Quad 306 DIY illustrated guidelines 

These are the illustrated step-by-step guidelines for upgrading your Quad 306 with the Dada Electronics upgrade-kit.

We will replace all electrolytic capacitors, the feedback Opamp chip, the in/output connectors and some resistors in the input-circuit like Quad did in the 606. 

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. 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 current-dumping amplifiers ever made with a better-than-original Quad-sound.

Stefaan & Joost – 16 February 2008

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
7.  Kontakt LR PCB-cleaner and Kontakt 61 Contact-spray are very useful

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

The components in the 306 upgrade-kit:

Cables, connectors & mechanical components:

1.  2x Gold-plated LS-connectors with red markings
2.  2x Gold-plated LS-connectors with black markings 
3.  2x 10cM  flexible 0,75mm flexible Hi-Q cable for internal wiring of the LS-connectors (Black + Red).

Components to be mounted on the motherboard (in both channels):

1.  2x Burr-brown Opamp-chips (OPA134)
2.  2x R 560R 1% for R1 (green-blue-black-black)
3.  4x R 22K 1% for R2 & R7 (red-red-black-red)
4.  2x R 82K 1% for R6 (grey-red-black-red)
5.  2x R 30R 1% for R13b (orange-black-black-gold) (*)
6.  2x R 36R 1% for R13c (orange-blue-black-gold)
7.  2x R 2M2 1% for R33 (red-red-black-yellow)
8.  2x C 330nF MKT  for C2
9.  2x C 1µF MKT for C3
10.  4x C 6800µF 63V for C10 & C11
11.  2x C 47µF 63V for C7
12.  8x C 100nF MKT (Decouple caps for the diodes)

All other Quad 306 components are also available from the Dada Electronics webshop

See also the Quad Spot weblog.

Step 2 – Dismantling the 306

Working on the 306 is simple. All components except the loudspeaker-connectors are soldered directly to the motherboard. The LS-connectors are connected with a small piece of wire.

On the back of the boards the component-numbers for the left channel are printed in white, for the right-channel in red. The schematic for both channels is identical but not the object-location.

The best way to proceed is to remove all components to be replaced (see the list above) in one channel and the in the other channel. After removing the components you can clean the board with Kontakt LR cleaner. Make sure all unnecessary solder and raisin rests are removed.

Step 3 – Fitting the components to the board 

Solder all the components to the board.

The original input-sensitivity was 0,375 Volt. If you want to change it to 1,0 Volt replace R13 with 30R – if you want to change it to 1,25 Volt (Line-voltage) replace it with 36R.

The alternative resistors are included in the kit.

If you are using the 306 with a 33, 34 or 44 preamplifier you would not change the sensitivity. For other preamplifiers you would prefer 1,0 Volt sensitivity. Of course you can always change it afterwards.

Mount the Loudspeaker-posts. The holes have the correct size so you won’t need to drill. Connect the posts to the board with a piece of wire.

Attention: the order is Red – Black – Black – Red.

Solder the small yellow 100 nF decoupling caps over the zener-diodes D1 to D4 on the backside of the board.

Mount the snap-in 6.800 µF Power-supply capacitors. Check and double-check the polarity.

If the polarity is wrong they will explode !!!

The + side is indicated op the PC Board. The white band on the capacitors is the – side.

You may consider cleaning the RCA-contacts with Kontakt 61 anti-corrosive contact-spray.

Step 5 - Testing the amplifier

If you have a scope and a sinus-generator you can measure the power and the input-sensitivity of the amplifier.

If you don’t have this equipment it’s not a problem. There are no necessary calibrations to be done as it is a Current-dumping design.

If you have a multimeter you could check the power-supply rails (+ 40 V and – 38V) and the DC-component in the output (< 0,1 V).

Following measurements are OK:  - 0,01 Volt DC on the outputs - Around 20 Volt AC on the outputs before clipping. This corresponds with 50 Watt into 8 Ohm. - The AC voltage you selected with R13 on the input before clipping. This corresponds with line-voltage for full power.  

Step 6 – Re-assembly 

Re-assembling the 306 is simply a matter of putting it in its case…

And that’s it.  

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

Price $115.00
DIY installation including all of the hard-to-find parts.

Price $285.00
Let us do the complete upgrade and revision