Nelson, it is nice to see you giving your time to this forum. We may have communicated years ago when I had problems with my 4000 (I have one of your Threshold business cards).
I've had a Threshold 4000 and Cas2 since the late 70's early 80's. I used to push them hard like everything else in my youth, and the 4000 failed several times back then. They are used with a stacked pair of DQ10's and Dahlquist active crossover. I just replaced my Bryston 1B with an old NS10. I have always left my pre-amplifier and crossover powered on.
I have two questions: Should pre-amplifiers be left on all the time? How much better would it be to send this equipment out to Jon at Vintage Amp for preventative maintenance than to wait for it to fail? Thanks for all opinions.
I've had a Threshold 4000 and Cas2 since the late 70's early 80's. I used to push them hard like everything else in my youth, and the 4000 failed several times back then. They are used with a stacked pair of DQ10's and Dahlquist active crossover. I just replaced my Bryston 1B with an old NS10. I have always left my pre-amplifier and crossover powered on.
I have two questions: Should pre-amplifiers be left on all the time? How much better would it be to send this equipment out to Jon at Vintage Amp for preventative maintenance than to wait for it to fail? Thanks for all opinions.
I leave preamps on all the time. 15-20 years is the range where
we see power supply caps beginning to fail - "dry out" as it were,
and I recommend that if you have the amp in for service in this
range, you definitely want to replace the power supply and any
tantalum caps (very early Threshold) in the circuit.
we see power supply caps beginning to fail - "dry out" as it were,
and I recommend that if you have the amp in for service in this
range, you definitely want to replace the power supply and any
tantalum caps (very early Threshold) in the circuit.
What causes the electrolytic caps to fail? Heat? Ripple current? Materials failure? Do they age just sitting on a shelf unused? I also have several older Threshold products and am considering refreshing them. I have suitable NOS caps, but they haven't been used in 10 years. I would like to know if I should avoid using them.
Are there other components that should routinely be replaced? Any that should be routinely checked? (transistors, diodes, etc)
Are there other components that should routinely be replaced? Any that should be routinely checked? (transistors, diodes, etc)
I don't know the degradation mechanism for tantalum caps, but electrolytic caps can be considered as bags of water. The rubber seal around the leads is only so good at retaning the water, so the caps will dry out over time. Elevated temperatures of course will speed up the process. Long-term interaction of the electrolyte with impurites in the aluminum foil (especially iron) can also cause failure.
Solid tantalum capacitors have a distressing habit of "scintillating" - the tantalum oxide breaks down in a localized area, and if the enough current is conducted, thae capacitor shorts. I have an 80's scientific instrument (multichannel analyzer) with a veritable forest of teardrop-style tantalum bypass caps in the analog section These fail and yank down the supply rails. One of these days I need to strip them all out and replace them with something decent.
Solid tantalum capacitors have a distressing habit of "scintillating" - the tantalum oxide breaks down in a localized area, and if the enough current is conducted, thae capacitor shorts. I have an 80's scientific instrument (multichannel analyzer) with a veritable forest of teardrop-style tantalum bypass caps in the analog section These fail and yank down the supply rails. One of these days I need to strip them all out and replace them with something decent.
Meaure their capacitance. As they dry out, the capacitance
declines dramatically toward the end. You can also observe
the ripple voltage on the + and - sides of a bipolar supply, and
if one of them is dramatically different and the amp is old, then
you probably have a cap drying out, or in the case where there
are parallel caps, one may already be dried.
When your old amplifier starts to buzz at 120 Hz for no new
reason, think about the ps caps.
I emphasize that this is an exercise for people with old amplifiers.
The caps do in fact last quite a long time - most of them well
beyond 20 years.
declines dramatically toward the end. You can also observe
the ripple voltage on the + and - sides of a bipolar supply, and
if one of them is dramatically different and the amp is old, then
you probably have a cap drying out, or in the case where there
are parallel caps, one may already be dried.
When your old amplifier starts to buzz at 120 Hz for no new
reason, think about the ps caps.
I emphasize that this is an exercise for people with old amplifiers.
The caps do in fact last quite a long time - most of them well
beyond 20 years.
Boy oh boy, if I did that I'd have to wear protection against shrapnel. Really and truly, I'd still consider the caps that survived the test to be time bombs. I'll just clear the whole lot out and replace them with something like FC switcher electrolytics. The ESR for a small FC cap is on the same order as a reasonable teardrop tantalum of the same capacitance and voltage rating. One of my colleagues nearly set his cubicle on fire with a largish teardrop tantalum. He accidentaly put the cap in backwards and blew it up. He shrugged and kept on working. A flickering in the corner of his eye got his attention - the red-hot tantalum slug from the capacitor had landed on a stack of schematics and set them ablaze...
Hi all,
I am hoping that someone might give me some guidance in replacing the PS caps in a Threshold CAS 2 poweramp.
The original caps are 6900uf 60v Mallory that are no longer available. Would 15000uf 50v Spargaue caps work okaY? They are the same size (2" D by 2.625" Tall--with raised screw terminals).
If those would not work, any suggestions?
Thanks!
I am hoping that someone might give me some guidance in replacing the PS caps in a Threshold CAS 2 poweramp.
The original caps are 6900uf 60v Mallory that are no longer available. Would 15000uf 50v Spargaue caps work okaY? They are the same size (2" D by 2.625" Tall--with raised screw terminals).
If those would not work, any suggestions?
Thanks!
Niconoise asked about the 10 year old new old stock caps he
has and if they were safe to use. No one pointed out that old
unused caps can go bad on the shelf and may need to be reformed. When in doubt I charge old caps through a 1k 5W
resistor just to get a rough idea if the cap's still good.
has and if they were safe to use. No one pointed out that old
unused caps can go bad on the shelf and may need to be reformed. When in doubt I charge old caps through a 1k 5W
resistor just to get a rough idea if the cap's still good.
Hi,
Yesterday I replaced the Original Mallory (30 years old) 6900uf in my Still going strong CAS 2 for Mundorf 10000 High Current Power cap. I believe it's worth giving a Threshold CAS 2 a second life. It's still one of Nelson's best poweramp ever made.
kind regards,
Marcella van Kraaij
The Netherlands
I absolutaly agree with that. Thats why I choose this poweramp in the '70, working together with an Audio Reseacht SP 6C pre-amp. Times has changed but I still enjoying listening to my Cas II in combination with a tube pre-amp. I also owned a newer Threshold S5000 poweramp, but honestly it is not an NP design 
.
.I always felt it was under appreciated, probably because the
marketplace was emphasizing "dynamics" at that time.
Fashion has changed a bit since then: witness the success of
lower power amplifiers such as tubes or FW, which have other
charms.
I just bought a Threshold model 4000 power amp from the second hand market today. The amp has "jarring" on both channels at medium
Volume levels. I love the sound of the amp though. Is this got to do with a capacitor dying or something ? Which section needs attention. Please help
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