Hi, this evening I tried the adjustable power supply for the first time and it seems to work. I adjusted the output just below 17v. Without load attached. One thing that I notice is that the rectifier diodes run quite hot. I can't touch the body more than a second or so. I measured the transformer output 23Vac. Seems high but mains is 235Vac instead of 220. Oh and I converted the pcb to place the primary coils in series. The diodes are mbr1045 and are without heatsink. The regulators stay cool. My question is if this is normal for the rectifiers to run this hot. Greetings, Vincent
Interesting. My rectifiers stay cold and my regulators get hot. That said I have been using the amp now for a few weeks and had no problem. I guess radiators help. My diodes are MBR1045 but my mains are 110V, or probably a bit more.
I've read about that. Interesting indeed. I'm just wondering if this a symptom of an underlying problem. I didn't expect this kind of heat from an idle running low power supply.
without a load drawing current the currents through the rectifiers should be just a few mA to power the regulators. Did you power ON via a Mains Bulb tester? Did the bulb filament glow for a brief period or continually or not at all?
The rectifiers should be cold.
You need to check where the currents are going to make the rectifiers hot.
I suspect an error in the wiring.
235Vac mains is completely normal. Any EU sourced transformer that is supplied for the harmonised EU mains voltage is OK on this. They have to operate correctly and safely from 216Vac to 253Vac.
The rectifiers should run warm when a small output current is drawn. They will run warmer whena higher output current is drawn.
You may require heatsinks if you know you need a higher continuous demand.
Thanks Andrew, I didn't try via a mains bulb tester. I can make one this evening and test. I'll check the transformer with the adapted pcb and post the results.
I tried the mains bulb tester and it lit shortly. Then I swapped the rectifiers with mbr1060's (they were locally available ) and tried again. It lit shortly again but now the rectifiers stay cold. Also when connected to mains directly. So it seems the problem is gone although I don't know why. Haven't tested under load yet but I think it will be fine now. Thanks for the support!
The gain is 10db. See posts 558 and 868 for discussions on lowering the gain (if needed).
Regarding terminology, this is an active preamp, even if the gain is lowered to unity (0 dB). Passive would mean no active devices like opamps.
Question on variable gain - would it be practical to connect the pads for R42 and R45 to a switch that allows 2 or more discrete values to be selected? For example, going to a toggle switch that allows 0 db or 10 db gain to be selected? Or would the length of the wires going to the switch compromise performance?
