• Most electrolytic capacitors tend to dry out after 15 years. Their value changes and in the worst case they give a short-circuit. This may cause a "rumble", a "hiss", more distortion and even a complete disfunctioning of the amp. Modern capacitors are smaller and perform a lot better. High-end capacitors have a life-time above 150.000 hours and less internal resistance.
• The Opamp technology in the 7-ties and the 8-ties was not at all as advanced as it is today. The LM301 that was used in most 405's can not match the performance of modern Opamps like the Burr Brown OPA604 (see the links on the left). CD's did not exist at the time the 405 was designed and CD's give a lot more dynamics in the sound dynamics vintage Opamps can't match.
• "Line-voltage" in the 7-ties was considered 500 mV. Today most CD-players or pre-amps produce +/- 1,5 Volt. Connecting a modern input-source to vintage Quads will cause distortion and an uncomfortable behavior of the Volume attenuator on the preamp. Reducing the input-sensitivity not only makes the 405 better adapted to modern input-sources but also reduces distortion and noise dramatically (<>

Instead of revising my 405, why don't I sell it on eBay and buy a new amp?

That's an option, indeed, if you have a budget of above 4.000 euros to match the same transparency and dynamics.

What useful modifications can be done to my 405?

• The capacitors have to be replaced by new ones. After more than 15 years capacitors dry out and change their specifications. Modern capacitors, by the way, are not only a lot smaller but also a lot better. For some caps it may be usefull to have "audiophile" caps inserted like Wima, Wonder Caps or MusiCaps if you have the perfect ear and a lot of money ;-) Good quality capacitors of a usual (and cheaper) brand will do as well. For 99% that is.
• The Opamp (usually a LM301 or a TL071) has to be replaced by a modern high-end audio Opamp. At the time the 405 was produced Opamp audio technology was new. Those veteran Opamps are absolutely no match for modern high-ends like the Burr Browns. CD's were not invented yet when the 405 was designed. CD's have much higher dynamics than LP's, dynamics those veteran Opamps can't match.
• Reducing the current-limiting may be an option. Quad designed the 405 for professional- and home-use at the same time. And for the ESL speakers. So they limited the current to 3 ... 4 Amps to stay on the (very) safe side.
• The output- and driver-transistors could be replaced by faster types available today like the Motorola MJE15031 for the drivers and the 2N3773 for the output-transistors.
• The internal wiring should be replaced. The cable-tree was good for reducing production-cost but for nothing else anyway. There is no use in buying expensive external cables when on the inside there is miserable bell-wire which is much too long.

For the rest the design of the current-dumping circuit is not critical about component tolerance. There is no use - for most components - to spend money on 1% tolerances when even 20% will do fine.

Will the 405 still have the typical Quad-sound after the upgrade?

Sure it will.

Even more than ever before.

The "behind the curtain" sound, due to the bad performance of worn caps will completely disappear and the transparency of the sound which is so typical for Quad will be outstanding. Modern Opamps will dramatically reduce distortion and improve dynamics.

But the current-dumping schematic remains the same of course. There is no amp below 4.000 Euro that can even match an upgraded 405 in a "blind test".

Many people who upgraded their 405 have thrown away half of their CD-collection because the OPA604's outperform the Opamps in most recording-studios.

You get used to the quality you're used to listening to music very quickly ;-) I don't ever go to pubs anymore. Because I can't stand what I hear there, especially when they put the music "loud".

What are the technical considerations when the Opamp is replaced?

• Most modern High-end Opamps like the OPA604 have a working voltage of + and - 15 Volt instead of + and - 12 Volt. The power-supply for the Opamp should be increased from 12 to 15 Volt by changing the Zener-diodes D1 and D2 with 16 Volt zeners. Otherwise there will be clipping at higher input-voltages and the undistorted power will be limited to about 70 Watt per channel.






• Modern Opamps eat more power. This may cause unwanted switch-off behavior ("Plops" in the speaker) when switching off the amp. See the other posts on my blog for solving this matter.
• In order to stabilize a "modern" Opamp one should add 2x 100 nF capacitors between pin 7/4 of the Opamp and the input-stage mass to avoid the input-stage oscillating and C3 has to be removed.
• For the local feedback I have the best experience with Bernd Ludwig's proposition (see the links on the left): replace R6 with 100K and C4 with 150 nF.
• For the general feedback I use 10 K for R4 and 47 mF bipolar for C2.
• This will get you an input-sensitivity of +/- 1 Volt, which is ideal for modern pre-amps and sufficient for the Quad 33 as well.

Can you revise / upgrade my 405 for me?

• Yes I can.No matter how old or how broken your 405 is, it can always be repaired and made sound better than a new 405-2. Just send an e-mail.

Quad 405 DIY illustrated guidelines - Step 1 to 3

This is the original 405-revision article published on this blog in 2006. We republish it on general demand.

Stefaan

I thought it was time to make an online step-by-step guide for upgrading a 405.

If you are in the US and you are looking for a DIY upgrade-kit, check out www.quad405.com. The guidelines remain the same but you won't have to pay more for low Dollar-rates and high shipment-costs ;-)

As I recently bought a very nice (but very old) 405-2 (thank you Leigh, I hope you had a good time in Antwerp) I will use this one as a photo-model. I will take pictures of everything I do and explain why I do it. All comments and tips are welcome of course.

The revision/upgrade will be a basic one without fancy or expensive things like the BB627, but I'll mention those options in the PS.

Click on the pictures to enlarge.

So here we go...

Step 1 - Getting the components together

This may be the hardest part... Aspecially if you are looking for audio-grade components at an affordable price. The components I will use in this revision are:



BHC Aerovox 10.000 MF 63 Volt for the power-supply. These are quite expensive (+/- 16 Euro each) but in the power-rails we need the best quality. A less expensive alternative may be BC-components or Philips.


• 100MF and 47MF 63V Audiograde capacitors for C5 & C10. In the 405-2 we will need 3 47MF per circuit-board.
• Bipolar capacitors of 10MF (for the clamp-circuit) and 47MF (for the DC-feedback) x2
• Metalfilm 1% 0,5W low-noise resistors for R2 and R6, and probably for R1, R3 and R4 as well (we'll come back to that).
• Burr Brown OPA604AP-chips for the input-channel. We'll need 100NF caps to stabilise the power-supply of the chips and 16V zener-diodes to make the chip feel happy.
• We'll also need some supplies like new fuses, IC-sockets, thermal compound, cables to replace the old cable-beam, LS & RCA connectors, PCB-connectors adl...
• Last but not least: the schematic that corresponds with the exact serial-number. That won't be a broblem: send me an e-mail.

What equipment will we need?




• The minimum is of course screwdrivers, pliers, soldering-equipment and a multimeter
• Better would be a 2x50V lab power supply, a LF tone-generator and a 2 channel scope (but it is possible to do without them)
• Ideal would be a low-distortion sinus-generator and a distortion-meter as well. I don't have those myself (yet) so don't worry;-)

Step 2 - Taking the 405 apart

The first step is to remove the top- bottom- and sidepanels. Sometimes, after 30 years, the screws are hard to remove. The best screwdriver to use is a Philips n°2 with a length of at least 20 cm.

We now understand why Quad made 4 hole's on the left- and the rightside of the backpanel: they were intended to facilitate manipulation of the screws of the circuit-boards.

I don't need to mention it's usefull to keep the screws apart. They can be replaced (they are M4 - which is a standard-size) but of course there is not much use in replacing the screws.

The best way to proceed is to remove the top-panel, then the bottom-panel and then the 2 side-panels.

The first impression of a newly opened 405 is usually a dusty one. This doesn't matter (in this stage ;-).

On the 405 on my table the voltage-selector is at 240 Volt. Switch it to 230 Volt. The connectors will have to be replaced (except the DIN-connector).

The LS-connectors were not only lousy in the first place, they are oxydated and will give a bad contact. The RCA-connectors are clearly worn. It's surprising there are any RCA-connectors, this is not standard. This amp has been modified.

The PCB-connectors have to be replaced anyway, they are oxydated and we will use new cabling.

I didn't spend time desoldering the cables, I cut them off. They will have to be replaced anyway.

The cable-beam of the 230V-side of the transformer should stay in place, there is no improvement in replacing it as there is only +/1 Amp max going through it. On the other side of the transformer we'll deal with up to 10 Amp.

Something is very strange with this amplifier. The Serial number is 42472 and the amplifier boards are M12565:6. The earlier version of the M12565:5 was used from serial number 59001 on. It says "Quad 405-2" on the front panel (launched in 1983 and) it says "1977" on the transformer. One can always find the year of production stamped on the transformer.

This is a recomposed 405! It has 405-2 circuit boards in a 405-1 case. It also has 2 clamp-circuits (one on the 405-2 board and one on the LS-outputs like in the 405-1).

That's no problem, we'll throw away the 405-1 clamp-circuit and make this a great-sounding 405-2.

Step 3 - Fitting in the Power Supply capacitors and the connectors

We'll do this step first and we'll fit in the capacitors with transparent Silicone, so it can dry for 24 hours before we continue tomorrow.

As modern capacitors are a lot smaller (and better ;-) than the ones used 30 years ago we can either buy new fixing-rings to fit them in or use Silicone to fix them in the original rings. Another alternative is to wind some self-adhesive tape around the caps. This will work if the caps are not nuch smaller than the rings.
We'll mount the LS-outputs and the RCA-inputs before we fit in the capacitors. This makes working on the back-panel easier.

The mass LS-outputs do not have to be isolated from the chassis but the "hot" LS-outputs have to be isolated. The new RCA-inputs have to be isolated as well as in the 405 there is a difference between the input-mass and the output-mass.

The best order to mount everything is:



1. The mass (black) LS-connectors with a (green) wire to the central mass-point on the frontpanel (this wire will be connected to the central mass-point later). We already put this wire in because it is easier to solder it when the capacitors are not in place. The mass LS-connectors don't need to be isolated from the chassis.
   
2. The hot LS-connectors. Those need to be isolated from the chassis.
   
3. The RCA-inputs. They are soldered to the L/R connectors of the 4-pin DIN-plug with normal wire.
4. The capacitors. The wiring of the power-supply will be done later, after the Silicone has dried. Make sure to fit the first capacitor with the + on the left and the second one with the - on the left. The left-side will be our central 0Volt mass of the power supply.











posted by Stefaan @ 2:00 PM  3 comments links to this post

Quad 405 DIY illustrated guidelines - Step 4 to 6

Step 4 - Upgrading the circuit-boards.

The number of this circuit-board is M12565-6 (this is about the first 405-2 circuit-board). This means that the clamp-circuit is integrated on the board and that some improvements have been made about the current-limiting and the input circuit.

The first thing we'll do is connect it to a lab + & - 50 Volt power-supply to see what amount of power it eats. The - power-line should eat about 110 mA and the + power-line about 120 mA.

It passes the test well. This means the transistors are OK. (Zero Killed can be taken literally in this case). Both boards are OK.

The 0 Volt power-line has to be connected to the transistor-chassis. There is a 10R resistor between the input-circuit mass and the power-circuit mass. It will smoke if you are confused between masses.

OK, we'll remove all components that have to be replaced. We won't touch the other board for the time being. This way we can always compare.

We'll replace R3 with 1% metal-film low noise 22K.

We'll replace D1 & D2 with 15V 1,3W.

We'll replace the electrolyts C4/C5/C18/C19 with new audio-grade caps.

We'll replace C2 and C10 with bipolar caps.

Of course we'll replace the opamp with BB604AP and the PCB connectors. The PCB-connectors have to be replaced because we have to redo the cabling. After more than 20 years they usually are oxydated anyway. We'll use 1,3mm silver-coated PCB-connectors here.

Soldering them to the PC Board is quite difficult as they tend to fall out and as they should be fixed very well in a horizontal way. I us a small carton box of 1 cm height to position them one by one.

We'll add 100 nF caps in the powerline of the chips on the backside of the PCB.

We'll also reduce the sensitivity of the input to 1,5V (from 0,5V). This will also reduce noise & distortion with another 10 dB.

We'll do this by increasing local feedback and DC feedback. We replace C4 with 150 nF MKT, R4 with 6K8 and R6 with 100K 1% metalfilm.

On this subject you should take a look at Bernd Ludwig's text and schematic (see the Quad-links in the left column).

Before adapting the second circuit-board we have to test the upgraded board to make sure it's OK. This way, if there is a problem, we can compare the voltages on both boards to locate the error.

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
- 30 .. 32 Volt AC on the outputs before clipping. This corresponds with 110 .. 125 Watt into 8 Ohm.
- 1,7 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 O VDC on the output and that the power-consumption in the power-lines is 120 .. 130 mA. In this case we'll do Step 6 first.

Step 6 - Cabling

We start by cabling the power-supply. For internal cabling counts: the shorter the better. We'll use high-quality flexible 1,25 mm in 5 colors for everything except the 230 Volt lines.

We'll use following colors:

• Yellow for AC power-lines (between the transformer and the bridge)
• Red for the +50 Volt line
• Black for the -50 Volt line
• Green for the output-mass
• Blue for the LS-output lines

We do all the cabling of the Power Supply lines and test the voltages first. They should be around + and - 51 .. 54 Volt DC. Before connecting the power re-check the polarity of the caps and the rectifier-bridge.

Don't forget to connect the mass-lines of the capacitors (one + to one - side of each cap) and the ground-line of the transformer to the central mass-point on the chassis.

It is better to twist all cables that have to be soldered to the same point together before tinning them, it makes soldering them a lot easier. Foresee cables to the boards as well.

Warning If the polarity of the caps is wrong they will explode!

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.

Before connecting mains-voltage we should check all cabling again with the Ohm-meter. We should alse 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 ;-)

Quad 405 basic DIY upgrade kit


Price $115.00 Includes all the capacitors resistors, opamps and diodes to upgrade the Quad 405. Installation manual included USPS $6.50 International $22.00

Quad 405 Basic kit with installation


Price $259.00 The basic Quad 405 kit and installed by us. USPS $28.00 International $38.00

 

Quad 405 Deluxe kit with installation


Price $309.00 Includes upgraded output transistors and opa627 opamps installed by us. USPS $28.00 International $38.00

Quad 405 Ultimate kit with installation


Price $449.00 All of the basic 405 kit included with upgraded output transistors, opamps and dual mono power supply installed by us. USPS $28.00 International $38.00

Dada announces the 405 High-End boards.





After a period of testing, improving, listening and testing again we can proudly announce the 405 High-End boards today.






Price $550.00 DaDa Electronics own new design of complete 405 boards. This sets a new standard for audio excellence. Two boards completely assembled and bench optimized. OPA627option USPS $11.50 International $28.00

Price $475.00 DaDa Electronics own new design of complete 405 boards. This sets a new standard for audio excellence. Two boards completely assembled and bench optimized. OPA604option . USPS $11.50 International $28.00

Quad Dual Mono 405 Power Supply


Price $205.00 Dada exclusive design. High quality capacitor and extremely fast rectifiers. This will give you more bass definition and can be wired to achieve 30db greater stereo separation USPS $11.50 International $22.00

They were designed by Dada Electronics and JP Engineering and we are convinced we will set new standards in High-End audio.




We applied the same philosophy as last year when we launched the 303 High-End boards. Except for some practical or obvious improvements we started with the latest original Quad 405-MK-2 schematic (M12333.10), but with today's very best Audio-grade components only.




We used:




• Burr Brown OPA627 opamps, the highest standard in precision operational amplifiers (an alternative board with OPA604 is available).
• Silvered Mica capacitors for HF-handling
• Wima MKS4 for decoupling
• Nichicon Low ESR electrolyts
• 1% Metalfilm low-noise resistors
• Epcos inductors
• MJ15003 Power-transistors and BD242C drivers

In this version we left out the current-limiters, you won't need them if you use the Dada LS Protection/Delay and they would have a negative impact on the dynamics of the sound.

You can now easliy upgrade every Quad 405 yourself by replacing the 2 amplifier boards, the power-supply and the LS protection circuit. As the concept is modular you can use one of the 3 options separately as well.

The new High-End boards are available in our Ebay-shop in a Burr Brown OPA604 and a Burr Brown OPA627 version.

Stefaan & Joost




Willem Tetteroo from NL was our first customer. Here is what he tells about the board (original NL text + my translation):

"Beste Stefaan en Joost,

Ik ben laaiend enthousiast! Super!

Na een heel weekend intensief geluisterd te hebben kan ik niets anders zeggen!

Sprankelend geluid tot in detail. Mooi strak en diep!

In vergelijking met het origineel vind ik dit een enorme verbetering, en ik was al gek van het origineel. Heb veelvuldig vergeleken en vind de Dada echt de fraaiste!"

"Dear Stefaan & Joost,

I am extremely enthousiastic! Super!

After a whole weekend of intensive listening I can't say anything else!

Sprankling sound upto every detail. Nicely neat and deep!

In comparison to the original I find this an enourmous improvement and I was already crazy about the original (450-2). I compared many times and I find Dada really the nicest one."

posted by Stefaan @ 4:43 PM



Stefaan