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Review and Measurements of Chord Mojo DAC and Amp

Jorj

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I love Le Mans rillettes de porc , best in France , best in the world.
I'm unclear what rillettes have to do with cheese or Chord Mojos. Although I'd be willing to eat rillettes de porc drizzled with a lovely raclette. Thanks a lot, now I'm hungry.
 

graz_lag

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graz_lag

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Going back to serious businesses, I have ordered a Topping DX7S this morning from an eBay's seller, @ $440 or so, so abt. $60 cheaper than Topping' $499.99 suggested price.
eBay's seller : szclever88, Hong Kong (apparently ...)
I'm going to post this in the relevant post as well.
 

Jorj

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Not much in there that seems like it should react that way.

1541797380116.png
 

graz_lag

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Some foil capacitors can be microphonic, what's inside the thing- let's have a look. :)
Ceramic or foil ones ? I thought ceramic ones tend to behave as microphones ...
 

Jorj

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Went back and reviewed the video @March Audio posted, and the microphonics hump is in the lower frequencies, but never gets much over -120dB, so it's definitely not audible. I'm just confused as to how that is even possible. Maybe I need to mount some Stillpoints on my Mojo. Don't want to jiggle those pesky bits.
 

Blumlein 88

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We need March Audio to do some more defined testing. We need the device subjected to tones around that 120 hz range at 100 db SPL at the surface of the enclosure. Then see if anything can be seen in the deepest FFT he has. Then we'll be able to estimate at what levels between -200 dbFS and higher external sound will impact the device. So we'll be able to estimate just how ridiculous that business is. :)
 

Blumlein 88

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My bet is the relay or the crystal oscillators (2).
I was thinking exactly the same thing. My first thought in the picture was the crystal. Those actually are usually pretty immune to that sort of vibration according to specs. So next I was thinking the analog out connection.

EDIT: well Amir beat me to it by a minute. At least my guess was good. So you probably need to use all right angle plugs on this device.
 

restorer-john

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That's exactly what I was just thinking also. High speed intermittent contact caused by impacts. Not microphonics as such.
 

Jorj

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That's exactly what I was just thinking also. High speed intermittent contact caused by impacts. Not microphonics as such.
Confused. Tapping a solid aluminum case creates a resonance in the low KHz range? And that resonance causes the HP plug to see a rise in a fairly wide spectrum of EM energy? This is not a piezoelectric system. How does that work?
 

restorer-john

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Confused. Tapping a solid aluminum case creates a resonance in the low KHz range? And that resonance causes the HP plug to see a rise in a fairly wide spectrum of EM energy? This is not a piezoelectric system. How does that work?
The signal is interrupted briefly by tapping the unit. Impact induced poor contact. Speaker relays in amplifiers can do the same. Easy to confirm, hardwire to the PCB an external HP jack and test again.
 

March Audio

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March Audio

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Confused. Tapping a solid aluminum case creates a resonance in the low KHz range? And that resonance causes the HP plug to see a rise in a fairly wide spectrum of EM energy? This is not a piezoelectric system. How does that work?
In vibration terms an impact is in essence a stimulus at all frequencies (within reason).

To test the response of a mechanical system you do what is called a bump test. This is quite literally hitting the object with a rubber hammer with an accelerometer attached to the object. The Fft derived from the accel will show the response and the resonant frequencies will stand out.

What you are seeing there is not the resonant frequencies, just the general vibration response.

Electronic components most certainly do respond to vibration, think about capacitor construction for a start.
 
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March Audio

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The signal is interrupted briefly by tapping the unit. Impact induced poor contact. Speaker relays in amplifiers can do the same. Easy to confirm, hardwire to the PCB an external HP jack and test again.
No this is not the case. Tried wiggling the headphone connector around and twisting it with no effect. Its a tight fit here. The relay could indeed a good candidate.

However this isn't the point as far as I am concerned. The device is affected by vibration whatever the cause, yet great claims are made about is lack of noise floor modulation, something which is claimed to be extremely important. It is microphonic - it reacts to input vibration.

Let's try this with another device, I will try my phone. Let's try other stimuli, sine and broadband White noise.
 
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March Audio

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OK, bashing crap out of my new phone.


Rummaged around in my box of crazy crap and dug out a small butt shaker. Sine at 1kHz


white noise to show resonances in the device. Note long averaging to make it clearer. Could be structure and or individual components.


Now dont get me wrong, stuff at this level I dont think is serious, but the manufacturer claims stuff at lower level than this is extremely important.

BTW, this Mojo has been my daily driver for several years, I like the sound, I just dont believe the marketing around the technicalities of the unit.
 
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March Audio

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Last one showing the microphony being acoustically induced, not just by direct contact

 
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