Tube Valve 5.1 Home Theater [Early Research]

[nanogennari]

Hello,

I'm researching to make what i am calling "The Ultimate Tube Valve 5.1 Home Theater", i am new here in the forum, but i have some background in electronics, mostly with digital things, never done something so analog.

My idea is to make something not so powerful, the focus is in sound quality. I want all digital controls with an analog feeling (some pot knobs connected to an microcontroler). And to complete things i'm thinking to add an Raspberry pi and an HDD or something running an MDP server or something like.

I will divide the project in four parts:

1. The amplifier electronics.
2. The control electronics.
3. The speakers.
4. The MDP server.

I wold love to hear some suggestions, tips and etc. The fist thing i want to decide is the kind of Tube Valve i will use, i have no experience with valves, so... (And unfortunately i live in Brazil and we don't have good suppliers here  , most of my things are bough directly from china, there are not a lot of suppliers who ship to Brazil and even less who ship at a fair shipping cost).

Sorry if my English bothers you, i still need to enhance it.

I will post updates here, and of course it will be opensource/openhardware, see you guys later... 

[nanogennari]

Reserved for future updates.

[nanogennari]

Reserved for future updates.

[calexanian]

The tube amplifier part is well covered all over the internet. The hard part you are going to get into is finding a suitable high quality 5.1 audio break out system that does not cost a small fortune. That's my two cents. Most of the cheap ones online are of terrible quality from what I understand.

[nanogennari]

The tube amplifier part is well covered all over the internet. The hard part you are going to get into is finding a suitable high quality 5.1 audio break out system that does not cost a small fortune. That's my two cents. Most of the cheap ones online are of terrible quality from what I understand.

I don't plan to put an audio break out (at least not from beginning) i use my PC for everything, including media/TV etc, so i can use the motherboard analog 5.1 output, and in the future i can put a good PCIe soundcard in the pc to enhance sound quality.

[VK5RC]

Isn't the real killer the impedance matching output /speaker transformers,  you will need 6 of them.  Linearity/Frequency response  will be a real challenge!

[dannyf]

-The fist thing i want to decide is the kind of Tube Valve i will use,-

you typically don't care much about sound quality in an av IE 5.1 system. People tend to invest in sound quality in a stereo ie2.0 system.

if I were you, I would think first about output requirement (what impedance, what type of speakers, ...), the topology, then output devices...

for topology, google Williamson amplifier. There are also hybrid amps too.

[calexanian]

Isn't the real killer the impedance matching output /speaker transformers,  you will need 6 of them.  Linearity/Frequency response  will be a real challenge!

You could skimp on the 4 corner amplifiers. Surround sound limits the low frequency responce to them and rolls off below 100 hz. The center channel should be 30hz to 20khz full power bandwidth and the sub needs to have a low freq roll off at 20 hz. Hammond has suitable output transformers in thier catalog, but you are looking at several hundred dollars worth of them! It may be. Easier and cheaper to buy used tube amplifiers and line them up.

[SirNick]

Why not just use (e.g.) an Outlaw Audio model 975 for the decoding and switching, and build your tube amps as normal power amplifiers?  Any time you have to introduce a general-purpose computer, the results are going to be a compromise.

[dannyf]

!Surround sound limits the low frequency responce to them and rolls off below 100 hz.-

that's just for some surround sound formats.

it is better and more flexible to make all channels identical, other than lfe.

[NiHaoMike]

Would tube preamps followed by modern HVIC amps be good enough?

[jaxbird]

Tube amplifiers are interesting and fun, but I really would not recommend them for a living room everyday use system.

They are highly inefficient, e.g. I have a pair of 300B SET mono amplifiers, they consume about 75W each side and deliver max 5W with several % distortion!! The single ended ones are pretty much harmonic distortion generators.

Besides poor efficiency they generally have very high output impedance meaning the frequency response of your speakers will change according to their impedance.

Tubes are expensive, run hot and require lethal level voltages, if you have kids or pets you'll need to make sure they cannot get near them.

If you still want tubes, go with something like EL34 or KT88 in push pull configuration and be prepared to spend a lot of money on transformers, both power and output

[SirNick]

!Surround sound limits the low frequency responce to them and rolls off below 100 hz.-

that's just for some surround sound formats.

it is better and more flexible to make all channels identical, other than lfe.

Technically, yes and no.  I looked at the spectral content of a handful of movies lately and anything goes in modern discrete multi-channel soundtracks.  Some rear channels had marginal content down to infrasonic.  Some were clearly rolled off at 30-40Hz.  None that I found were high-passed at 80 to 100Hz.. HOWEVER... it is common (and usually desirable) for the decoder to have a HPF on all channels (except LFE of course) since nobody has a room that behaves well at sub-bass frequencies.  Ideal placement for full-bandwidth speakers is often not the same as ideal placement for subwoofer(s), so best to leave the long-wave stuff to the one box that has a fighting chance of being placed optimally for that frequency range.

Although, in reality, people usually seem to stuff the sub anywhere it can't be seen, and then stack all five main speakers up around the TV, so "ideal" placement is pretty much out the window anyway. 

[calexanian]

I have found myself enjoying better quality sound, than proper placement, from 5 low cost tinny speakers. I just ran a cable from my TV over to my old mini stereo system and it actually sounds better. Lets just say I don't "Notice" the sound, or rather notice something wrong with it.I would rather have two decent sounding speakers and a sub (Modern movies need a sub) rather than 5 bad sounding ones. 

[Yago]

I have found myself enjoying better quality sound, than proper placement, from 5 low cost tinny speakers. I just ran a cable from my TV over to my old mini stereo system and it actually sounds better. Lets just say I don't "Notice" the sound, or rather notice something wrong with it.I would rather have two decent sounding speakers and a sub (Modern movies need a sub) rather than 5 bad sounding ones.

I have a stereo system for my PC/movies, and find that the dynamics are all over the place.
Richard Crowley said it could be down to poor encoding of the 5:1 to stereo "mix".

So, whilst in theory two good channels should win out, in practice they can be difficult to live with IMHE.

[dannyf]

Over time, I have migrated to stereo listening, even for av materials, through logic 7

[calexanian]

of course source material and the signal chain be it electronic or software digital decoding makes all the difference. garbage in, garbage out so to speak.

[dannyf]

I'm sure it differs from person to person . For me, dsp is better turned off.

[bob808]

You could go for a push-pull system for better efficiency. With sensible drivers also you don't need much power. But in hot summer days you wish you'd have a solid state system
Usually tube are used for listening sessions not movies but hey...you can do anything

[calexanian]

More on the philosophical side than technical, but  I want to be drawn I to the movie, not think about the sound system.

[dannyf]

Usually tube are used for listening sessions not movies but hey...you can do anything

Valves have a considerable advantage over solid state for materials with high crest factors, like dialogues or explosions -> AV content.

However, they are not that great in LFE.

[ampdoctor]

Coming from somebody who works with tube audio day in and day out, if I were to design a home theater or actually any home audio system I'd stay with solid state front to back. Why? Tubes are shit when it comes to audio reproduction where you want to accurately hear what the artists and engineers want you to hear. No distortion, coloration of the sound, or generally quirky behavior allowed, or at least reduced to an acceptable minimum.
Sitting back and visually appreciating the vibe of the the red and blue glow in blown glass reflected off of polished wood or metal in a beautifully engineered enclosure can be quite satisfying in it's own right but it's a completely different conversation. This is perfectly OK in my book, but it has nothing to do with the quality of the actual audio.

Now, where tubes really shine is in the area of audio production. Here you may actually want the distortion products as well as the sound colored in specific ways and impart a "feel" to instrument amplifiers and arguably microphones that are very difficult if not impossible to mimic using digital methods. It's one tool out of many that are used for creating the audio that they want us to hear.

[dannyf]

No distortion, coloration of the sound, or generally quirky behavior allowed, or at least reduced to an acceptable minimum.

Those may be your criteria for a sound system but hardly everyone else's.

[mark03]

Has anyone characterized tube-amplifier distortion and simulated it in a DSP?  I realize part of the fun is in the old hardware (hey, I just built a nixie clock myself), but if it's the "tube sound" someone is after, surely it can't be that hard to just emulate it in software?

[SirNick]

The recording and live sound industries try very hard at this.  There are plugins for DAW software, digital modeling amplifiers, stompboxes, and rack units galore.  The authenticity of such attempts is under much debate.  Some people will tell you it's similar enough to be convincing.  Others will tell you there's no comparison.  Some of the latter will be influenced by the fact that they're looking at a solid-state box and not glowing tubes, and some of the former might be equally biased.