Why do Tube Amps sound more romantic v SS amps

Please try to measure distortion of tube amp while adjusting bias/balance of the output tubes, and you’ll see how sensitive it is. Then please repeat the same after 50+ hrs. If you are luky, and your AB tubes are aging the same pace, then distortions will not increase much. There is a lso big issue with output transformers in the tube amp, depending on core magnetics, resistance of coils, symmetry etc you will get variety of imbalance/distortion/FR problems, which does not exist in SS

@westcoastaudiophile 

We've done that plenty of times. No measurable difference. You can avoid a lot of the imbalance issues in output transformers by using a Circlotron, since the issues in the transformer are usually related to DC components, which are minimized in a Circlotron. This is so successful that Circlotron amps made in the 1950s were class B and had no crossover distortion at all. However such amps are rare.

IME tube amps suffer less from corrosion than solid state. I've serviced literally thousands of amplifiers over the last 50 years. You can have a well preserved solid state amp that shows no signs of corrosion but its semiconductors are failing on that account. If a tube amp is given the same treatment its likely the only service it will need (in time) is filter capacitors.

About the only place I see your age argument holding any water has to do with filter capacitors. Because tube amps run warmer, the filter caps have a shorter life than in solid state amps. So 30 years instead of 35, unless the designer placed the filter caps in such a way that they really ran too warm.

I just purchased a Bryston 2.5 cubed amp (for small 14’ x 12’ x 8’ room) I can’t quite wrap my head around this amp. For example, I have two or three go-to female vocalist tracks (one is- Sam Brown’s solo on PF’s live (“The Great Gig in the Sky”) that literally gives me goosebumps or makes the hair on my arms stand up every time I play it, with the tube amp. I’ve yet to experience the “hair on my arms stand-up” playing this track on the Bryston ss amp?

@keeferdog 

In your case, the simple answer is the tube amp is sounding more real.

not really, AB imbalance does contribute directly into third (odd) order harmonic increase. Perfectly balanced second (even) only order harmonics distortion, AB designs “distort" A and B the same way only if tubes are perfectly matched, which NEVER happened. it is very hard to pick matched tube replacement, which will age at the same pace to the <1% point.

Good designed SS amps have many AB transistors in parallel, which reduces imbalance problems. SS amps I have all are “maintenance free”, and there is no need to change any transistors due to aging degradation in 100 000 hrs life time.

@westcoastaudiophile 

We’ll have to agree to disagree since my experience is different from yours! FWIW transistors rarely match at that well, often being quite a bit further apart than tubes. But they are a lot cheaper so you can afford to go through a few to find a decent enough match, a hidden cost in case anyone is wondering why high end solid state amps might cost more than their mid-fi brethren.

Our tube amps parallel of a lot of output devices as well, since they are lower power tubes and a lot are needed to drive speakers directly without a an output transformer. So we have the same advantage of the differences ironing out in the wash as you suggest happens in the output section of a traditional A or AB solid state amp. As these tubes age they tend to drift towards a common value; if tested a few months down the road they tend to test extremely close to each other! As a result (and also because of how the bias is controlled by a very low impedance circuit) the Bias and DC offset of the OTL is thus quite stable and not prone to drift. That kind of stability is part of why we’ve been able to stay in business nearly 50 years.

You may not get 100,000 hours on the equipment before corrosion has had a chance to damage the semiconductors, depending on how long it takes to log that much time. So there may well be a need to replace a device well before that. Just FWIW.

what is “”than that”, atmasphere?

Push-Pull amp tubes misbalance cause increase of odd harmonics, even 5% misbalance is causing more that 0.1% dist. increase easily.

keeping tube amp in a good performance condition is very costly, period. if not, you’ve got a “romance”

@westcoastaudiophile 

The statement to which I was responding mentioned that bias would be shifting in as little as 50 hours as well as resistors and capacitors. The simple fact is any tube amp is far more stable than that.

FWIW an imbalance in power tubes will cause a 2nd harmonic, not a third. The push-pull nature of the amp will cancel a lot of it but some will still be present due to the mismatch itself. Also FWIW dept.: the 3rd harmonic is treated much the same way by the ear/brain system as the 2nd in that it tends to be innocuous. Like the 2nd it does have the advantage in a tube amp of masking higher ordered harmonics- that is literally why tube amps tend to be smoother than traditional solid state (class D amps can make lower ordered harmonics in the same way, so they can share this characteristic with tubes depending on the design).

You are right about tubes being costly! They have always been expensive, which is why high efficiency speakers were so common back when tubes were the only game in town.

tube amp sound changes almost every 50hr due to tube emissions degradation, bias-balance degradation., accelerated resistor/capacitor aging, etc

This statement is incorrect. Tube amps in general are far more stable than that! With our amps its quite typical to not have to adjust the DC Offset after several months of operation. Back when we had a Bias control on our amps (about 17 years ago) people made similar comments about the bias not needing adjustment. If the amp is any kind of quality, its made out of resistors and capacitors that take 3-4 orders of magnitude to age out, similar to solid state in that regard.

To understand the dichotomy in tube versus solid state one must start forty or more years ago. Back then virtually all solid state was lean, trebly, and hard sounding. Tube equipment was warm and rolled off the treble and was wooly in the bass.

This statement is false. 65 years ago Harmon Kardon made the Citation 2 and a few years later the Citation 5, both of which had 100KHz response. The ’softness’ in the high end of tubes is correct. The brightness of solid state isn't- and is caused by distortion.

Generally speaking there has been a failure in the industry to recognize that the ear converts distortion of any kind into tonality: hence the 2nd harmonic imparts ’warmth’ and unmasked higher ordered harmonics as often experienced in solid state gear imparts harshness and brightness. The other inconvenient truth about the ear is that it uses the higher ordered harmonics to sense sound pressure.

These harmonics also have a lot to say about how instruments sound; if additional harmonics are present the ear will perceive things as being brighter than real life.

Tube amps generally have more higher ordered harmonic content than solid state amps do, but because of the ear’s masking principle (where a louder sound masks the presence of a quieter sound) their prodigious 2nd and 3rd harmonic mask the higher orders, allowing the amp to sound nice and smooth.

In case its not obvious the primary sonic differences between tubes and solid state, their ’sonic signature’, is really their ’distortion signature’.

If you could build a solid state amp with the same distortion signature as a tube amp, it would sound like a tube amp. That sort of thing is really hard to do with conventional A/AB solid state amps. But apparently it is possible with class D, since in some class D amps the things that cause distortion tend to create lower ordered harmonics (not talking about all class D amps, as they seem to have more variability in sound than tube amps do).

FWIW dept.: triode tubes are the most linear amplification devices known. So you might wonder what it is that tube amps tend to have more distortion. The answer is that tube amps tend to run less feedback as they have less overall gain, being a far simpler design. If you were able to have enough gain and therefore be able to run enough feedback the tube amp would sound just like a solid state amp.

Feedback is playing an enormous role!! One thing that limits feedback in conventional solid state amps and all tube amps is something called ’phase margin’ where if too much feedback is applied, at some frequency due to phase shift in the circuit the feedback is positive rather than negative. If this frequency is exceeded (for example due to harmonics caused by distortion) the phase margin is exceeded and so the amp goes into oscillation.

Another problem faced by all tube amps and most solid state amps is that of having enough gain and bandwidth to support the feedback. If it does not, feedback decreases with frequency at what is effectively a turnover point, usually at a higher frequency. This causes distortion to rise with frequency which is a recipe for harshness and brightness.

In addition, feedback is usually applied to a non-linear point in the amplifier, possibly the cathode of the input tube or the base of a transistor paired with an input transistor. This means the feedback signal is distorted before it can do its job, and so will add distortion of its own. It is for this reason the feedback has got a bad rap in high end audio.

Class D does offer some ways around these issues. Because it is very easy to get a high gain/bandwidth product, feedback can be supported at all audio frequencies, preventing brightness and harshness. If the amp is of the ’self-oscillating’ variety, you can add so much feedback that the amp goes into oscillation as soon as its turned on. The oscillation is then used as the switching frequency. By this method you can run quite a lot more feedback without it causing so many problems per conventional designs.

As a result you can have a class D amp that is as smooth as any tube amp, but with the greater neutrality (otherwise, without the brightness and harshness) of traditional solid state- best of both worlds.