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Old 14th September 2012, 02:23 PM   #21
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Default Ditton 15: Electronic Crossover

OK, so I got brave and pulled the crossover out the back... There are two coils... the large one has "732" written on it and the one large capacitor has a rating of 12uf... If I understand this correctly, this means that I have a crossover of somewhere between 16 and 1800 hz... since 1800 is the lowest my new tweeter can go, then if I want it to kick in at 2,000hz, then I need to change that capacitor to a 9.95uf and leave the coils alone?

2-Way Crossover Designer / Calculator

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Old 14th September 2012, 03:41 PM   #22
system7 is offline system7  United Kingdom
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HeeHee, Brave is actually just what you do with old speakers. Have 'em in bits and check it all out.

Presumably first order slope coil on the woofer and second order 12uF capacitor and coil on the tweeter. You're right it's crossing over quite low, maybe 1800Hz.

The Morel CAT 298/MDT 29 isn't going to like that too much and you'll lose some maximum power headroom. The old 12uF is probably due to be replaced by now with a new 50V electrolytic non-polar. This monacor HT-22/8 might be a good replacement too:
HT-22/8

Some good info on the CAT 298 here at Eltim:
ELTIM CA 620

Also a look at modelling 1800Hz 10uF first order crossover for a typical dome tweeter using 10W wirewound resistors:
Sreten & Speakerman go at series XOs
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Old 14th September 2012, 04:52 PM   #23
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Default Ditton 15: Electronic Crossover

I have a midrange in a home-made 3-way system (5") that is similar to the HT-88s. In fact, I ordered a new pair at the same time I bought the Morels because the the paper finally tore on one of them from child-abuse (ah, the joys of parenting... the child was not abused but the speaker was). Cheapest midrange out there and yet it was/is the best-sounding. Looks like I'll be ok with a 10 uf capacitor ...2,000 hz... providing that coil is keeping the woofer at 2400hz, then I imagine the 400hz overlap is a good thing? Or should I run two caps in parallel to bring it closer to the 2400hz?
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Old 14th September 2012, 11:43 PM   #24
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Default Ditton 15: Electronic Crossover

Went to see a speaker driver expert. He sells refurbished speakers and drivers. He pointed out that although we do not know the actual value of the second coil ("733" stamped on it's collar) it was similar in size and stature to the 6.8mH coil that he was selling... combined with that coil, he calculated that a 6.8uF capacitor would give me the 2400hz cross-over that I needed... a big stretch from the 12uF capacitor that was found in my speaker! We then reasoned that since my coil might have a slightly higher value, that Celestion may have used whatever was handy in the heat of mass production and that since I probably would not notice the difference between 12 and 10uF, it would be a good safe bet to go ahead and use an 8uF capacitor... some times logic and science DO conflict! We also took into consideration that Morels might not consider the original planned change to be enough of an accomodation ... so I'm banking that a resulting (hoped-for) output of somewhere between 2400 and 3000hz will create the ideal sound (collectively) from both speakers. Overall gain should drop slightly with the 4uF change and the in-bred 89db sensitively of the Morel MDT29s. On the negative side, I could be full-of-it and be out 20 dollars for the capacitors. The unknown variable: the actual value of that 2nd, smaller coil... the other fly-in-the-ointment is that the coils are mounted parallel to each other, as opposed to at right angles or at least, beside each other... this too, apparently, can effect the performance of the coils....aaaarrrrrggghhh! It just gets better!
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Old 19th September 2012, 07:38 PM   #25
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HI There, can anyone advise of the correct replacement unit for the celestion ditton 15xr bass driver? I bought a pair on ebay and unfortunately the bass on one of the speakers crackles - am i right to assume this needs replacing?
any help greatfully recieved!
thanks
James
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Old 23rd March 2014, 12:59 PM   #26
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Hi, went to the local charity shop yesterday and got two pairs of Celestion 15' they are the older ones not the xr's.

Both pairs work fine, can I mod these together to try to improve them? I was thinking of fitting one of the speakers into where the ABR is, effectively making it a 3way like the ditton 33. Is it worth it or should I restore as in and just update the internals, crossover etc?

Any thoughts appreciated!
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Old 3rd August 2014, 01:14 PM   #27
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Hi, is there anybody out there who can help me? I have recently restored a pair of 15's, new binding posts etc, replacing the original 12uf 50v crossover capacitors like for like ( they were 41 years old! ), the difference was remarkable. Deciding to go a step further i replaced the hf1300 tweeters with Morel Cat 298 ( 94mm version fits the rebate perfectly, just a bit of shaving for the magnet ) however although more detailed they do sound somewhat "bright" to say the least. I have heard that by replacing the 12uf cap with a 8uf may solve the problem?
Idea's anybody.
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Old 4th August 2014, 07:16 AM   #28
system7 is offline system7  United Kingdom
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I think that what you are running into here, Louis, is the Ditton 15 used the Celestion HF 1300 Tweeter, and the later 15XR used a more regular soft dome.

The Ferrofluid Morel CAT 298 soft dome is a good replacement for most of the old tweeters, being available in 94mm, which can help.

BUT, the HF 1300 crossed over much lower than regular soft domes. Maybe 1800Hz as opposed to the sort of 3.5kHz that would suit the Morel better.

So the 15XR had a different crossover. 4.7uF rather than 12uF in the treble section. I can't comment on coil values unless you measure them.

This is a very simple filter, and really not the last word in refinement. What you need to do is get a capacitor around 4.7uF on the treble section, then fit an attenuator to get level right. Say 7W wirewound or ceramic resistors.

Typical values:
1R/22R for 1dB.
2.2R/15R for 2dB.
3.3R/10R for 3dB.

41 year old bass units often sag and rub, sounding harsh, and turning them 90 degrees can help.

I include the sort of filter that I employ myself in this situation. A bit more sophisticated.
Attached Images
File Type: jpg Celestion_Ditton_15XR_Crossover.JPG (42.5 KB, 37 views)
File Type: png Simple Circuit Celestion Two Way.PNG (7.1 KB, 38 views)
File Type: png Simple Circuit Freq Response.PNG (20.0 KB, 38 views)
File Type: png Improved Circuit Celestion Two Way.PNG (7.3 KB, 39 views)
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Old 4th August 2014, 09:30 AM   #29
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Thanks Steve, perhaps i should have said that these are not the Ditton xr just the standard version with the as you say rather basic crossover,would the 4.7uf capacitor you recommend therefore replace the 12uf?
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Old 4th August 2014, 10:40 AM   #30
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Quote:
Originally Posted by louegee0151 View Post
Thanks Steve, perhaps i should have said that these are not the Ditton xr just the standard version with the as you say rather basic crossover,would the 4.7uf capacitor you recommend therefore replace the 12uf?
. I have checked with my local branch of Maplins for the wirewound resistor, they have a few versions of the 7w at varying ohm ratings, which would you say would be the most suitable?
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