Active Crossover frequency response - help needed HH X300 - diyAudio
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Old 1st May 2014, 02:41 PM   #1
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Default Active Crossover frequency response - help needed HH X300

Hello, I have a vintage HH Electronics X300 2/3 way active crossover which I am using in 3 way mode (with 3 HH VX series MOS-FET power amps) and I wonder if anyone can help me with a couple of points to do with its extremes of frequency response? Firstly, since it is intended as a professional device, it has a 35Hz high pass filter for driver protection. The FR graph I have shows this as starting at about 50Hz and rolling off at 18dB/octave (Butterworth filter I believe). I would like to remove this "sub-bass" filter from the crossover since my speakers will respond flat at least an octave below this point and it seems a shame to lose the bass. I have the schematic for this device (although I'm not sure how to upload it to this forum) but I need some guidance in what needs removing and what needs reconnecting to remove this function. Can anyone help?

I am also wondering about the upper frequency extreme, my power amps and speakers are fairly flat to well over 30KHz but this X300 FR starts to roll off at about 15KHz and is a few dB down by 20 KHz. The circuit is designed around TL071 op amps doing all the I/O buffering and 4739 op amps in the filter circuits. Are these limiting the FR? Also, are there any modern pin-for-pin replacements that would improve this crossover?

I look forward to any assistance you might be able to give
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Old 2nd May 2014, 02:44 AM   #2
andyr is offline andyr  Australia
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My only suggestion is ... go to Rod Elliott's web-site, get yourself a pair of his P09 PCBs ... + the P05 board, if you need a basic PS to power them.

Rod's site is here: ESP Projects Pages - DIY Audio and Electronics

Alternatively, if your speakers happen to have a bass LP / mid HP point at 330Hz and a mid LP / tweeter HP point at 2,600Hz, and your drivers can take 18DB bass LP with 12dB elsewhere, you might like to buy my current made-up P09 boards. (I will be removing them soon and going to a different XO regime.)


Regards,

Andy
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Old 3rd May 2014, 10:51 AM   #3
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Thanks for the idea, and it is a valid one, but what I really want to do is to modify the x-over I already have.

Quote:
Originally Posted by andyr View Post
My only suggestion is ... go to Rod Elliott's web-site, get yourself a pair of his P09 PCBs ... + the P05 board, if you need a basic PS to power them.

Rod's site is here: ESP Projects Pages - DIY Audio and Electronics

Alternatively, if your speakers happen to have a bass LP / mid HP point at 330Hz and a mid LP / tweeter HP point at 2,600Hz, and your drivers can take 18DB bass LP with 12dB elsewhere, you might like to buy my current made-up P09 boards. (I will be removing them soon and going to a different XO regime.)


Regards,

Andy
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Old 3rd May 2014, 11:04 AM   #4
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If you can't find a service manual/schematic, take a look here: Active Filters to help you recognize the appropriate filter section. I suspect in the 35 Hz high pass section you'll find at least one largish (1 f or so) value cap in series with the signal followed by a fairly high value resistor to ground. Check the circuit aroound the op amp that follows using Linkwitz' formulae to identify the section. Then you have two options:

Bypass the 35 Hz high pass filter by cutting appropriate traces and jumpering.

or

Turn the filter into a buffer by removing appropriate parts and jumpering as needed.
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Old 3rd May 2014, 11:13 AM   #5
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Thanks Bob, as I wrote in my original post I do have a schematic but thanks a lot I will look at the site you mention, I might be able to work it out from there. I could post the schematic here if I knew how to - using the Insert Image seems to just point to a URL but the schematic is on my computer....



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Originally Posted by BobEllis View Post
If you can't find a service manual/schematic, take a look here: Active Filters to help you recognize the appropriate filter section. I suspect in the 35 Hz high pass section you'll find at least one largish (1 f or so) value cap in series with the signal followed by a fairly high value resistor to ground. Check the circuit aroound the op amp that follows using Linkwitz' formulae to identify the section. Then you have two options:

Bypass the 35 Hz high pass filter by cutting appropriate traces and jumpering.

or

Turn the filter into a buffer by removing appropriate parts and jumpering as needed.
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Old 3rd May 2014, 11:22 AM   #6
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Ahh missed that you had the schematic. It's early here and I hadn't had enough coffee.

Attach the schematic file to a post rather than try to insert a picture.
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Old 3rd May 2014, 11:27 AM   #7
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Aha, I had missed the Attach icon. Here is the detail from the schematic. I have the whole drawing but it is a large file and possibly irrelevant to my question. Coffee hhhhmmmm must make some!

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Originally Posted by BobEllis View Post
Ahh missed that you had the schematic. It's early here and I hadn't had enough coffee.

Attach the schematic file to a post rather than try to insert a picture.
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Old 3rd May 2014, 11:28 AM   #8
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HH X300 Active Crossover 35Hz HP filter.jpg
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Originally Posted by delapoer View Post
Aha, I had missed the Attach icon. Here is the detail from the schematic. I have the whole drawing but it is a large file and possibly irrelevant to my question. Coffee hhhhmmmm must make some!
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Old 3rd May 2014, 11:39 AM   #9
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Multiple feedback topology. Use TI Filter Pro to calculate response. Active Filter Design Application - FILTERPRO - TI Software Folder

Looks like the first RC is an RF filter, but use Linkwitz to calculate the corner frequency.

Do you have the part around IC5? That 6F8 in series with the low pass looks suspiciously like a low frequency high pass filter...

Last edited by BobEllis; 3rd May 2014 at 11:41 AM.
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Old 3rd May 2014, 11:51 AM   #10
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The spec says it is a 35Hz sub-bass filter and I modelled it a Spice download which showed it starting to roll off at 50Hz and about 3dB down at 35 Hz so I think that is correct. I am getting an error message about the whole schematic (something to do with a missing security token) but I think that IC5 is part of the frequency division. I'll see if I can cut that section out of the drawing and post in a few minutes. Thanks for the help!

Quote:
Originally Posted by BobEllis View Post
Multiple feedback topology. Use TI Filter Pro to calculate response. Active Filter Design Application - FILTERPRO - TI Software Folder

Looks like the first RC is an RF filter, but use Linkwitz to calculate the corner frequency.

Do you have the part around IC5? That 6F8 in series with the low pass looks suspiciously like a low frequency high pass filter...
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