Need help ASAP:)

[msj965]

Hello,
I'm a newbie here and I wanna ask a question on capacitor ,resistor value to put.first of all my amps cd input impedance specs is 44k ohms. and I have a diy cd player. the problem is the output circuitry of audio....what DC BLOCKER value do I put and Ground resistor value (this is the one connected to rca plug l&R to ground).
Thanks and more power,

 

[duffy]

Like 10µf and 680Ω. The values aren't real critical, so long as you don't go TOO low.

 

[Hero999]

I've always found larger is better.

Don't use ceramic capacitors, film is best, electrolytic is all right as long as it's oversized by a factor of four or more.

Use the following formula to calculate the minimum capacitor size.

[latex]C = \frac{1}{2 \pi R F_C}\\
R =\text{Input impedance}\\
F_C = \text{Cutoff frequency, typically 20Hz for audio.} [/latex]

If you can't find a capacitor with the value calculated, use the next value up.

Use >220nF for an input impedance of 44k.

 

[msj965]

hello

Hi!!!
Is 3.3 uf and 22k ohms are also good?

Thanks guys for the quick respond!

 

[Hero999]

Rearrange the formula posted above.

Plug the numbers in.

Calculate it and see for yourself.

 

[audioguru]

I hate it when people reduce 20Hz to half-power.
4Hz should be reduced to half power so that 20Hz can rattle everything at almost full power.

 

[Hero999]

I think you'll hardly notice it as even most good speakers cut-off at 40Hz and average speakers only make it to 80Hz. The acoustics in a poorly designed room will also limit the bass response.

I agree oversizing by a factor of 5 is good as electrolytics will sound as good as film capacitors and cost less.

 

[msj965]

Hello

Hi Masters
Make some corrections on my thread. My Yamaha A1 CD input sensitivity/impedance is (100w/8ohms)150mV/47k-ohms.now I follow what Duffy said 10uf and 680ohm but when i played the CD, I notice that the bass sometimes is distorted or grumble....I used a bipolar 10uf electrolytic caps on this.Regarding on your computation and formula i don't understand it.but if you can give me the right value,watts,voltages maybe I'll be alright.OH by the way i only have a little player like PlayStation.
thanking you,
Ann

 

[Hero999]

Get rid of the resistor, I don't know why duffy suggested using it, try just the 10µF capacitor.

 

[audioguru]

Hi Ann,
You don't need to add a load resistor. Then the capacitor value can be less.

Remove the 10uF capacitor and 680 ohm resistor.
As Hero said, use a 220nF (0.22uF) plastic film coupling capacitor for a half-power frequency of 16Hz.
Keep the volume control of the playstation turned down low enough that it does not cause distortion.

 

[Hero999]

Agreed film capacitors are better, don't use ceramic for audio whatever you do.

Grossly oversized electrolytic i.e. ≥2.2µF is all right.

 

[msj965]

I'ts me

Hello,
I'll try it tomorrow and let you know what is the outcome.
Thanks,

 

[msj965]

Hello

Hi there,
Just to say thank you and more power. it works great and sound too,but a little Q's on caps. what will happen when I increase the value of caps,what will the sounds looks like.(does the bass increase or decrease?).
THanks you again guyz!

 

[audioguru]

Hi there,
Just to say thank you and more power. it works great and sound too,but a little Q's on caps. what will happen when I increase the value of caps,what will the sounds looks like.(does the bass increase or decrease?).
THanks you again guyz!

A coupling capacitor cannot boost low frequencies. If the value of the coupling capacitor is high enough then the low frequency response is extended to lower frequencies. If the value is too small then low frequencies are reduced.

The formula for calculating the -3dB bass frequency, the load resistance and the capacitor's value was posted and is very simple. The input impedance of your amplifier is 44k ohms so a 220nF metalized plastic film capacitor will cause 16.5Hz to be at -3dB (half the power) and lower frequencies will be reduced more. If the capacitor value is doubled to 440nf then the -3dB frequency will be 8.25Hz.

 

[acmefixer]

I hate it when people reduce 20Hz to half-power.
4Hz should be reduced to half power so that 20Hz can rattle everything at almost full power.

Let;s not get too pedantic. ;-) If you make the amp too wideband, then things that you can't hear can do some serious damage or just make the sound worse. For instance, if you have a really low freq response, you may be able to watch the cone of your (sub)woofer wander around as you play an album on a turntable, caused by warping of the vinyl. A Rumble Filter can then be a blessing. But you ear doesn't hear much at these low freqs, you feel it more than hear it. If you want earsplitting bass, use a good headset. Otherwise you'll disturb you neighbors. ;-)

 

[audioguru]

Turntable?? Vinyl?? Are you living in 1963?
Your neigbours will hear your bass if your walls are made of rice-paper.