DIYing high enough Q inductors for anti-imaging filters is a bit of a challenge so here's another way to approach this. I found its possible to build very high Q inductors by simply slipping ferrite beads over a fairly thick copper wire. The limitation though is that the beads I have offer about 1.2uH per bead. So making a ferrite bead version of a 660uH inductor will call for over 500 beads - rather impractical.

To make such a ferrite bead inductor filter a practical possibility its necessary to work at a much lower impedance. I've taken a 1ohm working impedance inititally to develop this filter. Now the largest inductor just needs 10 beads. Given this very low impedance the post-amplifier's noise performance becomes rather a challenge - but a transformer will probably do the trick nicely. I plan to try this with a 1:7 step up trafo and see how it goes.

This kind of filter is probably very suitable for DACs with higher output current - the communications type...

I'm really impressed with the bang for the buck with my 228rmb speakers, but have a theory they're rather being limited by their crossover. Especially the first order tweeter crossover which hasn't enough LF rejection.

In search of a steeper XO for the tweeter I've decided to go the whole hog and design a kick-*** filter that'll allow me to fully activate these puppies and see just how much they're limited by their electronics. kinku just pointed me to a filter design program called AADE which I've just finished using to design my first LC bandpass filter.

Its bandpass because I want to stick it straight after the DAC and it needs the anti-imaging function, meaning a steep low pass around 18kHz. The tweeter doesn't need this as they're fairly low on IMD, but the tweeter amp sure benefits from having no ultrasonics. Hence here is my first attempt at a tweeter bandpass filter, to go between the DAC and a dedicated tweeter amp.

For now I'll use the TDA1521...

Original article, by Ben Popper

~ my spin ~

There was the iPod. It was cool, and the distinctive while earbuds that came with it showed people you had an iPod, so they were cool, too. A few audiophiles invested in better IEMs, but they tended to be expensive and discreet and anyway were only ever a niche thing.

Meanwhile the Japanese headphone makers - JVC-Kenwood, Sony, Audio Technica - tried competing with the iPod, and they came up with a spectrum of earbuds and headphones of every shape, price, and color. They sold as commodities, but none developed any real kind of identity or reputation. Certainly there was little effort at building a brand.

On the other side, Grado, AKG, and Sennheiser continued doing pretty much what they always did, making nice, expensive headphones for home/studio/DJ use.

Neither group addressed the obvious hole in the market: non-audiophiles wanting "good" sounding over-ear...

The popular YouTube channel hosted by Dave L. Jones (Sidney, Australia bloke) just released his latest episode:

EEVblog #626 - Ceramic Capacitor Voltage Dependency

https://www.youtube.com/watch?v=TDDoi70cxw0

Of course some of DIYA's know-it-all will claim that this is not new info at all ... well if all you do DIY-audio and tweak and breadboard (and you've gotta lab bench in the little engineer's room ... so you can defecate-n-DIY at the same time) ... well, I suppose you really must know it ALL.

For those of you not familiar with the USA book scene ... yellow-cover "...for Dummies" series has been one of the most successful (=popular/best-selling) book series in U.S. history.


It was so popular that the style was copied by several other publishers' series including:
"...for Complete Idiots".
The term "idiot" or "Dummies" is used as hyperbole in claiming ensured comprehension. The approach relies on explaining a topic via very basic terminology.

But that is not subject of this Blog post ... so stay tuned for a bit... I've gotta take a dump...

...and need a cup o' tea, love ...


....OK,...

Looks like a bargain, around $120. Sorely tempted to get one to play with - what do you think ?

I've mentioned a few times the difficulty in using the software tool, DiffMaker - and others have experienced similar issues. So, I'm thinking seriously about attempting to put together a "better" utility, something that will be more intelligent in correlating between different versions of sampled waveforms, wherever they came from. And it will be specifically aimed at trying to ferret out the deep down differences, not the obvious stuff like frequency response, phase shifts and the like - but rather the low level, detail variations that seem to be so important in subjective quality evaluation.

To give an idea of the "challenge", consider taking 2 recordings from 2 vinyl plays of a particular record. Having already seen what results, this is impossible for the likes of DiffMaker to handle - the constant speed variation between the 2 captures completely defeats it. But this what I would aim to be able to deal with, to synchronise in meaningful ways between...

A while back I built some Ikea bowl speakers using Vifa bassmids and tweeters. The performance came out very good indeed, but when you are dealing with a 5 odd inch driver, there will never be masses of bass.

A subwoofer was always on the cards.



Given the spherical speakers perched on the retro "rocket like" stands, I initially thought of doing a spherical subwoofer - but in the end concluded that while I could do this, I was looking at using fibreglass on a "fit-ball", placement in the room was looking to be a challenge.

So I chose to do the absolute opposite - and came up with an off the wall approach to a conventional sub.





The idea was to move the implementation of a conventional sub well away from the "box with a driver stuck on the front".

I find it fascinating that...

A pair of these were delivered yesterday. At first I thought their bass sucked and the top end was too 'phasy' - it was only after a while I realized I'd connected them out of phase

Now they're wired up correctly on my TDA1521 amps, they're starting to come on-stream. I rate them as a bargain at the asking price of 228rmb (around $35).

After they've fully broken in I plan to explore what the lowest hanging fruit is by way of tweaks to the crossover....

Update1 - here's the XO, very simple 1st order. 250uH inductor on the bass (0.1ohm DCR, 6ohm bass/mid) and 1.5uF cap for the tweeter (8ohm). The NP cap for the tweeter has a rather high ESR (3ohms at 1kHz) so there might be some mileage in substituting this for a foil cap.

Plotting this arrangement on LTSpice gives a crossover frequency (if -6dB) around 7kHz which seems a little high. If we were to assume a -3dB crossover (because they're in quadrature for a 1st order) then it would...

I've posted several topics on DIYA over the past few mos. All of them -- almost predictably now it seems -- dissolve into non-issues. I.e., not a lot of outside-the-box thinking ... methinks
Most of my "DIY" time is now on non-English sites like Player.ru and a few sites from Asia.
While the language barrier is large, and all I can do is read (just barely) using Google Translate, etc., -- and can't really post -- these obstacles seem worth the bennies. Namely, modding or building-from-scratch very inexpensive projects.
Many of the members of these non-English forums seem younger ... so maybe more fresh ideas, with more zest to experiment, and members seem to be genuinely cash-strapped (unlike the English-based forums) ... so the economies-of-scale are a lot bigger.
Comparatively, the English-speaking-forum "DIYers", being older, have their bank accounts and retirement incomes ... and, hence, a lot of drive/passion are diminished ......