Articles, Reviews and Measurements of Audio Products

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:


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...

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:


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...

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:


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:



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...

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:


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:

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

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:


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...

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:


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:



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

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...

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:


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...

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...

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:

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...