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replaceing surface mount with normal size capacitor

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mikee55

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Hi Y'all,can I ask another?I have a car amp and I need to modify its 18db crossover from 80 hz to 40 hz,the cap is 0.0333 in value and is a surface mount type.Can I replace it with a non surface device? And will multiplying the value by 4 = 1.4uf set the frequency to 40hz?
Cheers A'll.mikee55 :D
 
mikee55 said:
Hi Y'all,can I ask another?I have a car amp and I need to modify its 18db crossover from 80 hz to 40 hz,the cap is 0.0333 in value and is a surface mount type.Can I replace it with a non surface device? And will multiplying the value by 4 = 1.4uf set the frequency to 40hz?

I would expect an 18dB/octave crossover to have more than one capacitor?, a 12dB/octave one uses two capacitors, an 18dB/octave is likely to use three.

Your maths also seems wildly inaccurate?, how does 4 x 0.0333 = 1.4?.

This is assuming you're right in multipling by four to half the frequency?.

However, there's no problem replacing a SM component with a conventional one - it's only the shape and size that's different.

What are you actually trying to do?, presumably this is for a sub-woofer?.
 
Cor,I'm terrible

Im trying to send a jpeg of the circuit.Yes,its for my mates sub.Alpine were kind enough to give me part of the schematic,but are not allowed to to give me any more details.My math skill is vey limited,shame because I loved electronics since I was 5.Normaly I try to fix things but... :oops:
 
Re: Cor,I'm terrible

mikee55 said:
Im trying to send a jpeg of the circuit.Yes,its for my mates sub.Alpine were kind enough to give me part of the schematic,but are not allowed to to give me any more details.My math skill is vey limited,shame because I loved electronics since I was 5.Normaly I try to fix things but... :oops:

So why do you want to change it?. At 40Hz there probably won't be a lot of audio anyway? - and cars are too small to reproduce bass (which is why all you get is a single note thumping noise). A four string bass goes down to 41Hz, or a five string to 31Hz.

Here's a quick quote about recording bass!

The lowest octave that can be heard (20Hz to 40Hz) virtually has no energy in most music. The lowest note on a bass has a fundamental frequency of about 41 Hz. So this first octave contains such things a "room rumble" and the lowest notes of a pipe organ. The second octave (40 Hz to 80Hz) contains the fundamental frequencies of the low bass notes and the Kick drum. So this is the first octave we are really concerned with, unless we are reproducing earthquakes and the like. This second octave is very difficult to judge, even for the most-experienced engineers. This is largely due to the speakers we use in listening.
 
Oops!

Sorry, forgot to add image. **broken link removed**
 

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I've been asked

I'm doing in exchange for some door speakers,Its a long standing argument :evil: between us about what is below 40hz.If he don't hear much,I get my door speakers and can tell him "I told you so!". :wink:
Thanks.mikee55
 
It is a Sallen and Key 12db/octave lowpass filter with its two capacitors fairly far off the required 2:1 values. If you make only the 0.033uF capacitor way too big then I think it would almost oscillate and have a big peak at only a single frequency, like a bongo drum.

Don't listen to the descriptions of frequencies of only guitars and other stringed instruments. Modern synth'd music goes down to very low frequencies.
Lookup Sallen and Key Lowpass Filters in Google, modify the values of both capacitors using a proper 2:1 ratio, use a good sub-woofer, play hiphop music and lose your bet. :lol:
12dB/octave isn't very steep, the filter will still pass higher frequencies.

PS. If you want to win, use two subwoofers connected out-of-phase. Your friend won't hear any bass.
 
With a second look at the 4:1 ratio of the capacitors, it might be an 18dB/octave lowpass filter with its 3rd RC network elsewhere. All 3 capacitors will need to have their values doubled.
 
I'm sending more image

Here's more image. Cheers, Y'all!
 

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I don't see the 3rd stage of an 18dB/octave Butterworth lowpass filter there. Maybe C201 and C203 don't have the proper ratio of 2:1 for a 12dB/octave Butterworth lowpass filter because they want it to provide a little boost just above its 80Hz cutoff frequency.
If you reduce the cutoff frequency of its lowpass filter then the Bass EQ circuit will still be set to boost and cut at the original higher frequency.

To cut its lowpass filter's cutoff frequency in half to 40Hz, double the values of C200 and C201. You won't find 0.066uF but you can use 0.068uF for C201, and you won't find 0.0164uF but you can use 0.018uF for C203 which is close enough.

A 12dB/octave Butterwoth lowpass filter will cut 40Hz to 1/2 power, 80 Hz to 1/4 power and 160Hz to 1/16 power. You will lose your bet because voices and ordinary bass frequencies will still be heard. :wink:
 
Okay

So I guess I loose the bet,thanks for your help.Should I lower the bass boost,seeing as its set at 50hz?Thanks everyone
Mikee55 :D
 
Re: Okay

mikee55 said:
Should I lower the bass boost,seeing as its set at 50hz?
50Hz is pretty low, and the Bass EQ circuit will also boost from 25Hz to 100Hz anyway so leave it like it is made.
 
Component removal

Thanks Mate,Do you mind me asking,I have a variable temperature controlled iron and a desoldering pump?The irons rated at 50wmax,and has a pointed bit,is there any precautions to observe when removing SMD's? I have allways steered clear of this technology. :D .Thanks for your advice.
Kind Regards

Mike
 
Re: Component removal

mikee55 said:
Thanks Mate,Do you mind me asking,I have a variable temperature controlled iron and a desoldering pump?The irons rated at 50wmax,and has a pointed bit,is there any precautions to observe when removing SMD's? I have allways steered clear of this technology. :D .Thanks for your advice.

A solder sucker isn't much help with SMD's, for removing a two terminal component (like a capacitor) repeatedly heat each end while applying pressure, till it pops off the board. Even better is to use a 'tweezer iron', effectively two soldering irons that squeeze together like a pair of tweezers (but you probably don't have one?).

However, you've no need to remove anything - simply stick a second identical value capacitor in parallel with the existing ones - this doubles the value, and halves the frequency as you wanted.
 
Hello again

Hi,sorry to bother you,can I use 0.01uf in parrallel with C203? I can't find a 0.018 .The idea of parallel sounds good,and half the value would be 0.09

Thanks again for your help :D .Kind Regards.Mike
 
Hello again

Hi,sorry to bother you,can I use 0.01uf in parrallel with C203? I can't find a 0.018 .The idea of parallel sounds good,and half the value would be 0.09

Thanks again for your help :D .Kind Regards.Mike
 
Re: Hello again

mikee55 said:
can I use 0.01uf in parrallel with C203?
0.01uF is fine. Do you have a 0.033uF capacitor to parallel with C201?
 
Thats it

Yes,got 0.033 too.Cheers mate!Thanks again for your kind help and your time.Now,time to operate,"Nurse,prep the patient whilst I scrub up!" :wink:
All the best.Mike
 
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