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Hakko FX-888 : ebay unhappiness

Posted 29th May 2013 at 12:12 PM by rjm (RJM Audio Blog)
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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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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Circuit O' The Day : A headphone output buffer.

Posted 28th May 2013 at 12:24 AM by rjm (RJM Audio Blog)
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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Posted in The Lab
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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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Headphone amplifiers: thinking aloud

Posted 20th May 2013 at 06:13 AM by rjm (RJM Audio Blog)
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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Posted in The Lab
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A catalog of headphone amplifier circuits.

Posted 19th May 2013 at 10:45 AM by rjm (RJM Audio Blog)
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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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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Which soldering station should I buy?

Posted 17th May 2013 at 07:47 AM by rjm (RJM Audio Blog)
Updated 20th May 2013 at 05:20 AM by rjm

Thinking I should get a new soldering station.

I've had my eye on a Weller station for the longest time, but put off getting one for one reason or another.

Looking at the selection, I think the choice comes down to the two following models, or, indeed the equivalent made by another company:

WTCPT (link)

WES51 (link)

The main difference is in the WTCPT the tip temperature is fixed, but rigorously controlled, while the WES51 has user adjustable power but the tip temperature is left unregulated.

I'm leaning towards the WES51 as being slightly more in line with my own style of work: I'm more likely to want higher or lower temperatures depending on the job at hand than I am to require "700F" exactly.

Update 1.

A little concerned the WES51 is only 50W max. That's less than the maximum I use now for the tough stuff.

Hakko has two models in the price...
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Doping of cloth surrounds on recone of subwoofer

Posted 14th May 2013 at 12:32 PM by googlyone

Well, you learn something every day. I suppose if you don't manage to learn as you go, then you probably stuff things up every day!!!

About 12 months ago I came across some RCF L18/551 eighteen inch subwoofer baskets. I reconed them using aftermarket parts, the process went OK but I was kind of bemused by the untreated cloth surrounds.

I was busy, and had no immediate plans so the drivers were shelved for a rainy day.

The Thielie and Small parameters were "OK" but not exact as OEM. I measured these using the addded mass method, an important fact for later. As an aside, they would do well enough as subs, but their Fs was a bit higher than I would have hoped.

Fast forward to last week, I loaded one into a 220 litre box tuned to 34Hz, and measured the impedance.

Bugger me if the resonance showed one massive peak at pretty much the driver Fs, and a tiny lump out at 80Hz. Huh?

I swapped drivers...
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Measurements with a sound card

Posted 13th May 2013 at 09:08 PM by alexcp (My DIY projects)
Updated 7th September 2013 at 09:36 AM by alexcp (Updated for ASIO4ALL)

I am using a USB sound card for measurements. It's a pain, but I have nothing better yet.

The sound card is the E-MU 0204. I've chosen it for the specs:
  • Dynamic Range (A-weighted, 1kHz, min gain): 113dB
  • Signal-to-Noise Ratio (A-weighted, min gain): 113dB
  • THD+N (1kHz at - 1dBFS, min gain): -101.9dB (.0008%)

The sound card is intefaced to the real world by Pete Millett's sound card interface.

The software is SpectraPLUS 5.0 by Pioneer Hill Software (PHS). (No link because my antivirus says their web site is infected.) The software runs on an old MacBook running Windows 7 in Boot Camp.

The results do not seem to be affected by nearby computers, flurescent lights, switching power supplies, etc.

The results are affected by:
  • Windows Mixer settings (levels and sampling rates)
  • Software settings (levels and sample rate)
  • Grounding of the sound card, the interface, and the device under test

The greatest source of pain is...
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