I'm almost finished building my Pearl phono pre, and I don't understand what I'm measuring w\ the power supply. This is the most involved DIY project I've ever tried, and I getting nervous about toasting either my Pearl PCBs or myself.
I plugged in the PS (built as Wayne described in the plans) before attaching it to the PCBs. I loaded the two DC supplies w\ 4K ohms each, which I figured should draw ~ 10 mA per channel.
Two things seem odd...
1- I'm getting ~ 47 VDC on each channel (DC + to DC -) which is a bit above the 36 - 45 VDC input stated by Wayne for the PEarl PCBs. The transformer is rated at 30 + 30 VAC RMS, so (I think) that should give me ~ 42 VDC. I measured my AC outlet and I'm getting 122 VAC there.
2- I measured the DC + output relative to ground (both PS chassis and phono pre chassis are tied to "earth" ground via 3rd wire from AC outlet). I measured only a few mV DC, but ~ 23 VAC.
It seems like a pretty simple PS, but I'm thinking I did something really wrong.
I plugged in the PS (built as Wayne described in the plans) before attaching it to the PCBs. I loaded the two DC supplies w\ 4K ohms each, which I figured should draw ~ 10 mA per channel.
Two things seem odd...
1- I'm getting ~ 47 VDC on each channel (DC + to DC -) which is a bit above the 36 - 45 VDC input stated by Wayne for the PEarl PCBs. The transformer is rated at 30 + 30 VAC RMS, so (I think) that should give me ~ 42 VDC. I measured my AC outlet and I'm getting 122 VAC there.
2- I measured the DC + output relative to ground (both PS chassis and phono pre chassis are tied to "earth" ground via 3rd wire from AC outlet). I measured only a few mV DC, but ~ 23 VAC.
It seems like a pretty simple PS, but I'm thinking I did something really wrong.
Ren,
To answer your first question about high voltage.... this depends on how your transformer is rated. If it is rated 30 volts at load, expect it to be higher by several volts while at low current draw.
You do not mention if the voltage you measure in the second part is before or after filtering.
Cyclotronguy
To answer your first question about high voltage.... this depends on how your transformer is rated. If it is rated 30 volts at load, expect it to be higher by several volts while at low current draw.
You do not mention if the voltage you measure in the second part is before or after filtering.
Cyclotronguy
Thanks.
I can't easily load the PS any more w\ parts I have on hand... an assortment of 1/4 W resistors. Wayne said the Pearl circuits will draw ~ 100 mA each, which is 10X my dummy load.
The measurments I made are at the PS output. On the Pearl, that means rectified DC w\ 10K uF of filtering. Two more stages of passive filtering and active regulation are on the Pearl PCBs.
I can't easily load the PS any more w\ parts I have on hand... an assortment of 1/4 W resistors. Wayne said the Pearl circuits will draw ~ 100 mA each, which is 10X my dummy load.
The measurments I made are at the PS output. On the Pearl, that means rectified DC w\ 10K uF of filtering. Two more stages of passive filtering and active regulation are on the Pearl PCBs.
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