diyAudio - Blog Entries
Go Back   Home > Forums > Blogs

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Old

D1080 Mk II 08 actives - XO mods

Posted 23rd December 2010 at 11:21 AM by abraxalito
Updated 5th March 2012 at 02:53 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...
Attached Thumbnails
Click image for larger version

Name:	D1080_modded.png
Views:	1062
Size:	66.0 KB
ID:	304   Click image for larger version

Name:	D1080_moddedfr.png
Views:	797
Size:	16.2 KB
ID:	305   Click image for larger version

Name:	D1080 XO modsJPG.jpg
Views:	1014
Size:	818.4 KB
ID:	306  
abraxalito's Avatar
diyAudio Member
Views 1177 Comments 0 abraxalito is offline
Old

D1080 MkII 08 actives - power supply mod details

Posted 17th December 2010 at 03:34 AM by abraxalito
Updated 5th March 2012 at 02:54 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,...
Attached Thumbnails
Click image for larger version

Name:	P1010001.JPG
Views:	1373
Size:	671.9 KB
ID:	303  
abraxalito's Avatar
diyAudio Member
Views 1330 Comments 0 abraxalito is offline
Old

Simple PSU

Posted 16th December 2010 at 01:36 PM by ferynov
Updated 17th March 2011 at 02:32 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...
ferynov's Avatar
diyAudio Member
Posted in Uncategorized
Views 1717 Comments 2 ferynov is offline
Old

Guitar Amps...

Posted 15th December 2010 at 04:38 PM by chris661

Now then (does that make sense?).

Today, I played a small gig at a college (6th form) talent show. Maybe 100 people or so in the audience.

So, some background... I bought an old, faulty guitar amp off ebay. A resistor (1/2 watt one) had burned, as well as one of the output stage transistors. This had got hot enough to short one of the rails to the speaker output. This killed off the vintage Celestion driver in there. Lovely. Next up, the power supply was under-done. The mains transformer had been replaced before I'd got it (odd screws used to hold it in), and the old 2,200uF caps failed to meet half that value. The rectifier was a small chip, stood on the circuit board.

So, using a spare Eminence driver (modified Alpha 10 - felt dustcap, looser suspension), I fired it up, hoping there was some life in it. Life, there was. Lots of volts DC on the output, with a 100Hz buzz on top of that. Needless to say, I switched it off again.
Replaced...
chris661's Avatar
diyAudio Member
Posted in Uncategorized
Views 994 Comments 1 chris661 is offline
Old

D1080 MkII 08 actives - crossover schematic

Posted 15th December 2010 at 02:28 AM by abraxalito
Updated 5th March 2012 at 02:54 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
Attached Thumbnails
Click image for larger version

Name:	D1080 XO.png
Views:	1755
Size:	66.3 KB
ID:	300   Click image for larger version

Name:	D1080 response.png
Views:	391
Size:	16.2 KB
ID:	301   Click image for larger version

Name:	d1080 respa.png
Views:	377
Size:	14.6 KB
ID:	302  
abraxalito's Avatar
diyAudio Member
Views 1821 Comments 0 abraxalito is offline
Old

D1080 MkII 08 actives - under the hood

Posted 14th December 2010 at 11:46 AM by abraxalito
Updated 5th March 2012 at 02:55 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...
Attached Thumbnails
Click image for larger version

Name:	d1080-tone ctrl.JPG
Views:	1870
Size:	864.1 KB
ID:	299  
abraxalito's Avatar
diyAudio Member
Views 985 Comments 2 abraxalito is offline
Old

From W Mclean

Posted 12th December 2010 at 02:37 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.
diyAudio Member
Posted in Uncategorized
Views 359 Comments 0 wmclean is offline
Old

How low can you go in active speakers?

Posted 11th December 2010 at 11:54 PM by abraxalito
Updated 5th March 2012 at 02:57 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...
abraxalito's Avatar
diyAudio Member
Views 921 Comments 1 abraxalito is offline
Old

Subwoofers...

Posted 11th December 2010 at 07:53 PM by chris661

Well, here we are again (unless, of course, you're here by mistake).

After much contemplation, I've decided that my subwoofer needs upgrading. Currently, it's a pair of MCM DVC woofers (you will probably have seen me going on and on about them), which, while good for the price, aren't that good compared to my Fostexes (which, now fully broken in, are fantastic). They're given ~100w between them, with a Linkwitz Transform to get them down low. Good for normal listening levels, but quickly run out of displacement below 40Hz at anything about normal listening levels.

So, a new bass system is in order. I've always wanted to try a Tapped Horn, so I've chosen a design originally intended for an Exodus 6.5" midbass, that's shown to work pretty well with the Tang Band 6.5" subwoofer... All the way down to 25Hz. Those will be fed by an amp1-b from 41Hz, with a +/-34V supply. Should be more than 100w per side. Ca suffice, especially for a bedroom system ...
chris661's Avatar
diyAudio Member
Posted in Uncategorized
Views 720 Comments 0 chris661 is offline
Old

First test post to blog - general audio gear

Posted 11th December 2010 at 01:48 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.
Attached Thumbnails
Click image for larger version

Name:	DSC07940.jpg
Views:	580
Size:	441.4 KB
ID:	295   Click image for larger version

Name:	DSC04938.jpg
Views:	385
Size:	336.1 KB
ID:	296   Click image for larger version

Name:	Resize of DSC00397.JPG
Views:	341
Size:	65.7 KB
ID:	297   Click image for larger version

Name:	sub couch drivers in.JPG
Views:	1273
Size:	45.9 KB
ID:	298  
diyAudio Member
Posted in Uncategorized
Views 754 Comments 0 googlyone is offline
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 04:40 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2