Ramsey Electronics SHA1 User Manual

STEREO
HEADPHONE
AMPLIFIER

Ramsey Electronics Model No. SHA1

Need a way to listen to line level audio from a tape deck or CD
player? Need a way of boosting up any low level signal to
earphone level for top quality stereo listening? This kit has CD
quality audio capabilities with super low distortion, a wide
frequency spectrum, and a superior signal to noise ratio!

• Uses the LM386 audio amplifier ICs.

• Better than 100dB Signal to noise ratio.

• 10Hz to 100kHz power spectrum (+-3dB)

• Almost 1W output per channel when run on 9V battery

• Accepts mike or line level

• Handy phono type input, and 1/4” stereo headphone output

• Operates on 9 to 15 volts DC

• Independent left and right volume controls

• Super easy hook-up with push-button sibilance filter.

• Informative manual answers questions on theory, hookups and

uses - enhances resale value, too!

• Add our custom case and Knob set for a finished “Pro” look.

SHA1• 1

RAMSEY TRANSMITTER KITS

• FM100B Professional FM Stereo Transmitter

• FM25B Synthesized Stereo FM Transmitter

• MR6 Model Rocket Tracking Transmitter

• TV6 Television Transmitter

RAMSEY RECEIVER KITS

• FR1 FM Broadcast Receiver

• AR1 Aircraft Band Receiver

• SR2 Shortwave Receiver

• SC1 Shortwave Converter

RAMSEY HOBBY KITS

• SG7 Personal Speed Radar

• SS70A Speech Scrambler

• BS1 “Bullshooter” Digital Voice Storage Unit

• AVS10 Automatic Sequential Video Switcher

• WCT20 Cable Wizard Cable Tracer

• LC1 Inductance-Capacitance Meter

RAMSEY AMATEUR RADIO KITS

• DDF1 Doppler Direction Finder

• HR Series HF All Mode Receivers

• QRP Series HF CW Transmitters

• CW7 CW Keyer

• CPO3 Code Practice Oscillator

• QRP Power Amplifiers

RAMSEY MINI-KITS
Many other kits are available for hobby, school, Scouts and just plain FUN. New
kits are always under development. Write or call for our free Ramsey catalog.

STEREO HEADPHONE AMPLIFIER KIT INSTRUCTION MANUAL

Ramsey Electronics publication No. MSHA1 Revision 1.2

First printing: September 1995

COPYRIGHT

14564. All rights reserved. No portion of this publication may be copied or duplicated without the
written permission of Ramsey Electronics, Inc. Printed in the United States of America.



1995 by Ramsey Electronics, Inc. 590 Fishers Station Drive, Victor, New York

SHA1 • 2

Ramsey Publication No. MSHA1

KIT ASSEMBLY

AND INSTRUCTION MANUAL FOR

STEREO HEADPHONE
AMPLIFIER KIT

How does it work .................... 4

Assembly Strategy ................. 6

Parts List ................................ 7

Parts Layout Diagram ............ 8

Part Values Diagram .............. 9

Schematic .............................. 10

Assembly Steps ..................... 12

Testing the SHA1 ................... 16

Troubleshooting ..................... 17

Price $5.00

SHA1• 3

RAMSEY ELECTRONICS, INC.

590 Fishers Station Drive

Victor, New York 14564

Phone [phone]

Fax [phone]

www.ramseykits.com

What is it and how does it work?

Let’s take a look at the schematic diagram, and we will follow
through from input to output to get a general idea how this kit
works, and why. We will look only at the left channel circuitry
starting at J1 since the right channel is identical to the left.

A line level audio signal is placed in J1. Line level means an audio
signal of around 1V peak to peak, and will give a reading of 0dB
on a VU meter. The audio passes through C1, a coupling
capacitor. This capacitor prevents DC from entering the circuit
from external components and interfering with audio quality. The
capacitor lets the audio pass through to R3, the left channel
volume control.

The volume control simply varies the incoming signals level that
goes into U1, the LM386. U1 is a fully integrated audio amplifier,
capable of driving low impedance loads. It requires very few
external components, runs very efficiently, and has great fidelity.
With the sibilance switch open, the audio passes directly into U1,
and the signal is amplified to drive a low impedance speaker like
those in your earphones.

With the sibilance switch closed, the capacitor C12 is switched
into circuit. This capacitor shunts some of the higher frequencies
to ground, but leaves the lower frequencies alone. C12 creates a
low pass filter when combined with R2, thereby reducing the level
of high frequencies that are amplified in U1. This is really handy if
you have a noisy weak station coming in, or the signal source is
really tinny sounding like from a poorly recorded CD.

R4 and C5 on the output side of the LM386 is for preventing
oscillations due to the inductive nature of a speaker coil being
driven by the LM386. This makes the load of the speaker look
more like a resistive one than inductive, which prevents
“motorboating” of the audio signal.

SHA1 • 4

C3 is another coupling capacitor, and it serves the same
purpose as C1 at the start of the circuit. This prevents the DC
portion of the signal on the output of U1 from being sent to the
earphones.

VR1, C15 and C16 supply the regulated DC voltage for the
circuit.

SHA1• 5

RAMSEY “LEARN-AS-YOU-BUILD” ASSEMBLY STRATEGY

Be sure to read through all of the steps, and check the boxes as
you go to be sure you didn't miss any important steps. Although
you may be in a hurry to see results, before you switch on the
power check all wiring and capacitors for proper orientation. Also
check the board for any possible solder shorts, and/or cold solder
joints. All of these mistakes could have detrimental effects on your
kit - not to mention your ego!

Kit building tips:

Use a good soldering technique - let your soldering iron tip gently
heat the traces to which you are soldering, heating both wires and
pads simultaneously. Apply the solder on the iron and the pad
when the pad is hot enough to melt the solder. The finished joint
should look like a drop of water on paper, somewhat soaked in.

Mount all electrical parts on the top side of the board provided.
This is the side that has little or no traces on it. When parts are
installed, the part is placed flat to the board, and the leads are
bent on the backside of the board to prevent the part from falling
out before soldering (1). The part is then soldered securely to the
board (2-4), and the remaining lead length is then clipped off (5).
Notice how the solder joint looks on close up, clean and smooth
with no holes or sharp points (6).

SHA1 • 6