I am building a pre-amplifier for connecting an electric guitar to a sound card mic input from this schematic (I'm hoping my mic input has the required DC bias). I need some guidance to know what types of capacitors to use. I read somewhere that ceramic capacitors are not good for audio circuits, presumably due to some noise generation, and that propylene or polypropylene (?) are good (are these "film?"). Also, on the schematic are three polarized capacitors. Since I have only run into electrolytic polarized capacitors, does the schematic imply those three should be electrolytic? Do non-polarized capacitors on the schematic imply they are not electrolytic? What types of capacitors should I be using for this circuit? Thanks for any help!

If I don't have what I need already, I'd be ordering from Mouser.

 

hi Greg,
Added the circuit image to your post.
E

 

If the cap is shown as polarized, it's typically electrolytic, but a non-polarized cap would work just fine in its place.

Yes, propylene or polypropylene are "film" type capacitors and are generally better for high-fidelity audio than ceramic caps.
But if it's for a guitar amp where distortion is often added on purpose, then it's highly unlikely the use of ceramic caps will be noticed.

 

Thanks!

 

C1, 1μF - use non-polar poly cap.
C5, C7, 10μF/16V - use aluminum electrolytic polarized cap.
C2, C3, C4 - doesn't really matter, mica is common at those values
C6, 1nF - poly is ok

 

C1, 1μF - use non-polar poly cap.
C5, C7, 10μF/16V - use aluminum electrolytic polarized cap.
C2, C3, C4 - doesn't really matter, mica is common at those values
C5, 1nF - poly is ok

Nice summary! But of the four classifications you propose, why did you select each type?

 

Don't forget, tantalum caps are also polarized.

 

tantalum caps are also polarized.

That because they are electrolytic, along with the aluminum type.

 

Nice summary! But of the four classifications you propose, why did you select each type?

Oh my, do I have to?

C1, 1μF - use non-polar poly cap.
C5, C7, 10μF/16V - use aluminum electrolytic polarized cap.
C2, C3, C4 - doesn't really matter, mica is common at those values
C6, 1nF - poly is ok

C1 is directly in the input signal path. Any noise in the capacitor will be amplified all the way through. Electrolytics are notorious for producing microphonics. Also their characteristics will change with bias voltage.

C5, C7 are used for power supply decoupling.

C2, C3, C4 are for frequency compensation and to prevent high frequency oscillation. They provide negative feedback and HF filtering.

C6 seems rather drastic. This will have significant impact on the preamp's frequency response. (Edit: a quick calculation reveals that the HF roll-off is at the high end of the audio range.)

 

I would use Tantalum caps in preference over Aluminum Electrolytics. They have a much longer life in my experience. Like, almost never having to replace one, but have done so with many Electrolytics.

 

Oh my, do I have to?

C1, 1μF - use non-polar poly cap.
C5, C7, 10μF/16V - use aluminum electrolytic polarized cap.
C2, C3, C4 - doesn't really matter, mica is common at those values
C6, 1nF - poly is ok

C1 is directly in the input signal path. Any noise in the capacitor will be amplified all the way through. Electrolytics are notorious for producing microphonics. Also their characteristics will change with bias voltage.

C5, C7 are used for power supply decoupling.

C2, C3, C4 are for frequency compensation and to prevent high frequency oscillation. They provide negative feedback and HF filtering.

C6 seems rather drastic. This will have significant impact on the preamp's frequency response. (Edit: a quick calculation reveals that the HF roll-off is at the high end of the audio range.)

This is the kind of commentary I've always wished I had whenever I look at a schematic. Oddly (to me), no schematic designer ever does it. Seems like I would learn electronics twice as fast. (I function best starting with a top-down understanding, rather than the more abstract bottom-up.) Even having blocks is currently useless to me.

 

I would use Tantalum caps in preference over Aluminum Electrolytics. They have a much longer life in my experience. Like, almost never having to replace one, but have done so with many Electrolytics.

Are they as quiet? Functionally, I don't need them at max. quietness, but I am curious.

 

I think Tants are very good caps. As long as you get them the correct way around! If not, the can catch fire, as I have found a couple of times after assembling a stack of boards, and doing the batch with one cap swapped!
They are more stable then elecros, but generally cost a bit more too, and are not available in a large voltage or capacitance.

 

For many audio applications ceramic capacitors are just fine. The main issue is distortion and to a minor extent microphonic response. Unless you are making something HIFI ceramic should be fine.

 

For many audio applications ceramic capacitors are just fine. The main issue is distortion and to a minor extent microphonic response. Unless you are making something HIFI ceramic should be fine.

Thanks for the useful added info. I am trying to learn enough so I won't be intimidated by building something Hi-Fi, because that is one of the few things I want to do. My current enormous limitation is my inability to debug a circuit, although my soldering sure needs a lot of work, too. If I solder on mental cruise control I overheat components.

 

The major difference between tantalum and aluminum electrolytics is in the ESR. Having low ESR tantalum in switching supplies or HF digital application is important.

Aluminum electrolytics in C5 and C7 in your AF circuit will be ok.

The point about microphonics in capactors is worth some attention. If you have 1mV microphonics in C5 or C7 biased at 1V or 9V, you are not going to hear it.

However 1mV microphonics into C1 is definitely undesirable.

 

Oh my, do I have to?


C2, C3, C4 are for frequency compensation and to prevent high frequency oscillation. They provide negative feedback and HF filtering.

C6 seems rather drastic. This will have significant impact on the preamp's frequency response. (Edit: a quick calculation reveals that the HF roll-off is at the high end of the audio range.)

Please explain more on this..Thanks

Is it the combination of C3 and C2 that provides negative feedback, correct?
If it was only C2, any feedback?

HF filtering?

Hmm, what was that quick calculation? "Quickest"have seen so far (not too far) is Open circuit time constant
Guessing your quick is something else then

 

The major difference between tantalum and aluminum electrolytics is in the ESR. Having low ESR tantalum in switching supplies or HF digital application is important.

Aluminum electrolytics in C5 and C7 in your AF circuit will be ok.

The point about microphonics in capactors is worth some attention. If you have 1mV microphonics in C5 or C7 biased at 1V or 9V, you are not going to hear it.

However 1mV microphonics into C1 is definitely undesirable.

RC filter the 1mV microphone before AC coupling

 

I am building a pre-amplifier for connecting an electric guitar to a sound card mic input from this schematic (I'm hoping my mic input has the required DC bias). I need some guidance to know what types of capacitors to use. I read somewhere that ceramic capacitors are not good for audio circuits, presumably due to some noise generation, and that propylene or polypropylene (?) are good (are these "film?"). Also, on the schematic are three polarized capacitors. Since I have only run into electrolytic polarized capacitors, does the schematic imply those three should be electrolytic? Do non-polarized capacitors on the schematic imply they are not electrolytic? What types of capacitors should I be using for this circuit? Thanks for any help!

If I don't have what I need already, I'd be ordering from Mouser.

View attachment 180074

What am I missing here? Why can't I find a power source in the schematic? Is said power being delivered by the mic input that would be connected to K2?

 

The circuit is not complex.
Would you like a complete run down of the function of each and every component in the circuit?