Hi everyone, it was great to find this theremin
website! It looks like a great resource.
Thanks! Originally, I'd hoped to build a tube
theremin, but the Theremax looked like it was
a lot more economical to build as a first
theremin, and building---and learning from,
that might make building a tube theremin easier
later.
While troubleshooting my Theremax, some of the
signal levels don't seem quite right to me and
I'd like to know how far off they are:
Junction of R6, D5 and D3: sine wave, approx.
0.25 Vpp.
Junction of R11, D5 and R26: a modulated signal
of about 0.04 Vpp
Base of Q8: approx. 15 mVpp modulated waveform
Collector of Q8: waveform is approx 12 mVpp
The DC voltages for Q1 through Q4, and Q8 and
Q9, seem to be somewhat in line with the
troubleshooting info from PAiA:
Q1 Q2 Q3 Q4 Q8 Q9
E 1.87V 1.65V 1.65V 1.87V 0.15V 0.16V
B 2.39V 2.19V 2.18V 2.42V 0.6V 0.6V
C 7.04V 7.03V 7.02V 7.05V 6.07V 6.01V
No output at IC2 pin 8, and no hum when
touching the base of Q10 with a piece of wire.
I'm wondering if the output from the modulator
section is sufficient to drive the following
stages (Q8 and Q9); e.g., about a 40 mV signal
at the D5, R11 and R26 junction and about
250mV after R5; the same level is measured
with C23 disconnected. I'm going to disconnect
C23 again and feed a low-level signal from a
signal generator in at that point to try to
verify operation of other parts of the
circuitry.
There were no noticable changes after
disconnecting the antennae.
At this point, I'm beginning to think that
the problem is in the circuitry for Q8 and Q9,
with Q8 and Q9 possibly being defective.
Perhaps there's a cold solder joint, although
things look ok to my eyes. My soldering iron
needs a new tip and only one that I could find
locally was an unplated copper tip from Radio
Shack, which I can no longer get to tin
properly and it keeps accumulating crud...
never had a problem like that before with a
soldering iron... anyway, a new tip will be
here soon. Still, I'm interested in learning
what others have measured for some of the
voltages above, particularly the outputs of
the oscillators.
website! It looks like a great resource.
Thanks! Originally, I'd hoped to build a tube
theremin, but the Theremax looked like it was
a lot more economical to build as a first
theremin, and building---and learning from,
that might make building a tube theremin easier
later.
While troubleshooting my Theremax, some of the
signal levels don't seem quite right to me and
I'd like to know how far off they are:
Junction of R6, D5 and D3: sine wave, approx.
0.25 Vpp.
Junction of R11, D5 and R26: a modulated signal
of about 0.04 Vpp
Base of Q8: approx. 15 mVpp modulated waveform
Collector of Q8: waveform is approx 12 mVpp
The DC voltages for Q1 through Q4, and Q8 and
Q9, seem to be somewhat in line with the
troubleshooting info from PAiA:
Q1 Q2 Q3 Q4 Q8 Q9
E 1.87V 1.65V 1.65V 1.87V 0.15V 0.16V
B 2.39V 2.19V 2.18V 2.42V 0.6V 0.6V
C 7.04V 7.03V 7.02V 7.05V 6.07V 6.01V
No output at IC2 pin 8, and no hum when
touching the base of Q10 with a piece of wire.
I'm wondering if the output from the modulator
section is sufficient to drive the following
stages (Q8 and Q9); e.g., about a 40 mV signal
at the D5, R11 and R26 junction and about
250mV after R5; the same level is measured
with C23 disconnected. I'm going to disconnect
C23 again and feed a low-level signal from a
signal generator in at that point to try to
verify operation of other parts of the
circuitry.
There were no noticable changes after
disconnecting the antennae.
At this point, I'm beginning to think that
the problem is in the circuitry for Q8 and Q9,
with Q8 and Q9 possibly being defective.
Perhaps there's a cold solder joint, although
things look ok to my eyes. My soldering iron
needs a new tip and only one that I could find
locally was an unplated copper tip from Radio
Shack, which I can no longer get to tin
properly and it keeps accumulating crud...
never had a problem like that before with a
soldering iron... anyway, a new tip will be
here soon. Still, I'm interested in learning
what others have measured for some of the
voltages above, particularly the outputs of
the oscillators.