Simple vs. Complex Amps

 In the world of amps there are two types: simple amps with few a controls and complex amp with  a litany of switches, knobs and bells and whistles. So what’s the difference?

First off I’ll list a few of guitar players most dreamed about amps: Marshall: Super Lead, JTM-45, JCM 800; Fender Tweed Deluxe, Tweed Champ, Tweed Bassman, Twin Reverb: Hiwatt Custom 100, Vox AC30, Trainwreck Liverpool and Matchless Spitfire.

What do these amps have in common? They are simple! No effects loops, line outs, or channel switching. Most do not have reverb or master volumes. So what is about simple amps that works so well?

There are two major factors in my opinion: less circuitry equals less signal loss and amp that are designed to do one two sounds well just work better than the Swiss army knife amps that attempt to have lots of sounds. Let’s quickly discuss those two points:

1.  Circuit design:

Amp can only do a couple things well. Let take a 60’s Marshall and a 60’s Fender Blackface. The Marshall is crunchy and with lots of break up and mid range punch.  It does this by having a circuit that let lots of mid range through and by keeping the plate voltage low.  The Fender Blackface is clean and sparkly.  It does this by removing mid range and making the plate voltage higher.  

A circuit cannot do both! So an amp that is supposed to do many sounds has to rely on compromises to get it done.  Which means the end result is not as good.

2. Less Circuitry Equals Less Signal Loss:

Try these two experiments out:  plug you guitar into in amp with the volume and tone knobs on the guitarall the way up and strum.  Now roll back the volume a bit and strum. You’ll notice a loss of treble and dynamics. The volume pot is a variable resistor so the more resistance the pickups see the less signal pass out of the output jack. When a signal pass though a capacitor the first thing you lose is low end.

Amps are filled with resistors and capacitors. No matter what you end up with signal loss when the signal passes through.  Every gain stage is connected to the next via a network of resistor and capacitors.  Tubes can amplify the signal and make up for the signal loss but the signal is never the same. For every feature an amp has there are more gain stages are needed to make up for signal loss. So the more circuitry ( i.e  features) the more caps and resistors the signal passes through and therefore the more signal loss. This accounts for the harsh and thin sound of so many modern amps. Even worse many modern amps usesolid state components that just ruin the sound.

So when designing an amp a person must weigh what features enrich the sound and which do not.  People are really surprised when they get an amp without anything but a volume and tone control and find they do not miss having other featuresat all!

Here are a couple of block diagrams of popular amps circuits that will help explain this visually.

 

5C3 Tweed Deluxe: A simple great sounding 50’s amp!

Input----Gain Stage----Tone and Volume Control---Phase Inverter---Power Tubes--- 

Output Transformer---Speaker

Marshall Super Lead: The Marshall of Legends!

Input----Gain Stage---Volume Control---Gain Stage---Tone Controls (Treble, Mid, 

Bass)---Phase Inverter---Power Tubes---Output Transformer---Speaker

 

Fender Twin Reverb (Reverb Channel):  Super Clean Sound but less dynamic and rich than the previous two amps !

Input---Gain Stage---Volume Bass, Mids and Treble Controls---

Gain Stage---Reverb Circuit (4 gain stages, a transformer and reverb pan)---Vibrato

circuit (two gain stages)Phase Inverter---Power Tubes---Output Transformer---Speaker

 

Peavey Classic 30 Lead Channel : It Sucks! Thin and harsh. 

Input----Gain Stage---Pre-master Control---Gain Stage---Channel Switch Relay---Gain

Stage---Channel Switch Relay---Reverb circuit with 3 TRANSISTOR gain stages and

reverb pan---Tone Controls (Bass Treble, Middle, boost switch---TRANSISTOR Gain

Stage---Effects Loop---Master Volume---Phase Inverter---Power Tubes---Output

Transformer---Speaker