Calling all electronics whizzes! [Archive] - Audio & Video Forums


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01-26-2004, 12:24 PM
Hey, I took 2 years of Electrical Engineering in college, but that was in the late 70s and I haven't dabbled much with it since.

I've got a relatively simple project here, needed to solve a little problem.

The problem? Using my preamps to automatically power on my power amps. Up until now, I've just been doing it the old-fashioned way...hitting the front panel switches to power up everything. But I've got a couple of new toys on the way...a pair of Jeff Rowland 201 monoblock amps and they have no front panel switches. They DO have BACK panel switches, but I don't think I want to grope around behind them everytime I turn them on or off.

It would be easy if I just had one preamp, but I use my Lexicon DC-1 for 2-channel and Dolby Digital sources and the Sony for SACD, DTS and DVD-A playback. In the habit of powering on only what's necessary, I'd like to hook up the control circuitry so that if EITHER the Sony or the Lexicon are powered up (or even both at the same time), the amps will get the turn-on signal.

According to the manuals, I've got a 12-volt DC signal coming out of the Lexicon as a control signal. The Sony outputs its signal via a "Control A1" line. When powered on, it puts out a +5 volt signal, but it's really digital. According to this site, ( bits will be transmitted by drops of the voltage to +0 for durations varying from 650 to 1240 microseconds, with a gap of 625us between them. I don't think that's long enough to signal the amps to shut down, but I could be wrong. I measured the DC output at about 4.7volts and it is sufficient to turn the B&K on. I didn't play with any functions that might transmit digital information on the line.

My thoughts are to mix the outputs of the Lexicon and the Sony using resistors as shown in the diagram below. I'm thinking it may also be wise to add a capacitor to the Sony leg. The mixed signal would be fed into my B&K AV5000 Series II power amp which accepts a trigger voltage from 5 to 24 volts. The B&K has a "Control Out" signal of +12V which will be ideal to feed to the Rowland amps via a "Y" connection.

So, here are my questions: Should I use resistors alone, or would diodes also be a good addition to ensure current doesn't flow into the Sony from the Lexicon or vice versa? Any suggestions for values of the resistors? Should I add that capacitor, and if so...your recommendation for it's capacitance? Do you have any better solutions/designs? Any knowledge of amp turn on circuitry? Will a 1.24ms "off" voltage be ignored over by most amps' circuitry?

Thanks in advance!

01-26-2004, 01:56 PM
Just do this here

01-26-2004, 01:57 PM
Pour yourself a beer!

01-26-2004, 06:22 PM
Come on all you high rolling electrical engineers out there. Lets hear what you have to say! Or maybe your not really electrical engineers at all.

01-27-2004, 04:41 AM
Im not an electrical engineer,but I did stay in a Holiday Inn last night!

01-27-2004, 07:04 AM
Just do this here
I think that if I went "digital" with your solution, I'd get slapped promptly in the face. Besides, I need to keep this project totally solid state...I wasn't considering going with mean "tubes".

Im not an electrical engineer,but I did stay in a Holiday Inn last night!Huh???

01-27-2004, 08:31 AM
My bad...but bubes,I mean tubes are warm and fuzzy!

Bill L
01-27-2004, 03:30 PM
Hey, that clap on, clap off thing might work! Could be the smokin' solution!

P.S. Maybe you'll get better response if you ask the wiz's instead of the whiz's!