JCM2000 DSL50 - thinking of buying one. Any advice?

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  • ICBMICBM Frets: 71960
    This is what the output board fix looks like.



    One wire on the left across the 16-ohm jack ground contacts, and three at the right across the impedance selector terminals.


    For what it's worth one of my jobs today is a DSL100 which belongs to a local rehearsal studio. It's died several times in the past, and I've not only done this to it but every other normal upgrade I do, and it's also running at 50W (having fried the main PCB around two of the valve sockets, I thought it easiest to simply remove them) so the power section should be under less stress. (The OT is running at the correct impedance, I swapped the taps.) To be fair, I haven't seen it for a couple of years.

    But even given all that, it's *still* blown the OT...

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • Thanks for the photo @ICBM ! :)
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  • ICBMICBM Frets: 71960
    edited September 2017
    … and another one bites the dust.

    One of today's repairs is a DSL100 with a badly burned PCB - it's a recent issue too, not one of the originals - and four blown power valves. Given the state of the valves it looks like the HT has got into the bias supply - a couple of the valves have started to literally melt. Even assuming there's no other damage, this is a £250+ repair. The new board and power valves alone come to about £170, and that's before labour and shop margin. Given that I would have to guarantee it I would want to do all the other known upgrades as well, which would add probably another £50. And that's even if it hasn't done anything more drastic like fried one of the transformers, which is quite possible.

    On that basis the owner has refused the repair estimate, which I entirely agree with. If it needs repeating, just avoid these amps unless you want to risk this sort of trouble and cost.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • jpfampsjpfamps Frets: 2723
     ICBM said:
    This is what the output board fix looks like.



    One wire on the left across the 16-ohm jack ground contacts, and three at the right across the impedance selector terminals.


    For what it's worth one of my jobs today is a DSL100 which belongs to a local rehearsal studio. It's died several times in the past, and I've not only done this to it but every other normal upgrade I do, and it's also running at 50W (having fried the main PCB around two of the valve sockets, I thought it easiest to simply remove them) so the power section should be under less stress. (The OT is running at the correct impedance, I swapped the taps.) To be fair, I haven't seen it for a couple of years.

    But even given all that, it's *still* blown the OT...


    The HT is already quite high in these amps (usually around 500 VDC in our workshop), and this would creep up with only 2 out of 4 valves.

    Regardless, I never understand why "cheap" amps use such high voltages, as say using 450 VDC would result in only a bit less volume but much better valve life and reliability.
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  • ICBMICBM Frets: 71960
    jpfamps said:

    The HT is already quite high in these amps (usually around 500 VDC in our workshop), and this would creep up with only 2 out of 4 valves.

    Regardless, I never understand why "cheap" amps use such high voltages, as say using 450 VDC would result in only a bit less volume but much better valve life and reliability.
    480V on that one with only two valves in.

    The real problem with the design isn't the static HT, it's the huge voltage spikes developed between the plate and screen of the last power valve - where they fitted that cap to suppress it, which is a clear 'band aid' solution. Even with a 1KV-rated cap, as I'm sure you've seen too the cap sometimes fails. What voltage is being produced here?!

    Of course this was one of the valves I removed, since the board had arced through here as well as frying the cap. The other one is the second one on the other side, which is also where the board tends to arc most often - and has done on this latest dead one as well, even with a later revision board.

    Something is deeply wrong with the stability of the circuit and/or layout for it to do this.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • I'm so glad I didn't bother. 
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  • I'm so glad I didn't bother. 
    Fargen
    Wizard
    Freidman
    etc

    They exist for a reason. 
    " Why does it smell of bum?" Mrs Professorben.
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  • Yea but they're also stupid money
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  • ricorico Frets: 1220
    Yea but they're also stupid money
    Ceriatone?
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  • ICBMICBM Frets: 71960
    While I was looking for some pics of the board to illustrate where this latest one had caught fire, I came across this page…

    http://www.lynx.net/~jc/TSL122.html

    The pic is this one, which is very similar to what I found today -

    http://www.lynx.net/~jc/lwMarshall1.jpg

    - but what's much more damning is the sheer number of design and manufacturing faults listed here - some are a bit technical, for the non-expert... but the point is that the designers at Marshall should be experts. It staggers me that a company with their apparent experience could have put so many serious mistakes into what should have been a flagship product.

    They're just an appalling piece of junk, and in my opinion it's really not worth throwing good money after bad on them.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • ICBMICBM Frets: 71960
    Just to be clear for anyone who might be slightly confused by the page above and by the apparent reputation for the DSL as being 'better than the TSL' - the DSL50, DSL100, TSL100 and TSL122 (combo) are all the same amp really. They use exactly the same main PCB and transformers, apart from the DSL50 which has smaller ones and is only fitted with two power valve sockets - including one of the ones that most often arcs in the 100s. The TSLs have different control and output boards, although the output boards share the speaker switching design fault. They do sound different, but it's just down to the control networks.

    Oddly the TSL60 is not a 2-valve version of the TSL100 but a different design more similar to the DSL401/201, which doesn't seem quite as bad for this type of failure, although the amp is slightly less well-built overall.

    The least bad of the series are the DSL401s, which although not fault-free either are actually easier to make fairly reliable - they don't seem to suffer from the same serious board failures. The DSL201 has very poor transformers, especially the OT.

    Even more surprisingly given what you would expect from the usual reputation of 'outsourcing to the far east', the new Vietnamese-made DSLs seem to be far more reliable, so far at least. I haven't yet seen a single one with any fault other than a blown valve.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • Yea but they're also stupid money
    Expensive yes, out of my reach yes, but so would a Marshall of equivalent quality. 


    " Why does it smell of bum?" Mrs Professorben.
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  • ICBMICBM Frets: 71960
    professorben said:

    Expensive yes, out of my reach yes, but so would a Marshall of equivalent quality. 
    But not a Jet City, which are cheaper than any of these by a wide margin and built very well - actually significantly better than even the new Marshalls and far better than the UK-made ones in this thread.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • Really like my DSL 50, it sounds great to me and is hugely versatile.   Perhaps I'm lucky I'm not depending on it in a gig situation, though plenty do.

    I take on board ICBM's misgivings and perhaps a Jet City is in my future but I'm perfectly happy at the moment, and I can live with the possibly imminent demise :)  I hope it's not imminent though, I would struggle to get this sound again :)
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  • professorbenprofessorben Frets: 5105
    edited September 2017
    ICBM said:
    professorben said:

    Expensive yes, out of my reach yes, but so would a Marshall of equivalent quality. 
    But not a Jet City, which are cheaper than any of these by a wide margin and built very well - actually significantly better than even the new Marshalls and far better than the UK-made ones in this thread.
    Yeah true, I really do need to try a few out at some point, I've played @digitalscream 50w I think, but only in a bedroom set up.

    hes just selling his Jet City and gone to a Helix, so I'll have to wait 18 months for him to sell the Helix and return to Jet City again.
    " Why does it smell of bum?" Mrs Professorben.
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  • ICBM said:
    professorben said:

    Expensive yes, out of my reach yes, but so would a Marshall of equivalent quality. 
    But not a Jet City, which are cheaper than any of these by a wide margin and built very well - actually significantly better than even the new Marshalls and far better than the UK-made ones in this thread.
    Yeah true, I really do need to try a few out at some point, I've played @digitalscream 50w I think, but only in a bedroom set up.

    hes just selling his Jet City and gone to a Helix, so I'll have to wait 18 months for him to sell the Helix and return to Jet City again.
    Do you want to borrow the 50W? I've got no use for it at the moment (although I won't be selling).
    <space for hire>
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  • ICBM said:
    professorben said:

    Expensive yes, out of my reach yes, but so would a Marshall of equivalent quality. 
    But not a Jet City, which are cheaper than any of these by a wide margin and built very well - actually significantly better than even the new Marshalls and far better than the UK-made ones in this thread.
    Yeah true, I really do need to try a few out at some point, I've played @digitalscream 50w I think, but only in a bedroom set up.

    hes just selling his Jet City and gone to a Helix, so I'll have to wait 18 months for him to sell the Helix and return to Jet City again.
    Do you want to borrow the 50W? I've got no use for it at the moment (although I won't be selling).
    Ooooh I thought that had gone?
    " Why does it smell of bum?" Mrs Professorben.
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  • Nope. Never selling that one - emotional attachment an' all that. Happy to lend it out, though :)
    <space for hire>
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  • jpfampsjpfamps Frets: 2723
    ICBM said:
    jpfamps said:

    The HT is already quite high in these amps (usually around 500 VDC in our workshop), and this would creep up with only 2 out of 4 valves.

    Regardless, I never understand why "cheap" amps use such high voltages, as say using 450 VDC would result in only a bit less volume but much better valve life and reliability.
    480V on that one with only two valves in.

    The real problem with the design isn't the static HT, it's the huge voltage spikes developed between the plate and screen of the last power valve - where they fitted that cap to suppress it, which is a clear 'band aid' solution. Even with a 1KV-rated cap, as I'm sure you've seen too the cap sometimes fails. What voltage is being produced here?!

    Of course this was one of the valves I removed, since the board had arced through here as well as frying the cap. The other one is the second one on the other side, which is also where the board tends to arc most often - and has done on this latest dead one as well, even with a later revision board.

    Something is deeply wrong with the stability of the circuit and/or layout for it to do this.
    Maybe the HT varies a bit with different transformer batches; I've often seen over 500VDC loaded.

    In addition to the extensive list of design cock up you've listed, I've also seen a few TSLs where a couple of film caps in the pre amp (from memory these are DC blocking caps for the DI out; irony a feature that is probably NEVER used) have gone leaky and this has dragged down the bias too.

    The caps are rated for 63V, but if the HT is energized before the valve are conducting, then then these can see a higher voltage.

    Again another very poor piece of design.


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