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!
photos
Thanks a ton!
photos
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 !
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 !
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
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
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.
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.
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
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
I might have the complete service manual in work. I will have a look on Monday and email it to you.
Cambridge Audio used to have all of their service manuals online but they recently removed them. Too bad they were actually very good amps but IMO suffered due to crap component such as input caps and PSU caps.
I used to have one and done some mods to it. I replaced the transformer with a 300VA one and the PSU caps with 10,000uF. I also replaced the input caps with poly caps I think.
Also I removed the VI limiter speaker protection. The amp rocked like F**k. I have no idea why I sold it on Ebay to this day.
Cambridge Audio used to have all of their service manuals online but they recently removed them. Too bad they were actually very good amps but IMO suffered due to crap component such as input caps and PSU caps.
I used to have one and done some mods to it. I replaced the transformer with a 300VA one and the PSU caps with 10,000uF. I also replaced the input caps with poly caps I think.
Also I removed the VI limiter speaker protection. The amp rocked like F**k. I have no idea why I sold it on Ebay to this day.
I would be grateful! I was looking for amp mods just today. As you modded yours, can you please also give me some advices? You probably did a lot of testing, and used your unit for a long time, I would not play the whole fitting and testing again, if you share the right mods I can do.
I figured out today, that the amp can do 43W for both sides in sinus, at 8 ohm in stock layout. That seems OK to me, thats maybe because I have a v2.
I'm thinking on adding two ~160W toroids, and make the supply totally split in two. Would that cause any improvement?
Would changing the rectifier diodes to a more faster type cause anything?
My opinion aboout smoothing capacitors is, that it's better to use many smaller ones in paralell, than one big one, so I would not touch the ones that are in the unit now. Also here in Hungary is not so easy to get quality capacitors, I think I would hurt more with one big but low quality cap., than using the stock thing.
The amp gives a light hum noise when there is no source connected at full volume. Can I anyhow fix that? Is that the supply or the preamp? (I think it's the supply, it seems a 50hz hum to me, and the well known, low amount of hiss is from the preamp does not really bother me.)
Thanks in advance!
I was looking for amp mods just today. As you modded yours, can you please also give me some advices? You probably did a lot of testing, and used your unit for a long time, I would not play the whole fitting and testing again, if you share the right mods I can do. I figured out today, that the amp can do 43W for both sides in sinus, at 8 ohm in stock layout. That seems OK to me, thats maybe because I have a v2.
I'm thinking on adding two ~160W toroids, and make the supply totally split in two. Would that cause any improvement?
Would changing the rectifier diodes to a more faster type cause anything?
My opinion aboout smoothing capacitors is, that it's better to use many smaller ones in paralell, than one big one, so I would not touch the ones that are in the unit now. Also here in Hungary is not so easy to get quality capacitors, I think I would hurt more with one big but low quality cap., than using the stock thing.
The amp gives a light hum noise when there is no source connected at full volume. Can I anyhow fix that? Is that the supply or the preamp? (I think it's the supply, it seems a 50hz hum to me, and the well known, low amount of hiss is from the preamp does not really bother me.)
Thanks in advance!
I will have to email you the manual due to the size.
As for the mods what you say will be fine. The seperate PSU for left & right should improve stereo seperation as well as bass. Using many smaller capacitors in parallel should be better than 1 large one.
I really just stuck to the basic mods on this amp and then sold it. As I said I wish I didn't now.
As for the mods what you say will be fine. The seperate PSU for left & right should improve stereo seperation as well as bass. Using many smaller capacitors in parallel should be better than 1 large one.
I really just stuck to the basic mods on this amp and then sold it. As I said I wish I didn't now.
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