Impedance Matching/Mismatch

[Simon_LDT]

I'm currently trying to understand Impedance matching and I'm a bit stuck on a few things. I've been trying to connect my headphone amp to the outputs on my DAC, but when I do I get distortion which sounds like something overloading. In the meantime, I've just placed my pre-amp in between (connecting the tape out to the headphone amp) but I'd like to remove it from the chain if possible.

Headphone amp is a Schiit Asgard and I was told by one of the engineers that it has an input impedance of 100k ohm. My DAC is an Arcam D33 and the manual states it has an output impedance of 47 ohm. From my understanding, it seems this should be okay as the amp has a higher impedance. My Arcam pre is a C31 and the manual says it has <50 ohm output impedance. Any reason as to why it works fine with the pre in the chain but not without it?

My other query is regarding passives. I'd like to try one but I'm not sure if my amp would match well. My amps have a quoted input impedance of 22k ohm, is that high enough for a passive?

[struth]

more likely just to much gain from dac for head inputs

[Simon_LDT]

Would some kind of attenuation between DAC and Headphone amp fix this? If so, would that degrade the sound?

[struth]

you would be best seeing what output voltage is from dac and see iff its acceptable to the headamp.might need a bit of attenuation and im not a fan of external attenuators

[RothwellAudio]

more likely just to much gain from dac for head inputs

Well, too high a signal from the DAC would be more accurate as DACs don't really have gain, but essentially yes. Still, you would expect a headphone amp to be able to cope with the output from a DAC without overloading.

Would some kind of attenuation between DAC and Headphone amp fix this? If so, would that degrade the sound?

Yes, attenuators would fix this. No, there won't be any degradation of the sound - it's overloading as it is!

http://www.rothwellaudioproducts.co....tenuators.html

[RothwellAudio]

I'm currently trying to understand Impedance matching and I'm a bit stuck on a few things.

The source impedance (also known as the output impedance) should be a lot lower than the load impedance (aka the input impedance), preferably by a factor of 10 or more. The 100k input impedance of your headphone amp should be fine with any source up to 10k output impedance. In practice you'll find that almost everything these days has a much lower output impedance than 10k.

Any reason as to why it works fine with the pre in the chain but not without it?

Not that I'm aware of.

My other query is regarding passives. I'd like to try one but I'm not sure if my amp would match well. My amps have a quoted input impedance of 22k ohm, is that high enough for a passive?

Higher than 22k would be nice but you'll ok. A pot impedance of 10k would be about right but I wouldn't go higher than 10k.

[Arkless Electronics]

There's no such thing as impedance matching in the context of hi fi. The matching of SUT's to cartridges is about as close as we get... It is a concept used mainly in RF circuitry. Even the term impedance is usually not strictly correct unless one wishes to be really pedantic as resistance is usually more apt a term. As Andrew says, all you really need is for the driving impedance to be much higher than the input impedance.

For the op I would check if the DAC has a selectable output level and can be turned down. Unlikely in the case of the Arcam but many pro DACs can have a higher output level selected.

[anthonyTD]

Trying to get my head around this, and just re-read through some of the earlier posts, I am a bit confused with what your refering to here Jez,
Dont you mean lower, as far as the driving Impedance, or am I not reading you correctly ?
A...

all you really need is for the driving impedance to be much higher than the input impedance.

[RothwellAudio]

DAC (phono output 1) > C31 > P1's
DAC (phono output 2) > H/phone amp
That caused distortion whenever I had just the DAC and H/phone amp on, everything else off. I never tried turning on the C31 at the same time

Powering up the C31 should be enough to cure the distortion.

I would expect also that c31 on would be enough to remove the short

Yes, no need to switch the P1s on as well.

The OP just has to try it and report back to us.

[Simon_LDT]

Powering up the C31 should be enough to cure the distortion.


Yes, no need to switch the P1s on as well.

The OP just has to try it and report back to us.

Yep, that also works (C31 on without power amps on too). Still don't like the idea of having the pre on for no real reason when using headphones so will be using the Tisbury and going through the loop output on that, at least for the time being.

Just want to thank all those that replied and helped me to understand the situation, especially Andrew.