Hi guys, I want to replace a pair of large main caps in an amp thats over 20 years old. The removal and insertion looks to be quit straight forward but my question is of voltage ratings on the caps.
The existing caps are 80V and 29000uF rating
The caps I found are 75V and 33000uF rating
Now I measured on the voltage across each cap's positive and negative terminal and get about 32.5V. I'm not an expert but the caps look like they are in series so should I be concerned at all at the 5V difference? I'm very far from the max voltage on the caps anyway...
Not sure if this pic will help but any suggestions regarding the swap will be welcome.
PS anything wrong with CDE brand caps? Originals are Mallory.
The existing caps are 80V and 29000uF rating
The caps I found are 75V and 33000uF rating
Now I measured on the voltage across each cap's positive and negative terminal and get about 32.5V. I'm not an expert but the caps look like they are in series so should I be concerned at all at the 5V difference? I'm very far from the max voltage on the caps anyway...
Not sure if this pic will help but any suggestions regarding the swap will be welcome.
An externally hosted image should be here but it was not working when we last tested it.
PS anything wrong with CDE brand caps? Originals are Mallory.
Yes you're very right. I inspected the amp closer and indeed on the back there is a fuse for the positve and negative rails. I guess I didnt look closely when I took that picture.
I think I will definitly try and source the parts. I mean the amp works but I have a very slight hum even with no input signal (nothing connected). The hum is barely audible in the speakers (a little more noticable on one channel than the other). I can hear the same slight hum from the transformer if I put my ear nearly right up on it.
Anyway I figured the caps are old so maybe start there
I think I will definitly try and source the parts. I mean the amp works but I have a very slight hum even with no input signal (nothing connected). The hum is barely audible in the speakers (a little more noticable on one channel than the other). I can hear the same slight hum from the transformer if I put my ear nearly right up on it.
Anyway I figured the caps are old so maybe start there
Hi,
I would be surprised if the cause of the hum are the caps. Is that the main reason you want to change them. Have you measured the ripple on them.
The killer of electroylitics is mainly heat. The bridge rectifier is in a strange place bad heat wise, good physically. Does it get hot ?
Most causes of hum are down to wiring errors and induced hum from the magnetic field of the amp.
I would be surprised if the cause of the hum are the caps. Is that the main reason you want to change them. Have you measured the ripple on them.
The killer of electroylitics is mainly heat. The bridge rectifier is in a strange place
bad heat wise, good physically. Does it get hot ?Most causes of hum are down to wiring errors and induced hum from the magnetic field of the amp.
There's one cap each for the positive and negative rails. The plate in the middle (doubling as heat sink for the bridge) is--or should be--at ground potential. Measure from that plate to the two other terminals. The one with the red wires should give you a positive reading. The one with the blue wires should give you a negative reading.
If you have 30-something volt rails, then the 75V caps are quite safe. In fact, you could quite easily do with lower voltage caps, possibly as low as 35V ratings if you're running 32V rails.
The thing to watch out for is over-doing the capacitance. If you put something like 100,000uF caps in the amp, then you'll put a great deal of stress on the bridge diode, particularly at turn-on. Your 33,000uF caps will not be a problem.
Which Threshold is that?
Grey
If you have 30-something volt rails, then the 75V caps are quite safe. In fact, you could quite easily do with lower voltage caps, possibly as low as 35V ratings if you're running 32V rails.
The thing to watch out for is over-doing the capacitance. If you put something like 100,000uF caps in the amp, then you'll put a great deal of stress on the bridge diode, particularly at turn-on. Your 33,000uF caps will not be a problem.
Which Threshold is that?
Grey
Lets be real careful here!!! I find it hard to believe that the rails in that amp are really that low! I would double check that reading.
Caps are expensive. and i doubt a MFG would use caps priced nearly double what a cap would cost for 30-ish Volt rails. It just doesn't make sense. I would make very very certain of the rail voltages before suggesting or connecting a lower voltage cap. a 35-40v cap across 70 volt rails could easily turn into an explosive situation!! So lets make double doubly sure of those rails first.
I would suspect that the rails are actually 70-75V rails. thats pretty normal for caps rated at 80V to see rails at that voltage. If that amp is a 150-200 watt per channel amp, 70V rails are about right. 32 volt rails would maybe be a 50 watt amp.
if the rails are 70V, you could use 75V rated caps, but your safety margin is less and the caps will run warmer, not last as long. Using 100V rated caps would be better, they will run cooler and last longer.
Please double check your meter settings, make sure your on DC Volts and re-measure those rails from the large flat ground plate to the outer terminals and see what you come up with.
I just don't want to see anyone get hurt by an exploding cap or something. I have had it happen to me and its not fun to have to dig shrapnel out of your face! So please double check and be careful.
ZC
Caps are expensive. and i doubt a MFG would use caps priced nearly double what a cap would cost for 30-ish Volt rails. It just doesn't make sense. I would make very very certain of the rail voltages before suggesting or connecting a lower voltage cap. a 35-40v cap across 70 volt rails could easily turn into an explosive situation!! So lets make double doubly sure of those rails first.
I would suspect that the rails are actually 70-75V rails. thats pretty normal for caps rated at 80V to see rails at that voltage. If that amp is a 150-200 watt per channel amp, 70V rails are about right. 32 volt rails would maybe be a 50 watt amp.
if the rails are 70V, you could use 75V rated caps, but your safety margin is less and the caps will run warmer, not last as long. Using 100V rated caps would be better, they will run cooler and last longer.
Please double check your meter settings, make sure your on DC Volts and re-measure those rails from the large flat ground plate to the outer terminals and see what you come up with.
I just don't want to see anyone get hurt by an exploding cap or something. I have had it happen to me and its not fun to have to dig shrapnel out of your face! So please double check and be careful.
ZC
It's not a Pass Labs piece, it's a Threshold (note the logo on the sticker on the power transformer). Plus the mechanical construction and heat sink profile are consistent with Threshold product.
I doubt the rails are anywhere near the 80V rating of the caps. So why use 80V caps? Because if you buy things in sufficient quantity you get a very good price. Rather than stock, say, six different voltage ratings, you buy the highest voltage rating you'll need and get them cheap, then use the big part in every amp.
I'm guessing that it's one of the smaller Threshold Stasis amps. With a little digging, I could probably even give you a reasonable guess as to which model, but I've been out sawing down trees that have succumbed to the ongoing drought, and I'm absolutely beat. Shooting from the hip, I say the 75W version.
Grey
I doubt the rails are anywhere near the 80V rating of the caps. So why use 80V caps? Because if you buy things in sufficient quantity you get a very good price. Rather than stock, say, six different voltage ratings, you buy the highest voltage rating you'll need and get them cheap, then use the big part in every amp.
I'm guessing that it's one of the smaller Threshold Stasis amps. With a little digging, I could probably even give you a reasonable guess as to which model, but I've been out sawing down trees that have succumbed to the ongoing drought, and I'm absolutely beat. Shooting from the hip, I say the 75W version.
Grey
Hi Mooly,
Actually thats why I'm replacing the caps. I figured maybe the hum might be due to the caps having degraded over time. I dont know any way of measuring ripple easily since I dont have a scope or anything - unless there is some way of figuring it out with a standard multimeter...
PS. The hum is very slight in one channel and I do notice inside the amp, the tranformer is not quite centered...infact the hum IS on the side that the transformer is closer to so I wonder if its just the left channel being closer to the trasformer...Hmmm[
QUOTE]Originally posted by Mooly
Hi,
I would be surprised if the cause of the hum are the caps. Is that the main reason you want to change them. Have you measured the ripple on them.
The killer of electroylitics is mainly heat. The bridge rectifier is in a strange place bad heat wise, good physically. Does it get hot ?
Most causes of hum are down to wiring errors and induced hum from the magnetic field of the amp. [/QUOTE]
Actually thats why I'm replacing the caps. I figured maybe the hum might be due to the caps having degraded over time. I dont know any way of measuring ripple easily since I dont have a scope or anything - unless there is some way of figuring it out with a standard multimeter...
PS. The hum is very slight in one channel and I do notice inside the amp, the tranformer is not quite centered...infact the hum IS on the side that the transformer is closer to so I wonder if its just the left channel being closer to the trasformer...Hmmm[
QUOTE]Originally posted by Mooly
Hi,
I would be surprised if the cause of the hum are the caps. Is that the main reason you want to change them. Have you measured the ripple on them.
The killer of electroylitics is mainly heat. The bridge rectifier is in a strange place
bad heat wise, good physically. Does it get hot ?Most causes of hum are down to wiring errors and induced hum from the magnetic field of the amp. [/QUOTE]
Hi Mooly, I think the transfomer is mounted from underneath via a bolt so maybe its movable. I should check into that. I have run the amp with only speakers connected but no rca cables attached - however I did not use any shorting plugs.
I found a document that said how to make some but I dont recall the link now. All I need is the resistor value I guess. I have a whole bunch of 1K 1/4 watt resistors but I dont know if 1K is ok to use or not. Time for google I guess
I read some people troubleshooting ground issues by using putting on an adapter plug that is missing the ground pin...but somehow this makes me paranoid so I dont want to do that.
The hum is very light and not audible even from a foot away. I wonder if i should leave it alone. I did take the amp to a local stereo shop and the tech said he couldnt find anything on the output that would be of any concern...he felt that everything was within spec. Still if I can get the amp to be more silent on that one channel, it would be nice.
I found a document that said how to make some but I dont recall the link now. All I need is the resistor value I guess. I have a whole bunch of 1K 1/4 watt resistors but I dont know if 1K is ok to use or not. Time for google I guess
I read some people troubleshooting ground issues by using putting on an adapter plug that is missing the ground pin...but somehow this makes me paranoid so I dont want to do that.
The hum is very light and not audible even from a foot away. I wonder if i should leave it alone. I did take the amp to a local stereo shop and the tech said he couldnt find anything on the output that would be of any concern...he felt that everything was within spec. Still if I can get the amp to be more silent on that one channel, it would be nice.
Mooly said:Is it easy to lift the transformer and temporarily extend the wires. Toroids can be usefully rotated to find a null point ( sometimes
Have you run the amp up with nothing but speakers connected and shorting plugs fited on the inputs. Nothing else connected.
Hi,
You don't need a resistor, just short the inputs directly. I take it they are phono ( RCA ) sockets. Just get two old plugs and short them out, center to outer.
As to lifting grounds, if the amp hums as I say, with just the amp speakers and inputs shorted, and NO other items connected it's not an external ground loop.
You don't need a resistor, just short the inputs directly. I take it they are phono ( RCA ) sockets. Just get two old plugs and short them out, center to outer.
As to lifting grounds, if the amp hums as I say, with just the amp speakers and inputs shorted, and NO other items connected it's not an external ground loop.
The SA/3 has a matched JFET differential input, like the bigger SA/1 and SA/2 models from the same time frame.
Shorting the input is no problem.
(the transformers and heatsinks of the 80s series were also identical, close to modular building block range, pretty neat. The SA/2 is an SA/3 in monaural disguise, with standard 80V caps it's a piece of cake to convert an SA/3 to an SA/2 )
Shorting the input is no problem.
(the transformers and heatsinks of the 80s series were also identical, close to modular building block range, pretty neat. The SA/2 is an SA/3 in monaural disguise, with standard 80V caps it's a piece of cake to convert an SA/3 to an SA/2 )
Hi Nelson. Let me say that I love this amp more than any other piece of audio gear I own. I've taken this amp quite a few times to stores and compared it with much more current and sometimes quite expensive amps and its not even close. The smoothness, huge soundstage and control. I love it. You are a wizard with electronics.
Any tips for me replacing the caps? If it were you, would you go with 37,000UF 75V caps or 30,000UF 100V caps? Also not sure if the very slight hum on the left channel could be cap related or maybe just a slight noise picked up by the transformer being closer inside the chassis to the left channel? Anyway its not noticable unless my ear is very close to the woofer so it might even be within spec. Regardless, this thing sounds fantastic regardless of its age.
One day I will have my dream of buying a mint condition Aleph 5.
Any tips for me replacing the caps? If it were you, would you go with 37,000UF 75V caps or 30,000UF 100V caps? Also not sure if the very slight hum on the left channel could be cap related or maybe just a slight noise picked up by the transformer being closer inside the chassis to the left channel? Anyway its not noticable unless my ear is very close to the woofer so it might even be within spec. Regardless, this thing sounds fantastic regardless of its age.
One day I will have my dream of buying a mint condition Aleph 5.
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