[Soymilk]

i'm trying to think of some way that i could make it so that when i turn the amp on, the led will slowly light up to full or do a slow pulse once or something like that to give it the sci-fi-ish feel (it'll be lighting up a design on the case). i can't think of anything short of including a microcontroller that controls the led and programming it so that when it gets power it does that though. anyone have any ideas?
 
 
this is going into a cmoy. if i plan on only wall powering it, i shouldnt need to worry about any of the potential issues that may come from the basic virtual ground circuit (just the resistor divider) right? as far as i can see, all the potential problems with the vgnd arise from the batteries not draining at the same rate or something like that, just want to make sure.
 
what would be a good wall wart supply to use? i was thinking of just using the same one as suggested for the ppa on tangentsoft, except that's listed as not available anymore on newark

 

[beerguy0]

Quote:

i'm trying to think of some way that i could make it so that when i turn the amp on, the led will slowly light up to full or do a slow pulse once or something like that to give it the sci-fi-ish feel (it'll be lighting up a design on the case). i can't think of anything short of including a microcontroller that controls the led and programming it so that when it gets power it does that though. anyone have any ideas?
 

 
Put a shunt capacitor after the series current limiting resistor for the LED. t=RC, so just pick a value of C based on the R you select for the LED. Bigger C, the LED turns on slower.
 
A 555 timer could give you a pulsed LED w/o a micro controller, but you will need a handful of parts around the 555.
 

 

[gimble]

An ATMEGA ATTiny would let you do pretty much whatever. You could also use a capacitor for the fade effect - which may or may not affect the circuit at large, and which would not let you come back in and reprogram the behavior later.
 
Wall power is still two voltages not three, unless you're buying a three-voltage supply? Battery drain is only one potential issue. Coming off wall power actually tends to make matters more complicated - batteries are a relatively simple / ideal source other than the drain factor and the power limitations. You should probably still employ a buffered virtual ground circuit instead of relying on a passive voltage divider - the divider will work, but the buffered circuit will be more consistent and reliable while not taking much more effort.
 
For the wall wart, you want a linear regulated supply. MisterX recently pointed out this one on Jameco. There's some question about its status - the specs say linear, the category is switched (you don't want switched), and the data sheet is silent. But it sounded like he had personal experience with it to confirm that it's linear.
 
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_174879_-1

 

[Soymilk]

i was thinking a capacitor might work but im rusty on my electronics so i wasnt sure if it would be feasible or if it would only provide me like a millisecond of fade-in.
 
as for power, should the basic one w/ the rail splitter shown on tangent's site work well enough? i'll just go ahead and order that jameco wall wart; i saw it being mentioned in the other thread asking about cmoy power and they seem to have come to the conclusion that it's linear, and it's not like it's a terribly expensive part to be ordering wrong

 

[gimble]

A cap will give you timing according to the local RC constant. A value on the order of milliseconds or seconds shouldn't be hard to reach. But be careful to consider the implications for the surrounding circuit, and both the initial and final conditions.
 
That wall wart has been pretty definitely confirmed as linear.
 
I'd suggest using something from the "Simple Buffered Virtual Ground Circuits" section. The divider does do the job, but the first several circuits in that section are on the same order of difficulty as what they'd be replacing.
 
http://tangentsoft.net/elec/vgrounds.html

 

[Soymilk]

so if i was to do something like this (sorry for the terrible drawing)
 
http://imageftw.com/uploads/20100908/untitled.JPG
 
that should be fine right? and just to make sure im not doing something dumb with my math, say i wanted a 1 second fade-in and R is 10Kohms, i would just put a 100uF cap in there?

 

[beerguy0]

Quote:

so if i was to do something like this (sorry for the terrible drawing)
 
http://imageftw.com/uploads/20100908/untitled.JPG
 
that should be fine right? and just to make sure im not doing something dumb with my math, say i wanted a 1 second fade-in and R is 10Kohms, i would just put a 100uF cap in there?

It takes 5t (five time constants) for the cap to charge completely. So, if you wanted a 1 second fade in, with a 10K resistor you would use 20uF.

 

[Soymilk]

oh right. man my brain really isnt wired for thinking anymore after finishing school D: thanks.

 

[Soymilk]

i found my box of extra stuff from when i built a ppa a few years back, and i have pretty much i think every opamp that was mentioned as a possible alternative for use in the ppa. i can just use one of these for each channel right?
 

 

[MisterX]

 
Quote:

 MisterX recently pointed out this one on Jameco. There's some question about its status - the specs say linear, the category is switched (you don't want switched), and the data sheet is silent. But it sounded like he had personal experience with it to confirm that it's linear.

 It is, I do and the datasheet is actually pretty clear.
 
The image below contains the schematic (from page 3), the mechanical drawing of the PCB (from page 5) and a portion of the BOM (from page 6).
 
 
 

 

[MisterX]

Oh and I suspect it is listed as a switch mode power supply because it does not conform to the requirements outlined by the energy independence and security act of 2007 but it would not surprise me if I am giving the people at Jameco more credit then they deserve.

 

[cobaltmute]

Quote:

Oh and I suspect it is listed as a switch mode power supply because it does not conform to the requirements outlined by the energy independence and security act of 2007 but it would not surprise me if I am giving the people at Jameco more credit then they deserve.

Considering this is listed as a linear:
 
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_1942788_-1
 
too much credit may be given.

 

[Soymilk]

well that's good news, i wont have to be ordering another one

 

[gimble]

 
Quote:

 
too much credit may be given.

Interesting website, Jameco.

 

[Soymilk]

shipping was $7.50. it cost me less to get a 24" monitor shipped to me >:[
 
 
so for my cmoy, as far as parts go im pretty much gonna follow tangent's parts list, replacing the power cap with a 470uF one and using 2k for R3 for a gain of 6. also throwing in the capacitor with Rled and a second led for the fade-in and more even lighting. need to decide which opamps out of my collection to use though, i have quite the large pile of them. i'll put up a list of what i have later tonight if anyone has any recommendations to be used with a hd555.