OUT
PA555
MADE IN USA
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IN 1
15 VDC
Power
Preamplifier
PA555
Preamplifier
What's in the box?
1 - Made in USA PA555
1 - 15V power supply PN PS27s
1 - This owners manual
1 - Love for great audio
PA555 Preamplier
SPECIFICATIONS
Input Impedance: 10K ohms
Max Output Gain: 11.1 dB
THD: 0.1%
S/N Ratio: 103 db, unweighted
Indicator: 1 Power LED
Frequency Response: 5 Hz - 198 KHz +/- 3 db
Crosstalk: -75 dB
Output impedance: 100 Ohms
Output Connector: RCA Stereo
Input Connectors: 1: 1/8" TRS Stereo jack
3: RCA Stereo jacks
PWR: 15 VDC 500mA
Size: 6"w x 2.5"h x 5.4"d
Weight: 2 lb.
Salt Lake City, UT
4/19
Connection guide
Thank you for purchasing the PA555. We hope you enjoy
using the PA555, and that it makes listening to your music
collection rewarding. We sincerely appreciate the opportunity
to build a product for you and participate in your love of quality music and sound. We love what we do and we’re happy
to help. All Bellari products are hand built in Salt Lake City,
Utah by people who care about high quality music.
The PA555 uses one 12AX7 tube running at 150 volts. The
input signal is connected directly to the grid of the tube and
all of the gain of the PA555 is from the 12AX7 tube. The output section is a pair of emitter followers to drive the output.
The PA555 has a no feedback circuit or integrated circuits in
the audio path, it is all analog.
CONNECTION:
1 - Connect your sources to the PA555's “in” RCA
jacks on the back or 1/8" stereo jack on the front.
2 - Connect the supplied PS27s adapter to the
jack labeled “15VDC”. Do not use any other
adapter, or the unit might be unhappy, and you would need
some repair work done.
3 - Connect your amplier to the "OUTPUT" RCA jacks, select the channel you want.
4 - Enjoy your music.
Q: Do dierent tubes have dierent gain?
A: Yes, but it is not a big enough dierence to worry about.
With a 12AX7 the PA555 has 11.1 dB of gain. With a 5751
the PA555 has 10.7 dB of gain. Even though the 12AX7 has
a gain factor of 100 and the 5751 (12AXWA) has a gain factor of 70 the slight decrease in max gain will not be noticeable as the PA555 has more gain than most preamps. Even
dierent brands of tubes will have a slightly dierent gain, but
it is so small you will not hear a dierence.
Q: Do dierent tube brands have dierent specs?
A: Yes, some tubes have better specs than others. The best
tube we tested for specs in the PA555 was a N.O.S. 1960's
Mullard long plate made in Great Britain 12AX7. The THD
was improved quite a lot in our testing. The crosstalk also improved. With most all tubes the frequency response and signal to noise ratio will be about the same. The bad news about
the Mullard tube is it is about a $180 tube if purchased from
a reputable tube seller. The included 12AX7 is a wonderful
sounding tube with very smooth response. Changing tubes
can be fun, but by no means necessary. The specs given for
the PA555 are with the included 12AX7.
TUBE TEMP:
The tube will get up to around 140 degrees fahrenheit, it will
be warm to the touch. The top chassis will also get warm
from the tube's heat. This will not be an issue as the chassis
will only get 20 degrees warmer than room temp. The entire
top of the chassis will seem hot after the PA555 has been on
for a few hours, this is normal and nothing to be concerned
about. Some tubes do run hotter than others. In our testing
the hottest tube we have seen was a NOS RCA 5751 made
in Canada it ran at 147 degrees, and did make the top of the
PA555 very warm to the touch after being on for a few hours.
This is normal and is not a cause for concern.
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