Quad 303 mods

[Pcspike]

I have a Quad 303 which I intend recapping. In recent months I have noticed too that it has developed a crackle on one channel, whether this is related to a deterioration in one of the caps or some other fault remains to be seen. With this in mind I am wondering if I should also be looking at replacing other components due mainly to its age.
Looking online I see that Dada provides replacement parts as well as replacement boards which seems like a tempting quick solution. From what I read, Dada is saying that their boards are superior to the originals due presumably to the advancement in component technology, but I'm thinking, if this is the way to go? With Quad being a quality amplifier built to a specific standard, should this standard be modified to something better (or different) and in doing so will it become a Dada 303 rather than a Quad? I do appreciate the fact that components standards have improved over time and perhaps would not have been available when the 303 was designed, but the question remains, should I replace and renew to the original standard or not? Your views would be appreciated as always.

[fetteler]

How long is a piece of string?

Realistically only you can say how important the issues you mention are - I personally I would repair the existing boards, go carefully as the copper tracks are prone to lifting. There's a recent thread on here where a 303 crackle was down to an aging transistor, see what results the recap brings and take it one step at a time.

Have fun!

Steve.

[Whaam68]

From memory their high end boards are based on the later versions of the Quad circuits but use better "premium" parts (it's been a while since I looked on their site so I may be wrong). If your amp works and the boards are in reasonable condition I'd be tempted to just buy their standard "refresh" kit and also replace the power supply and output caps. You could source the parts yourself but its nice to get everything in a single pack and saves postage buying from multiple vendors. I don't think there is much wrong with the sound of a 303 that necessarily needs improving but in my experience replacing some of the tired components has given my quad kit a new lease of life.
Mike

[Radio Wrangler]

Crackles suggest iffy resistors, transistors or connections more than capacitors.

The electrolytic capacitors have finite lives as they lose water content from their electrolytes. S a fresh set will re-start the ageing clock. High temperature parts of a good make are better sealed and so more reliable. 'Audiophile" grade just means premium pricing and premium marketing. But from a reputable mainstream distributor to reduce the risk of fakes.

Quad's PCBs were compressed resin-soaked paper. Not the most robust in the world. They saved money compared to glass fibre boards. Won't make an audible difference, but you may feel happier or you may feel it's not important. If you need to do any subsequent repairs, tracks are less likely to fall off n glass fibre boards. If you're doing major surgery, it's a better time to go for better boards if you feel inclined.

Resistors. Quad used reasonable resistors for the period. They didn't spring the extra cash for higher reliability lower noise ones which did exist back in the day. Resistors are cheap, even excellent ones. Lower noise is discernible. If you're doing much then a set of metal film resistors is worthwhile. Available in the same values, better tolerance and lower noise. No real downside.

Transistors. Some of the plastic encapsulated ones of the period are known to go noisy/crackly. There aren't many and replacements are cheap.

The dada boards are decent and known quantities, and don't go into silly territory.

That all leaves you with plenty of choice. One added bonus to the dada boards is if you come to sell it... also, keep the original boards, some people are funny about such things.

Is it a Quad preamp, or is it a Dada preamp? No, it's YOUR preamp!

David

[mikes08]

It really depends on how far you want to go? I have both options - Dada kit upgrade in two of my 303's and the high end boards in another only because a set came up in ebay for half the original price with a fault on one of the driver boards I have now since corrected and working fine. There is a difference but only slight over the standard Dada upgrade. If you are happy to invest then go that route but otherwise the upgrade kit is fine(and cheaper) and does make a difference over an aged 303.
The work is simple enough and provided you use a reasonable iron/soldering station and decent solder not a problem. I used the method to go in hot for a shorter period of time and a de-solder pump to remove parts.
Your crackle i suspect could be a transistor as i had similar and cured it by changing out one of them but i need to think which one it was (see one of my threads as mentioned above). It would start crackling after it had warmed up.
Crackle in one channel would suggest an issue on one of the driver boards rather than the regulator board.
Have you read all the downloads from Dada site - service manual and upgrade kit.
What pre am are you using as again Dada do and upgrade for the 33 which is worth doing at some point if you have one.

[nutteronthebus]

I have rebuilt many Quad 303 in the past few years and 1 had MK9 boards so damaged I had to replace it with a MK10 bare board from ebay ( kit with all caps and resistors but no transistors ) it works well and I used new transistors from RS including MJ15003 for the output pair

[Pcspike]

Originally Posted by fetteler

How long is a piece of string?

Realistically only you can say how important the issues you mention are - I personally I would repair the existing boards, go carefully as the copper tracks are prone to lifting. There's a recent thread on here where a 303 crackle was down to an aging transistor, see what results the recap brings and take it one step at a time.

Have fun!

Steve.

Thanks Steve

[Pcspike]

Originally Posted by Whaam68

From memory their high end boards are based on the later versions of the Quad circuits but use better "premium" parts (it's been a while since I looked on their site so I may be wrong). If your amp works and the boards are in reasonable condition I'd be tempted to just buy their standard "refresh" kit and also replace the power supply and output caps. You could source the parts yourself but its nice to get everything in a single pack and saves postage buying from multiple vendors. I don't think there is much wrong with the sound of a 303 that necessarily needs improving but in my experience replacing some of the tired components has given my quad kit a new lease of life.
Mike

Thanks for the info Mike

[Pcspike]

Originally Posted by mikes08

It really depends on how far you want to go? I have both options - Dada kit upgrade in two of my 303's and the high end boards in another only because a set came up in ebay for half the original price with a fault on one of the driver boards I have now since corrected and working fine. There is a difference but only slight over the standard Dada upgrade. If you are happy to invest then go that route but otherwise the upgrade kit is fine(and cheaper) and does make a difference over an aged 303.
The work is simple enough and provided you use a reasonable iron/soldering station and decent solder not a problem. I used the method to go in hot for a shorter period of time and a de-solder pump to remove parts.
Your crackle i suspect could be a transistor as i had similar and cured it by changing out one of them but i need to think which one it was (see one of my threads as mentioned above). It would start crackling after it had warmed up.
Crackle in one channel would suggest an issue on one of the driver boards rather than the regulator board.
Have you read all the downloads from Dada site - service manual and upgrade kit.
What pre am are you using as again Dada do and upgrade for the 33 which is worth doing at some point if you have one.

Hi and thanks for the info. My preamp is the Quad 34, grey.

After reading all the helpful replies posted here, I've weighed up all my options based on the advice and decided to take the plunge. I've ordered the Dada high-end boards and capacitor kit as I intend hanging onto this Quad setup.
I've downloaded the Quad service manual and the update kit info from Dada, but couldn't see anything specifically for the High-end board's option, do instructions come with the kit? Was looking on youtube yesterday https://www.youtube.com/watch?v=Yh2ub9XDs5M&t=51s he seems confused about the yellow wires that come with the kit and looking at the instructions (that he has) it didn't seem that clear to me either. I would be grateful if you could enlighten me on this given that you have gone through the installation.

Many thanks, Dave

[Pcspike]

Originally Posted by Radio Wrangler

Crackles suggest iffy resistors, transistors or connections more than capacitors.

The electrolytic capacitors have finite lives as they lose water content from their electrolytes. S a fresh set will re-start the ageing clock. High temperature parts of a good make are better sealed and so more reliable. 'Audiophile" grade just means premium pricing and premium marketing. But from a reputable mainstream distributor to reduce the risk of fakes.

Quad's PCBs were compressed resin-soaked paper. Not the most robust in the world. They saved money compared to glass fibre boards. Won't make an audible difference, but you may feel happier or you may feel it's not important. If you need to do any subsequent repairs, tracks are less likely to fall off n glass fibre boards. If you're doing major surgery, it's a better time to go for better boards if you feel inclined.

Resistors. Quad used reasonable resistors for the period. They didn't spring the extra cash for higher reliability lower noise ones which did exist back in the day. Resistors are cheap, even excellent ones. Lower noise is discernible. If you're doing much then a set of metal film resistors is worthwhile. Available in the same values, better tolerance and lower noise. No real downside.

Transistors. Some of the plastic encapsulated ones of the period are known to go noisy/crackly. There aren't many and replacements are cheap.

The dada boards are decent and known quantities, and don't go into silly territory.

That all leaves you with plenty of choice. One added bonus to the dada boards is if you come to sell it... also, keep the original boards, some people are funny about such things.

Is it a Quad preamp, or is it a Dada preamp? No, it's YOUR preamp!

David

Thanks for explaining all of that David. After weighing up all of the options, I've decided to go for the Dada boards and capacitor kit.

Dave

[Pcspike]

Originally Posted by nutteronthebus

I have rebuilt many Quad 303 in the past few years and 1 had MK9 boards so damaged I had to replace it with a MK10 bare board from ebay ( kit with all caps and resistors but no transistors ) it works well and I used new transistors from RS including MJ15003 for the output pair

Thanks for that info, I did consider that option but as I just do this as a hobby, I chickened out and went for the easier Dada boards option If all goes well I may well do as you have done and try it as a future project. Are the boards that you used still available? I couldn't see them.

Dave

[Whaam68]

The high end boards you have ordered I believe come pre populated so AFAIK you’ll just need to de solder the original boards, pop these in, re solder the existing wires to the pins in the same order and adjust the power supply voltage and quiescent current using the guidance in the basic dada kit manual. The blurb also says there are options to adjust sensitivity using jumpers on the board so I’m sure info about that will come with instructions. Most of the work should be done for you.
Mike

[Pcspike]

Originally Posted by Whaam68

The high end boards you have ordered I believe come pre populated so AFAIK you’ll just need to de solder the original boards, pop these in, re solder the existing wires to the pins in the same order and adjust the power supply voltage and quiescent current using the guidance in the basic dada kit manual. The blurb also says there are options to adjust sensitivity using jumpers on the board so I’m sure info about that will come with instructions. Most of the work should be done for you.
Mike

Thanks Mike. The confusion with the yellow wires supplied with the kit shown on the youtube video link are associated with the capacitors. I get the impression that they are supplied to replace the existing and are of a larger gauge.

[Radio Wrangler]

While fixing amplifiers in general, there is one little aspect that you don't want to miss, where you've picked up enough knowledge of the technologies and circuits, throw the whole damned thing on the floor and declare "I could do better than that!"

A remarkable number of firms began this way.

David

[nutteronthebus]

If you do run into problems I am only in Glossop and may be able to help ( waiting for a heart bypass at the moment ) so it is a timing issue when I am available

Dave

[mikes08]

The yellow wires are indeed used to connect up the capacitors to the rectifier though if you buy the 303 upgrade kit they supply red and blue. If you follow the instructions from the 303 upgrade it is simple enough and you might want to swap out the yellow wires and use as above. They might supply different from the website pictures and may include instructions with it - i bought mine second hand so not sure.
The boards are a straight swap but rather than solder the wires onto the pins you might want to get some connectors to solder onto the amp wires that slip on the pins to make a neat install - they may supply these in the kit also? I had some spares so this is what i did.
I can post some pictures of my installation if it helps and if your get stuck can help.
Once in you need to set quiescent current and again instructions in the 303 upgrade details. Do use a piece of wood to rest the boards on and keep away from the chassis. Just take notes as you remove the old boards or take some pictures.
I used the original mounting rings for the main caps but the capacitors supplied were smaller in diameter. I bought some 2mm high density sponge from e bay and cut a small strip (about 20-25mm wide) and glued it round each capacitor to 'pad' them out.

[Whaam68]

As others have said take good clear pics to refer to before disassembling anything. With the big can caps when replacing those just ensure you match the polarity (marked on the caps "+" by the terminal and "-" a stripe down the side. So the wire that went to + on the old cap goes to + on the replacement cap, etc. If you update the wiring to the caps the same principle applies. As other Mike said it's likely you'll have to update the mounting clips as the new caps will have a smaller diameter. Either pad out the existing clips or buy new clips and re drill new mounting holes. IF your 303 is an early one with the terminal end of the caps facing the PCB some people choose to reorient them as quad did on later serial numbers (although with modern cap construction techniques I'm not entirely sure that's really necessary....but I did it anyway). The extra wiring in the kit is probably to enable people that need to to do that. The colour of the wiring doesn't make any difference at all as long as the gauge (thickness) of the core of the wire is roughly equivalent.
Mike

[mikes08]

I will post some pictures over the weekend to help.

[mikes08]

First picture- more to follow. This shows the wiring for the capacitors. The yellow wires come from the transformer and are a straight swap. As mentioned by Mike ensure your polarities are replicated.

[mikes08]

Shows the foam packing i used...more to follow once i have opened the amp up....