Internal High Pass Filter

[rollo]

  I tried some Harrison lab high pass filters as an experiment. Except for the hardness and brightness of the treble the results were staggering. The ease and dynamics gained was quite impressive.
  I would like to install a 65Hz/ 12db slope high pass before the outputs of the Preamp. Is it just a cap and a resistor ? Trying to avoid a external crossover or DSP  if possible.


charles

[richidoo]

Some helpful links for you: http://www.sherlab.com/index.htm?/filter/filter.html 

The input impedance of your amp has a big influence on the frequency of the filter. If you can post that I will ask Sol to draw a filter for you. I am seeing him tomorrow.    I think you have Vcaps on the preamp output, right? Can you post what value those are, and if you already know the output impedance of the preamp, although I don't think that is as critical as the load Z.
Rich

[Face]

http://www.t-linespeakers.org/tech/filters/passiveHLxo.html

[richidoo]

Nice link Face! It shows the impedance compensation too. 

[rollo]

Some helpful links for you: http://www.sherlab.com/index.htm?/filter/filter.html 

The input impedance of your amp has a big influence on the frequency of the filter. If you can post that I will ask Sol to draw a filter for you. I am seeing him tomorrow.    I think you have Vcaps on the preamp output, right? Can you post what value those are, and if you already know the output impedance of the preamp, although I don't think that is as critical as the load Z.
Rich

  The amps have an input sensitivity of .6V. I'll have to do some research for the preamp. Thanks rich.

charles

[rollo]

http://www.t-linespeakers.org/tech/filters/passiveHLxo.html

  Perfecto Face thanks.


charles

[richidoo]

Input impedance is 100kOhms
http://www.opera-consonance.com/products/cyber211.htm

For the 12dB high pass filter:

R1 = 10kOhm
C1 = 244nF
R2 = 100kOhm?
C2 = 24nF

I assume your preamp can drive 10kOhm load.

Question: Does the amplifier act as R2? Or is R2 an additional discreet 100kOhm resistor?

[bpape]

If I'm reading it correctly, it's both.  R2 is sized to work in concert with R Amp to form the proper overall R for the circuit requirements.

Bryan

[rollo]

Thanks Rich. Yes the Preamp can handle the load.


charles

[richidoo]

Try it like Bryan says, with the physical resistor for R2. That should give nominal 50kOhm load to the filter. Then try it without R2. It should sound louder, but check the filter knee freq with SPL meter to make sure it's still ~65Hz. 

Here's some links to good parts from mouser to verify the design:
C2
C1
R1
R2

You might wanna buy some extra caps for tweaking the Frequency, these parts are cheap and MKT1813 caps sound good enough to hear what's really happening.  Shipping is the big cost if you have to order again.

If it works out the way you hope you can get copper V-Caps to match your output coupling caps.   

Don't forget the pics!