Cambridge Audio 640P Capacitor Upgrade

[Hypnotoad]

I recently picked up a used 640P Phono Preamp, I have been using a 540P in my bedroom system for a while and find it has a nice smooth sound. Nothing startling but easy to listen to.

My bedroom system consists of a Technics SL1700 with Grado Gold cart, Jolida 801A valve amp and some Polk Audio SDA 2A speakers.

I opened up the 640P and found it was full of Xunda electrolytic capacitors, after doing a quick search on badcaps.net I found that they are referred to as "Cheap Chinese rubbish", with wandering values and tolerances above what's printed on them. Maybe Cambridge Audio have them made to their own specs I don't know.

My wife and I listened to the 640P in stock form and found we liked the 540P better. It did have more detail and a bigger soundstage than the 540P but sounded harsh in the top end and could get flabby in the bass region.

I decided to change out all the electrolytics to see what and any difference it would make. I wanted to use Elna Simlic II's but found they were ridiculously larger than the stock caps. So I settled on Nichicon for the power supply and Panasonic FC's for the main board.

I switched out all except those in the MC section as I don't own a low output MC cart I will do that later if I get one.

One word of warning is the lead free solder used in this thing is a pain in the @ss. I had to really take my time and be very careful removing the old caps.

Here are before and after pics:

Power supply before. Notice the brown glue in places.



Power supply after:



Main board before:



Main board after:

Notice that the new caps are mostly bigger than the old ones, the Elnas were more than twice the size and the legs would not have fitted anyway.



So how does it sound now, even though I have only listened to it for a few hours it sounds great.

Immediately the harshness in the top end is gone, bass is tighter, no flabbyness. There is much more detail, I can hear every guitar pluck clearly and singers sound like they are standing in front of you. Before everything was slightly smeared now there is air between everything. The soundstage is wider as well and the backgrounds seem blacker.

Total cost was less than $30.00 U.S.

Will it beat an exotic phono preamp costing way more? No but to me for the money it's a very noticeable improvement and who knows it may improve even further with a bit more burn in time.

[DSJR]

Grado Golds don't have much treble either as I sold a good few at the time (my ex boss was a Grado fanatic) and always found them dull and rather bland. The baby ones tip resonance actually livens things up. We used to sell the Goldring 1012GX instead at the time.

I'm not in the slightest suggesting you did the wrong thing in replacing all the caps, but you also have to look at other reasons for the excessive smoothness commented on.

P.s. Did the makers plonk a load of goo around the bases of some of these caps? I'm still suffering the fallout of Marantz/Philips and Micro Seiki doing the same thing twenty odd years ago on my CD player

[Hypnotoad]

Grado Golds don't have much treble either as I sold a good few at the time (my ex boss was a Grado fanatic) and always found them dull and rather bland. The baby ones tip resonance actually livens things up. We used to sell the Goldring 1012GX instead at the time.

I'm not in the slightest suggesting you did the wrong thing in replacing all the caps, but you also have to look at other reasons for the excessive smoothness commented on.

P.s. Did the makers plonk a load of goo around the bases of some of these caps? I'm still suffering the fallout of Marantz/Philips and Micro Seiki doing the same thing twenty odd years ago on my CD player

I used to own a Goldring 1012GX and I found it very forward and grainy in the top end for my liking but that's just me I guess. The Grado Gold has that lush, plump Grado sound, the Blue was lacking in the top end but I find the Gold is just right.

I compared the stock 540P with the stock 640P and then the recapped 640P, it has definitely opened up in all areas.

The brown glue they used was seemingly squirted willy nilly around this thing.

Quality control doesn't seem to be a priority as on the solder side of the board the op amps seemed to have been put in using a blow torch, the board is really discoloured in that area.

[kcc123]

Hi Phillip,

Welcome to the Cambridge 640P club! I am also a happy owner of a modified 640P. Here is a picture of my extreme approach, full of boutique parts, a sort of extravagancy.

[DSJR]

I used to own a Goldring 1012GX and I found it very forward and grainy in the top end for my liking but that's just me I guess. The Grado Gold has that lush, plump Grado sound, the Blue was lacking in the top end but I find the Gold is just right.

Lush & plump? not High Fidelity to the original source is it really

The 1012GX can sound as you describe, but in a Rega deck/arm the excesses are well controlled. maybe i should have said ortofon OM Red or next one up? neutral balance without the "edge"

Don't mind me. I'm one of those dangerous people who hasn't had an issue with CD reproduction since 1985

[Tarzan]

Interesting post, l too have a 640P and was amazed at how musical and well this budget phono pre-amp sounded, looks like you have a good idea going on there, also how far could you take the upgrading?

[DSJR]

I tell you summat, stick that circuit in a flash box and hand make it in the UK. You could put a several hundred quid price tag on it!!!!!

Regarding the standard caps. I wonder if they've always been of basic grade or whether they've been downgraded (accidentally or on purpose) as happened to the Quad 909 in recent times?

[Hypnotoad]

Regarding the standard caps. I wonder if they've always been of basic grade or whether they've been downgraded (accidentally or on purpose) as happened to the Quad 909 in recent times?

I was thinking the same thing. In a lot of cases the designer comes up with something good and the bean counters and/or manufacturers dumb it down to meet a certain price point, regardless of quality.

I found this on the web regarding capacitor failures, notice the brand name, doesn't inspire confidence:

http://forum.eserviceinfo.com/viewtopic.php?t=26615

Next I might build my own, I have seen one with excellent reviews and you can buy the circuit boards from the designer and source your own "quality" components. It would be much easier doing it from scratch rather than having to remove components with that lead free stuff.

[colinB]

I used to own one and remember finding mods on the net which included upgrading the op amps and using bridging resistors. I think it was on vinyl engine.

[Hypnotoad]

Update on the 640P it has improved further with use.

I have also removed the two 220pf input capacitors after reading a nice article on cartridge loading. I measured the impedance of my tone arm and cables which came to around 200pf on their own. Plenty of capacitance their already.

I put two 47k metal film resistors in parallel with the shunt input resistors also, this lowered it to 23.5k which is close to perfect for the Grado Gold.

It really smoothed out the top end a lot. Makes the Grado have an almost holographic sound to it now.

Makes me wonder why more phono stages don't have variable input loadings as the 47k and 220pf suits only a small range of carts.

For the little bit of money I spent it has made a huge difference to it.