[mlundy57]

I'm looking at building a new in-line filter for the NX-Otica MTM monitors. MY power amps have an input impedance of 100k Ohms. Using the calculator it looks like I have a couple options for cap size, .01 and .022.

With a .01 the -3dB point is 160Hz, -9dB is at 80Hz, and -14dB is 40Hz.

With .022 -3 is at 72Hz, -9 is at 36Hz, and -14 is at 18Hz.

I understand the progression is not linear between octaves so I'm not sure where the -6dB crossover point would be.

From the standpoint of removing as much low frequency energy from the NQ drivers the .01 cap would be the best choice. However, is that what I should be looking at for best overall performance?  Also, the caps would be different. I can only get a .01 in a Sonicap Platinum and a .022 in Myflex KPCU.

Mike

[Tyson]

You can also parallel 2 of the .022 caps together and get a working value of .044. 

[corndog71]

Jupiters are available.

https://www.hificollective.co.uk/catalog/jcw020-001uf-600vdc-jupiter-copper-foil-paper-p-9967.html

[mlundy57]

You can also parallel 2 of the .022 caps together and get a working value of .044.

.044 would have a -3dB point of 36Hz. I would think this would be ineffective in keeping low frequencies from the NQ drivers.

I forgot to mention this is going to be a balanced filter so I'll be using two caps per channel as it is.

Jupiters are available.

https://www.hificollective.co.uk/catalog/jcw020-001uf-600vdc-jupiter-copper-foil-paper-p-9967.html

Thanks. The US sources I looked at didn't have either .01 or .022 in the copper caps.

[Captainhemo]

I'd  say the .01 is going to be in the ball park to  cross in that  100 - 120 hz  range  Mike, I'd imagine that's what  your  shooting  for.   That being said,  if the MTM's  are  sitting directly on  top of the  h-frames,   crossing a bit higher  is not a bad idea,  reduce that  workload on the  NQ's  even  a bit more

jay

[Tyson]

Of you could buy both and try them both to see which you like better.

And whichever ones you decide against can be re-used as bypass caps somewhere else in the crossover.

[SoCalWJS]

Is there a way to take actual measurements of an Amplifier to determine the input impedance? Or is it a matter of finding the manufacturers specifications?

I have a custom built amp with unknown specs that I would like to figure out at some point.

[poseidonsvoice]

Is there a way to take actual measurements of an Amplifier to determine the input impedance? Or is it a matter of finding the manufacturers specifications?

I have a custom built amp with unknown specs that I would like to figure out at some point.

Yes it can be measured and calculated:

http://www.sengpielaudio.com/calculator-InputOutputImpedance.htm





“ When the voltage V2 is equal to half of V1, then the measured
resistance value Rs (Rtest) is equal to the input impedance Zload.”

Of course, this is just at 1khz. To be complete, you should measure it from 20Hz to 20khz or at various points from 20-20k to be sure it stays within the region you want.

This is why instruments like the Audio Precision devices exist. They do these measurements easily and quickly.


Do you have internal pictures or a schematic to share?

Best,
Anand.

[SoCalWJS]

Yes it can be measured and calculated:

http://www.sengpielaudio.com/calculator-InputOutputImpedance.htm





“ When the voltage V2 is equal to half of V1, then the measured
resistance value Rs (Rtest) is equal to the input impedance Zload.”

Of course, this is just at 1khz. To be complete, you should measure it from 20Hz to 20khz or at various points from 20-20k to be sure it stays within the region you want.

This is why instruments like the Audio Precision devices exist. They do these measurements easily and quickly.


Do you have internal pictures or a schematic to share?

Best,
Anand.

I bought this setup from Danny. 

https://www.audiocircle.com/index.php?topic=156151.0

I'm honestly not sure I need anything inline, but I'm kinda paranoid. I use it to power the Panel section on my Super7's sometimes.

[Tyson]

See those sonicap input caps?  You could get the same result simply by using a smaller value cap on that input position. 

[poseidonsvoice]

See those sonicap input caps?  You could get the same result simply by using a smaller value cap on that input position. 

Yes, if you want to change low frequency extension in that amp, the easiest way is to change the value of the input caps so the F3 is higher.

Best,
Anand.

[mikeeastman]

This is what I made up using Jupiter .22 caps. I changed my system and can't us it any more. I noticed no difference with it in or out. I spoked with Danny before I took it out of my system and in his opinion it was not needed.

It won't matter in my system anyway as in a couple of months  I'm going to a full active x-over.