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Review and Measurements of Project Polaris HP Amp

amirm

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#1
This is a review and detailed measurements of the Project Polaris Headphone Amplifier. It is on kind loan from a member. Researching it, I was surprised that it is the brainchild of the member, @solderdude!

From what I understand a US outfit makes these either as kits or finished products. I received the latter:

Project Polaris Headphone Amplifier Audio Review.jpg


There are a myriad of jumpers to set gain, bandwidth, output impedance, LED status, etc. I tested the combination of first two.

The design goals seem to be around very high output level but with "tube like" distortion profile (and output impedance if wanted).

1568592047754.png


Headphone Amplifier Audio Measurements
Let's see our dashboard view with 2 volts in, 2 volts out:

Project Polaris Headphone Amplifier Low Gain High BW Audio Measurements.png


That is fair bit of distortion but is second harmonic dominated as tubes are said to be.

Was dismayed to see almost 1 dB of channel imbalance. Testing for that shows fairly large discrepancy at low volume levels:
Project Polaris Headphone Amplifier Channel Imbalance High BW Audio Measurements.png


Signal to noise ratio was surprisingly good at full volume:
Project Polaris Headphone Amplifier SNR High BW Audio Measurements.png


But not so good with just 50 millivolt output:

Lowest Noise Headphone Amplifiers Measured and Reviewed.png


Intermodulation distortion versus output level shows a ruler flat incline in distortion which I assume is on purpose:

Project Polaris Headphone Amplifier IMD High BW Audio Measurements.png


Frequency response shows that the two lower settings are made for people who want rolled off highs:

Project Polaris Headphone Amplifier Frequency Response Audio Measurements.png


Since even the medium setting rolls off at 20 kHz, for my testing I chose the high bandwidth mode. It made very little difference in other measurements anyway.

Here is the all important THD+N versus power at 300 ohm:

Project Polaris Headphone Amplifier Power into 300 Ohm High BW Audio Measurements.png


There is fantastic amount of power available despite the high impedance at whopping 720 milliwatts! This should enable the polaris to drive high impedance headphones with ease. In this regard it reminds me of tube amps with their unusually high output voltages. Unlike them though, plenty of output power is available at much lower impedance of 33 ohm:
Project Polaris Headphone Amplifier Power into 33 Ohm High BW Audio Measurements.png


I did my testing at the lowest setting of the output impedance:

Best headphone amplifier output impedance measurements.png


So quite good and able to drive even low impedance headphones without varying them. There are two other settings to more emulate the tube amp high output impedances.

Listening Tests
With both my Sennheiser HD650 and DROP + MRSPEAKERS ETHER CX headphones, the Polaris amplifier was able to get scary loud even in low gain mode. There is ample power available to create a very high dynamic range. I don't have time to perform careful AB tests. In casual listening, the audible distortion was not obvious especially at low to reasonable levels. At much higher output power I thought the highs got grungy but this may be placebo.

Conclusions
The Project Polaris Headphone Amplifier appears to build a tube amp without any of their weakness of tube aging, low power in low impedances, high heat and power consumption. On all of those, it wins. So if you are itching to have a tube-like amplifier, the Polaris makes a much better substitute in my opinion. It won't replace my low distortion amplifiers so I can't give a person recommendation.

------------
As always, questions, comments, recommendations, etc. are welcome.

This is my second review today. There is just so much gear here to review that I am having to work overtime (going from 2 hours to 4). So I hope I get some overtime money from you all by donating using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

Xulonn

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#2
Congratulations, Solderdude (who is, I assume, the "electrical mad scientist" mentioned below) on joining a few other designers/manufacturers who showed their ability to back up their comments here.

I see that you are selling it for $299 on eBay - and put the below excellent information in the eBay "Full Description." Well done!

(I pulled a Maty and copied and pasted a big technical and specifications thingie.)



THIS LISTING IS FOR A FULLY BUILT PROJECT POLARIS SOLID STATE AMPLIFIER, POWER SUPPLY AND CNC'ED ALUMINUM CHASSIS!

Project Polaris is our first Solid State design! Polaris is simply outstanding and is not a cheap toy with counterfeit parts on a cheap PCB. This is a beautifully designed & engineered amp you can truly own and enjoy for a lifetime.
G1217 consists of two audio enthusiasts, Myself (Jeremy H) based here in the US and our electrical mad scientist (Frans G) across the pond in the Netherlands. The short story: Frans designs our gear electrically and somehow comes up with this stuff – absolutely a master at his craft. Myself, I handle the physical designs and actual products you receive from G1217. We both really do 10x the work of that brief description, but it gets the basics across. We are all about getting the most for your money which is why we are factory direct only. This keeps prices low and value high. Our only advertisements are here on ebay and word of mouth. Offering excellent gear over the years, our customers have spread the word which has let us grow from a single amplifier offering to 4 designs with more products on the way!

Features of Project Polaris:
- Startup protection circuit
- Advanced cooling design to keep temps nice and low when demand is high
- Three output resistance settings from 0.1, 35 and 120 Ohm
- 3 selectable gain settings with a quick swap attenuation module effectively giving 6 settings
- Three bandwidth settings
- Pre-amp output so it can double as a volume controlled preamplifier
- Very efficient, low power consumption, low temperatures
- Awesome choice for headphones from 16-600 Ohm
- Loads of headroom and more than enough output power (up to 2.4W, depending on headphone and settings)
- Comes with power supply. Plug in your source to the RCA jacks, plug in your headphones and fire her up!
- Not an audiophile feature, but you can change the power LED's brightness or turn it off. You can also rather easily change out the LED without soldering to change the desired color
- Designed in the U.S. & Netherlands. Kitted - Built in the U.S. / 5 YEAR WARRANTY ON G1217 BUILT AMPS!
- All parts sourced in the U.S. From reputable distributors, NO FAKE COUNTERFEIT PARTS, CAPACITORS OR RESISTORS!
- Only top quality components used, such as Bourns pro audio potentiometer, Bourns trimmers, Low noise Vishay/Dale RN, CMF and CPF 1% resistors, Nichicon &
Vishay/Wima capacitors, Neutric phono jack, Rugged PCB RCA jacks, Rugged power switch ETC…
- Beautiful piano gloss black .096 thick double sided, 2oz PCB with top and bottom ground planes & gold wash.
- Chassis is beautifully laser cut and serialized
- Chassis hardware features all stainless steel allen bolts, washers and nuts. Stand-offs are aluminum along with stainless top cover thumb screws
- Each factory built amplifier is meticulously hand built and tested prior to shipping. Solder work is outstanding and clean with no flux or fingerprints left on the board.
Pride in workmanship is evident from every angle of this amp. What you see in photos is the quality of build you will get!
- Power supply - built by Meanwell


For Advanced Tuners:
- Input capacitor section is drilled for multiple capacitor footprints. 2, 2.5, 3.5, 5 or 7.5mm spacing available
- Output capacitor section is drilled for 7.5mm
- Power supply capacitor section is drilled for 7.5mm
- Variable output resistance, selectable from 0.1, 35 and 120ohm! Actual Project Polaris Measurements, No inflated, made up numbers to try to gain a sale.
- Solid state output stage with JFET input stage
- Power consumption: (0.03A cont, 0.25A peak)
- Power supply: 48VDC
- Input Resistance: 11k or 21k depending on gain setting
- Gain: 12.5X / 7.5X / 4.5X without Attenuation Module. With Module, reduce by ½.
- Max Output voltage: 16Vrms at 300 Ohm
- Max RCA Output voltage: 2.9V
- Output Resistance: Selectable 0.1, 35 or 120Ohm
- Frequency range (High BW - 30 Ohm load) -3dB: 2Hz-290kHz
- Frequency range (High BW - 30 Ohm load) -.5dB: 6Hz-100kHz
- Dynamic Range 108dB
- Noise level -109dB
- Crosstalk: -98dB
- THD: > 0.045%
- Phase shift: 180 (inverting amplifier) on wide BW and 30 Ohm load 15Hz - 28kHz (+/- 10)
- Slewrate: +16V/us, -20V/us
- Suitable for: 16-600ohm Headphones

NOTE: AMP SHIPS WITH US IEC320 CORD ONLY (SAME AS PC POWER SUPPLY WITH US EDISON PLUG) DIFFERENT COUNTRIES MUST SUPPLY THEIR OWN POWER CORD OR ADAPTER

SHIPPING / SHIPPING TIMES:
- We ship all amps, kits or pcb's via priority mail or global priority mail
- Kits generally ship within 3 business days of receiving payment. Each amp or kit is hand crafted or put together at the time of order
- We ship Monday - Saturday and go by the USPS holiday schedule


EXAMPLE OF THE FULL COLOR, DETAILED MANUAL DESIGNED TO MAKE ASSEMBLY AND SETUP PAINLESS!
 

trl

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#3
Frans told us on another page from this forum that these amplifiers were tuned to aim for a specific sound and not for measurements, because this is what people ask for. I personally love how the PCB looks like and how the traces are routed, I like all Garage1217 projects and I think that every DIY-er should build few of these amps and, if they really want to, they can change sound flavor per their liking. Auditioning different flavor-sounding amplifiers and understanding the internal schematic and how things work inside is what science is about.

Another example of "man tuned" amplifier would be http://www.pmillett.com/nuhybrid.html or http://www.pmillett.com/3B7.html that were intentionally created to sound like "a tube", per the FFT graphs from the above link. Yes, Pete Milett, the designer of Butte that should measure pretty close to perfect (the one with OPA551/552 in output buffers) was doing a great job in designing tube-like amplifiers.
 

solderdude

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#7
Indeed this amp is not about measurements. It measures poorly on purpose (except for the channel imbalance).
@maty should love the 2nd and 3rd harm. distortion (which is also level dependent).

This is NOT designed to win any awards in accuracy and super measurements but is designed to flavor sound in various ways (by the customer using jumpers) and to drive all headphones under all conditions.
At much higher output power I thought the highs got grungy but this may be placebo
Yes, that's the idea. For normal listening levels it should sound 'normal with a hint of tube flavor'.
Those that don't want this should buy other amps... this will not be for them.

A feature that hasn't been tested is the output resistance which can be set to 0.1 Ohm (at least that's what I measured), 35 Ohm and 120 Ohm (an old standard) so also headphones that are designed for high output Z can be used.

The 50mW will measure poorly but for this we have a solution (way way too much power for IEM as well) in the form of a passive attenuator.
1568610874653.png

With it you can add almost 15dB to the SINAD number of 50mV measurement.
It can also be used to get a bit less channel imbalance this way with sensitive headphones.
The channel imbalance is because of the high gain and pots.
From what the seller (Jeremy of G1217) told me he buys the pots in large and hand matches them and throws out the ones that measure even poorer.

The channel imbalance of the tube designs is even worse as that is determined by the tubes entirely (no overall feedback).

Jeremy (G1217) wanted me to design a SS amp that has the same properties as a tube amp (harmonic dist).
So distortion pattern and deliberate roll-off (the middle setting is intended to kind-of mimic the roll-off from R2R DACs and the severely roll-off response is because Jeremy liked it this way with some 'shrill' headphones.
The intention for owners is to play around with all settings to get the 'sound' they want.
There aren't many amps around that let you do this as an owner. One usually gets one flavor only and there already are so many 'normal' amps around.

The tested version seems to have the 'aggressive filter' options (preferred by Jeremy). This amp can also be ordered with more conservative bandwidth settings (as I designed it) when ordering.


In wide BW setting the measured FR is 8Hz - 35kHz (-0.5dB) = 2Hz - 100kHz (-3dB) with a 32 Ohm load.

It is also available with metal top and bottom plate. Jeremy likes to see the parts, I like fully closed metal enclosures but this is too 'plain' for Jeremy. His show ;)
P1CNC.JPG

I would like to mention I am not part of G1217 nor do I make money of it.
I just design it for a friend (Jeremy) on his request and help him with the layout a bit.
I do service them for EU customers but do not sell nor represent G1217.

Oh ... for the nerds.... the schematics
 

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maty

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#8
If Matey is me, some words. Better without tubes, the important thing is the harmonic profile. The famous must be H2 at -73 dB, with H3 at least 15 dB below and any more audible harmonics.

Why many people love the Quad II Classic Integrated, with tubes?

[Polish] https://audio.com.pl/testy/stereo/wzmacniacze-stereo/906-quad-ii-classic-integrated



If we want a less euphonic harmonic profile and much less distortion and noise there is no other than resorting to transistors, working with SET topology.
 
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maty

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#10
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maty

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I copy from a thread I have in other forums (somewhere over the rainbow, aka closed net).

https://www.crutchfield.com/S-tsJLGT1AUWe/p_033PMA800/Denon-PMA-800NE.html

[ Stars and wonders

Loretta from Sylvania, OH on 2/26/2019

The Denon PMA coupled with KEF LS50‘s prove, “You don’t need no million-dollar hifi’s, just get a little integrated and some good British two-way speakers.” Its 50 watts are better than the 80 of my old Denon DRA-395 receiver: the bass is solid and well defined, voices have more body and presence, the treble is detailed without any cringing sizzle. The tonality is spot on and natural: I attend the Toledo, Detroit and Cleveland Orchestras and hear no unpleasant surprises from the PMA. (Greta van Fleet benefits from this excellence as well.)

The headphone stage lets my low-impedance but efficient HiFiMan 400S sound as enjoyable as the KEFs. Its DAC is an improvement over my 2013 CD/DVD/Netflix box. The MM phono stage has no trouble driving my 2.1 mV Soundsmith Carmen cartridge, and it is good enough to detail the sonic differences between the Carmen and my Grado Reference Master. I look forward to trying the MC stage with a Denon true-mono cartridge. The Analog Mode and Source Direct (i.e, tone defeat) further demonstrate that Denon has used their technical skills to craft a special component with musical sensitivities.

Pros: Tonality!

Cons: The remote doesn’t have enough PMA-specific buttons. ]

- End off topic -
 
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minnend

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#12
I really appreciate the work that went in to this amp, and it seems like it's an unqualified success relative to the design goals. Congrats!

Potentially dumb question alert: If the overall goal is to have a tube-like sound, which essentially means high 2nd and 3rd-order distortion, isn't it borderline trivial to add that distortion with DSP and then use an accurate amp? My background is computer science so I may be underestimating the cost of a DSP solution relative to simply building the amp to do what you want, but it seems cool to have a little box (or software) that lets you select between an analytical sound (no alteration) and a tube sound (add in the distortion you guys have identified). I must be missing something so I'd love to learn what it is.
 

Jimster480

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#13
This looks interesting and unique. While I don't think its for me; I have to appreciate the engineering that went into this. Especially to mimic a tube without the downside of a tube!

As far as minnend's question..... I don't think that DSP would achieve the same thing so easily.... but I could wrong. @amirm should be able to answer this question as he knows basically everything about DSP.
 

solderdude

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#15
Potentially dumb question alert: If the overall goal is to have a tube-like sound, which essentially means high 2nd and 3rd-order distortion, isn't it borderline trivial to add that distortion with DSP and then use an accurate amp? My background is computer science so I may be underestimating the cost of a DSP solution relative to simply building the amp to do what you want, but it seems cool to have a little box (or software) that lets you select between an analytical sound (no alteration) and a tube sound (add in the distortion you guys have identified). I must be missing something so I'd love to learn what it is.
If the amp is only about tube amp type of distortion and roll-off then yes you can do that in the digital plane.
Hell.. you can even make the amount of tube distortion adjustable and manipulate everything you want.
That is if your source is a computer, tablet, phone or DAP that supports plug-ins.

Besides.. this would basically mean that we can safely say ALL but one powerful low distortion amp needs to be sold and no-one has a choice as all other amps are obsolete till the next one with better numbers comes out.

The output power level and output impedance feature cannot be mimicked by digital emulation and are an important part of the design and its capabilities.
Of course one could also use a good performance high power amplifier and add several series resistances in its output path.
Would be hard to find such a device with the looks the amp has.
It will probably have a higher quality volpot without the channel imbalance.
Will have a chat with the G1217 about the volpot.
 
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BillG

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#16
isn't it borderline trivial to add that distortion with DSP and then use an accurate amp
For the frequency response and distortion characteristics, yes... it's pretty easy, and there are numerous DSP plug-ins around that do so - I often run one on my Windows desktop media player as I find the results pleasing.

It's my understanding that tubes do some interesting things in terms of compression and limiting that contribute to the sonic signature - iZotope Ozone, the plug-in I use, emulates this as well along with FR and distortion.

The power characteristics are another matter entirely, though.
 

trl

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#17
Perhaps something like this would do: https://media63.musictribe.com/media/PLM/data/docs/P0582/SX3040_P0582_M_EN.pdf.

Also, I found a good explanation of how it works here: https://soundbridge.io/harmonic-enhancer/:
"Harmonic synthesis involves the creation of higher-order harmonics from the fundamental frequency signals present in the recording. As noise is usually more prevalent at higher frequencies, the harmonics are derived from a purer frequency band. This results in clearer highs. Exciters can also synthesize harmonics of low-frequency signals to simulate deep bass in smaller speakers".

There are several "Psychoacoustic Effects" devices available: https://www.thomann.de/gb/psychoacoustic_effects.html.
 

maty

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#18
I really appreciate the work that went in to this amp, and it seems like it's an unqualified success relative to the design goals. Congrats!

Potentially dumb question alert: If the overall goal is to have a tube-like sound, which essentially means high 2nd and 3rd-order distortion, isn't it borderline trivial to add that distortion with DSP and then use an accurate amp? My background is computer science so I may be underestimating the cost of a DSP solution relative to simply building the amp to do what you want, but it seems cool to have a little box (or software) that lets you select between an analytical sound (no alteration) and a tube sound (add in the distortion you guys have identified). I must be missing something so I'd love to learn what it is.
Leaving aside the discussion of how much H2 is necessary to avoid blurring the sound when playing complex music such as electronics or orchestral (a good compromise is H2 at -84 dB), the important thing is that the harmonic profile is always monotonously decreasing, whether harmonic or not audible (90 dB).

http://www.just-hifi.com/New-Portab...ow-available-as-complete-PCB_10359327-14.html



Reducing everything to a high SINAD value is too reductionist. The harmonic profile is indicative of the attention of the designer / builder in the musicality, tonality... and not only in the achievement of excellent measurements, concepts that are not always mutually self-exclusive.


A new single-ended class A design, headphones amp too, by Mark Johnson.

https://www.diyaudio.com/forums/hea...class-headphone-amp-using-transistors-t2.html

BTW,
Component L2 is a ferrite core from Laird Performance Materials, specially engineered to attenuate switch mode power supply noise in the frequency range between 100 kHz and 10 MHz. I've snipped out a graph from Laird's datasheet and presented it below as Figure 5. Notice that attenuation increases as the square of the number of turns on the core. Laird anticipated that customers would use big thick wires carrying great big currents, so at most three wire turns through the center hole would fit. But T2 draws less than 400mA, meaning we can use wires even thinner than AWG-28, which allows at least eleven turns through the Laird core. Mentally extrapolate Figure 5 to eleven turns: Cowabunga! That's a lot of attenuation...
 
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minnend

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#19
Thanks for all the responses! I've learned a lot from Amir's reviews and the forums here.

To use a DSP, you would have to digitize the signal, process it, and then convert to analog. Definitely a lot of cost for a stand-alone product like this.
Agreed. I imagined a digital source to avoid multiple DA/AD conversions. But I can see plenty of people wanting to stay in the analog domain.

The output power level and output impedance feature cannot be mimicked by digital emulation and are an important part of the design and its capabilities.
Really good point. I didn't mean to imply that the world only needs one amp, but it's fun to explore how easy or hard it is to mimic one sound signature with different hardware, especially if your preference varies with content. I only have an SS amp right now (JDS Atom), but already experience some of this between different headphones, e.g. the Fostex TH-X00 vs. Hifiman HE650 sound pretty different, and my preference depends on genre.

there are numerous DSP plug-ins around that do so - I often run one on my Windows desktop media player as I find the results pleasing.
Cool. I'm not surprised to learn that such plugins exist. I haven't explored such thing before but I'll check out the iZotope Ozone plugin.

Leaving aside the discussion of how much H2 is necessary to avoid blurring ...
Thanks for the additional details!
 

maty

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#20
In my last comment I wrote about another single-ended class A headphone amplifier, the T2. Tom Christiansen wrote a very interesting review with measurements, deficiences detected and graphs.

https://www.neurochrome.com/diy-audio-t2-headphone-amp/

Casual listening is more likely to occur at significantly lower power levels, however. Thus, I repeated the measurement at 1 mW output power into 32 Ω and 300 Ω as shown below. This is likely more reflective of the performance you will experience at casual listening levels.




BTW: clean power is ALWAYS important. It is something that many diyers do not value, there they always try to save money, wrong practice.
 
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