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-   -   Tantalum cap to set gain in LM386 (http://www.diyaudio.com/forums/chip-amps/191538-tantalum-cap-set-gain-lm386.html)

FenderBender11 26th June 2011 12:55 AM

Tantalum cap to set gain in LM386
 
Hi,

I know this isn't exactly hi-fi, but I'm building a friend a small amp for his birthday, and I'm looking for some help on parts selection.

I'm following the National schematic for setting the gain to 200. The vale to achieve a gain of 200 is a 10uF capacitor. Obviously, I could just use a 10uF electrolytic and call it a day, but what would happen if I put something like a 10uF tantalum in there...for kicks.

Would changing from a electrolytic to a tantalum have any difference in sound (in this application)? Is it worse or better? Tants are supposed to be better quality, but I'm just curious.

Thanks.

enzoR 26th June 2011 10:15 AM

are you sure you want a gain of 200?

anyway electrolytic or tant wont make a difference in this application.

AndrewT 26th June 2011 10:41 AM

I don't know the internal circuit, but I suspect the external cap is AC bypassing an internal gain setting resistor.
If that is the case then adding a series resistor with the cap should allow an intermediate gain setting.

woody 26th June 2011 10:47 AM

Going to a tantalium cap is probably a bad idea they sound bad. And by the way tantalium caps are electrolitic.

digits 26th June 2011 11:38 AM

Sound bad is a relative thing in this particular function, which is to try to add some grunge to a toy guitar amp....

FenderBender11 26th June 2011 06:26 PM

I have a question regarding gain..anyway. I know what the textbook definition of gain is, but I don't understand what it really means for sound/sound quality. It should be louder right? So...what would be the point of using a low gain?

Sorry if this a big quesiton.

sofaspud 26th June 2011 08:22 PM

Gain doesn't mean anything to sound/sound quality. If you want a 12V output, you can amplify a 1V signal 12x, or a 3V signal 4x, or an 8V signal by 1.5x. That's the reason for the question in post#2; 200x gain is likely to clip all but the smallest of your input signals. On the other hand, 200x may be what you need. It's nothing to do with loudness though. The LM386 has a specified output capability of watts into a load. The amount of gain doesn't change that. "It should be louder right?" is a big reason why there's a steady stream of "this car amp is broken" posts.

nigelwright7557 26th June 2011 09:42 PM

Gain should be kept as low as possible to get full output power.
The more gain the more you are amplifiying noise from components.
My amps usually have a gain for about 45.

FenderBender11 26th June 2011 09:44 PM

Thanks.

I'd like to remind you that I'm an idiot...

I understand now. I'm assuming that my friend will predominatley be using this with his Zune HD, but I also am including the option to use a 1/4inch input (like his guitar) and I'm using a DPDT switch to switch the mono signals. (3.5mm jack and 1/4inch jack).

So what is a "normal" voltage output from a Zune/iPod?

Thanks.

Tube_Dude 26th June 2011 09:58 PM

Quote:

Originally Posted by woody (Post 2619555)
And by the way tantalium caps are electrolitic.

Hi Woody

Tantalum capacitors are solid capacitors, not electrolytic in any way...

Maybe you mean they are polarized capacitors, like electrolytics are. ;)


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