[aceinc]

 I have a pair of GR Research OB subs I built DIY  (part of a set of 5 subs in my system). I pair them with a pair of Magnepan 2.7 speakers. At present I use effectively a speaker level "Y" which means the Magnepans run full range, and the low pass filter in the subs roll the high frequencies off.

My current Preamp is a Marantz AV7704 which has balanced & unbalanced outputs. My mains (Maggies & subs) are plugged into amps which are plugged into the AV7704 via the balanced connections. What I would like to do is to use unbalanced the line level out to drive the subwoofers, and the balanced to drive the amps which drive the Maggies. Which should work fine, except I would like to put line level high pass filters between the balanced connections and the amplifiers driving the Maggies.

I have found line level high pass filters but they are unbalanced. I could fiddle about with balanced to unbalanced cables and end up with a Rube Goldberg set of cables & filters, but I would prefer to either find balanced filters, or find a way to build my own balanced 12 db per octave high pass line level filters.

Does anyone know of where to get balanced filters or instructions for DIY balanced filters?

[Hobbsmeerkat]

For balanced/XLR you need to know the input impedance for the balanced inputs of the amplifier and the desired -3dB point.

Then once we know that information, you will need two caps per channel, one on each Hot & Cold lines. Preferably in a matched set.

Here's a diagram and one where both channels were built into a single box:





Image source for more info:
http://www.troelsgravesen.dk/High-Pass-Filter.htm

[aceinc]

For balanced/XLR you need to know the input impedance for the balanced inputs of the amplifier and the desired -3dB point.

Then once we know that information, you will need two caps per channel, one on each Hot & Cold lines. Preferably in a matched set.

Here's a diagram and one where both channels were built into a single box:





Image source for more info:
http://www.troelsgravesen.dk/High-Pass-Filter.htm

It would appear the Input Impedance is 47 kOhm. I was thinking -12 DB at 40 Hz. Which in a normal 12 DB per octave passive crossover would place the crossover point at 80 hz.

The Maggie 2.7s produce a good amount of bass below 80hz down to almost 30 hz, but I was thinking that taking the load of them may improve everything since I have the OB subs.

[aceinc]

For balanced/XLR you need to know the input impedance for the balanced inputs of the amplifier and the desired -3dB point.

Then once we know that information, you will need two caps per channel, one on each Hot & Cold lines. Preferably in a matched set.

Here's a diagram and one where both channels were built into a single box:





Image source for more info:
http://www.troelsgravesen.dk/High-Pass-Filter.htm

After reviewing the article either my ignorance of electronics becomes quite apparent, or there are some gaps in what is stated in the article.

It appears they are doing 6 DB per octave. Which I could certainly try, I would like my -6 DB point to be 40 hz, and -12 DB at 20 hz. To achieve this what does my -3DB point need to be? My guess might be ~70hz, but that is a unintelligent guess.

Also this is possibly obvious to those who know what they are doing, but when putting the balanced version together are each of the capacitor values set to the same as one cap value in the unbalanced, or double or half the value?

[Hobbsmeerkat]

Based on the graph on the other site, 70-75Hz will get you the closest to what you're looking for.

Cap value is purely determined by the input impedance of the amplifier for the connector you are using, and the roll off point.

Say you have 2 amps. One is RCA only, the other is XLR only.  If input impedance is 27,000ohm for both amps, the cap value needed will also be the same, but XLR will need 2 caps instead of just one.

With most amps that offer both RCA & XLR, the XLR inputs usually have twice the input impedance of RCA. So the cap value needs to be calculated based on the impedance for the connector you will be using.

Typically, if an RCA connector has, for example, an impedance of 27,000 ohms, the input of the XLR will often be ~54,000 ohms

If you can let me know the input impedance of your amplifier for the XLR inputs, I can let you know the cap value needed to get you -3db at the 70-80Hz range.

[rif]

Could the marantz receiver handle that?  I have a much lower down the line denon (denon A/V is related to marantz), and I believe there are menus to set crossover info.

[aceinc]

Based on the graph on the other site, 70-75Hz will get you the closest to what you're looking for.

Cap value is purely determined by the input impedance of the amplifier for the connector you are using, and the roll off point.

Say you have 2 amps. One is RCA only, the other is XLR only.  If input impedance is 27,000ohm for both amps, the cap value needed will also be the same, but XLR will need 2 caps instead of just one.

With most amps that offer both RCA & XLR, the XLR inputs usually have twice the input impedance of RCA. So the cap value needs to be calculated based on the impedance for the connector you will be using.

Typically, if an RCA connector has, for example, an impedance of 27,000 ohms, the input of the XLR will often be ~54,000 ohms

If you can let me know the input impedance of your amplifier for the XLR inputs, I can let you know the cap value needed to get you -3db at the 70-80Hz range.

I have two Emotiva XPA1 Gen 1 mono blocks driving each front speaker (Maggie & Sub) The XPA1 specification says its input impedance is 47k. It does not specify whether this is for the RCA or the XLR. I will send an email to Emotiva and ask this question.

[aceinc]

Could the marantz receiver handle that?  I have a much lower down the line denon (denon A/V is related to marantz), and I believe there are menus to set crossover info.

Yes the AV7704 has two sub outs.

At present I use the sub outs to control the other subwoofers in the system and run the fronts full range with the speaker level inputs being used on the subs.

[Hobbsmeerkat]

I have two Emotiva XPA1 Gen 1 mono blocks driving each front speaker (Maggie & Sub) The XPA1 specification says its input impedance is 47k. It does not specify whether this is for the RCA or the XLR. I will send an email to Emotiva and ask this question.

Interesting that the input impedance is the same across both inputs, but it seems to be due to the RCA signal being inverted on one side of the amplifier, to mimic the XLR signal, without the benefits of XLR.

For 47,000 ohm input impedance, you will need 0.047uF capacitors to get a -3dB point of 72Hz.

[aceinc]

Interesting that the input impedance is the same across both inputs, but it seems to be due to the RCA signal being inverted on one side of the amplifier, to mimic the XLR signal, without the benefits of XLR.

For 47,000 ohm input impedance, you will need 0.047uF capacitors to get a -3dB point of 72Hz.

I have corresponded with Lonnie at Emotiva and he says the XPA-1 Gen 1 (a monoblock amp) has 47k ohms impedance on each of the "hot" legs of the XLR input connector.

On Parts Express I can find .47 uf capacitors but the only "crossover cap" I can find under .1 uf is .01 uf. Where can I find a .047 uf cap?

[Hobbsmeerkat]

Partsconnexion.com

They have a much bigger selection of high-quality parts even in the smaller sizes. Jupiter, Miflex, Duelund, Solen, Audio Note etc. all available in 0.047uF
Personally I would go for the Miflex KPCU or KFPM copper foil caps.

[whydontumarryit]

I have corresponded with Lonnie at Emotiva and he says the XPA-1 Gen 1 (a monoblock amp) has 47k ohms impedance on each of the "hot" legs of the XLR input connector.

On Parts Express I can find .47 uf capacitors but the only "crossover cap" I can find under .1 uf is .01 uf. Where can I find a .047 uf cap?

Why don't you get Lonnie to show you how to mod the input (passive or in the feedback loop) of the amp. This is so much simpler and effective than what is proposed here. He could even send you the parts for free. You obviously aren't afraid to do some soldering so what have you got to lose. Major points for Emotiva on the customer happiness scale to boot. Unless everyone wants to do it.

p.s. The inverting and non-inverting input of a diff. amp never have the same input impedance if the the purpose is maximum common mode rejection. That's why instead of following basic electronic theory for filter calculations the xover point ends up being 'somewhere around there' and you end up having to measure to confirm.

[aceinc]

Why don't you get Lonnie to show you how to mod the input (passive or in the feedback loop) of the amp. This is so much simpler and effective than what is proposed here. He could even send you the parts for free. You obviously aren't afraid to do some soldering so what have you got to lose. Major points for Emotiva on the customer happiness scale to boot. Unless everyone wants to do it.

p.s. The inverting and non-inverting input of a diff. amp never have the same input impedance if the the purpose is maximum common mode rejection. That's why instead of following basic electronic theory for filter calculations the xover point ends up being 'somewhere around there' and you end up having to measure to confirm.

There are two major reasons;

• If I mod the amps, I would either need to put a defeat switch on the amp, or "un-mod" them before selling them. If I didn't the next person (or me if I forget) would wonder the %^&$ happened to the bass.
• While I am not afraid of putting a wire & a capacitor together and soldering it, my electronic skills rank up there with playing a piano.

I like the concept of a separate box with the high pass filters in it. While it may introduce some potential noise/degradation of SQ, it can easily be undone if someone donates a pair of MBL 101 X-treme Omnidirectional Loudspeakers to me

[whydontumarryit]

There are two major reasons;

• If I mod the amps, I would either need to put a defeat switch on the amp, or "un-mod" them before selling them. If I didn't the next person (or me if I forget) would wonder the %^&$ happened to the bass.
• While I am not afraid of putting a wire & a capacitor together and soldering it, my electronic skills rank up there with playing a piano.

I like the concept of a separate box with the high pass filters in it. While it may introduce some potential noise/degradation of SQ, it can easily be undone if someone donates a pair of MBL 101 X-treme Omnidirectional Loudspeakers to me

Are you saying you aren't much of a piano player?

Are you saying the MBL's are capable of an acceptable level of dynamic range and power handling without being hi pass filtered?

[aceinc]

Are you saying you aren't much of a piano player?

Are you saying the MBL's are capable of an acceptable level of dynamic range and power handling without being hi pass filtered?

I can, on a good day, pick out the "Do Re Mi" song with one finger on a piano.

The MBL system looks fairly robust, and when I heard it at an Audio Show it did not seem to need much help.

https://www.ecoustics.com/reviews/mbl-101-x-treme-omnidirectional-floorstanding/

[aceinc]

I finally got around to building the high pass filters.

I used 2 - .047uf  capacitors, one for each leg of the XLR connector based on a 47k ohm impedance. I was expecting a 3db drop at about 75hz.

Using REW, the observed change seems to be about a 3db drop at 700 hz.

How did I mess up so badly?

There was a question about the actual input impedance of the amps.

The owner's manual for the amp says it is 18k ohms for the balanced connection. When I contacted Emotiva, the CTO responded it was 47k ohms, Is there a way of measuring this?

Obviously plugging the wrong input impedance value into the equation would yield odd results, does anyone have any easy way of determining what the input impedance would be based on a .047 uf capacitor and - 3db at 700 hz?

[wgraft5]

This is the High Pass Filter Calculator Hobbs linked to,

http://www.learningaboutelectronics.com/Articles/High-pass-filter-calculator.php

Wayne in Oregon

[Speedskater]

Do you have a True RMS Digital Multi-Meter (DMM) with a sensitive voltage scale?

[aceinc]

Do you have a True RMS Digital Multi-Meter (DMM) with a sensitive voltage scale?

I have a digital multimeter, don't know how true it is .

It is about 10 years old , but I am not at home to see what model it is. It has quite a bit of functionality including capacitance.

If suitable what how can I use the DMM to analyze my situation?

[aceinc]

This is the High Pass Filter Calculator Hobbs linked to,

http://www.learningaboutelectronics.com/Articles/High-pass-filter-calculator.php

Wayne in Oregon

I know there is a difference between impedance & resistance, how would this difference impact using the calculator?