Are 1978 low leakage (LR) capicitors noteworthy today?

[62vauxhall]

Am about to start replacing electrolytic capacitors in a lowish end preamp and have obtained new Rubycons (mostly) from a nearby parts shop. As I examined the original capacitors to record their values, two in the phono section were distinctive with an orange wrapper and prompted a little research. Likely made by Elna and marked LR that from what I read indicates Low Leakage. I was advised by the parts store staff that it is an irrelevant distinction with modern capacitors as they would all be considered Low Leakage by 1978 standards.

There were some thread posts that concur with this while others say there would be some benefit in locating current even lower leakage replacements. In my case that would mean buying from an online US vendor and shipping to Canada. Since that would translate into $20 - $25 for two small capacitors, I cannot justify the expense.

Am I safe in my thinking that using a modern general purpose capacitor in this application would not be a downgrade from the originals as in introducing more noise? Or, just leave the originals in place?

Also, since the phono stage involves low level signal, is the capscitor's voltage rating going to be critical in this instance as long as not less than original is used? I could be wrong but from my minimal understanding, signal rarely passes through an electrolytic.

 

[rayma]

Am I safe in my thinking that using a modern general purpose capacitor in this application
would not be a downgrade from the originals as in introducing more noise? I could be wrong
but from my minimal understanding, signal rarely passes through an electrolytic.

Leakage is specified for most new electrolytics, so compare it to the original's leakage spec.
A higher voltage/temperature part will have less leakage, in general.
At any rate, you can be sure that the original electrolytic capacitors are way out of spec by now.

Signal current does go though the electrolytic capacitors in most circuits, but the capacitance
value is chosen large enough to minimize any signal voltage drop across the capacitor.

 

[62vauxhall]

The capacitors I got to replace those orange wrapped Elnas are Rubycon 63 volt 1uF whereas the Elnas are 50 volt.

Oddly, I cannot locate a data sheet on these Rubycons which have printed on their wrapper (blue) CE W which seems to be a valid series designation. Using Rubycon CE W series as a search term led to a reference for Rubycon TWSS but no data sheet for that either. Could be that what I have are NOS.

In any case, I guess they're going as replacements for the orange Elnas since, as you say, those are probably past their prime.

It almost seems humorous to be concerned about these because the cost was $1 for 5 capacitors - twenty cents each.

 

[Enzo]

When training technicians professionally, I often point out that parts are cheaper than labor. I do not recommend just shotgunning circuits, but when someone wastes $10 of labor trying to determine if a 20 cent part is bad, that is not efficient. if it is suspect, replace it.

 

[Mooly]

I can't remember the designation now but I seem to recall some orange wrapper caps were bi-polar (non polarised). Just make sure that all the originals do have a polarity marking on them.

I would have no hesitation using modern parts to replace so called 'low leakage' devices of yesteryear.

 

[woody]

If these were in the signal path you might want to replace them with film caps if you have the room for them.

 

[JMFahey]

In any case I would avoid using 1978 electrolytic capacitors, even more if they sat unused for 38 years.

 

[62vauxhall]

Thanks everyone for your replies.

Those capacitors are polarized and looking at the schematic, the positive leads are connected to pins 1 and 7 of an SJ4558 op amp IC with the negative going to the function switch. Circuit diagram says 2.3 volts at that point so my conclusion is that they are in the signal path.

There looks to be a fair bit of "shoulder room" on the board to accommodate a larger capacitor and the only consideration would be lead spacing but that could be negated with insulation tubing on the leads.

As I previously mentioned, ordering small quantities of inexpensive parts from a US vendor is cost prohibitive. But I see no reason why I should not be able to obtain film capacitors (probably polypropylene) with the required values from the local parts store I frequent. My work has me travelling throughout the city so finding myself in their neighborhood is likely during the upcoming week. If, for some reason appropriate film capacitors are not on hand, I will use the electrolytics I already have.

There is one concern I have about using a film capacitor in a phono preamp section and that is physical size vs induced hum.

It stems from my re-building a Heathkit AA-32 tube amp a few years ago which I assembled from a kit in 1968. I replaced every single thing inside that amp except for transformer and the switches/controls. I used Sprague Orange Drops to replace all the original film caps and everything was fine except for a hum present only on the MAG PHONO input. I spent a considerable amount of time troubleshooting and solicited help from a technician familiar with tube equipment who had it on his bench for several weeks. I have even posted on this site about it but the source of the hum remained elusive.

I found it odd that this hum started only after installing all new components. While reading online about this topic, I came across something suggesting that increasing the surface area of a capacitor may make it more susceptible to picking up noise especially in areas involving low level signals - like a phono preamp.

 

[Mooly]

imo there is nothing worse than seeing incorrect and oversized parts 'made' to fit in something. Your observations are correct on the hum too.

(one thing you might consider looking at is possible replacement of the 4558 opamps. You may well find that swapping those to a different device gives a noticeable improvement in quality)

 

[62vauxhall]

Alright then, I'll go with the parts I already have. And yes, I intend on replacing that op amp.

I read endorsements for NE5532 and OPA2134 so I purchased one of each. I also got a socket because I wanted to see if I can tell any difference between them - and the original too for that matter.

If the difference is subtle, I may not even notice. I spent too many years riding a motorcycle and playing in a band so at this point in my life, hearing is not what it was.

 

[rayma]

I found it odd that this hum started only after installing all new components. While reading online about this topic, I came across something suggesting that increasing the surface area of a capacitor may make it more susceptible to picking up noise especially in areas involving low level signals - like a phono preamp.

That's one reason why the outside foil plead of the capacitor should go to ground,
or else the lower impedance node of the two.

 

[62vauxhall]

That's one reason why the outside foil plead of the capacitor should go to ground,
or else the lower impedance node of the two.

Yes, that idea was put to me before but I was unable to determine which lead was which. It was suggested to touch the leads to an input of an amplifier and whichever produced the loudest hum would be the outside foil. It was never clarified but I assumed that would be by holding the capacitor body and not while touching the opposite lead. In any case, I was unable to tell a difference in hum loudness.

"Lower impedance node of the two"?

Since that is not resistance, I guess it's not something I can check with just a DMM?

 

[Mooly]

You would have to study the circuit and make a judgement which was the 'lowest impedance' point. Generally the lowest impedance point would be the output of a stage (such as an opamp or an emitter follower etc) and the other end (the input to the next stage) would be the high impedance end.

 

[rayma]

You would have to study the circuit and make a judgement which was the 'lowest impedance' point. Generally the lowest impedance point would be the output of a stage (such as an opamp or an emitter follower etc) and the other end (the input to the next stage) would be the high impedance end.

Remember ground!

 

[infinia]

When training technicians professionally, I often point out that parts are cheaper than labor. I do not recommend just shotgunning circuits, but when someone wastes $10 of labor trying to determine if a 20 cent part is bad, that is not efficient. if it is suspect, replace it.

consumer audio yes, medical equipment and test gear not so much.
this is fine IF you have the exact parts for replacement. which indeed is a very big IF esp. working on old and sophisticated gear, otherwise they can be introducing more problems esp if the shotgunner tech is essentially re designing the UUT. This could be a recipe for disaster depending on the tech and gear.

 

[62vauxhall]

Although it was I who started this thread, apologies for sidetracking it to the hum issue I experienced in a previous (and as yet uncompleted) project. Which was by the way a tube integrated.

With regards to the inexpensive preamp that prompted this thread.

I finished the wholesale capacitor replacement along with metal film resistor plus op amp in the phono stage. Even though it was over a week since I last listened to it in an unmolested state, it is better now than before. Can't say if sound quality is any better, maybe so but it is quieter. With no input signal there was hiss as the volume control got close to its limit and that is not so anymore. So with the assistance of those who chose to post, I can claim the new/better parts made a noticeable difference - thanks!

 

[Mooly]

I'd bet the opamp made a bit of difference... and you mention hiss levels going down.

A job well done.