Building a symmetrical psu B1 buffer

[Salas]

Yes, you know there is some variety of small off pcb ''wing'' light mass sinks like those they clip on LM317s. Some have only a clip, some only a hole, some both. Just to aid the CCS Mosfet that will carry the whole current all the time. But even a rectangular aluminum cut out will do. Is there capacitive coupling between the DCB1s and the input to LM318s?

[matt09]

I wasn't going to put any where they aren't necessary because the power amp output has a power on relay delay. I think I'm good to go with a single cap at each respective input to the dual preamp setup I'm using?

[Salas]

If the amp has output protection, then its a fortunate situation. Just measure its output on a dummy and see there is no DC during on/off (and for a little while after off) when all B1 driving is integrated. Must be switched from a main rocker as a whole. Does it sense DC also? If it does and its reliable, then you can rely on it even if one DCB1 rail ever fails and gives DC on output. If not, better ac couple to LM318s.

[matt09]

Yes it does, the audiophile design chip amp by Maurio is the best fully featured design in that forum probably. Could I even go with no caps at all as there is no dc offset at switch on from my source?

Thanks

[Salas]

If the output protection will reliably work always, Its a calculated risk for you to take. Are the speakers expensive?

[matt09]

Not hugely both sets are under £500 in total, I'll think it over

My transformer for the superregs with the 318 is a little high for this circuit in voltage, I wont lose anything in preregulating with a zener or 317/337 to attain the right dc voltage for the pre will I?

Many thanks

[Salas]

More circuitry is more circuitry. But its a solution. +/-17V is what needed for DC in to the shunts. 317s need 2.2V minimum headroom not to drop out regulation, remember.

[regiregi22]

Matt, what have you thought for controlling volume? I am going too with a DCB1 (already built) and a MyRef_C, will be using a Lightspeed attenuator before the DCB1.

[wintermute]

Originally Posted by Salas

More circuitry is more circuitry. But its a solution. +/-17V is what needed for DC in to the shunts. 317s need 2.2V minimum headroom not to drop out regulation, remember.

True, but the Datasheets quote Vin - Vout >= 3V for the rated load regulation specs (as well as others) so that to me implies you need to allow 3V margin for them to operate "within spec" even if the dropout margin is lower... certainly I found recently when simulating for the LM317 circuit I'm designing that I needed a higher voltage than I thought I would to get the results I expected.

So to be on the safe side (and to make sure your LM317 is actually being of some use), I'd add an extra 3V for your LM317 on top of what the shunt needs

Tony.

[AndrewT]

you also need to add the ripple coming from the PSU. In fact you measure the average and you actually need to add half the ripple peak to peak to find the lowest voltage in the trough of the waveform.