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Review and Measurements of New JDS Labs Atom Headphone Amp

Music1969

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RF is still an issue and should be considered, directly on the input connections and through casework. Metal case will perform better for shielding however it should be stressed that the end result, how sensitive the unit is to RF, will depend on many circuit variables and it really is not necessarily true that this unit would have any I'll effects due to a plastic case under normal conditions. Ie not living next to an AM transmitter.
Regarding the plastic case and RFI discussed here:

Has anyone had any audible interference issues with Atom?
 
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I would have been more concerned about the Atom's plastic case -except a few months before buying my Atom - I started using a Hagermann Bugle phono -preamp. The factory built version comes in a molded clear plastic case. Given decades of experience with phono stages -my eyebrows definitely went up when I saw this ??? The Bugle is very quiet -not the very most silent I own -but darn good and really impressive for the bucks spent on it. So I bought the ATOM and I find this to be really dead quiet - at least as quiet as my O2 in my system or the Benchmark headphone stage built into my DAC-3HGC. I think the real question has already been asked : Anyone had noise problems with a ATOM yet ?
 
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It is really weird that you should mention the bugle as I have a bugle that suffers a bit from RFI noise. It is approx 6' from my WAP and I can hear RFI when I am not playing a record and have the sound cranked way up on my non headphone amp and speakers. The Atom is just a couple of feet from from the WAP and does not seem to suffer audible RFI.

Until I recase the Bugle I have it living in a section of aluminium vent tube, which cuts out most of the RFI. Countdown to the first joke about a tube preamp .. 5 4 3 2 1 ...

 
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As the founding (only?) member of KAM (Kalishnikov Aesthetics Movement ,aka Butt Ugly Butt Works) - I really like this shielding treatment ! Noise is so often a individual system thing - when I went to Meridian DSP speakers it eliminated 60 hz hum from my current set up - this had been a oddball problem because it was intermittent (Oh Joy). I have a peculiar complex system mainly based on LP playback with multiple phono preamps - what I don't understand is that the guys who bought my amps and preamps are not having noise problems/humm -so ? Gone is good.
 

watchnerd

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use the digizoid power calculator to get it's power requirements (which will be at the impedance in question, which makes it tricky to directly compare the power requirements between cans that have different impedances).
Here are the numbers the Digizoid gives me for the 3 cans I use the most:

HiFi Man HE-400i

VLoud: 159mW
Painful: 502mW

AKG K7XXX

VLoud: 161mW
Painful: 509mW

Sennheiser 6XX

VLoud: 16mW
Painful: 50mW (3.8V)

Based on this, it seems like the Atom is borderline powerful enough, with not much headroom, for the HE-400i and K7XX, but should be fine for the 6XX, with more than enough spare power.

Is that a fair assessment?
 

JohnYang1997

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Here are the numbers the Digizoid gives me for the 3 cans I use the most:

HiFi Man HE-400i

VLoud: 159mW
Painful: 502mW

AKG K7XXX

VLoud: 161mW
Painful: 509mW

Sennheiser 6XX

VLoud: 16mW
Painful: 50mW (3.8V)

Based on this, it seems like the Atom is borderline powerful enough, with not much headroom, for the HE-400i and K7XX, but should be fine for the 6XX, with more than enough spare power.

Is that a fair assessment?
Atom should be able to output 2W with 50ohm load. I would say it's more than enough, not borderline enough. Also remember that the dynamic range is sealed by the dac. Meaning that unless you turn the volume all the way up at high gain and still not loud enough. It's ample. I never used it at max volume at low gain. I don't think you will ever need it either. Realistic speaking 100mw is all you need mostly.
 

AresHarvest

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Is that a fair assessment?
I own (or have owned, in the case of the 7XX) and have used all those headphones with the Atom. With a DAC supplying 2 Vrms, it gets more than loud enough for any of those models. Keep in mind how loud 115 dB SPL really is.

Also, there's something wrong with how you entered info into the calculator. For example, those AKG headphones are 62 ohm and 105 dB/V. That gives very different results than the ones you've posted.
 
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watchnerd

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I own (or have owned, in the case of the 7XX) and have used all those headphones with the Atom. With a DAC supplying 2 Vrms, it gets more than loud enough for any of those models. Keep in mind how loud 115 dB SPL really is.

Also, there's something wrong with how you entered info into the calculator. For example, those AKG headphones are 62 ohm and 105 dB/V. That gives very different results than the ones you've posted.
I just double checked for 62 ohm and 105 dBV and got the same results. Are you sure you're toggling the mW vs V button for sens?
 

AresHarvest

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Ah, that's my mistake. Was viewing on mobile and was accidentally looking at the current needed, not the power needed.

So even with the AKG needing 161 mW to get to "very loud," which is 115 dB according to the calc, that's louder than pretty much anyone will want to listen. So I think you'll be fine with the amount of power the Atom provides.
 

JohnYang1997

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One thing to point out, the listening loudness is stupid. There is absolutely no chance that you listen louder than 100dB. 105db is good enough for all the dynamic headroom. And you should listen no higher than 96db average. Quite frankly, you should really listen at 85db only when you doing critical listening. And for casual long session listening less than 80db is ideal. Every 6db in loudness is 4 times the power.
It should be
73db quiet
85db critical
96db loud
105db maximum instead.
 

Music1969

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It is really weird that you should mention the bugle as I have a bugle that suffers a bit from RFI noise. It is approx 6' from my WAP and I can hear RFI when I am not playing a record and have the sound cranked way up on my non headphone amp and speakers. The Atom is just a couple of feet from from the WAP and does not seem to suffer audible RFI.
Good to know. Using shielded RCA cables?
 
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Good to know. Using shielded RCA cables?
Yes, both from the turntable to the Bugle (Cardas 33AWG) and from the Bugle to the amplifier (DH Labs BL-1 Series II). There were no RFI issues until I changed a Cambridge Azur phono preamp for the Bugle. The aluminium tubing does a good enough job for me, The RFI without the tube is really not noticeable unless you crank the amplifier up to near max when there is nothing playing. It's just an annoyance to know that it is there.
 

Music1969

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Yes, both from the turntable to the Bugle (Cardas 33AWG) and from the Bugle to the amplifier (DH Labs BL-1 Series II). There were no RFI issues until I changed a Cambridge Azur phono preamp for the Bugle. The aluminium tubing does a good enough job for me, The RFI without the tube is really not noticeable unless you crank the amplifier up to near max when there is nothing playing. It's just an annoyance to know that it is there.
And Atom is 2 feet away from your WAP?

I know it's very silly but if you bring Atom 1 foot away from your WAP, can you hear any sign of interference with headphones?
 
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And Atom is 2 feet away from your WAP?

I know it's very silly but if you bring Atom 1 foot away from your WAP, can you hear any sign of interference with headphones?
The WAP normally resides on the shelf above the Atom and I just moved it down to the same shelf and a few inches away from the Atom. I have turned on the Atom, plugged in some Hifiman HE-4XX headphones and turned the gain and volume up to the max. I can't hear anything but silence. I am streaming to a CCA downstairs so I know the WAP is active.

The Atom is connected via shielded cables to a KTB DAC which is getting a shielded coax feed from a Raspberry pi with a Hfiberry Digi+streamer.

Nothing to report but silence.
 

Music1969

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The WAP normally resides on the shelf above the Atom and I just moved it down to the same shelf and a few inches away from the Atom. I have turned on the Atom, plugged in some Hifiman HE-4XX headphones and turned the gain and volume up to the max. I can't hear anything but silence. I am streaming to a CCA downstairs so I know the WAP is active.

The Atom is connected via shielded cables to a KTB DAC which is getting a shielded coax feed from a Raspberry pi with a Hfiberry Digi+streamer.

Nothing to report but silence.
Nice. I've seen numerous posts in this thread about concerns for the plastic case and potential for RFI but haven't read of anyone having any audible issues.

Shielded cables and keeping them short is probably more important.

Proper system grounding too I assume.
 
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