Hey guys,
I just bought a non-working Carvin DCA 800 from ebay. Anyways, its a really neat amp. One channel has like no gain, pretty much what goes in comes out, and the other channel blows the fuse. I measured the resistance between the +ve supply and ground on the amp channel and it was only 30 ohms or so, easy to see why the fuse blows.
I'm getting somewhere with these boards, but I have a big question. I'm familiar with class A, class B, or at least I like to think so. Now these amp channels each use 6 MJ15003 transistors per channel... That is, they're all NPN. So does this mean the amplifier doesn't use a complementary pair?!? Isn't that strange? Can someone point me to some schematics of amps using non-complementary pairs so I can inspect them.
Any help would be great guys!
Pete
I just bought a non-working Carvin DCA 800 from ebay. Anyways, its a really neat amp. One channel has like no gain, pretty much what goes in comes out, and the other channel blows the fuse. I measured the resistance between the +ve supply and ground on the amp channel and it was only 30 ohms or so, easy to see why the fuse blows.
I'm getting somewhere with these boards, but I have a big question. I'm familiar with class A, class B, or at least I like to think so. Now these amp channels each use 6 MJ15003 transistors per channel... That is, they're all NPN. So does this mean the amplifier doesn't use a complementary pair?!? Isn't that strange? Can someone point me to some schematics of amps using non-complementary pairs so I can inspect them.
Any help would be great guys!
Pete
Hey again,
I just wanted to add a few things. I was looking in Randy Slone's book (High power audio amplifier construction manual) (my bible). And out of list of availible output stages, I'd have to say this must be class A single ended. Is there such thing as class B single ended? I really doubt it since it would only output half the signal! Is there such thing as a push/pull (complementary) stage (of whatever class!) using all the same transistor? I don't think so. Man this is a tough one.
Pete
I just wanted to add a few things. I was looking in Randy Slone's book (High power audio amplifier construction manual) (my bible). And out of list of availible output stages, I'd have to say this must be class A single ended. Is there such thing as class B single ended? I really doubt it since it would only output half the signal! Is there such thing as a push/pull (complementary) stage (of whatever class!) using all the same transistor? I don't think so. Man this is a tough one.
Pete
If you have Slone's book - have a look at his diagrams for the BJT Quasi-Complementary output stage.
Your OPS most likely has a PNP driving an NPN (Complementary feedback pair) and an NPN driving an NPN (Emitter follower, full darlington connection) on the opposite rail.
It is indeed possible to have a push-pull class B output stage with only NPN transistors.
Consider the fact that tubes only come in "N" type devices, and they've had push-pull class B tube output stages since before I was alive.
Your OPS most likely has a PNP driving an NPN (Complementary feedback pair) and an NPN driving an NPN (Emitter follower, full darlington connection) on the opposite rail.
It is indeed possible to have a push-pull class B output stage with only NPN transistors.
Consider the fact that tubes only come in "N" type devices, and they've had push-pull class B tube output stages since before I was alive.
Ok I hate to be a mega poster but...
I just read about the Quasi-complmentary OPS. This appears to be a class B output stage using NPN transistors only! It requires complementary predriver transistors, and it appears that my amp uses RCA1C13/RCA1C12 for that (although there's also TIP31C and TIP32Cs on the board).
Neat!
I just read about the Quasi-complmentary OPS. This appears to be a class B output stage using NPN transistors only! It requires complementary predriver transistors, and it appears that my amp uses RCA1C13/RCA1C12 for that (although there's also TIP31C and TIP32Cs on the board).
Neat!
http://www.diyaudio.com/forums/attachment.php?postid=71431
If the 100µF cap in the feedback loop is open the amplifier will have unity gain.
If the 100µF cap in the feedback loop is open the amplifier will have unity gain.
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