CD Player Upgrades
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Quad 33 Upgrades
Full Upgrade
Disc Amplifier Upgrade
Tape Board Upgrade
Output Board Upgrade
Minimalist Output Upgrade

Quad 303 Upgrades
Quad 303 Upgrade
Capacitor Replacement

Quad 405 Upgrades
405 MK1/2 Upgrade
405 Full Upgrade
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These PCBs are a direct plug and replace boards for the current items found in a Quad 33 Pre-Amp and have been designed for ultimate transparency. They buffer the volume control and bypass the tone control circuitry negating the use of a second amplifier in the tone control section. This then provides more free circuit board area which can then be used to add extra circuitry to maximize the performance of the volume control buffer.

For ultimate CD replay (for tape and tuner as well) The source should be fed into the tape replay socket. The jumpers on the tape board should be set to Low (L) using the screws on the original Quad 33 tape adaptor board. These can be found under the tape adaptor board in the middle nearest the track end ot the adaptor board. This routes the input signal straight to the volume control to provide the shortest signal path from the source component, again to maximize transparency and signal integrity. The volume control then feeds the buffer directly, bypassing the tone controls and is used to drive the power amplifiers input circuitry. The buffer provides a low output impedance of 100 ohms compared to the original 33s 1200 ohms, giving it the ability to drive the cable and the power amp input without being effected by cable capacitance or amplifier input loading. These loading effect are most notably heard on a passive pre amp which tends to sound dull, lifeless and lacking in bass and bass slam compared to a buffered pre amp. The buffering preserves the dynamics and pace of the music, giving a more realistic sound with much improved bass control, separation and imaging without the wooly sound of a passive pre amp.

The Output Buffer boards can be used in either of three ways:-

• A PCB jumper is fitted to position 1, the left hand 2 pins, so that the pre amplifier has the same gain as a standard 33 and the normal balance control still functions. This uses some of the original 33s internal wiring and components in the signal chain to provide the gain change on the buffer amplifier to provide the balance function which causes a slight reduction in sound quality.

   

• The jumper is moved to position 2 as shown in the photograph below, this still provides the standard gain, but without the balance control functioning. In doing so the signal no longer passes through the pre amps internal wiring, through one of the original resistors and capacitor on the mother board and then through the balance control to ground. It instead passes through one small (about 2mm) resistor, and then through an audio grade Elna capacitor to the ground plane on the output circuit board, keeping the feedback signal path as short as possible and maximizing the sound quality in this mode.

   

• The jumper is removed. The output boards then have a unity gain (a gain of one) so that the pre amp can be used with a CD player fed straight into one of the radio inputs (if you have the tape link board fitted) or into the tape input if you have the 33 full upgrade without the use of in line attenuators, further improving the sound quality because the on board feedback circuit is now disconnected, reducing the number of components that effect the signal quality. This mode provides the best possible and most direct signal path through the 33 pre amp for maximum transparency.

   

• Very high quality Op-Amps with 0.00008% distortion are used for ultimate fidelity.
• Individual regulators on each PCB 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.

The treble is smoother and more incisive. Bass is better formed and easier to follow. Sound staging is bigger and wider with improved separation between individual instruments and voices with less smearing. Overall the sound quality is vastly improved over the original Quad Boards with it being more "out of the speakers" and realistic.

The Pre-Amp with the modified PCBs has been driven from a DAC with a digital volume control so that it can be compared with the DAC feeding the power amp directly. With the Pre-Amp in circuit with high quality cables the new PCBs are virtually totally transparent compared to the DAC feeding the Power Amp directly with no Pre-Amp in the signal chain.

For vinyl enthusiasts there is a Disc Input Amplifier Board available. With the mod to the PSU as listed above only the Disc Input Amplifier PCB or Output PCBs can be fitted but not together as the internal power supply cannot power up both upgrade PCBs. To resolve this problem a tape input card is available which has been extended in length to accommodate a DC power socket. This enables an external 18V - 24V power supply to be plugged in and power up all available cards. Removing the mains from inside the pre-amp has additional benefits on the sound quality. Any upgrade which includes the tape adapter PCB will not require any internal modifications to be made and are just plug in upgrades.

All signals from either the disc input (configured for either disc or CD), radio 1 and radio 2 passes through the link board in the tape adapter upgrade (if fitted) and then through the two output buffer PCBs and then on to the output connector.

Output Buffer Boards

When using the Minimalist buffer board, the tape replay input will produce the highest sound quality when the selectors on the Quad 33 tape adaptor board are set to the "L" position. These are the two screws on the left hand side of the picture below which are currently set to the "M" position.

If you require both the radio inputs to have the same sonic quality as the tape replay input then a tape link board is available. This is used to replace the original tape adapter board (shown above) and links the two radio inputs to the volume control, bypassing the original circuitry and therefore maintaining maximum sonic quality on all 3 inputs so that the full benefits of the Minimalist Buffer Board can be realised.

One source of interference in any audio equipment is the presence of the mains voltage. This contains many harmonics and high frequency noise and it is a good idea to remove it from the Quad 33s internals. The Tape Link PSU board does exactly that, it provides a clean, low noise DC voltage to power the internal circuitry whilst keeping the internal environment of the 33 electrically quiet by being fed from an external regulated power supply.

Output Buffer Boards Fitted inside a Quad 33

Quad 33 Minimalist Output Buffer Upgrade

Output Buffer upgrade includes:-

• Two Output Buffer Amplifier Boards
• Two preformed resistors.
• Full instructions on how to fit the upgrade modules (PDF Format)

Quad 33 Tape Link Board

The Tape Link upgrade includes:-

• One Tape Link Board

Quad 33 Tape Link PSU Board

The Tape Link PSU upgrade includes:-

• One Tape Link PSU Board
• One Regulated Power Supply