High voltage capacitors in audio

[ectoplasm]

In a pre-amplifier, I am replacing all relevant capacitors in signal
lines by 100V or 250V polypropylene film capacitors (i.e. big yellow
ones). These are much better for audio than standard alu elcos.

My question is:

1) the signal is only a couple of volts in amplitude. Is it bad that
the capacitors are way beyond this value? I mean, could it be that
these big caps handle low voltages not as well?

2) is it actually a good idea to replace *all* of these capacitors by
these big ones? (if you'd like, look at the circuit at <http://
sound.westhost.com/project24.htm>) Or would some good, small tantalum
capacitors do better in some locations?

 

[D from BC]

In a pre-amplifier, I am replacing all relevant capacitors in signal
lines by 100V or 250V polypropylene film capacitors (i.e. big yellow
ones). These are much better for audio than standard alu elcos.

My question is:

1) the signal is only a couple of volts in amplitude. Is it bad that
the capacitors are way beyond this value? I mean, could it be that
these big caps handle low voltages not as well?

2) is it actually a good idea to replace *all* of these capacitors by
these big ones? (if you'd like, look at the circuit at <http://
sound.westhost.com/project24.htm>) Or would some good, small tantalum
capacitors do better in some locations?

I'd install a switch so that one can select between "crappy 10 cent
capacitors" and "Honking Fat Ass Caps". Invite friends over and ask
them if they can tell the difference between "A" and "B". Be sure to
mention you have beer..

By the way...I have a switch on my amp that selects between active
inkwitz Riley crossover or constant power type crossover.
I can't tell the difference but I like flicking the switch every month
or two hoping I might.
Doesn't matter anyways with all the fkn loud Harleys driving by..

Also..forget the gold connectors...just solder the speakers wires
directly to the PCB.
Oh...use silver solder..
D from BC

 

[ectoplasm]

I suppose it all becomes meaninglessly undiscernible with brain damage.

 

[Eeyore]

In a pre-amplifier, I am replacing all relevant capacitors in signal
lines by 100V or 250V polypropylene film capacitors (i.e. big yellow
ones). These are much better for audio than standard alu elcos.

Better perhaps than *misapplied elcos*. Aluminium electrolytics used carefully
can perform excellently for audio and in typical circuits will give better bass
and very low phase shift at LF because you can use very large uF values that you
simply can't get and would never be able to fit in plastic film types.

My question is:

1) the signal is only a couple of volts in amplitude. Is it bad that
the capacitors are way beyond this value? I mean, could it be that
these big caps handle low voltages not as well?

No. It just means that the plastic film inside is a bit thicker. The voltage of
the cap is simply the maximum rated voltage it's designed to withstand without
dielectric failure.

2) is it actually a good idea to replace *all* of these capacitors by
these big ones? (if you'd like, look at the circuit at <http://
sound.westhost.com/project24.htm>) Or would some good, small tantalum
capacitors do better in some locations?

Tantalum caps used for zero bias coupling perform horribly. I expect you want a
large value ? Use 100-220uF/16V or similar al elco.

Oh yes, you'll have fun fitting 22uF and 100uF plastic films.

Let me guess. You're not doing this because you have a problem with the sound
but because you read somewhre that al elco are 'bad' for the sound ?

Graham

 

[me]

I'd install a switch so that one can select between "crappy 10 cent
capacitors" and "Honking Fat Ass Caps". Invite friends over and ask
them if they can tell the difference between "A" and "B". Be sure to
mention you have beer..

By the way...I have a switch on my amp that selects between active
inkwitz Riley crossover or constant power type crossover.
I can't tell the difference but I like flicking the switch every month
or two hoping I might.
Doesn't matter anyways with all the fkn loud Harleys driving by..

I had an amp with a sub-sonic filter switch, think about it. things that
make you go what?!?!

 

[Wimpie]

In a pre-amplifier, I am replacing all relevant capacitors in signal
lines by 100V or 250V polypropylene film capacitors (i.e. big yellow
ones). These are much better for audio than standard alu elcos.

My question is:

1) the signal is only a couple of volts in amplitude. Is it bad that
the capacitors are way beyond this value? I mean, could it be that
these big caps handle low voltages not as well?

2) is it actually a good idea to replace *all* of these capacitors by
these big ones? (if you'd like, look at the circuit at <http://
sound.westhost.com/project24.htm>) Or would some good, small tantalum
capacitors do better in some locations?

Hello Ectoplasm.

Whether better or not, depends on where they are in the circuit. When
the AC voltage across the capacitor is very small with respect to the
signal voltage, there is no problem with electrolytic capacitors. This
is the case for most decoupling applications where the capacitor is
only used for DC separation. This means that the cross over frequency
of the capacitor in the circuit must be far below the lowest working
frequency.

When they are part of a filter, foil capacitors are a better choice.
In a filter, a large part of the driving AC voltage can be across the
capacitor. You can use polypropylene, but why not using polyester?
They are smaller, cheaper and also very linear.

Your questions.
Small AC voltages on high voltage foil capacitors is OK. The voltage
on the capacitor mentions the maximum DC or AC voltage that may be
applied for a long time.

I think it is not a good idea to just replace all electrolytic caps by
foil type capacitors. As mentioned before it depends on the function
of the capacitor. You may run into a space problem and probably it
isn't worth the money.

Best regards,

Wim
PA3DJS
www.tetech.nl

 

[ectoplasm]

Tantalum caps used for zero bias coupling perform horribly. I expect you want a
large value ? Use 100-220uF/16V or similar al elco.

No, only 10uF, 22uF, 10uF. In this circuit:
http://sound.westhost.com/project24.htm

But I bought those yellow caps already, 100V ones. They are bigger
than alu ones, yes. But they're not expensive ones.

Let me guess. You're not doing this because you have a problem with the sound
but because you read somewhre that al elco are 'bad' for the sound ?

Yes, right. But 40 cents for an alu elco, 1.50 for these polypropylene
caps who have a better audio reputation....

 

[ectoplasm]

capacitor. You can use polypropylene, but why not using polyester?
They are smaller, cheaper and also very linear.

Thanks a lot for explaining. I get what you mean. I will take a closer
look on the functions of my capacitors.

But polyester, you say. Those are the plastic block ones, right?

 

[Eeyore]

Wimpie wrote:>

Hello Ectoplasm.

Whether better or not, depends on where they are in the circuit. When
the AC voltage across the capacitor is very small with respect to the
signal voltage, there is no problem with electrolytic capacitors.

Absolutely correct. The actual voltage *across* an electrolytic capacitor in
zero bias mode (as opposed to the signal voltage magnitude itself) that gives
trouble is when it exceeds ~ 100mV.

Since using a large value capacitance reduces Z and hence that voltage it's hard
to wrong with values of around 10uF for input coupling caps and 100uF for output
coupling caps in most real world circuits.

When they are part of a filter, foil capacitors are a better choice.
In a filter, a large part of the driving AC voltage can be across the
capacitor.

This the critical difference.

You can use polypropylene, but why not using polyester?
They are smaller, cheaper and also very linear.

Polyester is indeed the least expensive of the plastic film dielectrics and
works just fine. The obsession with polypropylene and indeed Teflon as
dielectrics is no doubt due to the audiophool idea that more expensisve = better
in some rather undefined way.

Graham

 

[Eeyore]

No, only 10uF, 22uF, 10uF. In this circuit:
http://sound.westhost.com/project24.htm

But I bought those yellow caps already, 100V ones. They are bigger
than alu ones, yes. But they're not expensive ones.


Yes, right. But 40 cents for an alu elco, 1.50 for these polypropylene
caps who have a better audio reputation....

1.50 for a 22uF, 100V polypropylene ? Somone's giving them away it seems.

You should ignore those ppl who just talk about a capacitor's 'reputation' without
applying any science btw. There are lots of idiots in audio whose life's goal seems
to be to use the most expensive components (including wire!) possible for no good
scientific reason. There are certain caps you *should* avoid btw and I bet they've
never mentioned them ! Notably so-called medium and high-K ceramic types. The
dielectric behaviour in these is known to be non-linear. Low-K ceramics are fine
though.

Graham

 

[Eeyore]

Thanks a lot for explaining. I get what you mean. I will take a closer
look on the functions of my capacitors.

But polyester, you say. Those are the plastic block ones, right?

They often come in 'box' construction but not exclusively by any means. Mylar is
the same stuff btw.

Graham

 

[YD]

In a pre-amplifier, I am replacing all relevant capacitors in signal
lines by 100V or 250V polypropylene film capacitors (i.e. big yellow
ones). These are much better for audio than standard alu elcos.

I much prefer the blue variety, clearer highs and less graininess in
the lows.

- YD.

 

[John Popelish]

In a pre-amplifier, I am replacing all relevant capacitors in signal
lines by 100V or 250V polypropylene film capacitors (i.e. big yellow
ones). These are much better for audio than standard alu elcos.

Better, how?

My question is:

1) the signal is only a couple of volts in amplitude. Is it bad that
the capacitors are way beyond this value? I mean, could it be that
these big caps handle low voltages not as well?
No.

2) is it actually a good idea to replace *all* of these capacitors by
these big ones? (if you'd like, look at the circuit at
http://sound.westhost.com/project24.htm

I see only one capacitor in that circuit that will have any
significant effect on the sound. It is the 1 nF. The rest
have essentially no changing voltage across them in the
audio frequency range, so will have almost no effect on
audio. That said, I think some of the capacitor values are
a bit small, like the two 22 uF caps in the output stage.

 

[John Popelish]

I had an amp with a sub-sonic filter switch, think about it. things that
make you go what?!?!

Subsonic energy being produced by your headphones or
speakers is a waste of amplifier power that can cause them
to distort the stuff you can hear. It is usually a good
thing to get rid of.

 

[MooseFET]

In a pre-amplifier, I am replacing all relevant capacitors in signal
lines by 100V or 250V polypropylene film capacitors (i.e. big yellow
ones). These are much better for audio than standard alu elcos.

The only capacitor that it is worth considering changing is the 10uF
at the input.

The 470pF on th efirst op-amp is shown hooked up wrong.

[.....]

these big ones? (if you'd like, look at the circuit at <http://
sound.westhost.com/project24.htm>)

What kind of resistors are those? They may be making more distortion
than the capacitors.

The 22uF feeding the pot serves no purpose.

 

[Eeyore]

The 470pF on th efirst op-amp is shown hooked up wrong.

Really ?

It looks like an active filter configuration to me.

What kind of resistors are those? They may be making more distortion
than the capacitors.

The 22uF feeding the pot serves no purpose.

Yes it does.

Graham

 

[John Popelish]

The 22uF feeding the pot serves no purpose.

I have a bigger problem with the choice of output
transistors. Can anyone see why 300 volt transistors with
gain that falls pretty sharply above 200 mA collector
current (and at 10 volts collector to emitter drop for the
PNP) were chosen for this design? With the output running
80 mA class A there is not much current capability left to
drive the headphones.
http://komponenten.es.aau.dk/fileadmin/komponenten/Data_Sheet/Transistor/MJE340.pdf
http://www.uib.es/depart/dfs/GTE/education/industrial/tec_analogiques/MJE350.pdf

I would like to see the amp tested, side by side with one
using a TIP29C, TIP30C output pair.
http://www.fairchildsemi.com/ds/TI/TIP29C.pdf
http://www.bourns.com/pdfs/tip30.pdf

Of course, if you change from class A to class AB (say, 5 to
10 mA idle current), you could probably use a pair of TO-92
output transistors, like ZTX692B and ZTX792A and cut the
power supply size in half.
http://www.zetex.com/3.0/pdf/ZTX692B.pdf
http://www.zetex.com/3.0/pdf/ZTX792A.pdf

 

[Eeyore]

I have a bigger problem with the choice of output
transistors. Can anyone see why 300 volt transistors with
gain that falls pretty sharply above 200 mA collector
current (and at 10 volts collector to emitter drop for the
PNP) were chosen for this design?

It's probably what he had on hand.

No worse than using 2N2222s in that respect.

With the output running
80 mA class A there is not much current capability left to
drive the headphones.
http://komponenten.es.aau.dk/fileadmin/komponenten/Data_Sheet/Transistor/MJE340.pdf
http://www.uib.es/depart/dfs/GTE/education/industrial/tec_analogiques/MJE350.pdf

I would like to see the amp tested, side by side with one
using a TIP29C, TIP30C output pair.
http://www.fairchildsemi.com/ds/TI/TIP29C.pdf
http://www.bourns.com/pdfs/tip30.pdf

Of course, if you change from class A to class AB (say, 5 to
10 mA idle current), you could probably use a pair of TO-92
output transistors, like ZTX692B and ZTX792A and cut the
power supply size in half.
http://www.zetex.com/3.0/pdf/ZTX692B.pdf
http://www.zetex.com/3.0/pdf/ZTX792A.pdf

Defeats the audiophile purpose of the Class A operation.

Graham

 

[John Popelish]

Really ?

It looks like an active filter configuration to me.

I think it and the 15 pF are an overcompensation scheme for
the NE5534.

 

[D from BC]

I had an amp with a sub-sonic filter switch, think about it. things that
make you go what?!?!

I made my own amplifier electronics and put it in an old (1970's I
think) amplifier box. The original front label has "solid state
amplifier". It still has the original rumble filter switch which I
think is the same thing..
D from BC