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transistors for front end

Posted 24th December 2010 at 02:18 PM by klewis
Updated 31st October 2012 at 12:55 AM by klewis

This thread.
http://www.diyaudio.com/forums/solid...tp-choice.html

Sources:

http://www.utsource.net/index.aspx

http://www.taydaelectronics.com/servlet/StoreFront

Sadly the 2SC2240 and 2SA970 (npn, pnp) super-low-noise trannies in TO-92 packages no longer appear on Toshiba's Bipolar Transistors Product List, and have been designated NRND by Toshiba (Not Recommended for New Designs). [link] This means the factory is presumably still taking (large) orders, but they are destined for the dust-bin of history. FYI, last chance, B&D still has some inventory.

But, not to fear, Toshiba offers what appears to be the same (or better) die in SOT-23 packages, the 2SC3324 and 2SA1312. These are stocked by Mouser, and cost only 15 cents qty 100. Their datasheets are fairly complete, including two NF contour plots. The 1kHz plot shows the 3dB contour dropping 35 ohms at 1mA and below...
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Old

D1080 Mk II 08 actives - initial listening and some refinements

Posted 23rd December 2010 at 01:49 PM by abraxalito
Updated 2nd March 2011 at 12:14 PM by abraxalito

Having disassembled the amp board from its backplate once and got heatsink compound in various undesirable places, I was hoping that the first round of mods would also be the last. No such luck

However, first listening was extremely promising, so I was definitely up for a second round of extreme messiness to gild the lily. I did notice that my grounding changes had introduced a slight hum (50Hz fundamental only it seems) which was only audible when no music was playing and was independent of volume setting. The main gripe I had was that the stereo image was shifted over to one side - this I decided was because the volume pot was being used towards the lower end of its range where the matching is poorest. The chip amps have rather high gain (32dB in bridged) and this can't be reduced. So the solution had to be modding the resistive dividers between the XO and the amp chips - in effect reducing the power amp sensitivity. I went for about a 9dB reduction, determined by the...
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Old

D1080 Mk II 08 actives - XO mods

Posted 23rd December 2010 at 12:21 PM by abraxalito
Updated 5th March 2012 at 03:53 AM by abraxalito

Here's the schematic showing the component value tweaks I made to the tone control board. I'll list the changes in detail - only the first three are depicted in the schematic. The remainder aren't as they don't show up on the sim plots

1) The original input stage has attenuation followed by gain. I have removed both, its now a unity gain stage and also no longer rolls off the HF response.

2) The low-end high-pass filter originally had a rather too high Q for my taste. It's been tamed.

3) The bass-mid low-pass filter was rather too low Q, so I've brought this up, making the response flatter across the band - now the hand over to the tweeter is tighter. The tweeter high-pass is left unchanged.

4) The decoupling regime has been changed so as not to contaminate the local ground. Thus the original 100nF ceramics to ground from either supply rail have been moved to decouple between the positive and negative rails. Ground is thereby...
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Old

D1080 MkII 08 actives - power supply mod details

Posted 17th December 2010 at 04:34 AM by abraxalito
Updated 5th March 2012 at 03:54 AM by abraxalito

When considering how to hot rod a particular piece of electronics, my first attention always goes to power supplies and layout rather than the somewhat more popular approach of swapping out components for boutique variants. This is because so far I'm not sure that I notice the differences between audiophile grade caps (for example) and the bog standard ones. But I am sure of the differences brought about by improved grounding - to my ears these aren't subtle changes at all. So if I turn out to be dissatisfied with the sound of my layout mods, then I'll turn to tweaks on individual parts.

On examining the layouts of the two PCBs (XO layout already shown in a prior post) it turns out the amp PCB is the one with the relevant power supply components. In more detail, it has two independent supplies coming from separate windings on a standard EI-core transformer. The higher current one is unipolar, unregulated and feeding only the TDA8947s, the small-signal supply is bipolar,...
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Old

Simple PSU

Posted 16th December 2010 at 02:36 PM by ferynov
Updated 17th March 2011 at 03:32 PM by ferynov (edit)

my own Simple power supply for my own use...

For DAC Reference TDA1541+salas shunt Reg.

Click the image to open in full size.

Click the image to open in full size.

For Power Amplifier DX Blame :

Click the image to open in full size.

Click the image to open in full size.

Another small pcb for power amp too :

Click the image to open in full size.

Click the image to open in full size.

if wanna download...
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Old

D1080 MkII 08 actives - crossover schematic

Posted 15th December 2010 at 03:28 AM by abraxalito
Updated 5th March 2012 at 03:54 AM by abraxalito

Here's a somewhat simplified schematic I entered to model the response curves in LTSpice. The volume control isn't shown (as LTSpice doesn't have the symbol) but happens before the first opamp. I've fudged up symbols for the bass and treble controls - they're simply variable resistance in the HF and LF feeds to the power amp board. LT1057 isn't actually used in this unit, its just the nearest library part to the TL084

<edit> I've added the response curves now - look and weep
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Old

D1080 MkII 08 actives - under the hood

Posted 14th December 2010 at 12:46 PM by abraxalito
Updated 5th March 2012 at 03:55 AM by abraxalito

I've been spending my free time these past couple of days reverse engineering these speakers, as a prelude to devising the mods. The first stage in doing that is to photograph the PCBs both sides and have both images up on the screen at once, the underside is flipped horizontally so its as though I'm looking through the board. I then annotate the components by hand with the mouse drawing tool. Sometimes I'll write the values in this way too, other times just paste text for the value next to the component. Most of the time though I'm too lazy to add any annotation.

Here's the result for the volume/tone control PCB - one of two PCBs in the design. There are two quad opamps, TL084s - they're marked up in magenta. Interestingly there's no tone control circuitry as such, the bass and treble controls just act as volume to the woofer and tweeter respectively! I've never seen tone controls implemented in this way before...
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Old

From W Mclean

Posted 12th December 2010 at 03:37 AM by wmclean

I have an old pair of MB Quartz 850S speakers that i gave to my daughter. One of the speakers has a blown tweeter. Where can i buy a replacement tweeter ? I believe there 1" titanium dome tweeters. Thank you for any help in advance.
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Old

How low can you go in active speakers?

Posted 12th December 2010 at 12:54 AM by abraxalito
Updated 5th March 2012 at 03:57 AM by abraxalito

On one of my regular pilgrimages to the computer plaza a couple of days ago, I noticed these little puppies. The price apparently was a shade over $80 the pair so I was indeed very curious. A quick peek around the back showed they were not using a standard speaker cable, rather a custom 4-way umbilical between the two boxes. Whenever I see this, my heart misses a beat because what floats my boat is genuine active speakers, not just powered ones which still sport passive crossovers.

Click the image to open in full size.

Not wishing to ask to disassemble the powered unit on the spot (and doubtless be turned down) I went back home to do some online research. I was pleased to discover these were indeed true actives, and what's more they're powered by TDA8947 chip amps. I'd not come across this part before but its cool at least on paper because its 4 channels in one package - they're using two...
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Old

First test post to blog - general audio gear

Posted 11th December 2010 at 02:48 AM by googlyone

Couple of projects of mine - not sure if the photos will load OK.

First is a pair of 25Hz horn subs I used to have - used 18inch p.audio drivers, placed facing one another along a wall to form part of the horn and achieve adequate mouth area for the 25Hz cutoff.

Efficiency was well over 100dB/w/m.

Second photo is one of my digital crossovers I built, 4 way AD1940 based audio DSP with an AD1939 CODEC as A/D and D/A. Works a treat, and makes setting speakers up a snip, as can program in delays, HPF / LPF, parametric etc.

Also included my subwoofer couch - I built this as a challenge from a colleague of mine. The carcass of the couch forms an 800 litre enclosure, the ports exit at the back of the headrest three of them, and I used four fifteen inch drivers. It is tuned to 19Hz, and achieves a -3dB point below 20Hz.
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