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A&R Cambridge A60 - rebuild thread

I have recapped my ancient (S/N 00105) A60, replacing the smoothing caps with the Vishays recommended by Robert. The originals on mine were 6800uF rather than 10000uF, so those are what I used. Is it still going to be beneficial to add the bypass caps? If so, should I alter the value as the main caps are smaller?
 
I am a soldering numpty, and have experienced, in the last 48hrs, having waited nearly 2 years to get round to it, an astounding difference with 2 10,000uF Kendeils, the best £15 I have ever spent, thanks Witch Hat!
 
lsinclair said:
I have recapped my ancient (S/N 00105) A60, replacing the smoothing caps with the Vishays recommended by Robert. The originals on mine were 6800uF rather than 10000uF, so those are what I used. Is it still going to be beneficial to add the bypass caps? If so, should I alter the value as the main caps are smaller?
Click to expand...

Bypass caps are not an exact science; the parts you have should be fine.
 
PigletsDad said:
Bypass caps are not an exact science; the parts you have should be fine.
Click to expand...

Thanks PD. I used the 330uFs as bypass caps for the 6800uFs and was very happy with the result. So was a friend, who asked me to refurb his as well. Which has resulted in two more questions...

The bias trim pots on his amp are very coarse - the slightest touch will send the voltage drop across the emitter resistor from 6 to 12mV. Is this just a dirty old pot or possibly symptomatic of something else?

Also the DC offset at the output is a little higher than recommended on one channel (32mV). Is there much I can do about that?
 
kirstysdad said:
I am a soldering numpty, and have experienced, in the last 48hrs, having waited nearly 2 years to get round to it, an astounding difference with 2 10,000uF Kendeils, the best £15 I have ever spent, thanks Witch Hat!
Click to expand...

You did just the smoothing caps, and not the bypass caps - just checking?
Where did you source the Kendeils? [UPDATE: just found Witch Hat on ebay - doh]
Thanks
 
Excellent piece, Rob.

Further to your suggestion re removing the phono stage op amps, you can go on to turn the unused input into a line level input by soldering in some bypass links, and also use padding resistors to get a sensible volume position for CD input.
 
kirstysdad said:
I am a soldering numpty, and have experienced, in the last 48hrs, having waited nearly 2 years to get round to it, an astounding difference with 2 10,000uF Kendeils, the best £15 I have ever spent, thanks Witch Hat!
Click to expand...

Ok. Just done that swap as well. Sounds great.
What shall we do next?
Any others worth doing - mine is one of the newer ones so not sure I need to do much more do i?
Ta
 
Depends how far you want to go, & how much you want to spend; I replaced all electrolytics 22uF & below with films. Sounds lovely, but I'd never recover the cost were I to sell :)
 
I need to take the board out to check a loose connection on the input sockets - lose left channel if the RCA cable is nudged.
While I have this off I intend to replace the four 22uF (C32, C33, C132, C133) as most people recommend. Going for Panasonic EEUFC1J220 from RS Components.

Thought I would do the four 10uf 35v (C28, C29, C128, C129) as well but everyone recommends the Elna Starget but they are not easily available now. What should I go for instead? What is the equivalent Panasonic? I get too confused on the options even for a simple capacitor!!

As my A60 is one of the later ones (#26412) I think I will leave it there...unless someone tells me otherwise.

Cheers
Paul
 
I used Panasonic NHGs for all the 10uF capacitors (except C9/109, where I used Wima film.) I'd also be inclined to change the emitter resistors while you have the board out.
 
Yes, R64 and its three little chums. I used the wirewounds (or their equivalent) suggested by Robert in his A60 thread in the reference section.
 
You might find that the diameter of the resistor leads wire is a little large for the hole from the older R64 & R164 ( and pals ) and you need to use a fine drill to carefully make larger hole without destroying the solder pad on the underside....

However the upside is that with some careful bending of the leads you can make a nice open ended loop that a multi-meter can clip to during the adjustment of the bias...

The old bias pots are rather crude, so I also recommend changing these out to nicer Bourne multi-turns.

Have fun
Julian
 
lsinclair said:
I used Panasonic NHGs for all the 10uF capacitors (except C9/109, where I used Wima film.) I'd also be inclined to change the emitter resistors while you have the board out.
Click to expand...


I Used wima Films to replace all 10uf electrolytics :)
 
Oh my. You guys are killin' me - I started with a simple project and now it looks like I am going to re-build my amp from the circuit board up!!

Another quick question if I may. There seems to be two different types of 10uF 50V caps on my board? One set is orange, the other is blue. What's the difference? Can I replace them all with my Panasonic 10uFs?

Now, off to get those Bourne multi-turns :)

While I am soldering, should I bypass all the tone controls? I don't use them.
If so, how?
 
The orange ones were a different voltage and uF range to the blue ones. Most of the 'thin blue ones are 10uF - 35 volt.
The oranges are thin 4.7uF 10 volt or fatter 47uF 10volt.

Replace them all with the same value uF Panasonics or if you want to to go "posh" then use WIMA films.

I tried bypassing the tone controls on one and it really made no audible difference. ( bit like the extensive use of WIMA's ) but if so inclined try it if you like it....

Julian
 
Ok, the board is out and I can actually see what I am doing, and I've had a shocker! My board is so "new" that most of the caps are 50v and *not* 35v like the older boards.

Need to review things!

Anyone need any lovely, unused Panasonic NHG 35v caps?

:)
 
The schematic shows the rail at 34V so you may think 35V rated caps are a little tight... however the one in front of me now (15904) has 35V ones as original, and they have survived OK.
 
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