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Old 4th September 2004, 10:10 AM   #1
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Default Raise psu voltage

I have intentions to build this amp because i have got 80% of the components; so, I have 3 simple questions. (see schematic)

For you is a good amp?

what kind of value c6/c7 and c11/c12 can be?

Can i use a psu of +/-68v that i already have? (in the schematic the psu has +/-56v)

regards
D.N.
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Old 4th September 2004, 10:21 AM   #2
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Schematic
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Old 4th September 2004, 03:17 PM   #3
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HI
classic amp with dual diffy-should be OK.
changed rails seem to not change anything, bias will stay unchanged
i guess values of r18 & c8 are swaped
check if components will 'survive' the higher voltage!!!!
especially im not sure about transistors
for higher voltage amplification you may use smaller r13 r14
reconsider the biasing to avid crossover distortion!!!
you have 3x Vbe +Iout x0.22ohm at output stage
so i would use bigger r15 , say 15k
i'm not very much sure about caps but they seem to be compensation only
then they should be some single nanofarads or even smaller

well I may be wrong though, i am a novice so wait for professionals answering your question....

wish you luck with this project
gonna be loud

cheers
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Old 4th September 2004, 05:09 PM   #4
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Default Re: Raise psu voltage

Quote:
Originally posted by m60gpmg
I have intentions to build this amp because i have got 80% of the components; so, I have 3 simple questions. (see schematic)

For you is a good amp?

Yes it'is...is a clone of the Rotel RB980 BX.

Quote:
what kind of value c6/c7 and c11/c12 can be?
I will try something near 100 pF in each.

About the voltage ,do your home work and see if the transistors have breakdown voltages of 140 V for operation with 68 volts rails...and if the dissipation is not to high for them.

Arriverdeci
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Old 4th September 2004, 05:19 PM   #5
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Quote:
Originally posted by darkfenriz

for higher voltage amplification you may use smaller r13 r14
Hi darkfenriz

If you decrease the value of R13/14 you will increase the current in the VAS stage with increased dissipation in U7/8.

I will not touch in R13/14 ....

Regards
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Old 5th September 2004, 07:39 AM   #6
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Thanks for reply.
Another question; how many watt it can push in 8 ohm and in 4 ohm?

Regards
D.N.
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Old 5th September 2004, 12:15 PM   #7
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when not overdriven up to about 250W/8ohm I think
for 4 ohm a bit less then double power, but it would be temperature-risky
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