As you all know (you would have to have been living under a rock not to know 
) I have been upgrading and experimenting with the Cambridge Audio 640P, a decent phono stage out of the box.
Here is a review and synopsis of the mods / upgrades.
1. All electrolytic caps were replaced with Panasonic FC's and SU's for the bipolars.
2. Op amps removed and op amp sockets installed.
3. Polystyrene caps installed in place of ceramic bypass caps on the op amps.
4. The two 220pf input caps removed completely.
5. Optionally input resistors changed to adjust impedance to the cart for best performance.
When I initially tried the stock unit in my system is sound alright but very laid back and two dimensional, it was easy to listen to but didn't set the world on fire. It was easily beat out by my Pro-Ject Tube Box II.
I modded mine and then Jim Reeves sent me his for the same mods. He has been a second set of ears and you know that it's easy to get carried away and subconsciously exaggerate the improvements on something you are working on. And I can't thank him enough for his work in testing out different op amp combination's, we have finally settled on one that seems to be a clear winner.
The upgraded unit needs a little while to break in, I leave it on all the time and it takes a couple of weeks to hit it's straps. It seems to get smoother over that time.
To give an idea of the difference in sound between the stock unit I would describe it as this. Imagine a group of musicians huddled together, shoulder to shoulder, they start playing and the sound seems to be all joined together coming from one spot. Then you tell them to move apart not only side to side but front to back. They move apart a little bit but you tell them keep going until they are all where they are supposed to be. All of a sudden you can hear the guitar clearly from it's spot then the drummer from it's spot, the drummer is not only in a different spot side to side but is behind the guitar as well. You now have a wide sound stage and a deep one as well. You can easily pick out the different positions of the musicians. Also the clarity and detail is unbelievable, I hear things on the records that I hadn't noticed before, probably because they were all smeared together. It's like all the layers of the music have been separated so you can hear them all clearly. The bass is deep but not flabby one note bass, you can hear the different drums and bass guitar notes. I was listening to The Wall by Pink Floyd yesterday and when they sing "Is there anybody out there", it's like being in a 3d movie where the voices get closer and closer to you. I started thinking I am going to need a bigger room. I find myself not only listening but pointing my head in the direction of one particular instrument now something I couldn't do before, and you don't get graininess or harshness anymore.
I told Jim he has backed a winner with his selection of op amps using the AD823 in the input stages and the LM4562 in the output stages. This is a match made in heaven, using all LM4562's was very very good but just had a little dryness to it. With the AD823 mixed in it extends the bass and really smooths everything out.
If anyone had told me before I started this little project it would improve to the point that it's at and I would sell my Pro-Ject Tube Box II because of it, I would have laughed, it's that good.
And with op amp sockets installed as Jim and I found out op amp rolling is cheap and a lot of fun.
Stock unit:
Upgraded unit:
) I have been upgrading and experimenting with the Cambridge Audio 640P, a decent phono stage out of the box.Here is a review and synopsis of the mods / upgrades.
1. All electrolytic caps were replaced with Panasonic FC's and SU's for the bipolars.
2. Op amps removed and op amp sockets installed.
3. Polystyrene caps installed in place of ceramic bypass caps on the op amps.
4. The two 220pf input caps removed completely.
5. Optionally input resistors changed to adjust impedance to the cart for best performance.
When I initially tried the stock unit in my system is sound alright but very laid back and two dimensional, it was easy to listen to but didn't set the world on fire. It was easily beat out by my Pro-Ject Tube Box II.
I modded mine and then Jim Reeves sent me his for the same mods. He has been a second set of ears and you know that it's easy to get carried away and subconsciously exaggerate the improvements on something you are working on. And I can't thank him enough for his work in testing out different op amp combination's, we have finally settled on one that seems to be a clear winner.
The upgraded unit needs a little while to break in, I leave it on all the time and it takes a couple of weeks to hit it's straps. It seems to get smoother over that time.
To give an idea of the difference in sound between the stock unit I would describe it as this. Imagine a group of musicians huddled together, shoulder to shoulder, they start playing and the sound seems to be all joined together coming from one spot. Then you tell them to move apart not only side to side but front to back. They move apart a little bit but you tell them keep going until they are all where they are supposed to be. All of a sudden you can hear the guitar clearly from it's spot then the drummer from it's spot, the drummer is not only in a different spot side to side but is behind the guitar as well. You now have a wide sound stage and a deep one as well. You can easily pick out the different positions of the musicians. Also the clarity and detail is unbelievable, I hear things on the records that I hadn't noticed before, probably because they were all smeared together. It's like all the layers of the music have been separated so you can hear them all clearly. The bass is deep but not flabby one note bass, you can hear the different drums and bass guitar notes. I was listening to The Wall by Pink Floyd yesterday and when they sing "Is there anybody out there", it's like being in a 3d movie where the voices get closer and closer to you. I started thinking I am going to need a bigger room. I find myself not only listening but pointing my head in the direction of one particular instrument now something I couldn't do before, and you don't get graininess or harshness anymore.
I told Jim he has backed a winner with his selection of op amps using the AD823 in the input stages and the LM4562 in the output stages. This is a match made in heaven, using all LM4562's was very very good but just had a little dryness to it. With the AD823 mixed in it extends the bass and really smooths everything out.
If anyone had told me before I started this little project it would improve to the point that it's at and I would sell my Pro-Ject Tube Box II because of it, I would have laughed, it's that good.
And with op amp sockets installed as Jim and I found out op amp rolling is cheap and a lot of fun.
Stock unit:
Upgraded unit:
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