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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 (RJM Audio Blog)
Updated 1st October 2015 at 07:04 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 thousands of different op amps to choose from in the first place? It's because there are thousands of combinations of op amp characteristics and properties ... not because companies...
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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 (RJM Audio Blog)

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 14th January 2016 at 03:56 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
Frequency

The frequency of sound is the rate at which...
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Old

Jenson JE-990 discrete op amp

Posted 8th June 2015 at 07:45 AM by rjm (RJM Audio Blog)
Updated 9th June 2015 at 12:09 AM by rjm

LTSpice copy (protection diodes removed) of the original JE-990 circuit. Even with BC327/337 subbed in for all the original transistors the simulation works without further modification.

C1 seems to be critical for stability. C2 and C3 damp overshoot seen on the simulated square wave response, hinted at by the high frequency rise in frequency response shown in the screen grab below.

My impression is that this circuit is of the heavily optimized, no-stone-left-untouched variety.

Sourced from m.nats page and The John Hardy Company.
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Old

New system hard disk

Posted 8th June 2015 at 02:47 AM by panson_hk

Thanks to the SMART feature of the hard disk and the utility which warned me the disk was dying. I was able to backup a WIN7 system image before things happening. Restoring the image on a new hard disk was done smoothly.
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Old

Bargain beaut - headphone amp

Posted 2nd June 2015 at 05:44 AM by abraxalito
Updated 9th July 2015 at 09:43 AM by abraxalito

When I found this on Taobao a few days ago I could not believe the price wasn't a mistake, or that it was just for the case with nothing inside. But it turned out to be real, so I ordered one - it arrived just now so I'm taking it apart before having a listen. The case oozes quality and the volume control feels silky smooth.

Here - 莱曼(lehmann) 耳放 莱曼构架的好声耳放,全铝机箱,一体耳放-淘宝网

When I've had a listen (gotta search for my 1/4" adapter) I'll get into modding.... Incidentally for those on 110V, it does have a mains voltage selector switch. Amazing.

I traced out the circuit (still haven't listened) and found its pretty much as shown on the Taobao page. 78/79 15V regulators feed BD139/140s and a TL072 sits between the volume pot and the discrete OPS. This stage resembles a diamond, but instead of the more familiar current sources to the rails, it has 1500ohm resistors. LTSpicing this arrangement (schematic shown) reveals its...
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