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Old 27th December 2005, 10:42 PM   #1
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Default Help for Cambridge A300 please

One channel of the A300 is out, it seems to be around the bias setting. The trim (RV202) is burnt and so are the R238,239(?) R260, R236. I guess what would help me the most would be to get the schematic: would anyone know where I can find it? I join here a photograph to show the burnt part . Have you ever experienced that or heard of that kind of problem? does anyone of you have any insight/idea/suggestion to help me solve it?
Thanks a ton!

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Old 28th December 2005, 01:34 AM   #2
anatech is offline anatech  Canada
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Hi "Dad"
Sounds like outputs and drivers have failed, plus the other parts you have listed.

Check the rest of the transistors in that channel. Also have a look at the low value resistors (<1K ohm). They may be open, but look fine.

-Chris
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Old 28th December 2005, 06:55 AM   #3
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Hi anatech,

Yes I guess that the SAP10 have failed, probably after a short at the output (It's my daughter amplifier), which are the drivers ? have you an idea of the output stage/drivers design? Before removing parts and check them I would prefer to know a little more about the design, If can't get the schematic, I will "backengineer" the PCB, but you know it's a little fastidious !
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Old 28th December 2005, 08:14 PM   #4
anatech is offline anatech  Canada
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Hi Richard,
Measure the resistance between the speaker output (before the relay) and each DC supply. Look for a short reading.

The drivers are the transistors the connect to the outputs, normally between the VAS ond outputs. I would need a schematic is give you more accurate answers.

Drawing the schematic from the board will take some time. I've had to do it, it's not fun.

-Chris
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Old 28th December 2005, 10:13 PM   #5
JohnW is offline JohnW  Hong Kong
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Hi Richard,

Cambridge A300 V2 Power section,

Good Luck,

John
Attached Files
File Type: pdf a300 v2 ops.pdf (36.4 KB, 820 views)
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Old 29th December 2005, 11:27 AM   #6
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Thank you very much JohnW, the schematic was very helpful, the problem is solved now I just replaced the 2 Sanken power Darlington’s and the burned resistors R214 R216 R225 R230 RV201 (on your schematic).

By the way, if you have some insight on this amplifier do you think that replacing the feedback resistors by better ones (Resista, Caddock) and capacitor C203, as well as the input cap by Black Gate NX ones, could significantly improve the sound? Or maybe have you other suggestions.

Thanks again.
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Old 11th January 2006, 04:22 AM   #7
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John,

You didn’t happen to design the A300 v2, seeing as you have a schematic, did you?

Just curious!

Regards,

Carl
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Old 13th January 2006, 02:25 PM   #8
JohnW is offline JohnW  Hong Kong
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Hi Carl,

The Cambrodge Audio A300 was designed after I left AP (Audio Partnership) the holding company for Cambridge Audio and many others.

The original CA amps, A1 & A2 where designed by Mike Creek of Creek Audio Fame...

Together, we had a many a "Fun" time in China getting the earlier AP products in production - like avoiding 10lb Rats and coming to terms with the holes in the ground called toilets (we soon learnt to carry own rolls of toilet paper...)

To the "good old days"

John
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Old 13th January 2006, 04:17 PM   #9
tja is offline tja  Netherlands
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Old 22nd January 2006, 09:43 PM   #10
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Hi! I'm going to buy one of the named amp. Can anyone of you send me the full schematic for the amp please? I would be much happier if i had the chance to repair it if anything goes wrong.
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