Articles, Reviews and Measurements of Audio Products

This is a review and detailed measurements of the EquiTech 1.5RQ (also called 1.5Q) Balanced Mains Power. It is on kind loan from a member and costs US $4,700.

The 1.5Q is not much to look at but boy, does it weigh a ton at 70 pounds!



The sole display either shows the incoming voltage or outgoing.


Balanced power takes a 120 volt RMS incoming feed and produces two out of phase 60 volt feeds which gives you the same differential 120 volt. This is said to do all kinds of things from reducing noise to making your music sound better. From the company:

"If you haven’t heard your sound system with a Model Q powering it, you are missing something truly great. You might just find yourself replaying all of your old music again and again as if hearing it for the first time with a new appreciation for detail, clarity and remarkable bass definition that you have never experienced before. Many of our customers have...

This is a review and detailed measurements of the ifi Zen Blue Bluetooth Receiver and DAC. It was sent to me by the company for testing months back and costs US $129 on Amazon with Prime shipping. There is now a version 2 of it. From my read of their description, it has a better antenna. Not sure what else is different.

The Zen Blue looks like the other recent ifi products:



The back side shows some interesting options:



The slide switch controls whether the output is digital or analog (can't be both). There is both coax and Toslink optical out. What is unusual is the balanced 4.4 mm that is normally reserved for headphones. Here, it is a mini balanced line out. Do not use it for headphone as it will play at full level and likely exceptionally loud!

ifi Zen Blue Measurements
From previous measurements of Bluetooth receivers, LDAC codec has shown to be most transparent. Other codecs degrade the signal...

This is a review and detailed measurements of the Japanese ZERO AUDIO Carbo Tenore ZH-DX200-CT In-ear Monitor. It is on kind loan from a member and costs US $44 from Amazon including Prime shipping. It has been around for a while and seems to have quite a following from scan of online reviews and forum discussions.

"Carbo" apparently refers to carbon fiber look (or is it real) of the body of the IEM:



As you see there is not much strain relief on the wires and what there is, is already split. People complain that the wire is thin but it is actually thicker than the ones on my Panasonic IEMs.

Note: The measurements you are about to see are made using a standardized Gras 45C. Headphone measurements by...

This is a review and detailed measurements of the Behringer NX1000D power amplifier with DSP. It is on kind loan from a member. Can't tell if it is discontinued or not but see it on sale at one place for $299. Retail cost is $549.

I am a fan of orange displays and NX1000D delivers on that (sorry my sample is not powered on):



What I am not a fan of, pun intended, is the super loud fan that stays on all the time. I walked away to go to the bathroom and was so surprised that I could hear it from very far distance in the house. Unless you can put it in a sealed cabinet, I don't see it being useful for hi-fi use. Maybe you can modify it to quiet the fan or make it temperature sensitive.

On the positive front, I really liked the look and feel of the control app that talks to it:


The only thing I did not like about it is that it is not clear when some processing is on or off. For example above, is the peak limiter on...

This is a review and detailed measurements of the Tortuga TPB.V1 Balanced Tube Preamp Buffer with various set of tubes. It is on kind loan from a member and costs US $1,695 with "Matched Pair Electro-Harmonix 6H30Pi Gold triode tubes."

There is not a whole lot to look at here other than the two tubes sticking out the back:



There is an internal gain setting which I left alone meaning the unit runs as a buffer (gain of 1). Architecture is tube front-end but back-end is transistor based (I assume to keep impedance low). There is some kind of protection and monitoring circuit that blinks until the tubes have stabilized.

Like the balanced configuration which is rare in tube products:



The transformer bolt had come loose and I could feel it by shaking it. Tried to tighten it from outside but keeps turning. Likely need to hold the nut inside to keep it from turning.

There are no safety marks on the amplifier...

This is a review and detailed measurements of the Polk T50 tower speakers. I bought this recently for $149 from Amazon.

As you can imagine, a floor standing speaker at this price has to be quite light and this one definitely is. I can easily lift it as it weighs less than many bookshelf speakers. What a marvel of cost optimization:



Yes, my system area is dusty. Do you want more reviews or clean listening room???

This is a 2-way speaker with two passive radiators to improve bass response.

Measurements that you are about to see were performed using the Klippel Near-field Scanner (NFS). This is a robotic measurement system that analyzes the speaker all around and is able (using advanced mathematics and dual scan) to subtract room reflections (so where I measure it doesn't matter). It also measures the speaker at close distance ("near-field") which sharply...

This is a review and detailed measurements of the VTV Purifi class-D amplifier with the optional Weiss OP2-BA Op-amp (buffer/input gain stage). It is on kind loan from a member and costs US $2,090. I just reviewed the same amp but with SIL 994EnH-Ticha Pro buffer so you can compare them.

As with the other variation, I am a fan of the more slim rack mount case (it is a lot deeper than this photo shows):



Back panel as expected:



VTV Purifi class-D amplifier with the optional Weiss OP2-BA Op-amp Measurements
Let's start with our dashboard and see if the power supply noise we had with the SIL buffer also exists here thereby telling us if the problem was that or something else:


Sadly the issue remains with the noise in the FFT spectrum. So...

This is a review and detailed measurements of the Takstar Pro 82 headphone. It was kindly purchased by a member and drop shipped to me. It costs US $90 on Amazon but I believe member got a better price.

The Pro 82 looks quite stylish despite its low price:



The soft touch material is indeed, quite soft. Maybe too soft. The pads are so soft that slightest touch deforms them. While this is good for initial comfort, not sure how long they will last before becoming totally compressed. There were also some fine scratches on the cups.

An unusual feature of this headphone is a switch on each cup which is supposed to adjust bass. See my measurements later on effectiveness of it.

These headphones are quite light:



Cup size is reasonable at 67x46x18 (height, width, depth).

Note: The measurements you are about to see are made using a...

With the recent talk and review of in wall speakers, I thought this might be an interesting topic. My main audio/video system is in my living room, so aesthetics play a big role in the selection and placement of equipment. As such, I decided to use in wall speakers for surrounds. There is no concern with sound bleeding to adjacent rooms as one wall is exterior and the other joins the dining room. I have an older home built in 1928, so walls are lathe and plaster. Speakers are mounted directly into the walls with no backer boxes or special enclosure. My thought is that this gives them quite a large enclosure, making them somewhat infinite baffle and perhaps improving low frequency output capability.

I selected Revel's cheapest in wall speakers for a number of reasons:
The spins don't look great look pretty terrible above 9KHz but to my eye, you have to move up quite high in the lineup to get a really good looking spin i.e. W893.
My budget was quite low for two reasons...

I just reviewed the VTV Purifi amplifier with SIL 994EnH-Ticha input gain/buffer stage. This is a quick teardown of the unit.

Click on this image for larger size:



Take care of the obvious, the two larger modules are Hypex SMP1200 power supplies. In between them, the little boards to the left are the Purifi amplifier boards (with green PCB). To the right of them is their custom input buffer that allowed interchangeable opamps. While this board is made for a ton of flexibility, I am not happy with the long path lengths here. They can pick up noise and interference. The reference design from Purifi uses PCB mounted XLR connectors that provide a very short path to the input buffer IC. Not so here with those long cables (in comparison).

I also find the placement of the upper channel rather odd. Why not have it...