Hi all,
I am new here and a n00b when it comes to t00bs (sorry, couldn't resist) and I'm wondering about their utility in today's silicon world. I have been looking into building my first valve amplifier and have come to understand through my reading that the desirable sound quality of the valve amplifier stems from the "soft" roll-off of the gain as opposed to the "hard" clipping that occurs with transistors. It would seem to me then that the usefulness of valves is primarily in sound production - the domain of guitarists (among others) driving their amplifiers deliberately into distortion as they play. I don't know of an occasion when anyone would deliberately drive an amplifier involved in sound reproduction into distortion. Thus the question - why a valve amplifier?
I am new here and a n00b when it comes to t00bs (sorry, couldn't resist) and I'm wondering about their utility in today's silicon world. I have been looking into building my first valve amplifier and have come to understand through my reading that the desirable sound quality of the valve amplifier stems from the "soft" roll-off of the gain as opposed to the "hard" clipping that occurs with transistors. It would seem to me then that the usefulness of valves is primarily in sound production - the domain of guitarists (among others) driving their amplifiers deliberately into distortion as they play. I don't know of an occasion when anyone would deliberately drive an amplifier involved in sound reproduction into distortion. Thus the question - why a valve amplifier?
They don't do it deliberately, they just do it. It's part of sound reproduction (especially analog sources) to occasionally go into overload, even when not playing anywhere near full volume. There is also the issue of how your speakers' impedance changes over the frequency band. If the impedance dips way low, say from 8 ohms down to 1 ohm, that can push the amp into overload even when it isn't pushing that hard at other frequencies.
The key is how does the amp react (does it generate a lot of high-order harmonics due to the sharp cutoff) and how does the amp recover (from feedback loops and blocking distortions). Tube amps aren't automatically immune to these things, either. However because many tubes can be setup in a circuit to operate very linearly without lots of (or any) feedback, they can be very accurate and very stable and actually sound better than a transistor amp in cases where the tube amp is only rated at a small fraction of the output power. Cheap transistor amps need a lot of headroom to prevent these overloads as much as possible, so you need many times the power output capability even though you are only using 1 or 2 watts on average.
That's not to say a transistor amp can't be made stable either, but they typically just aren't unless you pay big bux. Often their own power supply isn't rated anywhere near what is required to reach the claimed output power of the amp. The key to a good chip amp is a good PSU...an expense most manufacturers aren't going to bother with.
For completeness, I'd like to add that in some areas, there are no viable substitutes for tubes even today. If you have a microwave oven at home, it contains a special type of vacuum tube called a magnetron. I'm also thinking of industrial-scale induction heating, very high power RF finals, and large radar installations.
If you wonder why typical transistor-amps can show so low THD figures, it only depends on overall feedback at maybe 50dB. To this we can add that they mostly don't have any bandwith at all without GNFB. But off course there are better or worse ones, where the better use some kind of local feedback.
A triode-amp will be low distortion and full bandwith without any feedback at all.
A triode-amp will be low distortion and full bandwith without any feedback at all.
I listen to a fair amount of rock, metal, and techno and generally prefer tubes as well. Musical genre does affect which amp I will use, though.
I listen predominantly to rock.
I was tube curious especially after reading Audio Reality so I built a couple of preamps (Foreplay, Grounded Grid) and rebuilt and upgraded a tube poweramp (ST-70), each one drawing me deeper into the fold.
I drifted back into multichannel and solid-state for a year or so and didn't have the time to integrate the tube equipment but now, due to a temporary and unique living situation I'm back with my tubes with a vengeance.
Just built a new tube pre last week and just bought a DAC with the sole intention of grafting a triode to it (Lampucera). I've got an OTL project I'm pondering and looking at the ST-70 for possible new driver board and/or power supply. Oh and a Moskido looks like fun. But that's just my condition.
The sound is good, the circuits simple, and fun factor high.
tubes outside the box are idiot proof
One thing noone has mentioned is that outside the enclosure, tubes are more idiot proof. If you short a speaker wire whisker across the outputs, they don't blow up. If the speaker wire falls off, my ST70 never blew up. (some designs will) If they go bad, they tend to get sweetly wimpy (low power) instead of blowing up in a watt sucking fireball ( my transistor amp did that). If they go dead, the lack of light in a tube indicates to most idiots what is wrong. Tube designs were done before the 50 cent electrolytic capacitor, so they don't have hundreds of these that need replacing every 20 years. The ST70 has 5. My Sony TC250 that I was using while output tubes were scarce and pricey, has over 100 electrolytic capacitors that all need replacing. I can hardly see them, they are so tiny. Transistor amps frequently create a turn-on whump that can blow speakers (I didn't buy a Carver 1.5T recently because of reports of this built in defect) nor do they produce infinite frequency switching transients across the speaker line (like the power supply of the Carver 1.5T amp was reported to do). The stereo 70 in particular is not too likely to RF oscillate and blow up your tweeter. Of course, inside the enclosure, tubes will kill you deader than yesterday's mouse, but what fun is life without a little death defying repair work occasionally. I've been repairing tube devices since 1962, I learned about defying death on a 6VDC car radio in 1963, it had 440 VDC in it! I survived, and learned something, too.
One thing noone has mentioned is that outside the enclosure, tubes are more idiot proof. If you short a speaker wire whisker across the outputs, they don't blow up. If the speaker wire falls off, my ST70 never blew up. (some designs will) If they go bad, they tend to get sweetly wimpy (low power) instead of blowing up in a watt sucking fireball ( my transistor amp did that). If they go dead, the lack of light in a tube indicates to most idiots what is wrong. Tube designs were done before the 50 cent electrolytic capacitor, so they don't have hundreds of these that need replacing every 20 years. The ST70 has 5. My Sony TC250 that I was using while output tubes were scarce and pricey, has over 100 electrolytic capacitors that all need replacing. I can hardly see them, they are so tiny. Transistor amps frequently create a turn-on whump that can blow speakers (I didn't buy a Carver 1.5T recently because of reports of this built in defect) nor do they produce infinite frequency switching transients across the speaker line (like the power supply of the Carver 1.5T amp was reported to do). The stereo 70 in particular is not too likely to RF oscillate and blow up your tweeter. Of course, inside the enclosure, tubes will kill you deader than yesterday's mouse, but what fun is life without a little death defying repair work occasionally. I've been repairing tube devices since 1962, I learned about defying death on a 6VDC car radio in 1963, it had 440 VDC in it! I survived, and learned something, too.
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