can a musical fidelity pre drive my hd600 cans ? - diyAudio
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Old 16th August 2007, 11:14 AM   #1
fatgaz is offline fatgaz  Andorra
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Question can a musical fidelity pre drive my hd600 cans ?

Hello All !

I have a musical fidelity A3-cr preamp.

supposedly the specs are that the output unity gain buffer has high voltage and current drive, 20+ RMS and 3W total power, with possibly a 50 ohm output impedance.

can I drive 300 ohm headphones (sennheiser hd600) directly from the preamp ? (it's obviously designed to drive inputs with 10's of KOhm impedance - two orders of magnitude change !)

OR will the amp blow-up ? sound bad ? break the headphones ?

advice and help please !

(i don't have a schematic of the amp either)

Gareth.

PS anything i could do to avoid problems / make this work / mitigate against problems ?

PPS would a 10K to 600 ohm transformer be a good idea ?
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Old 16th August 2007, 11:37 AM   #2
AndrewT is online now AndrewT  Scotland
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Location: Scottish Borders
Hi,
it's your ears that will blow.
the headphones are loud with just a mW of input.
That output is capable of 30db more than you need.

The pre-out may be able to drive 600ohm.
If that is the case then arrange a resistor attenuator.
1k0 in series and then 20r to ground.
Feed the phones from the output across the 20r. Far better than any transformer.

Once you have the correct attenuation, you can think about buying 4 metal foil resistors from Vishay if you think better sound quality is worth chasing.

By the way that series 1k0 could be made from 2off 2k0 in parallel or even 3off 3k0 in parallel. Starting with 3k0 will allow attenuation to be adjusted by adding the second and then the third resistor if you need more volume.
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Old 17th August 2007, 03:06 PM   #3
fatgaz is offline fatgaz  Andorra
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Join Date: Oct 2006
Default xcan vs a324dac vs a3cr

just opened my preamp and compared it to both a schem of a X-cans V2 (traced by a3rd party" and the a324 dac schematic 'hifigeorge'posted here

they all have a very similar output stage - power darlingtons to a series 47 or 33 ohm resistor to a NP electrolytic cap. The dac has a 470uF coupling cap, the X-cans has a 220uF cap and my preamp has a 10uF coupling cap.

with a 10uF cap and my 300 ohm cans froming a high pass filter - I've got a 50-ish hertz -3db point.

So it looks like the cicuits are not taht dis-similar at all !

BUT I think i need to parallel a 100uF coupling cap if I want any bass....

should i also parallel some small poly caps across this big NP eletrolytic to tery and smooth the treble too ?

All advice greatfully recieved.

Gareth.
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Old 17th August 2007, 03:28 PM   #4
AndrewT is online now AndrewT  Scotland
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Hi,
measure the DC voltage across that coupling capacitor.
Then come back.
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