Strategy 400 Stereo Operating Manual 1
CONGRATULATIONS AND THANK YOU! You've just become the proud owner of the world's most musical power amplifier: The Strategy 400™ Stereo. All of our efforts have been directed at making this a special piece of equipment -- a fine hand-made musical instrument -- that we hope you'll enjoy and treasure for many years to come. Your total satisfaction is our highest priority and we appreciate your good word-of-mouth referrals.
INPUT CIRCUITRY The Strategy 400 Stereo offers extremely sensitive input circuitry: 0.2 volts will produce full power when the Level control is turned fully up. This means you can actually plug in many signal sources directly without needing a preamplifier. The output from virtually any effect unit is strong enough -- as is any keyboard, CD player, cassette deck... even electric bass plugged in direct produces full power with incredible tone.
POWER TUBES The main power tube used in the Strategy 400 Stereo is the MESA STR 415 type 6L6 GC which provides smooth, warm musical power and is very reliable. The 6L6 we use is extremely rugged and has very low 3rd harmonic output when overdriven. All twelve sockets should be fitted with STR 6L6's when the Strategy is being used in any application other than live guitar. We have specially adapted 4 of the sockets-- those along the rear edge-- to accept either 6L6's or STR 416 type 6CA7/EL34.
DRIVER TUBES The four small tubes are all type 12AX7, also known as 7025, ECC83 or MESA SPAX7. These tubes are very long lasting and trouble free in the Strategy, but best performance will result from using genuine replacements. The input stage of your 400 uses a special "instrumentation grade" differential amplifier with a proprietary constant-current-source diode.
tend to cancel themselves out and disappear (the original signal is also reduced so extra "gain" is designed in to more or less compensate). How much NFB is the "right amount"? It depends on the the amplifier. A "perfect" amplifier would have no need for negative feedback... and in-fact your Strategy 400 uses about one-fourth as much as the previous best tube designs.
swinging is confined to the region between the floor and ceiling -- isn't hitting either one -the lever (amplifier) is operating in its "linear region". This simply means that there is a constant ratio to the leverage: push the small end up and down two feet and the big end moves six feet; swing the short end three feet and the long end moves nine feet. So in this example the ratio (also called amplification factor or gain) is three.
The ear has a great tolerance for these overtones - because they relate in a musically consonant way and are are already present in the original signal, as either timbre overtones, upper harmony or both. For example, it is often possible to add up to 20% second harmonic to a single note before any change is audible. Then all that happens is that the ear hears the timbre change.. it does not hear "distortion trash." If you're a guitar player or keyboardist try this simple experiment.
