http://www.national.com/pf/LM/LM3915.html
http://www.qtopto.com/displays/d0402m3.pl5?MV5C164&MV5y164.pdf&191

Wiring them up is pretty simple normally, all + LEDs wire to voltage and all - wire to individual pins on the 3915s. By default the ICs are set for line level audio, just add the resistor of your choice to pick the current for the LEDs and you're done. I wired them so all 20 LEDs lit plus both ICs takes 12mA.

Then I discovered the LEDs I got were BACKWARDS! The anode/cathode config made the array from 1-10 being amber/red/green. So I had to reverse hook them or send them back. I braved the iron and did it myself. Talk about soldering practice! (stripping and tinning 20 tiny wires was the hard part actually)

I will never use perfboard again. Well, at least not the kind without pads. This stuff sucks to solder on, if you make a good electrical connection the component might still be loose because there's nothing to make it stick to the board. I ended up making it structurally sound by globbing up solder on the leads. Just like those example photos of how NOT to solder.

Luckily I had some 20-pin sockets from another experiment I'm doing (digital pots - more later) because the channel for where the control board would mount wouldn't have made the LEDs even close to flush with the panel. The socket was the perfect height though, the arrays ended up being 1/16" from the front of the faceplate.

After cutting out a 1x1" hole in the faceplate carefully (measure twice cut once) I got some smoked gray transparent sticky film from an arts & crafts store. 1 yard of 3' wide was $1.29. It looks just like film for tinting car windows. It sticks once and that's it so position carefully! I got it right on the 2nd try and trimmed the edges. Damn, that looks sweet! Total cost, $12.00

I only ran into one problem wiring it up. The volume pot makes the signal drop even though it's spliced into the line in before the pot. Ugh. Knowing that a diode would fix it, I tried a few different ones and stuck with 4002s. But THEN the diode is dropping voltage and the LEDs are lighting lower. I know I could have solved it mathmatically but ole newbie Apheared did the brute force method - I stuck in my test tone CD, hooked up the voltage reference/bias pin via a pot, and "calibrated" it. Then measured the pot and stuck in the nearest value resistor. It's probably not accurate at all... but hey, it's just for "ooh aah" factor anyways :)

Do you sleep ?

I am almost afraid to think about what you will come up with next ( I can see it now, a headphone amp the size of a suitcase strapped to the top of a generator to recharge a battery pack the size of a lunchbox,all on wheels with a handle to pull it along-or maybe have the generator power a small engine to drive the wheels-----or maybe also add some type of motion sensing unit so it will follow you,or maybe.........)

Just kidding dude,nice pictures-cool design

BTW-a few years ago Radio Shack carried a module that combined the chip and display,cost was about four bucks.you could get either a vertical or horizontal display.

Just cut a hole,wire it in,project done.

I do not even know if National makes these any more but I used to put'em in everything.My system got to be VERY distracting.

Now I just put a simple LED on the front panel and look to eliminate stuff ,including stages-I have become a member of the KISS Club (Keep It Simple Stupid) for better or worse.

Funny thing is-you are just getting into the DIY thing and you are still at the "build everything I can" stage.

Been there done that,and had lotsa fun in the journey-not to mention the education gained

Enjoy

Rick

You said "just add the resistor of your choice to pick the current for the LEDs and you're done. I wired them so all 20 LEDs lit plus both ICs takes 12mA." What resistor value did you choose?

There are three on the bench right now, my hybrid 4-headwize-projects mic preamp/mixer/limiter/amp, experimenting with getting toggles mounted for digi pots, and because I missed out on all the early days of this stuff I'm doing greg's ifr510 in a bulky "old school" metal project case with big-assed knobs and neon panel light and stuff. Right now it looks like a bench supply. I want to do a discrete opamp stage for gain, but I'm kinda glad I don't have to if I get lost. (as soon as someone specs a component, it's gone)

Chu, I think the led res was 1.2k. I did this last week or so (see it's still got that linear Piher pot?) It's buttoned up but I'll look. the V ref res also affects the led current and I kept tinkering... I wasn't too worried about power, c'mon it's 16 AA batteries. I just did it until I liked the brightness, and it just ended up being 18mA (12mA was a foobar). Also not mentioned was I had to bypass the +12, the bottom 2 leds kept staying lit.. noise. I thought I'd have to couple the input but just bypassing got rid of it (or at least lowered it so the leds stay off with no signal)

Now here's the question: Did I do it correctly? Is this normally how you'd add additional circuits to something? I thought stealing the power from the batteries might have made it sound different, and I also thought that tapping into the signal to get the feed for the VUs would alter the sound. Neither seems to be true... but would you normally build separate stages with regulators? and stealing signal, should I have buffered it with an opamp and stolen it from there? Another opamp before the gain stage to power the meter? I also thought I might fry something by taking power from only the +12 side and ground, cause it's virtual anyways... but hooking it to -12 didn't do anything so it had to go to ground. (My only references were a few web pages and the 3915 datasheet)

I'm lost, but hey its fun.

Since the meter is not in the actual "listening loop" you need not worry about how the input op-amp sounds.

Instead look for something with ultra low current use and a VERY high input impedance.You probably can use 1 meg ohm input resistors and then bandwidth limit the op-amp to 'audio frequencies"

Maybe even a bass cut in the meter response.I seem to remember from past experience with this type of circut the same problem with LEDS always on,but it stopped when I limited the bottom end to 50hz or so.

Matter of fact I think I used the ol' 741 op-amp and used it as a banpass filter with a high input impedance.To do this simply scale the R/C values shown on the datasheet

Still looks pretty cool though

Cheers

Rick

I was actually going to be using the VU for a mic preamp (originally a simple clipping indicator) that's still waiting in line, and then the gadget fetish set in and the amp was looking a little lonely. Good to see it works out!

If you want yet another project idea piled on top, a good DAC would be an interesting addition to a headphone amp. A high quality DAC combined with a AD825 based amp (and associated quality parts) would be a great unit. It's unfortunate that the DAC designs I've seen end up around $150 or so - I tend to funnel most funds to another hobby, a coral reef aquarium. A world where the lighting system was a steal at $450... :)

Have fun exploring! And keep us up to date, of course...

-Nikhil

Hame based is easy but portable gets tricky.

In order to keep down the weight and complexity a single power supply is called for,but you really want separate power supplies and grounds,at the MINIMUM isolation circuts are needed to decouple as much as possible ( keep digital noise outta the analog section ).

Then there is the DAC chip itself (input receiver and digital filter will work off 5 volts).

Low current/low voltage DAC chips are hard to find,but not impossible.

I just received two Analog Devices AD1861 DAC chips that spec out good for portable use.

Sound quality ?

Who knows,but I like AD parts so anticipation is high

All I need to do is GET TO THE #$#%^& THING !

But when I do,will post results (of course )

Prelim :

CS8412 input receiver,ZERO OVERSAMPLING ,passive filter to OP-275, or microphone transformer output

Hoping for the best but still should see improvement over portable (home ?) CD player DAC

Fingers crossed

Where did you buy that chip? Digikey lists it as an "obsolete item"... is there a replacement for it? Also, does anyone have more information on the radio shack kit? It seems like every thread has the line "a few years ago, radio shack used to carry it"

But all is not lost !

radioshack.com to the rescue,and yes the above parts are available

http://www.radioshack.com/ProductCatalog/ProductDetail/Index/1,2098,CTLG_7_9006841,00.html

and

http://www.radioshack.com/ProductCatalog/ProductDetail/Index/1,2098,CTLG_7_9006147,00.html

radioshack.com also carries a fairly extensive list of op-amps,no Burr-Brown but plenty of choices from Analog Devices,Linear Technology,National

Still no AD825 or LM1671 but we can hope ,nice site in a non pdf format,very clean and easy to navigate

Bad thing is Digikey has no pulse transformers in stock yet, and they're the only distributor for this company. Arrrgh!

I got it because I am trying to make a portable DAC/Headphone amp combo and this looks like a good solution due to the voltage/current requirements and the output stage is built in.

The other DACs in contention are the AD1866,a dual 16 bit and the AD1868, a dual 18 bit design.Both operate on a SINGLE +5 volt supply.

Options,always options.

For home use/main DAC I am leaning towards the AD1865 @ 18 bits,also a dual DAC chip.

But this stuff can be a bi*ch to DIY from scratch so the going is slow

BTW-Sheldons designs are real nice,he put a lot of time into those designs (PCB layout etc) .I just chose a different path,as usual !

Good luck with the DAC

Rick

I am looking for quality, not portability in this case.

Btw, what's wrong with Digikey? They seem pretty quick to me (2 days to Canada!) - as long as the stuff is in stock. Well, true, frequently the most useful stuff like parts in TO-220 case instead of some exotic one or DIL instead of SMD is "0 - backorder - we will have it in 4-5 months"...

Sheldons designs look like great price/performance. In this case I love the fact that I can reuse these very expensive chips later if I want to go to more refined (hideously expensive) design. One I've seen uses 7 (*SEVEN*) Jung super regulators, with AD797. Can you imagine price just for those AD chips? I will have to use something else instead. There was a comment where one guy sais "you can use NE5534 instead but I noticed that transients are not as good". Well that's great, but I will have a "transient" into bankruptcy if I use that. If you *really* need high bandwidth for a voltage regulator, why not put OPA132 or LM6171, they cost much less. Of course, I am going to do some analyzing before doing any substitutions, maybe there's something about 797 that's unique (other than price).

BTW-at the TNT website there is a project for a phono stage preamp modeled after the Lehman Black Cube

One of the supply options uses an OP285 as the feedback element with a series pass transistor.Maybe a good substitute

Digi-Key

Great service if they have what you need but it seems that everything I need is always "backorder" only or even obsolete.

Even obsolete is not a problem if enough were on hand to begin with.

But trying to find alternate sources is extremely frustrating and time consuming.Takes the FUN out.

When I get an idea I want to act on it now or,being me,I walk away.If I wait too long I'm on to other things or lose interest entirely.

As for DAC quality VS portability,yes there are tradeoffs,and as I said this is not to be my main DAC.

But there is definately a black hole where portable DIY DACs are concerned so I figured I would take a crack at it.

Not overly fancy or state of the art but maybe something usable,something that would for a low price be an upgrade of the built in DAC of portable Cd players with digital output.

Better yet just to see if I can do it !

Rick

P/S just doesn't look like an application where any of that stuff would be so extremely critical to warrant using a superamp. It's like killing a bug with a (plasma) cannon. What's important? Bandwidth, maybe. Noise? Well there's so much ripple that your added noise is a joke. Offset? Seems unlikely. But I am not going to pretend I know everything since I haven't even read the original article (got no 50 bucks to get the 1995 year of Audio Amateur). When I have time I am going to look into it and maybe even buy a good book on P/S design. The stuff is interesting.

Portable DAC indeed is an uncharted territory for DIY. I found a lot of DIY on DAC's, more than even headphone amps, but none portable. Since I haven't seen CD players with digital out I don't know how are you going to use it but good luck!

As stated the instant someone says "get this" it's freaking gone. 4 weeks ago they had hundreds of them. Try calling em, chances are they still have em unless someone with production needs discovered they were going bye-bye and bought em all. the National site still lists them as full production, and the obselescence file shows that LM3915N-1 will replace it.