Circuit Description; Principles Of Operation - Crown D-150 Service Manual

4.1 PRINCIPLES OF OPERATION
The D-150 has twodirect-coupled amplifier circuits which employ
a.dual.IC op.amp.and silicon transistors in all anplifier stages, The.
CROWN-designed and developed circuit represents a level of
quality and performance presently unequated in the field of audio
amplifier design.
Thé. dual 1C op ainp is of a low noise type having a large gain band-
width, The results of using Heres nut eeae real wis tats
record low values. The typical full output (75w, 'Bonms) SMPTEIM
is. 0.002%.. This. implies. that the. full power.1KHz. THD is inthe
vicinity of 0.0005% which is below the capability of present har-
monic distortion measurement systems. Multiple feedback loops
ara employed to allow a Maximum of overall feedback.
The lack of noise is evidenced by a typical 20Hz-20KHz effective
input noise of 1-25 0 volts which produces an effective B ohmicut-
ut.of. B0.micro-micro.(pica), waits.
The. output stage is a quasi-complimentary format employing the
CROWN. class AB+B technique which uses no bias current in the
output transistors. The result is maximum efficiency with min-
imum crossover notch distortion and idling amplifier-heat. Thus
16
SECTION 4
CIRCUIT DESCRIPTION
there is no bias current adjustment, as the output circuit is not
temperature-tolerance critical.
inthe new. output circuit, the driver transistors carry the bias.cur-.
tent, while the output transistors serve only as boosters. The out:
put transistors sense wher the driver transistors are delivering sig-
nificarit currentto the load anc take over and deliver the large load
currents.
The output circuit is protected by a V-I limiter which limits the
drive to the output configuration whenever the output transistors
are overloaded, V-! (volt-ampere) limiting Is inherently superior to
all other forms of protection as it directly senses the overload con-
dition and acts instantly to relieve the overload, actingonty so long
as the overload exists, The result is Coripiéte freedom from pro-
'Star delays with réliability arid iraximun safe output power.
The power supply is a continuous-duty type. The main OC sup-
plies are full-wave capacitor input type with a heavy duty bridge
rectifier assembly. Computer grade electrolytics furnish over 20
joules. of energy. storage.
The D-150 represents nothing short of the highest quality in both
circuitry and components: it should provide a lifetime of trouble-
free service for the most discriminating users. ,