Listening With Stereo Headphones; In Case Of Trouble - DYNACO Dynakit ST35 Instructions For Assembly And Operation Manual

or a sp"cial output on tJwir prc'amplifil'r hy
usin~
t!w follow-
iTlg
nlC'thod. A monophonic c'xtr'nsion
101ld~T)(';)kl'r
may bl'
conn('ctNl to
:1.
sl.!'rl'o systc'm in thl'
,-;:\111('
way.
T1H' circuit shown hC'1ow providC's OUt.Pllt from a central
loudspf'~k('r
with full control over its h'vl'l. For f1E'st results,
thl' speakc'rs uSNl shnuld bc idl'ntical.
BC' cNtain that the loudspeak,,!'.:;
;Ir<~
properly phased.
The StC'l'e:o
3;)
has been c::lre(ully engilwl'rc'd to give
long, trouble-free sNvicp. However, a mistake in assembly
or a dde-dive component
C:1!1
afTel't its pl'rformance or
make it inoper;ltivc'.
If
difficulty is ('ncountC'red, a method·
iCfll ;lnalysis of the trollbl,' will usually
Ic~ld
to a quick
CUrt'.
The: first thing to check is thC' wiring t.o be' surC' that
all of Uw steps havC' \)('C'n p"l'formed, ;\nd that all connections
ho.ve been
,~oldc'r('(l. It is especially helpful to have someone
other than the builder do the checking.
If the tubes do /lot light at all (on both channels), it is
likely that a.c. power is not being delivered to the amplifier.
In all likelihood, the fuse will have blown, indicating the
possibility of a short-circuit in eithN the fil.1ment or high
voltage supply lines. If tlw r<,sistlnce Iwtwf'cn ehasgis
ground ilnd the quad filter capacitor lugs is less than
100,000 ohms, this indicates a probable short-circuit in
the high-voltage supply,
If the
tube,~
of one channel h;;ht, but those' of t.he other
do not, the filament IC:1ds from the power transformer to
one of the circuit boards are probably not properly con-
neet.ed, or these may be defective in the power transformer.
If (Ill tubes light but one, the tuhl' in qUl'stion should
b<~
interchanged with one of the same type from another socket
on eitber board. This should show whethc'r the tube or
its associated circuitry is at falI1t; if the tuhe still fails to
light, it is faulty. II' it lights in its nr'w position. and the
tube inSNted in its place is now dJrk, a close examination
of the tube socket wiring will usually reveal the' source of
the difficulty. Should an output tuLt' {6B(1.'i) ever require
replacement, it is preferable, but not cssl'ntial, that thl'
pair be rep1.1ce'd.
If all of the tubes light, hut Uwrc is no sound from th('
loudspeakers when the
systr~m
is in operation, it is first
necessary to <'liminate other
c:omponL~nts
in tlw system as
possible causes of the trouble. InsL'ding or removing th<'
inpu t plugs at the input sockets of the Stereo .35, while it
is on should produce a loud momentary hum or "thump",
If the loudspeakers are properly connected, and no noise
is produced by inserting or removing the input plugs, the
high voltage supply is probably not connected. Check the
wiring around the quad filter capacitor. If one channel
plays, and the other does not, check the signal path in the
defective channel, as well as the high voltage supply. An-
other possibility is that strands of wire from the output
transformer leads going to the output terminal strip are
accidentally shorting, or that the wires leading to the loud-
speakers are touching the chassis or each other.
9 OR 16
n
COM~.ON
IN CASE OF TROUBLE
8 CR 16J1
CONNECTING A THIRD LOUDSPEAKER
TO YOUR STEREO SYSTEM
Tlw two lourlspf'akers used in ;) stereo system must he
phased propprly (or corre'ct stereo reproduction. The phas-
ing pracc'ss it.s('lf is simple', aftc'r tlw amplific'r is operating
and the two loudsTw~kl'rs
a
re' conn~ctpd.
Play a monophonic; record, or t.une in a monophonic
broadcast on your tuncI'. As you walk flcross the room in
front of the 10udsTwakers, there should be a smooth, con-
tinuous transition of sound from one side of the room to the
oth('r. When you an' directly betw('('n the'
loudspr~ak('rs.
the sound should appe:1r to corne from a source that is
directly in front of you, that is, also centered between the
[oudspe'akf'rs. If you hav!' any doubt as to whet.hN or not
the phasing is corl"l~ct. ,'1ftn making this test, transpose' th('
two connections at one of the' ;)mplifier terminal strips; that
is, connect the wire which was connected to "8" or
"16"
to
"C01\I", ;ll1d vice vns;.l. If you have cbanged to the corrc~ct
phasing, the' sound will now be distinctly centered, o.nd the
bass tones will appc'ar to have increased. If you have'
changed the connection to incorrect phasing, tbe sound
will sc'!'m to jump from one side to the other as you mov/'
slightly to tht' right and left of cente'r.
PHASING THE LOUDSPEAKERS
Headphones can be used with the Stereo
.'35
in place of
loudspeakers or connectt,d in addition to loudspeakers.
Most headphone manufadurers supply instructions and
special junction boxes which permit direct connection of
headphones to the loudspeaker outputs of the amplifier.
With low impedance headphones (4 to 16 ohm rating)
without instructions from the manufacturer.:l I-watt resistor
oi
about 100 ohms should
b~
connected in
sl~ries
with the
outpu
t
of each channel. This will attenuat0. the
si~nal
to each
headphone, improving the signal-to-noise ratio.
In most stereophonic systems, the usual arrangement of
two loudspeakers which form an equilateral triangle with
the listener's position will yield optimum performance, In
cases where the program contains exaggerated separation,
judicious use of the blend control on the preamplifier will
provide a more natural and pleasing effect.
When room arrangement or size does not permit the ideal
placement of loudspeakers, the addition of a third loud-
speaker, playing a combination of the left- and right-
channel material, may improve the spatial effect consider-
ably. Those listeners who feel a need for a third loudspeaker,
can try this arrangement without need for a third amplifier
LISTENING WITH STEREO HEADPHONES
The St('rl'n :J;i
may also hi'
u~('d with an F ~I tUON
without
01'('(1
for
:l
!In'ampliftrr, prnvidpd that
tlw
tunpr
is equiPl)('d with a volume control and 5witchl'r1 a.c. outld,
:md ha:; an output of :It 1(';\5t 1 volt.
T!w
loudsp('ak~'rs
chosen may be of
JllY
iTl1]1('danc(~
or
efficipncy, since thc' Stcn'o
:~[)
has sufficient pOWI'r reserv{'
bc~yond
that usually rl'quil'('d for home listening so that no
lack of volume is likely to bl' oosNv('d, ('v('n with
I'l~btivdy
incfficil'nt spl'akers. Thc' !oudspeflkpr connection (or pach
channpl is made b('twecm tlw COM (common) and either
the 8- or 16-ohm tap provided; the bottom
pbt(~
is print('d
to ident.ify thc'se tl'rrnin:1ls. The S-ohm tap wiH permit
satisfactory op('r:ltion with loudspl'o.kers of 4- t.o 12-ohm
nominal impedancp, whik the H>-ohm tap may be used with
loudspeakers of 12- to :W-ohm rating.
10