off the topic solid state amp kit vu question

[9 volts]

Hi there, I found and old solid state amp kit. Preamp has four inputs so it's great for my keyboards. The power amp looks similar to a silicon chip sc480 circuit, running on 40- and 40+ voltage (50 watt I think). The preamp runs on about 16+ and 16- volts. (this is all working). My question is that there are also some led vu's on the front. These work when I test with an independent power supply (a 9 volt battery) and I know they work up to a voltage of 15 volts. I just can't work out how to connect these to the amp power supply. When I feed the voltage from the preamp positive rail, the voltage drops on the preamp. I experimented with pulling the voltage from the power amp positive rail and then through a 5 watt 150ohm resistor to a 7805 regulator. This works but the 5 watt resistor seems to get very hot. Does anyone have any suggestions for a better solution.
I know this is off the topic (stomp box- sorry), but I I've always found some help and knowledge here. Thanks

[duck_arse]

how do the +/-16V's arrive? are they resistor dropped from the +/-40? do they feed 12V regs for the preamp? if so, take your newly recalculated dropper resistor from the 40V line instead of the 16V. and if you were to run the leds thing on a 12V supply instead of a 5V, you'd have a bunch less volts to drop, to cause heat and stress.

[9 volts]

16 volt from drop down resistors. I've just bought a LM2596 kit to try.

[duck_arse]

if you clump the extra load of all the leds onto the resistor that thinks it's dropping just for the preamp drain, the V will sag.

[tubegeek]

Ideally you would power the LEDs from the main power rails (or a lower supply derived from the main rails separately) and not the same rails that the preamp is using - you may get noise in the audio circuit as the LEDs switch on & off abruptly.

[mykaitch]

Hi. Go on Ebay and look for DC to DC converter. I just bought one at 1.49 incl pp.
Use the +40 and adj the out for what you need, 5v I guess.

[9 volts]

Thanks that's what I have bought. (dc to dc) This should solve the problem.
In the meantime I managed to blow an output transistor (no big deal) while experimenting with the original wiring. This was a second separate rectifier to a 7815 coming off the secondary wiring of the power transformer. (original owners attempt at getting the power). Two rectifier circuits from the secondary wiring, is this ever done? Seems to have been the original problem with the amp Current drain? Thanks again.