Effect of 10x Capacitor on Amplifier circuit

Thread Starter

Stas06

Joined Jan 16, 2022
13
Hi all,

I bought capacitors of 22kµ instead of 2.2kµ. I was wondering whetther this circuit could still work with the 22kµ and what the effect is on the circuit.
I'm not a electrical engineer so my knowledge is rather limited in this field. My best guess would be that these are used for the high and low pass filter.
So I guess the cut-off frequency is changing?

Feel free to educate me =D
 

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Ian0

Joined Aug 7, 2020
5,945
Don't use "kμ" - it doesn't make any sense.
But the only capacitors shown on your diagram are input coupling and supply decoupling. Increasing the supply decoupling will improve the supply, increasing the input coupling will make the low frequency response roll off at a tenth of its intended frequency.
 

Thread Starter

Stas06

Joined Jan 16, 2022
13
Indeed my bad for the units 22000µ and 2200µ it is.
I'm not entirely understanding what concept is of coupling (input & supply).
I thought the two capacitors of 2200 on the left were a filter and the two on the right were to balance any swings in the DC supply voltage.
For the filter: instead of filtering at 20Hz it would roll of at 2Hz?
 

Ian0

Joined Aug 7, 2020
5,945
Yes. If you replace the two 22uF coupling capacitors by 220uF it will reduce the cutoff from 2Hz to 0.2Hz (by my calculations, 22uF/3.9k gives 2Hz cutoff) It's not and exact calculation because the source impedances are not equal - the source will be lower than the drain.

If you increase the 2200uF capacitors in the power supply to 22000uF, it will mean that the power supply stores ten times as much energy, so it will have less ripple and change less if there is a change of load. Negligible effect on the operation of the circuit, presuming that 2200uF was enough in the first place.
 

Thread Starter

Stas06

Joined Jan 16, 2022
13
Sorry I wasn't specific enough.
I have the 22µF components. It's the 2200 µF ones I don't have. I bought 22000 µF by mistake.
So for the power supply it's ok to use the 22000µF ones. It's overkill but it will work (better, altough negligible for this intend)

What is the impact for the two 2200µF connected to ground in the middle of the schematic? this is the high pass filter I guess?
The cut off frequency will be 10x higher with the 22000µF than with the 2200µF?
 

Ian0

Joined Aug 7, 2020
5,945
What is the impact for the two 2200µF connected to ground in the middle of the schematic? this is the high pass filter I guess?
The cut off frequency will be 10x higher with the 22000µF than with the 2200µF?
They decouple the power input from the USB to your DC-DC converter. Same effect as any other power supply decoupling.
 

Thread Starter

Stas06

Joined Jan 16, 2022
13
Ok thanks.
Does it matter if the 22µF capacitors are polarised or not in this scheme? It says non polarised but i only have polarised 22µF for now
 

Ian0

Joined Aug 7, 2020
5,945
Ok thanks.
Does it matter if the 22µF capacitors are polarised or not in this scheme? It says non polarised but i only have polarised 22µF for now
No. The odds are that both the source and drain terminals of the jfet will be at a more positive voltage than earth, so fitting polarised capacitors the right way round will be perfectly OK.
 

AnalogKid

Joined Aug 1, 2013
10,113
1. The drawing needs reference designators for each component. Otherwise, confusion about which capacitors we are discussing will continue.

2. Yes, the polarization matters. As Ian said (while I was typing), they will be fine acoustically if pointed the right way.

3. Both the FET and the capacitors (which ones?) are barely rated for this application. The FET is a 30 V part with up to 28.7 V across it, and the caps are 16 V parts with 15 V across them. Aluminum electrolytic caps running at full voltage usually are rated for around 1000 hours (cheap) to 3000 hours (less cheap). That's not much. For way better long-term reliability, most electronic components should be rated for twice the operating conditions when possible.

4. Most electret cartridges have a built-in FET. Are you really using a bare electret element?

ak
 

Thread Starter

Stas06

Joined Jan 16, 2022
13
1. The drawing needs reference designators for each component. Otherwise, confusion about which capacitors we are discussing will continue.

2. Yes, the polarization matters. As Ian said (while I was typing), they will be fine acoustically if pointed the right way.

3. Both the FET and the capacitors (which ones?) are barely rated for this application. The FET is a 30 V part with up to 28.7 V across it, and the caps are 16 V parts with 15 V across them. Aluminum electrolytic caps running at full voltage usually are rated for around 1000 hours (cheap) to 3000 hours (less cheap). That's not much. For way better long-term reliability, most electronic components should be rated for twice the operating conditions when possible.

4. Most electret cartridges have a built-in FET. Are you really using a bare electret element?

ak
This is what i'm building :)
 
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