Cayin RU6 Discrete R-2R USB-C DAC/Amp

General Information

Cayin RU6.png

24-Bit Discrete R-2R Resistor Ladder DAC
User Selectable NOS/OS Digital to Analog Modes
High Precision Resistor Array Volume Control
Dual Main Boards Layout
DSD256 and PCM 384kHz

Latest reviews

Bitsir

100+ Head-Fier
Cayin Ru6 | Super Short Sound Review | 1:1 With The Vocal Chords
Pros: + Uniquely analogue tonality
+ Visceral & unapologetic in delivery
+ Fast & Unfiltered sounding (NOS mode)
+ Sounds raw and subsequently more "real", especially in the mid and highs
+ Pleasant warmth in bass
+ Quite wide expansive stage, immersive
+ Ameliorates BA timbre to large degree
+ Gets you closer to the vocalists emotion, has that naked touch
Cons: - Not as refined or microdetailed as competitors
- Slightly fuzzy imaging
- Sounds raw, rough, not necessarily unendingly desirable as it gets tiring after a while
Basically it should only be paired with non-warm IEMs or it turns too syrupy, lacking details.
What it does well I appreciate a lot. It has a noticably "unfiltered" or "unprepared" delivery of sound. This makes instruments
more convincing and authentic but less refined.
Last edited:
ej8989
ej8989
I'm curious how well these will pair with the U12t, which is an all-BA iem.
Answerfish
Answerfish
I have found using the Ru6 with older CD flac files such as Deep Purples greatest hits brings out the old analog sound I used to get while listening from my home stereo. With my delta sigma dacs such as the Dethonray Honey the recording sounds flat. I must also say that I use the Ru6 with my IFI griffon and the have either the Cayin C9 or the Aroma A100 TB as the amplifier. With this set ups the older recordings sound great. If I just go from the Dethonray into the Aroma or the Cayin they sound flat and thin.

Ichos

Reviewer at hxosplus
Resistive and Addictive
Pros: + Extremely musical and analogue sounding
+ Full bodied and visceral presentation
+ Lifelike mids - smooth, non fatiguing treble
+ Great technicalities
+ Holographic soundstage
+ NOS and OS modes
+ 4.4mm and 3.5mm headphone plugs
+ Very powerful can drive full sized headphones
+ Neat and simple operation
+ Hardware buttons
+ Not power hungry
+ Good build quality
+ OLED screen
Cons: - Technicalities not on par with the best delta-sigma rivals
- Could do with more extension and resolution
- A little bulkier than the competition
- More expensive than the competition
- Accessories pack is poor considering the price
- EMI interference can cause hissing issues
The RU6 was kindly provided by Cayin in exchange for my honest and subjective evaluation.
The selling price is $249.99 and you can order it from all authorized dealers across the world.
Full product specifications are available here.

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Introduction

The Cayin RU6 is a 24-bit USB dongle DAC/amp featuring a discreet R-2R ladder network.
The recent chip shortage, led many companies to revert back to the roots, the R-2R era where digital conversion was done with this particular method before the invention of the modern D/S DAC chip.

(The text includes comparison against the FiiO KA3)

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Back to the basics

The Cayin RU6 features a self-developed 24bit discrete R-2R resistor ladder circuit that can decode up to 384kHz PCM audio.
The basic idea of the R-2R ladder is a matched pair of resistors, the first is “R” and the other is “2R'' which has twice the value of R.
To achieve 24 bit decoding, RU6 equips 48 units of resistors (23 x R and 25 x 2R), and that’s for one channel.
So for a stereo 24 Bit R-2R decoder, RU6 features 96 units of resistors for life-like audio reproduction.
With the advent of the R-2R circuit, Cayin RU6 establishes itself as master of the fully-discrete resistor DAC topology in portable audio.
Cayin is using only resistors that can deliver extreme precision and remain stable during temperature changes.
0.1% Ultra precision low TCR thin film resistors are used inside the RU6.

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Oversampling and NON-Oversampling modes

Cayin offers both Oversampling and Non-oversampling DA modes in RU6. For Oversampling mode, the Digital Audio Bridge will upsample the digital audio data to 384kHz through digital filters.
This will enhance the resolution, reduce noise and improve the anti-aliasing of the digital signal.
The Oversampling DA mode will offer a noticeable improvement on details and frequency extension.
The playback is clean and sharp with a darker background.
On the other hand, NOS DA mode maintains the sampling rate of the original bit-stream and playback will become very musical with a natural and organic presentation.
This deactivates the digital filters and the signal is retained in perfect timing. That is, the phase distortion and jitter remain at a very low level with no artifacts in the output signal.

Analog resistor volume control

Most USB DAC/Amps will rely on the volume control of your mobile phone to control the volume of the headphone output.
Technically this was not a viable solution to Cayin RU6.
Understanding this issue, Cayin developed a fully analogue resistor array volume control circuit that provides 99 steps volume control through 9 segments of resistors and switching relays.
Resistor Array volume control features a very high-quality volume control design, extremely transparent when implemented correctly and it is found in a lot of high-end preamps and integrated amplifiers.
The resistance volume control includes a switching relay that mutes the output for a short moment in order to avoid crackling noises during level adjustment. As a result, however, a small delay in the volume adjustment has to be accepted.
Cayin therefore recommends a music player app for the smart device that supports Bit Perfect USB and thus bypasses the level control of the source device.

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Board design

To minimise audio signal interference, Cayin has split the RU6's circuit into two 6-layers PCB, with digital and analogue circuits installed on separate boards.
This safeguards the audio signal integrity and ensures the noise from the reference clock and DSP do not bleed into the amplification circuit. This architecture in turn delivers artifact free audio every single time. This circuit design combined with the R-2R architecture enables the RU6 to support hi-resolution PCM and DSD audio formats with support for 384kHZ PCM and DSD 64/128/256 natively.

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Power consumption

Discreet R-2R circuitry is a low power DAC circuit when compared to other highly integrated DAC chipsets.
This architecture minimises power drain from the mobile source allowing you to enjoy music without the need to worry about battery drain.
USB-C connection offers compatibility with a wide range of phones, consumer electronics and computers. The hardware has been designed in an intuitive manner, where the volume buttons double as menu selectors and the OLED screen displays playback information accurately.
The Cayin RU6 also offers two gain settings to enhance performance with various IEMs and headphones.
I measured the power draw with an inexpensive USB power meter and I found it was about 0.12A / 0.55W while playing music with the FiiO FD7.

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Build quality and appearance

The RU6 has a rectangular shaped body which is bulkier and heavier than the usual D/S USB DAC/Amps like the EarMen Sparrow.
The net weight is 28g and the dimensions are 65x25.4x13.7mm.
Still for a device featuring an R-2R network and resistor array volume control, it is quite compact and lightweight, not that larger than the FiiO KA3.

The chassis is made from CNC aluminium while the side with the small OLED screen is protected by glossy glass.
The appearance is quite modern and minimalist while finish and build quality are excellent with the only negative being that the glass surface is a fingerprint magnet but if you ask me, I wouldn't care a lot.
The three physical buttons that are located to the one side of the chassis are of good quality and offer tactile feedback.
At the top of the device there are the two headphone outputs and at the bottom lies the USB type C socket.

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Accessories

The Cayin RU6 comes bundled with a short USB-C to USB-C cable and a USB-A adaptor.
The leather case for extra protection and a lightning cable for iOS users are sold separately.

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User interface

The RU6 is plug'n play compatible with all USB-OTG devices (iOS and Android), Mac OS, Windows PC through the available driver and it can also be connected to Digital audio players that support USB out.
The DAC itself is power efficient so you don't have to worry about draining the host device battery.
The OLED screen will display sampling rate, volume level, gain H/L and whether you are using NOS or OS mode.
You can use the mode button to enter the menu and configure gain settings, NOS/OS mode and screen timeout.
While adjusting the volume, sometimes you can hear a clicking noise, that is instant and doesn't affect the performance.
Neat and simple it has the advantage of the hardware buttons and the OLED screen but it doesn't offer the same kind of customization as the FiiO KA3 does through the supporting application.

EMI interference

The RU6 is prone to picking EMI interference from a phone that causes background noise which can range from a faint hiss to a louder humming especially when using more sensitive earphones.
The effect is more pronounced when streaming and not as severe when playing music from local files but still there.
You can try using a longer USB cable or other DIY solutions, like wrapping the cable with aluminium foil in order to shield it but in the end I didn't manage to completely get rid of the noise.
This hissing noise is present when cellular reception is active.
In contrast the FiiO KA3 was dead silent with all mobile phones that I have tested.

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Power output

I was asked to burn the RU6 for 100 hours minimum before listening and thus I did.
I used various earphones and headphones ranging from budget to more premium to find out that the RU6 not only scales very well but the use of higher quality partners is quite mandatory in order to get the most of it.

The RU6 with its full 4V swing and 213mW/32Ω of power output, is powerful and can drive a wide range of headphones with good grip and plenty of headroom.
This is one of the most powerful USB DAC dongles together with the FiiO KA3 and a few others.
The performance was very satisfying with headphones like the Sennheiser HD660S and the Focal Clear Mg while the gain setting proved very useful for driving more sensitive earphones like the FiiO FA7S.
Sometimes the faintest hissing was still present even with host devices without cellular antenna but it must be related to the host device power supply.
With my laptop was completely silent.
In contrast the KA3 which has a discreet power rectifying circuit remained dead silent under all circumstances.

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The RU6 provided a great listening experience with the Sennheiser IE600.

Sound impressions

The sound performance of the Cayin RU6 is stellar with a touch of a pleasant, tube-like, euphonic warmth without lacking in transparency.
With the mode set to NOS, it sounds exceptionally musical with a very natural timbre, smooth texture and the presentation is realistic but still precise and true to the source.
Voices and acoustic instruments are heard organic with natural overtones and plenty of harmonic wealth, a wonderful combination which leads to an engaging and authentic listening experience.
At the same time, technicalities are good and close enough to D/S performance but not in the same ballpark as top D/S performers like the FiiO KA3.

The bass is visceral, weighty but still tight and well controlled, fast, clearly defined and multi-layered.
Attack and decay are very convincing as is the dynamic contrast but then it doesn't have the lighting speed or the boldness and ruthless impact of the KA3.
Nonetheless, with all my music the RU6 was punchy, full sounding with great macro dynamics from electronic music to classical.

The mid range is the star of the show, not because of the lack of linearity but due to some kind of a pleasant effect that seems to be imbued from the R-2R design.
It has a well sculpted texture with great liquidity, voices and solo instruments sound very engaging, fluid, articulated, large and three dimensional.
Timbre is utterly natural and so close to reality that in the end you forget about the technicalities as you are immensely drawn to the music, song after song as the time passes by without noticing.
One of my favorite albums is entitled "Hush", a fuse with Nora Fischer singing baroque arias accompanied by the electric guitar of Marnix Dorrestein.
With the RU6 her amazing voice perfectly blended together with the distorted guitar in the most charming way and I literally forgot how many times I listened to the track named "Cum Dederit".

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Treble is silky smooth with the impression of being laid back, not too extended but very well behaved without a hint of brightness.
Natural is the word to use again, not only to define the timbre but also for expressing the decay, the notes are born and then fade away with the perfect timing.
High pitched percussion instruments sound full blooded with a convincingly natural decay, not splashy or thin.
In contrast the KA3 is more extended, faster, with increased clarity and more detailed presentation but it sounds somewhat leaner while it can't touch the naturalness and physicality of the RU6.
The tuning is very easy to the ear but it cannot be said that the RU6 is not resolving, missing in clarity and agility or lacking in energy as to sound dull or slow.
Tonality is very cohesive from top to bottom and there is great consistency of note intensity throughout the whole frequency range where the KA3 tends to lose some of its weight while reaching the higher frequencies.
A good example of the even treble performance is in the following album where the solo recorder can become very strident with some USB DAC dongles that I have tested.

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R-2R DACs usually have the edge when it comes to soundstage and the RU6 certainly delivers.
The soundstage is not as extended and wide with the same laser sharp positioning of the FiiO KA3 but it has far better holography, a more dimensional shape and it is further convincing in communicating the ambience of the recording venue.
The FiiO KA3 might have the technicalities edge for electronic music and such genres or be better suited for ultimate detail and clarity lovers but the RU6 with its more natural timbre and grander soundstage is the obvious choice for classical and acoustic music.

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Except for the timbre and texture qualities of the RU6, the next more notable sound characteristic is the complete absence of the so-called digital glare that is plugging a lot of D/S implementations.
No artifacts heard, no metallic harshness, no edginess to the sound which in contrast gets close enough to the analogue ideal at least as this is possible for such a USB powered device.
The FiiO KA3 is one of the best examples of a well implemented D/S USB dongle with the least possible digital imprint but the RU6 is a step above with a more organic and natural texture.

NOS or OS?

Switching to the OS mode doesn't induce extra digitus but the sound somewhat loses some of its analogue, organic magic.
To be honest, it is quite difficult to tell the two settings apart and it requires attentive listening and good headphones.
With the OS setting you give up some timbre, fullness and staging abilities in order to gain a little extra clarity, better definition between the lines, a leaner, tighter presentation and a touch of treble extension.
As said, differences are not night and day while the overall sound characteristics remain the same.

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In the end

Thanks to the Cayin RU6, it is the first time that the user can experience the analogue like sound characteristics of the well designed R-2R technology from a USB powered DAC dongle.
In a market already flooded with delta-sigma USB dongles that sound more or less the same, the RU6 with its natural timbre and organic character is a welcomed addition.
Sound-wise the RU6 is an absolutely stellar performer and more than highly recommended especially if you are already a fan of the R-2R technology and you would like to experience it from a portable device or if you seek to discover the R-2R sound without breaking the bank.
Judging from sound performance alone, the RU6 is a five star rating without the slightest hesitation.
Unfortunately the possible hissing due to EMI interference would not allow for the full rating and is forcing a half star deduction.
But in the end, the RU6 is so good that it is fully enjoyed at home and not from your phone.
Without hesitation is one of the best sounding and most powerful USB DAC dongles available right now.

Test playlist

Copyright - Laskis Petros 2022.
Last edited:
Ichos
Ichos
Sorry no experience with these but I am waiting for the Go bar.
OCC7N
OCC7N
Technicalities not on par with the best delta-sigma rivals - Who is the competition?
Could do with more extension and resolution - Like how?
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Ichos
Ichos
The FiiO KA3 that is pictured and mentioned in the review?
How could do with more extension and resolution?
You know, more resolving, as detailed and finer sounding?
More extension, like deeper sub-extension, sharper, better defined and splashing treble?
Thanks for reading.

asifur

100+ Head-Fier
Cayin RU6 : Arguably Best Dongle with R2R capabilities in $250 range
Pros: + Superb build quality
+ Small & Portable
+ Discrete R2R
+ Powerful enough to drive most IEMs
+ Analogue tuning
+ Great staging & imaging
+ Most Affordable R2R capable device till now
Cons: - Resolution may not be the best when compared to the other Delta-Sigma dongles
Cayin RU6 : Arguably Best Dongle with R2R capabilities in $250 range

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Summary & Objective:

The Cayin RU6 is the first ever dongle to feature R2R in such a portable size. It comes with great build quality and some great sound performances. It has support for balanced output and comes with nifty features like NOS & High Precision Resistor Array Volume Control and is powerful enough for most IEMs.

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Introduction:

The Cayin RU6 comes with great build quality and outstanding sound performance within the price bracket. It is the first ever dongle to feature Discrete 24 bit R2R capabilities and have some very nifty new features built-into it.
The Cayin RU6 is priced at $249.99.

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Design, Build & Features:

I wouldn't want to make this a very long review by describing each feature but for people who want to know, here are some extracts from the Cayin website.

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Specifications:

The Cayin RU6 comes with $249.99 price tag and the specifications are as below:

https://en.cayin.cn/products_info?itemid=140

OR

https://shop.musicteck.com/collecti...r-usb-c-dac-amp-dongle?variant=39638791618622

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NOW LET'S TALK ABOUT THE SOUND....
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Items Used for this Review:

IEMs:

IEMs of different ranges:
$200-300: BQEYZ AUTUMN, @DUNU-Topsound Falcon PRO, @CampfireAudio Honeydew
$500-700: Campfire Audio Holocene, TINHIFI P2 Plus
$800 - 1200: @DUNU-Topsound ZEN PRO, @CampfireAudio Dorado 2020
$1500 - 2000: @UniqueMelody MEST MKII
$3000: @Vision Ears EXT

Well these are the ones I have with me presently... and have used for the review.


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Source : iPad Pro, iPad Mini 6, iPhone 13 Pro max
Streaming Source: QOBUZ
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Tracks Used:
The tracks I have used can be found from the below playlist that I have used and generally use for most reviews...


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CAYIN RU6 Sound Impressions in Short:

Tonality:


The Analogue Discrete R2R tonality is something I have grown very fond of. The Cayin Ru6 delivers the R2R performance within a very portable size and the tonality is comparable to any R2R DAP. It has the warmth of any R2R typical tuning and can no way be considered bright.

The BASS:

The Bass sounds just Superb. Bass has details in the sub-bass region and is thick and creamy with enough muscle in the mid-bass to make the instrument attacks sound very natural and realistic. In tracks like : "Anna R. Chie (Remastered) - Konstantin Wecker" and "Dreams (2001 Remaster) – Fleetwood Mac" you can feel the the deep attack of the different instruments with just enough details. The thumps and slams are very enjoyable.

The MIDS:

The Midrange is just great in terms of every single element. It is able to produce an good creamy smooth and textured midrange that is soothing to the ears while having enough details in it. The vocals are natural and both male and female vocals come with good amount of details. Instruments sounded natural and I love the analogue tonality and the sound seems very real. In tracks like: "Anchor - Trace Bundy" and "Ruby Tuesday - Franco Battiato" while you will love the overall midrange specially transients of the guitars, violins etc... instruments and the vocals.

The TREBLE:

The Treble is very natural with enough extension & air as the track commands. It has enough details and despite being very natural it doesn't come with any harsh peaks in the treble region.

STAGING & RESOLUTION:

The staging and resolution is just great and just the amount the track requires. Nothing artificial here. Tracks like: “ She Don't Know – Melody Gardot” or “Bohemian Rhapsody (live aid) – Queen” sound good & enjoyable. Resolution is amongst the best in the price bracket and can rival many full-sized $700-800 range DAPs easily.

Amplification:

The Cayin RU6 comes with good amplification traits and doesn't depend on the source for volume control. It has it's own Volume Control mechanism and is powerful enough to drive any IEM that I've tried so far.

Pairing:
The analogue R2R tonality makes it ideal pair with just about any IEM. It pairs well with most IEMs that I had tried from the various price ranges and various traits.

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Comparisons:

I have compared all 4 of the dongles I had in my possession for this review - @iFi audio Go Blue, Qyestyle M12, Luxury precision W2 and the Cayin RU6 dongles. Not because they had many things in common - but mostly because people asked for a dongle shoot-out and so here it is from me.

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The Jack of All:

That would be the @iFi audio Go Blu. It comes packed with single Cirrus Logic CS43131 DAC chip and good build and some nifty features including BT and the volume dial.
However, when it comes to sound - it just lacks the iFi signature clean sound and also sounds quite thin when compared to others so far.

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The creamy & buttery:

That would be the @Questyle M12 which comes ES9281AC ESS Sabre DAC chip.
While there's a general tendency of ESS Sabre chips to be slightly bright... this one is quite the reference grade with very smooth & creamy music performance specially the midrange & treble.
The bass response is also very good.

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The Most Resolving:

That would the the Luxury & Precision W2. Powered by Dual Cirrus Logic CS43131 DAC chips, these are amongst the most resolving and powerful IEMs I've heard so far. Quite powerful and I've seen some reviewers compare them with $700-800 DAPs - while I have no comments regarding that, it is really the most resolving and very powerful with reference grade tuning.

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The Musical Bliss:

That would be the Cayin RU6. the worlds ONLY full discrete R2R Dongle DAC/AMP.
While owing to the analog tonality of all R2R tech devices - this may not be the most resolving one but the Oversampling mode somehow takes care of it quite well and the resolution is just great.
While based on the specs mW stats this is slightly less powerful than the W2 - but in real life scenario I found this to be quite powerful and can easily power even power hungry IEMs.


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CAYIN RU6 vs Luxury & Precision W2 vs Questyle M12 vs iFi Audio Go Blu:

Build quality:
This is a string trait found amongst all 4 dongles. All of them look very premium and come in great build quality. The W2 & Ru6 being amongst the larger ones while the M12 is the smallest sized.

Features & Amplification: BT features of the Go Blu not taken into account as that would be unfair for the others. All of the dongles come with great features and amongst them the W2 and the RU6 are the most powerful ones. Interestingly, while the RU6 has lower max mW power output than the W2, it seemed more powerful to me in most cases due to it's implementation.

Sound performance: While not going very deep into each category as that will make this review very long - I will comment on the overall sound performance here. The RU6 seemed the more musical to me while the W2 is the most resolving. However, the resolution of the RU6 is undeniably good by all means.

Resolution & Staging: While all dongles have equally good staging performance but the W2 and RU6 were better performing than the others. The Go Blu lacked slightly in terms of resolution to my ears while others did just great.

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Conclusion :

The superb performance of the Cayin RU6 makes it an easy recommendation to anyone who is looking for a dongle with R2R capabilities. Just like the W2 - the RU6 can rival performances of many full-sized DAPs below $800 range. Such commendable performance in such a portable form is something many audiophiles had been searching for. I would be happy to recommend this to anyone in a heartbeat.
R
Rubai
Nicely and most importantly concisely covered everything. How the RU6 compared with ifi HIPDAC in terms of sound quality ??
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Reactions: asifur
asifur
asifur
@Rubai I don't have the Hipdac with me and hence wasn't able to compare. However, based on what I may recall from my previous experience with the 1st gen Hipdac... I would say that I prefer the RU6 more due to it's R2R based analogue tonality ... while the Hipdac comes with Burr Brown chip
searchingtom
searchingtom
Excellent review !

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