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Old 29th November 2002, 12:14 AM   #11
diyAudio Member
 
Join Date: Feb 2002
Location: Western Sydney
Question DC across phones?

wouldn't the circuit at
http://space.tin.it/scienza/fladelle/Page31.htm

put DC across your phones?
(oK, less than 3V, but still.....)
any ideas on how to fix this?
(earth the load resistor & feed phones from a cap???)

The simplicity of the circuit appeals, though.
Pete McK
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Old 29th November 2002, 03:18 AM   #12
halojoy is offline halojoy  Sweden
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Join Date: Nov 2002
Default Too much is not good.

But some little will not do any harm.

High Quality HPs can take up to
0.1-0.5 watt something.
That is 100 to 500mW. Usually is given for AC-power.
For DC-power this will be lower, I think.
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Old 29th November 2002, 04:32 AM   #13
paulb is offline paulb  Canada
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Join Date: Jun 2001
Location: Calgary
Default Re: DC across phones?

Quote:
Originally posted by PeteMcK
wouldn't the circuit at
http://space.tin.it/scienza/fladelle/Page31.htm
put DC across your phones?
It looks like they forgot the cap. Should be one in series with the phones.
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Old 29th November 2002, 10:03 AM   #14
halojoy is offline halojoy  Sweden
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Join Date: Nov 2002
Default No cap is needed???

Quote:
Originally posted by paulb
It looks like they forgot the cap. Should be one in series with the phones.
I am not sure there is going to be any cap.
Gain is set for up to 300 ohms, R3/R1 = 6.8
And 1.5 V over 300 ohms is
is only 7.5mW.

The only danger is when you put very low quality
16 ohms HP in. Gives 140mW at DC.

But then you almost certain can change the
R3 to 10 kohm for gain=1
This gives a DC voltage at outputbelow 1.0 volt
Like 56mW over the phone.

To publish a "dangerous" construction on the web,
and not be corrected if,
seems to me unlikely.

This design has been around for several years.

If you have very low impedance HP, 16/32 ohms, of course you
can use a good Output cap.

For 100 ohm and and higher, the max power
will be below 25 mW.
If the circuit is built so it puts out 1.5 Volt DC.
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