What people say about their 405 revision.

Michael (California, USA) upgraded his 405 himself. He wrote: "The amp sounded quite good before the modifications, but it seems
cleaner, clearer, and more detailed now than it was before. And, with all the electrolytics replaced, it should run for years and years. Not bad for $137 on ebay, about $50 worth of parts, and a few hours of
work putting it all together."

Jean-Cluade dit: "

Le Quad est bien arrivé chez moi hier en fin de matinée. Je l’ai mis en route comme vous me l’aviez conseillé, ensuite vint le moment de la vérité ; « le brancher sur la chaine ! ». J’ai cru qu’il ne fonctionnait plus du tout ! Même en collant l’oreille sur les hauts parleurs je n’entendais pas le moindre bruit. Mais lorsque j’ai inséré un disque et appuyé sur Play, quelle merveille ! Je n’avais plus le souvenir d’un tel son, neutre, sain, dépoussiéré, clair et pourtant percutant quand il le faut. Il s’accorde magnifiquement avec les Kef Q5, du piano au violon en passant par la harpe, les cuivres, les percussions et surtout les voix, tout semble couler de source, et cela sans aucune coloration (mes hauts parleurs sont très neutres aussi). Un exemple tout à fait marquant, lorsque j’ai écouté « Roberto Alagna et Réno » ma femme m’a dit ; tient ! Ils n’ont plus la même voix ; pour vous dire la différence. Je suis entièrement satisfait du travail que vous avez effectué ; si je n’étais pas tombé sur votre annonce par hasard j’aurai acheté un nouvel ampli, mais surement pas de la même qualité ¨les prix sont trop élevés¨. Je vous joins une publicité qui était parue au moment où je l’ai acheté, je crois qu’elle en dit plus que je ne le pourrai, pour moi il va même mieux qu’il y a 27 ans. Je vous laisse car je vais encore écouter mon Quad.

Jan said:

Uiteraard heb ik onmiddellijk de 405 aangesloten en uitgeprobeerd. Inderdaad minstens zo goed als het origineel. Na jaren van muzikale miserie herleeft het huis in al zijn tonaliteiten!.

Nogmaals hartelijk dank, een betere investering kan ik me moeilijk voorstellen!!!

Jan

How good are your languages?

Stefaan

Quad Antropology: Who are those Quad fanatics?

After revising more than 50 Quad 405's and some other Quads amps I started to wonder: who are those Quad fanatics?

What's their sex?

All are male. Never, even once, I heard about a female vintage Hifi-lover.

What's their age?

Around 40. This may be logical as one has to have lived the 7-ties to know the real value of a 405 or a 33. There also are some younger guys who herited a Quad from their father.

What's their occupation?

It may seem strange but several Qaud-lovers are medical doctors. We also have train-drivers, informaticians, builders and university-professors.

In general those who listen to a 405 have a technical or a scientific occupation.

Where do they live?

They live in the UK, the Netherlands, Belgium, France and the USA.

Tony from Thailand added:

"I'd like to add an owner type to your list! I have found that a lot of
artistic people own Quad and I myself am employed in the field of
design. I had a friend who was a potter - his Quad was in his studio -
splattered with clay but used everyday as the background to his work. I
have noticed that a lot of left handed people seem to own Quad as well -
not sure what this means as I am also left handed!"

Stefaan

Quad Revision Live: Walters' Quads revision

I rarely saw a series of Quads (33 - FM3 - 405) in such excellent condition as those Walter brought me last week. He bought them around 25 years ago and spent half his life listening to excellent music. I'm almost jealous ;-)

I have to revise and upgrade them although they work fine already. Of course , after 25 years a midlife-upgrade is obvious...

Step 1: Let's start with the FM3 Tuner.

In the original FM3 there were 4 light-bulbs, 1 to give light on the front-panel (12V) and 3 indicator-lamps (2 for tuning and 1 for FM-stereo) (7V, 1 is broke). Those have to be replaced by LED's anyway.

Led's live forever - at least till 2500 - and they don't influence the power-supply rail like old neon-lamps do. I replaced them with yellow Led's and a 390R resistor. I sticked them in with 2-component glue.

For the rest I only changed one very old 220 mF capacitor for a new one.

I won't care about changing the Tantalum capacitors, the FM3 perfoms a lot better than the FM-broadcast quality anyway, so there is no reason to care about high-end components like we'll do in the 405 or in the 33.

Steps 2 ...

Well, sometimes it goes fast ;-)

The 33 and the 405 were upgraded and Walter is listening to them as we speak.

He says the sound-quality has improved a lot but the level of the Record-Player input of the 33 is too low and there is a lack of dynamics.

Fortunately it is very easy to modify the sensitivity of the PU-input of the 33 (changing 4 restintances on the board allows for almost every possible sensitivity of MM-elements). MC-elements might not be applicable because of the low output, although I heard there alternatives for that too now.

He'll buy a new PU-element and then we'll adapt the sensitivity to it's specs.

Stefaan

Quadrevision Live: Peter's 303 Explosion

Peter wrote:

"Helaas is mijn 303 gisteren met veel brom en audio-explosies (de woofers lagen zowat in de kamer) overleden. Het bleek dat één van de voedingselco's was bezweken. Ik heb inmiddels de twee voedingselco's van 2000 mu vervangendoor één van 4700 mu en de doorgebrande zekering vervangen. Bij inschakelen ontstond een lichtflits op een versterkerbordje en toen ben ik maar gestopt...."

Unfortunately my 303 has deceded yesterday with a lot of rumble and audio-explosions (the woofers were almost laying in the middle of the room). Obviously one of the power-supply capacitors was broke. I have replaced both capacitors by one 4700 mF and I replaced the fuse. When switching it on there was a flash of light on one of the amplifier-circuits and so I decided to give it up...

This morning Peter's 303 arrived in Antwerp. A first visual inspection of the 303 does not show a nice picture, but we've seen worse than this, haven't we?

Revision Step 1: Checking the power-supply

The first step is to disconnect the power-supply from the rest of the amp and to measure the voltage. Wow !!! It shows tho be 83 Volt instead of 67 Volt as it should be.

In fact 83 Volt is the unstabilised voltage on the capacitor so it is clear that the stabiliser-circuit no longer does it's job. This has probably blown up the output-circuits as well ;-(

Removing the stabiliser-circuit and connecting it to an external stabilised power-supply soon showed that the faulty component was the small trimmer-potentiometer on the board.

It is always fascinating to find out what components in old vintage Hifi cause the problem... Usually it are the capacitors and things like potentiometers that are aging in a very bad way.

The Printed Circuit-board itself shows some burn-spots - it's had it too hot lately. But for the rest this won't influence the good functioning as far as all the components are OK.

After replacing the trimmer with a new one and calibrating it, we measure 67 Volt. Tomorrow we'll check the amplifier circuits.

Revision Step 2: Checking the amplifier-boards

It's even worse than I tought.

On the PCB-board a complete track has gone up in smoke...

This is not difficult to fix with some wire but this means there has been some very serious overload on the circuit.

The other channel still works as it should, obviously (there is 37,5 Volt on the output-line before the output capacitor).

Checking the transistors shows that, indeed, TR1, TR2, TR105 and TR107 are blown up.

TR1 & TR2 Wont' be a problem, they can be replaced by a (good quality) 2N3055, which is the most common power-transistor ever made. TR107 won't cause any problems neither, this is a simple BC109.

But what about TR105 (the PNP driver)?

In the original design "38495" (NPN) and "38496" (PNP) were used as drivers. Of course they don't exist anymore.

Some surfing on Google learned that they were replaced by BC441 and BC461 resp. Actually BC441 has been replaced by 2N5320.

So I ordered 8 of each. It's not that I like to blow them up but I want some reserve if it works;-)

And BTW if I change them in one channel I'll have to change them in the other channel too, we want exactly the same sound in both channels of a 303, don't we?

Spending my time in a good way, waiting for the transistors to be delivered, I already replaced the output-capacitors with 4700 mF 100V.




Revision Step 3: Solving logistic problems ;-(

The new BC461 that replaces the original 38496 (TR105) has a different casing, of course... So we'll have to order adapted heat-sinks.

This is the usual problem when repairing Vintage amps or vintage cars the like: finding the replacement-parts ....

(Picture Copyright Farnell.com)

Revision Step 4: Mission accomplished ;-)

Apparently the TO-5 Heatsinks don't exist anymore, my suppliers tell me... It's a problem we see more and more when looking for vintage components: "Product-lifecycles" get shorter and shorter.

With some heath-conducting glue I managed to put the new TR105 in with the old heatsink. I checked it with my Fluke thermometer for an hour playing disco @ maximum volume and it did fine (40° C).

I also had to change TR107 and MR105/106.

Then came the final calibration:

- The power-supply-voltage (with RV200) to exactly 67 Volt
- The output DC before the cap (with RV100) to exactly 33,5 Volt
- The rest-current to 33 mA (with RV101), this means 20 mV between pin 4 and 6 of the driver-board

After 2 hours of playing music @ maximum volume those calibrations were repeated.

The 303 sounds very transparent now and no trace of crossover-distortion can be measured on my scope.

Up to the next project...

Stefaan

PS. Joost added:

The transistor equivalents are as follows:
TR105 39496 BC461 2N5322
TR106 39495 BC441 2N5320

PPS. Chris (UK) says that the TO5 hetasinks are still available @ www.cpc.co.uk