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Fountek (Rhyme Acoustic) active speaker A-100

Posted 24th July 2015 at 08:18 AM by panson_hk
Updated 28th July 2015 at 01:37 AM by panson_hk

I purchased a pair active speaker. This is manufactured by Fountek under the brand Rhyme Acoustic. The model number is A-100. It uses a 4" full-range driver with vented box. The electronic is contained in the right channel enclosure. The amplifier is LM4766 chipamp. The overall build quality is good. I just paid RMB 399.00 during its sales period. What a good deal!

Chinese product link is https://item.taobao.com/item.htm?spm..._u=od0rlto94d1 The frequency response shown in this product page does not match with that given the user's instruction of my pair. The curve shown in user's instruction does pretty much match with my initial listening impression: lack of treble.

I measured the speaker with my CLIO Pocket. Measurement shows left and right enclosure response are matched very well.

The last figure shows the left box (passive) driven by another amplifier. We can then see what filtering or EQ is...
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Old

Another incredibly cheap Taobao toy

Posted 19th July 2015 at 10:00 AM by abraxalito
Updated 22nd July 2015 at 01:03 AM by abraxalito (Listening report added)

When browsing Taobao I can't resist the temptation to try the very cheap stuff. This little TFcard player really takes the biscuit for the lowest price of a digital audio source - 9.9rmb. So I ordered up three, I might just order more soon.

First powering up I tried some FLAC files, these don't work but wav and mp3 work fine and it even finds files below the root directory. Power supply is nominally 12V but its using an EF fed by a zener diode, not an IC reg so almost anything from 6V will probably work. I haven't managed to find the technical blurb for the chip so far so a little reverse engineering was needed. It incorporates a 3.3V regulator to power the IR receiver and the TFcard - I have fitted an additional regulator for the first mod because I wondered if the low-level noise I was hearing was due to interference from the flash card's power draw. Turns out no as when playing .wav files this noise disappears.

Incidentally the 9.9rmb cost includes the remote...
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Baffle mechained by a desktop CNC

Posted 14th July 2015 at 02:37 AM by panson_hk

I use DeskProto to generate toolpath for the CNC controlled by Mach3.
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Old

Building a cube enclosure

Posted 14th July 2015 at 01:44 AM by panson_hk

I am enjoying all the fun of building speaker enclosure. An inexpensive 2" full-range is employed. The cube is made by MDF. I have measured TS parameters of the driver and its response with a big baffle. I use Basta! and LEAP-5 to simulate the box's response and impedance. Once the box is built, I can compare actual and simulated data.

Two cubes will be built. One is sealed and the other is with passive radiator.
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Old

Measuring compliance of passive radiator

Posted 14th July 2015 at 01:32 AM by panson_hk

I am using a handheld force meter and caliper to measure compliance of passive radiators. The force meter is clamped to the caliper. Caliper is used to show the panel displacement whereas force meter displays the corresponding force. I can then obtain compliance C mm/N. I am planning to use an Arduino controlled Z-axis for automatic measurement. The force meter has a USB interface for data acquisition.

I should be able to measure BL vs displacement of a driver by adding a programmable DC supply.
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Old

Audio Op Amps

Posted 26th June 2015 at 02:59 AM by rjm
Updated 13th July 2015 at 02:23 AM by rjm

I'm often asked "which op amp sounds better".

The reply is usually a scowl and muttered "does it look like I care!?" Which is something of a lie... I do care about getting op amps to sound good. It's the phrasing of the question I dislike.

Op amps do not come in "good, better, best" flavors. All it is - and this is pretty obvious I would have thought but apparently not - all this is about is matching an op amp to the job it's going to do; the circuit it's going to be sitting in.

The op amp you'd choose to use as a DAC IV converter is different from the one you'd choose to back a 100k volume potentiometer in a preamp is different from the one you'd choose for an MC phono preamp input stage...

Why do you think there are like a gazillion different op amps to choose from in the first place? It's because there are about a gazillion combinations of op amp characteristics and properties ... not because...
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Old

From Tube CAD Journal by JRB

Posted 25th June 2015 at 08:05 PM by alexcp (My DIY projects)

For every hobbyist-built amplifier in existence there are probably one thousand amplifiers which are planned on being built and maybe one hundred amplifiers that have all their parts collected in a box waiting to be built and ten amplifiers that are partially built and collecting dust in a closet.

(see full post here)
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Old

AKM's new "VERITA" AK4490EQ 120dB 768kHz/32-bit 2ch New Generation Premium DAC

Posted 15th June 2015 at 09:47 AM by hollowman

Click the image to open in full size.
Supposedly, Astell and Kern are using this in their latest AK-380 high-end/high-$ DAP:
Click the image to open in full size.
I proto'd this DAC recently (along with AKM's new premium ADC)....what can I say ... I'm floored! This is the best digital I've ever heard to date.

Some hold-outs of antiquated multi-bit DAC religiosity may never be able to step outta their cognitive dissonance -- or warm-fuzzy nostalgia -- 'cause of their loss of virginity with their first loves (= classic R2R multi-bit) oh G A W D ... memories are so precious ... man -- I'm lookin' at my Philips CD650 and gettin' misty-eyed ....WAKE UP DUDE!!!
Folks, this is 2015 and technology does EVENTUALLY improve (tho', it takes time and is often 3 steps fwd, 2 back).

Unless Philips decides to revamp their TDA or SAA lines, AKM's your ticket ... or...
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Old

capacitance measurements with the hp 4192A

Posted 10th June 2015 at 01:10 PM by rjm

Work stuff. I was writing Labview vis for an hp 4192A LF impedance analyzer and needed something to measure to check the data acquisition program. So I stuck some of my audio capacitors I happened to have into the 16047A test fixture "just to see".

I have no idea what these measurements are telling me other than yes, the 0.47 uF capacitors are indeed 0.47 uF ... up to about 0.5 MHz anyway. Maybe someone can do some technical analysis. I was struck though by just how quickly the inductance of these big film caps kicks in. As audio coupling caps they are fine, but if you are silly enough to use them as power supply bypass for example...

There are some reproducibility issues I'm still coming to grips with, but the differences shown in the plots is definitely from the capacitors themselves and not the leads or random variations. I've measured them several times over with similiar result.
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Old

Resources for acoustic measurements

Posted 8th June 2015 at 03:32 PM by MartinAndersen
Updated 8th June 2015 at 05:43 PM by MartinAndersen (new link)

This is my collection of everything related to speaker measurements. Better to share it than hide it away in my bookmark collection

Understanding Cabinet Edge Diffraction
"One of the most misunderstood topics in audio is the subject of diffraction. Diffraction, acoustic phase, and how listening rooms impact our reproduction of sound, based on what I see posted in many discussions on the internet, are subjects of much confusion. In this article I will attempt to clear some of the fog on the topic of cabinet diffraction, and hopefully, present it in such a way as to make it much easier to understand."
SPEAKER DIRECTIVITY
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