[Anthrox]

Although I'm starting to take electrical engineering in university my experience with electronics currently only extends to high school courses and modding a few consoles.

I was wondering how hard it would be to add a circuit that would activate on a signal from the input jack (ie. music starts to play) and turn off when it stops (maybe a few seconds delay so it doesn't turn off at the slightest pause?). Also, blue leds seem to come only at a higher voltage and I'm not quite sure how that affects the accompanying resistance i need for it. Also can i simply skip the volume control since my music device has one already? From the diagrams on audiologica it seems like itd be pretty easy to eliminate the potentiometre. Can I simply remove it or do I now have to add something to compensate? I'm hoping to make the amplifier as unobtrusive as possible. Haven't decided on a casing yet.

Here are the parts I currently have selected from digi-key based on suggestions from http://tangentsoft.net/audio/cmoy-tutorial/ should I change/add any? Are 0.1% resistors worth it? I saw in another post that a poster recommended different faraday/voltage ratings, should I be using different ones as well? I'll probably try to pick up the board from the source.

Index Quantity Part Number Description Customer Reference Backorder Quantity Unit Price Extended Price
1 2 P5552 CAP 220UF 35V ELECT NHG RADIAL 0 0.53000 $1.06
2 2 P3104 .1 UFD POLYPROPYLENE CAP 0 1.09000 $2.18
3 5 10.0KXBK RES 10.0K OHM 1/4W 1% METAL FILM 0 0.13600 $0.68
4 5 4.75KXBK RES 4.75K OHM 1/4W 1% METAL FILM 0 0.13600 $0.68
5 5 100KXBK RES 100K OHM 1/4W 1% METAL FILM 0 0.13600 $0.68
6 5 1.00KXBK RES 1.00K OHM 1/4W 1% METAL FILM 0 0.13600 $0.68
7 2 CP-43502PM CONN JACK AUDIO 3.5MM 4COND 0 4.66000 $9.32
8 1 OPA2227PA IC DUAL PRECISION OPAMP 8-DIP 0 5.00000 $5.00
9 1 67-1748-ND LED 3MM BLUE/BLUE DIFF LENS 0 2.82000 $2.82
10 1 296-6548-5-ND IC 1/2 RAIL VIRTUAL GRND 8-DIP 0 1.64000 $1.64

(prices are canadian if they seem off)

 

[Pars]

Quote:

Originally Posted by Anthrox Although I'm starting to take electrical engineering in university my experience with electronics currently only extends to high school courses and modding a few consoles. I was wondering how hard it would be to add a circuit that would activate on a signal from the input jack (ie. music starts to play) and turn off when it stops (maybe a few seconds delay so it doesn't turn off at the slightest pause?). Also, blue leds seem to come only at a higher voltage and I'm not quite sure how that affects the accompanying resistance i need for it. Also can i simply skip the volume control since my music device has one already? From the diagrams on audiologica it seems like itd be pretty easy to eliminate the potentiometre. Can I simply remove it or do I now have to add something to compensate? I'm hoping to make the amplifier as unobtrusive as possible. Haven't decided on a casing yet. Here are the parts I currently have selected from digi-key based on suggestions from http://tangentsoft.net/audio/cmoy-tutorial/ should I change/add any? Are 0.1% resistors worth it? I saw in another post that a poster recommended different faraday/voltage ratings, should I be using different ones as well? I'll probably try to pick up the board from the source. Index Quantity Part Number Description Customer Reference Backorder Quantity Unit Price Extended Price 1 2 P5552 CAP 220UF 35V ELECT NHG RADIAL 0 0.53000 $1.06

I'd use 470uf instead
Quote:

Originally Posted by Anthrox 2 2 P3104 .1 UFD POLYPROPYLENE CAP 0 1.09000 $2.18

Use 0.22uf or 0.47uf for better bass response, or if your source does not have any (or very low) DC offset, you can omit the input caps. If you go larger, check their physical size!

3 5 10.0KXBK RES 10.0K OHM 1/4W 1% METAL FILM 0 0.13600 $0.68
4 5 4.75KXBK RES 4.75K OHM 1/4W 1% METAL FILM 0 0.13600 $0.68[/auote]You have a rail splitter below, do you need these for gain resistors?
Quote:

Originally Posted by Anthrox 5 5 100KXBK RES 100K OHM 1/4W 1% METAL FILM 0 0.13600 $0.68 6 5 1.00KXBK RES 1.00K OHM 1/4W 1% METAL FILM 0 0.13600 $0.68 7 2 CP-43502PM CONN JACK AUDIO 3.5MM 4COND 0 4.66000 $9.32 8 1 OPA2227PA IC DUAL PRECISION OPAMP 8-DIP 0 5.00000 $5.00 9 1 67-1748-ND LED 3MM BLUE/BLUE DIFF LENS 0 2.82000 $2.82

I'd use a 5mm LED, but its your choice. 3mm LEDs are pretty small and mounting them might prove fun
Quote:

Originally Posted by Anthrox 10 1 296-6548-5-ND IC 1/2 RAIL VIRTUAL GRND 8-DIP 0 1.64000 $1.64 (prices are canadian if they seem off)

And yes, you can build this without a volume control, although you might want to order 1 of the Panasonic pots just in case, as Digikey is the only place you can get these, and they have a minimum order. The auto on I don't know exactly how you might do that, but it would probably involve another opamp as an AC comparator or something like that. The delay would also involove some additional circuitry, as well as some means of actually turning the power on/off. The blue LED will require less resistance... 4.7K usually works well for me. There are some LED resistance calculators on the net; you could probably do a search here to find one.

 

[Anthrox]

1 2 P3104 .1 UFD POLYPROPYLENE CAP 0 1.09000 $2.18
2 5 10.0KXBK RES 10.0K OHM 1/4W 1% METAL FILM 0 0.13600 $0.68
3 5 100KXBK RES 100K OHM 1/4W 1% METAL FILM 0 0.13600 $0.68
4 5 1.00KXBK RES 1.00K OHM 1/4W 1% METAL FILM 0 0.13600 $0.68
5 2 CP-43502PM CONN JACK AUDIO 3.5MM 4COND 0 4.66000 $9.32
6 1 OPA2227PA IC DUAL PRECISION OPAMP 8-DIP 0 5.00000 $5.00
7 1 67-1748-ND LED 3MM BLUE/BLUE DIFF LENS 0 2.82000 $2.82
8 1 296-6548-5-ND IC 1/2 RAIL VIRTUAL GRND 8-DIP 0 1.64000 $1.64
9 5 4.75KXBK RES 4.75K OHM 1/4W 1% METAL FILM 0 0.13600 $0.68
10 2 AE7313 IC SOCKET .300 8 DIP GOLD 0 1.17000 $2.34
11 1 BC2076-ND CAP FILM MKP 1UF 63VDC 2% 0 1.83000 $1.83
12 1 2238K STRAP BATTERY 9V I-STYLE 4"LEAD 0 0.58000 $0.58
13 1 P10275 CAP 470UF 25V ELECT FC RADIAL 0 0.72000 $0.72

Here's an ever so slightly updated list. I took off the 4.75k resistors then realized that I would need one for the led anyways. Holding off on the 5mm led until I actually see the size difference in person to make my judgement. Changed the 220uF cap to a 470uF. Also added sockets for the ICs. Tangent seems to add a 1 uF cap (labeled cnr) for the rail splitter implementation so I added one of those as well, although I'm not entirely sure I added a cap with suitable specs other than the 1uF part. I'm going to wait to see what other parts I may still need before adding a panasonic pot just to avoid handling costs.

I tried measuring the dc offset with a fairly cheap digital multimetre. It gave me a fairly constant 3mV at the highest gain. Although I'm not really sure what to do with that info

Still hoping to avoid using an on/off switch although if the added circuit would seriously detriment battery life or sound quality I'd rather have an extra switch on the box. I guess I'll peruse the web a bit for something like that, but what I'll find will probably make my head explode.

I'm thinking of a silver/metallic casing for my cmoy but I have no idea where to aquire one.

 

[tangent]

Quote:

Originally Posted by Anthrox I was wondering how hard it would be to add a circuit that would activate on a signal from the input jack

I don't have a specific circuit in mind, but my initial impression is that it wouldn't be seriously difficult to design. I'll give it some thought.

Quote:

maybe a few seconds delay so it doesn't turn off at the slightest pause?

That part's easy. The hard part is making it sensitive enough that it will turn on quickly with music that comes up slowly: it has to be sensitive, but not so sensitive that it refuses to turn off, such as due to noise and such.

Quote:

Also, blue leds seem to come only at a higher voltage and I'm not quite sure how that affects the accompanying resistance i need for it.

The Ohm's Law derivative I give here still applies. The only thing that changes is the LED's brightness vs. current behavior. Blue LEDs tend to be a little less efficient than traditional red, amber and green ones. At most, it's a factor of 2x: halve the resistor that you would choose for a red LED and it'll be bright enough.

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Are 0.1% resistors worth it?

No.

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different faraday/voltage ratings

The unit of capacitance is indeed named after Faraday, but it is called the "farad".

 

[Anthrox]

Quote:

Originally Posted by tangent I don't have a specific circuit in mind, but my initial impression is that it wouldn't be seriously difficult to design. I'll give it some thought.

It would be greatly appreciated if you could make some sort of circuit or direct me towards at least how to search for that type of circuit.

Quote:

The unit of capacitance is indeed named after Faraday, but it is called the "farad".

Ooops. Thought it sounded a bit weird.

On your site you show a schematic for using a rail splitter and there's, what I believe to be, a capacitor with a 1uF capacity. Since there's no polarity is it supposed to be one of those small ceramic ones (i think i remember those having no polarity), and is BC2076-ND CAP FILM MKP 1UF 63VDC 2% 0 1.83000 $1.83 suitable? There are so many different options on those parts sites it makes me dizzy.

Also, what would an led mount like the one in this picture be called? http://www.runty.net/kitty2.jpg

 

[ATAT]

I believe any nonpolarized caps (pretty much non-electrolytic) work as long as they're 1 uF... $1.83 sounds expensive.. i think you can get away with cheaper.

 

[Anthrox]

Quote:

Originally Posted by ATAT I believe any nonpolarized caps (pretty much non-electrolytic) work as long as they're 1 uF... $1.83 sounds expensive.. i think you can get away with cheaper.

how about this?

10 PCC2354CT-ND CAP 1UF 25V CERAMIC 0603 X5S 0 0.21100 $2.11

unfortunately for the cheap caps, you have to buy em in bulk. 10s the smallest. it only get bigger from there.

 

[tangent]

Quote:

Originally Posted by Anthrox It would be greatly appreciated if you could make some sort of circuit or direct me towards at least how to search for that type of circuit.

I did some work on it this morning, but ran out of time to finish it. My idea is to run the audio input to a precision rectifier circuit: two op-amps, two diodes, and a few resistors. (Google for examples.) Then run that to a smoothing circuit: 1M resistor in series with any 0.1uF cap. This turns AC voltage into a fairly flat DC analog. That much is working fine here.

What I didn't have time to do next is handle the scaling and threshold detection. Throughout this process, I had in mind to use either a quad op-amp package, or two duals, so I have plenty of parts left to implement this. The scaling is just a gain issue, and the threshold detection will involve using the final op-amp as a comparator, possibly with some hysteresis. The comparator output will drive a pass MOSFET to control power to the amp.

The only real unresolved issue is choosing the op-amp. You'll want a really low-power unit here, because it will be powered all the time.

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is it supposed to be one of those small ceramic ones (i think i remember those having no polarity)

Only electrolytics and tantalums are polarized. But yes, for this task, a ceramic should work just fine.

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what would an led mount like the one in this picture be called?

Um, "ugly"?

 

[steinba]

Quote:

Originally Posted by Anthrox It would be greatly appreciated if you could make some sort of circuit or direct me towards at least how to search for that type of circuit.

I'd guess it would be possible to apply some (5-6 pin) shorting jack and a relay of sorts to operate a power switch. ...Or am I assuming something impossible?

 

[Anthrox]

Quote:

Originally Posted by tangent I did some work on it this morning, but ran out of time to finish it. My idea is to run the audio input to a precision rectifier circuit: two op-amps, two diodes, and a few resistors. (Google for examples.) Then run that to a smoothing circuit: 1M resistor in series with any 0.1uF cap. This turns AC voltage into a fairly flat DC analog. That much is working fine here.

It seems that analogue devices has the ad736/737 which will act as a precision rectifier circuit and from what I gather, runs at fairly low voltages (although I don't know whether these are low enough).
http://www.analog.com/en/prod/0,2877,AD737,00.html

Quote:

What I didn't have time to do next is handle the scaling and threshold detection. Throughout this process, I had in mind to use either a quad op-amp package, or two duals, so I have plenty of parts left to implement this. The scaling is just a gain issue, and the threshold detection will involve using the final op-amp as a comparator, possibly with some hysteresis. The comparator output will drive a pass MOSFET to control power to the amp.

Now you've COMPLETELY lost me

although this is sounding like it'll make the circuit a lot larger than an altoids tin can contain?

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Um, "ugly"?

I can't help it. It's my asian intinct kicking in. Anything shiney or blue.

 

[Pars]

Quote:

Originally Posted by Anthrox Now you've COMPLETELY lost me although this is sounding like it'll make the circuit a lot larger than an altoids tin can contain?

Unless you can find an IC in about an opamp-sized pkg (or SMT) that does all this other than perhaps the MOSFET, that was pretty much a given from the start, I would think

 

[Anthrox]

oops double post

 

[Anthrox]

Quote:

Originally Posted by Pars Unless you can find an IC in about an opamp-sized pkg (or SMT) that does all this other than perhaps the MOSFET, that was pretty much a given from the start, I would think

well i initially got the idea for the auto-power on/off from a cmoy amp i saw on ebay which was fitted into a circular altoids can. So i figured it was possible, if not i'll probably just go with the smallest switch i can possibly find.

 

[tangent]

Quote:

Originally Posted by Anthrox Now you've COMPLETELY lost mep

Trust me, this really is not a complex circuit I'm proposing. Give me a few more days to get back to it.

Quote:

this is sounding like it'll make the circuit a lot larger than an altoids tin can contain?

It shouldn't be that big. About the same size as a CMoy circuit. Suitably packed, you could get an amp, plus this circuit and a single 9V into a regular mint tin.

 

[dsavitsk]

Quote:

Originally Posted by tangent The only real unresolved issue is choosing the op-amp. You'll want a really low-power unit here, because it will be powered all the time.

Ironic.