[Gaudeamos]

Ok cornman! You solved your problem while I was composing my last post. 
 
re. using your CMoy (or any other electronics) within your vehicle's electrical system: You should assume that your vehicle's cigarette lighter is designed to .... light up cigarettes. It may not be regulated, so that higher (or momentary negative) voltages may be present. It's not only the higher voltage that the vehicle's charging system puts out; an automotive electrical environment is a really nasty place for an unprotected little circuit like your CMoy to be.There are all kinds of ugly spikes (in the KVs), surges, etc caused by other devices connected to the vehicles electrical system. It's nowhere near as benign as connecting to a 9V battery.
 
The very first mod that I made to Chu Moy's basic circuit was to add reverse polarity protection. It's too easy to just touch the battery's terminals the wrong way around when replacing the battery.There's no guarantee that the opamp, the filter caps, or even the LED would survive even a momentary reverse contact.

 

[cornman]

Hmm, I had no idea about the reverse polarity thing, I'll have to be careful when replacing the battery. Also, do you know of any way to improve the battery life besides just hooking up batteries in parallel? The new op amp I'm using requires at least 18 volts and these 2 9 volts hooked up in series are running low very quickly. I'm thinking of using a few of those big 6 volt batteries hooked up in series to run it in my car.

 

[GermanGuy]

Happily reading that you finally have replaced the OpAmp so you can enjoy your amp again.

 

[GermanGuy]

Hmm, I had no idea about the reverse polarity thing, I'll have to be careful when replacing the battery. Also, do you know of any way to improve the battery life besides just hooking up batteries in parallel? The new op amp I'm using requires at least 18 volts and these 2 9 volts hooked up in series are running low very quickly. I'm thinking of using a few of those big 6 volt batteries hooked up in series to run it in my car.

 
 
 
http://www.amazon.com/Anker-10000mAh-Multi-Voltage-Camcoders-Recorders/dp/B005NGKR54/ref=sr_1_fkmr0_1?ie=UTF8&qid=1370510997&sr=8-1-fkmr0&keywords=accu+pack+tec++10000ma
 
I use this nice gadget for various purposes:
 
This item: Anker Astro3 10000mAh Multi-Voltage (5V 9V 12V) Output Portable Power Pack External Battery Charger for iPads, Samsung Tablets, iPhones, Android Smart Phones, Camcoders, Digital Cameras / DV Recorders (Dual USB Output: 5V, 2A; DC Output: 9V / 12V, 2A) [12 connectors for mobile phones, 6 connectors for tablets, US AC adapter included
 
Other name in Germany, same device, can deliver up to 2.1 Ampere DC 5V 9V 12V, has a capacity of 37 Watt. you can charge nearly everything using the adapters, i use it to greatly enhance the bass quality on my colorfly c4. This one also has just the same size as a colorfly c4.
 
Can be charged by any DV 9 to 12 Volt 1 Ampere source. Just Use it or another accu pack as buffer between your cars 12 volt and the cMoy or as general rechargeable power supply part integrated into your cmoy and maybe replace the cmoy battery with a buffer stage (resistor, capacitor, resistor ( ? wonder that your OpAmp should not work with 12 or 9 Volts). DON´T USE THIS TOGETHER WITH A BATTERY!

 

[cornman]

That looks good but a bit expensive considering the amp only cost around $20 to build. I'd like to find a cheaper option.

 

[GermanGuy]

There are smaller and much cheaper devices also from the same company. I don´t think buying batteries or new OpAmps the rest of your life will be cheaper

 

[Gaudeamos]

>> Also, do you know of any way to improve the battery life besides just hooking up batteries in parallel?
 
There are other cMoy variations out there that have simple charging circuits for rechargeable 9V batteries (cMoyBB and Mini^3 for example). If you're circuit-savy enough you could incorporate parts of other designs into the Tangent build that you're using.
 
>> The new op amp I'm using requires at least 18 volts ...
 
Are you sure that it requires 18V? +/-18V is a common absolute maximum value for the supply voltage of a lot of opamps, but they will happily operate at voltages less than that. If your headphones are high impedance and inefficient, you will need higher voltage output from your amp. For most low-impedance phones (16 - 40 Ohms), a single 9V battery should provide adequate voltage headroom. Low-impedance headpones require more current, and the cMoy is not an optimal design for that case.
 
 
I'm also wondering about why you're using your headphone amp with your vehicle's sound system. Is there really an audible benefit compared to plugging your headphones directly into the sound system? 

 

[cornman]

Maybe I didn't make that very clear but I was not using my headphones with my sound system, rather, I was using the cmoy to preamp the signal coming from my sansa fuze going into my stereo and playing through my speakers and subwoofer.
 
Without the cmoy I have to turn the fuze and the stereo all the way up and there is noticable distortion and the overall sound is very flat and boring.
 
With the cmoy I only need to have it at half volume and its plenty loud enough and there is a huge improvment in sound quality overall especially in the lower frequencies.
 
Is there any reason why this might be a bad idea assuming I'm powering the cmoy with batteries?

 

[Gaudeamos]

>> I was using the cmoy to preamp the signal coming from my sansa fuze...
 
OK, that makes sense: you're feeding your Fuze's output (designed to drive low-impedance phones, ie low voltage/high current) into your vehicle's amp (high impedance requiring higher voltages). The cMoy is a good fit for that job.
 
>> Is there any reason why this might be a bad idea assuming I'm powering the cmoy with batteries?
 
No, this is cool... as long as you stay away from that cigarette lighter! For your situation it would probably be best to invest in a few NiMH batteries and a good charger (which you may use in your vehicle 

). By 'good' I mean one that doesn't overcharge: it would use methods like 'negative delta V', 'maximum voltage detection', and/or 'delta T'. [rambling off topic]