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The classic QUAD 33 although very good for its vintage is now behind the times as far as sound quality and technology are concerned. The sound quality of the 33 can now be brought up to very high performance levels with  new plug in circuit boards (PCBs) which have been specifically designed to fit inside the chassis just as the originals did, but with much improved performance.

These PCBs are a direct plug and replace boards for the current Tape Adapter Board found in a Quad 33 Pre-Amp and have been designed for ultimate transparency. The Tape Adapter Board buffers the signals coming from the disc input board as well as signals from the Radio 1 and Radio 2 input sockets before these are passed onto the volume control. It also used to match the Tape input and output levels to suit the tape recorder you may be using. This is done with user selectable jumpers.

The Power Supply

As with all audio equipment the power supply plays a crucial role in overall performance. A weakness in the power supply will always produce deterioration in sound quality. Important aspects of the power supply is how the PSU voltages are produced and also their return path from the audio circuitry back to the power supply (the ground). A PSU which radiates a lot of electromagnetic noise in a sensitive piece of equipment such as a pre-amp can only degrade performance. Ideally this should be outside the preamp itself in either a screened casing or kept a few feet away.

In this case raw semi-smoothed DC at 18-24V is fed into the newly designed Tape Adapter Board where it is further smoothed and then regulated to provide an ideal power source for the rest of the pre-amp. There is then also further smoothing and additional regulation for the local circuitry on each individual plug in card. This provides the best possible Power Supply for the active circuitry. As for the ground return, this is done using very low impedance ground planes which have been specifically 'split' to direct the ground currents back to the regulator ground with minimal interference of the sensitive signal grounds. This provides the best solution for the power supply design.

The Tape Adapter Board must be used if more than one other option is purchased as the internal power supply in the Quad 33 is not capable of supplying the required current for the additional boards.

The Tape Adaptor Board in now in MK2 form for improved sound through the Disc and Radio inputs.

Features of the circuit are: -

  • A FET buffer is used with associated circuitry for great sound.
  • No electrolytic capacitors are used in the signal path or biasing stages.
  • Individual regulators on each channel giving improved bass, cleaner sound, better channel separation and reduced cross talk.
  • PCB is a Ground Plane design improving the signal integrity.
  • Surface mount resistors (underneath the PCB) are used providing shorter signal paths and improved sound quality.
  • Long life components are used in the power supply providing improved reliability.
  • Improved power supply over the MK1 for increased fidelity and channel separation.
  • The Tape Record Output can be disconnected for less internal internal cross talk and buffer loading.

For more info on upgrading please see the Full Upgrade Page.

The new MK3 Tape Adaptor board is now in production. It is powered from the internal PSU and requires the NET Audio PSU to function correctly as it works of a higher voltage than the original Quad Tape board. With the new internal PSU it is the best sounding NET Audio tape board.


Tape Adapter Board - photo of the new board will be published soon.

Tape Jumper Locations (pdf)


Fitted Tape Adapter Board Showing Power Connector


Quad 33 Tape Adapter Upgrade MK3

Tape Adapter upgrade includes:-

  • One Tape Adapter Board - Must be used with NET Audio Internal PSU
  • Full instructions on how to fit the upgrade modules (PDF Format)
  • Board overlay diagram for Tape Adapter Board Jumpers (PDF Format)
Total Price with no PSU excluding P+P = £65