New project

[RR1957]

On the LS3/5a front: I’m not going to go into the ethics of buying clones, but there is a very accurate reproduction of the 11 ohm original (a good match for the 303) which received a glowing review from Steve Guttenberg:

https://m.youtube.com/watch?v=9IOB9LaDKIY

Remember to budget for good stands, though.

Thx, yes, the (vintage like) stands will be a challenge too.

[CJG in Wolfsburg]

Re. Dada, it appears that they have recently ceased trading. The best course of action is probably to send the amplifiers back to Quad for a full service. AFAIK this is still possible.

[CJG in Wolfsburg]

At least your 303 isn’t the version with the “upside down” reservoir caps which spill their corrosive guts all over the circuit board when they fail…:smiley:

[RR1957]

For a set of compact speakers I have a budget less than 1000 euro.
That doesn't say anything, because a lot of -good- vintage speakers
can be found on a Dutch marketplace (Marktplaats) for example and
for nice prices.
I just have to choose between brand, size and design.
And a satisfactory sound of course.

I have a lot mono records and I found out the Quad 33 has a nice
functional choice in mono left or right or both speakers mono.

The overhaul of the FM3 is not really needed, because I will not use it.
Radio will be listen by blue tooth.

[Hallvard]

As mentioned by others the 303 does not like low impedance loads. Figures are roughly 25w at 4ohm, 45w at 8ohm and 28w at 16ohm. In other words the ideal speaker has a nominal impedance of 16ohms.
Hook a 4-6ohm nominal speaker onto a 303 and you have the recipe for a complete rubbish performance.

This particular trait of the 303 is because of the current limiting circuit, which makes the 303 foolproof in the sense that you can short circuit the outputs without killing it (not saying anyone should do that...)

If yours is functional, it is not particularly complicated to service it. IMO replacing all trim pots is essential (they will fail), replace all electrolytics (they are usually not of a particularly reliable type). Finally, there are a couple of resistors that usually die because of too much current (this is often clearly visible on the outside). You can see there is an area on the PSU print with browning.

I did this exact service on my 303, and it has been switched on 24/7 for the last 20 years with no problems. Well, except for not the lowest noise floor. Ideally I should replace the outputs, but when doing that it is very important to use hard-to-find, old and slow transistors. If they are too fast, the 303 will oscillate.

Congratulations, and good luck! 

[RR1957]

An acquaintance of mine as I mentioned earlier will restore my set.
He knows Stefaan and Joost of Dada and did his own set as was advised by them.
I did get the report he has of Dada Electronics (2018) about the 33.

[RR1957]

As mentioned by others the 303 does not like low impedance loads. Figures are roughly 25w at 4ohm, 45w at 8ohm and 28w at 16ohm. In other words the ideal speaker has a nominal impedance of 16ohms.
Hook a 4-6ohm nominal speaker onto a 303 and you have the recipe for a complete rubbish performance.


Congratulations, and good luck!  

Thank you!

I am not sure if this is correct. People I know and informed me about my catch will not confirm this.
"I have never heard of that. They are known for their stability across all impedances"
is one of the replies.
I myself are an absolute amature in this and have to learn in the next months.

[Hallvard]

Thank you!

I am not sure if this is correct. People I know and informed me about my catch will not confirm this.
"I have never heard of that. They are known for their stability across all impedances"
is one of the replies.
I myself are an absolute amature in this and have to learn in the next months.

Ok, let's split this in two.
1. Anyone who says that is not correct, unfortunately has not bothered to look in the user manual. The power curves are there.
Now we should not confuse stability with good sound reproduction. As I said the current limiting means you can safely shortcut the outputs. In other words, the amp is technically stable from 0ohms to infinity. I would say this is only of interest to engineers, or those who are so unlucky to short their amps outputs.

2. Some of the 303-modifiers change the values of the current-limiting circuit.  That will completely change the behavior of the amp in response to lower impedance. And it will no longer be short-circuit-proof. This will also put more stress on the power supply, necessitating compensatory actions to not kill it.  I do not know if the Dada mods include this? Or was that perhaps the ones called NET audio?

The ideal speaker for the 303 is the 57, but as you said it does not fit. There should however be plenty of other speakers from that era with higher impedance.

[RR1957]

Ok, let's split this in two.
1. Anyone who says that is not correct, unfortunately has not bothered to look in the user manual. The power curves are there.
Now we should not confuse stability with good sound reproduction. As I said the current limiting means you can safely shortcut the outputs. In other words, the amp is technically stable from 0ohms to infinity. I would say this is only of interest to engineers, or those who are so unlucky to short their amps outputs.

2. Some of the 303-modifiers change the values of the current-limiting circuit.  That will completely change the behavior of the amp in response to lower impedance. And it will no longer be short-circuit-proof. This will also put more stress on the power supply, necessitating compensatory actions to not kill it.  I do not know if the Dada mods include this? Or was that perhaps the ones called NET audio?

The ideal speaker for the 303 is the 57, but as you said it does not fit. There should however be plenty of other speakers from that era with higher impedance.

Thx

[JacquesD]

[…]

The ideal speaker for the 303 is the 57, but as you said it does not fit. There should however be plenty of other speakers from that era with higher impedance.

Well, the 303 doesn’t necessarily sound badly with low impedances. The impedance of the ESL57 goes down to about 2 Ohm in the 10-15 KHz area and yet the amplifier still sounds very good with music where these frequencies are important, like with historical pianoforte and harpsichord instruments. Obviously there isn’t lots of Watts to be delivered, either, in a domestic environment.

I have listened to a 303 modified along the Dada guidelines, with  complementary MJ15003/15004 pairs for the output stage. It had lost some of it’s quality, high tones became more aggressive/harsh etc. This was an A/B comparison with a serviced 303 with fresh electrolytics, trimmers, some resistors and new internal cabling. There appeared no need to “enhance” the original circuit. Only my personal experience, in my listening environment.

[RR1957]

https://hometheaterreview.com/quad-33-preamp-and-303-amp-reviewed/

[Hallvard]

Yes, Jacques I should have been more nuanced.
My experience was a brutal loss in bass response, even at lower listening levels. This is of course very dependent on the impedance profile of the loudspeaker, but if you have a 4ohm nominal speaker it may happen that it drops down to 2ohms minimum. At such a low impedance the 303 will quite quickly reach its maximum current allowed.

The ESL57 is a strange speaker, impedance-wise, in comparison to "normal" speakers. I have never seen any official reference from quad on whether the 303 was intentionally optimized for the ESL57, but in combination with the 303 things do become interesting...

[Colin_EJJ]

Regarding servicing, the Netherlands seems to be particularly keen on Quad gear. One company I came across does full upgrades, including replacement PCBs for both the 33 and 303.

But this one is more traditional, judging by their newsletter.

https://vintageaudiorepair.nl

Vintage Audio Repair · Steegoversloot 54 · Dordrecht, Zuid-Holland 3311 PP · Netherlands

[RR1957]

Regarding servicing, the Netherlands seems to be particularly keen on Quad gear. One company I came across does full upgrades, including replacement PCBs for both the 33 and 303.

But this one is more traditional, judging by their newsletter.

https://vintageaudiorepair.nl

Vintage Audio Repair · Steegoversloot 54 · Dordrecht, Zuid-Holland 3311 PP · Netherlands

Indeed I had contact with this company. They were my first choice.
But the person (who I know for 20 years) who will do the service
for me is also very qualified. The work on his own set is wonderfull.
This week I bought three new prints for the 303.
In fact, Quad did not use extraoribairy parts. It is the design of the
tech that makes it great amps. In the whole production they hardly
did not change anything. Maybe this is very Brittish....

[RR1957]

New prints for the 303. The start.





More and more I do become fond of the Rogers LS2. Sad today is
- as it was in the seventies and eighties in audio shops-
you cannot listen to them to compare and which will fit your ears.