"Warm Sounding" Solid State Amplifiers

There are quite a few "great" sounding SS amps, now, and, as far back as the late 70's!

One of those was the H/K Citation 16. If you found one though, expect to get the filter caps replaced.

You may find that finding a transistor amplifier that has the warmth associated with real music (and tubes) to be harder than replacing the occasional tube.

IOW, if you seek the musicality of tubes, why not just get a tube amp and be done?

Csontos, I play in a band and have played sting bass in orchestras since I was in 7th grade. Not that that makes me an expert, but I do attend a lot of concerts. I agree that concerts with amplification are anything but warm.

But if I go to an unamplified concert, I like to close my eyes and imagine listening to a stereo. Try it sometime- and critique what you hear- is it too bright, too warm? What I find is that warmth is more often the thing I hear rather than bright and harsh, the latter being a common hallmark of solid state, hence the existence of this thread :)

Tubes BTW do not have an emphasis on a certain range of frequencies. A lot depends on the amp!! What is commonly associated with the 'tube sound' is the 2nd harmonic, which does not have to exist in a tube amp as the harmonic distortion signature is highly dependent on the topology of the amplifier circuit. This is true whether tube or solid state. If you recall, triodes are universally regarded as highly linear; moreso than most semiconductors, so where does that 2nd harmonic come from? It comes from the topology.

For example if you design to be fully differential and balanced, the primary harmonic product will be the 3rd harmonic, not the 2nd.

Transistors have a non-linear capacitive aspect that is multiplied by the current through the device at their junctions. This property is well-known, for example there is a device that is used for tuning FM radios known as a varactor diode that takes advantage of this capacitance.

This aspect makes it difficult to avoid odd ordered harmonic distortion and despite large amounts of negative feedback, will remain present in solid state amps where it is absent in a tube amp. Because our ears use those harmonics as loudness cues, they are more sensitive to them than state of the art test equipment- we can hear their presence quite easily while they are hard to measure with test gear.

So as I see it, the point of this thread is what amps are lacking this particular distortion while also being solid state? The answer is 'none' and is part of the reason the tubes/transistor debate has raged in the audiophile world longer than the existence of the Internet.

Audio is often a set of compromises, in engineering parlance certain aspects are sometimes deemed 'negligible' when actually they are not. Trace amounts of odd ordered harmonic distortions are an example.

So again- to Pontifex, consider a tube amp- they are not as unreliable as you suggest in your initial post. You are going to be chasing the Holy Grail for a long time in the solid state world if you do not. So if you really can't do a tube amp, just accept that such will be the case and Good Luck!

Csontos, thank-you for your reasoned reply. I thought you might like to hear a number: 600, as in 600V/uS, the risetime of the output section of our amps. Tubes don't have to be slow nor dull any leading edge transients.

I agree with Mapman- there is something that is neutral, neither bright nor dull. The thing is, when audiophiles talk about bright or dull it is rarely about actual frequency response errors. The brain translates distortion into tonality. This is why single-ended circuits (tube or solid state) tend to sound 'warm'; its not a frequency response error, its the brain translating a 2nd ordered harmonic into tonality.

Our ears use the higher orders, 5th and above, as loudness cues- the brain uses these harmonics to calculate how loud a sound is and does not rely on the fundamental tone for that. As a result, our ears are more sensitive to these harmonics than the best test equipment- we can easily hear these harmonics as distortion where its difficult to measure.

This is why two amps on the bench might have the same bandwidth, but one might be bright (has a trace of higher ordered harmonic distortion) while the other does not. In addition, the ear/brain system while translating higher ordered harmonics into brightness, also translates the same into harshness.

Its my stipulation that it does not matter whether the amp is solid state or tube so long as these harmonics are not added by that amplifier. IMO/IME the best systems have a sense of ease at any volume and there is never the quality of 'loud' no matter how loud its actually playing. This BTW is a property of real music.

Sunn made some guitar amplifiers that were solid state back in the 1970s. Now if anyone here plays guitar and uses an amplifier, they know that most guitar amplifiers are vacuum tube, on account of if you want to overdrive (distort) them, you need tubes to have them still sound like music. But Sunn made solid state amps that at the time and to this day were recognized for having a 'warm' sound to them. When you look at the schematic its obvious why: the preamp section employed FETs in a single-ended topology with zero feedback (the FETs being very linear did not need feedback; the primary distortion product being the 2nd harmonic), and the power amp section was also single-ended until converted to push-pull by a driver transformer. So the power amp was rich in 2nd orders as well.

Now I am of the opinion that the 2nd order that is traditionally associated with tubes does not have to be there. That is why we make our amps fully differential and balanced; even orders are canceled not just in the output section but at every stage inside the amp. So while they sound smooth and are detailed and fast, they don't have the warmth associated with a lot of tube amps. The take-away is that topology plays a bigger role.

The Sunn amplifiers are considered obsolete designs, but if you really want warmth as a sonic attribute finding an amplifier of that type (or building one) might be a consideration.

Csontos, it does not matter if it is live or reproduced, our ears listen for those harmonics (which are always there) regardless. We can't change that!

Quite simply, the application of physics to design equipment to honor our human hearing/perceptual rules will result in better sounding equipment:

What we *can* is change our approach to how we are going to playback recordings; i.e. design the equipment with intention to simply not make those distortions to which our ears are the most sensitive. These distortions are IM (which might also be termed a special form of 'inharmonic distortion') and the higher orders of harmonic distortion, the 5th and above.

(Our amps (Mk3.2) are full power out to about 300KHz since you asked.)

Those designers like Nelson Pass and Charlie Hanson (Ayre) that have sorted out that feedback can be dispensed with are also demonstrating that such leads to a more musical approach. Norman Crowhurst is required reading for anyone designing audio circuits. About 60 years ago he wrote about how the application of loop negative feedback in an amplifier that does not exhibit higher ordered harmonic distortion (like an SET which might have the 2nd, 3rd and 4th harmonics) might well reduce the lower orders to vanishingly low levels, but in the process higher orders (starting with the 5th harmonic) will be added going clear up to the 81st harmonic! In addition, intermodulations can be introduced at the feedback node in the amplifier.

The result is that the noise floor is fundamentally altered. In an amplifier that has no feedback, the noise floor is hiss, not unlike that of the wind and the sound of water moving. Not by coincidence, our ears are adapted such that they can hear into such a noise floor, some say as much as 20 db but to be safe 10 db for sure; this is the *one* exception to the human ear's masking rule. This allow us to hear detail that exists below the noise floor of the amplifier and if you think about it, essential to our survival.

When loop negative feedback is applied (per Crowhurst) this noise floor is altered and while it might sound the same, the peculiarity is that our ear's making principle is in full force- we cannot penetrate that noise floor, so the detail below that point is lost.

This is why amplifiers that employ loop feedback seem to loose low level detail in which room ambiance and imaging detail in the rear of the soundstage resides. To hear this occur, you must start with a recording that has plenty of depth, then you can audition that difference between the two approaches.

Since the application of loop feedback also adds harmonics, this is why any amplifier using it can sound brighter as well, since our ears sense those added loudness cues.

Nelson Pass has a wonderful article on distortion on his website: https://www.passdiy.com/project/articles/audio-distortion-and-feedback; Nelson is one of the leading designers worldwide.

^^ The number on the bit of paper is a good example of the Emperor's New Clothes.

We all know this- can you definitively say how an amplifier will sound by looking at it specs? We all know we have to take the amp home and play it to see if it will work in our systems. The paper specs are for marketing- the specs were not designed to have very much to do with how we hear; they have everything to do with selling the amp.

Now if we developed specs based on human hearing/perceptual rules then progress would be made.

^^ :) so you are saying you can tell how an amplifier sounds from its specs? Like many analogies there is a certain point where it falls apart.

I find that if anything, there is an inverse relationship with THD (higher will likely sound better) a positive relationship with IM (lower will sound better) and wider bandwidth is usually good. But even knowing that I still can't predict how it will sound.