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Old 11th March 2013, 07:15 PM   #1
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Cool Modding a cheap practice amp (aka polishing turds)

Okay, so we have all been there. We have a 5w solid-state budget, and 100w tube dreams. There is hope! This guide is for the weekend hacker, more experinced DIY'ers will rightfully cringe at half the suggestions, but many may be unknowingly using equipment that has these mods included as part of the design.

This quick post concerns guitar amps, specifically those with distortion / gain stages, and how to make them sound better. For this example I'm messing with a Marshall branded G-10 II, but the mods discussed will work on most amps. Opening an amp of ANY kind, (yes even ss!) can be deadly if you have no idea what you are doing. Please remember to UNPLUG the amp, DISCHARGE capacitors, and don't defeat any built-in protection by using incorrect fuses.

***WARNING!***
* The 'suggestions' below will VOID YOUR WARRANTY, isolate you from your girlfriend, and possibly DESTROY your amp! I'm not responsible for some jackhole (thats you!) who rewires his mains voltage to his guitar input and fries himself and his rare vintage telecaster.*

1. Pot replacement - This is a bit controversial, and should not be attempted unless you don't really care if you blow the amp. Replacing stock gain and tone pots with a larger value can SOMETIMES give you that "goes to eleven!" sound. Sometimes, it just adds too much (or little) resistance to your circut and starts burning things out. If you have a 10k, you can try a 25k, maybe even a 50k... 100k is pushing it however. Do note the difference between a standard 'linear' taper pot and an audio (log) taper pot. If at all possible you want an audio, but a log will make due, but it will go from zero to hero way too fast. You can add a resistor to get better volume control as described in this rather lengthy and technical document for further mojo ( ESP - A Better Volume Control ). I replaced my little gain and tone pots with higher values (only because it's what i had on hand) and got some great results. Sound now goes from dark and earthy to uncomfortably bright in a flick of the wrist. Gain is a lil better, but not much change.

2. Speaker replacement - A very under-rated and under ulilized mod for cheap amps is to replace the speaker with a better, or in my opinion 'worse' one. Note when dicking around with speakers - keep ohm's similar, higher is almost always okay, but lower can stress your amp really hard in a bad way. If the speaker does not show the ohms, you can measure it with a meter *in comparison* to the old one, these measurements (for reasons exceeding the scope of this post) are not accurate. Okay, lets take this marshal i'm using, it has a pretty decent sounding 6" already, but that "cone honk" when driving a smaller is even better, and gets me that loud sounding aggression, without destroying my ears (and property value). I grabbed an old 1950's no-name speaker out of a portable record player. Wired up, the speaker is a bit louder when quiet (higher sensitivity) but when driven, give a satisfying midrange resonance and breakup seldom experienced in a transistor amp. Can this blow your speaker? Sure it can, but we are concerned with getting killer tone on a budged and damn the repercussions!

3. Cabinet mods - Another under-utilized mod. Changing the sonic signature of the cab can yeild HUGE differences in tone and perceived volume. This one is a bit more subjective, and dependent on your model amp. Mine is a mostly open back design that already sounds good, and after experimenting, i put it back to stock in this regard, but previous amps (crate, peavy) have benefited. Is yours a closed back? Open it up and see how it sounds! Already open? Put a cover on the back. Open backs give 'louder' mids, while closed backs have punchier bass. You can also experiment with adding foam, fiberglass, or my personal favorite rockwool to get a more controlled muffled sound or to increase the bass response of an already closed design. Try to eliminate any loose screws, panels, etc that may buzz when cranked.

4. Diode mods - This may be the most profound mod on overdrive tone. Most solid state amps use diode-clipping for the distortion circuit to chop off the tops of the waveform and give you that nice fuzz. Small changes in this arrangement can yield HUGE differences in tone. Circuits that use LED's tend to sound cheap to me, as do circuits with symmetrical clipping. My suggested mod is to locate on the chassis a pair of LED's that don't seem to be there for lighting anything up. Replace one with a selenium diode (i pulled a random one off an old circuit board) or 2 seleniums in series. Some people will replace both LED's but I think the asymmetrical clipping sounds a bit more musical, and is more likely to highlight some harmonics. And thats it. Here is a MUCH more detailed write-up on the subject: ( AMZ Warp Controls ) For the more advanced readers and solder-heads, you can also use zeiners, transistors and mosfets. ( AMZ - Guitar Effects & diode clipping )
Edit: Doides are POLARIZED and must be installed the correct way or risk fireworks. Your circuit board may show you the orientation (the stripe goes in the direction of the arrow) but many do not. Note the polarity of the old diode as you remove it, and orient your new diode in the same fashion.

5. Gain mods - This may be a bit basic for many readers, but it really sounds better if you Drive your Inputs! Any pedal that makes your guitar louder will help drive more clipping from your amp. I have in the past taken guts from an old abused stompbox and integrated it into my amp for convenience and added the amp from a pair of computer speakers (maybe a bad idea, but it sounded good). Another (possibly ill-advised) mod I have gotten results from is changing the value of resistor on the input to push more juice thru your guitar and amp.

6. Guitar mods (aka it's not the amp, dummy!) - Your pickups probably suck. Replacing your single coils with some humbuckers, or hot-wound boutique coils is going to help you get more sound from your guitar to your amp. Also consider some heavier gauge or higher nickel content strings to boost the signal that the pickups, well, pick up. On that note, change your damn strings! I see so many players that only replace them as they break, and are missing out on some tone. A good example is Metallica's black album (put down your pitchforks, it's relevant!). They changed strings dozens of times per song. Sometimes for each take! Would they bother if it didn't make a difference? (maybe.) Upgrade your pots, add a tone knob, delete a tone knob!

7. Ear mods - Yup, you heard me. If you get stuck, or frusturated with your tone, or can't find 'your' tone, take a break. Listen to some music outside the genere you prefer. Metalhead? Listen to old blues and jazz. Rocker? Check out some skiffle or some country. Pop? Listen to some 4-track basement recordings. Learning about how different tones and styles mesh is invaluable, and can protect you from the dreaded 'ear-fatigue' of listening to the same sound over and over again until you are not perceiving the bulk of the sound, but only the nuances no one else will ever notice.

8. Effects mods - Stop using your damn effects all the time. Turn down that reverb, bypass that chorus. Take some time to actually hear the sound your instrument is making. It's amazing what you might be missing. Effects are used way too much by many noobs looking to cover-up or 'enhance' their sound, when some more practice would do better. Having a cleaner sound will allow you to progress in your abilities MUCH more quickly. Save your "wall of sound" blast of everything on 10 for the recording session.

9. Recording mods - Just one thing here, but of vital importance to noobs recording their guitar sound. Don't plug your amp into the mixer. Seriously. Don't do it. Even direct boxes and amp-modeling equipment are crap. Use a microphone and put it in front of the amp's speaker. Instant improvement in tone. Direct recording is a last resort. Even when playing live, it's much better to mic your cab than run direct to the pa.

10. Cable mods - This may sound obvious, or pointless at the same time. Use good quality cables, and use the SHORTEST cable that is practical. A longer cable acts like both a resistor and an antenna. Both are bad for your guitar sound. If buzz or radio is super awful, i have seen ferrite's help (put them on your power cords too!) when you are next to a radio station, but are not going to make a perceptible difference for most players. Bad buzz is usually due to bad grounding or a lifted connection in your plug however.

Ok, hope this helps someone. Feel free to flame, correct, and add to anything here. This info is directed at the budget shredder, so highly technical discussion, while welcome, might be better received in another thread.

Rock out with your... err....
Jam out with yo... uhmmm....
Nevermind
Just go make some music!

Last edited by MereTenacity; 11th March 2013 at 08:35 PM. Reason: Added note about diode polarization.
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Old 11th March 2013, 09:28 PM   #2
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Join Date: May 2010
Location: was Chicago IL, now Long Beach CA
Some guys prefer the treble-cut from the capacitance of a long guitar cord, but I'm with you. If I want treble-cut that's what capacitors are for.
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Old 11th March 2013, 09:42 PM   #3
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Quote:
Originally Posted by cyclecamper View Post
Some guys prefer the treble-cut from the capacitance of a long guitar cord, but I'm with you. If I want treble-cut that's what capacitors are for.
I considered mentioning that, and I totally agree that a cap is the better way to go. But in the end, I thought such nuances were a bit subtle for the weekend warrior crowd this is aimed at.

My next post may be an upcoming experiment in which I build a guitar amp from parts (trash) around the house. Horrid hacks like long wire for capacitance, belt-buckle transformers, and borax diodes all stand to make a ghastly appearance. I'm also considering a diy 'verb after reading about axelvilhelm's slinky and car speaker creation (Post your Musical Instruments here. ), which sounds surprisingly lush and dark. The Audiophools will be crappin their pants in horror.

Last edited by MereTenacity; 11th March 2013 at 09:48 PM.
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