Updated 3/29/2025
In order to pack more data onto a vinyl record, the recording industry reduced low frequencies and increased the high frequencies. To corect for this, the output of record player (phono) passes through a preamp that does just the opposite. In the audio industry, this is refereed to as RIAA equalization.
Unfortunately, on many jukeboxes, the preamp stage and linear amplifier stage are in the same unit, and there is no auxiliary linear input for tape and mp3 players.
You can antenuate the output from an mp3 player to the same levels and the phono cartridge. However, the output to the speakers will not be liner. However, if you pass the output of an mp3 player through a Inverse RIAA filter and antenuator, then the output to speakers will be linear.
Thus. to send the output of an mp3 player to a phono preamp, you need to pass it through a inverse or reverse RIAA filter antenuator.
Another problem with sending an mp3 output to a jukebox is that the amplifier (including) the pre-amp is muted when a record is not playing. This is to prevent the noise from the record being mounted from being amplified.
To set this up, I followed references [1-3]
However, his installation of pipewire is out of date.Just use the following:
sudo apt install pipewire pipewire-audio
This will install pipewire, wireplumber and libspa-0.2-bluetooth
Next install python3-dbus for his python script:
sudo apt install python3-dbus
Place the following python script into ~speaker-agent.py:
#!/usr/bin/python3
# SPDX-License-Identifier: LGPL-2.1-or-later
import argparse
import dbus
import dbus.service
import dbus.mainloop.glib
from gi.repository import GLib
BUS_NAME = 'org.bluez'
AGENT_INTERFACE = 'org.bluez.Agent1'
AGENT_PATH = "/speaker/agent"
A2DP = '0000110d-0000-1000-8000-00805f9b34fb'
AVRCP = '0000110e-0000-1000-8000-00805f9b34fb'
bus = None
class Rejected(dbus.DBusException):
_dbus_error_name = "org.bluez.Error.Rejected"
class Agent(dbus.service.Object):
def __init__(self, bus, path, single_connection):
self.exit_on_release = True
self.remote_device = None
dbus.service.Object.__init__(self, bus, path)
if single_connection:
bus.add_signal_receiver(self.signal_handler,
bus_name='org.bluez',
interface_keyword='org.freedesktop.DBus.Properties',
member_keyword='PropertiesChanged',
arg0='org.bluez.Device1',
path_keyword='path'
)
def signal_handler(self, *args, **kwargs):
path = kwargs['path']
connected = None
for i, arg in enumerate(args):
if type(arg) == dbus.Dictionary and "Connected" in arg:
connected = arg["Connected"]
if connected == None:
return
if not self.remote_device and connected == True:
self.remote_device = path
print("{} connected".format(path))
elif path == self.remote_device and connected == False:
self.remote_device = None
print("{} disconnected".format(path))
def set_exit_on_release(self, exit_on_release):
self.exit_on_release = exit_on_release
@dbus.service.method(AGENT_INTERFACE,
in_signature="", out_signature="")
def Release(self):
print("Release")
if self.exit_on_release:
mainloop.quit()
@dbus.service.method(AGENT_INTERFACE,
in_signature="os", out_signature="")
def AuthorizeService(self, device, uuid):
if self.remote_device and self.remote_device != device:
print("%s try to connect while %s already connected" % (device, self.remote_device))
raise Rejected("Connection rejected by user")
# Always authorize A2DP and AVRCP connection
if uuid in [A2DP, AVRCP]:
print("AuthorizeService (%s, %s)" % (device, uuid))
return
else:
print("Service rejected (%s, %s)" % (device, uuid))
raise Rejected("Connection rejected by user")
@dbus.service.method(AGENT_INTERFACE,
in_signature="", out_signature="")
def Cancel(self):
print("Cancel")
def start_speaker_agent():
# By default Bluetooth adapter is not discoverable and there's
# a 3 min timeout
# Set it as always discoverable
adapter = dbus.Interface(bus.get_object(BUS_NAME, "/org/bluez/hci0"),
"org.freedesktop.DBus.Properties")
adapter.Set("org.bluez.Adapter1", "DiscoverableTimeout", dbus.UInt32(0))
adapter.Set("org.bluez.Adapter1", "Discoverable", True)
print("RPi speaker discoverable")
# As the RPi speaker will not have any interface, create a pairing
# agent with NoInputNoOutput capability
obj = bus.get_object(BUS_NAME, "/org/bluez")
manager = dbus.Interface(obj, "org.bluez.AgentManager1")
manager.RegisterAgent(AGENT_PATH, "NoInputNoOutput")
print("Agent registered")
manager.RequestDefaultAgent(AGENT_PATH)
def nameownerchanged_handler(*args, **kwargs):
if not args[1]:
print('org.bluez appeared')
start_speaker_agent()
if __name__ == '__main__':
options = argparse.ArgumentParser(description="BlueZ Speaker Agent")
options.add_argument("--single-connection", action='store_true', help="Allow only one connection at a time")
args = options.parse_args()
dbus.mainloop.glib.DBusGMainLoop(set_as_default=True)
bus = dbus.SystemBus()
agent = Agent(bus, AGENT_PATH, args.single_connection)
agent.set_exit_on_release(False)
bus.add_signal_receiver(nameownerchanged_handler,
signal_name='NameOwnerChanged',
dbus_interface='org.freedesktop.DBus',
path='/org/freedesktop/DBus',
interface_keyword='dbus_interface',
arg0='org.bluez')
dbus_service = bus.get_object('org.freedesktop.DBus',
'/org/freedesktop/DBus')
dbus_dbus = dbus.Interface(dbus_service, 'org.freedesktop.DBus')
if (dbus_dbus.NameHasOwner('org.bluez')):
print('org.bluez already started')
start_speaker_agent()
mainloop = GLib.MainLoop()
mainloop.run()
What was not obvious was that the Unix name of the computer will show up when you pair or connect it as a bluetooth speaker
The next step was not obvious from the references [1-3]
sudo mkdir ~.config/systemd/user
Inside this directory create the file:
touch speaker-agent.service
Place the following inside speaker-agent.service:
[Unit]
Description=Bluetooth speaker agent
[Service]
ExecStart=python speaker-agent.py --single-connection
[Install]
WantedBy=default.target
Enable it manually using:
systemctl --user enable speaker-agent.service
Configure the BlueZ daemon to allow re-pairing without user interaction:
To change the pipewire's volume:
If the volume is too low, use:
wpctl set-volume @DEFAULT_AUDIO_SINK@ 0.8
