The SAP16's should work - ideally you should replace all with the same type.
Profusion have these for sale - www.profusionplc.com
Profusion have these for sale - www.profusionplc.com
ok, so we replaced the four darlington transistors with sap15n/p and a few burnt resistors R216 R214 the others seems to be ok. Trouble is it's still not working. My friend (the one with the knowledge) thinks that the transistor Q208 may have been affected by the power surge from whatever blew the resistors above, question is how do I test the transistors, i'm going to do this myself as my friend has now gone off to work for a few weeks and has no time to do it. Any help or further advice for things to test would be appreciated. I know the OP said that RV201 had gone on his but that seems ok as is showing a 60R resistace, not sure if that what it's supposed to be but it looks ok. and that's under the 100R it's listed as.
Thanks for taking an interest.,
Thanks for taking an interest.,
Has anybody resolved the hum problem in their Cambridge Audio A300? I am working on one here and I am getting nowhere. I have replaced all the filter caps and checked my grounds and nothing has made a difference. Any suggestions? Also does anyone still have the service manual for the A300? Mine isn't a V2.
Hi Guys, I'm currently having a repair session from all my blown gear, got through quite a few repairs so far and today it's been A300 day which has brought me to this post. I will now list the problems i found very similar to erichz's and i will also be asking for help as i don't know exactly how i should set the bias.
The cause: I believe the speaker wires had shorted together (whilst the amp was lent to a friend)
Faults i found.
1. SAP10 PNP blown on left Channel.
2. R216 (47ohms) & R214 (270ohms) Blown.
3. Bias potentiometer was crunchy, not showing open circuit but no longer 100 ohms.
4 Zenner diode D205 Blown (this is a 1N4148).
5. Q208 blown.
Basically once the SAP10 shorts it draws too much current through the drive circuit blowing the above components until something gives.
I hope i found all of the blown components, i am about to order them. To the others who experience a blown PNP SAP10 i would advise replacing all of the above parts.
I'm very happy to find the schematic posted on here (especially being the left side so i didn't have to backtrack to workout the component numbers). I had worked everything out except that the zenner diode was too small to read it's value, i was going to take a guess by buying a high voltage zenner to match the amps voltage rail.
I would appreciate some help here if anyone could walk me through how to set the bias, i've never done this before but i'm keen to set it correctly once i get the new potentiometer. I suppose it's a case of matching the - amount of voltage pd to the + pd of the NPN and PNP's but i'm still a little lost so some help here would be much appreciated.
Hope this helps some people.
James
The cause: I believe the speaker wires had shorted together (whilst the amp was lent to a friend)
Faults i found.
1. SAP10 PNP blown on left Channel.
2. R216 (47ohms) & R214 (270ohms) Blown.
3. Bias potentiometer was crunchy, not showing open circuit but no longer 100 ohms.
4 Zenner diode D205 Blown (this is a 1N4148).
5. Q208 blown.
Basically once the SAP10 shorts it draws too much current through the drive circuit blowing the above components until something gives.
I hope i found all of the blown components, i am about to order them. To the others who experience a blown PNP SAP10 i would advise replacing all of the above parts.
I'm very happy to find the schematic posted on here (especially being the left side so i didn't have to backtrack to workout the component numbers). I had worked everything out except that the zenner diode was too small to read it's value, i was going to take a guess by buying a high voltage zenner to match the amps voltage rail.
I would appreciate some help here if anyone could walk me through how to set the bias, i've never done this before but i'm keen to set it correctly once i get the new potentiometer. I suppose it's a case of matching the - amount of voltage pd to the + pd of the NPN and PNP's but i'm still a little lost so some help here would be much appreciated.
Hope this helps some people.
James
I have the A300 v2.0 with a blown toroidal transformer. It's rated +27.5 0 -27.5 @ 2A, and I assume that the amp runs at about 40V.
Does somebody know whether these SAP10 chips can run at a lower voltage, let's say 25V ? It will have less power of course, but I am interested to know whether it will work. There is also a pair of lm317t on the circuit board, which I assume that is powering the preamp.
Does somebody know whether these SAP10 chips can run at a lower voltage, let's say 25V ? It will have less power of course, but I am interested to know whether it will work. There is also a pair of lm317t on the circuit board, which I assume that is powering the preamp.
All transistors, including Darlingtons like SAP10, SAP15,SAP16 etc. can operate at lower voltages. It is the analog circuit and possible voltage references like zeners that determine whether there will be problems at low (say, <12V) supply rails.
If you mean to use a transformer with 25VAC windings, the resulting 36VDC rails will scarcely make a difference in performance but if you mean 25VDC rails, the amplifier will still work OK but power will be noticeably less. In either case though, bias current will likely change and so need resetting (also check the condition of the RV201 etc. pots)
If you mean to use a transformer with 25VAC windings, the resulting 36VDC rails will scarcely make a difference in performance but if you mean 25VDC rails, the amplifier will still work OK but power will be noticeably less. In either case though, bias current will likely change and so need resetting (also check the condition of the RV201 etc. pots)
Thank you very much for your help. I have replaced the toroid unit with a similar one and the amp is working now. However, while idling the amp takes about 15W of power and I have a slight concern about the rails voltage which seems to be higher than expected, at about 42V.
On the SAP10 datasheet it is mentioned about idling current which needs to be controlled by an external resistor:
I found this resistor set at 44 ohm for a channel and 46 ohm for the another.
Considering the slight increase in the rails in voltage (+3V), the value of this resistor needs to be changed as well ?
The common sense says to me that it should be set at around 49-50 ohm, but I am not sure. Any ideas ?
On the SAP10 datasheet it is mentioned about idling current which needs to be controlled by an external resistor:
I found this resistor set at 44 ohm for a channel and 46 ohm for the another.
Considering the slight increase in the rails in voltage (+3V), the value of this resistor needs to be changed as well ?
The common sense says to me that it should be set at around 49-50 ohm, but I am not sure. Any ideas ?
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