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Revisiting Jim Rogers JR149s

Thanks for your reply’s, David are you saying to take out the wire link and insert a capacitor in there ?

I’ll message Falcon and see what caps are in the kit that they sell for the 149’s

At the moment they sound fine but I just want to restore them...
Correct, the capacitor cuts the <3kHz power reaching the tweeter. I think the kit should contain the additional capacitor as it is used in the later crossover, but check.
I cannot read all of the resistor values in your photo, can you compare against the circuit I posted.

I would try to measure the speakers if possible to see where you are starting from, it might be worth adding the felt around the tweeter that is fitted on later units.
 
Note that the crossovers with a wire link also have an extra resistor compared to the non-link type.
 
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All these crossover variations are fascinating. It would be very interesting to reverse-engineer the red-logo version and figure out what exactly is different. It is only recently I realised there is more than the fuse! I find the apparent randomness of resistor values baffling.

One can assume the fuse was added as a reaction to more returns than expected, that is perfectly logical. The deadsheet and foam around the tweeter, plus the additional component are the opposite of cost-cutting, so all must have been added an ‘improvement’, though there seems to be no consensus that later ones are any better. The red-logo ones actually seem to be worth more. I’d love to hear the difference as my first pair back in the late-‘70s were red-logo, my current ones I think are about the last of the gold-logos.
 
All these crossover variations are fascinating. It would be very interesting to reverse-engineer the red-logo version and figure out what exactly is different. It is only recently I realised there is more than the fuse! I find the apparent randomness of resistor values baffling.

One can assume the fuse was added as a reaction to more returns than expected, that is perfectly logical. The deadsheet and foam around the tweeter, plus the additional component are the opposite of cost-cutting, so all must have been added an ‘improvement’, though there seems to be no consensus that later ones are any better. The red-logo ones actually seem to be worth more. I’d love to hear the difference as my first pair back in the late-‘70s were red-logo, my current ones I think are about the last of the gold-logos.

Any comparison between Red and Gold label variants would at least need to use the exact same drive units to rule out that variable. I briefly owned a pair of red logo 149s (freshly recapped with ALCAPs) and didn't rate them, but there have also been gold logos I didn't like the sound of. I suspect drive unit condition is the biggest influence in all of this.
 
Or off value electrolytics. Using them in tuned filter circuits did not have long term performance in mind. Reduce a value by 50% and a quack notch will completely miss its target and actually boost it.
 
Or off value electrolytics. Using them in tuned filter circuits did not have long term performance in mind. Reduce a value by 50% and a quack notch will completely miss its target and actually boost it.
True, but one would hope that relatively fresh ALCAPs would still meet their basic ±10% spec, or tighter ±5% spec, if that's the spec that was purchased.
 
Also remember that in this thread we have seen one of Tony Ls? boards with a wrong value resistor fitted. Mistakes do happen, especially when people recap a board without a circuit diagram of component references.
 
Also remember that in this thread we have seen one of Tony Ls? boards with a wrong value resistor fitted. Mistakes do happen, especially when people recap a board without a circuit diagram of component references.

I’m certain that the red logo board pictured in the Flikr link on the preceding page is factory stock. I am with my mismatched pair too. Mine have to be an error, there is no legitimate reason they should be the way they were. I can understand the resistor brand differences just being what was to hand at that particular time, likely as ine batch ran out and a replacement was opened, the value difference being a mistake as there was a component elsewhere on the board of that value.

The red-logo pair look like a different circuit. There is a component less and at least one cap of a different value. I’d love to see it modelled as I suspect it is exactly as it is meant to be, and if they were mine that is how I’d rebuild them, i.e. I’d keep the 3uf cap as I’d assume it was meant to be there on that early board revision.

PS Just to get them on the same page here are Woadl’s red logo pair:

33777709118_616b28d2f6_b.jpg


Here’s my rebuilt gold logo:

46669333415_d52fab95b2_b.jpg
 
Notice the yellow box plastic capacitor. I think that this is the 1.5uF bass notch, so arguably the most critical value. On later boards this became an ecap, supplier reduction or cost perhaps?
 
I would love to keep them exactly the same but I cannot find 3uf NP caps anywhere
Any suggestions ?

I must admit this is fascinating reading and the fact that there is so many variants is amazing
 
Just doing a basic count there isn’t a ‘missing component’ on the red logo board, both have 15 not counting the fuse! Where did that idea come from?
 
Would you like more pictures ? I can give you the track side as well...just need to take them apart and photograph

By the way .....how do you embed pictures in the message ?
 
I would love to keep them exactly the same but I cannot find 3uf NP caps anywhere
Any suggestions ?

What was the original spec? If it was +/-10% 3.3uF is actually within, and if you could persuade a seller to select you a pair that read low you’d be well in!

PS On Flickr chose the bent arrow share icon and then choose BBCode.
 
On the tweeter section 3 and 3.3 are a straight swap. Just make sure left and right are the same.
The only precision part is the series tuned circuit in the bass
 
Hey i'am new here and i own since a few months a pair of Jr149 mk1 gold with serial number;7268 they don't have a fuse and they don't have the 1.5mf capacitor for the notch filter but instead mine has a 2.2mf capacitor. i recapped them with Mkp caps, and this was really necessary because the old elcaps drifted al over the place! i also changed one t27 that was killed in action. I placed the filter externally in a bamboo cabinet bought from ikea. wired it up with 4pol cable and a neutrik speakon 4pol connector. They sound absolutely amazing. Also would like know if there are more differences in filter part al over the productian range. Cheers Marc
 
Just a note on these speakers which I thought people looking at this thread might appreciate. In a paper by Hardwood, Whatton and Mills, "The Design of the Miniature Monitoring Loudspeaker Type LS3/5A", BBC RD 1976/29, pub. Research Dept., Eng. Div. British Broadcasting Corporation, 1976 October

There is a need to monitor sound programme quality in circumstances where space is at a premium and when head- phones are not considered satisfactory. Such circumstances include the production-control section of a television mobile control-room, where the producer responsible for the overall production of the programme needs to monitor the output from a sound mixer but at levels lower than those used for mixing.

Not surprising that Tony's getting good results from quiet near field listening, given the design objectives.
 


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