Manley JUMBO SHRIMP - Manual (Page 7)

FEATURES AND APPLICATIONS
1. VERY SHORT SIGNAL PATH WITH ABUNDANT POWER GAIN.
Each of the JUMBO SHRIMP’s five sets of input jacks subjects the incoming signal source to loading
of no less than 100,000 ohms, while the output can comfortably provide over 3 volts into a test load of
600 ohms. This implies a POWER gain of better than 22 deciBels, even though the VOLTAGE gain
is held to no more than 12 dB when the volume attenuator is at maximum. In this case, for example,
with 1 volt at the selected input and 1 volt present at the output under test, the power gain would be
more than 22 dB, or about 166 times more power out than in, even though the VOLTAGE gain between
input and output is zero! When this amount of gain is present in circuitry containing very little negative
feedback, the tendency is to reveal the inherent nature and personality of the devices used in the circuit,
along with the circuit itself. Here, for example, the choice of input tube has a bearing on what the final
sound character will be.
The JUMBO SHRIMP’s two pairs of output connectors have been hard-wired in parallel for conveni-
ence in routing output signals about for special applications such as bi/tri amplification, or for driv-
ing satellite speakers plus subwoofer. For best performance, however, keep the combined load on the
outputs to a minimum of 1500 ohms or higher, and preferably above 5000 ohms total. When connecting
two loads to the outputs, the total load in ohms may be figured as follows:
(Zin of amp 1) x (Zin of amp 2) = Ztotal, Total load impedance (Zin
of amp 1) + (Zin of amp 2)
Where (Zin of amp 1) and (Zin of amp 2) are the rated input impedances of the two amplifiers intend-
ed for use with the JUMBO SHRIMP outputs. Example: Amp 1 has an input impedance of 15Kohms
(“K” designates thousands of ohms here, hence Zin =15,000 ohms) and amp 2 has an input impedance
of 100Kohms (Zin=100,000 ohms). Then:
(15,000) x (100,000) = Ztotal = 13043 ohms, or 13kilo-ohms thus
(15,000) + (100,000) 13 Kohms
The choices of 15K and 100K above reflect typical input impedance ratings of transistorized and
vacuum-tube based power amplifiers respectively. Notice that no matter what the two power ampli-
fiers’ input load impedances are, the combining of the two in parallel will always be smaller than
either one standing alone. In the case of two power amps with identical input Z ratings, the total load
impedance would simply be half the value of either, i.e.: two 15Kohm amps in parallel would present
a 7.5Kohm load.
That is your math lesson for the week. There will be a quiz next Tuesday.
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