High voltage capacitors in audio

[MooseFET]

Here's a simple headphone amp !

Take say, 10 high-performance audio op-amps per channel and 'combine' their
outputs via 82R each.

That'll give you an 8 ohm output with ~ +- 300mA drive capability.

How about using an LT1206
Just one will do it.

 

[ectoplasm]

Brain damage appears to be synonomous with audiophoolery.

What do you mean? Please explain.

 

[ectoplasm]

Brain damage appears to be synonomous with audiophoolery.

What do you mean? Please explain.

 

[Eeyore]

Eeyorewrote:

How about using an LT1206
Just one will do it.

A joke I assume ?

Graham

 

[Jasen]

Surely measurable and hearable should be reversed in that sentence ?

LOL! You surely know audiophools

Bye.
Jasen

 

[Jasen]

Well, presumably, LPs are rich in 0.55 Hz noise.

I've seen some with that noise 100dB above the signal,
but the bandwidth of the tone arm doesn't go that low.

If you never play records, it's probably not an issue, no.

Bye.
Jasen

 

[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?

Hello Ectoplasm,

Something off-topic.

I looked to the circuit diagram, although it can be used as a
headphone amplifier, I have some doubts about the safety of the
design.

When the connection from the potentiometer to the output breaks, you
will have full output (about 13Vp) that may be harmful for your
hearing. Are you using headphones with a sound level protection? If
not, I would not be happy with a circuit that can deliver so much
output.

I hope I overlooked something in the design

Best regards,

Wim
PA3DJS
www.tetech.nl

 

[MooseFET]

A joke I assume ?

Kind of. The LT1206 would drive a head phone just fine all the way up
to about 50MHz.

 

[MooseFET]

Yeah, but what if you were super man? Would you want your
ears to be denied the range of full quality noise ?

There is always a trade off. Very little of musical value is below
10Hz or above 40KHz.

 

[z]

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?

Well, electrolytics are sometimes not functional with tiny voltages,
IIRC from high school. Otherwise, probably not bad.

 

[Eeyore]

Well, electrolytics are sometimes not functional with tiny voltages,

Pardon ? What do you mean by that ?

Graham

 

[ectoplasm]

Do you have any idea what kind of capacitor this is?

(85kb jpeg)
http://img213.imageshack.us/img213/8192/capac0.jpg

 

[John Popelish]

Do you have any idea what kind of capacitor this is?

(85kb jpeg)
http://img213.imageshack.us/img213/8192/capac0.jpg

Almost certainly metalized polyester (Mylar) film.

 

[ectoplasm]

from this data sheet, I would prefer the narrower gain range
and higher minimum gain pair 2SD2400A, 2SB1569A (minimum
gain 100, maximum gain 200 at 1 amp). I would like to see
the actual gain versus collector current and safe operating
area curves, though. All of these are much better choices
than the MJE340, MJE350 pair in the original design, in my
opinion.

Hi John,

regarding the 2SD2400A, 2SB1569A, I cannot find *any* data sheets
besides the one you found (your link). So I also was not able to look
at those curves (I would guess from the numbers that they would be
within safe operating area because of abs max values Vceo and Ic
compared to TIP29, 30). But isn't this information (the curves)
supposed to be in a transistor's datasheet?

 

[Eeyore]

Do you have any idea what kind of capacitor this is?

(85kb jpeg)
http://img213.imageshack.us/img213/8192/capac0.jpg

Yes.

10uF 100V 10% tolerance plastic film (probably polyester).

Graham

 

[ectoplasm]

As to the suitability of the 2SD1763, 2SB1186 pair, here are
the data sheets:http://rocky.digikey.com/WebLib/Rohm/Web Data/2SB1zzz, A and ...
With a 1.5 amp rating and designed as complementary pairs,
they would work just fine. They each have a minimum current
gain of 60, maximum gain 200 at 1 amp, and I suspect might
have a bit more at the half amp expected peak current. But
from this data sheet, I would prefer the narrower gain range
and higher minimum gain pair 2SD2400A, 2SB1569A (minimum
gain 100, maximum gain 200 at 1 amp). I would like to see
the actual gain versus collector current and safe operating
area curves, though. All of these are much better choices
than the MJE340, MJE350 pair in the original design, in my
opinion.

(I sent this reply before but it got lost I guess)

I am also unable to find any complete datasheet for 2SD2400A,
2SB1569A. They only show some tabular data, curves are not included.

From the absolute maximum ratings I would think it would be in the

safe zone, but for hFE curve, I am unable to make a comparison with
TIP29, 30.

Is it normal that these curves are not shown in the datasheet? Or is
there another way to check this?

 

[ectoplasm]

Thanks, Wimpie. If you are right I'll have to be extra careful also
when I finished this circuit & go to test it. After that... the
connection must never be broken (that is, take extra care connecting
those pot wires).

 

[ectoplasm]

By the way,

is it true that for transistors (like TIP29) there can be more than
one manufacturer, and that their specifications may differ?

Because for TIP29 I found a datasheet from Fairchild, and from Power
Innovations Limited. There seem to be small differences.

If so, then when buying a transistor, one should be careful to
consider which manufacturer?

 

[ectoplasm]

I just thought I could use the 5532 instead of 5534, because I need
two 5534's (left + right channel), and 5532 is a 'two in one'.

Then the compensation capacitor (at pins 8 and 5) is not required
because compensation is internally set in the 5532.

So far so good.

As a side issue, I came across following page:
http://www.dself.dsl.pipex.com/ampins/webbop/5532.htm

Quote:

"DECOUPLING & STABILITY. 5532 and 5534 type opamps require careful
supply-decoupling if they are to remain stable; otherwise they appear
to be subject to some sort of internal oscillation that degrades
linearity without being visible on a normal oscilloscope.
The essential requirement is that the +ve and -ve rails should be
decoupled with a 100nF capacitor between them, at a distance of not
more than 2 inches. It is NOT necessary, and often not desirable to
have two capacitors going to ground; every capacitor between a supply
rail and ground carries the risk of injecting rail noise into the
ground. The main rail decouple electrolytics can be used to do the job
for several 5532/4 packages nearby, and this cost saving is an
important layout point. Likewise, it is not normally necessary to
decouple each package individually. One capacitor every few inches is
sufficient if the power tracks are of reasonable thickness. (ie 50
thou)"

So according to the author there must be a 100nF (electrolytic, he
says) capacitor between the Vcc and gnd pins of the 5532 nearby the
5532.

Has anyone ever heard of this requirement and is it a necessity? I am
just surprised it is missing in the headphone amp's circuit (there are
100nF's in the power supply).

 

[martin griffith]

I just thought I could use the 5532 instead of 5534, because I need
two 5534's (left + right channel), and 5532 is a 'two in one'.

Then the compensation capacitor (at pins 8 and 5) is not required
because compensation is internally set in the 5532.

So far so good.

As a side issue, I came across following page:
http://www.dself.dsl.pipex.com/ampins/webbop/5532.htm

Quote:

"DECOUPLING & STABILITY. 5532 and 5534 type opamps require careful
supply-decoupling if they are to remain stable; otherwise they appear
to be subject to some sort of internal oscillation that degrades
linearity without being visible on a normal oscilloscope.

I heard, about 10 years ago, that one manufacturer of large audio
consoles, stuffed with 553xs was supprised to see noticable noise from
finished consoles, in the 3GHz region.
This was not noticable on single channel strips, but only on the
complete console, of say 64 input channels. IIRC


snip


martin