It's not High-Definition, but Hybrid-Digital
I have been fighting (and complaining about) all that adjacent channel hiss-noise from the digital component of the IBOC broadcasters for several years. I now admit that it isn't going
away soon ... so, I guess it's time to join in and see what it's all about, the benefits and the shortcomings.
I selected the Sangean HDT-1X tuner as the framework basis for this receiver. The tuner has good bench specs with an added firmware feature of being
capable of receiving digital and analog signals in split mode.
The tuner will demodulate digital information to the Left channel and analog to the Right
channel. Stereo recovery is sacrificed, but that's of little consequence when utilizing the
benefits that "A" and "D" recovered audio have to offer ... and their shortcomings.
I added a sub-panel to the HDT-1X which brought it up to a 2U rack panel height (3.5").
The tuner outputs have been routed to a 2-channel audio mixer so that both levels may
be adjusted independently. The mix-bus signal is then fed to an 8-Watt power amplifier.
There are both preamp and power amp outputs so that the receiver can still feed a
line-level signal to a quality Hi-Fi audio system. Both channels have LED VU meters to
monitor signal levels.
I have also incorporated a Master Gain control with its own VU indicator. There's a
selector switch for internal or external speaker and headphones. The power amp is
switch selectable between "LINE" (preamp) and Hi Level (speaker) modes.
Note that I had to add an RF Gain control, since very strong local AM stations can
overload and desensitize the receiver.
In its incomplete form, the construction shows ample
room for adding circuitry. Center-front is all the
Sangean D/A circuitry and firmware. The back board
is the factory regulated power supply.
At left is the added regulated 2 Amp supply for the
power amplifier which is mounted at the front left in
None of the new wiring and cables have been
installed in this pic. But the major modules can be
seen easily, along with the new connectors; preamp
out, power amp out, IEC AC socket (with chassis
ground), SO-239 AM antenna port, and F-type FM
The sub-panel unattached and prior to wiring, showing
the placement of the mixer pots, selector switches and
LED bargraph VU meters.
The sub-panel is 3/4" aluminum angle and the rack
mount ears are 1" angle. The 3" rack handles are
standard electronic hardware
Wiring completed. Some
dressing and rerouting
is necessary for
Note: all audio and RF
signals are routed with coax.
DC control lines, power and
8-Ohm speaker lines use
plain hookup wire.
Closeup of audio
control lines, mix bus
and Pwr. Amp.
Closeup of regulated
and highly filtered power
supply - very clean DC
output to keep noise
and hum below the
S/S+N figure of the
Thanks for looking !
Actual size graphic (on a 1200 pixel screen) of the second
panel decal. It's 17 inches wide but cut into two pieces to fit
this page. The full graphic, as designed to complement the
original panel, is shown below.
I design the graphics in Pagemaker (tm) and print it with a
laser printer on heavy paper. It gets laminated on both sides,
then cut to size. All cutouts for the controls are cleaned out
with a #11 blade and double-sided tape fixed to the back.
Then it is carefully "peel 'n' stick" applied to the panel.