Q-tron design philosophy

Minimalistic design
Use as few components as ever possible. This could be seen as something obvious but even many of the so called High-end companies use unnecessary complicated circuitry giving unclear "muddy" sound.

One of the main reasons why tube amplifiers can give better sound than solid state amplifiers is just because it is possible to achieve the same results with fewer active elements. As an example of the result of this philosophy our 25W OTL power amplifier use only 6 active elements which can be compared to typical high-end solid state amplifiers with normally more then 20 transistors.

All tube design
At Q-tron we design and build all audio circuits using only vacuum tubes, we do not use any solid state components in any place where they can effect sound quality.

When we use solid state components for rectification and sometimes as voltage references we eliminate any detrimental effect on sound quality by careful de-coupling. We completely discourage the use of any hybrid designs where tubes and solid state components are mixed as we have found these designs to approach solid state sound quality without adding any positive effect of using tubes.

Minimise coupling elements, (transformers and capacitors)
Both transformers and capacitors introduce distortion, we therefore try to eliminate these as far as possible in our designs.

Point to point wiring
At Q-tron we still use point to point wiring for all our designs as we believe that this positively affect sound quality.

In the old days all tube equipment was built using point to point wiring, that is components was soldered to isolated binding posts and connected using isolated wires. Later in the 1950's Printed Circuit Boards started to be used where components where soldered to isolated boards and the connection between the components where done by copper foil. Today most electronic equipment use circuit boards and even multilayer boards are getting common also in audio equipment.

It is important to realise that the main reason to use circuit boards instead of point to point wiring in an audio circuit is in order to reduce cost, there are no other advantages either electric or sonic to use this technique in audio circuits, instead the usage of circuit boards introduce some problems that doesn't exist with point to point wiring.

Some problems we have found when using circuit boards for audio designs are:

Cross talk between connection layers, or between closely mounted components introduce small amount of distortion. This can be minimised by careful circuit board layout but is best avoided altogether.

Distortion introduced by imperfections in the circuit board isolation material. As described in the text about: LTCC, (Low Tension Capacitor Coupling) isolation material in capacitors affect sound quality, the same effect is present when using circuit boards as the copper foil layers together with the circuit board isolation material function as capacitors.

Even high end equipment still use low grade circuit board materials as phenolic or paper but negative effects are also present in equipment using glass filled epoxy boards like FR4 as this is also a highly polar isolation material. Teflon based circuit boards have their own specific problems that is all to well known by designers of microwave circuits, (stepwise changes in dielectric constant due to temperature differences).

At Q-tron we build all our equipment using point to point wiring using standoff posts with ceramic isolation that have no ill effects of the circuit performance.

Active/passive RIAA correction

There is a constant on-going debate whether passive or active RIAA correction is preferable with arguments for and against each technology. At Q-tron we believe we have found the best solution by using a combination of both active and passive correction, the active part take care of the low frequency correction and the passive part handles the higher frequencies. The advantages of our solution is:

Precise RIAA correction, with active RIAA correction it is not possible to precisely follow the RIAA correction curve, this problem is eliminated in our design.

Low noise, hum and distortion, an all passive RIAA correction will give higher distortion then an all active solution, our design will give the same low distortion as with an all active design without any of the usual problems.

Feedback
Feedback can if used correctly be used for lowering output impedance in power amplifiers or in order to stabilise gain in low level amplifier gain stages. Feedback must NOT be used in order to reduce distortion from high levels or in order to increase bandwidth.

In the seventies it was normal to build transistor amplifiers with open loop bandwidth of only 100Hz and distortion levels of up to 50% and then to use heavy feedback in order to restore bandwidth and lower distortion, it is easily understood that these amplifiers sounded awful. Note that even today many solid state amplifiers have marginal open loop bandwidth.

Williamsson that design the famous Williamsson amplifier in the fifties put up the following criteria for the design of a good sounding power amplifier, these criteria is still valid today.

High bandwidth before feedback is applied, the bandwidth must exceed the audio frequency range.

Low distortion before feedback is applied, the amplifier must have low distortion even before feedback is applied, otherwise new higher order distortion components will be created, also see below under if the amplifier have high distortion and feedback is applied new higher order distortion components will be produced, 2nd harmonic will create 4th harmonic, 3rd harmonic will create 6th harmonic aso.

Ample phase margin, the amp lifer must be unconditionally stable in order to not create phase distortion and/or in-stability with different loads.

These design criteria are followed for all our amplifier designs and feedback therefore give an improvement by stabilising gain and lowering output impedance without adding any ill effects.

"Designer" components
"Designer" components usually give bad value for money, our findings show that it is possible to find better and cheaper components if you know what to look for.

Created on ... April 7, 2002