KEF 103 Reference Crossover Update

[bencat]

Good Afternoon

I have a pair of the original 1970's KEF 103 Reference speakers that I use daily and have owned for about four years. Ever since I bought them I have wanted to update the crossover as the originals have never been touched and are by now probably quite a bit out of alignment .

The issue I have always had is that if I change the fitted crossovers and find that it has changed the speaker voicing then it is not too easy to just reverse things.

Over two years ago I bought a full set of replacement Capacitors and resistors (I think I also bought Inductors as well but can not remember will check tonight) along with cable for a rewire and new foam strip sealant for the cabinet .

Just by chance today on checking e-bay I have been able to buy a pair of crossovers with mounting panels which means I can now sit and replace all the items at my leisure then remove the old crossovers and retain them safely in case I need to put them back rewire and replace the foam strip and I should have one updated pair of speakers .

Are there any pitfalls I should look out for ? Often more modern items are more efficient than those originally used and this can some times mean you need to change the resistor on the tweeter to get back the sparkle or tame the increased treble that you get . Should this be done by trial and error or is there a way to test for it ?

My soldering skills are not that great but should be able to manage this . Would you suggest fixing all components firmly to the circuit board ro is that not that important ?

 

[vintageaxeman]

Good Afternoon

I have a pair of the original 1970's KEF 103 Reference speakers that I use daily and have owned for about four years. Ever since I bought them I have wanted to update the crossover as the originals have never been touched and are by now probably quite a bit out of alignment .

The issue I have always had is that if I change the fitted crossovers and find that it has changed the speaker voicing then it is not too easy to just reverse things.

Over two years ago I bought a full set of replacement Capacitors and resistors (I think I also bought Inductors as well but can not remember will check tonight) along with cable for a rewire and new foam strip sealant for the cabinet .

Just by chance today on checking e-bay I have been able to buy a pair of crossovers with mounting panels which means I can now sit and replace all the items at my leisure then remove the old crossovers and retain them safely in case I need to put them back rewire and replace the foam strip and I should have one updated pair of speakers .

Are there any pitfalls I should look out for ? Often more modern items are more efficient than those originally used and this can some times mean you need to change the resistor on the tweeter to get back the sparkle or tame the increased treble that you get . Should this be done by trial and error or is there a way to test for it ?

My soldering skills are not that great but should be able to manage this . Would you suggest fixing all components firmly to the circuit board ro is that not that important ?

All sounds like a good idea to me.  I have done this several times before.

Don't worry about efficiency if you are replacing like with like values.  Modern capacitors and resistors of the same value, voltage rating, and either the SAME or LOWER tolerance (use 1% or 2% rather than 5% for example)should be used.

In the case of inductors, there are physically a few different types....if they're the same value, they will do the same job, BUT you should always orientate/position them the same way as the originals, or you may find that the crossover induces hum. Air cored inductors tend to be larger than iron cored ones, so if your replacements are air cored, you may have difficulty getting them to fit.

I also usually bypass (parallel up) large value film capacitors with 1/100th of their value using small 160v polystyrene capacitors. Does that make sense?

I also either use tie wraps or silicon sealant to secure components down.

Personally I would check the existing boards to see if they have a part number on them. You might find that they are the same as, OR DIFFERENT VERSION to the ones on eBay. Use the appropriate OR the most recent ones.

As I say, all sounds like a good idea to me. David

 

[SergeAuckland]

All sounds like a good idea to me.  I have done this several times before.

Don't worry about efficiency if you are replacing like with like values.  Modern capacitors and resistors of the same value, voltage rating, and either the SAME or LOWER tolerance (use 1% or 2% rather than 5% for example)should be used.

In the case of inductors, there are physically a few different types....if they're the same value, they will do the same job, BUT you should always orientate/position them the same way as the originals, or you may find that the crossover induces hum. Air cored inductors tend to be larger than iron cored ones, so if your replacements are air cored, you may have difficulty getting them to fit.

I also usually bypass (parallel up) large value film capacitors with 1/100th of their value using small 160v polystyrene capacitors. Does that make sense?

I also either use tie wraps or silicon sealant to secure components down.

Personally I would check the existing boards to see if they have a part number on them. You might find that they are the same as, OR DIFFERENT VERSION to the ones on eBay. Use the appropriate OR the most recent ones.

As I say, all sounds like a good idea to me. David

Just one word of warning:- Aircored inductors are not the same as cored inductors, even for the same inductance value. The difference is that an aircored inductor won't saturate, whilst a cored one will,  so if the originals are aircored, keep it that way. Secondly, a cored inductor will have much less wire, so the DC resistance will be different, which will in turn affect the Q of the tuning. 

So again, keep to the same type of inductor. Having said that, unless the coils have been overheated, and it's visually easy to see that, inductors have no ageing mechanism, so will not need changing. Non polar electrolytic Capacitors do age, and there's some evidence resistors do too, so worth changing, but unless you know the design calculations made for the crossover, K would always change like for like, and not make 'improvements' which may be anything but. It's quite easy to make the loudspeaker different to the original, much harder to make it better.

S

 

[vintageaxeman]

Just one word of warning:- Aircored inductors are not the same as cored inductors, even for the same inductance value. The difference is that an aircored inductor won't saturate, whilst a cored one will,  so if the originals are aircored, keep it that way. Secondly, a cored inductor will have much less wire, so the DC resistance will be different, which will in turn affect the Q of the tuning. 

So again, keep to the same type of inductor. Having said that, unless the coils have been overheated, and it's visually easy to see that, inductors have no ageing mechanism, so will not need changing. Non polar electrolytic Capacitors do age, and there's some evidence resistors do too, so worth changing, but unless you know the design calculations made for the crossover, K would always change like for like, and not make 'improvements' which may be anything but. It's quite easy to make the loudspeaker different to the original, much harder to make it better.

S

Thanks, Serge....for clarifying about air cored inductors for both Bencat AND myself. Very helpful info...I wasn't been sure of the specifics... Cheers mate. David

 

[bencat]

Thank you both for your advice it will be noted. David I know what bypassing is and have done this in the past . Forgot about how it can help but will keep this in mind . KEF were and probably still are a very professional and rigorous outfit and they have full Circuit Diagrams for all of their crossovers which not only show the value of all the parts used but also the reference for the board (in this case SP1050) and the issue number on the front (in this case P100293)  . As can be seen from the information I have they very kindly sent me a copy and I checked the two items I bought had the same references.

Just as a bit of belt and braces gave the KEF tech team a call and they very kindly confirmed that for this model there was no changes or upgrades of the crossover circuit board or parts over the like of the model .

I can confirm that all of the replacements I have are direct value replacements for the original but in most cases better Tolerances and different composition (Solen Caps rather than standard Electolytic) .

Given what Serge has said I think I will leave all of the Inductors as they are even if I have bought replacements and just change the other items to the modern equivalents I have .

 

[vintageaxeman]

Fantastic. Great advice from Serge as usual. Glad KEF are helping too! I used Solens on one of my important jobs and they are great!

 

[bencat]

Just a line to say after being able to study the pictures of the crossovers on e-bay when I got home I think I am a little luckier than I thought . I have pictures i took of my own crossovers inside the speakers and the capacitors are all bipolar electrolytic of reasonable but not not very high quality .

The boards I purchased have had all the Capacitors on the board except one a 4.7uF replaced with Monacor Metal Film caps which while they may not be the very best are a very good quality cap so the replacement work looks as if it has already been done for me. Checked this out with KEF and they never used this Capacitor the Engineer  I spoke to said they would be too expensive .

I have sent a question to the seller to find out if he knows anything about the boards and if he perhaps made the changes and if he changed the resistors as well which are two 10 R items .If these have been changed as well then aside from the 4.7uF electrolytic having to be replaced it will be a straight baord swop with very little work from me. All Caps have the values clearly printed on them including being + - 5% and they all match the original item according to the circuit diagram.

That is what you call a result .

 

[bencat]

Right crossovers arrived yesterday and as my wife Linda has been taken out by my eldest son for Mother Day I have had the house to myself . So the changeover has been made and despite my rather awful soldering technique I am pleased to say they are back in place in my computer room system and singing away in the back ground as i type this.

Firstly I am just delighted they work often when I have tried things before I have been greeted with silence and then spent long and sweaty hours chasing the work until I find the obvious mistake .

Now the really contentious bit , do they sound any different ? before anpiyone asks no I have not measured them before or after as i possses no equipment that will offer me anything meaningful nor would i probably understand any of the results . Apologies but I can only tell the truth about my lack of knowledge (or if I am honest interest) in the science of audio .

So deep breath yes they do in my opinion sound different . The overall voicing is the same as it was but there does seem to be more low bass and the midrange is a little more prominent than it was . All told I would class it as a difference at this time and not an improvement but will leave things to settle down for a few days and see how the speakers work after they have a had a few days music running through them .

 

[bencat]

Okay crossovers have now had few hours of constant music playing and I am starting to suspect that these have never been used after they were upgraded . As I do not have any real solid knowledge of this I was a little reluctant to stick my neck out when I first tried them but they sounded like quite a few component changes I have made over the years in paticular the change of the Mains Caps on my Krell . Replacements were great quality slit foil items but when I first lstened to them sound was okay but not much more . Two weeks later after a number of music sessions they opened out and sounded not only good but better than I had ever heard the Krell before .

Same sort of sonic signature with these crossovers quite nice bass increased lower bass but treble a little shut in and rolled off. Now after a good blast of music not the same at all Low Bass is still deeper and more detailed , midrange is now much closer intergrated with the treble which has opened out beautifully . Best example I can give is just listened to Neil Young playing Harvest Moon on Radio Paradise the flac stream . Neils voice is truly beautiful and now the inflections and nuances on the pjrasing are easier to hear . Sound stage has grown and I promise these are not a pair of speakers set up for that as I am listening to one side and not in anyhting like a central position but now the sound stage sounds like it should exactly as if I was listening to one side .

I am very pleased with this upgrade and will not be bothering to try any further changes to the new crossovers it amight well wring a little more out of the speakers but given how good they sound now I don not think the panic and sweat it would induce in me is worth it . I have alwasy liked these speakers ever since I heard then at a Bake Off and was really happy to get a pair .Now I can realise just how good they are and may have to give these a spin in my main system .

 

[oldius]

Great speakers the 103.