Skip to main content ↑ ↓

Notice

Please note that most of the software linked on this forum is likely to be safe to use. If you are unsure, feel free to ask in the relevant topics, or send a private message to an administrator or moderator. To help curb the problems of false positives, or in the event that you do find actual malware, you can contribute through the article linked here.
Topic: Vacuum Tube Amps v. Transistor designs (Read 3247 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.

Vacuum Tube Amps v. Transistor designs

I am seriously considering switching to a vacuum tube based amp for home audio use.  I know all about transistor/mosfet designs as I've had several over the years.

Can someone offer a quick education of validity of using Vac amps or if this is folly?

A fast heads up on what a Mono Block amp is would be helpful as well.  All I can find on the net related to momo blocks is specs.  Not what, how and why.

Many thanks
Somebody has to do something, and it's just incredibly pathetic that it has to be us. Jerry Garcia-Grateful Dead

Vacuum Tube Amps v. Transistor designs

Reply #1 –
Quote
I am seriously considering switching to a vacuum tube based amp for home audio use.  I know all about transistor/mosfet designs as I've had several over the years.

Can someone offer a quick education of validity of using Vac amps or if this is folly?

A fast heads up on what a Mono Block amp is would be helpful as well.  All I can find on the net related to momo blocks is specs.  Not what, how and why.

Many thanks

1. Mono Block amps are what the name states ... monaural amplifiers that will drive one channel only and thus would be needed in a pair configuration for stereo. Their practical use does not show ... well ... any hard advantages over a stereo amp of the same output power rating (ignoring channel crosstalk here because the speaker pair itself will show stereo crosstalk way higher than even the worst amp)

2. Tube amps create a higher amount of 2nd-grade harmonic distortion which may sound "pleasant" to your ears (many so-called audiophiles claim it does) ... hard clipping @ overall high loudness (as being experienced with most transistor amps) does not occur in that degree known from transistor amps (tubes rather get saturated with high cathode currents which leads to higher distortion IIRC) ... thus your speakers won't suffer from DC signal amounts which is one reason why e.g. guitar players choose tube amps.

3. Tube amps are often more expensive than transistor amps of the same quality

4. The tubes themselves need correct calibration of their BIAS values in regular intervals

5. Tubes show a decreased efficiency when being compared with transistors.

There are many topics around here (there is a cable discussion around here that leads to a very interesting site about audio chains in general) and one hell of web resources (I am no electronics engineer so what I state might not be that much reliable) so you should just search and draw your own conclusion.

Personally, I would always prefer a solid-engineered transistor amp over a tube amp of the same price class.
The name was Plex The Ripper, not Jack The Ripper

Vacuum Tube Amps v. Transistor designs

Reply #2 –
I was designing and building tube amps myself for a long time, and dont ever touch them again.

The warm and elegant sound of tube amps had captured me for a very long time, until i found what the REAL reason for the 'warm sound' is :

Tube amps have a poor 'damping factor', caused by a high internal resistance on the output ( the output transformers have a rather high internal ohmic resistance, > 5 Ohm in most cases ). Main Reason for this is a very low feedback ratio, and the feedback ratio is directly responsible for the damping factor of an amp.

What many people dont know, the bass speaker of an amp is damped by the amp, and if the amp has a low damping factor, the total Q value of the bass speaker goes up and this will give a 'warm', but fuzzy bass, and generall speaking ( for most speakers on the market ) a higher amplitude in the frequency range from 80 - 200 Hz.

Now, how did i loose my interest in tube amps ?

Well first of all the BIAS of the tubes is extremely critical. I once measzred distortion of tube amps, by modifying the BIAS constantly. The results were shocking !! I started to replace the good old potentiometers for the tube BIAS setting against OP amp based auto-control circuits, which proved to be very helpful, but still the tubes were aging a lot and you had to reset the setpoint automatically all the time.

Second, at that time we started to understand that the damping factor of the amp had a direct influence on the amplitude response of the total system, depending on the impedance curve of the speakers, so we started to use L-R-C elements to equalize the impedance curve of the speakers. This was improving the sound in many cases extremely, and i still recommend to do that. However, as a sideeffect the sound differences between tube amps and  good, fast MOS FET amp with a good power supply shrank significantly, in fact the only remaining difference was the fuzzy, unclear bass of the tube amp, and a bit more charming treble, but that was basically it.

I was healed, once and for all times  ....
 

Vacuum Tube Amps v. Transistor designs

Reply #3 –
Quote
What many people dont know, the bass speaker of an amp is damped by the amp, and if the amp has a low damping factor, the total Q value of the bass speaker goes up and this will give a 'warm', but fuzzy bass, and generall speaking ( for most speakers on the market ) a higher amplitude in the frequency range from 80 - 200 Hz.

True for most modern bass cabinet/speaker/crossover compositions whose total Q ist tuned to a value of 0,7 which is regarded as the best compromise between low-end and impulse response ...

A lower total Q (if you encounter a speaker that is tuned that way) could benefit from the tube amp's lower dynamic damping IMO ...
The name was Plex The Ripper, not Jack The Ripper