|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
82.145.216.6
What exactly is the purpose of filter caps in a back to back transformer tube pre amp PSU? I'm building a pre amp using 2x 5670's and the power supply on the schematic uses 2x 12v back to back transformers and 3x 350uF 385v filter caps might that be a bit too much I'm having a lot of earth noise
Follow Ups:
If you're getting hum, it's not from the amount of capacitance but more likely how you have grounded everything. The preamp and power supply grounds should be as close as possible to each other, and as short as possible. Good grounding solves a lot of problems. I suggest you google grounding, ground loops and star grounding.
Also the back to back transformers is just another way to do a 1 to 1 isolation. You could have just used a 240V transformer.
Dan Santoni
Thank you so much for the help guys. So I took all the earth wires out and did the star grounding and replaced the input and output wires with shielded cable it worked like a charm no more noise
Can you post a schematic?
This is the schematic
The negative side of the first 350 uF cap should connect DIRECTLY to the negative side of the recitifer bridge. Keep the ripple current to a loop that does NOT include the chassis. NEVER run any AC current through the chassis - connect power supply return to chassis at LAST filter cap.
There isn't anything particularly wrong with that, though it's not a very efficient setup if you're just supposed to end up with a 1:1 voltage ratio.
Regardless, if you have noise issues, it's related to the actual construction.
The reason for these things are 2 fold. One is that someone got a mess of cheap 12 volt transformers they are trying to use in production. The second is that they are trying to get around UL issues by making it able to use a 12 volt AC wall wort instead of plugging into the wall directly. This seems like the former. I have used this power supply once to build a S. Bench tube tester where you use the 12 volt for heaters. The power supply was supposed to be saggy and tolerant of faults.
Well, If you are using electrolytic polarized capacitors on AC, yes you will have hum because they will be destroyed. The caps are on the DC if you really look. Lots of causes of ground loops. Bad caps might be one, bad design might be another.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: