Articles, Reviews and Measurements of Audio Products (As an Amazon Associate I earn from qualifying purchases)

Vintage Audio: Measurements of Arcam Black Box 3 mk1

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As requested by @andreasmaaan here I made some measurements of an old DAC: the Arcam Black Box 3 MK1 which I bought new in 1991 (without MK1, see below). It retailed for around € 780 then (converted). Here are the front and the back:

arcam bb3 front.jpg

arcam bb3 back.jpg
It supports 44.1 and 48 kHz samplerate with 16 bits - that was the standard back then ...

Somewhere later around 1997 I fell victim to op-amp rolling and replaced the original op-amps (LM627CN) by OPA134PA. Two can be seen on this photo of the internals on the right PCB (audio mother board).The LF411 is used as DC servo. Two others are hidden on the backside of the left PCB (digital audio board). The result is my version MK1:

arcam bb3 intern.jpg


The measurements are done with REW, using an RME ADI-2 PRO fs, an old Edirol...

Review and Measurements of Teac AX-501 Amplifier

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This is a review and detailed measurements of the Teac AX-501 integrated power (speaker) amplifier. It is on kind loan from a member. The AX-501 is part of the reference series from Teac so doesn't come cheap as desktop products go. I see the price at USD $999 on Amazon plus $35 shipping. There is a discount for silver a USD $899 but Amazon doesn't sell it for some reason.

When I reviewed the Teac HA-501 Headphone Amplifier, I heaped praise over its modern retro look. The AX-501 takes that to an entirely different level with addition of a couple of super cute, yellow background VU meters:

Teac AX-501 Integrated Amplifier Audio Review.jpg

What is that? I should have took the shot with the VU meters working and the light turned on? Well, the owner played a cruel joke on me by not supplying me with the remote and leaving the setting to off for the VU...

Review and Measurements of Teac HA-501 Headphone Amp

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This is a review and detailed measurements of the Teac HA-501 headphone amplifier. It is on kind loan from a member. The HA-501 in black costs $549 including Prime shipping from Amazon. Oddly, the silver color is much cheaper at $354! Black anodizing must have become very expensive. :) The black does look a lot nicer though so it would be tough to settle for silver.

The HA-501 is one of the most attractive desktop audio products. If you are a fan of the 1970s and 1980s hi-fi gear, the Teac is the best way that look could have been modernized yet hold its retro appeal:

Teac HA-501 Headphone Amplifier Audio Measurements.jpg

The controls feel fantastic and the head of the class for sure.

Controls are not unusual other than addition of "damping factor" which simply adds a resistor in the path of the headphone output (measurements later).

The other odd thing is the auto-muting. When you unplug the headphone, the red audio mute LED comes on and will not go off until you turn the...

Rolling Op-amps in Gustard H20 Headphone Amplifier

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I reviewed the Gustard H20 which is a high-end headphone amplifier yesterday. Its owner kindly sent me some high-end op-amps to "roll" in there to see what difference it makes.

The task was pretty easy. The top screws come out of the H20 and if you tilt the unit, the lid falls out exposing its pretty guts:

Gustard H20 Headphone Amplifier Teardown Review.jpg

Everything is surface-mounted so not replaceable other than the pair that are socketed. You can see that I swapped one of the channels to Sparko's Lab SS3602 from TI/National LME 49720:

Gustard H20 Headphone Amplifier Sparkos Lab SS3602 LME 49720 op amp rolling.jpg


There is massive price difference with the LME retailing for just $2.68 and the Sparko's for whopping $79.80. There better be good bit of improvement for it to be worth putting two of those in there for nearly USD $160.

Op-amp Rolling Audio Measurements
Since the Gustard H20...

Review and Measurements of Gustard H20 Headphone Amp

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This is a review and detailed measurements of Gustard H20 balanced input and output headphone amplifier. It is on kind loan from a member. The H20 costs USD $930 but I see it on sale from shenzhenaudio for USD $840. I think it was also sold on Massdrop for $800. Either way you look at it, it is not cheap.

The H20 comes in black and silver. The unit I have for testing is the silver:

Gustard H20 Balanced Headphone Amplifier Audio Review.jpg

The H20 is quite heavy and large. Controls feel good although I am not a fan of relay controlled volume. There is a racket that is sharp pitched as you adjust the volume.

The two 1/4 inch jacks are not the same. The first one has a resistor inline (see measurements). The second is straight through.

On balanced XLR output, you have a choice of stereo 4-pin or dual three pin. I tested with the former.

The back panel sports a good set of connectors:

Gustard H20 Balanced Headphone Amplifier Audio Review Back Panel.jpg

There are a set of RCA inputs to the left and two...

Review and Measurements of ENCORE mDAC DAC & Amp

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This is a review and detailed measurements of the ENCORE mDAC battery operated portable DAC and headphone amplifier. It is on kind loan from a member. As far as I can tell, the mDAC came out in 2014/2015. It cost USD $129 when released.

It is chunky metal box with sharp edges which bother me a bit:

ENCORE mDAC DAC and Headphone Amplifier Audio Review.jpg

The on/off button is quite hidden on the side. The volume controls are on top but controlling the down button is a challenge with headphone jack plugged in.

The mDAC runs a bit warm so good thing it has battery or it would suck up the phone one down.

PC connectivity is a bit strange in that the data USB jack does not charge it so I had to connect two cables to charge and use it.

I won't bore you with more and will post the Z reviews on the functionality.

Audio Measurements
Testing the mDAC as a DAC was not that functional as at full amplitude, it clips even into a very high impedance load (i.e. not stressed at all). So I had...

Review and Measurements of ENCORE mDSD DAC & Amp

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This is a review and detailed measurements of the ENCORE mDSD portable DAC and headphone amplifier. It is on kind loan from a member. The mDSD costs USD $126 on Amazon with free (non prime) shipping.

The encore is quite chunky and blocks adjacent USB ports as a result:

ENCORE mDSD DAC and Portable Headphone Amplifier Audio Review.jpg

It is a solid chunk of aluminum so no worries about throwing this in your case/backpack when travelling.

There are a set of volume up/down controls. They adjust the output level without being connected to the Windows/OS volume control which is nice.

There is not a whole lot to talk about here as far as operation other than it running a bit warm so power consumption is going to be on the high side.

DAC Audio Measurements
Our dashboard shows that typical of many of these portable DACs, the output level is insufficient (less than 2 volt) to be reliably used as a pure DAC:

ENCORE mDSD DAC and Portable Headphone Amplifier Audio Measurements.png


THD+N is just slightly over the spec (which is measured...

Follow Up: Lounge Audio LCR Mk III measurements

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In a recent review of this phono stage, there was some discussion of the approach taken for measurement and interpretation of phono stages. This post is a follow up with additional measurements which I (and other designers and users of phono equipment) find necessary for evaluation. This a "in addition to" rather than "instead of" for Amir's review, but I'd like to not only present measurements, I wish to also go into the whys and hows of things which are peculiar to the genre.

And I'll start things out by thanking Amir for sending the unit to me, as well as @dinglehoser who volunteered his unit to let me dissect its performance a bit.

As usual, my test setup is centered on an APx525 analyzer, but I also pressed into service a Hewlett-Packard 3466A volt-ohm meter and a Kikusui COS6100M 100 MHz scope.

Let's start with the basics. I...

Review and Measurements of Klipsch PowerGate DAC & Amp

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This is a review and detailed measurements of Klipsch PowerGate Multifunction streaming power amplifier, DAC, Bluetooth and phono preamplifier. It normally costs USD $499 but for some reason it is on Amazon for USD $150 including Prime shipping! This puts the PowerGate in direct competition to SMSL AD18 and Topping MX3.

The front panel of the PowerGate is plastic and not all that nice looking:

Klipsch PowerGate Streaming Amplifier Audio Review.jpg

The buttons and rotary control have good feel though. Strangely the LED bar showing the level only goes 2/3 of the way up on the left and not all the way around.

There is a headphone jack which I will be testing in the review.

The back panel shows a very feature rich set of options...

Class D Amplifiers 101

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This is a quick overview of how class D amplifiers operate. Note the “D” does not mean “digital”; it is simply the next letter in order as standards bodies enumerated amplifier types (A, B, C, D, E, F, G, H, I, etc.) It takes an analog, not digital, input and produces a pulse width modulated (PWM) output. I apologize in advance for the length.

The figure below is a simplified schematic diagram of a class D amplifier. It is a rather busy diagram, so we’ll step through each piece from input to output. First the input signal, Vin, is applied to the input buffer (shown as an operational amplifier, opamp). The negative input of the opamp receives the feedback signal (Vfb) from the output (Vout). The output of the buffer is the difference between these two signals, providing a modified signal to the rest of the amplifier. The feedback signal allows the amplifier to correct any errors at the output, improving linearity (e.g. lowering distortion) and stabilizing the circuit so part...

Review and Measurements of SMSL AD18 DAC & Amp

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This is a review and detailed measurements and comparison of SMSL AD18 DAC, Headphone Amplifier, Power amplifier and Bluetooth Receiver. I will be contrasting its performance against the Topping MX3. I purchased the AD18 in February of last year through Amazon. Seems like the price has gone down to $140 and it now includes Prime shipping. Topping MX3 is still cheaper at $130 from Amazon.

The look of the front panel is not bad:

SMSL AD18 DAC Headphone and Speaker Amplifier Audio Review.jpg
I left the screen protector on so that if I sell it, the next owner can have the satisfaction of taking it off. :)

I wish the volume indicator was displayed in large font instead of the small values in top corner.

The rotary encoder for the volume control feels wobbly and cheap. And it has very sharp burr around that machined silver ring. The Topping MX3 one is worlds better in...

Review and Measurements of Topping MX3 DAC & Amp

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This is a review and detailed measurements of the Topping MX3 DAC, Bluetooth, Headphone Amplifier, and Power amplifier. You even get a remote control with it. Despite all that functionality it costs just USD $130 from Amazon including Prime shipping. I bought mine from Massdrop 10 months ago. I don't know what I paid but likely less.

From the outside, the MX3 looks quite attractive:

Topping DX3 DAC Bluetooth Power Amplifier USB Audio Review.jpg

It has the same design language as the Topping DX3 Pro but even more attractive with that slanted logo.

The volume control is digital and very sensitive.

There is a ton of functionality here which I won't go into as there is a good review of it from Z which I will post after this review. Suffice it to say, it is very feature rich and well designed for such a bargain product.

Everything is powered by an external laptop sized switching power supply:

Topping DX3 DAC Bluetooth Power Amplifier USB Back Panel Audio Review.jpg

Not only is extra expense incurred in getting a...

Review and Measurements of Amazon Link Amp

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This is a review and detailed measurements of Amazon Echo Link Amp power amplifier, DAC and network streamer. I purchased this from Amazon for USD $299 and it arrived yesterday.

While rather featureless from front, the overall feel of the plastic and case is quite good:

Amazon Echo Link Amp Amplifier Audio Review.jpg

When you rotate the volume control white LEDs light up to show a coarse volume control. They time out very quickly though so I could not capture them on the camera.

Not sure what the hole is for. Maybe it is for a remote control but none was provided.

The back panel is the more interesting bit:

Amazon Echo Link Amp Amplifier Back Panel Audio Review.jpg

In addition to the power amplifier, we have a nice little DAC and pre-amplifier here. There are digital inputs in the form of both Coax and Toslink S/PDIF. And of course we also have streaming capability with the Ethernet jack and wifi.

Surprisingly we also have S/PDIF and Toslink output for digital connectivity to other...

Review and Measurements of Ayre CODEX DAC & Amp

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This is a review and detailed measurements of the Ayre CODEX balanced DAC and headphone amplifier. It is on kind loan from a member. The CODEX is a current product but seems like it was released 3 or so years ago. It costs USD $1,795.

I am puzzled by the look of the CODEX as it doesn't match the rest of the Ayre products:

Ayre CODEX DAC and Headphone Amplifier Audio Review.jpg

If you are not familiar with Ayre, it is a US company and is probably best known by its late founder, Charles Hansen. He has been active on forums for years. The company is in high-end audio business so my expectations were high on this DAC and headphone amplifier.

I was pleased to see a set of balanced XLR connectors on the unit and inclusion of mains power supply despite its rather diminutive size:
Ayre CODEX DAC and Headphone Amplifier Back Panel Audio Review.psd.jpg

Then again, closeness of the mains input gives me some pause regarding its noise immunity for the RCA outputs.

In use the CODEX runs very warm. The marketing material...

Review and Measurements of Acoustic Power APL1 DSP

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This is a review and detailed measurements of the Acoustic Power Labs APL1 digital audio signal processor. It is on kind loan from a member. The APL1 comes in a number of formats. The one under review is the automotive version and costs 510€ or USD $570. This is for the bare hardware. Software that let you program its internal "FIR" filters costs 262€ or USD $295. I am surprised that given the cost of the hardware, the software is not bundled in for free. For this testing, I only focused on the measurements of the hardware as the software seems non-trivial to use.

The automatic configuration of APL1 is nice and slim with phoenix connectors for power:
Acoustic Power Labs APL1 Digital Signal Processor Filter and EQ Audio Review.jpg

The LEDs change color depending on where you leave the slider switch. In my case I set the switch to bypass.

Here are the back connectors:
Acoustic Power Labs APL1 Digital Signal Processor Filter and EQ Inputs and Outputs Audio Review.jpg

We have analog RCA input and output. In addition there is also S/PDIF and Toslink for input and...

Measurements of Classé Sigma SSP Mk2

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The Classé Sigma SSP is an AV-preamp targeted for audiophile music lovers who don't want to setup 2 different systems (one for audio, one for home cinema). It is optimized for very high quality on the stereo channels and somewhat less performance for the remaining surround channels: the stereo channel has both one balanced input and one balanced output (XLR) while the remaining analog IOs (2 x stereo in, 7.1 out) are single-ended (RCA). The specs are as follows (selected):

Frequency response: 8 Hz - 200 kHz < 1 dB (stereo digital bypass), 8 Hz - 20 kHz < 0.5 dB (all other sources)​
Distortion (THD+noise): 0.0005% (digital source / bypassed analog source), 0.002% (processed analog source)​
Maximum input level (single-ended): 2 Vrms (DSP), 4.5Vrms (bypass)​
Maximum input level (balanced): 4 Vrms (DSP), 9 Vrms (bypass)​
Maximum output level: 9 Vrms...​

Review and Measurements of Cyrus soundKey DAC

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This is a review and detailed measurements of the Cyrus soundKey portable USB DAC and headphone amplifier. It is on kind loan from a member. It costs USD $98.99 from Amazon with prime shipping. It comes in a few colors.

I like the flat form factor with detachable USB cord:

Cryus Soundkey Audio Review.jpg

I received two short USB cables, one of which you see in the picture above. I don't know if that is how Cyrus ships it or the owner sent it me as such.

There are no volume controls so you would be relying on your software player for that.

One of the differentiators for the soundKey is low power consumption according to the company. I will be measuring and reporting on that later in the testing. For now, there was no rise in the temperature that I could feel on the unit.

Audio Measurements
As usual, we start with our dashboard view of 1 kHz tone:

Cryus Soundkey Audio Measurements.png


Typical of these small dongles, there output is too low to use the soundKey...

Review and Measurements of Lounge LCR MKIII Phono Amp

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This is a review and detailed measurements of the Lounge Audio LCR MKIII Phono stage (amplifier). It is on kind loan from a member. The LCR MKIII costs $300 from the manufacturer direct.

The LCR MKIII is a very simple, typical DIY box:
Lounge Audio LCR MKIII Phono Preamp Audio Review.jpg

A touch of class is intended to be provided by that lexan sheet with blue LED. It doesn't do much for me especially since the lighting is not uniform.

The back panel is simple too:

Lounge Audio LCR MKIII Phono Preamp Back Panel Audio Review.jpg
Since this is a moving magnet only phono amplifier there are no switches or controls. We have our simple RCA in and out plus a ground lug. Power is provided through an external AC adapter which is not a bad idea to keep mains inductance from the transformer leaking into sensitive amplifier stage.

As the name technically implies, this phono amplifier sets itself apart from others by using an inductor ("L") to implement RIAA equalization instead of just using capacitors. In...

Review and Measurements of Lake People G109-S Amp

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This is a review and detailed measurements of the Lake People G109-S headphone amplifier. It is on kind loan from a member. It costs USD $520 as of this writing but I see it has been offered on Massdrop for lower price.

Lake People is located in Germany and designs and builds its products there. Alas, the industrial design is ordinary and doesn't impart what I associate with German engineering:

Lake People G109-S headphone Amplifier Audio Review.jpg

I saw the anniversary edition (?) with gold letter and larger feet and that looked better. I know enclosures are expensive but over $500, I like to see a more professionally designed writing, logos, etc.

The volume control is analog but has notches in it. There are two headphone out jacks but they are identical (unlike some others where one is lower gain). I would have wished one was 3.5mm to accommodate IEMs without adapters.

Missing from the unit is any kind of external gain control. If you open the unit which requires removing...

Review and Measurements of Dynaco ST 70

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This is a review and detailed measurements of the vintage Dynakit Dynaco Stereo 70. It is on kind loan from a member who bought it used online and repaired it. Previous owner hand upgraded it but could not get it working.

Given that it is 60 years old, one can forgive the rust and dust:

Dynaco Dynakit ST-70 Power Amplifier Audio Review.jpg

Some of the online samples I have seen are a lot more crusty.

The unit I received came from matched pairs of tubes from Apex. While each pair had the same parameters, the ones for each channel varied quite a bit. As you will see, this is reflected in the measurements.

This unit has an upgraded driver board:

Dynaco Dynakit ST-70 Power Amplifier pre-amp Audio Review.jpg

There is a single bias control for each pair of tubes which is not optimal. I went ahead and adjusted both for 1.56 volts as stated in the manual.

I am not sure what output transformer tap is used. I tested it as is with my 4 ohm load. Hopefully the owner will advise what it is wired for...
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