Ditton 66 for dummies ...

[Rigster]

Hi - I've had a warm welcome in the intro forum. This feels like a friendly place - thanks to all the respondants so far.
As I mentioned there - I think every piece of audio equipment I own comes under the 'past masters' remit. I haven't upgraded or introduced anything new since 1989.
I've spent the intervening years just enjoying the sound it made. The problem I've come across though follows a 2 year layup of the equipment due to
"decorating" reasons. Now that I've reininstated everything to where it belongs I've noticed the sound to be flat, uninvolving and right speaker biased - not as I remember it once was. I know that there
may be an element of rose tinted spectacles going on but I really don't think so.
The setup is:
Audiolab 8000A amp
Systemdek turntable with Linn arm / AT cartridge
Nakamichi RC202 tape (I have a large tape collection ..)
Sony CDP228esd CD.
Celestion ditton 66.

I made the decision (largely due to the vastly impressive sticky thread in this forum) that I need to give my Dittons some TLC. They're looking a bit sad & secondhand and I suspect that they are the source of the
problems above. The drive units seem to be mostly ok but I've noticed that the metal dome on one of the tweeters is beginning to come a little lose, the mids seemed fine until I tried a tone test cd & at about 100 hz & above there's an unpleasant almost mechanical sound on the right mid. The bass units both appear fine. My suspicion is falling on the crossovers.
The left side crossover has some different capacitors to the right. I'm sure Celestion didn't release them like that - the person I bought them from in 1989 worked for celestion so I would hope that they would be kosher but
I'm wondering if the crossovers in general might be a bit tired now & letting the side down?
If there are any 66 owners out there willing to help an amateur out I'd gladly trade knowledge for beer tokens ...
Thanks - sorry it's a long post,
John

[walpurgis]

Hi John.

The HF2000 tweeter phase plate (perforated metal cover dome) is well known for coming loose. It's just held on by thin double sided tape and can be refixed easily. Care should be taken in it's removal though. I'd suggest doing both as the adhesive on the 'good' one will be suspect too.

The odd sounding midrange unit may not be defective. It could well be a capacitor in the crossover failing. I'd suggest taking both mid units out and measuring the DC resistance at the connections. It should be around 6 ohms I believe. If that's OK test them using a capacitor in series, 8Mfd should do and listen at moderate volume on a music signal for output, they should sound similar. Check all crossover capacitor values. Most on AOS will likely tell you to upgrade them for modern equivalents. I'm sure somebody here can show you a crossover circuit or you can find one online.


Here goes, just found this. It may help:



I'd be inclined to remake all soldered joints too, including at the terminals, which may benefit from replacing. You may want to upgrade the internal wiring quality too.

[DarrenHW]

the mids seemed fine until I tried a tone test cd & at about 100 hz & above there's an unpleasant almost mechanical sound on the right mid. The bass units both appear fine. My suspicion is falling on the crossovers.

Hi John, I have Ditton 44's not 66's and I'm only in the early stages of restoring / modding them and I'm by no stretch of the imagination an expert, but I suggest simply rotating the drivers 180 degrees as the first place to start if you have not already done so. On the first pair of 44's I picked up I had a issue which sounds similar to yours which was caused by sagging in the rubber, I rotated it and problem solved, I have since treated the surrounds with a rubber restorer in an attempt to keep them in good shape.

The left side crossover has some different capacitors to the right. I'm sure Celestion didn't release them like that - the person I bought them from in 1989 worked for celestion so I would hope that they would be kosher but
I'm wondering if the crossovers in general might be a bit tired now & letting the side down?

The second pair of 44's I picked up have miss matched (yet what appear to be original) capacitors, so maybe some pairs left the factory this way?

Ken (Qwin) is the man to offer the best advice, is it his thread you referred to in your earlier post (http://theartofsound.net/forum/showt...light=ditton)?

[Rigster]

Thanks for the advice - I'll check the things you mention.
Does the fact that mine is one with the printed circuit board make any difference to the values on the diagram please?
A problem I forgot to mention, which may be diagnostic I don't know, is that occasionally the left speaker goes 'dead' with no output at all. If I put the balance completely over to that side & turn the wick up on the amp for a second it springs into life suddenly (and quite loudly). It will stay good for some time after that. My suspicions were that there is a bad connection (possibly the terminals you mention).
It does surprise me that we go to the expense of running decent cable throughout the signal path to suddenly hit what looks a lot like half a strand of bell wire inside the cabinet. Was that a deliberate design feature or a cost saving exercise?
John

[Macca]

The 66 is from before fancy speaker cable was invented.

[walpurgis]

Rotating the 66 midrange driver is unlikely to cure anything. It has a relatively low compliance suspension, and the old rotation dodge is most likely to work on units that have soft high compliance surrounds that have sagged, more usually bass units.

The cutting out and then coming back on under power is typical of dirty contact areas, perhaps new plugs & sockets may help, it could also be a 'dry' soldered joint. I doubt the use of a PCB has any influence on what you are hearing.

[Qwin]

Rigster - The circuit posted is for the early tag board x-overs and has slightly different values for two caps.

Find the later diagram linked on my thread.

Nipping out to hear some live blue's, will give a better answer tomorrow.

[Rigster]

Good point Martin - I hadn't considered that.
Sorry Geoff. I didn't mean the effect on the audio of the PCB. I meant does the fact that it is the PCB board mean that the components are different?
Thanks,
John

[Rigster]

I got ninja'd by Ken ...

[walpurgis]

Good point Martin - I hadn't considered that.
Sorry Geoff. I didn't mean the effect on the audio of the PCB. I meant does the fact that it is the PCB board mean that the components are different?
Thanks,
John

Ken seems to have answered that. Somebody here may have a Ditton 66 PCB crossover diagram showing values. Yours should be marked though.