Celestion Ditton 25 help needed

[Ted Kendall]

I think the point here is that the speakers in question sound different to the OP from a nominally identical pair. Given his comments about the bass end, I wonder about the condition of the ABRs, besides the crossover question.

[ajgriff]

I think Ted's point about the passive radiators is very pertinent. It's also evident from the photo in post #1 that the mid-range drivers differ in some way which would more than likely cause the two channels to be unbalanced in terms of frequency response. All this leads me to wonder whether of not upgrading the crossover components is the real solution. Also, if one driver has been changed in the past that might explain why someone has changed the crossover capacitors. It would be interesting to know if the current capacitor values are the same in both units.

Alan

[m0cemdave]

Originally Posted by landlesspesant

And i wonder if the choice of pp caps was also a compromise .. As the XO was made with electrolytic in the early days ..
Someone said that ALCAP or MKP would be a good replacement ...
I don't know the pros or cons of either !

The compromise would have been in the use of reversible electrolytics - they were cheaper and smaller than plastic film types.

The electrolytics are only available in low voltage ratings and can be expected to have a definite service life, 25 years or so. They are likely to deteriorate gradually with age and eventually need replacing.
They were very commonly used in home hi-fi speakers rated at, say, 50 watts or less, and are probably OK for that application. But plastic film capacitors would, from a technical point of view, be considered an upgrade.

When I worked for a loudspeaker manufacturer we always used polypropylenes (sourced from SCR in France) and wouldn't dream of using electrolytics. This was because they were available in higher voltage ratings (we made high power systems for professional use, not domestic hi-fi) and were expected to be more reliable, with an indefinite service life. But they are a lot bigger, and considerably more expensive.

[landlesspesant]

Originally Posted by Ted Kendall

I think the point here is that the speakers in question sound different to the OP from a nominally identical pair. Given his comments about the bass end, I wonder about the condition of the ABRs, besides the crossover question.

I've found that the internal cross bracing need attention where the glue has failed.. this is the likely culprit ... I hope

Originally Posted by m0cemdave

The compromise would have been in the use of reversible electrolytics - they were cheaper and smaller than plastic film types.

The electrolytics are only available in low voltage ratings and can be expected to have a definite service life, 25 years or so. They are likely to deteriorate gradually with age and eventually need replacing.
They were very commonly used in home hi-fi speakers rated at, say, 50 watts or less, and are probably OK for that application. But plastic film capacitors would, from a technical point of view, be considered an upgrade.

When I worked for a loudspeaker manufacturer we always used polypropylenes (sourced from SCR in France) and wouldn't dream of using electrolytics. This was because they were available in higher voltage ratings (we made high power systems for professional use, not domestic hi-fi) and were expected to be more reliable, with an indefinite service life. But they are a lot bigger, and considerably more expensive.

Thanks Dave ... If I proceed with alcap ..to get the 3.2uF all I can find at the mo is 2x 1.5uF = just 3 and not the 3.2.. about 7% off is that acceptable ?
...And I'm gonna have to mix a 50v 1.5uF with a 100v 2.2 uF to get the 3.7uf also is that acceptable ??

After reading this in another thread
::::::
"" I'm now trying to decide whether to swap the polyprops I put in the bass filter for alcaps or to add resistors in to try to compensate for the reduced ESR of the PPs. Or something else entirely. Either way, it's been an enjoyable experience and the results so far have been very entertaining indeed"" :::::

I don't have the ability to know what ESR means ... But the Bass is so warm on my old pair that .. I'd hate to cool it down by putting in PP

But this decision is just a guess ... All help appreciated and Needed
Thanks Dom

[landlesspesant]

Hi there ... thanks for all the help with this
So I've removed 1 board and the values are
25 uF
2.2 uF
3.2 uF
3.7 uF
Red ones say Metallised on them ...
After reading up what i can ... I'm thinking to get all Alcap low loss .From Falcon acoustics.. If any one thinks this is a bad idea .. Please let me know ASAP

[landlesspesant]

Originally Posted by RojDW48

I have (so far) re-capped one of my Radford Studio 60 T-lines and the difference is just about discernible. Don't expect miracles - maybe we could compare these 'upgrades'? Whereabouts in Bristol are you? I'm in Whitchurch Village.

I'm in Royate Hill not far from J2 M32

['LIVEWIRE?']

E.S.R. = Effective Series Resistance, which should be as low as possible. (It's the internal resistance in series with the capacitance and is present in all capacitors)

[dave cox]

Forget ESR. It’s really not relevant in this crossover.

Using 'film' caps has the advantage of closer tolerance and better reliability.

Closer tolerance is better for the stereo image, as the typical range of values that come from (reversible) electrolytic types mean than one speaker does something audibly different from the other and both are nearer to the design specification. Its possible (just barely) that the manufacturer selected electrolytic components to give a better spec but you need to buy a lot to make this work and have somewhere to dump all the rejects.

Reliability is not much of an issue for typical domestic use, the capacitors do not get worked hard and will last a looooooooog time! A bit different for PA, but typically the high power stuff won’t have passive crossovers anyway.

dc

[landlesspesant]

So I'd just like to say a thanks to every one for all the help ...
So it looks like I will use Solen 400v MKP ..
But I'm still toying with the Idea of using ALCAP 100V low loss for the 24uF
from Falcon ...

I'd like to make the order Today Saturday 28/7/18 .. !! but might hold off till Monday ..

[landlesspesant]

So I've just started on repairing the bracing

[Edward Huggins]

That red and black internal wiring looks to have a rather thin gauge.

[landlesspesant]

I was thinking that too ....

[ajgriff]

I'm sure that securing the bracing will make a worthwhile difference. Referring to my earlier post (#22) are the mid-range drivers identical and do the capacitor values in each crossover match? Just interested.

Alan

[landlesspesant]

So Am I
The 1st Photo in this thread .. Is of 2 different pairs .one is an earlier set than the other .... I got the 2nd (newer) set last month June 2018 for £100
these are the ones I'm messing with now .. each pair has identical boards .. but the caps are different in each pair ... due to different factories and age I guess

[ajgriff]

Thank you for the clarification. So, are the capacitor values the same in each crossover or is it just that different makes/types have been used?

Alan

[landlesspesant]

I've not taken the older ones apart yet ... so not had a close look at the values.. Here is a pic of the older XO .. I think they are gonna be the same .
There is a difference between the newer pair and the Values from previous posts about 25's ..

my newer pair values seen = 25 uF 2.2 uF 3.2 uF 3.7 uF

and an old thread schematic = 24uF 2 uF 3uF 3.5 uF
The caps in the older thread looked like they were the older Electrolytic type

Any Ideas which values I should go with ?

[landlesspesant]

I don't have a good amp that can handle the 4 25's at once . I had them running on a horrible pioneer amp .. it gave off a wall of sound rarely heard in a terraced house lucky I've got great neighbours ..
But the quality wasn't there ... So now I just have 1 pair running on a quad 405 and 34 pre ... its a beautiful thing

[landlesspesant]

Originally Posted by 'LIVEWIRE?'

E.S.R. = Effective Series Resistance, which should be as low as possible. (It's the internal resistance in series with the capacitance and is present in all capacitors)

Thanks ... I'm still learnig

Originally Posted by dave cox

Forget ESR. It’s really not relevant in this crossover.

Using 'film' caps has the advantage of closer tolerance and better reliability.

Closer tolerance is better for the stereo image, as the typical range of values that come from (reversible) electrolytic types mean than one speaker does something audibly different from the other and both are nearer to the design specification. Its possible (just barely) that the manufacturer selected electrolytic components to give a better spec but you need to buy a lot to make this work and have somewhere to dump all the rejects.

Reliability is not much of an issue for typical domestic use, the capacitors do not get worked hard and will last a looooooooog time! A bit different for PA, but typically the high power stuff won’t have passive crossovers anyway.

Thanks .. All helpful to know

[ajgriff]

Perhaps I should explain my thinking. Basically I believe that it's worth trying to understand why the newly acquired pair of speakers sound different from one another.

The loose bracing will certainly have some affect and it would be worthwhile having another listen once the glue has set and before changing anything else. Ideally listen to each speaker in turn driven by the same amplifier channel with exactly the same source.

As always with these things it is best not to change more than one thing at a time so that you can be relatively sure about what does and does not make a difference.

Hope this helps.

Alan

[landlesspesant]

""As always with these things it is best not to change more than one thing at a time so that you can be relatively sure about what does and does not make a difference.""

Ive cut some of the caps out to see there values .. so thats not happening at this point .. But eventually I will be swapping the XO from the new pair to the old pair to compare the difference.

And it is a big help thanks