Cambridge Audio 640P Capacitor Upgrade

[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.



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.

[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_...distortion.pdf

Great stuff.