How can I understand if it is time to replace capacitors?

[beppe61]

Dear Sirs,

I have bought a 30 years old integrated amp.
How can I assess if the capacitors (originals) must be replaced?
Aestetichally they appear in good shape.
There is no form of leakage or other.
They are SPRAGUE 36DX and rated 7200 uF /50 VDC.
There is also a serial number 7552.C.

Thank you so much.

Kind regards,

beppe61

 

[wintermute]

One of these can help ---> http://www.dse.com.au/cgi-bin/dse.storefront/434e6659064fcaa8273fc0a87f9c06ff/Product/View/K7214

basically if the ESR is too high then the cap probably needs replading... this is something I need to add to my test gear.

Tony.

 

[RetroAudio]

I think the question is: do you WANT to replace them?

 

[beppe61]

One of these can help ---> http://www.dse.com.au/cgi-bin/dse.storefront/434e6659064fcaa8273fc0a87f9c06ff/Product/View/K7214
basically if the ESR is too high then the cap probably needs replading... this is something I need to add to my test gear.
Tony.

Dear Mr. Tony,

thank you very much for your kind and extremely valuable reply.
If I understand well your point is that ESR tends to get higher with the time (plaese excuse my naive english).
So the charging and discharging speed slows down.
Have I understood well ?
Thank you again very much.

Kind regards,

beppe61

 

[beppe61]

I think the question is: do you WANT to replace them?

Dear Sir,

to be honest, yes.
Please let me explain a little and then kindly ask you a question.
I have noticed that all the power amps with great dynamic properties have very big capacitors.
On average I can find 20.000 uF /channel of capacitance in the power supply.
In my 70+70 W stereo amp there are only two of this very good Sprague 7200 uF caps.
It seems too little to me indeed.
So yes, I would like to increase the capacitance at least to, let's say, 15.000 uF x 2 , doubling the total capacitance in the pS.

Then let me to ask you a question.

I have still a big doubt about power supply.
With short term impulsive signals which are more important: the caps or the transformer?
A friend of mine told me that only caps deal with short term impulsive signals so the dynamic capability of the amp are related to the electricale properties of the caps (ESR, capacitance).
I really do not know if this is true or not.
But if it is true, then fitting very good big caps should improve things in an evident manner.

Thank you so much for your kind reply.

Kind regards,

beppe61

 

[RetroAudio]

well beppe61, this is partially true and thus part of the story. Good caps are always welcome in a power supply no matter what, but one needs to remember that the transformer isn't exactly invisible here. It does refresh the caps at a rate up to 120 times/sec and is therefore in parallel with the caps supplying current to the circuit's demands. Although signal peaks or dynamics can be quicker than that rate, they can occur at the same instant that refreshes take place. Also something else to think about is that bigger is not always better, a notion not too popular with some around here to be sure. Perhaps doing some light reading on the subject to form your own ideas would be a positive step.

 

[I_Forgot]

I have bought a 30 years old integrated amp.
How can I assess if the capacitors (originals) must be replaced?
Aestetichally they appear in good shape.
There is no form of leakage or other.
They are SPRAGUE 36DX and rated 7200 uF /50 VDC.

There are several things to consider:

How old is the equipment?
30 years is old enough to warrant wholesale replacement of all
electrolytic caps. Electrolytics are the least reliable electronic
components.

How much will it cost?
This size cap is dirt cheap. In fact, put in a bit more capacitance
while you're at it. Modern electrolytic caps are about 1/2 the size
of 30 year old caps, so even if you get 2X the capacitance, it will probably fit in the available space. All this assumes you will do the work yourself. If you have to pay someone to do it, it probably isn't worth it unless the equipment is something really special.

How easy are they to get?
You can get them from any electronics distrbutor or surplus outlet.

All things considered, I'd say replace them.

I_F

 

[wintermute]

Hi beppe61,

Yes the esr gets higher as the cap gets older.... I'm not sure whether your description of why this is a problem is correct or not I just know it isn't desirable

here is another link, which tells the different ways you can use an esr meter to tell if a cap is bad. This one is a bit closer to home too!

http://www.qsl.net/iz7ath/web/02_brew/15_lab/06_esr/

Tony.

 

[anatech]

One thing you can try. Hang an oscilloscope on the capacitors and look at the waveform. If the ESR is getting high, you will see "pips" on the leading edge of the waveform. This gets more pronounced as the ESR and inductance goes up. So will any music waveforms. Try it.

-Chris

 

[beppe61]

well beppe61, this is partially true and thus part of the story. Good caps are always welcome in a power supply no matter what, but one needs to remember that the transformer isn't exactly invisible here. It does refresh the caps at a rate up to 120 times/sec and is therefore in parallel with the caps supplying current to the circuit's demands. Although signal peaks or dynamics can be quicker than that rate, they can occur at the same instant that refreshes take place. Also something else to think about is that bigger is not always better, a notion not too popular with some around here to be sure. Perhaps doing some light reading on the subject to form your own ideas would be a positive step.

Dear Sir,

thank you sincerely for your extremely kind and above all valuable reply.
My idea of increasing capacitance in the PS is driven by some considerations.
Some very well regarded power amps sport really huge capacitance in their PS.
The Krell KSA 50, if I am not wrong, has 4 x 40.000 uF/each caps.
Odyssey Audio offers a caps upgrade in their amps.
This must mean something.
I understand that caps is not the full story.
There is also the trasformer that acts.
My problem is:
if I want to upgrade the PS do I have to start with caps or with transformer?

Thank you very much again for your kind and valuable suggestion.

Kind regards,

beppe61
ITALY

 

[beppe61]

Re: Re: How can I understand if it is time to replace capacitors?

Thank you very much Sir for your kind and valuable reply.
Let me please quote you:

> There are several things to consider:
How old is the equipment?
30 years is old enough to warrant wholesale replacement of all
electrolytic caps.
Electrolytics are the least reliable electronic components.
How much will it cost?

Yes, the unit is about 30 years old unit.
It was quite good in its time. The caps replacement and upgrading (I am thinking of doubling the capacitance) should be cheap.
I am also thinking to remove the trasformer and put it in a separate case to make room for the new caps.

> This size cap is dirt cheap. In fact, put in a bit more capacitance
while you're at it. Modern electrolytic caps are about 1/2 the size
of 30 year old caps, so even if you get 2X the capacitance, it will probably fit in the available space. All this assumes you will do the work yourself. If you have to pay someone to do it, it probably isn't worth it unless the equipment is something really special.

All by myself (Aduio it is my main hobby and I want to try to so something).

> How easy are they to get?
You can get them from any electronics distrbutor or surplus outlet.
All things considered, I'd say replace them.
I_F

Dear Sir,

thank you so much for your extremely kind and helpful comment.
Do you have any suggestion on brands particularly good for audio purpose?
At the end I will need 2 caps 15.000-20.000 uF each / 63 VDC (to stay safe).

Kind regards,

beppe61

 

[beppe61]

Hi beppe61,
Yes the esr gets higher as the cap gets older.... I'm not sure whether your description of why this is a problem is correct or not I just know it isn't desirable
here is another link, which tells the different ways you can use an esr meter to tell if a cap is bad. This one is a bit closer to home too!
http://www.qsl.net/iz7ath/web/02_brew/15_lab/06_esr/
Tony.

Dear Mr. Tony,

thank you so much for your kind and very helpful information.
I have provided me with a lot of interesting things to study in depth in the weekend.

Thank you so much.

Kind regards,

beppe61

 

[wintermute]

My problem is:
if I want to upgrade the PS do I have to start with caps or with transformer?
ITALY

Hi beppe61,

that is going to depend on the design of the existing PS.... sometimes large capacitors are used to "prop up" an inadequate transformer....... if the transformer has enough VA to provide continuous current to the amp, when it is running at full load, and it doesn't make any noise (mechanical or electromagnetic) then you probably don't need to worry about it.

As for the caps, if you have an adequate transformer (as described above) then if there is enough capacitance to reduce the ripple to an acceptable level, then there probably is no gain to be made by putting in more capacitance. You may of course be able to use "better" capacitors of the same value for an improvement in sonics, as RetroAudio said more isn't necessarily better, have a read of Hugh Dean's ideas on power supplies here ---> http://www.aksaonline.com/discussion/discussion_papers_psupply.html

Tony.

PS. you don't need to be so formal a hi Tony would be fine

 

[beppe61]

One thing you can try.
Hang an oscilloscope on the capacitors and look at the waveform. If the ESR is getting high, you will see "pips" on the leading edge of the waveform. This gets more pronounced as the ESR and inductance goes up. So will any music waveforms. Try it.
-Chris

Dear Mr. Chris,

thank you so much for your extremely kind and interesting reply.
What you suggest me is out of my possibility for pratical reason.
I have already problems to concile my audio hobby with the family.
Anyway I have already decided to replace them and doubling the capacitance with very good new ones.
It is a try.
I will see.

Thank you very much again.

Kind regards,

beppe61

 

[beppe61]

Hi beppe61,
that is going to depend on the design of the existing PS.... sometimes large capacitors are used to "prop up" an inadequate transformer....... if the transformer has enough VA to provide continuous current to the amp, when it is running at full load, and it doesn't make any noise (mechanical or electromagnetic) then you probably don't need to worry about it.
As for the caps, if you have an adequate transformer (as described above) then if there is enough capacitance to reduce the ripple to an acceptable level, then there probably is no gain to be made by putting in more capacitance. You may of course be able to use "better" capacitors of the same value for an improvement in sonics, as RetroAudio said more isn't necessarily better, have a read of Hugh Dean's ideas on power supplies here ---> http://www.aksaonline.com/discussion/discussion_papers_psupply.html
Tony.
PS. you don't need to be so formal a hi Tony would be fine

Well, Hello Tony,

thank you so much again for your really kind, friendly and valuable comments.
As I said to RetroAudio, my idea of increasing capacitance in the PS is driven by some considerations.
Some very well regarded power amps sport really huge capacitance in their PS.
The Krell KSA 50, if I am not wrong, has 4 x 40.000 uF/each caps.
Once I listened to the KSA 50.
What a wonderful amp !
Odyssey Audio offers a caps upgrade in their amps.
This must mean something.
I understand that caps is not the full story.
There is also the transformer that acts.
The transformer should be about 600 VA.
All considered I am thinking of doubling the capacitance and pull the transformer out of the case to make room for the new caps.

Do you think it should be a wise move ?

Kind regards,

beppe61

 

[wintermute]

sarcasm and cynicism alert in this post

Hi Beppe61,

Well I don't know enough about the subject to really make any definitive comments, but at the risk of starting a war, I'll say this:

Sometimes companies do things not because it is better but because it will sell more!

I'm not saying this is the case with the Krell, but is it beyond the realms of possibility??...

Think about Joe Richman, he's looking for something that he can use to impress his rich mates. He takes a look at the Krell and says wow this amp has 160,000uF in the power supply, Bobs amp has 40,000uF, I'll show him. (I'm in no way implying that all buyers of a Krell would have this motive )

We are talking about pretty high end equipment here, and sometimes at this end of the market it is as much (or more) about brag factor than about sound quality. I haven't listened to a Krell (that I can remember) so these are all completely speculative and opinionated words I'm just a bit cynical by nature

8<----------------------------------------------------------------------------------
end sarcasm and cynisism

Really I can't say whether it is a wise move or not. It might be, you may get a big improvement, but then again maybe you won't.... It's a chance you will have to take, unless someone else who has this amp and has done the same modification pops in and tells you what their experience was.

Tony.

 

[beppe61]

Re: sarcasm and cynicism alert in this post

Hi Beppe61,
Well I don't know enough about the subject to really make any definitive comments, but at the risk of starting a war, I'll say this:
Sometimes companies do things not because it is better but because it will sell more!
I'm not saying this is the case with the Krell, but is it beyond the realms of possibility??...
Think about Joe Richman, he's looking for something that he can use to impress his rich mates. He takes a look at the Krell and says wow this amp has 160,000uF in the power supply, Bobs amp has 40,000uF, I'll show him. (I'm in no way implying that all buyers of a Krell would have this motive )
We are talking about pretty high end equipment here, and sometimes at this end of the market it is as much (or more) about brag factor than about sound quality. I haven't listened to a Krell (that I can remember) so these are all completely speculative and opinionated words I'm just a bit cynical by nature

8<--------------------------------------------------------------------------------
end sarcasm and cynisism

Really I can't say whether it is a wise move or not. It might be, you may get a big improvement, but then again maybe you won't.... It's a chance you will have to take, unless someone else who has this amp and has done the same modification pops in and tells you what their experience was.
Tony.

Hi Tony,

thank you sincerely for your extremely kind, nice, honest and very valuable indeed reply.
I would like to elaborate a little my opinion.
The Krell, which had indeed a huge PS, IMHO sounded terrific.
Please let me stress "TERRIFIC".
That said I do not really know if this performance came from those 4 beer can sized caps, but I have the sensation that it could be related also to them, at least partially.
What terrified me in particular was the bass.
I have never heard a bass like that. Think of an heartquake.
It was an experience even shocking .
Of course there is no hope to achieve the room-shaking bass of the Krell with my amp, but I would like to increase the bass power just a little and I am starting to think that doubling the capacitance should be a reasonable move.
After all also a not overtly expensive experiment.

I will report on it.

Thank you very much again,

Kind regards,

beppe61

 

[jacco vermeulen]

Re: sarcasm and cynicism alert in this post

but at the risk of starting a war

Isn't it hot enough already where you are, WM ?

Beppe, care to tell the type and brand of your amplifier ?

 

[beppe61]

Re: Re: sarcasm and cynicism alert in this post

Isn't it hot enough already where you are, WM ?
Beppe, care to tell the type and brand of your amplifier ?

Dear Mr. Vermeulen,

thank you very much for your kind reply.
The amp is identical to the following:
http://cgi.ebay.it/STEG-Amplificato...ryZ14968QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

It sports a pre-main splitting option and I currently use only the power amp section.
The pre section is much a cheap addition because the power amp part was also sold as power amp only in another case option.

What is your opinion?

Kind regards,

beppe61

 

[wintermute]

Re: Re: sarcasm and cynicism alert in this post

Isn't it hot enough already where you are, WM ?

Yes maybe I should have chosen my words more carefully

Tony.