advertisement


Choosing caps for Quad 303 driver boards

John_73

John_73

pfm Member
Hi folks

I said to myself I wouldn't let this happen with this project, and it's happened: the dreaded case of...... capacitor paranoia! (Cue B-horror-movie dramatic music crash!).

The project is an absolutely mint condition Quad 303. I've already replaced the trim pots, and a pair of carbon comp. resistors that had gone high (the drugged up bounders!). The only other items to be replaced are the large psu and output caps topside, and the three electrolytics on each driver board. It took a lot of care not to lift any tracks, so I want the replacements to last long, and perform well.

Basically, I want to use the correct parts for each capacitor position, but am not sure what roles each of the following perform. Not sure which caps ('audio' or 'industrial') would be best suited for each 'role' - have listed the ones I have to hand, but would buy others if need-be:


C101 = 300uF 10V, changed to 470uF as per Quad's later revisions:

I have 25V Panasonic FC, FM and Nichicon FG (KZ type too big for this position alas) types to hand in this value.


C104 = 12uF 50V, changed to 10uF as per Quad's revisions:

Panasonic 50V FC and Nichicon KZs.


C106 = 50uF 50V, changed to 47uF nearest equivalent value:

Panasonic 50V FC and Nichicon KZs.


The topside pair of psu caps are already taken care of: 2200uF BHC/Kemet ALT22A types, and the pair of output caps are 4700uF BHC/Kemet. Used these types many times and always been happy with them - Bypassed the paranoia with these ;)

Mine's a circa 1969 era 303, so uses the earlier circuit:

http://www.meridian-audio.info/public/quad303_m12056_iss3[4166].pdf

I'm sure I'm fretting needlessly and any cap will be an improvement on those original 46 year old ones. But I'd like to do this right. Any advice would be appreciated.

Cheers.

John
 
Thanks for that. I'll just go with the Nichicons then, if only because they appear to be a little more robustly built; The 10uF Panasonic FC is tiny by comparison to the KZ.
Cheers.
 
Any reputable modern electrolytic cap is going to be a great deal better than anything Quad could source in the sixties.
 
Nice work - looks like a pair of Nichicons (KZs?) and a Panny FC. Any reason you used a mixture?

I'm one of those who actually quite enjoys the 'sound' of tantalum caps, in spite all their negative press, after trying different kinds in DIY and recapping projects over the years. I'll be using a 1uF tantalum there to retain the type of cap (and sound) originally used in that position.

What did you use for the chassis mount caps?
 
P.S. Noticed you used a 22uF for C104 instead of the stock 12uF (later 10uF). Wonder what, if any, the audible effects of raising that value has?

Here's where mine stands as of today - still need to replace the chassis mount caps, the input cap and C101:

Photo%2013-06-2015%2019%2048%2041.jpg
 
Most of my choice was due to what I had in 'stock' and what fitted the hole spaces. I like the KZ Nichicons and Panasonic FC / FM ranges and generally keep a range of them.
I think I saw something on Netaudio or Dada about using 22uf in place of the 10uf. It has no effect on sound as its part of the 33.5 volt half rail voltage setting circuit.

As you have the early 'silver' chassis caps are you sure they need replacement? I think there is a belief they are very reliable. If they have not leaked or bulged it might just as well to keep them. It's the Erie / TCC blue and yellow ones that were always popping their insides out. I had to change those in mine.
 
Very nice work indeed stuffing those caps! Looks great. What did you use to neatly cut open the ends? Looks like the new caps fitted inside perfectly. Did you have to glue them in or was it an interference fit?

Yes the chassis-mount caps on my 303 look visibly fine, no signs of leaking, and they're apparently the reliable earlier type. But my unit is a 1969 one, and I'm not comfortable with 46 year old caps in the power supply. As I tend to leave my gear on all day, and am sometimes out of the room I'd be wary with using those caps. My speakers dip to 6-ohms so I've been told the standard 2000uF output caps won't cut the mustard here, and 4700uF types would be a better bet.

I will however try the 303 with them all in place and monitor the voltage readings, and see how it sounds.

John
 
All simple tools. Used a hacksaw to very carefully cut through the base ring. The ally is soft and the ring keeps you neat if you roll the cap round a little at a time. Pull out the gunky bit of foil and electrolyte. Then clean the tar from inside the can. That's the hardest part. Then file / sand the rough edge of the can nice and flat and smooth. Wash the inside of the cans out with soapy water and dry over night.
I found I needed a thin spacer to hold the new cap inside. I actually used an old ice cream tub cut into strips, then trial and error for a perfect tight fit, but still just able to just get the cap out if I needed to or twist it round a little to align the terminals with the old can markings (maybe that is a bit too far...). No glue used. The clamp when tightened holds everything in place.

Sorry resorted to Google for the pictures, Flikr is so **\**.
https://plus.google.com/photos/1087...ms/6160188692004285153?authkey=CJTS3oes2KjhCQ

I just hated to see a venerable 303 with new caps stuck in old clamps with miles of tape or foamy bits.
 
Seconded - really looks good! Thanks for posting the 'how to' pictures as well. That'll come in handy for future vintage projects :)
 
You must log in or register to reply here.


advertisement


Back
Top