Quad 606 DIY illustrated guidelines 

These are the illustrated step-by-step guidelines for upgrading your Quad 606 MK I or 606 MK II with the Dada Electronics upgrade-kit.

We will replace all electrolytic capacitors, some HF MKT capacitors (in the pF range), the in/output connectors and the cabling. 

We will also adapt the input-sensitivity (as an option) by increasing the feedback in the input-circuit. This increases signal-to-noise ratio and makes the amplifier better adapted to modern input-sources.

We will do the upgrade step-by-step. This is important because some steps are more difficult after other steps are taken. For every step these guidelines will tell you what to do (in Underline) and give you some tips, tricks and advice (in Italics).

You should have some soldering-experience for bringing this project to a good end but you don’t have to be an electronics-expert.

When there are any problems, send an e-mail to info@dadaelectronics.eu with a good description of the problem. Some pictures may help. We will do our best to answer within 24 hours 7/7.

When the project is a success you will be listening to one of the best high-end amplifiers ever made with a better-than-original Quad-sound.

Stefaan

Step 1 – The tools & the Components

The tools you need:

1.  A good quality soldering iron with a fine point (max 30) Watt or a soldering-station.
2.  A desoldering-pump
3.  A micro cutting nipper, a wire-stripper and a miniature plier
4.  A Philips n° 2 screwdriver and a small flat screwdriver
5.  Tin/lead solder wire
6.  A digital multimeter

If you don’t have these tools you can order them in the Dada Electronics webshop.

You should also have the 606 schematic and the Service-manual at hand. If you don’t have them just end an e-mail to info@dadaelectronics.eu and we will reply with the documents attached.

There are 3 versions of the 606 upgrade-kit.

1.  The Basic version includes the in/output connectors, internal cabling, capacitors for the driver-boards, PCB-connectors and other small components.
2.  The Power transistor option contains 12x 2N3773 transistors.
3.  The PSU Capacitor option contains 4x BHC Aerovox 10.000µF 63 V capacitors.

The components in the 606 basic upgrade-kit:

Cables, connectors & mechanical components:

1.  2x Gold-plated LS-connectors with red marking and plastic insulation-washers
2.  2x Gold-plated LS-connectors with black markings
3.  2x Gold-plated RCA-sockets with Black and Red markings
4.  4x 1M  flexible 0,75mm flexible cable for internal wiring (Green for mass,  Blue for the LS-outputs, Black for – DC-current, Red for + DC current).
5.  Stereo shielded audio-cable, 50cm
6.  10x Silver plated PCB-connectors, male + female
7.  Thermal insulation-gain, 30cm 

Components to be mounted on the driver-boards:

1.  2x 150 nF 10mm MKT or MKS4 for C2
2.  6x 330 pF Silvered Mica for C1 / C4 / C6
3.  2x 47 µF 63V Nichicon for C7
4.  2x 47 pF Silvered Mica for C8
5.  2x 47 nF MKS4 for C10
6.  4x 470 µF 63V Nichicon for C9 / C11
7.  2x Metalfilm resistors 12 Ohm 1/2W for R11 (see below)

Options (you can order these options from the Dada Electronics webshop

1.  12x 2N3773 Power-transistor
2.  4x BHC Aerovox 10.000µF 63V capacitor for the power-supply
3.  Velleman K4700 Loudspeaker protection kit, stereo with switch-on delay
4.  Velleman K4701 Loudspeaker DC-protection, mono
5.  all other 606-components are also available

See also the Quad Spot weblog.

Step 2 – Dismantling the 606

1.  Remove the bottom-cover (Philips n°2, 4 screws)
2.  Remove the wires from the 2 driver-boards (5 wires per board)
3.  Remove the driver-boards (2x 3 screws)
4.  Remove the heat-sink compound from the driver-boards with kitchen-roll paper (don’t use cleaning-products)
5.  Remove the 4  PSU-capacitors and mounting-rings.

Step 3 - Fitting in the Power Supply capacitors and the connectors  It is important to do these steps in the right order as it makes it more practical to reach certain components.

If you don’t use the upgrade-kit but your own components you can fit the capacitors in the old mounting-rings with transparent Silicone. Make sure it dries for 24 hours.

Step 4 - Upgrading the circuit boards. 

 If you have a stabilized power-supply (+ 57 and – 54 Volt), a function-generator and a scope you might test the boards before upgrading them. If you don’t, no problem, you can upgrade the boards without them.

When you connect a dual power supply to the board (+ and – voltage to the PCB-connectors, mass to the aluminum heat-sink (don’t use the input mass for this!), you should read about 110 mA in the – power-line and 120 mA in the + power-line. This means the power- and driver-transistors are OK.

It is a good practice to upgrade the boards one by one. So we can compare between the boards if we want to see the polarity of capacitors or diode’s or if something goes wrong.

Replace all the components in the above component-list.

Replace the PCB-connectors with silver-plated connectors.

If you want an input-sensitivity of 0 dBm (0,775 mV), which is standard, replace R11 with 12 Ohm. If you leave R11 in place the input-sensitivity will be 0,5 Volt.  Step 5 - Testing the circuit boards  When both boards are upgraded we'll connect them to a sinus-generator and to the scope. We'll connect + and - 50 Volt with our lab power-supply and connect a true-RMS multimeter to check the input- and output voltages.

Following measurements are OK:  - 0,01 Volt DC on the outputs - 32 .. 36 Volt AC on the outputs before clipping. This corresponds with 130 .. 150 Watt into 8 Ohm. - 0,775 Volt AC on the input before clipping. This corresponds with line-voltage for full power.  If you don't have all this lab-equipment, skip this step. We will make sure later that there is 0 VDC on the output and that the power-consumption in the power-lines is 120 .. 130 mA.

Re-check both sides of the boards to make sure that the polarity of the electrolyt capacitors and the diodes is correct and that there are no soldering short-circuits between the PCB leads. 

Step 6 – Cabling & Re-assembly  We start by cabling the power-supply. For internal cabling counts: the shorter the better. We'll use high-quality flexible 0,75 mm in 5 colors for everything except the 230 Volt lines. 

We’ll use the following colors:

1.  Red for the +50 Volt line
2.  Black for the -50 Volt line
3.  Green for the output-mass
4.  Blue for the LS-output lines

For the inputs we’ll use shielded cable between the RCA-connectors and the driver-circuits.

Before connecting the power re-check the polarity of the caps and the rectifier-bridge. Compare with the schematics.

Warning If the polarity of the caps is wrong they will explode!  It is better to twist all cables that have to be soldered to the same point together before tinning them, it makes soldering a lot easier. Foresee cables to the boards as well. 

Once the power-supply is OK, we fix in both boards adding thermal paste to ensure maximum heat-conduction with the chassis.  We can now connect the + and - power-lines to the boards (don't switch them or you'll kill the output-transistors!) as well as the LS-output cables to the red LS output-plugs.

It is no luxury to use some Raychem (or other) Heat Shrinkable Tubing for insulating the +, - and output connections, as there are large voltages between them.

 Connect the “+” and “-“ leads from the power-supply to the boards

 Connect the LS-outputs of the boards to the circuit-boards or the Velleman LS-protection

 Connect the inputs to the RCA-plugs with shielded cable

 Install the boards using new Heat Sink compound

 Re-assemble the amplifier is reverse order

 Before connecting mains-voltage we should check all cabling again with the Ohm-meter. We should also re-check that each channel uses 120 .. 130 mA in the + and the - power-line and that there is less than 1 Volt DC on the outputs (typically 0,01 Volt).  If it passes these final tests we can now connect the speakers and the preamp and... enjoy the music ;-)

If there is any problem don’t hesitate to send me an e-mail (info@dadaelectronics.eu). A picture and a good description will help to solve the problem.

Stefaan