[jparkhur]

Ok.  I needed to make some inline x overs for my copies of Ninjas 81 mm mortar Boom boxes.  I have limited soldering skills and even less skills with small parts.  I had Danny help me figure out the cap value for the amp impedance that I had. The formula is 159155/amp impedance x C = hz.  I have some new amps thanks to Trung and it's input impedance is 100kohms. I wanted the xo slope to start at 80 hz, so went with the appropriate size.  I ordered some Cardas RCA ends from Somiccraft and picked up an electrical box at the hardware store. The following is a picture version only creation that took 15 minutes of time. 

I asked that you make improvement suggestions and use this post as a learning tool for those like me and a teaching tool if you can help improve my skills.  I will not hold it against you .

[jparkhur]

First drilled six holes in box for my right left and sub bypass. Then connected all RCA ends to box and locked them down.  I could not use the nice Cardas brass nuts because I did not order the Long version.  If you order these pick the long ones, they are the same price.

[jparkhur]

I am using a sub bypass so that I can have a single set of outs.  You can skip this step if you don't need this.  I wrapped the common ground wire around the sub bypass and sent each end to the negative lead at the base of each RCA.   A little fiddling and they lock in nice before soldering. Once those were in place for each side, I attached the bypass wire from the in RCA to the sub on the positive lead. Thus is done in the white wire only.  I will seal the wire with some silicon spray when I am done. I had no small silver hook up wire to use so I used some Electra wire from the LGK kit.  After these were pressure fit in place I cut the caps to fit tight so I could solder them in place.  I soldered all my ends and grounds well and put some super gorilla glue on the insides of the rca's so not to twist them in the future.

Feel free to let it ride and let the learning continue. 

[jparkhur]

[jparkhur]

[jparkhur]

Ok. There you have it.  15-20 minutes and some money for parts.  I have asked Danny to chime in later with help on appropriate values of caps and any errors in production I have made. Hope the info pictograms helped some of those who are a little timid.  I went back too and cleaned some of my joints. There were some that were solder heavy.   Can't screw this one up to bad.  Jon

[ebag4]

The formula is 159155/amp impedance x C = hz.  I have some new amps thanks to Trung and it's input impedance is 100k.  I wanted the xo slope to start at 80 hz

Hi Jon, great post!  Nice job overall, it makes sense to me to do both channels in a single enclosure.

I have a question, is the amp impedance supposed to be in kohms (100 in your case) or in the full value (100,000).  I'm not at all certain but representing it in kohms (100) seems to make more sense.  What is the value of your cap?

Thanks,
Ed

[jparkhur]

Ed.  Fixed and you are correct.    My cap value is a .033uF for a 3 db down at 48 hz but remember the roll starts on octave higher- so about 80 hz or a little higher.

[jparkhur]

Here is a better example with silver wire and a switch integrated in to it to switch between two different caps.  This was done by big Dave at Pi Audio.  This box is actually a mono box and only 2 inches square.  Compare this to my giant box that is 2 deep x 4 x 4.  Dave's is tight and a model. 

JP.

[ebag4]

Ed.  Fixed and you are correct.    My cap value is a .033uF for a 3 db down at 38 hz but remember the roll starts on octave higher- so about 80 hz.

It is good to have the formula, not realizing it varied with input impedance I used the same value cap on my BH 2a3 that I had used on my ClassD amp (.047), turns out I am only high passing at about 55 Hz  .  Anybody want to trade some .047 Sonicap Platinums for some .25s?

Best,
Ed

[jparkhur]

We learn.   

[mlundy57]

Could you clarify the formula? When I work it out I get C = 0.05 instead of 0.03

159,155 / 100 *C = 80
1591.55C = 80
C = 80 / 1591.55
C = 0.05

[jparkhur]

It's actually down 3 db at 48 hz.  But remember the roll starts about an octave higher.   
 And it's 100,000.   

159155/100000x.033=hz


Here is a calculator that I think is good.

http://www.v-cap.com/coupling-capacitor-calculator.php

Also, here are my values. 
A .033uF value will give you a -3db down of 48Hz.
A .022uF value will give you a -3db down of 72Hz.
A .015uF value will give you a -3db down of 106Hz.
A .01uF value will give you a -3db down of 159Hz.

Keep in mind also that these make a first order slope. So the effect of lowering the output will start an octave higher.  My only other choices were limited too on SC generation 2

[jparkhur]

The math has been checked and fixed.

[jparkhur]

Could you clarify the formula? When I work it out I get C = 0.05 instead of 0.03

159,155 / 100 *C = 80
1591.55C = 80
C = 80 / 1591.55
C = 0.05

And everyone says you don't need algebra in life

[mlundy57]

I'm not an engineer but have found algebra and geometry to be extremely useful more times than I care to count 

[jparkhur]

I'm not an engineer but have found algebra and geometry to be extremely useful more times than I care to count 

I agree!

[bdp24]

If your coupling cap value turns out to be lower than the stock input cap in your amp, and you want to put the filter on the input jack of your amp (for less connections), can the stock cap be left in place and the new cap simply added to the input jack, or does the stock cap need to be removed?

[jparkhur]

If your coupling cap value turns out to be lower than the stock input cap in your amp, and you want to put the filter on the input jack of your amp (for less connections), can the stock cap be left in place and the new cap simply added to the input jack, or does the stock cap need to be removed?

Ahhh, help???     Buller?   Buller?       


 


 

[mlundy57]

Which input impedance are you looking for, the preamp or the power amp?

does it make a difference if you have separates or if the amp is integrated?