Hi blacktone,
Yes there is an A5 without the i, I have both of them, the "i" means it has gold plated terminals, a larger, better spec toroidal, extra decoupling capacitors and copper shields for the 3 buffer opamps. Not sure how much more these cost back then but they're some nice upgrades.
You're right, the designs are very similar indeed, the A5i just uses SAP15s, and also has the power rectification for the opamps on the main board. If you wouldn't mind calculating the quiescent current for me i'd be very grateful, even if you take the readings of the trim pots i'm sure they will be 45-55ohms as mentioned in my previous post.
My A5 is also broken (I bought them both cheap off of ebay in this broken state). My A5 has damaged components exactly like in that thread you have linked to, so in theory must have the exact same fault. Basically this is what I have found out about this type of amplifier:
If the PNP transistor of the pair fails, the S and C pins short, which basically destroys every component in that path, primary those 3 resistors in that thread you mentioned, plus the trim pot melts and sometimes the capacitor close to it blows up. This is quite a major problem because this fault doesn't blow the rail fuses.
Now if the NPN transistor of the pair fails, the rail fuses blow, the C S and E pins are all shorted on the NPN, and no components are damaged.
Obviously, these aren't the only way this circuit can fail, but it seems to be pretty common. Out of the 2 amplifiers I have a total of 3 PNPs had failed and 1 NPN.
by the way, also forgot to mention before, anatech, after fairly heavy running in, the quiescent current only increased by about 5mA on both channels, therefore i think i will set them both to 40mA and allow them the 45mA once warmed up, the amplifier won't be used for very loud music anyway.
Thanks to all for all the help you've given me in repairing these amplifiers, i'm extremely grateful.
Andy
Yes there is an A5 without the i, I have both of them, the "i" means it has gold plated terminals, a larger, better spec toroidal, extra decoupling capacitors and copper shields for the 3 buffer opamps. Not sure how much more these cost back then but they're some nice upgrades.
You're right, the designs are very similar indeed, the A5i just uses SAP15s, and also has the power rectification for the opamps on the main board. If you wouldn't mind calculating the quiescent current for me i'd be very grateful, even if you take the readings of the trim pots i'm sure they will be 45-55ohms as mentioned in my previous post.
My A5 is also broken (I bought them both cheap off of ebay in this broken state). My A5 has damaged components exactly like in that thread you have linked to, so in theory must have the exact same fault. Basically this is what I have found out about this type of amplifier:
If the PNP transistor of the pair fails, the S and C pins short, which basically destroys every component in that path, primary those 3 resistors in that thread you mentioned, plus the trim pot melts and sometimes the capacitor close to it blows up. This is quite a major problem because this fault doesn't blow the rail fuses.
Now if the NPN transistor of the pair fails, the rail fuses blow, the C S and E pins are all shorted on the NPN, and no components are damaged.
Obviously, these aren't the only way this circuit can fail, but it seems to be pretty common. Out of the 2 amplifiers I have a total of 3 PNPs had failed and 1 NPN.
by the way, also forgot to mention before, anatech, after fairly heavy running in, the quiescent current only increased by about 5mA on both channels, therefore i think i will set them both to 40mA and allow them the 45mA once warmed up, the amplifier won't be used for very loud music anyway.
Thanks to all for all the help you've given me in repairing these amplifiers, i'm extremely grateful.
Andy
Hi Andy,
Good to hear. I might set it for 20 ~ 30 mA. The cooler it runs, the longer it will last. I didn't expect the bias to climb very much in that amp. That's a good thing.
When you see a situation where you have one PNP blown and three NPN's blown, it pretty much guaranties that the PNP was the first to blow. The NPN's went fighting a short trying to maintain the DC offset as commanded by the front end.
-Chris
Good to hear. I might set it for 20 ~ 30 mA. The cooler it runs, the longer it will last. I didn't expect the bias to climb very much in that amp. That's a good thing.
When you see a situation where you have one PNP blown and three NPN's blown, it pretty much guaranties that the PNP was the first to blow. The NPN's went fighting a short trying to maintain the DC offset as commanded by the front end.
-Chris
Hi,
is this the time to re-evaluate the output stage design and maybe decide that putting SAPs back in is not the best way to repair?
That many failures tells us something has been skimped. We British did have a tendency to put all else after sound quality, but no sound is never better than some enjoyment.
How about putting in a true darlington pair with separate sinking on the drivers using a little piggy back board to support drivers and the extra resistors/diodes.
is this the time to re-evaluate the output stage design and maybe decide that putting SAPs back in is not the best way to repair?
That many failures tells us something has been skimped. We British did have a tendency to put all else after sound quality, but no sound is never better than some enjoyment.
How about putting in a true darlington pair with separate sinking on the drivers using a little piggy back board to support drivers and the extra resistors/diodes.
Faulty A5 amp up and running
Thanks to elaar for sharing his blues about his faulty A5 Amps. I got an A5 in silver for next nothing with one one channel down. A look inside revealed some blown resistors but no blown fuse. I could very much guess the SAP15P (PNP) was the culprit as the trim and most the resistors in its path were fried, making it even difficult to read the resitor values.
Schematics were impossible to find but I discovered that the power amp is the same as the A300 which has been posted in a thread under A300. (only the the A5 uses SAP15s and not SAP10s) Unfortunately the schematic is for the left side and my amp had blown the right side. Yes they are identical but the part numbering seems to make no sense between identical components. I spent more time deciphering than fixing it.
To cut the long story short I could not find any SAP15s so I went for SAP16s which I replaced plus the trim pot and burnt resistors. I just set the trim to about the same position as the ok channel and fired it up working at the first time of asking. I havent even bothered to measure anything else apart from the DC across the speaker outputs which is less about 4~mV across both channels.
I have had it up and running for 48 hours straight just touching the heatsinks now and again to see that nothing is getting too hot.
Does anyone know the value of R12 which is on the board just behind the RCA connectors by the PRE OUT. (Just behind the heatsink fins its next to a ceramic you cant miss it.)
Its badly fried and with no schematics I have just soldered a 22k on top (too much hussle to dismantle the thing to get under it)
I hope someone can tell me the value of R12 on the A5.
Thanks
Thanks to elaar for sharing his blues about his faulty A5 Amps. I got an A5 in silver for next nothing with one one channel down. A look inside revealed some blown resistors but no blown fuse. I could very much guess the SAP15P (PNP) was the culprit as the trim and most the resistors in its path were fried, making it even difficult to read the resitor values.
Schematics were impossible to find but I discovered that the power amp is the same as the A300 which has been posted in a thread under A300. (only the the A5 uses SAP15s and not SAP10s) Unfortunately the schematic is for the left side and my amp had blown the right side. Yes they are identical but the part numbering seems to make no sense between identical components. I spent more time deciphering than fixing it.
To cut the long story short I could not find any SAP15s so I went for SAP16s which I replaced plus the trim pot and burnt resistors. I just set the trim to about the same position as the ok channel and fired it up working at the first time of asking. I havent even bothered to measure anything else apart from the DC across the speaker outputs which is less about 4~mV across both channels.
I have had it up and running for 48 hours straight just touching the heatsinks now and again to see that nothing is getting too hot.
Does anyone know the value of R12 which is on the board just behind the RCA connectors by the PRE OUT. (Just behind the heatsink fins its next to a ceramic you cant miss it.)
Its badly fried and with no schematics I have just soldered a 22k on top (too much hussle to dismantle the thing to get under it)
I hope someone can tell me the value of R12 on the A5.
Thanks
Hi,
I'd also like to say a big thank you to anatech and AndrewT for helping me with that past repair, for some reason I wasn't notified of your later posts.
You're completely right AndrewT about the design needing to be re-evaluated, if you check ebay as an indicator you will often see a few A5s each week that have the exact same fault as the one described in this post. I blame it entirely on the severe lack of temperature handling. The heatsinks are cheap to say the least and even under moderate listening become extremely hot.
Because of this in the end I have followed anatech's advice and kept the quiescent current low to preserve the amp.
Many thanks,
Andy
I'd also like to say a big thank you to anatech and AndrewT for helping me with that past repair, for some reason I wasn't notified of your later posts.
You're completely right AndrewT about the design needing to be re-evaluated, if you check ebay as an indicator you will often see a few A5s each week that have the exact same fault as the one described in this post. I blame it entirely on the severe lack of temperature handling. The heatsinks are cheap to say the least and even under moderate listening become extremely hot.
Because of this in the end I have followed anatech's advice and kept the quiescent current low to preserve the amp.
Many thanks,
Andy
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