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Better sounding anti-imaging filter

Posted 5th June 2013 at 01:46 AM by abraxalito
Updated 5th June 2013 at 02:00 AM by abraxalito

Still in the vein of AIF designs which utilize off-the-shelf inductors, I'm currently listening to this one and its thoroughly enjoyable. I built it with some very cheap bobbin-wound (unscreened) 10mH chokes I found on Taobao.

I don't recommend using unscreened inductors for this but if that's all you have the results are still aural candy. They do pick up a little low level mains hum, not noticeable except when close to the speaker. Also they interact - when I was checking the prototype filter for continuity I hooked up the LCR meter to the 4 inductors in series and found different answers - none measured 40mH. The result was from 32mH to 45mH (from memory - my filters are balanced so I have four sets of series Ls). I have them spaced apart by almost one coil diameter (about 6mm) so if you're going to build this I suggest greater spacing.

You'll note that this one's industrial strength in terms of its stop-band rejection - around 60dB. Whether this is obtained...
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Old

Hi-end audio, as seen from outside the bubble.

Posted 3rd June 2013 at 11:28 PM by rjm
Updated 3rd June 2013 at 11:32 PM by rjm

In early May Trent Wolbe traveled to the High End trade show in Munich, Germany. This is part one of a two part series exploring the cutting edge of audiophile technology.

By Trent Wolbe, writing for The Verge. A feature on high end audio part 1 and part 2.

Quote:
It was halfway through the next selection, a quietly seductive 24 / 192 recording of “Cielito Lindo,” that I realized I was enjoying the music quite a lot, not because I particularly enjoy bossanova versions of Mexican classics, but because the Evolution One speakers were recreating one of my favorite things about eating psychedelic mushrooms.
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Old

A Low Power Desktop Amp [LPDA]

Posted 1st June 2013 at 11:24 AM by BuildMeSomething

Well, this little project is finished and working. Quite pleased that measured offset dropped to <1 mV on both channels once the amp was in the chassis and wired.

Listening impressions: This is where I state that it's the best amp I've listened to, and it is... Unfortunately, it just highlights any shortfalls with the speakers. The Mission 773e have never performed better or sounded clearer. However, you are just as aware on how quickly these speakers lose the plot with more complex music... In the long run I hope to match the sound of the Sennheiser HD-650 driven by "The Wire" se-se HPA, the FH3 are my first try at achieving this...

Paul
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Old

Hakko FX-888 : ebay unhappiness

Posted 29th May 2013 at 12:12 PM by rjm
Updated 29th May 2013 at 11:59 PM by rjm

Oh, for Heaven's sake...

Just got the FX-888 soldering station I bought on ebay.

It does not power up.

Do you know why it doesn't power up?

So glad you asked...

It does not power up because - pause for effect - the fuse board that fits on the power transformer is inserted the wrong way round. That's right, the full "rotated 180 degrees" deal.

Fortunately I have another soldering iron. You know, so I can fix my soldering iron...

*****

I would just return it, but the shipping would cost me half again what I paid for it. Perhaps ebay will refund me anyway. We'll see.

I think I know what happened: The people selling these are modding them by changing the voltage and power cord. The soldering stations are officially bound for the Chinese domestic market, 220 VAC. The box, when it came, had "110V" hand-written on it, though the instructions...
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Old

Simple anti-imaging filter

Posted 28th May 2013 at 04:57 AM by abraxalito
Updated 4th June 2013 at 07:34 AM by abraxalito

If you're curious to see how an anti-imaging filter affects the SQ of your NOS DAC but have been hitherto put off by all the coil winding involved, then this circuit might be just the ticket.

I was curious to see how well just two inductors could do and it turns out not at all badly - there's about 23dB stop-band rejection here and the 10mH inductors are off-the-shelf Fastrons. The capacitors can be all 1nF 0805 C0Gs - just buy a strip of 40 and use parallel and one series combination.

I intended to build one and listen to how it fares against my more complex efforts...

Update - a quick listen and its clear on switching back to the original filter that this new filter's noise floor isn't as low. That's not directly perceived as a rise in hiss mind - this is the subconsciously perceived noise floor which translates to more attention given to the music. So I'll put the two inductor filter aside and work on slightly more complex filters next.
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Old

Circuit O' The Day : A headphone output buffer.

Posted 28th May 2013 at 12:24 AM by rjm
Updated 28th May 2013 at 12:08 PM by rjm

Experimental : For Research Use Only

It's bring-your-own-voltage-gain. This output stage is a unity gain buffer. A sort of diamond-buffer-meets-sziklai-pair hybrid. It lets the driver pair bias the output pair without the complexity of an additional bias network, but, unlike the basic diamond buffer, the output pair can have a much higher bias current than the drivers.

LTspice file attached, if you'd like to play along.

*****

I did my best to shut my eyes and design this just by messing about in LTSpice from the starting idea of a "level-shifted-complementary-sziklai-pair" (i.e. mirrored J-Mo mk II), but I see now a shout-out to 47 Labs is due as the 0247 Treasure uses the same stage.

Ah well, I guess my neat idea isn't new after all.

*****

The general performance is in the order of 0.01% THD for 50 mW / 16-300 ohms at 100 mA bias though the output pair. I've been trying to...
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Old

More on Doping Speakers

Posted 25th May 2013 at 10:25 AM by googlyone

I got a question or two on doping of speaker surrounds.

Here is the thing: If you buy an OEM cone kit it will either come with a pre-doped surround, or be provided with the doping material and instructions.

I have reconed a lot of drivers and until recently either used OEM kits or kits from providers who have looked after this for me.

A good example of a provider that gave doping compound was BEYMA. The instructions etc for this were idiot proof, and the material nicely packed in the kit.

To apply this I used a stiff "cleaning brush" as you would but from your local hardware store - a steel handle about 100mm (4") long crimped onto stiff bristles. Worked a treat.

The beyma doping material looked and smelt for the world like really thick PVA glue. The difference was that when dry it did not go that hard, and remained almost but not quite tacky.

The before shot is:
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Old

Headphone amplifiers: thinking aloud

Posted 20th May 2013 at 06:13 AM by rjm
Updated 21st May 2013 at 12:00 AM by rjm

The sobering fact is that the built-in headphone jack on most modern consumer electronics provides pretty decent performance. Taking that output and routing it through an external headphone amplifier rarely improves things, and frequently has a negative impact owing to increased background noise.*

[* This is a simple consequence of adding a volume control which attenuates the signal, and a gain stage which amplifies it back up. Even if the gain stage has the same noise floor as the input signal, the S/N is reduced by the amount of attenuation.]

There are specific use cases, particularly with "outlier" headphone models that require unusually high voltages or currents to drive, but in the main, for generic 16 ohm IEHs and the generic headphone ICs used in consumer electronics, I've found that external headphone amplifiers aren't worth the trouble and expense.

Instead, I've taken (I realise now) an elitist approach to focus on a desktop...
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Old

A catalog of headphone amplifier circuits.

Posted 19th May 2013 at 10:45 AM by rjm
Updated 21st May 2013 at 12:12 AM by rjm

Lots of circuits out there, but most are variations of a small set of archetypes. Let's see if I can put together a list:

1. Dedicated headphone amplifier IC. e.g.(lme49860)

2. Battery powered, single stage, generic audio op amp. The ever-popular mint tin cmoy.

3. Op amp + buffer (complementary transistor pair, diamond buffer, unity gain op amp, etc, in either integrated or discrete package.)
a. closed loop connection or "compound amplifier" configuration as developed by Walt Jung.
b. open loop, two stage circuit, e.g. nwavguy o2 and my sapphire amp.

4. simple 2 or 3 transistor "introduction to electronics"-style amplifier

5. The "little big amp", a scaled back version of a transistor or vacuum tube power amplifier design. (Zen, DoZ, transformer coupled SET amps)

6. The power follower. Single-ended MOSFET or BJT, with or without CCS load, voltage...
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Old

Nearly There - A Low Power Desktop Amp

Posted 17th May 2013 at 07:09 PM by BuildMeSomething

Well, this project is nearing completion. The very last pieces needed have been ordered and will be delivery early next week. The chassis and custom PCB enclosure/heat spreader were collected on Thursday morning from FedEx and UPS. Thursday night was spent drilling and tapping holes for the various parts. Now its some wire placement and waiting on the last pieces...

Problems: None really, a few sizing issues for connecting wires and the caps to the boards. Though, all are just big enough with a little patience. Certainly no issues that require a halt to the project or new PCB's.

Speakers: Decision made, Frugel-Horn Mk 3 with Mark Audio Alpair7.3 drivers... Why? I love the strong imagining and detail given by the little 3" FC full range speakers, so thought I'd give some proper full rangers a go. Should be fun trying to build these
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