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β24 in pure class A

beta24

Re: β24 in pure class A

Postby cobretti » November 23rd, 2017, 10:08 am

I would like to know the differences in 1.01 revision.
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Re: β24 in pure class A

Postby amb » November 23rd, 2017, 1:05 pm

cobretti wrote:I would like to know the differences in 1.01 revision.

It has been v1.01 from the beginning, except for the first few boards I shipped which were v1.0. I made a topology change and eliminated a pre-driver stage for the main output MOSFETs because it was making the amp unstable. Those few people that received v1.0 boards were given instructions on how to build the equivalent of the v1.01 design by leaving out some parts and adding some jumper wires. Your β24 should have v1.01 boards.
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Re: β24 in pure class A

Postby shonne » December 1st, 2017, 3:58 am

amb wrote:Yes you're correct. Just build the high-power class AB version but bias the output stage to about 1.4A quiescent. To do that you need to change R25, R26, VR2 and VR3 to the pure class A variant's values. All other parts can remain the same as the high-power class AB version. If you want a max of around 80-100W output then you can reduce the σ22 output voltage to ±30V and the unregulated supply to ±25V.

Note that you will need even more heat dissipation capability due to the higher rail voltages than the lower-power pure class A variant! The dissipation will be about 140W per channel while idling!


with unregulated supply +/-25V, bias 1,4A will be 30-40W in A class, σ22 ouput voltage +/-30V around 80-100W in AB...what will happen if I choose σ22 ouput voltage +/-36V,... more power?
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Re: β24 in pure class A

Postby amb » December 1st, 2017, 4:51 am

shonne wrote:with unregulated supply +/-25V, bias 1,4A will be 30-40W in A class, σ22 ouput voltage +/-30V around 80-100W in AB...what will happen if I choose σ22 ouput voltage +/-36V,... more power?

No, the output power is determined by the unregulated supply's rail voltage (for the output MOSFETs), as long as the regulated supply (σ22) voltage is a few volts higher than the unregulated supply.
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Re: β24 in pure class A

Postby obee » December 1st, 2017, 8:05 am

amb wrote:
shonne wrote:with unregulated supply +/-25V, bias 1,4A will be 30-40W in A class, σ22 ouput voltage +/-30V around 80-100W in AB...what will happen if I choose σ22 ouput voltage +/-36V,... more power?

No, the output power is determined by the unregulated supply's rail voltage (for the output MOSFETs), as long as the regulated supply (σ22) voltage is a few volts higher than the unregulated supply.


If the unregulated power is +/-15v, then is it okay to use +/- 18v regulated DC? Which means 20V AC transformer.
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Re: β24 in pure class A

Postby amb » December 1st, 2017, 2:17 pm

obee wrote:If the unregulated power is +/-15v, then is it okay to use +/- 18v regulated DC? Which means 20V AC transformer.

That's a little too close to the unregulated voltage and will limit your output power. That's why I specified ±24V at the beginning of this thread.
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Re: β24 in pure class A

Postby obee » December 1st, 2017, 7:30 pm

I see, thanks a lot! That's really a lot to know.
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