Hey, do you guys know what the purpose of a rectifier is? Since they're near the power source, I thought maybe they were like a transformer, but amps already have transformers. Also, where in the signal chain are rectifiers? Thanks.
A rectifier changes an alternating current (AC) into a direct current (DC).
I started with nothing - and I've still got most of it left.
Did you know that the word "gullible" is not in any dictionary?
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A rectifier converts AC from the wall into DC for the power supply. The weird thing is that the amplifier then converts the DC back into the AC signals that represent your guitar sound, which are then sent to the speaker.
Transformers convert AC signals from one voltage to another to match the desired range or load.
-Laz
The reason is that most components are DC. A diode or an electrolytic capacitor will simply not work with AC - they are both polarised, i.e. they are designed to only allow the electrons to flow in one direction - an absolute no-no in the AC world.
SS rectifiers are constructed from 4 diodes.
I started with nothing - and I've still got most of it left.
Did you know that the word "gullible" is not in any dictionary?
Greybeard's Pages
My Articles & Reviews on GN
The power supply of an amplifier is a critical circuit area because the supply provides both the voltage and current demands of the amp. The power supply determines the musical characteristics of the amplifier. The type of rectification can be very influential on the overall sound of the amp. Rectifiers provide the DC voltage for the tubes and circuitry. Up until the advent of solid state rectifiers, vacuum tube amps used tube rectifiers. The rectifier converts AC voltage to DC. The rectifier needs to provide high voltage and high current.
The sound of an amp using a tube rectifier is characterized by a phenomenon called sag. The result of all this is a brief drop in volume as perceived by the listener. It is brief, and sometimes you have to listen very carefully for it. But it is there. Vacuum tube rectifiers are slow to respond to power demands in general. This slowness plus sag are partly responsible for the characteristic sound of vacuum tubes.
Solid state rectifiers behave differently than their tube counterparts. No sag is experienced with solid state. As current demand increases, the DC voltage supplied remains constant up to the specifications of the power supply. In addition, solid state rectifiers are quick in response. This gives a solid state amp a faster sound compared to tube rectification.
I have found that solid state rectified tube amplifiers have certain characteristics of solid state amps, quick response time and more edge. In contrast, tube rectified amps are slower in nature and less sharp in sound. The music from these amps is more round and mellow. Solid state rectified tube amps are aggressive in nature whereas tube rectified amplifiers are laid back. In general, Which type of amp you use all depends on your music taste.
Joe
Answering the still unanswered part of the original question:
[AC- Mains Signal] => Power Cord=> Transformer => Rectifier => Power Supply Filter => [DC Power Supply Voltage, a.k.a., Rail]
This is more than a bit pedantic :roll: :
Rectifiers don't really convert AC voltages and currents to pure DC. They process an AC waveform so it contains a significant DC component, basically through one-way valving action. The output of a rectifier still contains a fair amount of AC energy, but the composite signal is now unipolar: it now swings between a positive voltage and a reference (usually ground) (or negative voltage and a reference). The lowpass (or integrating) filter circuit following the rectifier removes the remaining AC components to leave a hopefully "clean" DC rail voltage. So in reality the rectifier and the power supply filtering convert the AC mains voltage to a DC power supply voltage. This is why an amp has a bad AC mains hum when the BF* capacitors in the power supply filter fail -- all post-rectifier AC components end up on the amp DC supplies and at the amp output.
Joe's explanation of solid state versus tube rectifiers is the part that most guitar amp users/buyers wish to know. The size of the power supply capacitors also play a role in the dynamic nature of the supply sag that Joe describes: Smaller caps => faster sag.
-Greg
* BF is the actual electrical engineering acronym for big. A power supply cap is routinely called a BFC, as in big ...<you figure it out>... capacitor.
-=tension & release=-
Greg, Joe, you guys rule. Ya make me wanna go back to school. 'cept I'd probably end up a fossil specimen after being left behind in the curriculum
And, Gneases explanation was perfect to prove the simple point that I always forget from my "basics in electronics" school days. The more changes a pulse goes through the cleaner it gets. Which is what processing "guitar vibrations" is all about.
Once a signal is cleaned, what ends up on the final output is a pure carrier for the tone from the guitar. If I remember correctly that is why tubes produce a cleaner and more consistent sound since they also convert in and out one more time.
Now I know I have to go buy another amp
