advertisement


Revisiting Jim Rogers JR149s

There are a pair of “cryogenic” Type 24s in eBay here. Very interesting to look at them closely as they look to be pretty much hard-wired on a generic board rather than a professional production. Given the crazy low-cost of modern low-run bespoke PCBs it would be possible to do them a heck of a lot more neatly now if there was any real benefit to the underlying design. Not something I’d pursue as I just love the originals as what they are, but an interesting project.
 
This site contains affiliate links for which pink fish media may be compensated.
I find any electrical item that has been ‘cryogenically treated’ somewhat suspect.
At Oxford Uni. I was involved in a certain amount of cryogenics and know what effect low temperatures have
on various materials.
That knowledge makes me extremely cynical about some of the claims made by some purveyors of audio equipment.
 
Yank said:
Any less baffle step than the original and they'd need to be wedged against the wall Kan-style.
Click to expand...
The original crossover has quite a high amount of baffle step, does it not? It certainly looks that way from the amount of cone excursion that can be seen from the B110 at what would be considered pedestrian SPLs. I don't think it would be physically possible to employ any more baffle step without pushing the B110 beyond its limits. I think the amount of baffle step in the original crossovers is perfectly adequate for a small monitor and makes the JR149 sound surprisingly 'solid' for its size, though I suspect the inertness of the cylindrical enclosure is also responsible for this 'solidity' and lack of colouration in the lower registers.

A bit off topic, but for years I've owned a pair of IMF MCR2A mini monitors fitted with KEF T27 SP1032 tweeters and B110 SP1003 bass units and a very simple crossover, instead of the stock IMF TW2100F tweeters, 5/36 bass units and corresponding crossovers. It's a very long and in parts conflicting story, but apparently these were put together with KEF units at short notice near the end of IMF's trading, to be used to demonstrate Ambisonics surround sound technology. At the time I was puzzled as to why these monitors were so bass-shy compared to the likes of the LS3/5A and JR149; I had no understanding of baffle step correction and crossovers needing to be designed to act as EQ to counter LF rolloff in small speakers. Being such a basic crossover I also doubt if there is any "anti-quack" filter present so the response is unlikely to be flat. I have not listened to them for many years (they are safely boxed in their original packaging) so I haven't measured them, but I do remember them sounding incredibly open, present and revealing; perhaps a little too revealing! This was also the first time I discovered just how much effect those little perforated brass grilles on the T27 have. With the grilles on the treble becomes significantly more incisive and extended.

48299925781_55fab46c19_b.jpg
 
They look really nice, rather similar to a Kef R101! It would be interesting to see how they compare to a Kan as I guess that is entirely without baffle-step too.

How does the JR149 compare to the LS3/5A when it comes to baffle-step and cone excursion? Subjectively I’ve always had the impression that 149s like walls rather more than the 3/5A as they lack the upper-bass ‘bump’, which surprised me given the BBC OB vans etc suggested use for the 3/5A where they’d have been very close to both walls and a mixer/table. I definitely feel the 149 is too lean fully in free-space, though it needs more space than a Kan.
 
American walnut is a lovely finish, I wish more speakers used it. I'll dig them out of the cupboard at some point to measure them as I'm curious as to how much the bass drops off. The only other speaker I've had with a similarly lean bass output is the original Goodmans Maxim.

PS - I have a 2nd pair of MCR2A cabs in my cupboard equipped with their stock crossovers and 5/36 bass drivers, but patiently awaiting the arrival of a pair of TW2100F tweeters. If anyone has or knows of a pair, please let me know, because I've been searching for 9 years without success! This is what they look like:

2114204-imf-irving-m-fried-mc2ra-bookshelf-speakers-england-clone-of-rogers-ls35a.jpg
 
In the years where all British speakers had teak veneer, all American speakers used walnut.
 
Tony L said:
They look really nice, rather similar to a Kef R101! It would be interesting to see how they compare to a Kan as I guess that is entirely without baffle-step too.

How does the JR149 compare to the LS3/5A when it comes to baffle-step and cone excursion? Subjectively I’ve always had the impression that 149s like walls rather more than the 3/5A as they lack the upper-bass ‘bump’, which surprised me given the BBC OB vans etc suggested use for the 3/5A where they’d have been very close to both walls and a mixer/table. I definitely feel the 149 is too lean fully in free-space, though it needs more space than a Kan.
Click to expand...
The JR149 was voiced to use a sub, the LS3/5A was not meant to be a full range speaker
 
davidsrsb said:
The JR149 was voiced to use a sub...
Click to expand...

I don’t think that is true; the original 149 had been out a good couple of years and gained many rave reviews as a stand-alone mini-monitor before JR brought a sub out. I’d find it far easier to believe the unreleased Type 24 crossovers were designed for the sub given they seem to reduce the bass output.
 
Tony L said:
Very interesting to look at them closely as they look to be pretty much hard-wired on a generic board rather than a professional production.
Click to expand...

The Type 24 was indeed a 'cottage industry', produced by Graham H. I think it was his attempt to bring the Type 24 to the masses, being of limited interest to anyone other than 149 owners, a more professional production/presentation would not have been cost effective. I think Graham's interest in producing items for the 149 was more out of interest rather than being motivated by profit or ' building/promoting a business'. The last time I saw Graham he had made a Dalesford 'D' type cabinet and was playing with a B110/T27 combination with them.
I'm in agreement with Tony, I think the Type 24 x/over could well have been designed with a sub in mind, when I get time I'll swap x/overs and see how they fare with a JR sub (passive) and a Rel (active).
 
Hi All,

I've a very early pair 2400's and I seem to have mullard caps built into mine! Anyway I have a couple of questions. I wish to keep the originality of the JR149's but I'm a little confused about the types of caps and resistors. I've read all 34 pages and I believe that the resistors are carbon film and the caps are electrolytics. I've decided to go with Takman 2% tolerance resistors. I'm undecided about the Caps. The Falcon Acoustics website uses 5% toleranced Alcap Low Loss and Polyester. So do I use Polyester or Electrolytic for originality. Finally do I have my resistor and cap values correct :-

CAPS

There was a 1.5uF, 2.2uF and 3.3uF in the woofer circuit, and two 3.3uF on the tweeter.

RESISTORS

4.7, 5.6, 22, 82, 15

Thanks in advance.
 
Rexton said:
Hi All,

I've a very early pair 2400's and I seem to have mullard caps built into mine! Anyway I have a couple of questions. I wish to keep the originality of the JR149's but I'm a little confused about the types of caps and resistors. I've read all 34 pages and I believe that the resistors are carbon film and the caps are electrolytics. I've decided to go with Takman 2% tolerance resistors. I'm undecided about the Caps. The Falcon Acoustics website uses 5% toleranced Alcap Low Loss and Polyester. So do I use Polyester or Electrolytic for originality. Finally do I have my resistor and cap values correct :-

CAPS

There was a 1.5uF, 2.2uF and 3.3uF in the woofer circuit, and two 3.3uF on the tweeter.

RESISTORS

4.7, 5.6, 22, 82, 15

Thanks in advance.
Click to expand...
Interesting, when I purchased my replacement cap set from Falcon ALCAPs were the only option, a polyester option was not listed.
 
I’ve just won what look like a tidy pair of JR149 crossovers on eBay (link), the same version as my current pair (same 4-pin plug etc) with a view of rebuilding them with nice film caps etc. Could prove quite interesting as it will be so easy to swap them in/out with the current pair as a control reference.
 
This site contains affiliate links for which pink fish media may be compensated.
Should be good, he's got some other crossovers, for the JR149? The inductors look very low loss.

What I'd like to try is LS3/5a crossovers in the 149.
 
The other crossover pictured doesn’t look like a 149 crossover at all to me. No idea what it is, I don’t care either as I don’t think it is part of the sale and don’t want it. Looks like someone has written on the rear of one of the real crossovers as though they were reverse-engineering it or something. As long as the inductors and level pots are fine I’m sure they’ll be fine as I’ll be swapping everything else.

Assuming they turn up safe and sound and work ok I’ll likely go with the Kiwame resistors again as they seem really nice and are what I used in the other pair (plus have the values printed in text so I’m far less likely to make mistakes!). Caps will probably be Mundorf MKP as the 250V ones are available in all the right values and actually look like they will fit (the main issue here!). It will be interesting to see what value resistors are actually in them (I may need some help there as I struggle with the colour bands) and if they are the same both sides given what I found with my original pair. If the resistors are all identical types and values left to right I may even leave them be. I only swapped mine out to correct an error, and they all measured spot on with their colour-band values IIRC.
 
Got my second set of crossovers:

48687616731_7e851e15fe_b.jpg


They look in very tidy condition aside from the resistor at about 5:30 on the pic which looks to have cooked quite badly (obvious discolouration plus a slight scorch mark on the board). Now I don’t care about this in the slightest as I’m going to replace every resistor and capacitor on the board. All I’m bothered about are the inductors. I can get a multimeter continuity ‘beep’ across all of them. Is there anything else I can check with a basic multimeter to assess their health? The one next to the burned resistor clearly got hot enough that the cable-tie, which would have been resting against the resistor, failed (I’ve just replaced them).

Everything else looks fine, no cracks, lifted tracks, corrosion etc, pots look real nice (much nicer than my other pair), pins are clean. I don’t want to plug them into the speakers to test as-is in case they damage my drivers, so any advice as to establishing inductor health would be welcome.
 
Radfordman said:
Obviously, you can check that the inductors are not a direct short with you multimeter
Click to expand...

Unfortunately nothing is obvious to me when it comes to electronics, I only have the most rudimentary grasp of the subject at this stage! I seem to be getting about 0.4 Ohm for all of the inductors in circuit, so I assume that qualifies as ‘not a short’?

I suspect they are actually alright as I’d have thought the wax potting would show some obvious signs of heat leakage had any of them got hot enough to actually fuse together.

I’ve no idea what happened to them in their past life as I don’t know what that resistor does, i.e. were they just played too loud by an idiot, or did some crappy solid state amp ‘go DC’? I’ve no idea.

PS If anyone who isn’t colour blind has sufficient time on their hands it would be interesting to know if the resistor values on these boards match the schematic upthread somewhere? Given my other pair didn’t even match left to right it would be an interesting thing to know.

Here’s one of my current corrected/as per the schematic crossovers for reference:

46669333415_d52fab95b2_b.jpg
 
0.4 Ohms sounds reasonable, what reading do you get when shorting out the meter probes? If there is a reading, you need to subtract that from your reading of 0.4 Ohms. Unless one can see evidence of burning, I guess that the inductors will be fine.
 
You must log in or register to reply here.


advertisement


Back
Top