[Carlman]

I've just ordered 4 LED's from Allied.  I'm only using 2... I had to order 4 due to their $25 minimum.

I'm getting part number MLED-4390C55/Q which can be found here:
http://www.alliedelec.com/catalog/pf.asp?PreviousCatalog=True&FN=559.pdf

It's listed just below the 'Exit sign' parts.  There's no photo but, it's 3.5 volts, 3mm, and blue.  

Did I just make a mistake and now have ~$25 worth of useless LED's?  Normally I ask first but, thought this might be easier to work backward to get the right resistor to make it work.  

I have a couple of choices with these LED's:

1. To indicate that there is power getting to both channels in the amp.  I really don't care at what point this is indicated... just something that says, "hey, I'm on!"  

2. To indicate that power was making it to the final stage of amplification... saying, "hey, everything is good all the way to the output!"

I think the benefit to 1 is that I would not be adding a potential source of impurity in the signal path to avoid any loss of sound quality.  The benefit to 2 is knowing the amp is operating properly...however, the sound would probably tell me that as well.

I know there are some instructions that come with the amp (which is ordered and will arrive before too long).  However, any input is appreciated.  Especially with resistor values.  In the FAQ section of 'aksaonline' there is a formula but, I don't have like values to compare and/or use... unless I'm missing something.

Thanks for any and all suggestions,
Carl

EDIT... Would this kind of resistor work?:
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F010%5F001%5F001%5F003&product%5Fid=271%2D1131

I can get a few different ones at only .99 each and experiment ... just wanted to see if this was in the ballpark.

[PSP]

Hi Carl,
I have two blue LEDs, one for each channel.  I've wired them between the hot side of the power supply and SPG.  For my LEDs, I want about 1 milliamp of current, since this gives me the right degree of brightness.

So, we have E = IR

E = 36 volts (for a 55w AKSA)
I = 0.001 amp

R = 36/0.001 = 36K

So, you want somewhere around 36K ohms resistance in series with the LED.  To try to reduce any noise from the LED, I wire as follows:

+36v--18Kohm--LED--18Kohm--SPG.

This way neither the positive 36v rail nor the SPG sees any direct noise from the LED, it's attenuated on either side by the 18K resistor.  I have no idea whether or not this is necessary or even if it helps, but I feel better about it this way.

You also have to pay attention to the anode/cathode orientation of the LED, but I'm at work right now and can't remember which way it goes (I figured it out once and have a diagram on my workbench).  Personally I would not put the LED anywhere near the signal... the AKSA is so sweet, you won't want anything getting in the way of the music.

Good luck,
Peter

[Carlman]

I really appreciate your comments.  The formula is starting to sink in now.
Thanks,
Carl

[AKSA]

Hi Carl, Peter,

Peter, my thanks.  Your approach is great!

LEDs are pretty quiet beasts, in fact, and there's no special need to split the dropper resistor.  It's customary to put the dropper on the anode, from the positive supply, with cathode of the LED to ground.  This also means any wiring accidents would limit short current to 1mA, which, if you accidentally put the LED in wrong way around, might not actually destroy it outright.  (LEDs don't handle high reverse voltages well, but if the current is limited, sometimes you can get away with it.)

The blue LEDs vary greatly in efficiency.  I've had blue LEDs which bored a hole in your head at ten feet with only half a milliamp!  So you might like to use a higher dropper to limit current in this case.  On one 55W AKSA I recall using 220K for around 0.16mA!!  

Cheers,

Hugh

[SamL]

Hi all,
Any disadvantage of using illuminated power switch? They are widely avaialable and don't need additonal work.

Sam

[John H]

Hi Carl:

When I connected an LED + dropping resistor across the Positive DC supply and ground as an on-off indicator, it worked fine EXCEPT that, on switching off, the LED did not immediately turn off but, instead, just gradually dimmed until it was off (presumably due to juice still being supplied by the PS capacitors).

This was a source of annoyance to me (but maybe not to you), so I added a diode to the LED + resistor circuit and connected this combination between one end of the transformer AC secondary winding and ground.  Now the LED is off immediately on switching off.

I used a 400V/1A diode (!N4004).  This is tremendous overkill but, what the heck, you can buy 10 for 40 cents!  The value of the dropping resistor was about 2/3 of the value used for the positive DC connection since the voltage applied was less.

The diode was connected with it's anode end connected to the AC, followed by the dropping resistor, followed by the anode of the LED, followed by the LED cathode connected to ground.

Hope this is helpful.

[Carlman]

Thanks for posting your idea, John.  Fading lights probably won't annoy me but, I'll use your idea if they do.  I only plan to turn the amp off maybe once a month or even less for weekend trips.  (Unless that's not the best way to operate this amp.)  

I know this off-topic and I'm hijacking my own thread.... but I'd really like to know:
What's recommended for normal operation?  Can it sit idle (no music) for long periods of time?  Or is it better to turn off/turn on when using?

Thanks,
Carl

[U4EA]

What does SPG stand for?  Star ground?

[John H]

Hi Carl:

Take a look at the Aspen Amplifiers forum of  www.harmonicdiscord.com. On page 3, you will find a post "Any issues with leaving AKSA on "forever"?". Also, the post immediately preceding that one  gives more info about LEDs.

[PSP]

U4EA,

Apologies... yes, SPG = single point ground = star ground

[U4EA]

PSP 10/4....

[Carlman]

Thanks for the reference to Harmonic Discord.  I'm fairly new to AudioCircle so, I forget there was another forum that existed before this one.

For future reference if anyone searches and finds this post, I'm pasting links to the specific threads PSP mentioned, and started, and etc...

LED Primer

"How long can my amp stay powered on?"