Guitar Tube-Amp Entusiast Seeks A/V Advice

[Proraso Man]

Hi there- I'm new here but not entirely new to tube amps- I own three tube amps for my guitar rig and have done a small amount of soldering and circuit assembly. I wanted to find out about building a good sounding, simple and pure A/V system based around tube technology.

I envision a tube preamp and monobloc amplifiers driving some speakers. How do things get changed when 5.1 or Dolby/THX sound get involved? What are some minimalist solutions?

I'm not sure if I'm interested in hours and hours of tweaking small component values in the garage; rather I'm interested in building some tried and true circuits that can help me create an awesome sounding home theater system.

thanks!

[ChrisA]

Originally Posted by Proraso Man

I'm not sure if I'm interested in hours and hours of tweaking small component values in the garage; rather I'm interested in building some tried and true circuits that can help me create an awesome sounding home theater system.

thanks!

First off it is clear that this CAN be done. An example would be a Hammon organ in a large church. These were all-tube sound systems and could literally shake the walls in a venue that seats 1,000 people.

No way around it. You are going to have to do some planning. It will not be cheap either.

The first step is to start with the speakers. No. Even before that, start with an assessment of the room to determine what speakers are needed. How big is the room and how much volume do you need. Almost certainly you will need large and very sensitive speakers on the order of 96 to 100 dB/W. Cheap solid state AV receivers can push 500W through small in-efficient speakers. Tube amps don't work that way. You will be pushing low amount of watts through big efficient speakers. The larger and more sensitive the speakers you can fit into your room the easier the amps will be to build. If you can fit a large 15", full range open baffle speaker in to the room then you can get buy with a small and simple single ended tube amp. Small speaks would require a more powerful and complex amp.

The way Hammon did it back in the 50's was to have one mono-block like tube amp for each speaker. They'd drive the treble speakers with one amp and the bass with an other. Today we'd call this a "bi-amp'd powered speaker" but Hammon called these "tone cabinets" and they would install several of these cabinets around the room.

If you are looking for a THX-like sound quality in 5 or 7 channels, I think you might do the same.

You will never be able to design the surround sound decoder with tubes. It needs a computer (DSP). You are going to have to buy an A/V preamp and then have it feed your collection of "tone cabinets"

If you are dead set on the idea of small speakers then you will need some serous wattage and a subwoofer with it's very impressive bass tube amp. Have you have seen a 200W bass amp? They're huge and not well suited for first time builders. But five 5W amps each pushing a pro-audio 15" driver will shake the walls in the house across the street.

I think you'd have a better chance of success building the smaller 5w to 18W amps. Get one to work that set up a production like and build 4 to 13 more.

My opinion is that it is NOT worth the time and money for for movie soundtracks. For music (stereo) yes. But a $6,000 audio system for explosions and dialog?

[Proraso Man]

First off, thank you!

It was this article that originally got me interested in the idea of a tube sound system, be it for movies or music. I happen to enjoy more of music, but I would like the same system to also perform the function of a home theater.

Stereophile: Definitive Technology Mythos STS SuperTower loudspeaker

In terms of efficiency- I am well aware of what SPL ratings mean for speakers. The speakers in my 30watt EL84 Vox AC30 guitar amp are 105db celestion blue's- one of the most efficient speaker designs due to the AlNiCo magnet.

For stereo applications, I am not aware of many speakers that are much beyond 96db. I thought the legendary klipschorn was incredible because of it's 105db sensitivity.

The speaker system that caught my eye that would be cool for music or home theater was the Mythos by Def Tech:



If not these speakers, what would you recommend that would be good for music, movies, and high sensitivity, and not above the cost of the Def Tech's?


In terms of amps, I have found a couple of schematics that use the 300b tube and are very simple power amplifiers.

What would you recommend for a multi-source pre amp that has the dolby/thx ability to process sound?

Thanks! This is the first step of a long journey I know....

[funkytek]

sensitivity in the high 90's is usable.
The size and type of room is critical, as previously mentioned.
Then you need to find a surround processor that has preamp outputs for all the channels. As it turns out this is more difficult than you might imagine. The vast majority of processors are receivers with their built-in amps. Few of these have a full set of preamp outputs. You have to find something like an Aragon Stage-One. This is what I use.

My system is something of a compromise. I have a Velodyne powered sub (solid state) and use Magnaplanars powered by solid state amps for the surrounds. Then I have heavily modified Altec A7 Voice of the Theaters for my mains. These are powered by tube amps. I only use the mains when listening to music. I use the full setup when watching movies.

The Maggies are excellent for surrounds and blend pretty well with the mains for the movies. Good enough anyway. When I finish restoring my old Citation II, I will use that to drive the side speaks. It has plenty of power for the maggies.

That is also an option. You can drive most any speakers with PP KT88 class amplifiers. Though they are big and heavy and warm, but then you can run pretty much any theater speakers. Unless you have a very large room....

[rman]

HI .

I use low lowered set amps for music and movies. my listening room is small, a 10 foot wide apartment living room. My front speakers are Mission m32i's and are rated at only 90db/w. They are driven by a 6em7 "accordion" ( see Broskies tube cad journal ) amp my rear speakers are value village finds, really old Sony's with 8 inch alnico woofers rated at 97db/w. they are powered by Gary Kaufmans 6em7 DC amp. For music, I run the rear speakers in a Hafler matrix mode.

For movies, I use my pc as the source. The player is a free download called media player classic. I have it set to mix the centre and sub woofer channels to the front with the soundcard set to four speaker mode. I keep reading how low power amps need incredibly sensitive speakers, however I used to use the smaller amp with the Missions in a huge living room of an old farmhouse for music and I loved it!

This may not suit everyone but I think it shows that good results can be had with modest means.

Creative labs has a stand alone surround sound decoder the takes the digital output from a dvd player and output front center and rear channels from 1/8 inch stereo jacks. I have one of theses and used it with a set of 5.1 altec lansing computer speakers for home theater in the above mentioned farmhouse. It would work fine with your multiple tube amps as well. I just checked it is still available and is a great little product.

Cheers.
Rolf.

[Proraso Man]

thanks for the advice so far- I think the pc based approach for the front end of things would work well for my set up.thanks for the tip on the creative unit- i assume you're referring to this:



now I just have to figure out my sources- I want to have blu ray, pc cable box and antenna all display on the tv easily. I can see why a/v receivers are appealing...

[rman]

Actually, I was referring to this
Creative Decoder DDTS-100 - Dolby Digital EX, DTS-ES, Pro Logic II & DTS Neo:6.

It works with a regular dvd player. What you found would be great for the pc based approach.

[ChrisA]

Originally Posted by Proraso Man

In terms of efficiency- I am well aware of what SPL ratings mean for speakers. The speakers in my 30watt EL84 Vox AC30 guitar amp are 105db celestion blue's- one of the most efficient speaker designs due to the AlNiCo magnet.

For stereo applications, I am not aware of many speakers that are much beyond 96db. I thought the legendary klipschorn was incredible



In terms of amps, I have found a couple of schematics that use the 300b tube and are very simple power amplifiers.

If you are going to buy a full set of 5 speakers five of those klipschorn could get expensive. A lot of people are going with "full range" drivers. Some of these are as good as your Celestions and maybe even made by them and sold as "pro audio" drivers. Look at these Iris drivers for $145 each. they are 96db.
Drivers

Thar 300b tube is not inexpensive. I think you'd do as well with 6L6, EL34 or KT88 tubes. But the really the big ticket item in a amp like this is the output transformer. The choise of OPT matters more than the choise of tube. The OPTs also cost more then the tubes too (unless yu are into esoteric types like the 300b.)