[lostspyder]

I just got one of my regulators in the mail, assembled it and it helped some to eliminate the drops from my wallwart, so I installed a 4700uf cap over the inputs, and the AC ripple was gone and all that was left was 200mv on both the output of the regulator and the input (they looked identical, only one was at about 18v and the other 10v (what I have the regulator set to)). So why would I want to use a regulator when a big cap looks like it will fix my problem?

Mainly I'm looking at TREAD. Is the advantage only that it is a fixed voltage? Why would TREAD be good for a headphone amp then?

 

[amb]

A big cap helps, but that alone could never match an active regulator wrt. line and load regulation. A good regulator also offers lower output impedance, wider bandwidth and improved transient response compared to a passive cap. The 3-terminal regulator ICs (LM78xx, LM317, etc.), are quite good at a low price, but even better performance could be had with more advanced designs.

By the way, if you still have 200mV of ripple/noise at the output of a regulator then either something is not working right, or your measurement is suspect.

 

[LawnGnome]

Try putting the cap after the regulator.

But 200mv of ripple seems pretty bad. A 15$ computer psu puts out less ripple.

 

[ericj]

Yeah, 200mv of ripple after the regulator is unacceptable. Something is seriously wrong.

 

[lostspyder]

I put the cap in after the regulator and that dropped ripple down to 60-80mv. Im using the oscilloscope to measure it (it spits it out automatically) but cant measure it physically because it is out of range on anything smaller than 500mv/div. It looks about right tho.

Is this what I should be seeing. I'm using a ADP667.

edit: Just realized vin is from 3.5 to 16. Im probably over that with my wallart Could that be it ?

 

[LawnGnome]

Quote:

Originally Posted by lostspyder /img/forum/go_quote.gif I put the cap in after the regulator and that dropped ripple down to 60-80mv. Im using the oscilloscope to measure it (it spits it out automatically) but cant measure it physically because it is out of range on anything smaller than 500mv/div. It looks about right tho. Is this what I should be seeing. I'm using a ADP667. edit: Just realized vin is from 3.5 to 16. Im probably over that with my wallart Could that be it ?

That can damage the regulator.