Yes. I am pretty sure the RCA output and the headphone output are exactly the same. However, the RCA outs are only active when there is no headphone connected.
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Review and Measurements of New JDS Labs Atom Headphone Amp
- Thread starter amirm
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magicscreen
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I have managed to burn in my Atom amplifier! 
I put it between the Loxjie P20 and MCTH like a sandwich.
The P20 and MCTH became very-very hot (it is hot summer now) and so the Atom as well.
I put it between the Loxjie P20 and MCTH like a sandwich.
The P20 and MCTH became very-very hot (it is hot summer now) and so the Atom as well.
Question for somebody that knows how to do the math: what would the headphone amp power output be on the Atom with the Apple USB-C dongle used as a DAC given its 1V output?
The reason I ask is people are always asking about the ifi Zen DAC over on Reddit, and we know how it measures
https://www.audiosciencereview.com/...ds/ifi-zen-dac-and-headphone-amp-review.9885/
I've been wondering if the Atom/Apple dongle is the best option in this price range?
The reason I ask is people are always asking about the ifi Zen DAC over on Reddit, and we know how it measures
https://www.audiosciencereview.com/...ds/ifi-zen-dac-and-headphone-amp-review.9885/
I've been wondering if the Atom/Apple dongle is the best option in this price range?
MRC01
Major Contributor
I think you probably care more about voltage sensitivity than power, but you can compute one from the other, for a headphone of given impedance.
Amir's review showed the Atom delivering 0.25 W into 300 ohms at high gain (no clipping). That's 29 mA of current and 8.6 V. If he used a 2V input for the test, the max gain ratio was 2:8.6 which is 20*log(8.6/2) = +12.6 dB.
If the input voltage were only 1V, that's cut in half, which means the output voltage would be cut in half, which is 4.3 V. This is enough voltage to drive Sennheiser HD600 beyond hearing-damaging levels (115 dB SPL).
Simlar calculations suggest that with a 30 ohm load, the max Atom voltage output is 6 V. That is, the Atom is current limited. Half of this is 3 V which still drives an HD600 to about 112 dB.
In short, it looks like the Atom has enough gain to drive low voltage sensitivity headphones to ear-splitting levels, even if the input is limited to 1.0 V.
Half the voltage is 1/4 the power (into the same load). So for an input limited to 1.0 V, take Amir's power measurements and divide them by 4. That would be 250/4 = 63 mW into 300 ohm and 1100/4 = 275 mW into 33 ohm.
PS: I just noticed that my calculations, which I backed into from Amir's measurements, are almost the same as the figures @NTK posted above from the Atom specs published by JDS.
Amir's review showed the Atom delivering 0.25 W into 300 ohms at high gain (no clipping). That's 29 mA of current and 8.6 V. If he used a 2V input for the test, the max gain ratio was 2:8.6 which is 20*log(8.6/2) = +12.6 dB.
If the input voltage were only 1V, that's cut in half, which means the output voltage would be cut in half, which is 4.3 V. This is enough voltage to drive Sennheiser HD600 beyond hearing-damaging levels (115 dB SPL).
Simlar calculations suggest that with a 30 ohm load, the max Atom voltage output is 6 V. That is, the Atom is current limited. Half of this is 3 V which still drives an HD600 to about 112 dB.
In short, it looks like the Atom has enough gain to drive low voltage sensitivity headphones to ear-splitting levels, even if the input is limited to 1.0 V.
Half the voltage is 1/4 the power (into the same load). So for an input limited to 1.0 V, take Amir's power measurements and divide them by 4. That would be 250/4 = 63 mW into 300 ohm and 1100/4 = 275 mW into 33 ohm.
PS: I just noticed that my calculations, which I backed into from Amir's measurements, are almost the same as the figures @NTK posted above from the Atom specs published by JDS.
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Thanks! That's very helpful. So So it is a better alternative to the ifi Zen for single ended use for less money.
solderdude
Grand Contributor
It's not quite true for low impedance headphones as the current limiting isn't reached at 1V input voltage but it is an easy rule of thumb
Current is limited to 177mA given the max power rating at 32 Ohm.
At 1V input the output voltage with 4.1x gain will be 4.1V.
At 1V in on 32 Ohm 4.1V is reached as the current is only 130mA so isn't limited yet while it is using 2V in.
So for 32 Ohm output power will be 0.53W
Thanks guys. So the next time somebody asks for a recommendation for an amp/DAC for well under $200, I will share these numbers for the Atom/Apple combo
530mw at 32 ohm
63mw at 300 ohm
530mw at 32 ohm
63mw at 300 ohm
Yes
I think so, but I can't say for sure ( I'm using a different amp now)
But that's from JDS site :
"PREAMP OUTPUTS
Unplug your headphones and Atom Amp's knob adjusts volume of its RCA preamp outputs, so that you can control volume of your powered speakers"
Gradius
Addicted to Fun and Learning
You can also do a simple mod and install a switcher (yeah, it could be a bit better designed).
This way you don't need to plug and unplug all the $%#$!* time.
This way you don't need to plug and unplug all the $%#$!* time.
Yes and yes.
Correct. SE only.
I thought about doing this. Are you aware of any pictures or instructions from someone who's done it?
Gradius
Addicted to Fun and Learning
I haven't done yet as I still didn't got the enough time to do it.
But its simple, you just need to trace from that relay closer to that 6.5mm female jack (headphones) and volume.
Btw, a nice addon (not my idea):
https://www.amazon.com/Taiss-Aluminum-Electronic-Potentiometer-Knobs，Switch/dp/B07FVLVB55
Attachments
Gradius
Addicted to Fun and Learning
I'm not sure what you mean. I was thinking that I would need to insert a DPDT switch into the circuit to bypass the HP socket and route L & R signals directly to the RCA outputs (regardless of anything being plugged in the socket).
Here is my crude diagram...
I assume that this would involve either breaking traces on the PCB or desoldering some of the pins on the HP socket (which would be preferable to me as it's less destructive).
Is there an easier way to do this?
Thanks, I know about the knob
https://www.audiosciencereview.com/...cal-clear-hd600-around-400.10063/#post-273346
solderdude
Grand Contributor
Is it a problem when the line out is always connected ?
In the latter case the modification is extremely simple.
In the latter case the modification is extremely simple.
Ideally, yes. But if the modification is much simpler, then it would be considered.
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