High voltage capacitors in audio

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 ) Or would some good, small tantalum capacitors do better in some locations?

Reply to
ectoplasm
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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. :P Oh...use silver solder.. :P D from BC

Reply to
D from BC

I suppose it all becomes meaninglessly undiscernible with brain damage.

Reply to
ectoplasm

D from BC wrote in news: snipped-for-privacy@4ax.com:

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

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Reply to
me

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

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Reply to
Wimpie

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?

Reply to
ectoplasm

Late at night, by candle light, ectoplasm penned this immortal opus:

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

- YD.

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Reply to
YD

Better, how?

No.

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.

Reply to
John Popelish

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.

Reply to
John Popelish

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.

[.....]

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

The 22uF feeding the pot serves no purpose.

Reply to
MooseFET

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.
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I would like to see the amp tested, side by side with one using a TIP29C, TIP30C output pair.

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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.
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Reply to
John Popelish

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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

Reply to
D from BC

You are right. The cheapest ones are the metal "colored" block capacitors (the leads will come off easy). Just look to MKT or MKS, they come in a variety of shapes and enclosures (both radial and axial versions).

Best regards,

Wim PA3DJS

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Reply to
Wimpie

...

Do you mean "The Brown Noise"?

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;-) Rich

Reply to
Rich Grise

I hadn't looked at that issue. You are right. Obviously the right transistors in this circuit are a TIP35C and TIP36C.

That would be only because he din't have a TIP35 and TIP36 in his junk box.

headphones.http://komponenten.es.aau.dk/fileadmin/komponenten/Data_Sheet/Transis...http://www.uib.es/depart/dfs/GTE/education/industrial/tec_analogiques...

pair.http://www.fairchildsemi.com/ds/TI/TIP29C.pdfhttp://www.bourns.com/pdfs/tip30.pdf

Those are way to whimpy. You need great big transistors to make it sound good.

Oh, no, it has to be class-A

Reply to
MooseFET

John Popelish wrote in news:IJudnXc2LKqSp-TbnZ2dnUVZ snipped-for-privacy@comcast.com:

Sure, if it was there to begin with.

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Reply to
me

headphones.http://komponenten.es.aau.dk/fileadmin/komponenten/Data_Sheet/Transis...http://www.uib.es/depart/dfs/GTE/education/industrial/tec_analogiques...

pair.http://www.fairchildsemi.com/ds/TI/TIP29C.pdfhttp://www.bourns.com/pdfs/tip30.pdf

I didn't see a smiley in there, anywhere, but I assume you are being sarcastic. Lets stick to the actual situation for a moment. What impedance headphones do you think this unit was intended for. It may be there in the page, but a quick look didn't find it. If I assume 32 ohm headphones, a +- 12 volt sine wave would produce about 2.25 watts, electrical, a huge amount of power for headphones, I think. But the peak current would still be the bias of 80 mA plus the peak load current of 375 mA or 455 mA. That is getting pretty far over the peak of the current gain curve for the 340 350 pair. But quite comfortable for the TIP29,31 pair.

For religious reasons?

Reply to
John Popelish

Okay.

Reply to
John Popelish

My headphones are 32 ohm ones, but you might as well plug in 70 ohm ones, ok... and if 300 ohm, it should also be ok (but they might require higher voltage).

I think output power in one pair of headphones (32 ohm) would be around 500 mW max? I guess output voltage of around 3 volt max is reasonable. The circuit would have around 10x gain (adjustable by the AOT resistor).

The output voltage is the same no matter what you plug in, isn't it? What if you'd plug in 300 ohm headphones, wouldn't they sound too silent?

As MooseFET says TIP35, 36 would be a good choice... I must take a closer look on those data sheets later and make comparisons with the original ones.

Reply to
ectoplasm

headphones.http://komponenten.es.aau.dk/fileadmin/komponenten/Data_Sheet/Transis......

pair.http://www.fairchildsemi.com/ds/TI/TIP29C.pdfhttp://www.bourns.com/pd...

Yes the suggestion of the TIP35 was intended to be funny. Even if you assumed 8 ohm head phones, you would destroy someones hearing long before you needed a TIP35.

Yes, that is way too much power. At that volume the small bones in the ear clattering together make more distortion than the amplifiers.

In truth, I fully agreed with your selection.

Its marketing. A "class A shoe" is better than a "class B shoe". A "class A dinner set" is also better so a "class A amplifier" must be the best.

I once saw a 25W class-A audio amplifier. It also would serve as a space heater.

Reply to
MooseFET

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