Hi everyone,
I purchased recently a new Cambridge Audio P500. I fired up the amp and curiously enough the music played immediately through the speakers with no delay,no clicks from relays,just nothing.I switched off and the music faded until disappeared.
Very curious I opened the case and I could not locate any protection circuit for the speakers against DC.
I attach the schematic I found on a site.It uses Sanken SAP15-16 transistors.I do not know at all these transistors. Is there any protection in the schematic? I'm considering to install a DC protection circuit as I do not understand this lack of some circuit of this sort. 😕
-The lowest impedance for this amp is 6 Ohms. Will do any damage If I am going to use 4 Ohms for a short period?
Thank you very much
I purchased recently a new Cambridge Audio P500. I fired up the amp and curiously enough the music played immediately through the speakers with no delay,no clicks from relays,just nothing.I switched off and the music faded until disappeared.
Very curious I opened the case and I could not locate any protection circuit for the speakers against DC.
I attach the schematic I found on a site.It uses Sanken SAP15-16 transistors.I do not know at all these transistors. Is there any protection in the schematic? I'm considering to install a DC protection circuit as I do not understand this lack of some circuit of this sort. 😕
-The lowest impedance for this amp is 6 Ohms. Will do any damage If I am going to use 4 Ohms for a short period?
Thank you very much
Attachments
There is only VI limiting and no protection against DC. I agree, this is a lousy thing for Cambridge to have left out.
The Sanken SAP transistors are basically power Darlington transistors with built in temperature sensing diodes, and a built in emitter resistor of about 0.22 ohms. They were discontinued and replaced by the STD series - which is the same device, without the emitter resistors as they were prone to fail.
4 ohm loads, I would not recommend it. I don't know about the P500, but the A500 (integrated amp version) has a very poor heatsink made of a metal L-angle and bent sheet metal for fins. If you want to run 4 ohms, consider replacing the heatsink with a proper solid aluminium extrusion.
The Sanken SAP transistors are basically power Darlington transistors with built in temperature sensing diodes, and a built in emitter resistor of about 0.22 ohms. They were discontinued and replaced by the STD series - which is the same device, without the emitter resistors as they were prone to fail.
4 ohm loads, I would not recommend it. I don't know about the P500, but the A500 (integrated amp version) has a very poor heatsink made of a metal L-angle and bent sheet metal for fins. If you want to run 4 ohms, consider replacing the heatsink with a proper solid aluminium extrusion.
That heatsink is totally useless, it does about as good job as just the alu plate on its own. Those fins have almost no contact with the plate.
The SAP15 are rated 15A/150W and although not documented in the datasheet
they seemingly have a Ft in excess of 50Mhz.
Looking at the schematic , it is good enough and is largely better than
a gainclone.
If not used at full volume for long periods it should withstand 4R load ,
although , given the size of the heatspreader i wouldnt venture going
at high volume....
they seemingly have a Ft in excess of 50Mhz.
Looking at the schematic , it is good enough and is largely better than
a gainclone.
If not used at full volume for long periods it should withstand 4R load ,
although , given the size of the heatspreader i wouldnt venture going
at high volume....
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The circuit looks reasonable, filtering on rails to input stage, input emitter degeneration and cascode in Vas. The heatsink looks inadequate and also the smoothing caps look a bit small. Greek summer temperatures could be too much for this design
This amp is typical Cambridge Audio of the time. Many SAP15's fried due to overheating because of that heatsink. Also suspect is the Chinese manufacturing and cheap parts, especially electrolytic capacitors. A shame, because the circuit itself is actually pretty decent.
Would it be possible to replace some of these suspect parts to improve it? Only asking as I have a pair of them (as you already know, you've just posted in one of my threads 🙂 )
I have bridged 2 of these amps to monoblocks with a proper bridging module. I have been waiting for the "magic smoke", but a few weeks in and many hours use they are still going (4 Ohm speakers) and don't really get hot at all. However I must get some speaker protection done.
The main improvement would be to replace that excuse for a heatsink. Would have to measure it to say more.
Also worthwhile would be replacing the main power supply capacitors - those are the 8 capacitors in the middle of the board. Last time I looked they were using some crappy no-name brand here.
Also worthwhile would be replacing the main power supply capacitors - those are the 8 capacitors in the middle of the board. Last time I looked they were using some crappy no-name brand here.
I have to say I've never felt mine get particularly warm, but then that could because all the heat is being kept in the components as opposed to being transferred through the heat exchanger.
All i know is i've repaired a fair few Cambridges with this circuit in, and it usually went along the lines of "I was having a party and i think it overheated, it stopped working and it was hot when i turned it off". Sure enough dead SAP15's.
The problem is that the internal emitter resistor is not very resilient and fails easily before the transistor die itself does. Sanken abandoned them and brought out the same transistors as the STD series - only difference being no internal emitter resistor
The problem is that the internal emitter resistor is not very resilient and fails easily before the transistor die itself does. Sanken abandoned them and brought out the same transistors as the STD series - only difference being no internal emitter resistor
Cambridge P500 is humming....
I have a Cambridge P500. Bought it a couple years ago, secondhand.
There have been hum coming out of the loudspeaker from day one. I tried to take the transformer out of the chassie, just to hear if the humming would go away, but the hum was still there. The hum comes from both loudspeakers. Anybody out there who have the same problems? Perhaps the capacitors are defect?
I have a Cambridge P500. Bought it a couple years ago, secondhand.
There have been hum coming out of the loudspeaker from day one. I tried to take the transformer out of the chassie, just to hear if the humming would go away, but the hum was still there. The hum comes from both loudspeakers. Anybody out there who have the same problems? Perhaps the capacitors are defect?
What pre-amp are you using? Mine are absoloutely silent when paired to the Cambridge Audio C500 pre-amp. However, since I have started using the Yamaha DSP-E800 as the pre-amp they have picked up a slight hum. This I believe is down to the P500s picking up and amplifying the noise from the Yamahas 'dirty' inferior transformer.
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