Cambridge Audio P55 Schematic

[madtecchy]

Hi.

I have a Scematic for the Cambridge Audio P55. It is a scan of a very poor quality photocopy. I now have it drawn in Eagle . However drawing the scematic was not too hard i wish i could say the same for the board layout. If anyone would like a copy drop me a line and i will post on forum or mail it too you. Also would anyone be kind enough to do a layout. Or even a few tips on using eagle layout editor. As im a newbie to eagle would anyone like to take a look at my attemp to see if there are any errors.

Best Wishes Ian

[davidsrsb]

Something is very wrong with the Q18 Q19 -ve side of the output stage. Those transistors should be in parallel and the diodes are also wrong

[jaycee]

That looks suspiciously like the Cyrus 2 power amp.

[madtecchy]

Thanks david ill sort that now . Well i hope so as the original scematic is barley readable. and my mistake is so blatent now you have pointed it out

Hi jaycee thanks i will have a look at the cyrus 2 As i may be able to get a clearer schem for that . I was also told it was similer to a AR model but that one uses complimentary output stage.

Regards Ian

[madtecchy]

schematic Is now fixed hopefully.

[davidsrsb]

Looking better, but 1N4002s on the output? - a bit under rated
0R22 in series with the output gives a low damping factor with 4R woofers

I guess this was a Stan Curtis design, which would explain the Cyrus similarity

[madtecchy]

Hi. Thankyou David.

Im guessing from what you say it would be a good idea to uprate the 1n4002's with somthing a little larger for reliability issues maybe. also i have just read the circuit description for the p55 it says
" Wire wound resistor R49 ensures a negative feedback signal under output short situations . Thus it is an aid to stability with reactive speaker loads."

Do you think replacing R49 with an inductor and series resistor would improve the damping factor and at the same time aid stability too.

Would increased damping factor improve sound quality. My guess is it would maybe improve the bass on higly reactive and also lower impedance speakers.
Ps Im still learning. And yes you are correct it is a stan curtis design.

Kind Regards
Ian

[davidsrsb]

I would leave it alone, stability problems could be very expensive.
This is a design that will work best with "valve friendly" speakers, avoid those with very low imedances as the extremes like Maggies and ribbon tweeters

[jaycee]

What rail voltages does the P55 use?

The circuit does work well, however if you're after building a clone the original Sanyo parts are probably difficult to get. I don't think i'd bother with the quasi-comp output stage either.

[madtecchy]

Originally Posted by davidsrsb

I would leave it alone, stability problems could be very expensive.
This is a design that will work best with "valve friendly" speakers, avoid those with very low imedances as the extremes like Maggies and ribbon tweeters

Hi David.
Well i dont have any maggies or ribbon tweeters. I do use as my main speakers a pair of DefTech BP8's. However for testing i have a set of old celestion DL4 into wich i have installed some 4700 uF in series with the input connectors for testing purposes as i dont realy like the sound of them. The amplifier as is drives the DefTechs very well they are bipoles and are quite a friendly 4 Ohm load also at 91 db W m they are quite sensitive so i dont need to use much power to get a decent listening level. Also i like Risk and i dont have a lot to lose as the amplifier cost very little im using it as a learning exercise to create a clone and learn eagle at the same time . Thankyou very much for the warning but hey im a big boy lol responsible for my own actions and wont comes shouting at you if it lets out the blue smoke. The first thing im going to do is use a seperate psu for each channel and totaly bypass The pre and tone controls as that will remove over 2 feet of track and unscreened wire each input has to travel before entering the power amp section as i only use A Dac as source i dont even need a volume control as the dac as one built in.

Kind Regards Ian