rectification

[boogie-man]

I once tried a VHT Pitbull 45 combo which sounded great, and one of the things I noticed was that it has a valve rectifier.

Looking at various preamp-power amp units I can't seem to see where this would go. Is it in the power or pre amp stage?

Also are there any rack units that use valve rectification over diodes?

[dmk]

the valve rectifier (.sp?) is part of the power amp section.

i know some boogie poweramps have switchable valve/diode rectifiers.

sure some others do to, but i dont know.

someone else on here will be able to help you better.

[El Grinder]

Actually, the rectifier won't be in the signal path AT ALL. It is neither part of the preamp nor power amp signal chain.

 

The purpose of a rectifier or silicon diodes is to turn AC current from the wall into DC current that the tubes (or transistors) can use. Using a tube rectifier tends to change the tone a bit since it handles current differently than a silicon diode (solid state) rectifier.

 

The only rack units I know of that use tube rectifiers are the rackmount mesa/boogie rectifier 100 watt head. Those are no longer in production (to my knowledge) but can be obtained used occasionally.

[EddieMack]

That is correct. The rectifier is not in the signal path, but since it runs inefficiently when converting the power from AC to DC, it has a impact on the tone of the amplifier (refered to as a power "sag"). That is what supposedly give the Mesa Recto's thier unique tone.

 

There is no stand alone power amp that I know of that uses a tube rectifier. Even the Boogie Recto 100 power amp uses a silicone diode. There may be some boutique stuff out there, but nothing I know of.

 

Cheers,

Ed

[eeka-chu]

The rectifier is part of the signal path, just indirectly at first glance.

 

The others are right to say that the rectifier changes AC to DC. All valves require DC to operate, be they in the pre or power amp stage. All valve, and even transistor, amplifiers will have a rectifier in their power supply.

 

The rectifier is part of the signal chain because even though the initial signal into the amp is from your guitar, all the amplifying is being done through the amp's power supply. Of which the rectifier is a part. As such, the rectifier is capable of distorting the signal as it is amplified.

 

I've written a gazillion and one words on this topic on HC.

 

In short, the rectifier becomes a greater percentage of how your amp sounds the louder you turn it up.

 

Before it starts getting very loud, the power supply's filter capacitors will have an equal, if not greater, effect on how the amp sounds.

 

Because preamps use such tiny amounts of power it'd be much harder to notice a difference between a valve and a solid state rectifier in it's power supply.

 

The difference is due to how the rectifiers work.

 

Valve rectifiers are less Hi-Fi. They take a long, long time to response to changes in power demand. A valve rectifier can take whole seconds to fully reach what is being asked of it. The decreased responsiveness produces signal compression. Which is why valve rectified Mesa Boogies sound smoother and more rounded.

 

Solid State rectifiers respond incredibly quickly. Within literally millionths or even billionths of a second. The faster response lets the amp track the input signal more closely, to a higher fidelity. That's why Marshall's sound more defined and upfront. And why people say it's harder to sound good through a Marshall.

 

In terms of Hi-Fi, a Marshall's rectifier will produce a higher fidelity result. But even a lot of Hi-Fi guys prefer the smoother sound of rectifiers and they're not playing the music in the first place.

 

Neither is better or worse for guitarists. It's apples and oranges.

 

Guitarists are trying to create a new sound, not perfectly reproduce the input from their guitar.

 

As I've said, generally you will only start to hear the difference as you ask the rectifier to deliver larger amounts of power. Cranking your power amp real loud for example. I doubt you'd hear anything seriously significant between the two in a preamp.

 

The entirity of an amp behaves like an elastic band. When you plug your guitar into it and strum a chord you cause the whole thing to vibrate electrically inside. There is more to it than the direct wire going from the input to output of the amp.

 

Since I have no idea how much you know about electronics or amps I'm not totally sure what level of detail I can reply in, so please excuse me if I've made this too complicated or simple.