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Revisiting Jim Rogers JR149s

Discussion in 'classic' started by Tony L, Mar 21, 2013.

  1. Tony L

    Tony L Administrator

    When measuring DC offset have no input connected and the volume right down. I’d just leave the amp on a day or two away from the speakers to properly form the new caps etc, then have a look at the DC offset and as long as it is no worse it should be ok. Those values are rather higher than I’d expect, and imply distortion will be a bit above original spec, but they’ll do no harm to the speakers.
  2. martin clark

    martin clark pinko bodger

    50mV dc offset into a B110 is only 6mW dissipation and a cone offset of 0.02mm (calc from the Thiele-small data)
    Utterly trivial, don't worry about it.
    Jeddy likes this.
  3. littleaudioco

    littleaudioco Trade: the little audio company

    I’d be scared of replacing the crossover or drivers in mine for fear of them not sounding the way I’m used to them sounding anymore...I like the way they sound, but I can’t help think what they would sound like with everything updated. I have two pairs, so I suppose I could butcher one pair... :)
  4. Jeddy

    Jeddy Member

    Hmm, possibly not good news. I tried the amp against some other speakers and they sounded ok which gave me confidence to try them with the JR149s. It sounds like there is no bass at all. :( I then tried the amp against some Stax headphones (yes, they connect to the same speaker posts) and it sounded fine (normal bass and treble). I've opened up the JR149 again and the bass are definitely connected, so I either have a problem with the bass units again or the cross-over (which has had new cap kit from Falcon installed). Pushing a little on the bass units they didn't move, pushing a little harder one has suddenly freed but now when I move it in and out I can hear it rubbing at the back (sort of paper on paper noise, but slightly deeper). I have a horrible feeling I need yet another pair of B110s. :( Unless there is any way to 'fix' these (even if only to test the cross-over before installing more B110s).
    £10 worth of caps is becoming very expensive in terms of subsequent damage.
  5. Jeddy

    Jeddy Member

    I agree with you and the 'if it ain't broke' principle, unfortunately in my case when I tried to resurrect mine which I'd not used in ages with an amp not used in a while it blew the bass driver(s) so I was forced into replacing them. Given I'd not used them in quite a while, I wasn't going to notice a sudden difference if changing the caps in the cross-over changed the sound slightly. So long as nothing is broken in yours you also have the option of reversing any changes if you don't like the way they sound after the changes, but I have to say if you like the sound I'd leave them alone.
    littleaudioco likes this.
  6. jtrade

    jtrade pfm Member

    Is it a sort of "chuffing" noise ? If so, it might be what is called "voice coil rub" & might be fixable.

    One example (nothing like a B110, I'm afraid) :
  7. Jeddy

    Jeddy Member

    Yes, chuffing describes it nicely. Nice idea and thanks for the suggestion, however the back of the B110s is all sealed up, not quite sure how to open anything up (without damaging it beyond use).
    Chuffing annoyed too!
  8. Dowser

    Dowser Learning to bodge again..

    If the cones moved ok on the B110s when you received them from Falcon, and were then locked, 99% the coil has overheated melting the varnish and causing the rub. If you tested the amp on other speakers OK, then there must be something wrong in the crossovers you recapped - photos would help in diagnosis.
  9. Jeddy

    Jeddy Member

    Sorry, the chronology is confusing.
    I wanted to get the JR149s going again as a second hifi, they'd not been used for a while having been lent to my nephew. Also the Roksan amp hadn't been used for a while either as I'd been using my late fathers hifi since he passed away. When I tried using the JR149 / Roksan something was obviously wrong, I worked out it was the original bass drivers so bought 2 new B110s from falcon. I assumed my nephew had just returned them having burnt them out so didn't think much about it. They weren't used much for a while but when I tried to use them it was apparent I again had problems with one, I returned to falcon who said it had burnt out. I bought 2 more! Again after occasional minimal use I found I again had problems somewhere. This prompted me to start looking elsewhere and question my amp / preamp. I took this to a hifi repair chap who looked and said the caps in the amp were leaking and wanted £200-£300 to replace 12 caps. I declined. I've now replaced the 12 caps myself (around 8 were obviously leaking) and tested the amp with other speakers and earspeakers and the amp is now fine, however it appears the amp has 'blown' the second pair of falcon B110s, or as you suggest, melted the varnish. It occurred to me I still had one good B110 which I've tested in one speaker and that's fine now, so I think my amp blew original bass drivers and one B110 replacement. However the amp is now fixed, but I only have one working bass driver.
    Is there a way to fix the melted varnish or do I need yet another pair of B110s? (Expensive game this, all for the sake of 12 caps).
  10. ToTo Man

    ToTo Man the band not the dog

    I'm still confused. Did you buy one pair of replacement B110s from Falcon or two pairs? If you bought two pairs and your amp has apparently been able to burn its way through three brand new drivers, then I'd be very hesitant to ever use that amp again on your JR149s unless it has been given the 100% all clear by a professional. Like you say, new JR149 drive units aren't exactly cheap. If it were me I'd probably just cut my losses and buy a different amplifier for them!...
  11. Dowser

    Dowser Learning to bodge again..

    I’d say another pair of B110s I’m afraid. However, which caps did you replace in the Roksan? I’m not familiar with their design, but can’t imagine an aged capacitor causing the necessary DC output to the speakers to cause the damage to the B110 Drive Units (maybe someone else can comment?) - I’d really like to be sure the amp Problem was fixed before risking another set of B110s.

    It may also be worth discussing with Falcon - they manufacture these units, so may offer you something for the dead ones if they can rebuild them with new coils.
  12. Jeddy

    Jeddy Member

    So far I've bought two pairs of B110s from falcon, both before the caps were replaced in the amp.

    The amp has 14 caps in it, 12 normal smallish caps (e.g. 1-2cm long) between the audio input and output all of which have just been replaced most of which were leaking and 2 large caps (e.g. 8cm long) at the transformer end of the board which appear fine and are also well away from the heat of the mostfets etc. I also cleaned the electrolyte from the board.
    Getting the amp checked out is a sensible option, although given the last chap wanted £200-£300 plus the £40 booking in fee just to replace 12 caps (which didn't even take me that long, for someone with all the professional equipment it shouldn't have taken more than an hour) I need to find someone else.

    I'll have a chat with falcon, but unfortunately they were all off with flu late last week. (Hope it's not that horrible Australian one, nasty.)

  13. Tony L

    Tony L Administrator

    So all drivers were damaged before the amp was recapped and DC offset checked?

    PS These days I’m only really prepared to use amps that are properly designed to fail-safe (speaker protection etc) or otherwise can’t damage valuable vintage speakers! Quad are excellent here, as are tube amps. I could just about stomach something taking out my B110s as they are replaceable, but not my Tannoys!
  14. Jeddy

    Jeddy Member


    Since the amp was recapped I've been listening to some music I'm familiar with through my Stax earspeakers (which use speaker posts) and that sounds as great as ever.
  15. davidsrsb

    davidsrsb pfm Member

    No crossover fault can break a woofer.
    I suspect an amplifier fault
    Jeddy likes this.
  16. Jeddy

    Jeddy Member

    Sorry, any chance you could link to that please, I'm having problems finding the FAQ.
  17. Jeddy

    Jeddy Member

  18. Tony L

    Tony L Administrator

    Excellent, many thanks.
  19. Tony L

    Tony L Administrator

    I know I said I’d never ‘mod’ my JR149s and my aim was only ever to restore them to stock, but, prompted by a rather argumentative thread in the audio room, I bypassed the tweeter fuses today. I figured it was such an easy and easily reversable thing to do it was worth a punt out of curiosity as my original red logo pair back in the ‘70s would never have had fuses (they were a later addition with the gold logo along with foam and dead-sheet around the tweeter). I just soldered a strap of solid core copper (actually some fancy Jupiter cloth covered stuff I had left over from building a passive pre for Lordsummit) on the back of the crossover board well out of sight, i.e. the fuse and fuse holder are still in place if I ever want to reverse it. I doubt I will as I really can’t picture ever selling these speakers, and driving them with valves I avoid any risk from DC etc. I’ve never blown a hi-fi tweeter in my life.

    It is certainly an audible change. I guess unsurprisingly they sound rather brighter and more dynamic in the treble range. Too much so to be honest, so I ended up backing the tweeter level off a tad (there is a pot on the board). Initially I had it just a little beyond the mid-way point, maybe three or four minutes on a clock face, I’ve now centred the pot exactly and it sounds bang on to me. They now sound exactly as they did previously tonally, not over bright at all, but with a little more acoustic space around things and rather better treble dynamics. Just a little freer and more open somehow despite these being real strengths already. They sound spectacularly good, but they did before too! I’m currently listening to the stunningly recorded and mastered Miles Davis Bootleg Series Vol 5 and they put the listener right in the control room.

    Worth a go if you are competent at soldering IMO, and don’t be put off by the initial brightness, a tiny tweak to the level pot fixes that completely.
  20. Martyn Miles

    Martyn Miles pfm Member

    I doubt Falcon will take the damaged '110s back. They can probably repair them, but they couldn't sell them on as new of course.
    Mind you, I could probably find a use for them. Doubtless other PF members could, too.

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