Can I use an electrolytic capacitor instead of a monolithic one?

Thread Starter

mRoy62

Joined Dec 31, 2020
12
I have a missing 1uF capacitor for this kit amp (see image). The missing piece is a 105 monolithic capacitor. I do have some 1uF electrolytic caps. Can is use one of these? I believe the monlythic caps are non-polarized but the electrolytic one are polarized. I’m new to this so feel free to correct me. If I can use the electrolytic cap, how do I know which way to insert?
 

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SamR

Joined Mar 19, 2019
2,898
Depends on the voltage. In a pinch, you can use an electrolytic even though most 1uF are ceramic which are typically rated for 50V. Ceramics are also much cheaper... 1uF is a value to have a small stock of.
 

jpanhalt

Joined Jan 18, 2008
10,933
If it is a decoupling capacitor, the low esr of ceramic may be preferred. A capacitor connected from the power pin to ground is likely for decoupling. Sometimes there will be two or three of them in parallel and in a sequence, such as 10 uF, 1 uF, and 0.1 uF.
 

jpanhalt

Joined Jan 18, 2008
10,933
From the datasheet for the TPA3122 (TI) amplifier used:

The TPA3122D2 is a high-performance CMOS audio amplifier that requires adequate power supply decoupling to ensure that the output total harmonic distortion (THD) is as low as possible. Power supply decoupling also prevents oscillations for long lead lengths between the amplifier and the speaker. The optimum decoupling is achieved by using two capacitors of different types that target different types of noise on the power supply leads. For higher frequency transients, spikes, or digital hash on the line, a good low equivalent-series-resistance (ESR) ceramic capacitor, typically 0.1 µF to 1 µF placed as close as possible to the device VCC lead works best. For filtering lower frequency noise signals, a larger aluminum electrolytic capacitor of 220 µF or greater placed near the audio power amplifier is recommended. The 220-µF capacitor also serves as local storage capacitor for supplying current during large signal transients on the amplifier outputs. The PVCC terminals provide the power to the output transistors, so a 220-µF or larger capacitor should be placed on each PVCC terminal. A 10-µF capacitor on the AVCC terminal is adequate. [emphasis added]
So, according to TI, using a capacitor with higher esr (i.e., an electrolytic instead of the ceramic) or leaving that capacitor out will probably "work" but lead to greater THD. That may not make a difference, or it may even be an enhancement, depending on the music you listen to. :)

Edit: spelling
 
Last edited:

Bernard

Joined Aug 7, 2008
5,717
C-13,14 & 15 all have one lead at ground, check to see where your Cs ground. If cap is dark color, white stripe is most likely on the side of the neg. pin. Neg. to ground.
 

dl324

Joined Mar 30, 2015
12,224
The missing piece is a 105 monolithic capacitor. I do have some 1uF electrolytic caps. Can is use one of these?
It might work and it might not. A ceramic cap is better at bypassing higher frequencies than an electrolytic cap.
 

Audioguru again

Joined Oct 21, 2019
2,374
Do not use an electrolytic capacitor!
Since the class-D switches at a frequency as high as 270kHz then ceramic capacitors are used for all the high frequency decoupling and bootstrap capacitors. 220uF electrolytic capacitors are parallel to the 1uF ceramic capacitors for decoupling at low frequencies.
 

BobaMosfet

Joined Jul 1, 2009
1,292
I have a missing 1uF capacitor for this kit amp (see image). The missing piece is a 105 monolithic capacitor. I do have some 1uF electrolytic caps. Can is use one of these? I believe the monlythic caps are non-polarized but the electrolytic one are polarized. I’m new to this so feel free to correct me. If I can use the electrolytic cap, how do I know which way to insert?
A monolithic cap is a high-density ceramic cap (usually). MLCC technology. In your case, use the same cap as you see nearby- the little yellow/gold (C3, C4 etc) caps nearby are what you want. It will likely be polarized- notice how the other caps are marked and mounted.
 

Thread Starter

mRoy62

Joined Dec 31, 2020
12
From the datasheet for the TPA3122 (TI) amplifier used:



So, according to TI, using a capacitor with higher esr (i.e., an electrolytic instead of the ceramic) or leaving that capacitor out will probably "work" but lead to greater THD. That may not make a difference, or it may even be an enhancement, depending on the music you listen to. :)

Edit: spelling
Thank you so much for this reply. It has helped me understand a lot more. I tested this without the cap and it works. There is some hiss and the high frequencies seem a little distorted. I have an identical unit that I built a few weeks ago and so was able to compare the two. That one also has the hiss and distorted high frequencies... I'm guessing that is just a consequence of the fact this is a $18 kit. Anyway, I have gone up a learning curve here as a result of the missing capacitor and the great feedback of this community. Thanks!
 

jpanhalt

Joined Jan 18, 2008
10,933
Some advice:
1) Don't buy the minimum components for a project, unless they are specialized ICs.
2) For common ceramic capacitors, I buy a lot. I switched to mostly SMD a long time ago. Strips of capacitors, even partial reels can be cheap (or were).
3) Electrolytic (aluminum and tantalum) are more expensive, but the price break for 10 ea. is often enough to make it worthwhile.
4) Resistors are pretty much the same story as capacitors..

As for this project, I am certain I could not hear the difference in THD. I can't even hear 2 of my 3 daughters on the phone, but I trust TI.
 

Audioguru again

Joined Oct 21, 2019
2,374
The amplifier IC is class-D with fairly high distortion. It ain't hifi.
My hearing aids allow me to hear almost like I am young again (I am 75 now) but I still would not be able to hear the 18kHz 3rd harmonic distortion of a 6kHz tone at 0.5%.
 

Thread Starter

mRoy62

Joined Dec 31, 2020
12
The amplifier IC is class-D with fairly high distortion. It ain't hifi.
My hearing aids allow me to hear almost like I am young again (I am 75 now) but I still would not be able to hear the 18kHz 3rd harmonic distortion of a 6kHz tone at 0.5%.
I'm just a beginner into this and so I'm not following what you are saying.
 

Thread Starter

mRoy62

Joined Dec 31, 2020
12
Some advice:
1) Don't buy the minimum components for a project, unless they are specialized ICs.
2) For common ceramic capacitors, I buy a lot. I switched to mostly SMD a long time ago. Strips of capacitors, even partial reels can be cheap (or were).
3) Electrolytic (aluminum and tantalum) are more expensive, but the price break for 10 ea. is often enough to make it worthwhile.
4) Resistors are pretty much the same story as capacitors..

As for this project, I am certain I could not hear the difference in THD. I can't even hear 2 of my 3 daughters on the phone, but I trust TI.
I've only just started into this hobby and so buying a cheap components to learn on. What are SMD's? Regarding your last point are you basically saying there will be no difference in sound quality whether the capacitor is in or not, right?
 

Bernard

Joined Aug 7, 2008
5,717
SMD = surface mount device. Surface mount caps. with band on one end are polarized , band end is +, no band = non polarized.
 

jpanhalt

Joined Jan 18, 2008
10,933
What are SMD's? Regarding your last point are you basically saying there will be no difference in sound quality whether the capacitor is in or not, right?
I am saying that at my age (late 70's), I have difficulty hearing. Someone with good hearing might be able to tell a difference. More important, some audiophiles seem more interested in what an instrument can measure than in what a person can distinguish.
 
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