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Old 14th August 2003, 02:59 PM   #11
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They should be connected between the base and collector as on PCB (if they are necessary at all
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Old 15th August 2003, 03:39 AM   #12
Diode is offline Diode  United States
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Looks like a pretty typical design.

I will say that if you get 300W from only 2 devices per rail, you'll be pretty lucky. I guess you might with a higher voltage 75-90V rails but you had better have a hefty heat sink and fan to cool those poor transistors.

Good luck,

Chris
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Old 15th August 2003, 05:11 AM   #13
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Default OPS

Diode,

I believe the amp uses 4 devices per rail. Thats 8 ops per channel. Q10 to Q13 and Q14 to Q17.

I also think that C6 polarity on the schematic and pcb is wrong.

Am I correct? Or just sleepy....

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Old 15th August 2003, 05:28 AM   #14
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Default C6

JojoD818 got a point!
C6 has to be reversed = "+" to GND and "-" to the -15VDC, otherwise "PUF"
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Old 15th August 2003, 05:26 PM   #15
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Default Bad luck?

It seems this amp has a lot of errors. And I haven't even started yet.

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Old 16th August 2003, 02:34 AM   #16
MGR is offline MGR
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JoJo

At the power supply given you could expect only 80 to 90 watts at 8 ohms and about 130 watts at 4 ohms.To achieve 300 watts you should have at least + and - 82 volts DC.



MGR
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Old 16th August 2003, 03:07 AM   #17
sam9 is offline sam9  United States
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"It seems this amp has a lot of errors. "

yep. The longer I lokk, the odder it looks. For instance it looks like nfb is applied to both the inverting and non-inverting inputs. Add to that the compensation caos (at least I think that's what they are intended be) in ops being possibly in the wrong spot, the rails bearingr little relation to the power implied to the name (unless tha's "music power" x 2 channels), and I would definately make SPICE simulation of it (just to see if it remotely works) before I spent a penny on components.

My interesst lies in the idea of using an opamp as an input stage. The notion is it would make the unit simpler to construct and reduce the pcb "real estate" So far it seems the components that need to be added to get it to work with the discrete stages nearly cancel out the advantages I had imagined.
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Old 16th August 2003, 03:13 AM   #18
Diode is offline Diode  United States
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If I read it right, C6 is the filter for the zener on the negative rail..... Yes, it is backwards! The posative goes to ground and negative to the negative rail.

My mistake, I was sleeping. I see the 4 outputs now..... Yup! It should do. Still, a large H.S. is in order and maybe a fan!!!!!

Chris
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Old 16th August 2003, 09:25 AM   #19
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Maybe I'll just have to find another amp project that uses opamp at the frontend and with a "more realistic" supply rail that can deliver >300 watts.

Any ideas?

JojoD
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Old 16th August 2003, 09:39 AM   #20
sajti is offline sajti  Hungary
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I have only one schematic, but it contains no opamp:

310W/4ohms

There is another one, with opamp, but lower output power:

275W/4ohms

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