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DIY for Dummies?

Posted 5th June 2014 at 04:37 PM by hollowman
Updated 6th June 2014 at 07:07 AM by hollowman

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.
Click the image to open in full size.

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...
Click the image to open in full size.
...and need a cup o' tea, love ...
Click the image to open in full size.

....OK,...
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Old

Linsley Hood amp on Taobao

Posted 4th June 2014 at 06:27 AM by abraxalito

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

A Better Audio Comparison Tool

Posted 2nd June 2014 at 08:25 AM by fas42
Updated 14th July 2014 at 03:01 AM by fas42

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...
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Posted in Tweaking
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Old

Cubist Subwoofer to go with Ikea bowl Speakers - just looks wrong!

Posted 1st June 2014 at 01:20 PM by googlyone
Updated 1st June 2014 at 01:24 PM by googlyone

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.

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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.

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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...
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Old

Cheapo passive speakers breaking in

Posted 1st June 2014 at 07:02 AM by abraxalito
Updated 2nd June 2014 at 04:54 AM by abraxalito

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...
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Old

Philosophy of boring DIY...

Posted 1st June 2014 at 06:02 AM by hollowman
Updated 1st June 2014 at 05:36 PM by hollowman

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 ......
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Old

TDA8932 class D amp

Posted 27th May 2014 at 01:39 AM by abraxalito
Updated 16th June 2014 at 02:09 AM by abraxalito

One channel is completed - barring the off-board hexacap shunt - second channel under construction. Then for a comparison with the TDA1521s

Update1 - both channels running now, 160,000uF on each. Bass is tuneful but LF colourations noticeable on piano (Ashkenazy Diabelli Variations). Solution to this is simple - more caps

Update2 - an extra ring of caps around the original hexacaps now, so we're around 250,000uF. Bass is so much better than from the TPA3116 but the HF is more ragged, less transparency overall than the TPA3116. So I'll next try an outrageously decoupled implementation just to check I'm not limiting the chip with poor PSU hygiene....

Update3 - I have over 30 1206 10uF caps per side now as local decoupling - HF problems are slight. Makes me wonder if I use it only on the bass/mid and a TDA1521 for the tweeter duty we might reach audio nirvana.... Looking at the DS its easy to see why the HF's a bit of a mess - the PSRR is about...
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Posted in Power chip amps
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Old

TDA1521 chip amps rock!

Posted 23rd May 2014 at 04:13 AM by abraxalito

Here's my prototype TDA1521 dual mono arrangement - two chips per channel in bridged/parallel, sat atop 400,000uF hexacaps. The neutrality has taken a while to get used to but I'm lovin' em....
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Old

Technics SU-9070

Posted 20th May 2014 at 01:01 AM by rjm
Updated 20th May 2014 at 03:15 AM by rjm

The Technics SU-9070 is a 2U rack mount stereo preamplifier from 1977, matched to the SE-9060 amplifier. The preamp was sold as the SU-9070II in Japan.

The circuit is shown below, for educational purposes.

The power supply regulation is quite elegant, I hope to get to that in a future post. Here, just note that there are separate regulated lines for the MC stage, the input/VAS sections of the MM and line amps, and the output sections of the MM and line amps.
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Posted in The Lab
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Old

Technics SE-9060

Posted 19th May 2014 at 01:04 AM by rjm
Updated 20th May 2014 at 12:58 AM by rjm

There was a series of relatively slim (2U chassis rather than 4U), upmarket audio separates put out by Technics in 1977: the ST-9030T tuner, SU-9070 preamplifier, and SE-9060 amplifier. They are two degrees of separation from the top of the line models at the time, the range went 9600>9200>90x0.

I recently acquired the tuner (more on that some other time) and have the others in my sights.

For educational purposes, the amplifier schematic for the SE-9060 is shown below. The input stage and voltage amplifier was driven from regulated 55 V supplies (Va+ Va-), while the driver stage was powered directly by the rectified DC at about 50 V (Vb+ Vb-) filtered with 18,000 uF per rail per channel.

Note that there were 9060 and 9060II as well as 9070 and 9070II models in Japan, but the export model of the preamp which sold as the 9070 was actually the 9070II rather than the 9070 domestic version. Likewise the SE-9060 shown below (from a European...
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