Q-tron Audio PA34B4 User manual
Q-tron Audio
Q-tron Audio Manual PA34B4R1 Page 1(9)
Q-tron Audio PA34B4 OTL amplifier
user manual
Q-tron Audio
Q-tron Audio Manual PA34B4R1 Page 2(9)
1. INTRODUCTION ..............................................................................................4
2. CONTENT OF DELIVERY................................................................................4
3. UNPACKING BOX............................................................................................4
4. SETUP..............................................................................................................5
4.1 Function..............................................................................................................................5
4.2 Start-up procedure....................................................................................................................... 5
4.3 Switch off procedure..........................................................................................................6
If the amplifier has been switched on less than 60 minutes:........................................................6
If the amplifier has been switched on more than 60 minutes:............................................................6
5. CONTROLS AND CONNECTORS...................................................................6
5.1 Front panel..........................................................................................................................6
5.2 Back panel..........................................................................................................................6
5.3 Unbalanced/balanced switch.............................................................................................7
5.4 Speaker connectors...........................................................................................................7
5.5 Mode ...................................................................................................................................7
5.6 Indication LEDs..................................................................................................................7
5.7 Mains power inlet with integrated fuse holder and mains switch....................................... 7
6. Q-TRON AUDIO AUTOMATIC BIAS CALIBRATOR........................................7
6.1 Automatic bias tuning of new power tubes............................................................................. 8
7. PERFORMANCE DATA: ..................................................................................9
8. CONTACT INFORMATION...............................................................................9
Q-tron Audio
Q-tron Audio Manual PA34B4R1 Page 3(9)
Fig 1 Front view
Rear view
Q-tron Audio
Q-tron Audio Manual PA34B4R1 Page 4(9)
1. Introduction
Thank you for choosing the PA34 OTL amplifier from Q-tron Audio. The PA34 is a new
improved OTL amplifier with 10 times lower distortion than other OTL amplifiers of
similar output power. The PA34B4 version described in this manual is equipped with an
automatic bias calibrator that removes any need for manual adjustment.
2. Content of delivery
Box 1
1. Amplifier PA 34B4
Box 2
1. Tubes 6C33C 4 pcs
2. Tubes 6N2n-EB 3 pcs
3. Tubes 6N6P-I 2 pcs
3. UnpackingBox
Put the wooden box on a table or other steady surface. Make sure that the box is
oriented correctly, i.e. that the side marked top is facing upwards. Open the box by
prying open the metal flaps that are holding the top lid using a screwdriver. When all
metal flaps are bent so they point upwards, the lid can be opened.
Remove packing material so that the amplifier can be lifted out of the box, be aware of
the weight and handle the amplifier carefully.
Put the amplifier on a steady surface with the front panel facing you.
Unpack all tube cartons and put them aside. Unpack all tubes one by one and put them
into the correct tube sockets as indicated by the figure. NOTE! Output tubes are
matched as a set of 4 and to each individual amplifier, make sure that the tubes are set
in their correct position in each amplifier.
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Q-tron Audio Manual PA34B4R1 Page 5(9)
Tube placement
Note! V1, V3 and V4 are 6N2-EB, V2 and V5 are 6N6P, V6 – V9 are 6C33C-B
4. Setup
1. Connect the amplifier to the mains voltage with a standard IEC 320 mains cable
2. Connect speakers to the isolated binding posts
4. Connect a preamplifier to the connectors marked input
4.1 Function
The amplifier is equipped with XLR and phono connectors for the input signal and
isolated binding posts for connecting speakers. The amplifier is equipped with an output-
offset voltage protection circuit that protects connected speakers in the case the
amplifier would give a too high DC voltage on the output. A fail-safe soft-turn-on-circuit is
also included.
4.2 Start-up procedure
Switch on the mains switch on the back panel to position 1. Push in the front panel bush
button for 1 second, the area around the push button will then be lit with a green dim
light, after approximately another 1.5 seconds a “click” can be heard, this is an indication
that the soft-turn-on-circuit is activated.After approximately 90 seconds the area around
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Q-tron Audio Manual PA34B4R1 Page 6(9)
the front panel push-button will go from dimmed green to bright green and the amplifier
is then ready for operation.
4.3 Switch off procedure
If the amplifier has been switched on less than 60 minutes:
When the front panel push-button is pressed the amplifier will switch off
immediately.
If the amplifier has been switched on more than 60 minutes:
When the front panel push-button is pressed the green light around the push
button will first be lit dimmed and will continue to be so until the automatic bias
calibration has been completed when the green light will be extinguished, and the
amplifier will be switched off.
If the mains switch on the back panel is in ON position the control circuits are
energised and the power consumption is about 5 W. In the OFF position all
circuits in the amplifier are switched off and there is no power consumption
NOTE! The amplifier must be connected to speakers or another load to operate
correctly, if not the offset voltage protection circuit will switch off the amplifier
automatically directly after the start-up sequence has been completed.
5. Controls and connectors
5.1 Front panel
On switch with integrated indicator, this is a switch button which when pushed in
will start the switch-on-sequence of the amplifier.
5.2 Back panel
Input connectors
Phono This connector accepts standard RCAphono plugs
XLR This connector accepts standard XLR plugs
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Q-tron Audio Manual PA34B4R1 Page 7(9)
5.3 Unbalanced/balanced switch
This switch should be in the U position when using the RCA connectors and in
the B position when using the XLR connectors. NOTE! Do not connect both RCA
and XLR connectors at the same time.
5.4 Speaker connectors
Live, and ground. These connectors accept 4mm banana-type plugs, bare wire
and spade-type connectors.
5.5 Mode
This connector is used to set the mode of the amplifier, normal or tuning mode.
The tuning mode is activated by connecting the tuning plug.
NOTE! Do not connect the monitor box that was used with earlier versions of the
PA34 nor connect anything else to the Mode connector except the tuning plug
when needed.
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Q-tron Audio Manual PA34B4R1 Page 8(9)
5.6 Indication LEDs
These LEDs indicate fault conditions as described in the table.
Alarm
Service
Indication
Power tubes out of specification, change
power tubes
Power tubes are worn, and time for service
5.7 Mains power inlet with integrated fuse holder and mains
switch.
The power inlet accepts a standard power cord with an IEC320 plug. The 2 mains fuses
can be accessed if the power cord is removed and the fuse cover/holder is removed,
replace the fuses only with fuses of the same rating, (for 230VAC mains power fuse
rating is 4A slow blow and for 120VAC mains power fuse rating is 6.3Aslow blow). The
mains switch to power up the amplifier if it is set to position 1, in position 0 the amplifier
is disconnected from mains power.
6. Q-tron Audio Automatic Bias Calibrator
Automatically control bias and offset in our OTL amplifiers and also automatically tune to
correct bias when installing new power tubes.
1. Automatically tune bias and output offset voltage to optimal values
2. Controls the real quiescent, (idle) current, see https://qtron.se/en/articles/q-tron-
audio-bias-calibrator-technical-background for a complete in-depth analysis and
explanation).
3. Automatic tuning of bias when replacing power tubes
The circuit automatically measures and if necessary, adjusts quiescent current and
output DC offset and works in the following manner:
If the amplifier has been on for less than 60 minutes, it will turn off instantly when the
power switch is pressed. If the amplifier has been switched on for more than 60 minutes
and the power switch is pressed to switch off the amplifier the microprocessor circuit will
start measuring the quiescent current and output DC offset, this is indicated by that the
area around the switch-on button change from being brightly lit to dimly lit.
Most times the bias values don’t need to be adjusted and then the amplifier will switch
off almost immediately indicated by the area around the switch-on button becoming dark.
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Q-tron Audio Manual PA34B4R1 Page 9(9)
If adjustments are necessary these will be performed automatically and when these
values are correct the amplifier will switch off. The values for bias are stored in non-
volatile memory.
When the amplifier next time is switched on, the stored values for bias will be applied.
If the power tubes start to get worn so that they need very different bias voltage an
orange "Service" LED will be lit at the back panel, the amplifier can then still be used but
will not be optimally tuned.
If any value is completely out of specification even after adjustments, (as in the case that
a tube catastrophically has failed or got too weak) there will be a red "alarm" LED lit and
the amplifier can then not be used for playing music, (the inputs and outputs will be
shorted) until the fault has been corrected.
6.1 Automatic bias tuning of new power tubes
The bias auto calibrator also automatically sets the correct operating parameters for new
power tubes.
Procedure:
1. Switch off the amplifier completely, also with the switch on the rear.
2. Set the amplifier in tuning mode by connecting the tuning plug to the connector
on the rear panel
3. Put a new balanced set of 4 power tubes in the channel where they should be
replaced
4. Note all other tubes must be installed in the amplifier
5. Note! the new power tubes must be matched to within 2V difference in grid
bias at 200mA anode current and 160V anode voltage, e.g. 2 tubes that
need -55V and -57V are OK. The grid voltage of power tubes must be in any
case between -55 and -65V.
7. Performance data:
Output power in 8 ohm load 80W at 1% distortion at 1kHz
Output power in 4 ohm load 60W at 1% distortion at 1kHz
Output impedance <0.4ohm
Harmonic Distortion 0.01% at 1kHz and 2W output power
0.1% at 1kHz and 25W output power
Power bandwidth 10 – 150000 Hz -3dB
Noise and hum 90 dB below 80W output power, (10 – 200000Hz)
100 dB below 80W output power, A-weighting filter
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Q-tron Audio Manual PA34B4R1 Page 10(9)
Line voltage 230V or 120V ± 10%
Power consumption 600W maximum
Dimensions chassis 275 x 370 x 225 mm, (W x D x H)
Dimensions overall 275 x 370 x 350 mm, (W x D x H)
Tube complement 9 tubes in total, (6C33C x 4, 6N6P-I x 2,
6H2n-EB x 3
Input connectors:
Unbalanced Gold plated phono
Balanced Gold plated XLR
Output connectors CE-approved isolated binding posts accepting 4mm
banana connectors, spades and bare wire
Line voltage connectors IEC320 jack with integrated mains switch and dual
fuses
Weight 18kg
8. Contact information
Manufacturer Q-tron Audio Sweden
www.qtron.se sales@qtron.se
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