Capacitors for Amp Circuit

[Thayne]

The datasheet for the TDA1517 has a sample circuit that calls for two, 1uF capacitors for the left and right inputs (pins 1 and 9). In a pinch. can I use 10uF capacitors? What difference to the sound would it make?

Thank You.

 

[Audioguru]

The TDA1517 is obsolete and is not made anymore. An old one has a datasheet that shows it driving 4 ohm speaker speakers with output capacitors. Then the -3dB (half the output power) frequency is simply calculated to be 40Hz using 1000uF or 85Hz using your 470uF capacitors and lower frequencies cut at -6dB per octave.

The 1uF input capacitor is feeding the 60k ohms input resistance of the amplifier and its -3db cutoff frequency is simply calculated to be the very low frequency of 2.7Hz. Using 10uF causes the input cutoff frequency to be the earthquake frequency of 0.27Hz and it would noticeably charge slowly causing a delay then distortion when the power is turned on. Since the output capacitor cuts frequencies that are much higher than the input capacitor then the value of the input capacitor can be reduced to 0.22uF (shown on the datasheet I have) without a noticeable effect.

 

[Thayne]

OK, I think I understand the relationship a little better -- still a long way to go. This is my first circuit from scratch. After some searching, I was able to find a few 0.10uF and 0.47uF (and have one 1.0uF) capacitors and also the datasheet you mentioned with the 0.22uF capacitors. So, would I be safe in assuming the 0.47uF capacitors would be the best choice based on what I have on hand?

Thank you.

edit: I also found about twenty 0.01uF capacitors. What would that do? Can you explain it like you did the effect of the 10uF? That was really helpful. I would like to know the two, somewhat, "extreme" ends of the spectrum to help understand better. I am not experienced enough yet to be able to translate numbers to sounds -- other than high and low, but with no idea where on that spectrum. I don't have an oscilloscope, or anything like that yet.

 

[Thayne]

I think I will try out the 0.1uF input capacitors with 1000uF output capacitors.

edit: I forgot to ask... For the output capacitors to the speakers what will happen if I use 1000uF/16v instead of 1000uF/25v? Is there going to be a difference in sound?

 

[barry]

It your output exceeds 16 volts you better not use a 16v cap.

 

[Thayne]

I am using a 12v power supply. But, the circuit works best closer to 16-18v (so I read). Eventually, I will have other power supply options, so I would rather plan for that. So, I will go for the 25v.

My main concern now is whether I should go with 0.1uF or 1uF input capacitors. Will it really make a noticeable difference in sound?

 

[barry]

If you're so concerned with the sound, use the correct capacitor. Or do your own analysis.

 

[Thayne]

Not really too concerned. Only concerned enough to post some questions.

 

[KlausST]

Hi,

Fc = 1 / ( 2 × Pi × R× C).
With R = 60k and C = 0.1uF then fc = 26.5Hz.

Now that the output capacitor already suppresses those 26.5Hz you won't see or hear much difference.
Additiinally you'd need a very big bass speaker that is able to reproduce 26.5Hz.

I don't see a drawback in using a 0.1uF input capacitor. It's very unlikely that you will hear a difference - at least no negative difference.
What I want to say: in case there is some very low frequency included in the music, it is unlikely you will hear this frequency (because of output capacitor and speaker size), but the amplifier will amplify this signal. At high volume this may cause the amplifier to clip, causing distortion. This usually is not what you like.
Thus I rather see a benefit in using a 0.1uF capacitor against a 1uF capacitor.

Depending on what music you want to hear, what volume you want to use and what size and quality of your speakers...I recommend to use an even lower value capacitor...to reduce early clipping.
It doesn't make much sense to amplify a signal that you can't hear.

In either case use a foil capacitor, no electrolytic, no ceramics.

Klaus

 

[Thayne]

Hi,

Fc = 1 / ( 2 × Pi × R× C).
With R = 60k and C = 0.1uF then fc = 26.5Hz.

Now that the output capacitor already suppresses those 26.5Hz you won't see or hear much difference.
Additiinally you'd need a very big bass speaker that is able to reproduce 26.5Hz.

I don't see a drawback in using a 0.1uF input capacitor. It's very unlikely that you will hear a difference - at least no negative difference.
What I want to say: in case there is some very low frequency included in the music, it is unlikely you will hear this frequency (because of output capacitor and speaker size), but the amplifier will amplify this signal. At high volume this may cause the amplifier to clip, causing distortion. This usually is not what you like.
Thus I rather see a benefit in using a 0.1uF capacitor against a 1uF capacitor.

Depending on what music you want to hear, what volume you want to use and what size and quality of your speakers...I recommend to use an even lower value capacitor...to reduce early clipping.
It doesn't make much sense to amplify a signal that you can't hear.

In either case use a foil capacitor, no electrolytic, no ceramics.

Klaus

It is especially helpful to have the practical effects and an "overall picture" of what you hear, based on the numbers, described -- especially comparing different size capacitors, in this case. I found an online tone generator last night that helped a lot too.

Thank You!

 

[KlausST]

Hi,

I found an online tone generator last night that helped a lot too.

A good headphone should be able to reproduce 27Hz.
I´m curious whether your speakers can. At least you should see the membrane to move .. as long as the amplifier outputs this frequency.

Klaus

 

[Thayne]

I can barely (ear to the speaker) hear it with a megaboom speaker. My headphones can play it a little better. It is more like I notice it is gone when I shut it off and hear silence. The speakers I am using for this project are decent 4.0 Ohm speakers.

I soldered everything yesterday and it works -- except, one of the output capacitors is dead. Luckily, I found several more even better replacements.

Everything is recycled from all kinds of electronics that were headed for the trash. I didn't copy anyone's design, but it ended up looking like one of those cheap amps you buy from alixpress. I guess it is difficult to avoid with cheap parts. Anyway, it doesn't matter. This project was just to learn.