Amp building FAQs

“Can I add an FX loop?” is another common question. The answer is very similar to that for adding reverb. The short answer:Yes, but it’s not trivial, and it’s difficult to get it sounding good. The long and detailed answer:The main reason for having an FX loop in an amplifier is to add time-domain effects, such as delay, chorus and/or reverb. However, all of these sound best when placed AFTER compression and distortion. If you look at the typical FX chain in a multi-FX pedal, guitarist’s pedal-board, digital modeller or backline+PA rig, you will almost always find that these are

“Can I add reverb?” is probably the most frequently asked question of all. The short answer: Yes, but it’s not trivial, and it’s difficult to get it sounding good. The long and detailed answer: Reverb is a time-domain effect, and is best placed AFTER compression and distortion. If you look at the typical FX chain in a multi-FX pedal, guitarist pedal-board, digital modeller or backline+PA rig, you will almost always find that reverb is the last effect applied. The reason is that it sounds natural and musical. If reverb is applied to a signal BEFORE distortion and/or compression, the result

No. For a few troubleshooting issues, having an oscilloscope available is useful. But you would also need the training to know how to use one (not difficult, but not trivial). If you enjoy amp building so much that you want to get into the real detail of waveforms, distortion, etc, then it might be worth the initial expense and time spent educating yourself. OK – how about a signal generator? Again, this is not required, but is potentially useful as a companion gadget to use with the oscilloscope. For example, you can feed a 100mV sine wave into the amplifier’s

No – as long as it matches the output impedance of the amplifier that it’s plugged into. In a valve amplifier the output transformer’s windings match the speaker to the power valves. So the amp will sound the same if you use a 4-ohm speaker plugged into the 4-ohm output, or a 8-ohm speaker cabinet plugged into the 8-ohm output, etc. There are a few postings around the Internet that claim it’s always best to use all of an output transformer’s secondary winding, which usually translates into using the 16-ohm output with a 16-ohm speaker. Assuming the output transformer has

All assembly and testing and tweaking of electrically powered equipment should be done with care. Mains voltages (100-240 Volts AC) themselves are dangerous and almost all valve-powered amplifiers have higher voltages (250-500V DC). The latter can be stored within capacitors insude the circuit – even when the amplifier is switched off. What this means, in practice, is that any device which has ever been connected to the mains and powered up should be treated as if they contain potentially lethal electric charges and then properly tested to make sure that any such charge has safely dissipated. Only then is the

I always recommend running within the rated power rating of your speakers. So, if I am using an 18W amplifier, I do not run it into a single 1x12inch cabinet with a 15W-rated Celestion Blue. I know that some people do, but the speaker is so expensive the risk is not worth it. Going the other way, running a low-powered amp into a speaker rated at a much higher power is fine. I typically use my SE-5a into my 120W Marshall 4×12 cabinet. Don’t worry that the amp cannot drive these high-power speakers – it’s plenty. (And loud!) (As a

This is possibly the #1 question that I get asked, and I have two answers. 1) Short answer: Celestion G12H 30W for british/overdriven tones. JBL E120 for cleaner tones. This is entirely my own subjective preference; you may hate them! 2) Longer answer: The speaker and its cabinet is a very significant factor in the sound of any guitar amp. Guitar speakers and cabinets don’t have a flat frequency response; and all of them can accentuate or suppress certain parts of the audio spectrum. For example, I find the G12M 25W ‘Greenback’ to be quite mid-focused, and quite ‘nasal’ in

To build an amp kit you need a combination of electronics tools and a few hand tools: 1) Soldering iron. 20-30W is fine. You don’t need to spend a lot of money on a temperature controlled model (although they are nice to have if you plan to build a lot of projects). Don’t use a ‘soldering gun’ type. 2) Wire cutters. To cut wires and component leads to length. You can use the side-action cutter on pliers. 3) Wire stripper. If you’ve got the knack and finesse, you can also use the side-action cutter of your pliers to strip wire

Valve rectifiers are an unnecessary expense and complication for a guitar amp. In a few vintage amplifiers they do contribute to the tone, but in many amplifiers they don’t provide any sonic benefit at all. Here’s why… Valve rectifiers’ most important feature is that they have an internal resistance. Let’s say that it’s 100ohms. When there’s a big change in current drawn through the amplifier – for example, when you go from silence to a big power chord – there’s a corresponding change in the voltage drop across the valve rectifier. This is called sag. If the change in current