background image

062702

20      Theremax

Tuning and Testing

First time tuning can be tricky because both the Pitch pair and Volume
pair of oscillators must be close to a null in order to hear anything at all. If
the Pitch pair are close, but the Volume pair are far apart you won’t hear
anything because the Volume doesn’t come on. If the Volume pair are
close but the Pitch pair aren’t, you won’t hear anything because of no
pitch signal. In either case, there’s no clear indication of what needs to be
adjusted to hear a sound. You can eliminate this complication by tempo-
rarily disabling the heterodyne part of the Volume control circuitry and
forcing the VCA “on” while the Pitch pair of oscillators is nulled.

Use the clip lead supplied to temporarily connect the V+ line (the banded
end of the zener D1) to the “high” side of the volume control (lug 3 of
R83). When using this trick, it is very important to set the front panel
Volume Control to mid-range or slightly less. The V+ voltage is almost
double the normal maximum CV and too high a Control Voltage causes
the VCA to saturate and effectively turns it off. If you forget, don’t worry,
nothing will be damaged by having the Volume set too high, you just won’t
hear anything until you turn it down.

Set the Pitch Trim and Volume Trim controls on the panel to mid-range
and the Pitch CV, Timbre and Velocity controls fully Counter-Clockwise.
Turn the slugs of all the coils L1-L4 fully “out” (Counter-Clockwise) just
until you feel resistance - the coils can be damaged by applying too much
force while turning the slugs. From the fully “out” position, turn the slugs of
the two coils L1 and L4 one full turn “in” (CW). These coils will not be
adjusted again.

Plug the Tmax output into an amp and turn both on. During initial setup you
may need to adjust the volume for comfortable listening levels or to
prevent overload and distortion. Make these changes with the amplifier’s
volume control only. Do not change Tmax’s Volume Control from it’s
mid-range setting until told to do so later is these procedures.

Nulling Pitch

Slowly adjust the slug of L2 “in” (Clockwise) while listening for the hetero-
dyne tones that slide down form a very high pitch then go through zero
frequency and begin to climb again.. If you have the gain of the amplifier
that you’re using set high, you may find a couple of places where tones
can be heard, but as you adjust the slug continuously from one end to the
other you will hear one in particular that is very much louder than the

Содержание Theremax 9505

Страница 1: ...imo of a symphony orchestra were like nothing anyone had ever heard before Was it a hit You bet theremin concerts were SRO in halls where audiences were ordinarily sparse The place of the Theremin in...

Страница 2: ...r easy reference during assembly THE CIRCUIT BOARD Theremax is built on a single sided solder masked circuit board No special preparation or cleaning is necessary before assembly The top of the board...

Страница 3: ...d on a joint there is the danger that a conducting bridge of excess solder will flow between adjacent circuit board conductors forming a short circuit Accidental bridges can be cleaned off by holding...

Страница 4: ...bove form and install the eight wire jumpers used on the circuit board RESISTORS Solder each resistor in place following the parts placement designators printed on the circuit board and the assembly d...

Страница 5: ...10 1500 ohm brown green red R15 1500 ohm brown green red R51 15k brown green orange R52 15k brown green orange listed below 1megohm brown black green R24 R25 R54 R57 R43 2200 red red red R53 2200 red...

Страница 6: ...OSCILLATOR COILS The oscillator coils are housed in metal cans to shield them from interaction with one another Notice that the coils can be mounted only one way with the case tabs going though the l...

Страница 7: ...Solder each capacitor in place as it is installed and clip the excess leads off flush with the solder joint Four of the disk capacitors are temperature stable NPO types These are separately packed an...

Страница 8: ...ious components electrolytic capacitors are polarized and the leads are not interchangeable Leads are marked and or and the lead must go through the hole in the circuit board Frequently the positive l...

Страница 9: ...em from their packing until you re ready to install them if they get mixed up you will have a hard time sorting them back into types Diodes are polarized and must be installed so that the lead on the...

Страница 10: ...parts to be damaged this way ICs are polarized in one or both of two ways A dot formed into the case of the IC corresponding to pin 1 or a semicircular notch that indicates the end of the package with...

Страница 11: ...Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10 Q11 Q12 FLYING WIRES i e those which go from circuit board to panel mounted parts In the following steps wires will be soldered to the circuit board which in later steps will...

Страница 12: ...knife blade or a ball point pen This will expose the separately insulated inner conductor On one end trim the braid off flush with the outer insulation On the other end pull the strands of shield to...

Страница 13: ...e later wiring easier and less prone to error Using the flat washers and nuts provided mount the miniature toggle switch S1 as shown Fully tighten the hardware Using the nuts and washers supplied moun...

Страница 14: ...rked ns for NO SOLDER On these unsoldered connections simply push the end of the wire through the lug and crimp it back to mechanically secure it Begin wiring using the single strand bare wire supplie...

Страница 15: ...wn R79 1 s2 R79 3 ns R86 270 ohms red violet brown R80 1 s2 R80 3 ns The Gate LED D15 and it s associated current limiting resistor R78 wire directly to the solder lugs of J2 as shown in fig 3 Locate...

Страница 16: ...inues by connecting the wires previously soldered to the circuit board to the pots and jacks as detailed in fig 4 Notice that previous wiring has been eliminated from this drawing to give a better vie...

Страница 17: ...he case For a pleasing contemporary blond finish try several coats of Tung Oil Allow previous coats to be absorbed by the wood fully before applying the next and keep adding coats until there is a ple...

Страница 18: ...on Connect the free end of the wire originating at circuit board point G to the solder lug on the circuit board DO NOT SOLDER Connect the free end of wire originating at lug 3 of S1 to the solder lug...

Страница 19: ...HE ELECTRONIC AND MOST OF THE CASE ASSEMBLY OF THE Theremax Before plugging the unit in and testing it take a break then come back and admire your work it ought to look pretty cool right about now It...

Страница 20: ...ged by having the Volume set too high you just won t hear anything until you turn it down Set the Pitch Trim and Volume Trim controls on the panel to mid range and the Pitch CV Timbre and Velocity con...

Страница 21: ...ed with pitch for a while and have a feel for the interac tion of the tuning slug and Trim control it s time to move on to setting up Volume Leave the Pitch Trim set so that there is some easily audib...

Страница 22: ...motion range turn the slug out a little more and adjust the amplifier gain accordingly You will know you have carried things too far when you still hear a tone with your hand on the antenna but you sh...

Страница 23: ...the antennae Again a very theatrical presence rooted in necessity A theremin doesn t respond only to the motion of your hands it also responds to body motion If you re moving around while playing it...

Страница 24: ...So if volume is really timbre how do you control volume This is the cool part As with most synthesizer patches the dynamics of the sound how fast it builds up and dies away is controlled by an Envelop...

Страница 25: ...type as typified by transistor Q2 and associated circuitry The primary of Oscillator coil L2 and capacitor C10 from a resonant tank circuit load for the transistor which is configured as a common base...

Страница 26: ...28 to R24 so that the rising edge of the square wave produces a positive going pulse On falling edges of the square wave D11 forward biases and quickly charges C28 for the next pulse while also clampi...

Страница 27: ...the response non symmetrical which adds even harmonics to the output to give the sensation of being played hard The Velocity CV also is routed to the Schmitt trigger consisting of IC1 c and associated...

Страница 28: ...C27 C34 1 33pF C37 6 470pF C7 C11 C15 C19 C28 C31 2 100pF NPO C6 C10 2 68pF NPO C14 C18 Mylar 3 1 uF C24 C25 C30 Electrolytic 1 1000uF 10V C3 3 100uF 10V C1 C20 C42 2 10uF 10V C21 C26 5 1uF 10V C23 C...

Отзывы: