What makes an amplifier "bright", "warm", or "neutral"?

[Ren Hoek]

I hate them too, man.

Ren

[AudioFreak]

For SE Class A output stages MOSFET's are SWEET!

[fmak]

Originally posted by JohnS
Which component, components, or circuits make an amplifier "bright", "warm", or "neutral"?

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bright - lightly biased Class B/AB stages; some opamps; cheap metal film resistors; some metallised pp caps; most cheap lytics; hf noise or oscillations in circuit adds brittleness

warm - polyester caps; oil filled ones; some class A stages.

Just a few descriptors from experience

[JoeBob]

fmak, are you telling me you like the sound of polyester caps? I've always heard they were the worst poly cap. Sometimes I have to use them due to cost though...

[tschrama]

Does anybody know any software which can add some harmonics to the signal ( 2nd or so) to perform the test?

You can try to build a analog octave device.. used for guitar effects.. look at http://www.geofex.com/

gr,
Thijs

[DocP]

Originally posted by Koy
Reading the first post an indea struck me. People say the tonality can depend on amout of upper harmonics ( prevailing even or odd harmonics). Does anybody know any software which can add some harmonics to the signal ( 2nd or so) to perform the test?

I am of the opinion, from my own experience, that it is not as simple as 2nd v's 3rd harmonic. Rather it is the relative distribution of harmonics that is important. Also, there seems to be a strong similarity between the distribution of harmonics in valve amps and class A transistor amps, class B being quite different to these two. This might help to explain why class A are reputed to have a warm "valve sound".

I have done subjective experiments in audio in the past and they are very difficult to design so that they give you unbiased results. The best way to go about it would be to capture some suitable music samples from a CD and then pre-process them using something like Octave running on your PC (free Matlab clone found at www.ocatave.org). If you are not familiar with DSP there is a steep learning curve to using programs like this but they are hugely powerful. You then would need to perform double blind tests using processed and unprocessed versions of the same track and analyse your results later. You have to be very meticulous to avoid biasing the results but if you go for it, I'd love to hear your results.


DocP

[fmak]

Originally posted by JoeBob
fmak, are you telling me you like the sound of polyester caps? I've always heard they were the worst poly cap. Sometimes I have to use them due to cost though...

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No, just that they are warmer than pp

[mrfeedback]

Distortions spectrums and tiny abberations in static and dynamic frequency response, and source and load dependance, and slew rate limitation.
0.1 dB frequency response ripple is audible and apparent.
Also reaction to noise input.
Noise spectrum input and load noise spectrum can both be modified and substantially alter the percieved sonic character of a system.

Regards, Eric.

[Brett]

<b>What makes an amplifier "bright", "warm", or "neutral"?</b>

Bright: uses thoriated tungsten tubes
Warm: turned on, esp if uses tubes or SS class A
Neutral: beige chassis

[HarryHaller]

Way to go Brett! Maybe the only honest rational answer possible to such a broad question. All one has to do is design amplifiers for about 10 to 20 years for the real answers to this question. I would not even dare to propose an answer and I don't think anyone else in his right mind would either as there are thousands of things that can effect this highly subjective classification.