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Class D Switching Power Amplifiers and Power D/A conversion

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Old 12th November 2010, 10:31 AM   #1
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Location: Coventry
Default Advice for/questions from a complete noob to amplifier DIY.

Hi guys.

I am currently doing a lot of trolling and reading regarding DIY audio.

My main interest is in diy loudspeakers. I ultimately intend to build three way speakers and probably augment these with subwoofers at a later date. My main inspiration for these is Troels Gravens Jensen 1071 and the Focal designs that use separate boxes for the tweet, mid and woofers. I would like deep, full bass that is tight and fast, powerful and accurate mids and sweet highs (wouldn't we all?). I would probably use scanspeak revealator drivers throughout (as Troels design but with the revealator ring radiator tweeters) but know that changing any aspect of the design will affect the crossover (something which I don't have the ability to design myself in passive format). They will be made using the cnc translaminate method.

As I am currently on a limited budget and realise that throwing a huge wad of money at a project when you are just starting out is foolish, I am first going to build a similar design with more traditional boxes and using the Peerless CSX-176H (800122) mids, Scanspeak 2905/9000 (sticky dome) tweeters and the odds and sods I already have (things like speaker wire, binding posts etc). This leaves me needing woofers, which will probably be the Peerless SLS-263 as they are cheap and seem like good drivers for the job.

To get over both the cost and the immense difficulty of building passive cross-overs for such a design, I want to use two minidsp modules in 4-way advanced crossover configuration. This leads me into needing 6 channels of power amplification - hence this (seemingly rambling!) post......

I have been looking at the BK electronics Mosfet class A/B amp modules they sell. These have a good reputation and for a complete electronics novice (with a mechanical engineering degree, for what it is worth!) like myself, little required expertise. I would simply need to box them, add power and input/output plugs and away I'd go. I am still a little confused about gain structure but I am getting there..

In my quest for cheap, quality amplification I have begun to look at your class-d projects.

I would like to build something along the lines of: One large, or three middle sized Hi-Fi width boxes containing 2 * 50-100 watt, 2 * 100-150 watt and 2 * 200-300 watt power amplifiers. These would need to accept input from the MiniDSP boards (either rev 1,2 or balanced, whichever would suit me best). I would want that much power not for absolute volume, but for head-room and upgradeability. A bit less certainly wouldn't be the end of the world as I do have neighbours on both sides!

I intend to use the pre-amplifier on my Dennon AVC A-10SE (old, but an awesome AVR) so attenuation will be done before the DSP units. I know the DSP modules can be fitted with a pot to control the output so this too is an option.

Now you have my back-ground I would like to ask a few questions: I am slowly getting there but need to ask some basic questions as A: I have very limited knowledge of electronics, and B: there is HUGE ammounts of info out there and I am having trouble finding answers to my simple (noob) questions. Apologies for the basics:

Am I right in thinking I stand a chance of DIY building class-d amps that will sound very 'hi-fi' with modules and kits? (ie, a bit of soldering, machining, matching)

Would this be cheaper than buying the BK electronics complete amp modules? (though obviously not as simple)

How would the performace (in terms of sound quality) compare between a cheap-ish class-d kit and the mosfet BK modules? (I like what some would call a 'clinical' sound, in my mind the idea of hi-fi is to reproduce the source material, not colour it)

Can you point me in the direction of any resource?

Can you make suggestions and point me to similar projects that are documented?

Can you forgive the up-coming barage of basic questions that I will have as I start to purchase parts for my 'winter project' (mu summer project is always my E30 BMW fitted with an E36 M3 Evo engine and MCoupe running gear....).

Kind regards,

Jai Stanley
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Old 12th November 2010, 06:03 PM   #2
gooki is offline gooki  New Zealand
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If you get a dual voice coil 4ohm sub, you could probably use the a 4x100 watt Sure Electroncis class d module for each side.

This would give you up to:
100 watts for the tweeter
100 watts for the mid
2x100 watts for the subwoofer

Price all up would be around $200 inc power supplies.

http://www.sureelectronics.net/goods.php?id=1102
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Old 12th November 2010, 08:49 PM   #3
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Originally I wanted to build the three ways as 2.1 one ways if that makes sense.. Using peerless 10" xls subs in a sealed box, and crossed over at about 80hz (midbass sealed in a separate cabinet with a q of about 0.5. Since reading up more and learning about things like intermodular distortion (right word? - where lower frequencies distort the higher frequencies) and the ammount of energy in the midbass region I've leaned toward having the woofers crossed at about 300hz. That means the XLS subs are out and the SLS are in. They are more woofer like than subwoofer.

Finding a dual voice coil woofer (rather than a subwoofer - ie will play 300zh cleanly and not break up shortly after that) might be tricky; especially at the right price and locally.

Is there no way to bridge class D, or doesn't it work like that? I could model using two woofers, or even load them isobarically to make the effective box volume higher or reduce the size.. Hmm...

The price is very appealing though.. Is the Ł200 to get both channels (left and right) or is that per side? I shall take a look in one moment...

Thanks for the reply.

Jai
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Old 13th November 2010, 09:15 AM   #4
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Quote:
Originally Posted by jaistanley View Post
Is there no way to bridge class D, or doesn't it work like that? I could model using two woofers, or even load them isobarically to make the effective box volume higher or reduce the size.. Hmm...
Some amps can be bridged. Most can, actually, but some are "pre-bridged", like basically all the TK2050 amps and most other Tripaths – they can't be bridged further.

I'm sure you can find an amp that you can bridge, but I'm pretty sure that you won't need to. What was your goal with bridging?
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Old 13th November 2010, 10:32 AM   #5
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I was just speculating about the previous post... If I could bridge two channels of a four channel amp, it would give me two lower power and one higher power channel to run the three ways.

Another option would be to run a four channel to the tweeters and mids, left and right, then get a higher power two channel for the two woofers. No bridging or dual voice coils needed...
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Old 13th November 2010, 05:11 PM   #6
gooki is offline gooki  New Zealand
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$184 USD for both sides - i.e. 8 channels of amplification + 2x powersupplies

The class d ic's are already bridged to get them to 100watts per channel and can't be bridged further.

Quote:
Originally Posted by jaistanley View Post
Another option would be to run a four channel to the tweeters and mids, left and right, then get a higher power two channel for the two woofers. No bridging or dual voice coils needed...
Which would have been my next suggestion.

PS the sls 10 inch is only rated for 110 watts rms. So you could just get 1x4 channel module 1x2 channel module at a single power supply. Price would be around $135 USD from sure electronics.

Last edited by gooki; 13th November 2010 at 05:38 PM.
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Old 15th November 2010, 06:11 PM   #7
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I'm not too worried about running too much power to the speakers.. I've learned a little self control over the years and you can hear the kind of distortion that kills speakers a mile off.. I'd be more concerned with not having enough control, dynamic range or headroom to run speakers! Crank it up loud, go into clipping and fry something.

I've been scouring pages for a few days and have a million questions, I just need to take a step back and put a few together into a coherant post and see what you guys think.

So far (in my head) I have built a diyhifi that consists of an HTPC, USB dac/pre-amp/DSP, power amps, matching hifi rack and TV stands, subwoofers, large there way speakers and god knows what else. I need to have a dose of reality (ie, add up the costs and time it'll take to biuld them)!

The great thing about doing this DIY is that I can build in stages, replacing components whilst enjoying the music. I currently have a nice PC as a source, a nice Denon AVC-A10SE as my DAC/Pre/Power, B&W DM602s3 speakers and a cheap and cheerful Eltax 10" sub.

I'm also lucky in that my girlfriend has vito'd the idea of a massive screen, but says I can 'go nuts' on the stereo.. Awesome.
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Old 15th November 2010, 06:14 PM   #8
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Many channels of great quality amplification is surely a necessary foundation for any such ambitious project.
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Old 15th November 2010, 06:57 PM   #9
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I agree.

I first got back into the idea of DIY when I was looking for a crossover for my car. The Clarion HX-D2 has a dsp built into it, and I really wanted that head unit but couldn't afford it; so went onto the internet to look for a dsp. I chanced upon the minidsp and realised I could use one to make a fully adjustable, eq'able and time aligning active cross over for some three way speakers and stereo sub. I really like the idea of using the REW software to get the response in my front room to relatively flat from 20-20hz and keep a sealed alignment on all woofers, along with proper time alignment. Hypex are about to release a VERY promising dsp system soon, from what I have read elsewhere on this forum. I can't wait to get started (unfortunately budget means this will take me a while to finish...).

The amplification is fundamental as without it I can't utilise the minidsp at all, with it I can even power my existing speakers by taking the crossovers out and running them active two way. Four channels of amplification and one minidsp and I can begin practising and customising the sound of my system to get the best from it as is.. The amplification is the first step...

I really like the look of the Hypex UCD180's and 400's but can't stretch my budget that far (for six channels it would get very expensive to me).

Are there comparable products in terms of power and quality to be had at the cheaper end of the scale? I have been looking at the Hifimediy T2 and T3, at the modules on Connexelectronic and at the modules on 41hz in particular.

I have 8ohm drivers for the tweeter and mid, and intend to buy the 8ohm peerless sls-263 woofers. This means I need the amps to deliver good power into 8ohms (at least then as I upgrade the drive units I can choose 4ohm to get a reduction in distortion and increase in power).

I really like the look of the modu.biz cases and can see a fully matching system of various sized cases in my future. One for the HTPC, one for the amps, one for the DSP (with room to make a full pre-amp with buffer stage, input switching, DAC, 8-way attenuation (somehow!!)). Again, I'm getting completely ahead of myself!

One thing that it has done, is completely change my mind about surround. Suddenly I just want a nice stereo audiophile system again. My Denon sounds very nice at stereo, but I only use it for stereo music these days and it still only sounds very nice for an AVR; not for an audiophile system.

Last edited by jaistanley; 15th November 2010 at 06:59 PM.
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Old 15th November 2010, 07:14 PM   #10
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I can definitely vouch for the 41Hz amps. They sound simply amazing. The Tk2050-based Amp4 is ... just incredible. Definitely on par with Hypex. I'm sure there are other TK2050 implementations out there that are good too.

Definitely keep us posted as you see progress!
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