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.

http://i729.photobucket.com/albums/ww297/Hypnotoady_photos/PSBefore.jpg

Power supply after:

http://i729.photobucket.com/albums/ww297/Hypnotoady_photos/PSAfter.jpg

Main board before:

http://i729.photobucket.com/albums/ww297/Hypnotoady_photos/640PBefore.jpg

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.

http://i729.photobucket.com/albums/ww297/Hypnotoady_photos/640PEnd.jpg

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 :steam:

[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 :steam:

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. :)

http://i166.photobucket.com/albums/u114/KCCTKC/MCphonoprepreamp289copy.jpg

[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 :ner:

[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.

[Hypnotoad]

Having the upgrade bug I took the CA640P to the next level so to speak.

I put in op amp sockets and some audio friends and I experimented with different op amp combination's and at the moment have settled on AD823's in the input stages and LM4562's in the output stages. I also put in polystyrene bypass capacitors on the op amps instead of the lowly ceramics.

It's a match made in heaven and there is simply no comparison between them and the stock units, they can be done cheaply and quickly. It was compared to a well respected valve phono preamp costing a LOT more and it beat it hands down, the valve preamp was quickly sold and the upgraded 640P now in it's place. It was also compared to a high priced solid state phono stage with exotic components and not only held it's own but was found to be superior in a few areas.

http://i729.photobucket.com/albums/ww297/Hypnotoady_photos/Jim640P.jpg

I suspect that CA had a good design but the bean counters dumbed it down with cheaper components or the manufactures in China are substituting components.

If anyone wants to give it a try I can list all the components that I use.

[RochaCullen]

Hey Philip,

I'd love to give this a go, please supply a list of parts and what you did with them. Thanks a bunch,

Nathan

[colinB]

Have you upgraded the wall wart psu ? I have heard of smoke comming out of the DAC magic psu in the uk. They had to recall them 2 years ago and offer a replacement .

[Hypnotoad]

Hey Philip,

I'd love to give this a go, please supply a list of parts and what you did with them. Thanks a bunch,

Nathan

Nathan,

1. Remove the electrolytic capacitors and replace them with the corresponding value from the parts list.

2. Remove the NE5532 op amps and install the op amp sockets in their places, remember to orientate them to the outline on the PCB.

3. Remove the ceramic bypass capacitors next to the op amps and replace with the corresponding value polystyrene's.

4. Optionally you can also remove the two 220pf MM input capacitors either side of the MM RCA inputs, there is enough capacitance in the tonearm wires and phono cables. Added to that you have over 400pf which can cause a spike in the upper frequencies.


For the 640P here are all the parts and part numbers you need for http://www.digikey.co.uk/:

2 x Op Amps AD823 = AD823ANZ-ND (I put these in the input sections)

2 x Op Amps LM4562 - LM4562NA-ND (I put these in the output sections)

4 x Op Amp Sockets - ED90105-ND

Panasonic Electrolytic Capacitors:

2 x P1179-ND CAP ELECT 47UF 25V SU BI-POLAR
4 x P1144-ND CAP ELECT 220UF 6.3V SU BI-POLAR
4 x P1146-ND CAP ELECT 470UF 6.3V SU BI-POLAR
4 x P11258-ND CAP 330UF 50V ELECT FC RADIAL
2 x P10305-ND CAP 1000UF 35V ELECT FC RADIAL
1 x P10312-ND CAP 1UF 50V ELECT FC RADIAL
3 x P10269-ND CAP 100UF 25V ELECT FC RADIAL
1 x P11212-ND CAP 10UF 25V ELECT FC RADIAL
4 x P10275-ND CAP 470UF 25V ELECT FC RADIAL
5 x P10278-ND CAP 1000UF 25V ELECT FC RADIAL

The Polystyrene bypass caps to replace the ceramics on the op amps I got from Parts Connexion in Canada any voltages over 63 volts would be fine, maybe you can get them locally:

2 x 22pf 160v

2 x 33pf 160v

2 x 47pf 160v

Some have used silver mica caps with success to replace the stock ceramics.

You will be amazed at the difference so let us know how it goes. The good thing about installing op amp sockets is that you can try different combination's. Any further questions just ask.

[RochaCullen]

Hi Philip,

Thanks for all that detail. I found all the caps on rs electronics, and will see about ordering them soon. I have enough kit arriving over the next few days. But i have saved the list so that I can order it quickly when the time arises.

Thanks again,

Nathan

[zanash]

I've modded several of these for friends.....

one of the best mods is to get rid of the nasty plastic and base metal rca sockets ......



I've used a variety of rca sockets and even the most humble [maplin] bulkhead mount type ...linked to the board by silver in ptfe ...had a dramatic effect on the sound .


another really good mod ..thats not going to break the bank is to remove the noisy 1n000x diodes and fit 11dq10's ...

these shottky diodes don't create switching transients ..and are there fore very quiet ...so you drop the noise floor of the device ...very important in a step up device !


if your feeling brave and confident ...losse the dc blocking caps on the output ...especially if your preamp has dc blocking caps in its input ...

unless your using silver in oil or paper in oil at this point ...any caps will emasculate the output.


I opamp swapped and found that opa 2222 or 2228 sounded prety good but I did not have some of the more modern stuff to try ..

replacing resistors in the signal path is also worth the effort ....

note and warning ...its a cheap pcb and uses nasty solder so you need to use extreme caution whien removing components.

One modded unit had a persistant hum on one chanel ...to the point where I returned the unit to unmodded ....a lot of work ...

once the hum had gone away I replaced the parts ....with the last thing to be done replacing the rca out sockets ....bugger the hum was back ....

on very close inspection the ground of the closest rca socket to the psu was forced up against the mu metal shield...causing the hum ...bugger bugger bugger ! swining the ground tab round away from the shield cured it !

two weeks of head scratching solved in an instant !

[Hypnotoad]

I will try the RCA connectors out, I am actually upgrading another one at the moment, I got a rush of blood and changed out all the caps in the RIAA section and the polypropylene bypass caps with Polystyrene's so I will see what difference that makes. I will try the diodes when I put in an order from Digikey.

I know all about the lead free solder, I posted in another thread about the Hakko 808 desoldering gun I bought, it makes removing components even from the 640P like shelling peas. It's also pretty tight in the case and the hole's in the PCB are pretty small so it makes it hard to fit larger components in.

It's just astounding the difference that modding this thing makes.


I've modded several of these for friends.....

one of the best mods is to get rid of the nasty plastic and base metal rca sockets ......



I've used a variety of rca sockets and even the most humble [maplin] bulkhead mount type ...linked to the board by silver in ptfe ...had a dramatic effect on the sound .


another really good mod ..thats not going to break the bank is to remove the noisy 1n000x diodes and fit 11dq10's ...

these shottky diodes don't create switching transients ..and are there fore very quiet ...so you drop the noise floor of the device ...very important in a step up device !


if your feeling brave and confident ...losse the dc blocking caps on the output ...especially if your preamp has dc blocking caps in its input ...

unless your using silver in oil or paper in oil at this point ...any caps will emasculate the output.


I opamp swapped and found that opa 2222 or 2228 sounded prety good but I did not have some of the more modern stuff to try ..

replacing resistors in the signal path is also worth the effort ....

note and warning ...its a cheap pcb and uses nasty solder so you need to use extreme caution whien removing components.

One modded unit had a persistant hum on one chanel ...to the point where I returned the unit to unmodded ....a lot of work ...

once the hum had gone away I replaced the parts ....with the last thing to be done replacing the rca out sockets ....bugger the hum was back ....

on very close inspection the ground of the closest rca socket to the psu was forced up against the mu metal shield...causing the hum ...bugger bugger bugger ! swining the ground tab round away from the shield cured it !

two weeks of head scratching solved in an instant !

[Hypnotoad]

It lives!

My newest creation is finished and working, it's still burning in and sounding better and better.

Right out of the blocks it sounded similar but better than my regular upgraded 640P's. It has more detail, more bass extension and smoother sound so far.

I swapped out all the polypropylene caps in the RIAA section and the electrolytic bypass caps with the same value in polystyrene's. They are nothing to look at but sound smoother IMO.

I also put green Nichicon Muse caps in place of regular bi polars, the ones near the inputs just fit and I mean just. I had to spend over an hour filing the legs down so they would fit through the holes in the PCB. Even then there is only a few millimeters between the top of them and the case, the ones near the outputs I put on their sides as the space was too tight.

The op amps are my favorite AD823's in the input and LM4562's in the output sections.

http://i729.photobucket.com/albums/ww297/Hypnotoady_photos/003-6.jpg

[cellistic]

Hi All,

Really exciting to see everyone having fun with this sort of thing - I've not played with electronics since my EE/ Analogue Circuit days in college. I just got in a stock 640p, and have to say that even before break-in, I think it does a lot right! The noise floor is clearly decent; as with all higher end gear you have to remind yourself that 'loud sound' = distortion, and that you can turn up a quiet piece of gear well past sensible before you realise it.

That said, I think all your exploits look too fun to pass up, and so I'm embarking on my own modding adventure. I'll be making some slight changes though...

-I'll be using Panasonic FM caps where possible, as they have lower reported impedance than Panasonic FC's;

-I'll use the (near) universally accepted LM4562, but will also try LT1469's and the LM49860. Reason being - I don't have any inherent love of JFET's (OPA2134, etc), and these two seem to come reasonably close to matching the performance of the AD797 but in a dual package, thus eliminating the need for those crazy SOIC-DIP8 adapters. I am going for neutrality above all else; not to say that I don't want a bit of class and grace along the way!

-Rather than going nuts with boutique audio parts, I'm going to spend a long time matching component values. I'm a price/performance guy, and like several others have commented on in various mod threads; if I wanted something that sounded ten times better, I'd have started with something a little more high end to begin with.

I'd love to take it a bit further, but honestly I think these tweaks will satisfy my needs, and perform on par with the rest of my system. Details forthcoming!

[cellistic]

Oh! Dang.

I forgot the reason I wrote that last post in the first place - - I thought you tweakers might be interested in a lovely resource I found. It's a small tome of real-world measurements and commentary on applications for different op-amps, with a focus on distortion and transfer linearity. I realise there is some excitement in just trying new stuff, but I believe in the right tool for the job. Have a gander:

http://www.sg-acoustics.ch/analogue_audio/ic_opamps/pdf/opamp_distortion.pdf

Great stuff.

[cpr1979]

Hi Hypnotoad. Are you still performing the 640P upgrage and if so, how much does it cost? What is the turn around time?

[The Grand Wazoo]

Collin,
Have you got this wrong or have I? I'm afraid I don't have the time to dig too deep into it, but I suggest you read the thread carefully.
I think this is a thread where an enthusiast has described the modifications he's made to his own unit and described those changes for the benefit of others. I don't think he's offering a modification service to anyone.
Apologies if I've got it wrong.