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Damage output cap's by letting them drain?

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Anonymous
October 3, 2004 5:27:18 PM

Archived from groups: rec.audio.tech (More info?)

Hi Group,

I still frequently use a very old Nikko Alpha II poweramp that has
been my workhorse for over 20 years. It will be replaced soon. It's
been getting a bit fussy in the last years where distortion is
sometimes getting audible etc. The protection circuit has been
bypassed for a very long time now without trouble so it is now
possible to turn off the amp and let the cap's discharge as they play
the input signal for a few seconds. This is not standard practice but
sometimes I do it when I'm fidling with inputs or outputs and let it
go thinking it can do no harm.

Anyway, although this amp has slowly been getting raggedy, the other
day I let the cap's dischange and when I turned on the amp 10 minutes
later the sound was gritty and distorted and non-symmetric. It took
about 15 minutes to snap to and I think it's not completely the same
anymore although pretty close. Nothing "bad" happened to the amp
during this; no shorts etc.

Does draining the cap's like this hurt them or something else in
there?

Thanks,
Wessel
Anonymous
October 3, 2004 6:14:20 PM

Archived from groups: rec.audio.tech (More info?)

In article <87db8cb7.0410031227.6a1e828e@posting.google.com>,
wdirksen@p-we.com (Wessel Dirksen) wrote:

> Hi Group,
>
> I still frequently use a very old Nikko Alpha II poweramp that has
> been my workhorse for over 20 years. It will be replaced soon. It's
> been getting a bit fussy in the last years where distortion is
> sometimes getting audible etc. The protection circuit has been
> bypassed for a very long time now without trouble so it is now
> possible to turn off the amp and let the cap's discharge as they play
> the input signal for a few seconds. This is not standard practice but
> sometimes I do it when I'm fidling with inputs or outputs and let it
> go thinking it can do no harm.
>
> Anyway, although this amp has slowly been getting raggedy, the other
> day I let the cap's dischange and when I turned on the amp 10 minutes
> later the sound was gritty and distorted and non-symmetric. It took
> about 15 minutes to snap to and I think it's not completely the same
> anymore although pretty close. Nothing "bad" happened to the amp
> during this; no shorts etc.
>
> Does draining the cap's like this hurt them or something else in
> there?
>
> Thanks,
> Wessel

Electrolytic caps do go bad but they self-heal. It has nothing to do
with letting the amp run extra, though. They self-discharge anyway.

It's probably one of the caps in the signal path that's going bad. The
output bias could be low too, causing high frequency oscillation until
the amp gets warm.
Anonymous
October 3, 2004 7:46:01 PM

Archived from groups: rec.audio.tech (More info?)

In all likelihood the caps would have been drained by bleeder resistors
anyway. This is unlikely to have caused your problem.

You've been skating close to the edge by disabling your protection circuit
though. It's there for a reason.

Mark Z.


"Wessel Dirksen" <wdirksen@p-we.com> wrote in message
news:87db8cb7.0410031227.6a1e828e@posting.google.com...
> Hi Group,
>
> I still frequently use a very old Nikko Alpha II poweramp that has
> been my workhorse for over 20 years. It will be replaced soon. It's
> been getting a bit fussy in the last years where distortion is
> sometimes getting audible etc. The protection circuit has been
> bypassed for a very long time now without trouble so it is now
> possible to turn off the amp and let the cap's discharge as they play
> the input signal for a few seconds. This is not standard practice but
> sometimes I do it when I'm fidling with inputs or outputs and let it
> go thinking it can do no harm.
>
> Anyway, although this amp has slowly been getting raggedy, the other
> day I let the cap's dischange and when I turned on the amp 10 minutes
> later the sound was gritty and distorted and non-symmetric. It took
> about 15 minutes to snap to and I think it's not completely the same
> anymore although pretty close. Nothing "bad" happened to the amp
> during this; no shorts etc.
>
> Does draining the cap's like this hurt them or something else in
> there?
>
> Thanks,
> Wessel
Anonymous
October 4, 2004 1:21:09 AM

Archived from groups: rec.audio.tech (More info?)

In <87db8cb7.0410031227.6a1e828e@posting.google.com>, on 10/03/04
at 01:27 PM, wdirksen@p-we.com (Wessel Dirksen) said:

>Hi Group,

>I still frequently use a very old Nikko Alpha II poweramp that has
>been my workhorse for over 20 years. It will be replaced soon. It's
>been getting a bit fussy in the last years where distortion is
>sometimes getting audible etc. The protection circuit has been
>bypassed for a very long time now without trouble so it is now
>possible to turn off the amp and let the cap's discharge as they play
>the input signal for a few seconds. This is not standard practice but
>sometimes I do it when I'm fidling with inputs or outputs and let it
>go thinking it can do no harm.

How did you "bypass" the protection circuit? Does this mean bypassing
the relay? Did you cripple the output current monitors? I'm not sure
this is a great idea. From a sonic standpoint, I don't appreciate
relays in the speaker lines, but relays do protect speakers from a
catastrophic output transistor failure. If you disconnected or defeated
the current limiters, you are taking a risk that the amplifier can be
over driven. (Normally, the current limiters will force the amplifier
to clip before it is destructively over driven. One can argue about the
sonics when this clipping starts, but I'd rather have the amplifier
protected from accidents. The clipping serves as a warning to back off
a bit.)

>Anyway, although this amp has slowly been getting raggedy, the other
>day I let the cap's dischange and when I turned on the amp 10 minutes
>later the sound was gritty and distorted and non-symmetric. It took
>about 15 minutes to snap to and I think it's not completely the same
>anymore although pretty close. Nothing "bad" happened to the amp
>during this; no shorts etc.

Nothing "bad" happened this time. Next time, now that your protection
circuit is defeated, if a capacitor shorts and causes a major shift in
the output DC level, your speakers are at risk.

>Does draining the cap's like this hurt them or something else in
>there?

The capacitors don't care about how often or how fast or slowly you
discharge them.

I suspect that one or more capacitors are failing due to age. Many
times you can visually inspect the capacitors and pick out the ones
that have failed. The failed ones may buldge a bit or be physically
leaking. (often there are green deposits)

If both channels were distorted, then look for a capacitor that is
comon to both channels. I'm not familiar with this particular
amplifier, but some designs use a common power supply decoupling
capacitor or bias supply for the early stages of the power amplifier.

-----------------------------------------------------------
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wordgame:123(abc):<14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
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[sorry about the puzzle, spammers are ruining my mailbox]
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Anonymous
October 4, 2004 2:45:42 AM

Archived from groups: rec.audio.tech (More info?)

On 3 Oct 2004 13:27:18 -0700, wdirksen@p-we.com (Wessel Dirksen)
wrote:

>I still frequently use a very old Nikko Alpha II poweramp that has
>been my workhorse for over 20 years. It will be replaced soon. It's
>been getting a bit fussy in the last years where distortion is
>sometimes getting audible etc. The protection circuit has been
>bypassed for a very long time now without trouble so it is now
>possible to turn off the amp and let the cap's discharge as they play
>the input signal for a few seconds. This is not standard practice but
>sometimes I do it when I'm fidling with inputs or outputs and let it
>go thinking it can do no harm.
>
>Anyway, although this amp has slowly been getting raggedy, the other
>day I let the cap's dischange and when I turned on the amp 10 minutes
>later the sound was gritty and distorted and non-symmetric. It took
>about 15 minutes to snap to and I think it's not completely the same
>anymore although pretty close. Nothing "bad" happened to the amp
>during this; no shorts etc.
>
>Does draining the cap's like this hurt them or something else in
>there?

Charge a cap, disconnect and walk away. How long before the charge
disappears from leakage? No, you're doing no harm.

I take it you disabled the protection for audiophile reasons, not
because it was operating? It means when you DO have a wiring fault,
it may be catastrophic. But if you really notice a difference and
think the risk is worth it, I believe it's the sort of thing
audiophiles sometimes do :-)

After 20 years, I wouldn't be surprised if the electrolytics needed
replacing. If it's a nice amp, why not try this instead of dumping
it?
Anonymous
October 4, 2004 6:04:43 AM

Archived from groups: rec.audio.tech (More info?)

Laurence Payne <l@laurenceDELETEpayne.freeserve.co.uk> wrote in message news:<tas0m05gjgu6ro8j5126a5cofimcmjjpl2@4ax.com>...
> On 3 Oct 2004 13:27:18 -0700, wdirksen@p-we.com (Wessel Dirksen)
> wrote:
>
> >I still frequently use a very old Nikko Alpha II poweramp that has
> >been my workhorse for over 20 years. It will be replaced soon. It's
> >been getting a bit fussy in the last years where distortion is
> >sometimes getting audible etc. The protection circuit has been
> >bypassed for a very long time now without trouble so it is now
> >possible to turn off the amp and let the cap's discharge as they play
> >the input signal for a few seconds. This is not standard practice but
> >sometimes I do it when I'm fidling with inputs or outputs and let it
> >go thinking it can do no harm.
> >
> >Anyway, although this amp has slowly been getting raggedy, the other
> >day I let the cap's dischange and when I turned on the amp 10 minutes
> >later the sound was gritty and distorted and non-symmetric. It took
> >about 15 minutes to snap to and I think it's not completely the same
> >anymore although pretty close. Nothing "bad" happened to the amp
> >during this; no shorts etc.
> >
> >Does draining the cap's like this hurt them or something else in
> >there?
>
> Charge a cap, disconnect and walk away. How long before the charge
> disappears from leakage? No, you're doing no harm.
>
> I take it you disabled the protection for audiophile reasons, not
> because it was operating? It means when you DO have a wiring fault,
> it may be catastrophic. But if you really notice a difference and
> think the risk is worth it, I believe it's the sort of thing
> audiophiles sometimes do :-)
>
> After 20 years, I wouldn't be surprised if the electrolytics needed
> replacing. If it's a nice amp, why not try this instead of dumping
> it?

This is a multiple response in one. Thanks for your input everyone. I
got this amp 20 years ago because it was "broken"; the protection
relays were faulty then. I temporarily bypassed them to test the
theory and when I replaced them I found the sound to be not nearly as
good, so yeah, for audiophile reasons they're bypassed now since 20
years and I must be careful with it but there's never been an accident
so far. (a few near accidents)

OK good to know that this is not per se bad practice, so its something
else. Even though I will replace this amp, I really want to ressurect
it for another system because it's really quite cool. 2 huge input
trafo's etc. I would like to find either an amp guru in the area
(Netherlands/Belgium these days)or do some value for value replacing
of parts inside. Which parts are best to "upgrade" to beter quality if
I do this?

Thanks again,

Wessel
Anonymous
October 4, 2004 2:37:06 PM

Archived from groups: rec.audio.tech (More info?)

On 4 Oct 2004 02:04:43 -0700, wdirksen@p-we.com (Wessel Dirksen)
wrote:

>Even though I will replace this amp, I really want to ressurect
>it for another system because it's really quite cool. 2 huge input
>trafo's etc. I would like to find either an amp guru in the area
>(Netherlands/Belgium these days)or do some value for value replacing
>of parts inside. Which parts are best to "upgrade" to beter quality if
>I do this?

Just replace the electrolytic capacitors. You need components of the
correct value and of a size that fits in the available space. No need
to pay double for "audiophile" hype.
Anonymous
October 4, 2004 2:37:07 PM

Archived from groups: rec.audio.tech (More info?)

Laurence Payne <l@laurenceDELETEpayne.freeserve.co.uk> wrote in message news:<ca62m010hciumvetc48e2t8732iqdli63q@4ax.com>...
> On 4 Oct 2004 02:04:43 -0700, wdirksen@p-we.com (Wessel Dirksen)
> wrote:
>
> >Even though I will replace this amp, I really want to ressurect
> >it for another system because it's really quite cool. 2 huge input
> >trafo's etc. I would like to find either an amp guru in the area
> >(Netherlands/Belgium these days)or do some value for value replacing
> >of parts inside. Which parts are best to "upgrade" to beter quality if
> >I do this?
>
> Just replace the electrolytic capacitors. You need components of the
> correct value and of a size that fits in the available space. No need
> to pay double for "audiophile" hype.

Thanks Laurence, so I would ideally replace the eletrolytics probably
with metalized film caps then I guess, or is this the expensive hype
you are referring to. Does this mean that resistors and
semi-conductors don't get old and/or are not worth replacing with
"beter" types? Can the big output transistors be blindly part for part
replaced with higher performing substitutes. They are NEC 2SB600 +
2SD555 as a pair per channel.
Anonymous
October 4, 2004 11:31:10 PM

Archived from groups: rec.audio.tech (More info?)

The B600 and D555 transistors were rated at 200W each. You'd be hard pressed
to find a modern equivalent which would surpass them AND be well matched and
reliable. Transistors are often counterfeited these days, and instead of
matched NEC product you'd have to hope that the ONSEMI devices you get from
a distributor are up to par.

Mark Z.


"Wessel Dirksen" <wdirksen@p-we.com> wrote in message
news:87db8cb7.0410040856.64024cc7@posting.google.com...
> Laurence Payne <l@laurenceDELETEpayne.freeserve.co.uk> wrote in message
> news:<ca62m010hciumvetc48e2t8732iqdli63q@4ax.com>...
>> On 4 Oct 2004 02:04:43 -0700, wdirksen@p-we.com (Wessel Dirksen)
>> wrote:
>>
>> >Even though I will replace this amp, I really want to ressurect
>> >it for another system because it's really quite cool. 2 huge input
>> >trafo's etc. I would like to find either an amp guru in the area
>> >(Netherlands/Belgium these days)or do some value for value replacing
>> >of parts inside. Which parts are best to "upgrade" to beter quality if
>> >I do this?
>>
>> Just replace the electrolytic capacitors. You need components of the
>> correct value and of a size that fits in the available space. No need
>> to pay double for "audiophile" hype.
>
> Thanks Laurence, so I would ideally replace the eletrolytics probably
> with metalized film caps then I guess, or is this the expensive hype
> you are referring to. Does this mean that resistors and
> semi-conductors don't get old and/or are not worth replacing with
> "beter" types? Can the big output transistors be blindly part for part
> replaced with higher performing substitutes. They are NEC 2SB600 +
> 2SD555 as a pair per channel.
Anonymous
October 8, 2004 7:50:04 PM

Archived from groups: rec.audio.tech (More info?)

Hi Guys,

I'm gonna resurrect this one with the following last request. I'm
hoping those in the know will comment on the following strategies that
I think are sound in replacing parts in my amp (assume value for
value):

1 Cap's which bridge the output of a DC power source as a current
buffer can be beefed up (increased capacitance)as far you want to go
without getting rediculous.
2 All cap's + resistors in DC power supply path can be of lower
quality
3 All cap's + resistors in the signal path, especially in series,
should be of highest possible quality without getting rediculous.
Which is better polypropelene or tautalium (spelling?)
4 Semi-conductors are less necessary to replace and cannot be
appreciably upgraded without design modifications. Exception might be
the "speed" of diodes in the rectifier circuit? (so I have read)

Thanks,

Wessel
Anonymous
October 9, 2004 4:37:58 AM

Archived from groups: rec.audio.tech (More info?)

Wessel Dirksen wrote:

> Laurence Payne <l@laurenceDELETEpayne.freeserve.co.uk> wrote in message news:<ca62m010hciumvetc48e2t8732iqdli63q@4ax.com>...
> >
> > Just replace the electrolytic capacitors. You need components of the
> > correct value and of a size that fits in the available space. No need
> > to pay double for "audiophile" hype.
>
> Thanks Laurence, so I would ideally replace the eletrolytics probably
> with metalized film caps then I guess,

NO. Just replace them with new equivalents.

You won't find metallised film in the large values you need - nor do you need metallised film for power supply caps.

> Does this mean that resistors and
> semi-conductors don't get old and/or are not worth replacing with
> "beter" types?

Yes.

> Can the big output transistors be blindly part for part
> replaced with higher performing substitutes. They are NEC 2SB600 +
> 2SD555 as a pair per channel.

Don't mess about. You'll have to re-adjust the output stage if you mess with those devices and likely do damage if you don't
know what you're doing ( which seems to be the case ).

Graham
Anonymous
October 9, 2004 5:27:28 AM

Archived from groups: rec.audio.tech (More info?)

In <87db8cb7.0410081450.57e07a95@posting.google.com>, on 10/08/04
at 03:50 PM, wdirksen@p-we.com (Wessel Dirksen) said:

>Hi Guys,

>I'm gonna resurrect this one with the following last request. I'm
>hoping those in the know will comment on the following strategies that
>I think are sound in replacing parts in my amp (assume value for
>value):

>1 Cap's which bridge the output of a DC power source as a current
>buffer can be beefed up (increased capacitance)as far you want to go
>without getting rediculous.

Beyond a certain point, you'll start blowing up the power supply
diodes.

>2 All cap's + resistors in DC power supply path can be of lower
>quality

Different properties are important in power supply areas, than in the
signal path. For example, installing premium low drift or tight
tolerance parts in the power supply would probably be wasted money.
Installing cheaper diodes as the main rectifier after you've beefed-up
the capacitors as above, could easily result in diode failure (after a
while).

>3 All cap's + resistors in the signal path, especially in series,
>should be of highest possible quality without getting rediculous.
>Which is better polypropelene or tautalium (spelling?)

If you are looking for physically small, tantalum is the choice. In an
AC application, tantalum is a poor choice. For some reason, I see a lot
less polypropylene failures then tantalum failures.

> 4 Semi-conductors are less necessary to replace and cannot be
>appreciably upgraded without design modifications. Exception might be
>the "speed" of diodes in the rectifier circuit? (so I have read)

If they are too fast you may notice more power supply related noise in
the unit.

---

Years ago I had a fellow work in my service department who had worked
for an amplifier manufacturer. He had lots of stories about
"improvements". This particular brand was the darling of the "mod
squad" (not to be confused with the company of similar name). The
manufacturer's service department had a steady stream of units come in
for major service to repair the damage done by tinkerers who thought
they new more than the designer. Yes, it was possible to improve the
sound of the unit, but the modifications often ruined the stability of
the unit. An unstable unit is prone to quirky, unpleasant behavior at
seemingly random times.

-----------------------------------------------------------
spam: uce@ftc.gov
wordgame:123(abc):<14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13> (Barry Mann)
[sorry about the puzzle, spammers are ruining my mailbox]
-----------------------------------------------------------
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