Can I add reverb?

“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 is messy. The compression causes the natural reverb tail to be increased in volume in relation to the initial transient and the dry guitar signal. So instead of the reverb being able to tail off naturally (as it does when played through a clean amplifier), the decay of the reverb gets boosted, and it can sound boomy and this makes it hard to mix in with the dry signal. Typically you end up reducing the reverb and/or distortion levels to try to stop this mess from smearing the dry signal.

What has this got to do with the WF-55, SE-5a, PP-18, SL-18, PP-36, etc? Well, all of these amplifiers are designed with power valve distortion as a significant part of the amp’s overall distortion tone. So, if you were to place a reverb circuit within the amplifier’s preamp signal path, you get the problem mentioned above – the power valve distortion and compression messes with the natural reverb. This is true of many vintage-style amplifier circuits, too: Tweed Deluxe, Vox AC-30, JTM45, etc.

So why not keep the power amp clean?
That’s usually the best approach, but – of course – you lose the power valve’s contribution to overdrive and distortion tone. In most vintage-style amplifiers you end up with a very clean amplifier tone, because there’s little distortion in the preamp circuit itself. It’s no coincidence that the best sounding vintage reverb amplifiers are like this: the Fender Blackface and Silverface models, such as the Super Reverb and Twin Reverb.

To get good amounts of distortion and good-sounding reverb in an amplifier circuit, you need:
1) a preamp circuit that can provide plenty of distortion, running into…
2) the reverb circuit, running into…
3) a clean power amp.

For example, I like Rivera amplifiers (Paul Rivera designed many ‘80s Fender amplifiers before setting out on his own). But this is a very different sounding amp to one that uses power valve distortion. It’s also quite a bit more expensive and significantly more complicated to build as a project.

Back to the Amp Maker amplifiers: we’d be adding 2 or 3 extra valves to achieve the same sort of distortion levels and to drive the reverb tank and recover the reverb tank’s output signal back up to a decent level to mix back in with the dry signal and then to drive the output valve(s). That’s such a big change that it’s better to start with a clean sheet of paper (IMHO!). Which I will do.