OTL tube amplifiers with unique design made in Sweden.
"A tube amplifier that redefines what is possible in a push-pull design."
See review by Dick Olsher in Enjoy the Music
Due to our unique driver stage we have been able to reduce distortion by more than 10 times achieving <0.01% at 1W and <0.1% at 10W in our 25W design, (PA12).
By using active noise cancellation we reach a noise level better than 100dBA below max power.
Our OTL design allows for low idle power and high output power using only few tubes thereby improving reliability. We have not had one tube failure in any customer amplifier in more than 7 years of production, our prototype has been in use since 2004 without power tube replacement.
Our preamplifiers are equipped with a high performance stepped attenuator for volume control that offers excellent channel balance, much better than what is possible using potentiometers, see here for a technical description.
Read what people think about our products
Q-tron Audio Automatic Bias Calibrator
A circuit that automatically controls bias and offset in OTL amplifiers and also automatically tune bias when changing power tubes
Q-tron Audio has developed a unique circuit for controlling the real quiescent current and output DC offset in our OTL amplifiers.
The circuit which is based on a microprocessor automatically measure and if necessary adjust quiescent current and output DC offset just before the amplifier is being switched off. The circuit works in the following manner:
When the power switch is pressed to switch off the amplifier the microprocessor circuit will start measuring the quiescent current and output DC offset and adjust those, if necessary, when these values are correct the amplifier will switch off completely. The whole procedure normally takes less than 1 minute even if the bias values need to be adjusted and the values for bias are then stored in a non-volatile memory. Normally the bias values don't need to be adjusted at all and then the amplifier will switch off immediately after measuring current and offset.
To ensure that the amplifier has been thoroughly warmed up and have reached its stable condition when the adjustment is performed, the circuit will only perform calibration if the amplifier has been switched on and operating for at least 30 minutes before it is switched off.
When the amplifier next time is switched on the stored values for bias will be applied.
The circuit will also give an alarm if it is not possible to adjust bias correctly, if so an orange "service" LED is lit, the amplifier can still be used but will not be optimally adjusted.
If any value is completely out of specification even after adjustments, (as in the case that a tube catastrophically has failed) 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.
Automatic bias tuning of new power tubes
The bias auto calibrator also automatically set correct operating parameters for new power tubes.
When old power tubes are exchanged for new the owner should set the amplifier in test mode and switch the amplifier on. The amplifier will then heat the amplifier to stable conditions and automatically adjust the bias and offset to correct values, when the amplifier next time is switched on the stored values for bias are applied.
For more details see "Bias Calibrator Technical background”
Q-tron was founded already 1976 by my brother Ulf and myself Hans Beijner to develop and produce advanced electronics. Throughout the years we have developed and produced special designs for the Swedish Military and Industry. Both of us have a background at Ericsson where my brother worked with sales and support and myself with electronic circuit design and product management.
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