoffman Amps
As good as the original combo version of the VJr was, it had some shortcomings, too--completely understandable in an amp this inexpensive. First and foremost is it's propensity to hum. In fact, the amp hums in two completely different ways--a low-level background hum that is independent of the amp's volume setting, and a more obnoxious "buzzy" hum that builds as the volume is increased. On the VJr combo I bought, the former was practically unnoticeable to me, but the latter was pretty bad with the volume up past 2 PM or so. I found several different mods that were designed to reduce either or both of these hum types, ranging from very simple to fairly involved. The good news is that none of them are expensive, so I elected to do several of them and see how much improvement I could get. (Note: These hum deficiencies were addressed in the head version of the VJr, and I understand new production of the combo incorporates the fixes, too.)
A second shortcoming that I noticed in my VJr was a rather dull tone, lacking "top end". I found myself maxing out the treble tone controls on all of my guitars when I played though it. Though the mod sites listed above tended to go after the hum issues as the primary improvement need, all of them made changes that boosted the amp's top end to some extent, as well, so I was obviously not alone in my opinion. Since I don't often crank the volume up into the range where the buzzy hum gets bad, I actually considered this need for more brightness to be my first priority. I swapped the stock Sovtek tubes for JJ's from Eurotubes.com, and though the amp's tone improved and brightened slightly, the improvement was nowhere near what I was looking for.
In addition to the above two issues, a number of other mods were described at these various websites, mostly falling into the category of enhancements to the VJr's intentionally sparse feature set. These included things like adding a high gain switch, an additional 8 ohm output jack, or installing a small light bulb to act as a signal attenuator. However, I had no personal need for or interest in any of these, and opted to pass on implementing them.
To deal with the hum issues, I decided to make the following four modifications:
Progress as of 6/20/06:
Hum Fix: Finished #1 and implemented a temporary version of #2, basically using a rubber washer and some strategically applied electrical tape to isolate the stock metal input jack from the chassis. In the meantime, the parts for #'s 3 and 4, plus a real nylon insulated jack to do #2 right, are on order from Mouser.com. At this point, the background hum is essentially inaudible, but I haven't implemented the fixes (esp. #4) that will hopefully tame most of the volume-dependent buzz.
Brightness Boost: Completed #5, resulting in a noticeable boost in the high-end, but I still want more. Additionally, the amp's effective gain was increased by changing the resistor to ground to 1M ohm, sending more signal to the preamp. This made the amp noticeably louder at a given volume setting. It makes the volume-dependent buzz proportionally louder, too! I have the parts on order from Mouser.com for mod #6, as well--a simple on/off toggle switch and some ceramic capacitors in sizes of 50, 68 and 100pf. I'll start out by installing the 68pf cap and see how the brightness sounds when switched on. If it's not enough I can go up to the 100pf cap, and if it's too much, I can back off to the 50pf. These caps cost less than a buck each, so I figured why not get a couple to experiment with?
I'll update this thread further after I receive and install the additional mod parts, hopefully by later this week. BTW, the total of all the parts only came to about $22, so these are definitely not expensive mods to make!
But rather than further effuse over its goodness, which Nelskie, Tone2thebone and others have already done in the aforementioned thread, I thought I'd post my experiences, both completed and in progress, with modifying this amp to improve its tone and performance further. Nelksie talked about swapping tubes and changing the stock speaker, but I want to get into some more fundamental changes here, involving making additions and substitutions in the amp's electrical chassis componentry. These modifications are covered in much more detail on some other websites, and I won't endeavor to go into the technical depth they do. But these are the websites where I found all of the information that I base my following comments upon, so check them out if you want more detail:
Erik Miller's VJr Mods at Euthymia Electronics
Dennis Cronin's VJr Mod Site
Svokke's VJr Mod Page
Brian Oddi's VJr. Mod thread at Kluge Music
VJr Mod Thread at Hoffman Amps
As good as the original combo version of the VJr was, it had some shortcomings, too--completely understandable in an amp this inexpensive. First and foremost is it's propensity to hum. In fact, the amp hums in two completely different ways--a low-level background hum that is independent of the amp's volume setting, and a more obnoxious "buzzy" hum that builds as the volume is increased. On the VJr combo I bought, the former was practically unnoticeable to me, but the latter was pretty bad with the volume up past 2 PM or so. I found several different mods that were designed to reduce either or both of these hum types, ranging from very simple to fairly involved. The good news is that none of them are expensive, so I elected to do several of them and see how much improvement I could get. (Note: These hum deficiencies were addressed in the head version of the VJr, and I understand new production of the combo incorporates the fixes, too.)
A second shortcoming that I noticed in my VJr was a rather dull tone, lacking "top end". I found myself maxing out the treble tone controls on all of my guitars when I played though it. Though the mod sites listed above tended to go after the hum issues as the primary improvement need, all of them made changes that boosted the amp's top end to some extent, as well, so I was obviously not alone in my opinion. Since I don't often crank the volume up into the range where the buzzy hum gets bad, I actually considered this need for more brightness to be my first priority. I swapped the stock Sovtek tubes for JJ's from Eurotubes.com, and though the amp's tone improved and brightened slightly, the improvement was nowhere near what I was looking for.
In addition to the above two issues, a number of other mods were described at these various websites, mostly falling into the category of enhancements to the VJr's intentionally sparse feature set. These included things like adding a high gain switch, an additional 8 ohm output jack, or installing a small light bulb to act as a signal attenuator. However, I had no personal need for or interest in any of these, and opted to pass on implementing them.
To deal with the hum issues, I decided to make the following four modifications:
- Improve grounding on the PCB by adding a jumper wire between two of the traces. This corrects a grounding design deficiency.
- Replace the stock input jack with a nylon insulated jack, to isolate it from the chassis.
- Add a larger filtering capacitor (100uf/450V) to the main high voltage supply to supplement the smaller stock caps.
- Convert the voltage supply to the tube heater filaments from AC to DC, requiring the addition of a small bridge rectifier and 1000uf/25V capacitor.
To improve the brightness characteristics of the amp, I opted for two additional mods:
- Boost the amount of input signal going to the preamp stage and reduce the signal bleed to ground by changing two resistors on the PCB. The resistor change also causes a net increase in the input impedance of the amp, which effectively boosts the highs a bit.
- Add a switchable tone capacitor to an open position on the PCB, i.e. install "brightness switch".
Progress as of 6/20/06:
Hum Fix: Finished #1 and implemented a temporary version of #2, basically using a rubber washer and some strategically applied electrical tape to isolate the stock metal input jack from the chassis. In the meantime, the parts for #'s 3 and 4, plus a real nylon insulated jack to do #2 right, are on order from Mouser.com. At this point, the background hum is essentially inaudible, but I haven't implemented the fixes (esp. #4) that will hopefully tame most of the volume-dependent buzz.
Brightness Boost: Completed #5, resulting in a noticeable boost in the high-end, but I still want more. Additionally, the amp's effective gain was increased by changing the resistor to ground to 1M ohm, sending more signal to the preamp. This made the amp noticeably louder at a given volume setting. It makes the volume-dependent buzz proportionally louder, too! I have the parts on order from Mouser.com for mod #6, as well--a simple on/off toggle switch and some ceramic capacitors in sizes of 50, 68 and 100pf. I'll start out by installing the 68pf cap and see how the brightness sounds when switched on. If it's not enough I can go up to the 100pf cap, and if it's too much, I can back off to the 50pf. These caps cost less than a buck each, so I figured why not get a couple to experiment with?
I'll update this thread further after I receive and install the additional mod parts, hopefully by later this week. BTW, the total of all the parts only came to about $22, so these are definitely not expensive mods to make!
) 
