A U D I O... P A P E R

Audiophile Home Theater

Overcoming obstacles in blending two channel and
5.1 with the goal of having the same fidelity on both.

April 2011
by Steve Deckert

I remember the first time I tried to create an audiophile home theater... it was before I started Decware and I was given a good Denon Home Theater Receiver as payment against a bad debt.  I used great speakers for the front two channels and experimented with a variety of things for the rest.  It was OK for watching movies and by most standards probably sounded pretty good.  Of course the real test is to remove the TV and try serious two channel listening with the same system and it was always a sobering reminder of why my two channel system consisted of Single-Ended Triodes and a good source as opposed to a cheap DVD player.

It's easy under these typical conditions to take the attitude that home theater and two channel just don't mix.  You have one or the other, or keep them in separate rooms.  Then when you consider that big screen TV sets placed between your loudspeakers ensure compromised imaging it's pretty easy to build a case against having any success of blending the two.

Nevertheless, I got my hands on a DVD player with discrete outputs for each channel that was actually listenable when playing CD's so I got the great idea to hook up my tube amps to all 5 channels, which I did.  This takes the Denon 5.1 receiver out of the picture and it should sound pretty good.   I set it all up and put a good movie in and put my TV between the speakers and had an interesting problem.  The TV was a bit small, the room was set up for imaging and sound-stage in a big way for two channel use and now suddenly the movie was imaging so big and so well it made the TV seem like a tiny spot in the middle.  It was so distracting in fact that it became impossible to follow what was going on in the movie.  I had to restart it more then once after realizing I forgot to watch it... so wrapped up in the sound I was.

I quickly gave up because it was impossible to focus on the movie.  I put the Denon back in and with the two-dimensional boring performance it brought to the table, I could once again watch the movies.  My conclusion was that a big screen would be required if I were ever going to make this work.  At that time projectors were not an option and a big screen TV would be too big to move from between my speakers when I wanted to listen to two channel.

Years later I set up a small studio in my garage, a free standing building, where I found myself spending a lot of time listening and recording.  After the first several years of weekly recording sessions I started using a HiFi VCR as a live two track machine as an inexpensive way to have analog masters that came directly off two room mikes.  We hooked up a black and white video camera to it figuring why not, and found listening to these tapes and watching the video was really enjoyable after a session. 

Since we're out there watching these videos all the time anyway, it might be fun to set up a home theater and watch a few movies out there.  Well times changed and now flat screen TV's were just becoming available.  I wanted something large enough that a room full of people can see and of course I wanted a great picture so I started to look at plasma sets.  After realizing I wasn't going to spend five grand on a TV I looked into projectors and was pleasantly surprised to discover they had come a long way and had gotten affordable.  In fact for less than 1/3 the price of the Plasma I would have liked to have owned, I was able to get a higher resolution picture that was over twice as large with the projector.

Projectors are the answer because it allows you to set up your room for two channel, ie., nothing between the speakers but empty space and perhaps some diffusers so that you have maximum sound stage depth and focus.  The worse thing you can do is to put a reflective flat surface between your speakers if you want stable and focused imaging with good depth.  So you simply do one of two things;  Use the wall behind the speakers for the screen and cover it with drapes during two channel use,  or if you have diffusers on the wall behind your speakers (like you should) you simply pull a retractable screen down from the ceiling when you want to watch a movie.

So this is what I did out in the studio where I had an excellent setup for two channel playback.  Basically I set up an ideal test bed to explore the potential of audiophile home theater.  In this studio, every speaker and every amplifier Decware makes is tested 7 days a week so it would be easy to try multiple different types of speakers, amplifiers, cables and so on.

We set up the system based on two decent DVD players with discrete outputs for each channel and jumped in with both feet.  Our original motivation was to watch music videos and concerts which we did - with mixed results.  Regrettably there were more than several that simply didn't sound good.  When this happened, we would explore every possible option including different amps and or speakers or DVD players until we found some way to make it sound good so we could watch it.

Often the amount of bass was an issue, or that the bass simply didn't blend well with the rest of the sound.  Often the sound was harsh or thin.  Often the engineers had wild ideas about how they should distribute the sound to 5.1 speakers and had us shaking our heads in disbelief several times.

This was about the time that I decided if I had to use one more poky on-screen setup menu I was going to start shooting things.  We had already figured out that some movies sound better in stereo and some sound better in 5.1 but some sounded dreadful either way.   You see, it's what they put where that makes it work or not work.  Many movies or music videos would try to do all the vocals from the center channel and all the music from the fronts which does not sound right.  Others would blend both music and vocals on the center and use the main speakers for only ambiance or effects and that doesn't sound right either.  Some would have sound come from the rear channels only on occasion, which is also less than realistic.

So you need a way to access every channel and if you don't like the sound of it, you pull the signal for it from somewhere else.  In our case this meant about an hour or sometimes two hours re-arranging how the gear was hooked up.  Then when you finally get a usable sound from the movie or even perfect the temporary satisfaction is burst when you put the next movie in because now everything has to be set up differently.

A preamp  or analog control center will have to be built so we can accomplish all of these configurations and adjustments on the fly without having to unhook anything.

You can't run around the room and adjust the volume on each tube amplifier for very long without growing tired of it, and you can't use a solid state receiver to control things as it would completely ruin the sound quality, so there is no other solution.

The right preamp would allow us to hook all 6 channels from the DVD player to 6 different amplifiers and have all the knobs in one spot.  Of course making such a preamp is complicated and making it good enough to be left in during two channel playback would make it even more challenging.  If I find myself having to take the preamp out of the loop to get the best sound on two channel playback there would be no point to this project for me.  I had to combine both Home Theater and 2 channel in the same space because it was the only space for either that I had at the time.

This would be interesting, because many nights by the time we got the movie to sound good, we were too tired to watch it.  Having the ability to adjust the volume and sources for every channel from one device was going to be a God send.  You see, the pre-flight check on your DVD player via the on-screen set up menus where you adjust the levels of each speaker with pink noise is almost worthless.  The movie will determine how loud each speaker plays at any given point and assuming your have all the levels matched before the movie starts, you can be reasonably sure something will be too loud or too quiet.  

How many times have you stuck your head by the rear channels to see if they're on?  Hard to tell considering many movies don't put any sound out on the rears except in certain scenes.  How many times have you wanted to adjust your sub woofer and found that's impossible unless you wait for the first explosion to occur in the movie, and of course being either too loud or too quiet, it's back to the on-screen set up menus again and about that time you press the wrong button and end up at the main menu having to start the movie all over again!

You get the idea...  so I pondered the circuit design for a new preamp for several weeks until I figured out a way to accomplish cross channel mixing without the sound of one channel effecting the other.  The main front channels would be used as my main two channel system and I didn't want to ever hear the sound of those front channels change when other channels were engaged or switches were thrown.

Then there was the other consideration, and that is that very few DVD players are considered "audiophile grade" so what can we do to make the DVD player sound better?  Up till now we ran three ZBOX's on the output of the DVD player to make it sound better, and it does.  So what I decided to do is build an 8 channel preamp where 6 channels are used for home theater and the remaining two channels are for hi-fi.  The hi-fi channels will serve double duty and handle the front main channels during movies but with different circuitry.  Then on the 6 movie channels I'd incorporate the ZBOX circuit right into the preamp but kick it up a serious notch by using tube rectification and tube regulation on each channel.  That's something the ZBOX does not have, plus the absence of the extra cables and power cords can only improve things further. (ZBOX technology puts back the even order harmonics that are continually stripped out of the music my solid state devices including the DAC chip itself.)

Once these ZBOX circuits fix the sound from the DVD player, the signal is passed on to another triode gain stage so that we have more than enough control and dynamics to work with the vast majority of amplifiers.  As you can see it's hard for me to build anything that's just for myself.  In the back of my mind is always the thought that if it works and I really like it I might decide to manufacture it.

The next trick was going to be a way to move the inputs around.  There will be 4 pair of front main inputs so we can have 4 sources.  I expect two of them to be used with the DVD player and the other two for my good 2 channel sources.  On the first pair of inputs we'll connect the Front Left and Front Right from the DVD player.  (the Center, Sub, Left Rear and Right Rear from the DVD player will also be plugged into their dedicated jacks on the preamp) On the second pair we'll hook up the Left and Right stereo outputs from the same player.  This way I can mix the remaining 4 channels (center, sub, rears) from either input when the soundtrack isn't pleasing.  When a soundtrack in a movie is all screwed up, you'll be able to down-mix to any channel from the Left Front and Right Front inputs OR the Stereo Inputs that will have all the information in them.  Depending on how the soundtrack is mixed and decoded depends on which way works better.

Then we need a bridge switch for each of the remaining 4 channels, so we'll install one for the Center and Sub, and one for the Rears.  This way we can switch the inputs for these channels from what's coming direct from the DVD player's Center/Sub/Rear outputs TO what ever is coming out of the main channels.  For example, movie starts and there is no rear channel information except for some occasional noise effects.  Most annoying.  Find the bridge switch for the rear channels and flip it.  Problem solved.  Now you have signal going to the rear channels at all times creating ambiance for the front channels.  Another example, center channel holds most of the movie and the main front channels only play on certain scenes.  Again, most annoying.  Fix, flip the bridge switch for the center/sub channel and switch the front mains to the stereo inputs.  Problem again is solved. 

This also allows you to complete your adjustments before the movie even starts.  How?  As you know most previews that you watch before the movie starts are not in 5.1 so there is no way to know how loud your center channel, rears, or sub will be until after the movie starts.  Well, now you can simply flip both bridging switches and have the sound come from all your speakers and then simply adjust the levels of the center/sub and rears to your liking.   Then return the both bridging switches to their previous position and enjoy the movie in 5.1.  No more waiting for a bomb to go off in the movie to find out if your sub is working and set to the right level.

Since we're talking about subs, we found out fairly quickly that having a separate volume control for the center channel and the sub woofer was a mistake.  In virtually 100% of every test, we observed that the sub woofer level must always be proportional to the center channel level.  If the center channel is raised in level, the sub must come up with it, and visa versa.  So we tied the two together with a single control and it made life much simpler with one less thing to think about...

By this time things are working extremely well.  We're batting 100% now with every movie and every music video, all adjustments are easily made on the fly, usually before the movie even starts, during the previews.  If part way through the movie we want a bit more rears, bit more center or a bit less fronts, it's so easy, just 3 simple knobs.  No more pausing the movie or trying to find the light switch.

Of course there was a nice side effect from all this.  During serious two channel listening, I found out how easy it is to add a touch of center channel which is kind of fun.  You know the first stereo invented was actually three channels.  A mono summed center channel and a left and right.  Now you can recreate this at will.  Also found out that blending a touch of sound to the rears for ambiance almost always enhances the experience.  The trick to doing this without screwing up your imaging is moderation.  Very tiny amounts are needed.  It may take several minutes for you to find the right levels, usually just a tease that you can't really hear unless you put you ear up to the speaker.  Now that these levels are set, your going to instantly want to hear it without the additional speakers so you can compare the sound with and without, but if you turn the levels back down, you'll loose your settings!

Enter the Master Volume control for the Mixed channels.  After you have added that delicate amount of center, rears or both, you simply turn them up and down as a group with the master control.  This lets you hear your two main channels by themselves and then the stuff you added in comes at the turn of the master.  The master makes it possible once you've got the ratio of center channel to rear channels set where you want it, to adjust these added channels as a group up or down, independent of the front channels which have their own volume control and can not be effected by anything else on the preamp.

So the Master control was also implemented and that completely satisfied all of the needs we had for this rather radical preamp.  I built a production prototype and put it into service and have used it every day since for listening to music, and almost weekly for watching movies.  That was in 2001.  It is now 2011 and I have never once during that time had an issue, desire to tweak, desire to add a new feature or change it in any way.  I've simply just used and enjoyed it for 10 years.  This how I know it's good, because those who know me will tell you that if there's anything I don't like the sound of, it either leaves the building or goes under the soldering iron until I like it.

I'd like to also make the observation that with an all tube system, and serious speakers for the fronts center and rears (all exactly equal in importance contrary to popular belief) the fidelity of good movies is stunning.  A CD has to try damn hard to get close.  Imaging is unreal, and yes if you turn of the projector so there is no video to look at the sound is so 3D and to proper scale that it's like no one even turned the projector off.  Simply amazing.

So this approach requires a source player, ie., DVD or BLURAY player that has 6 discrete outputs which also means it will have an on board decoder.  Can't have one without the other.  This will be fed directly into the Zen Ultra Preamp I just discussed and it will feed your tube amplifiers for each channel.  No HDMI cables to poison the sound, no nasty solid state receiver/processors to ruin it either.  This can not be done any other way.  If you're using a computer as your source, get a 5.1 channel 24 bit USB DAC and hook it directly to the preamp.  Be warned however that Windows will constantly change your sound settings.  There will be sound setting for the DAC, sound settings for the computer's DSP which must be off, sound settings for the Movie player software, and your default computer's sound settings.  They will all overlap and other programs that have nothing to do with movies will randomly change these settings.  The result is lots of frustration and a few occasional happy accidents when everything was accidentally set right.

Bluray is definitely where it's at sound quality wise, at least as I write this.  I've seen several good Bluray players, that in front of this preamp will give more than usable fidelity.

I researched if such a preamp as this existed before I finished mine in 2001 and the closest thing had none of the features and was packed with circuit boards and op amps despite the fact that it was tubes.  Now 10 years later I searched again, and nothing has changed except that the few I did find are around $7500, have none of the features, packed with boards and being sold for 1/2 price to get rid of them.  That's not going to happen with this one, as you've probably figured out by now because it actually solves all the problems and is good enough for the hard core SET guys needing a full time, fully transparent preamp.

Hopefully this will encourage those of you who love serious two channel setups but also enjoy movies but only have one room.

Of course for those who are steadfast against polluting their wallpaper with vibrations from home theater, this preamp is highly desirable as a two channel only piece where you can run a bi-amp or tri-amp system with complete control over each amplifier OR set up 3 combination's of your favorite tubes and have basically 3 different preamps to listen to on any given night!  A tube roller's dream machine for sure.

The tube regulation is used as a filter to reduce ripple by 10 times and block all the grunge that makes it into your equipment's power supply via the wall outlet and power cords.  The result is as good or better than adding a power generator, such as the PS AUDIO power plant to name one.  Grain free, and black backgrounds as though you were listening in the middle of the night, anytime come standard with this approach.  Nice to save a few extra thousand by not having to buy a power generator, and forget about most power conditioners, many make the sound worse.

This is also a preamp I tend to leave on the vast majority of the time and so far I've only changed tubes twice in 10 years.  It uses 8 6N1P or 6922 tubes, a rectifier tube and 4 Voltage Regulator tubes.  A nice bonus is watching it turn on as the VR tubes wait to ignite until the preamp heaters are warmed up and then they fire on independently.  Turning it off is about 5 times cooler because the VR tubes will go off and then come back on and then go off several times over about a minutes time.  You'd have to see it to appreciate it.

I'm writing this article while I wait for a new batch of chassis to get here for the production units.  I've decided to call it the Zen ULTRA.  Here's a few pics of what it will look like.

-Steve Deckert


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