There are different opinions around...
Most guitar tube amps are built from a rectifier tube, followed with a proper CLC filter while the common hifi tube amps often working well with SS too. Also, sometimes there is a use of in "half-way" with hybrid tube rectifiers.
My question is, is there a precise reason for a choice instead another? I mean, not only the proper rectified voltage and current, but a speech of the influence on the overall sound. I'm talking about the PSU on tube hifi systems.
Most guitar tube amps are built from a rectifier tube, followed with a proper CLC filter while the common hifi tube amps often working well with SS too. Also, sometimes there is a use of in "half-way" with hybrid tube rectifiers.
My question is, is there a precise reason for a choice instead another? I mean, not only the proper rectified voltage and current, but a speech of the influence on the overall sound. I'm talking about the PSU on tube hifi systems.
Rectifier tubes find favour in guitar amps because they introduce 'sag'.
On high current demand, the HT voltage sags or falls away, which contributes to the 'feel' and playability of valve guitar amp.
This effect is undesirable in hifi tube amps.
'What is "Sag"?'
www.aikenamps.com/index.php/what-is-sag
On high current demand, the HT voltage sags or falls away, which contributes to the 'feel' and playability of valve guitar amp.
This effect is undesirable in hifi tube amps.
'What is "Sag"?'
www.aikenamps.com/index.php/what-is-sag
Usually under 10W 300B SE tube rect is used and with 6C33 SE and higher SS bridges is used.
Most guitar amps use tube rect by tradition not good sound intended, they sometimes use the SS diode adapter that will wild increase the tension and no soft start:
Solid State Rectifier
| TubeDepot.com
Note that in Hi Fi tube amps tube rect are used to better sound at expense of higher cost, when SS bridges are used is to lower the costs usually in big tube amps.
Yes I agree, that's because guitar amps match well with a "harsh" sound that is often preferred by guitarists...
With class A amps, sag is not a problem as the current drawn by the output valves is always at maximum so the HT voltage stays constant.
With class AB amps the current drawn by the output valves increases in size as the amplifier is turned up, so replacing the valve rectifier with silicon diodes gives a more stable HT voltage.
Studies show that moderately overdriving a valve amplifier produces even order harmonics (second, fourth etc.) resulting in the warm sound that some electric guitar players seek.
Strongly overdriving a valve amplifier produces odd order harmonics (third, fifth etc.) resulting in the harsh sound that other guitarists seek.
With class AB amps the current drawn by the output valves increases in size as the amplifier is turned up, so replacing the valve rectifier with silicon diodes gives a more stable HT voltage.
There is a certain dynamic 'feel' to playing through a valve amplifier that is difficult to emulate in a solid state amplifier.
Studies show that moderately overdriving a valve amplifier produces even order harmonics (second, fourth etc.) resulting in the warm sound that some electric guitar players seek.
Strongly overdriving a valve amplifier produces odd order harmonics (third, fifth etc.) resulting in the harsh sound that other guitarists seek.
It is not true. Nothing produces second order only harmonics. A-symmetric distortions produce all of them, symmetrically distorting amp suppresses even order harmonics.
But when a guitar amp clips a sinusoidal signal, even order harmonics are attenuated. However, the signal going from a guitar is not sinusoidal, and guitar strings wobble, so spectrum is more "live" than from a clean string. When high order harmonics are attenuated by a guitar timbre control, and an amp is overdriven, the sound resembles a clarinet that almost has no even order harmonics.
To be clear, overdriving a valve amp produces both even and odd harmonics.
A general characteristic of valve amplifiers is a shift from even order to odd order harmonics with increasing gain.
The story is not so simple however, as the relative amplitudes of the even and odd harmonics change with gain.
A general characteristic of valve amplifiers is a shift from even order to odd order harmonics with increasing gain.
The story is not so simple however, as the relative amplitudes of the even and odd harmonics change with gain.
I am not used with guitar tube amplifiers and I barely heard about "sag" before. I thought the translation of the word sag = sawtooth, but it was just the opposite I said before
Anyway, so it's a kind of compression effect....In term of PSU sag is related to a lack of rapidity in converting AC to DC (what doesn't happen with S.S.), and this is reflected to the sound.
Another reason people in Hifi like to use tube rectifier is the gradual rise of B+ at power-on. This gives the other tubes time to heat up without full HV on the plates. Some say this extends tube life. For tube amps with solid-state rectifier you can install a standby switch or a timer/relay to circumvent this issue. I'm a firm believer in SS rectifiers.
BTW, for guitar amps, you can achieve the same thing by using a relatively large resistance in the PI filter. More current draw -> more sag. YMMV
BTW, for guitar amps, you can achieve the same thing by using a relatively large resistance in the PI filter. More current draw -> more sag. YMMV
Correct for a class AB amp, but won't work for class A (see my earlier post #7).
Neither you tried for yourself.
Not if it is a well balanced amp.
Please read my complete description above. And google for Fourier Transforms, it helps more than repeating after "Gurus".
PS: it is not a theoretical question to me. Reading such "Gurus" and their pupils, people demand from me to design for them amps that add "euphonic even order harmonics". However, I can add square-law rectifiers to signal path, but they would spit on me then. And I would loose all respect to myself.
Right. But Fender's input stages are cold-biased to work over a long range of even-order flavor before they break into odd-order. The output stages are strongly odd-order. The player has some control of how much of which via various gain knobs and playing level.
Playing a turned-down 20W amp at the sub-Watt level, even my wax ears can hear the 2nd order in the Fenderish preamp (on a 2-preamp Ampeg where the other side was dead-clean). Of course when you play the 20W amp at "40++ Watts!", there's "no" 2nd, your ears are full of odd-order products.
The rectifier is like the stitching on a baseball. Some things, tradition over-rides all else, change is not welcome.
Back in 70'Th I organized a laboratory where we experimented with sounds designing synthesizers, guitar effect, and other musical stuff. The only way to generate even only harmonics was a direct synthesis. No distortions can ever provide even order harmonics only. A quadrature rectifier, 2'nd order only (of course, never ideal) can be used to get 2'Nd order distortions, but not 2'N2, 4'Th, etc...
And, as I mentioned above (if you ever read that), the real guitar string wobbles. It makes distorted sound more alive than a dull sound of an electric guitar string without any added distortions.
When I played a solo guitar, I made for myself a pedal with variable distortions, from clean, through soft a-symmetric, to hard symmetric distortions. It was very convenient to express feelings.
I did read your complete description.
You introduced several factors which can influence the harmonic structure of an amplifier's output signal and I've listed them below to prove I was paying attention!
Symmetrical/asymmetrical distortion; clipping; the non-sinusoidal vibration of guitar strings; attenuation by tone (?) control; overdrive.
All very interesting, but each factor would benefit from further amplification (pun intended!).
P.S. I have no need to google 'Fourier Transform' as I was introduced to the topic many years ago when but a lad at university!
Sorry, I wasn't getting at you - just making sure that owners of single ended amps don't attempt to introduce sag.
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