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DN13 Crossover Upgrade or Replacement

 
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Larry
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Joined: 25 Jan 2006
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Location: Regina, Canada

PostPosted: Sat Sep 16, 2006 3:57 am    Post subject: DN13 Crossover Upgrade or Replacement Reply with quote

I'm looking at options to upgrade the DN13 crossovers in a pair of 2-way TL speakers (B200-SP1014, T27-SP1032) that I built in the early 80s. After 25 years I don't think there is much doubt that the capacitors are no longer functioning properly. As Colin had suggested to me some time ago I was going to simply replace them with the Falcon 37Ks, but as Falcon is no longer in business I obviously have to look at other alternatives. I guess that's what happens when you procrastinate Rolling Eyes

I could, I suppose, just upgrade the caps with polypropylene, but then I'm still dealing with a crossover that is only designed for low power amps, plus I wouldn't have an aB for the T27. Ideally if I could get my hands on the schematic for the 37K I would probably go that route, but failing that I suppose I could build my own using a generic design. I've found a website that provides basic crossover info and has calculators for various types of crossover designs http://www.lalena.com/audio. Has anyone reviewed this site for accuracy?

Whatever I do I only want to do it once as when I built the speakers I didn't put the crossovers in the most accessible place Rolling Eyes

This is a fantastic forum and the wealth of knowledge is amazing. Any guidance or advice from the experts would be appreciated! Smile
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ColinR
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Location: Staffordshire

PostPosted: Sat Sep 16, 2006 9:31 am    Post subject: Reply with quote

Before playing with theoretical calculators.

Make a copy of the schematic at the bottom of this webpage

http://home.eol.ca/~ifftay/tangent/tm1.html

and here if you want the KEF version of the aB tweeter section.

http://www.hifiloudspeakers.info/Anatomy/Crossovers/104aB/KEF104aBcrossover.gif

Fatten up the bass inductors and add polystyrene capacitors to taste, job done Shocked .
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Larry
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Joined: 25 Jan 2006
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Location: Regina, Canada

PostPosted: Sun Sep 17, 2006 2:54 am    Post subject: Reply with quote

Thanks Colin! Very Happy

Sounds like the best option may be to combine the LF section from the Tangent circuit and the HF section from the KEF circuit. Once I use larger gauge wire for the bass inductors does this combination then come close to what the Falcon 37K offered?

I also noticed in the KEF schematic that the output polarity for the HF section has been inverted. I'm assuming that this circuit must cause a 180 degree phase shift. Confused Correct?
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ColinR
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PostPosted: Sun Sep 17, 2006 10:04 am    Post subject: Reply with quote

I've no idea about the Falcon 37K as I never got round to asking Malcolm Jones for a copy of the schematic.

However, as it's a marriage between the bass section from a design in Electronics Today International, May 1977, with fatter inductors and a KEF aB tweeter section, a library search might prove fruitful.

The Tangent TM1/TM3 crossover is really good sounding "state of the art" design.
If you change the 1mH bass inductor to a 2mH one in the circuit and the bass unit from a SP1014 to a SP1022, you get the KEF Exhibition bass section, which also sounds really good, ie the Falcon 103SP for the Cadenza.

Regarding the phase shift, follow the instructions on Falcon's "hints and tips" and listen closely.
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Larry
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Joined: 25 Jan 2006
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Location: Regina, Canada

PostPosted: Sun Sep 17, 2006 6:35 pm    Post subject: Reply with quote

After giving this a bit more thought, and considering your comment that the Tangent crossover is a really good sounding design (which is what I was really looking for), I think I'll simply go with the full Tangent circuit rather than mixing the Tangent and KEF sections.

There is a company in the U.S. by the name of North Creek Music http://northcreekmusic.com that claims to offer high quality air core inductors (custom made too) using wire up to 8 gauge Shocked . Considering my speakers are only rated for around 50W what gauge of wire would you consider adequate for the inductors in the bass circuit? I'm sure that at a certain point the cost of using larger gauge wire outweighs the return in performance.
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ColinR
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PostPosted: Sun Sep 17, 2006 8:33 pm    Post subject: Reply with quote

0.71mm or 22 gauge was the most common "large sized wire" used for KEF based circuit designs supplied by M.J. when you asked him about 50-100W crossovers for >100W amplifiers.

So I'd say a 1mm to 1.25mm, 19 or 18 gauge is going to give you the "best bang for your bucks" if you are going to use air cores.

Quote:
8 gauge


Er that's what we use for 6000-15000 Volt A.C. local power distribution in the UK Shocked .
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Larry
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PostPosted: Sun Sep 17, 2006 9:06 pm    Post subject: Reply with quote

Thanks Colin. I think I have enough info now to start this project. Yeah, those 8 AWG inductors would be HUGE Laughing, and they're expensive too. Obviously not for the home stereo market. All the info is on the company's website.
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Larry
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PostPosted: Sun Nov 19, 2006 7:15 am    Post subject: Reply with quote

Well, I had planned on upgrading these crossovers as a "winter project", but things moved along a bit quicker than I had anticipated. With some guidance from Colin I put together a couple of Tangent TM1/TM3 circuits using Solen polypropylene capacitors and custom wound, 18 AWG, air cored inductors from North Creek Music. My initial plan was to use point-to-point wiring, but I found a good piece (and large enough for two crossover boards) of printed circuit board material in my electronics stock pile so I designed a PC board layout instead. Before installing these new crossovers I was going to bench test them for frequency response using a signal generator that I built some time ago, but that idea didn't work out so well as the load was simply too much for the generator to handle. Sad The only thing I could tell from the scope was that someplace around 3500 Hz there appeared to be a crossover point.

In lieu of the bench test I opted for a simple subjective test. I replaced the crossover on the right speaker only while leaving the left speaker with the original DN13 (SP1106) installed, and then played a number of selections while listening first to the right speaker and then to the left (balance fully right and then fully left). While this wasn't very scientific it did provide some insight as to what I could expect. The speaker with the new crossover had tight bass and the overall sound seemed to "fill" the space in the vicinity of the speaker - if that makes any sense Confused. On the other hand, the speaker with the old crossover had, in comparison, loose bass and prominent mids while the sound seemed to be coming from a specific point on the speaker. Needless to say it didn't take me long to install the new crossover in the left speaker Smile

Over the last couple of weeks I have been listening to all types of music - country, folk, rock, and even opera - and I still can't believe just how much better these TLs sound Shocked . The clarity of the vocals and the instrumental subtleties that were invisible before make my CD collection (and 70s/80s vinyl collection Laughing ) seem new again!!

This upgrade was well worth the time and cost. The only downside for me was that I couldn't mount the new crossovers internally as they are quite large and the speaker cabinets are "finished" so I would have had to work through the B200 mounting hole - not worth it so they're mounted on the back.

Thanks again Colin for your help!
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