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In Reply to: RE: Pardon the 1st grade Bridge rectifier question... posted by Audiodyssey on June 21, 2012 at 10:48:06
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of the whole circuit and tell us what the strange readings are?
Trying to guess what your problem is based on the tiny amount of information you gave is a waste of time.
Recommending a diode without knowing the operating parameters is also a waste of time.
.
Follow Ups:
Ok, see above. I came up with 4.8VDC. I ran the CT through the negative side of a 10,000uF cap...and the cathodes into the positive. I wanted to add another section of filtering as well, but...my voltages were off.My winding is 6.3VAC with CT...2 amps plenty of current for my needs.
Do I need to tie the negative to chassis ground?
"I KNOW you can hear it, but are you REALLY listening?"
Edits: 06/21/12 06/21/12 06/21/12 06/21/12
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Your circuit uses 1/2 the secondary for each half cycle whereas a bridge uses the whole thing on each 1/2 cycle.
The math is 3.15 V RMS for each half cycle so 3.15 x 1.414 = 4.5V peak
minus the diode drop and filtered should get you somewhere around what you got if the line voltage is a little high and/or the secondry a little higher than it should be. Without a load drawing current it will be higher as the xformer is probably rated at full load so the 4.8VDC makes sense.
Use a full wave bridge to get a higher VDC
.
Initially, I had a bridge (I think). There I used four 1N5822 diodes and just left out the center tap. My voltage was at 9VDC which was, well, too damn high. I thought it had something to do with not using the center tap, so I changed the configuration to the full wave rectifier.
I guess I just needed a larger dropping resistor in my bridge? My bridge was positive/neg out with the positive side through a 10,000uF cap, then a .2 ohm resistor, then another 10,000uF cap, then out...
Should my negative side have been to chassis ground??? That was where I was stumped and now I'm thinking it should have been grounded. This was just a dry run on a power supply for my phono preamp...
"I KNOW you can hear it, but are you REALLY listening?"
Ground is irrelevant as far as output voltage. You'll get 9V unloaded, but it will drop under load. How MUCH it will drop will depend on transformer and other losses. Due to the "peaky" distorted current waveform, the voltage drop will be more than you'd expect. You can estimate it with PSUD if you know the winding resistance, etc... here's an example with some guesses...
Voltage is a bit high - maybe 1.0 Ohm would do - but could be considerably different from this model. Current in transformer is about 1.8A. As mentioned, biasing it to a fraction of the B+ voltage (with AC bypass cap to ground) will minimize noise. But just grounding one side of the DC supply may be enough.
Audiodyssey
Use the four 1N5822 diodes
10,000uF - 3R resistor - 10,000uF
It's quieter if you have the negative rail at about +40V.
Use a voltage divider from your B+ to get it.
DanL
Use choke resistance are part of voltage drop & final tune voltage with resistor.
I don't have the real estate for a choke, Neff This is a very small Phono preamp on two chassis, the PS chassis is about 6" x "6"
"I KNOW you can hear it, but are you REALLY listening?"
Edits: 06/21/12
Make it 6 by 8 ....sound familiar DW ??
Jeff Medwin
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