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LXH2 ultra-low-power EL84 tube amp with speaker simulator

From: lxh2 <lxh2 at netaxs.com>
Organization: http://www.netaxs.com/~lxh2
To: Michael at amptone.com
Subject: Ultra-low-power EL84 tube amp

>I designed the super low power EL84 amp for just the purpose of getting that real power tube sound at apartment volume. There is other interesting stuff at the general lxh2 website.

>You can hear some examples of the sounds gotten from some of these circuits at the Nakedchurch website. [to do: link to exact pages]

>The Marshall simulator I designed should be portrayed as a whole system, rather than a separate amp simulator and cabinet simulator. The flux modulation effect of an overdriven speaker you alluded to [such as speaker dynamic compression and feedback to the power tubes] has been taken into account and designed into the amp simulation section. I have fooled many local golden-eared Marshall guys into believing that my setup was a genuine Marshall. I did the same with the local Fender tweed guys. They keep bugging me to manufacture these circuits as products and offer them for sale.

>I would like feedback from people who read these pages and build these projects.

His page has the following projects as of this writing:

You would use any of these:

I have a page, Inductive load project; low-watt power tube project idea.

His page also has these tech notes:

As far as the Celestion "frequency response specs" one often sees, people seem to assume that a frequency curve can adequately describe a hard-driven guitar speaker which is interacting with a hard-driven power tube. But based on my experiments with related equipment, I believe that the complex dynamics of such a system are distinct from a mere EQ curve and are crucial to cranked-amp tone, which includes cranked-speaker tone, which is very much a moving, quirky, physical, nonlinear, complex dynamic system.

At 12:33 AM 10/20/98 -0400, lxh2 wrote:


You wrote about the power tube-transformer-speaker relationship, and proposed to use low-watt power tubes and a speaker isolation cabinet, to preserve the complexity of actual physical speaker motion. I will try to explain my test results on the very subject.

Listening tests:

We conducted a broad array of listening tests to determine the weight of each discernable characteristic of the guitar-amp-speaker synergy. The test subjects were guitarists the we determined had very good ears. This included us.

The listening tests were conducted on the actual amps and the simulators in various combinations. The results allowed us to hone in on the actual parameters that gave the sonic signature of a given amp.

Test conditions:

In a room 18' by 22' that was reasonably neutral acoustically, the setup was:

Before we get to the results, I will comment on your idea. All is well and good until you get to the miniature guitar speaker in the silencing box. The characteristics that are so important in creating the Marshall sound are found in the breakup resonances of the Celestion 12 inch speakers. This, coupled with the added resonances of the 4-12 cabinet and their interactions, are crucial for getting the correct duplication of the Marshall sound. If you want a more generic sound, then this factor becomes somewhat less important. A miniature speaker stuffed into a fiberglass-filled box with a mic in it will sound nothing like a Marshall cabinet. But why bother with this building-block approach you dislike so much? There need be none of the arbitrary walls placed here either. The speaker dynamic compression effect can be added to the tube compression before the sound reaches the speaker or speaker simulator. Therefore we need not create the loudness levels and therefore a cumbersome speaker isolation box.

A case in point is the micro power tube amp. I connected this directly to the Marshall 4-12 cabinet and the all-out crunched, full-tilt speaker compression sound was there, but only at a sound level that normal conversation was easily heard over (45 to 50 db spl). All the low-end chunk was still there too. This experiment proves that you can get "that" tone with just the little amp and a real Marshall cabinet; the speaker does not have to be driven hard. If you want to mic the cabinet, then put it in another room and mic it up as you would normally close-mic a Marshall cabinet. This really works too! Why did I design the speaker simulator then? For when you need absolute silence. [as I do when I put time-effects after the total "tube amp" and don't want to hear the sound until after the post-amp effects -- Michael] We included all the breakup resonances and the stored energy modes of the real thing. Contrary to what some may say, this can ALL be done with active filters.

Some talk about the interaction comb filtering caused by the four speakers in such an array. But when you think about the close mic position that has given us great results, the mic is aimed at only one speaker. This will swamp out any effect that the other three may have. There is much specious reasoning in the industry. They, more times than not, place significance to the wrong things. This misinformation then trickles down to the public, and leads people away from what will give them the Tone they search for. My website will become a clearing house for the clearing up of these misconceptions.

Now the test results.

The real Marshall was compared to the other combinations mentioned above.

The Marshall amp simulator with the real Marshall cabinet sounded exactly like the real thing!

The Marshall amp and cabinet simulator with the 4311 sounded quite convincing as if a Marshall was recorded and ended up on a record that was played through a 4311. Way better than the Red Box and other cabinet simulators!

You can also get a great sound by connecting the micro power amp to the Marshall cabinet, as described above.

-- lxh2

I would like to hear these amp and simulation circuits, and the ultra-low-power EL84 power tube circuit. I'm interested in pure amp tone without effects before or after -- and, I'm interested in combining this Tone, once it has been safely established, with effects. That's why I'm interested in using the micro-amp both ways: with a guitar speaker, and with only the speaker simulator. There are times when I want to not hear the sound at that point in the chain, but only want to hear it after I have digitally added room reverberation and post-amp EQ. I spend a lot of time playing with pure amp Tone, but my real goal is to program both that basic tone and special effects, together.

FX people should not be afraid of power-tube circuits. They think they'll have to get into 100-watt Matchless or Marshall stack design, but that old misconception is fading at last.

At last someone has started making projects involving power tubes. The fx people are alienated from power-amp circuits, and this is a barrier that must be torn down. Guitarists do not really want one expert working on "preamp circuit kits" and another working on 50-watt conventional amps -- and yet another working on attenuator and "speaker simulation" technology. These barriers must be broken down.

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