Upgrading Quad 405 Series 1

[Canetoad]

I've just sourced a Quad 405 Series 1 and Quad 33. Both came with original packaging, manuals and receipts for a full Quad service in 1991. I was mostly after a Quad 405 to use with my Croft Micro 25R. The problem I have is I don't know where to go with upgrades/modifying it. I know Net Audio and DaDa do upgrades etc but I have a few questions.

Do I give it a service and just use it in stock form? (speakers are an 8 Ohm load)
Do I modify it to 405-2 specs?
Do I go with something like this (http://www.ebay.co.uk/itm/200407529887?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649#ht_469wt_1122)?

I'm after the best bang for my buck rather than just spending a heap of cash replacing everything with new boards and components.

Any advice would be greatly appreciated. :)

[tubehunter]

Hi Berni

I've just serviced two of these to great success http://theartofsound.net/forum/showthread.php?27749-FS-Quad
The Fischer & Tausche 22,000uf 63v can be bought from Rapid at a very reasonable price, they are the bolt in variety but you can just remove the threaded stud.
http://www.rapidonline.com/Electronic-Components/22000-F-10-30-63V-Screw-terminal-Mounting-Bolt-Aluminium-Electrolytic-Capacito-50-4012

Further to the power supply caps I've upgraded the op-amp's to OPA604AP really opens up the sound. Check the zener diodes are 15volt on some early revisions they have 12volt ones which will need changing and by-pass them with 100n caps. The positive diode will also need a 220uf cap to stop noise on switch off.
The other electrolytic caps on the board I replaced with Elna Cerafines.

These amps are seriously under rated and I've built most types.

Duncan

[Barry]

+1 Berni.

The supply to the op-amp was increased to +/- 15V on board no M12368 Iss. 9 and 10. I have never experience any switch off noise with any of the three 405s I own, but agree with you on the use of bypass capacitors.

Would recommend replacing R7 and R8 (3K3, 0.5W) with 1W rated resistors. They dissipate 0.4W, so run close to limit. I had one fail, sending the amp into a paroxysm of oscillation.

Essentially, the simplest upgrade to make on an early version 405-1, is to replace the lousy LM301 op-amp.