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Old 19th October 2008, 07:59 AM   #1
nkg is offline nkg  Australia
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Default Steve Bench's tube crossover

Hi
Has anybody out there built Steve Bench's tube crossover and were they happy with it .
thanks nkg
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Old 19th October 2008, 11:22 PM   #2
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I haven't built it yet but I am slowly working on an integrated amp with a built in crossover based on it. It may take a few months but I will let you know how it goes.
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Old 20th October 2008, 02:21 AM   #3
kevinkr is offline kevinkr  United States
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I know someone who has, and that person is quite pleased with it.

Note that Steve's site is gone as of the end of this month - if you need anything I would grab it now. Select run from the windows start menu, type cmd and navigate (cd or dir commands as needed) to the right directory then you can use wget to grab it all at one time, just remember use this syntax:

wget -mr h tee tee pee colon slash slash the_name_of_a_site.whatever (com, net, org, etc.)

Sorry the automatic url parser forced me to create the above travesty, but I think it is kind of humorous.. Hope this is obvious.. This will completely recursively mirror the site in question to your hard drive. (The location where wget lives on your drive actually.)

For windows go here: http://gnuwin32.sourceforge.net/packages/wget.htm

For linux go here: http://www.gnu.org/software/wget/
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Old 20th October 2008, 11:46 AM   #4
nkg is offline nkg  Australia
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Thanks Kevin for your reply good to hear that somebody has built it and is happy I found 2 6dj8's in my collection and will proceed to build it , and it's a shame that his site is closing down.
Many Thanks
Nigel
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Old 20th October 2008, 06:38 PM   #5
pchw is offline pchw  United States
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Quote:
Originally posted by nkg
Thanks Kevin for your reply good to hear that somebody has built it and is happy I found 2 6dj8's in my collection and will proceed to build it , and it's a shame that his site is closing down.
Many Thanks
Nigel
It is due to AOL is sunsetting their old hometown product, not under Steve's control ........
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Old 22nd October 2008, 04:06 AM   #6
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It looks like the terms Steve has put on his site will let other people mirror it if they attribute him. ("Feel free to put these schematics or other information on your web sites, but give the author credit.")

I have the webspace to support it, I might look at mirroring all of the content in the next couple of days.
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Old 22nd October 2008, 05:38 AM   #7
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Quote:
Originally posted by pchw

It is due to AOL is sunsetting their old hometown product, not under Steve's control ........
For the greater good methinks - they were completely unable to control the spambot hacking/registrations

Cheers!
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Old 30th October 2008, 03:33 AM   #8
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I need to get schematics off of another computer on to this one to post them but I have been playing with the design in LTspice. My topology has a 50Hzish LP for the subwoofer and a 50-200 bandpass for the helper woofer. The full range will be run um... full range as it starts rolling off at about 200 hz anyway but I will include a simple low order passive high pass that can be switched in.

I am investigating a couple of things unique to my situation.

One is that I wanted to tune the high pass part of the band pass to a higher Q that normal because the normal configuration gives a big round peak in the middle of the passband which is not good in this case. I did not have a formula for the Q of a 3rd order S-K so I inferred some things from the Q factor in a 2nd order and started diddling with the resistor values. By increasing the value of the first resistor to ground in the high pass portion and adjusting the feedback resistor as necessary to keep the turnover frequency where I wanted I was able to get the desired boost right before cutoff. When I followed this with a more standard low pass section at the 200Hz point I got a very nice slope of about 3dB/8va downward as frequency increased in the pass band. This along with the use of highish Q driver should provide good integration in the open baffle speakers I am using.

I found that I could diddle the caps similarly in the lowpass section to get a lower than normal Q resulting in a steeper slope but I liked the looks of the 3dB slope better and I think that it will be superior in the long run. Of course experimentation of the actual circuit will tell the story in the end with the proof being in the pudding and all that.

The second thing I looked at was the tube choice. I had been designing with the idea of using 6N1Ps as the final CF in each band but really wanting to use those in a phono amp project I decided to try the sim with 12AX7s of which I have four on hand. This is probably one of the worst tubes to choose but there they sit on my bench so what the heck. If it doesn't work it won't exactly blow up so why not give it a try.

Given the lowish frequencies involved I thought that the AX7s might work OK if obviously not optimally. Sims seem to support this. Even into a tough load of 10k I was able to maintain good slopes (though with about 1.5dB less gain). It required a somewhat larger but still manageable (2.2uf) output cap for the subwoofer section and the woofer filter seemed to be just fine with as low as 0.68uf which would allow a poly cap to be used there. Seems like a reasonable compromise.

By wiring for the 12A family I can start with the AX7s I have on hand and switch to the more capable 12AT7 at a later date by simply switching tubes and reducing Rk to draw more current.

At first both the woofer and subwoofer will be driven by sand but eventually the woofer will be a tube amp. With this in mind I tried the bandpass with a 47k load and it tightened up the curves so that there was no discernible difference before and after the output cap.

Just wanted to let you know where I was heading with this. Will get schemos up as soon as I can.
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Old 30th October 2008, 10:38 PM   #9
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I should have added that the next pass at the simulator will be to add parasitic capacitance to the output to simulate cable and amp input capacitance. The aim is to get an order of magnitude type of idea of how much capacitance the little AX7s can drive.
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Old 31st October 2008, 01:45 PM   #10
kevinkr is offline kevinkr  United States
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Last day SB site will be available, and the last chance to get the information you need. See post #3 for a way to grab the entire site at one time..

I'm assuming someone will mirror at some point soon, but until they do best to have it local. It's not a very big site in terms of MB.
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