[D2Deets]

hey

thanks for the quick replies (also thanks for pointing out my error missing the zero on the value, life saver haha)
I've just found the that yes those caps are quite hard to find, (especially in Australia)

if I were to use a 0.047uf with a roll off at -3db around 72hz/-6db at 55db, would that be affecting the speakers natural roll off to much? i just assumed this inline filter idea was more towards rolling off bass the speaker cant produce?

and also, in Australia the decent caps i find here are janzten but the shop doesnt stock values that small, can you please recommend some other good brands i should look into, i know Danny likes the soni platinum/miflex, are there any other caps brands that are also recommended or that have sounded decent used in this apllication?

regards

[jandrews]

Question regarding integrating the sub back in once the filters are built:

I get the cap value is being selected to high pass the power amp and the connected speakers based on both the -3dB point of the speakers and input-Z of the power amp.  But , then how do you determine the -6dB point to crossover the subs in?  Would that also be a spec from the speaker manufacturer or is there an easy way to approximate that frequency?

thanks
JS

[HAL]

For a single pole high pass filter, the -6dB point is one octave below the -3dB point.  That is why a single pole filter can be both a Butterworth and Linkwitz-Riley filter. 

As an example, if the -3dB point is 100Hz, the -6dB point will be 50Hz. 

[jandrews]

Ah… makes sense.
So if the cutoff freq were 70hz, the crossover freq for the sub would be 35Hz?
Does this still apply if the speakers are sealed?

[HAL]

The input to the amp impedance does not change, so the frequency response of the high pass filter does not change no matter what speaker load is on the amplifier. 

Now, if the response of the speaker is not flat in that frequency range, it is a combination of the responses.  That is why there is an electrical frequency response and an acoustic frequency response when they are combined for the total acoustical frequency response.

[jandrews]

Thanks for that
To be specific, I'm asking about where to set the crossover frequency on the sub

For instance:
If Amp input Z is 10k Ohms
& desired high-pass cutoff (-3db) down on the monitor is say 80Hz
...so cap is .2uF.
All good, but ...to blend at the 6dB down point, you just set the crossover frequency at 40Hz?

[HAL]

Depends on the amp. 

The A370XLR3 servo amp has an 80Hz low pass filter setting and it is -6dB down.  There is also an 50Hz setting on the amp at -6db down.  If other mode is needed when the AVR mode and external low pass is needed at different frequencies.  That is according to the spec sheet for those amps. 

In that case the high pass filter -3dB point would be 160Hz at -3dB for a 80Hz -6dB point for the main speakers.  For a 10K Ohm input impedance, the series connected input cap would be 1000pF or 1nF in value.  You want two matched caps to make sure the channels are both the same.

[Rakeem]

Hello, can i use Danny roll-off filter between DAC and integrated amplifier, in my case Marantz PM6007?
I dont understand why he claims it doesnt work.

[richidoo]

I dont understand why he claims it doesnt work.

The filter will only affect the DAC and the other sources on the integrated will be unfiltered.

If it's a tube DAC with output capacitor then adding another series cap may not work as expected. But if it's all solid state DAC then the filter should work as expected, but only on the DAC.

[Danny Richie]

Hello, can i use Danny roll-off filter between DAC and integrated amplifier, in my case Marantz PM6007?
I dont understand why he claims it doesnt work.

You can, but it will roll off the bottom end across the board.

[Rakeem]

The filter will only affect the DAC and the other sources on the integrated will be unfiltered.

If it's a tube DAC with output capacitor then adding another series cap may not work as expected. But if it's all solid state DAC then the filter should work as expected, but only on the DAC.

Thank you.
The DAC is a solid state and is the only source i use.
Just want to add two active bass sections and cut bookshelfs for better presentation, but dont want to use DSP or commercial active cross.
At final, the Danny's solution will work in my case, right?

[richidoo]

You have to take the unfiltered signal for the active bass from the DAC before it's filtered, using RCA splitter cable.
You can't use the subwoofer output jacks from the Marantz to your active bass because the highpass filter already peeled out the bass, like Danny said above.

So then, if you take bass signal from DAC with no delay, but your Marantz DSP amp converts all analog inputs to digital for DSP before amplification then the amp might be adding a delay which makes the active bass and main speakers out of acoustic alignment, causing blur through freq band they overlap.

If the Marantz has a pure analog signal path including volume control, etc, then it won't add delay and it should work. But if it's typical of modern receivers and DSP integrateds where analog inputs are digitized and every signal goes through DSP then it might not work.
Fun to try, can't hurt.

[Hobbsmeerkat]

One issue with connecting the sub directly to the DAC is that unless the volume can be controlled digitally via the source, the sub will remain at a constant volume and will need to be independently adjusted up or down any time the integrated amp is adjusted.

You will also need to know the input impedance for the integrated amplifier as a whole, and I'm not sure how available that information is.

[jeffdavison]

My main amp is a DIY 300B, the input stage is a WE437@ but instead of a grid leak (which is a resistor to ground before the input tube), I'm using a grid choke instead, no coupling cap and inline grid stopper of 100 ohms. The DCR of the grid choke is 1.3K ohm, but it's AC impedance is 500 Meg ohm. I'm using a modified Dahlquist Low pass active, high pass passive crossover. If I use 1.3K the calcs say if I use a 1.5uf cap, my freq of roll off is just a tick over 80hz. I assume it's the DCR that needs to be used in this case, rather than a conventional "input impedance, as I have no way of physically measuring it, and there are no "specs" for this DIY amp