CurtPalme.com Home Theater Forum

[barclay66]

Hi,

Does anyone know why the 10µF caps on the Convergence Amplifier Board have to be high voltage types (250V min.)?
I know, it's how it's shown on the schematics (see below) and how the boards are equipped, but the input voltage is 24V only! Is there any special ripple current requirement or is there a typo somewhere?

Scott?

[Nashou66]

From what Scott told me about the 10uf electrolytics on the same rail is that VDC just might have had a huge inventory of that value and just used them to run inventory down. Probably the same for the film caps.

Nashou

[barclay66]

Hi,

This sounds plausible, especially if you consider that the ceramic caps next to them are rated for 50V only. What makes this explanation less probable is the PCB design. In case of overstocking the wrong caps, the PCB would have been designed for the smaller footprint of the lower voltage caps and the 250V ones would have been squeezed into that place. Also, the schematics would mention the originally designated voltage.
I just want to make sure that I understand the circuit correctly. After all we're dealing with very fast amplifiers and running frequencies up to 1 MHz (my calculation) on an inductive load (convergence coils) can create funny effects...

Regards,
barclay66

[gjaky]

I guess they are because of the high ripple current, we made tests on plain 47uF 25V capacitors on an professional wayne-kerr component analizer and the results showed that the effective capacitance fell to 50% even at 2kHz, and had a resonant frequency at about 600kHz, meaning over that it behaves like an inductor instead of capacitor.

[Nashou66]

Also Chris Stevens use 22uf 50vdc caps to replace the 10uf 250 volt ones.