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nishant's β24+α10 integrated amp build log

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Re: nishant's β24+α10 integrated amp build log

Postby tommarra » November 19th, 2013, 11:57 am

amb wrote:I think the AC voltage reading is a phantom DMM peculiarity (with measuring AC voltage while there is a high DC voltage present).


Okay. So should I still try and change the R25 to 620R?
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Re: nishant's β24+α10 integrated amp build log

Postby amb » November 19th, 2013, 12:12 pm

Try shortening the power supply (and more importantly, ground) wires first. If you're able to then dial-in the output bias and have it be stable, then you're done. If you are max-ing out VR2 and VR3 and unable to get the desired bias, then change those resistors to 620Ω.
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Re: nishant's β24+α10 integrated amp build log

Postby tommarra » November 19th, 2013, 12:22 pm

amb wrote:Try shortening the power supply (and more importantly, ground) wires first. If you're able to then dial-in the output bias and have it be stable, then you're done. If you are max-ing out VR2 and VR3 and unable to get the desired bias, then change those resistors to 620Ω.



Okay let me try that tonight.

Other thoughts on this:

The voltage between V+ and V- under lo load condition is ~ 100V.

I was looking at the spec sheet of the MOSFET and it says that the

V(BR)DSS Drain-to-Source Breakdown Voltage is 100V @ VGS = 0V.

Could it be that at the time of switching on, this is causing the MOSFET to breakdown?
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Re: nishant's β24+α10 integrated amp build log

Postby amb » November 19th, 2013, 12:30 pm

No, the four output MOSFETs on each differential side are in series, each "seeing" only a fraction of the full rail-to-rail voltage.
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Re: nishant's β24+α10 integrated amp build log

Postby tommarra » November 19th, 2013, 12:47 pm

amb wrote:No, the four output MOSFETs on each differential side are in series, each "seeing" only a fraction of the full rail-to-rail voltage.


Got it.
AMB Projects built: B22 (Active ground), S22, S25, LCDunio, D1, D2, A20
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Re: nishant's β24+α10 integrated amp build log

Postby cobretti » November 19th, 2013, 1:12 pm

amb wrote:OK. I still think that maybe the problem is with the wiring to the power supply. Maybe it's too long and is causing the amp to go into oscillation as the bias is turned up.


Yes, there is a chance that's the case. I was experiencing "some" oscillation when playing with σ11 putting output transistors on external heatsink using longer wires. This may be the similar problem. That's also why I was questioning earlier using PSU in external enclosure.
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Re: nishant's β24+α10 integrated amp build log

Postby tommarra » November 19th, 2013, 1:28 pm

cobretti wrote:
amb wrote:OK. I still think that maybe the problem is with the wiring to the power supply. Maybe it's too long and is causing the amp to go into oscillation as the bias is turned up.


Yes, there is a chance that's the case. I was experiencing "some" oscillation when playing with σ11 putting output transistors on external heatsink using longer wires. This may be the similar problem. That's also why I was questioning earlier using PSU in external enclosure.


Okay. I will try running really short wire runs and see if that helps.
AMB Projects built: B22 (Active ground), S22, S25, LCDunio, D1, D2, A20
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Re: nishant's β24+α10 integrated amp build log

Postby tommarra » November 19th, 2013, 5:15 pm

The more I try to simplify the power supply, more it is getting apparent that I need to simplify the whole project.

I think I should have gone with separate power amp and pre-amp configuration. In the integrated scheme I need way too many components and wires in a single box.

So I am taking apart my power supply and re arranging into two separate boxes, one for the power amp and one for pre-amp.

This will also reduce the length of wire runs and simplify the schematics.

Will be a few days before I reassemble everything...
AMB Projects built: B22 (Active ground), S22, S25, LCDunio, D1, D2, A20
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