Anyone can tell me how to create vacuum tube like sound ?

As title,
I've been hearing some of the DSP-based tone generator which wanna be close to vacuum tube sound, but they mostly sounds not real.
Therefore, I'm appreciate if anyone in this forum can give me some advice.

Re: Anyone can tell me how to create vacuum tube like sound

focusdeepwarm01,
Careful!!! Mentioning "vacuum tube sound" in audiophile circles is akin to beating on a hornet nest. Nevertheless, here goes:
~
Vacuum tube amplifiers are characterized by "soft limiting". This means that as the output level increases, the harmonic content and intermodulation product content gradually increase. Many experts attribute the vacuum tube (valve) sound to this characteristic. If the vacuum tube amplifier is push-pull, and perfectly balanced, then there will be no even harmonics. A Fourier anlaysis will show this (all symmetrical waveforms are free of even harmonics). The gradual flattening of the input-output characteristic (soft limiting) can be simulated by a DSP.
~
Others attribute the vacuum tube sound to other mystical properties involving the phase of the moon, visits by the Easter bunny, and the listener's shorts being too tight. I'm afraid that I can't help you there.
Regards,
Kral

Re: Anyone can tell me how to create vacuum tube like sound

Hi Kral,
Thanks for the reply, and could you advise me where do you have the info ( that I might dig them as well ) ?
Thanks ~

Re: Anyone can tell me how to create vacuum tube like sound

focusdeepwarm01,
I'm not sure exactly what you need. You can consult a tube manual to get a look at various characteristics. Typically, for a triode such as the 6SN7, you can find a plot of Plate Current vs Plate voltage for various values of grid voltages. From this you can plot Plate current vs grid voltage for a given plate voltage. This will give you an idea of the non-linearity that is characteristic of the tube. A higher power tube is the 2A3, which is a high power triode. You could also look at the EL34, EL84, 6L6 which are high power pentodes. The gain of pentode tubes is characterized by Hfe. This is equivalent to the forward transconductance of a MOSFET. By plotting plate current vs grid voltage, for a given plate voltage, you can get an idea of the non-linearity of a pentode.
Regards,
Kral

Re: Anyone can tell me how to create vacuum tube like sound

Kral,

According to you, "the gradual flattening of the input-output characteristic (soft limiting) can be simulated by a DSP". I'm not sure about the word "simulated" here, you meant emulated right? Based on your explanation, if one were to obtain the impluse respose of the tube, one can readily replicate its effect using a modern DSP chip. Isn't this right? If so, then how come marshal, and in turn its loyal clients, insist on incorporating this obsolete hard-to-maintain technology in their products? There has got to be some rather complex maybe non-linear effect to it such as emulating the effect of our beloved tube is beyond what current real-time DSP technology has to offer. I would really like to hear your opinion with this regard as you sound pretty exposed to this subject hehe.

Cheers.

Re: Anyone can tell me how to create vacuum tube like sound

Manny,
After re-reading my last response, I see that it is not a model of clarity. The non-linear characteristics that I'm referring to are time independent. They represent static characteristics. The vacuum tubes that are used in audio work were all designed for RF applications. As a result, for audio work, the frequency responses can be considered to be infinite with no significant errors.
~
You are correct; "emulate" is a better word.
~
One way to emulate the vacuum tube would be to represent the input-output characteristic by a polynomial expression y(Vin). For example:
Vout = C1 X Vin + C2 X Vin^2) + C3 X Vin^3 + ...
This is well within the capability of DSPs. Then the output would contain the same harmonics and intermodulation products that the vacuum tube would produce.
~
Guitarists seem to like the characteristic sound of tube amplifiers. Marshall et. al. are happy to acoommodate them. One reason might be that the addition of harmonics to the fundamental just sounds pleasing. Of course, the higher order harmonics sound dissonant, but the amplitude of the higher order harmonics is generally quite low, until the output approaches "hard" saturation (flattening).
~
Regarding "sounding pretty exposed"; that's one of the few advantages to being ancient. Engineers of my generation were all exposed to tubes.
Regards,
Kral

Re: Anyone can tell me how to create vacuum tube like sound

Kral,

Thanx for the elaboration. However, I still haven't got a direct answer to my question. Bearing in mind how difficult it is to maintain tube-based amplifiers, the burden of running a production line for obsolete tubes, and how cheap it might be to mass-produce a modern Signal Processing chip (I'm talking in here about custom-made chip analogous to the image processing one often seen in everyday's optical mice!) that replicates the tube unique characteristics. Bearing in mind all these factors, why not replacing tubes if their characteristics are very much understood and can be easily emulated in todays hardware (which by the way doesn't have to be digital of course i.e. no need for A/D & D/A overhead)?

Thanx in advance.

Cheers.

Re: Anyone can tell me how to create vacuum tube like sound

Manny,
In my opinion, there is no reason that the tube characteristics can not be adequately emulated. Double blind listening tests would surely confirm this. There are, however, some caveats:
~
Assuming that the output stage is linear (as opposed to class D),
it must be class A in order to avoid the crossover distortion
characteristic of class AB that tube aficionados claim that they
can hear.
~
The tube (glass audio) crowd is zealous, almost to the point of
being a cult. You have to deal with the customer acceptance
factor. Many potential customers simply will not accept
a product that does not have a tube output stage. I have read
articles about commercial and do-it-yourself amplifiers that use
tube rectifiers (e.g., 5U4s) in the power supply because of claims
that there is a difference in sound between amplifiers with
tube rectifiers and amplifiers with silicon diode rectifiers! This
is the same crowd that purchases $1000 audio cables made
of genuine imported, oxygen free, galvanized mahogany
Regards,
Kral

Re: Anyone can tell me how to create vacuum tube like sound

Kral,

Thanx for the "enlightening". You definitely sound like knowing exactly what you'r talking about hehe. Did I mention that I'm big 80's & 90's heavy metal/hard rock fan so I know exactly that people in this sort of "cult" will never replace their beloved old fashioned amplifiers with anything, not in million years.

Cheers.

Added after 6 minutes:

Though big time dumbheads, we can't help but saluting them for their incredible talents <Bows>, hehe.

Re: Anyone can tell me how to create vacuum tube like sound

On the oxygen free mahogany, There are so many built in bimetal contacts that can cause distortion that minimizing this unmeasurable source is useless. Inside the transistors there are four different materials, silicon, aluminum, gold and whatever the lead frame is made from. On the PC card there are copper-solder contacts. Inside the speaker there are more of the same.

The major source of distortion in an audio system is the speakers. One source is non-uniform magnetic fields around the voice coil.

I had an interesting experience many years ago. I was at an audio shop and they were playing classical music from the romantic period which had large 100+ number of musicians. When switching between the highly aclaimed Acoustic Research AR3a speakers and the upstart Advent company speakers I noticed that on the Advent ones I could hear triangles being played in the background. On the Acoustic Research there was so much IMD in the higher octaves that the triangles could not be heard.

Re: Anyone can tell me how to create vacuum tube like sound

Hi Flatulent,
Thanks for your reply, here I have some questions,
1. what does it mean in your reply "oxygen free mahogany" ?
2. how do you know the bimetal contacts can result the distortion ? any analysis ?
or just hearing by ear ?
3. what does "IMD" stand for ?
4. to my understanding, Acoustic Research is a branded company, how come the
newer company Advent performs better that AR ?
5. Do you have any information regarding "how to build a speaker" ? Here I
mean how to build the loudspeaker itself, not regarding the cabinet, I search
quite a lot in bookstore, ebay, or internat, but most of them are talking the
enclosure design.

Re: Anyone can tell me how to create vacuum tube like sound

Sorry to be so late but I just noticed your post.

1. I was making fun of the statement earlier about galvanized mahogany. The big sacred cow now is that oxygen in the copper speaker cables form rectifying contacts which cause distortion. Some decades ago the 'damping ratio" was the sacred cow. This was the ratio of the speaker impedance to the amplifier output impedance. This was a meaningless term since the speaker voice coil has a DC resistance of about 80% of the AC impedance.

2. Bimetal contacts have contact potential and form pn junctions that have mild rectifying characteristics.

3. IMD is intermodulaltion distortion. This is easy to detect by listening than harmonic distortion which makes an instrument sound somewhat like another instrument.

4. Older companies tend to drive away talented people and retain incompetent boasters. Newer companies are the opposite. Good boards of directors of older companies notice the sales declining and boot out the incompetent executives that retain incompetent boasters and toadies. Bad boards do nothing and the company fades away. Do you remember the late RCA and Marconi?

5. I have no knowledge about actually building speakers.

Re: Anyone can tell me how to create vacuum tube like sound

The sound of vacum tube amplifiers, is like the sound of british rock guitarrists, warm, vintage, understandable ...
Anyway any experienced musician can notice about the difference, of a DSP or real vacum tube amp simulator.

Re: Anyone can tell me how to create vacuum tube like sound

these types of effects as thats what it is simply introduces 50 or 60Hz to simulate the grid sound that will leek into the audio as smoothing in thse amps is crap
and pickup is great from poor cables etc

what i do to get a vacum sound is wind a lenght of your input cable around a 28mm copper tube 2ft long

and then place a small bulb inside
the bulb is driven from a transformer the audio is modulated to the lamp also
but out of phase by 180 deg
you can use ac to drive the bulb but use a bridge recifier and no smoothing cap after it as your supply power

pull the lamp in and out the tube to increase or decrease the effect

you can also tune the modulation also add other noise to it maybe a room mike

so... ill draw the circuit if you like its quite simple


and very effective ...hoho

pm me if you want me to do this




forgot to add you can also add a control winding to the tube end and also cut slits in the tube

lots of things
did think of it as a commercial product however i protected the idea anyway

i found sewing machine bulbs are good and also fluresant tubes can be used but dont work as well as a long tube from the fishtank

the warmth in the sound is caused by room or ambiance triggered microphonic reverbiration
where the wires in the valves move around as the amp body moves and shakes
{microphonics} so its sits and hums but instead of it altering the sound or giving a feedback
all it does is alter the phase and interphasial relationships that the tubes plasma fields generate when its on and turned up a little

so... to add this just use the control winding and modulate that with inphase audio but taken from a tap on the bulb and amplified {i just also pass the lamp feed thru it}

Re: Anyone can tell me how to create vacuum tube like sound

everyone who answered seems to try to digitze everything infact every topic where stupid engineers try to invent a device in the analogue realm and cant
jump at the all powerfull dsp

and totaly miss the goal

here a tube based sound is no use unless an analogue depth is preserved

digital shmigital
bring back the plexiglass