DIY Guitar Amp with Mods

So after reading all about the various amp designs online, I just had to build one and try it... It has to be a all-tube amp, I was going to order the Ceriatone kit based on the famed Dumble OTS design. But since shipping it to China might be a bit of hassle, not to mention being way more power than what I need. But for the price US$450, it is very tempting.


Browesing through Taobao, I came across a simple 5W amp based on the Fender Princeton '65 design, the kit has three band tone control and send/return loop, but basically just a simple 12AX7 based amp.

The schematic is:
I will build it and play with it for awhile to see how it sounds, I will use the 12AX7 tubes from my old Houston integrated amp instead of the stock tubes that it comes with.

I may also fool around with the tone control values to see the amp's tone could be improved, there are many designs available, from the Dumble tone-stack to Peavey IIC as shown below.

Real Amps vs. Guitar Sims

Yet more things to think about... Even with a cheapo Marshall (transistor too the horror) or a Vox Valvetronix combo, it is just quicker to get a usable sound than fussing around with the guitar sims on the computer. Many online complain about the sims as "plastic" or "lifeless" sounding vs. the real thing, I am not sure how the tests were done, or what the various gears were used, but there seems to be a consensus among guitarists that real amps especially tube ones driving real speaker cabinet is still the way to go after all that's what they were designed for!!

For the guitar sims to sound good, there seem to be some options such as driving them with some OD or other effects ahead of the soundcard, use IR cabinet sims (instead of the stock ones in the sims themselves or just use the amp sim output and send the signal back out to a real amp/speaker. May be worth trying out later...

There is also an issue with the sound level, as we know, that the "tone" of amps, especially tube ones are only apparent when they are driven hard - where tube and speaker saturation and power supply sag kick in but that means playing very loud levels - a problem for most people playing at home. The Vox does have a output soaker to retain the distortion at low volume, so that helps.

In one of the online discussion group, someone made an astute observation, without actual test results to back it up though, but intuitively it makes sense, what he said was that the guitar sims all fail at simulating non-linear distortion, while it is easy to simulate effects like chorus, phase, delay, etc. Non-linear distortion generated by the tube and speaker combo is very hard to achieve in software, they come close but just never quite getting there due to precisely the non-linear, random nature of the distortion involved.

The learning continues...

Guitar Rig Setup

For the past few months, I have been building up my guitar rig - both standard and via computer sims. Here is a summary of the current setup:

Pedals
ProCo RAT -> MXR Phase 90 -> Ibanez DE7, Fat Basterd and the latest addition, Dunlop ZW-45 Zakk Wylde Custom Cry Baby.

Guitar Amps
Vox Valvetronix 15
Marshall MC15CDR

Both amps are small combo type made for bedroom practice, but they are plenty loud already. The Vox Valvetronix uses a 12AX7 tube as power tube to drive the transistor stage - yes, the amp does not have tube output, I should have looked closer before purchasing the amp... But after programming some of the user submitted settings from Valvetronix.com, the amp does not sound half-bad, so it is a keeper for now... There are also some DIY mods that may be considered - 1) an effect loop kit, and 2) a DIY VF55 foot-switch.

Nothing special about the Marshall, as it was purchased for Gaby to practice her guitar when we were in Singapore, it is just a cheapo 15W transistor combo with the FDD distortion, gonna sell it soon I think.

Computer Based Guitar Simulators
After researching online, I demo'd a few of the well-known sims on the market - Guitar Rig 4, AmpliTube 3, Overloud TH2, and Peavey Valvelator Mk III. So far, I like TH2 the best, but its UI does take a bit getting use to. AmpliTube came with good reviews but the most troubling aspect though was the MIDI implementation, I could not get it to work at all under Ableton Live.

When I started using the guitar sims, I just plugged the guitar straight into the AudioFire input, because the level was too low, I then use a Radio Shack "Hi-Z to Low-Z" adaptor between the guitar and the small mixer, then into the AudioFire. I did manag to boost the level (with the mixer) which matched the impedance a bit better.

But of course, this was not the right way to do it as I soon found out - the Radio Shack adaptor was still a poor load for the guitar, which really required a high impedance load (typically 1M), where as the Radio Shack had at most 25K, so a lot of the highs were rolled off from the guitar, not an ideal solution.

I also tried using the headphone output from the Vox, after pulling the plug out one click from the jack based on the suggestion at the Valvetronix online forum, unfortunately, the level is still too low, with barely any level registering on the Ableton input.

Reading further online, there are many tempting DIY projects for guitar preamps, anything from simple opamp buffers to full-blown preamps based on classic designs. Since simple is never good enough for me - where is the fun in that! - I am digging deeper into it, at the end, I am not sure just how good the preamp will make me sound or really make that much a difference to the guitar sims, but it sure is fun to go through some of the designs and admire some of the great DIY projects. See the Fat Booster/Fat Basterd that I built for more...

Stay tuned...