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Flattening the NOS droop

Posted 14th April 2012 at 03:13 AM by abraxalito
Updated 14th April 2012 at 03:48 AM by abraxalito

Having been a fan of NOS DACs now for something over a year I've decided it was high time for sorting out their most serious drawback - the roll off in the HF. This is an unavoidable result of using a zero-order hold function to reconstruct the original (impulse) samples. Droop exists even with oversampled DACs, its just at its most severe in NOS.

One of the most popular ways to flatten the response is to add on some kind of analog filter with a rising response (to 3.16dB @ 20kHz). A first order shelving filter can't quite cut it though so an LC tank circuit has been employed by a few. This needs to have a moderately high Q to achieve the correction.

I've played around with inductors to achieve this and haven't much liked the resulting sound. Whether this was due to the particular inductors I was using I didn't experiment. Admittedly they were very cheap ones. In general though when I've used high Q circuits in crossovers I haven't much liked the colouration...
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Old

X-reg Evaluation Boards

Posted 7th April 2012 at 12:15 AM by rjm
Updated 9th April 2012 at 03:37 AM by rjm

Once in a while I get emails asking after the X-reg evaluation boards. These are handy little 5x8 cm test boards for the X-reg voltage regulator - or they would be, if I had ever bothered to get a set made.

Since the circuit is built into the VSPS300 and Phonoclone 3, it wasn't really a big priority.

Anyhow, yesterday I re-drew the evaluation boards and I'll be getting a batch made in the near future, along with some of the stereo VSPS that people were also asking after recently. They won't exactly fly off the shelves, but I started to feel bad for those few people who actually wanted them.
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Old

Recycling?

Posted 2nd April 2012 at 08:37 PM by DigitalJunkie

So,one of the monitors I use decided to die yesterday,it came back from standby,but had rainbow lines all over the screen..Something in the TFT panel itself,COF or something.Gaw.

Anyways,it had built in sound,using a TDA7496L chip for the amp..I got to looking at it,and decided to pull it off the PCB and build a (headphone)amp with it.

It's basically the schematic on the datasheet,with slightly larger input and output caps,and it's all powered by a 3-cell Li-ion pack for a Vcc of about 11-12V.

Here's the datasheet.
http://www.st.com/internet/com/TECHN...CD00001216.pdf

It doesn't sound tooo bad,really. It's not the best thing ever,but for a couple hours of tinkering with junk that was on the bench, I'm pleased.
It's got more than enough power for 'phones,some care needs to be taken to prevent any accidents.

So yea,yesterday was more or less; Troubleshoot monitor,discover...
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Old

Time for a new Digital Crossover - ADAU1442

Posted 2nd April 2012 at 01:29 PM by googlyone

Well, it has been a few years since I built my last digital crossover - like six I think.
It is not that I was planning to do this - but a conversation with someone about my seemingly modest choice of the AD1941 DSP chip for my old crossover made me look at what else Analog Devices are offering.
The ADAU1442 is on the surface a very similar chip to the AD1940, but it has a lot more integrated into it, and offers significantly greater capacity.
So I set about designing a new crossover that used this, and also addressed a few of the shortcomings of my original design.
The goals were broadly:
- A modular DSP based crossover
- That provides a standard interface for the ADC
- That provides a standard interface for the DAC
- That includes SPDIF in and out
- That anybody can design digitisers and dacs for - no code level drivers built in, though the interface does ALLOW for SPI control of these
- That is controlled from a simple...
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Old

Headphone Amplifier Gain

Posted 2nd April 2012 at 08:45 AM by rjm
Updated 2nd April 2012 at 11:43 AM by rjm

I posted this earlier today, but I think it deserves to be put in the blog - if nothing else so I can find it again next time ... and there always seems to be a next time when it comes to calculating headphone amplifier gains.

Starting at the beginning, the encoded data on a CD goes from 0 to 1 in 2^16 steps, but in a typical CD player or soundcard, the DAC output is -2.8 V to 2.8 V or 2 V rms or 6 dB. Many sources, such as phono stages and portable audio, are lower, perhaps as low as 250 mV.

How loud the sound is depends on the source signal amplitude, the position of the volume control, the circuit gain, and the impedance and sensitivity of the headphones.

As a practical matter, most people would want the volume control at the 9-10 o'clock position for "normal" listening.

For standard "line level" source, the gain required to keep the volume control at a 9-10 o'clock varies depending on the impedance...
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Old

Pimp My Board Contest Results

Posted 31st March 2012 at 12:20 PM by rjm
Updated 31st March 2012 at 12:28 PM by rjm

I did get a couple of responses to my invitation. Well, two, actually.

So congratulations! Free boards will be heading your way in about a month, and I'll throw in most if not all the parts, too.

First was simonov's entry. He's clearly done this several times before. His confident layout ticks all the right buttons: ground plane (check), thermal isolation (check), clean, geometric layout (check). One jumper required, but that's a very minor offence.

Click the image to open in full size.

While I allowed modifications of the circuit, simonov went and redesigned pretty much the whole thing. CCS replaces the source resistor, current limiter and capacitance multiplier blocks added. The BOM was starting to spiral, and no longer uses my standard parts set so I'd have difficulty supplying kits based on his design. His modifications, although certainly improvements, ended up counting against him....
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Old

Conduction Angle, Or Why You Need a Bigger Power Transformer Than You Think You Need

Posted 29th March 2012 at 04:35 PM by rjm

I tell people: "Buy a nice, heavy power transformer. It will sound better."

They are skeptical, because the circuit only draws a couple of watts, and less than 100 mA current.

The image below shows how the power transformer, and rectifier diodes, actually work much harder than you would estimate from looking at the output power.

It shows a zener regulated supply with a load drawing 100 mA at 20 V. That's 2 W.

As a result of the capacitor input filter directly after the diodes, however, the diodes and transformer do not conduct current all the time, but instead for just a couple of milliseconds twice every cycle of the AC wave. They have to supply all the output current in just that short space of time. As you can see in the simulation, the diodes are pushing peak currents well in excess of 1A or 10x the output current. This is a typical "normal" power supply with a initial ripple ratio of a modest 1/40, things...
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Old

Why do some chip amps / gainclones sound so bad? (updated 2012-03-30)

Posted 29th March 2012 at 04:56 AM by dunndatt
Updated 31st March 2012 at 12:23 AM by dunndatt (clarification fix)

Years ago when getting started into DIY audio, I picked up three different chip amps from my local electronics shop. They were cheap and easy enough to build according to the data sheets, so I had a go at them. To my dismay, they sounded HORRIBLE! I couldn't figure out what went wrong until I really started digging into the data sheets.

While I didn't build the LM3886, I'm going to pick on it since it is a very common chip amp:
National Semiconductor LM3886 (from national.com, bought out by ti.com)
Claims 68watts into 4ohm speakers with 0.1% THD+N from 20-20kHz

National did pretty good with most of their claims, but I'll focus on something that stands out: The Distortion Vs. Power graphs. (As a comparison, I discovered that one of my other chip amps did their power testing at 10% distortion... which is pitiful. Every chip amp data sheet I've looked at has some kind of failing with this graph.)

Click the image to open in full size....
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Old

Chigusa Modern Jazz and Coffee

Posted 28th March 2012 at 07:41 AM by rjm
Updated 28th March 2012 at 07:57 AM by rjm

I was fortunate to stumble across this place on a trip to Yokohama earlier this week.

http://g.co/maps/nzebr

I was walking around the area near Sakuragicho Stn. after dinner, and, through the windows I could make out a back wall filled with LPs, two turntables built into the bar countertop, and a pair of giant multi-way speakers. The sign out front said "Modern Jazz and Coffee". So, naturally, I went in.

First, the history of the place as it was explained to me:

First opened in 1933. Destroyed by American bombs during the war, 6000 SP records gone, re-opened, and was in business until the owners death in 1994, then taken over and run by the owners younger sister until 2007, when, at the age of 77 (!) she gave it up. Volunteers somehow managed to preserve the records and furnishings, including the sound system, and, some 5 years later, decided to relocate and reopen at a nearby location just, if I've got this right, a...
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Old

the crooked ones :-/

Posted 25th March 2012 at 01:45 AM by cberger

Cut my boards today and screwed up the first one. Used a ruler as a guide and it moved during the cut. Not happy!
The only thing that worked was my router and the template for the driver cutouts. Drivers sit recessed and flush.
Tomorrow I'll have to make the boards match.
You live and you learn I guess...
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