Hacker News Reader

Comment by irrational | Hacker News Reader

I have some questions. My son has been taking guitar lessons using a classic guitar. Using the advice of his instructor we are getting him a begginer's electric guitar for christmas. We also need to get him an amp.

Is the amp in this article the same kind of amp that you could plug an electric guitar into? I know nothing about music or instruments, but I do know about electronics so I was thinking it might be fun to build an amp with my son.

I went to the diyaudio link you suggested, but I didn't immediately see information like in the article (buy this, this, this and this to build the amp). Can you point to where I could find a similar purchase list and assembly instructions on diyaudio? Thanks!

View on HN

Short answer: No. Guitar amps are weird, not like hi-fi amps at all. In a hi-fi amp, distortion is the enemy. In a guitar amp, distortion is sought after. Driving the pre-amp section of a guitar amp into clipping is extremely common and desirable. Doing the same with a hi-fi amp is not. A hi-fi amp will be typically connected to speakers with a woofer and a tweeter and maybe a mid-range, trying to accurately reproduce all frequencies. A guitar amp typically has nothing but 12 inch speakers. A guitar amp is literally half the instrument. Plugging a guitar into a hi-fi amp is faithfully amplifying 1/2 of an instrument. You'll end up buying a guitar amp anyway. Just get a guitar amp.

> A guitar amp is literally half the instrument.

I'm not a musician and this confused me for some time. I'd see electric guitars with their own amp & speakers then a microphone for the the PA system in front of said speaker. I couldn't understand why the electric guitar wasn't just plugged in, something I read a few years ago was a light-bulb moment.

[Professional Musician / Hobbyist Maker]

Yes, this amp can work — experimental musicians run instruments through much weirder things — but it'll sound strange.

Whether you build an amp or not, you should definitely buy a standard guitar amp, so that he can focus on his guitar playing. A standard guitar amp (solid state or tube, to taste) will let him hear how his playing compares to other musicians (who also use standard guitar amps), helping him gain a critical ear. He'll learn what parts of the tone come from his fingers.

When he's ready to go experimental, then he can start playing with (say) ripping pickups out of guitars and wiring them up to headphones as portable EM detectors. When he gets to that phase, that's the time to start using line amplifiers like the one in this article instead of instrument amplifiers. And drilling hundreds of screws into his guitar.

While you probably could use an amplifier like this for guitar, you usually wouldn't want to unless it's being used for acoustic guitar or vocals. The reason being, an electric guitar amplifier is going to add a lot of character to the guitar tone that you actually would want, where as an amplifier like this is going to strive for a perfect clean reproduction of the original audio. This is why a lot of guitar players prefer to use old tube-based amps, they add a lot of character to the sound through the preamps and power amps that match what you hear on the recordings of your favorite artists and sound great (though, some argue today solid-state modeling amps sound just as good). With that said, there are a lot of projects and schematics on the web which try to recreate some of the popular guitar amps like the Vox AC30 and Fender Twin Reverb, which would be fun to try and build.

Now if you wanted to make a PA system, I don't see why you couldn't use an amplifier like this with some modifications.

You couldn't, not without reengineering the circuit. Guitar output level is much lower than the line level a standard power amp will take.

> Is the amp in this article the same kind of amp that you could plug an electric guitar into?

I'm no expert, but as far as I understand, this is a power amp, which takes an input at line level (~1 volt) up to a level that can power a speaker. Guitar pickups produce a signal around 100 mV, and typically need a "pre-amp" stage before the power amp to amplify this signal to line level.

An amplifier like in this article does just one of the many things a normal combo guitar amp does.

1. Preamp with hi-Z input from guitar to line level

2. Ability to drive into distortion

3. EQ of some sort

4. (Sometimes) reverb

5. Amplify line to speaker level (this article)

6. Midrangey speaker+cabinet that sounds nothing like a normal flat speaker cabinet used for HiFi/PA/keyboard/etc.

However, as others have said, you can use a guitar modeler which performs steps 1-4 outright and simulates step 6 leaving only a need for step 5 and a "normal" speaker.

I used to build guitar amps for fun and repair them for friends. I have parts of a Sound City, Plush, Harmony, Gibson amps in my storage unit. I have some old heathkit thing from the 60s. I have two different Traynors.

Depending on your budget, I'd get a Vox Pathfinder, AC4, or AC10, and then take him to get a pedal or two after Christmas. You can usually find an AC4 used easily. Some of the digital amps are fun, but if he really gets into it, he's more likely to keep one of the amps I mentioned and buy pedals anyway. An AC4 (especially an AC10) will be something which usually sounds really good on it's own.

You can absolutely use stand-alone "hi-fi" amplifiers for guitar; that's what I do. You just can't plug your guitar straight into that; you need some pre-amplifier gear. My gear is old-school in a big rack, described below.

Nowadays, there exist units that provide complete signal processing for guitar: simulating guitar pre-amplifiers, amplifiers and speaker cabinets digitally. You plug your guitar into this, and then it can go straight into a PA system, or your recording console. Something like that can be used with an amplifier like the one being built here.

My rig consists of a 6U portable rack case with a few pieces of gear. The guitar goes into an ADA MP-1 MIDI-programmable tube pre-amp (built in 1987, revamped by me). This goes into a splitter-mixer (called the SMF-1 that I built myself) which bifurcates the signal through a digital effect unit that provides reverb, and then mixes it again. The dry signal remains analog. Then it goes into a 31 band equalizer, and from there to the power amplifier, an Alesis RA-100, which feeds a guitar "4x12" speaker cabinet (four 12" speakers). I could take out the amplifier and drop-in replace it with any rack-mountable amp, provided it doesn't require more than 3U spaces. QSC, Yamaha, Yorkville, whatever.

There also exist dedicated rack-mounted power amplifiers intended for guitar, like the Rocktron Velocity or Marshall Valvestate 8008 (both of these examples are stereo). Many of these kinds of ampls have been produced. These are just power amps; they can't produce any overdrive tones and have only minimal tone control or none at all. The 8008 has a switch on the back for "tube like" behavior, which just means current feedback. That will give it more of a mid-scooped frequency response, induced by the reactive speaker load. I can do something like that with my equalizer.

The amplifier project we see here could be turned into a guitar amp by adding a preamp circuit board into the chassis, fed by a guitar input jack, and exposing some tone and gain controls. The stereo function of the amp could be useful if we add jacks for an external effect loop and make it stereo (mono out, stereo in). Then we need a stereo guitar cabinet: minimally a 2x10 or 2x12 wired for stereo.

For a beginner, I'd get a decent, pre-built guitar amp that "just works" with decent sound and only basic controls (as opposed to a digital amp with millions of mediocre effects). You can always add some DIY effect pedals, or get a whole new amp - but if your son wants to practice and needs to fiddle with the electronics because something is not right again with the DIY amp, this might distract him too much from actually practicing his instrument.

Maybe take him to a store so he can find out which guitar/amp combo he likes most.

No, guitar amps are a totally different beast with many different components.

Amen. Ask a guitarist. Kid needs a real guitar amp. And a couple of decent FX pedals.

Well... I dunno about that. Digital has gotten really really good. I bought a Helix about a year ago and sold my tube amps a few months ago... not that they were BAD, but I could get all the sounds (and way more) out of the Helix.

But obviously a new player isn't going to want to drop $1500 on a rig like that.

I would go with one of the new generation of solid state guitar amps like the Boss Katana. These are Class D amps like the one in the article, but voiced for guitar, and with distortion and reverb effects built in. They're very reasonably priced, and get good reviews from enthusiasts (much better than the solid state amps of 10+ years ago).

The Boss Katana is an ideal beginner amp that can handle bedroom practice through small gigs.

It's extremely versatile and sounds great.

Not very cheap and probably outside OPs range. But the Boss Katana Air is an amazing little amplifier, Bluetooth speaker, pedal modelling device etc. And it allows you to connect your guitar to the amp wirelessly. It really works fantastic.

https://www.boss.info/us/products/katana-air/

I'm but an amateur guitarist. I can't detect any latency caused by the radio communication. But I have not been able to find pro muscicians trying out the Katana Air and complaining on the latency. It really works. Over quite long distances too.

The only thing I would have wanted in the Katana Air is rechargable batteries in the Amp itself (the transmitter is charged by the amp). But that is not a major issue.

Your practical options are:

* Get a standard amp/cab combo.

* DIY something, I'm sure there are guides and such you can follow, but this is only practical in so far as it's a fun project.

* Use your computer. You can get inexpensive cables that plug into your computer USB and there's a variety of software to emulate amps.

Buy a Zoom G3x (or other good multi effects box with amps Sims) you can then chuck that straight into any semi decent guitar amp.

Reply on news.ycombinator.com