DIY digital PWM amp project

I wonder if it would be advisable to use screened cable between the input and the board? There's a lot of RF spraying about inside the case, which may or may not matter. Or possibly run the unscreened wires closer together.

I guess you won't see any problem without an oscilloscope, so out of sight etc...

Paul

 

This is true paul, although braiding the three input wires together will also get the ground to act as a bit of a screen for the other two wires. Also trimming the lengths down somewhat could help too.

 

I wondered about braiding the three input wires together....damn, they are a real bastard to solder and un-solder off the board

What about wrapping the wires in aluminium foil?

Still - I've just spent the first 10 minutes listening to it at decent levels and it's sounding pretty spectactular . I could go on tweaking it for ever and never listen to it properly....

Michael.

 

Any pictures of the unit from the front ?

 

I'll take some more pictures inside and out, maybe later today but for now here's my updated "system" picture with the amp fitting in nicely :



Since the case has no feet I've had to nick the Michell "Tenderfeet" (shallow metal cones) off the DAC64 (where I was only using them in an attempt to aid cooling rather than any sonic benefit) and use them under the amp where they work well (as feet - don't know about any sonic effects).

Michael.

 

Nice

 

Pretty elegant looking setup. But you need another shelf with a TT on it really.

-- Ian

 

I knew you'd say that Ian .

I wonder how I'd make a TT cat resistant? It would have to have a cover for starters, which would have to be able to withstand a cat jumping on it, and if that happened whilst a record was playing it would ideally have to be able to handle that without creating a nice radial groove in the LP

Michael.

 

So will you have your ears on tonight then Michael?

regards,
Rob.

 

Might be listening to a bit of music tonight, yes .

Here are a couple more pics which I posted over on diyAudio.com:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=33832

Closeup of one of the modules in action:


Different shot of the amp with the lid off:


Michael.

 

More, more, Michael!

Would the 800VA and supply be enough to properly run 4 channels?

I notice lc state "We recommend a transformer of 2 X 42 V AC secondary, 500 VA to drive 2 - 4 ZAPpulse modules. " But do you think 4 modules would benefit from a supply per pair like you have used?

Would cooling become an issue such a case for 4 modules?

I'm thinking of active bi-amping. In theory I've read that I wouldn't benefit from the back cap SE's for the two bass channels?

I'd probably work out not too costly, as I could then sell on my pair of 2-ch THX Ultra power-amps currently driving my Linns.

My ideal would be to pre-plan the case to allow up to 8 modules to be incremetally installed, to also drive the other 4-channels in an AV system.

Do I assume the 5th module onwards goes in parallel off the psu?

regards,
Rob.

 

It depends. They recommend 500VA for 2-4 channels but IMO that's a bit low, which is why I went for 800VA for just two channels.

I think for 4 modules you could use the same PSU but I'd use at least 800VA for the xformer, probably 1000VA. It all depends how high you want to crank them up.

I don't think cooling is really an issue. The modules really only get luke warm, nothing to worry about. As long as you have them bolted to the bottom of the case that will give them plenty of heatsinking.

As for bi-amping, yes, they suggest you can manage with the non "SE" modules (who's only difference is that they don't use Black Gate caps on the output) for the bass but if it were me, I'd go for SEs all round, otherwise it would just bug me. Silly probably but there you go!

That PSU can run upto 8 modules in theory, the 5th to 8th modules would be connected in parallel off the PSU. I think that running 8 modules off one PSU at, say 200Wpc would need a monster xformer in order to be any good though.

I had in mind originally (and there's enough space there) to maybe add a 3rd module to run the centre channel in my AV system but now I've finished I don't know if I could ever be arsed to dismantle it and drill the holes etc for a 3rd module. I guess I really should have done that to start with and blanked them off. Also, I'd rather not muddy the waters of my stereo system with AV bits. Will now probably build a 3ch. amp for the centre and rears, but not for a while

Michael.

 

Thanks Michael,
What I'd probably do is pre-drill holes for 4 zap cards, try two first,
It strikes me it makes sense to pre-drill holes for mounts and connections for 4 zap modules, even if only initially going 2-channel. However this is only after reading your good notes.

Out of interest, what made you go for the rs 800VA as opposed to the 1000VA for only £5 more and just a bit taller?

Thinking about it paralleling the modules might be a bit of a pain for neatness, so 4 per psu is a sweet spot, although it would mean doubling the psu, xformer and iec costs.

One 4-ch amp can initially bi-amp the front mains, then once confidence and funds are available, a duplicate 4-ch could run the bi-amp trebles, starting with just one single module for running center, if it's such a leap from what I run now, as it sounds it might be.
e.g.
amp1:
Front left bass
Surr left
Surr right
Front right bass

amp2:
Front Center
Front left treble
Rear Center
Front right treble

This would ensure no psu interaction between the 1000VA for bass and 1000VA for treble with 2-channel music.

Hmm. 4-channels seems a strangely sensible number, although I'd probably plan one of the amps to become 5-channels to (passive) bi-amp the front center channel and to make it useable and re-saleable as a 5-channel 250wpc amp in it's own right.

I found this quite an interesting pwm history: http://www.psaudio.com/articles/sdat.asp
Review of the ps audio 500Khz design: http://www.hometheaterhifi.com/volume_9_2/ps-audio-hca-2-power-amplifier-6-2002.html
Also a stereotimes review of the Bel Canto eVo detailing class-T v.s. class-D http://www.stereotimes.com/amp102300.shtm

Any thoughts appreciated.
regards,
Rob.

 

I don't know really, I guess I thought it would be overkill.

If I build a second, 3ch, amp I'll probably go for a 1000VA xformer.

4ch. is probably as much as you'd want in a single box. Another thing worth remembering is that LC Audio recommend syncing the modules off an external clock if you're going to run "several" channels in the same enclosure to improve sound quality and reduce "EMC noise". They don't specifiy what they mean by "several".

The modules occilate at a natural switching frequency of about 490kHz but they do have a sync input so you can drive them from an external clock at any frequency from 250kHz to 1Mhz. Naturally they suggest that their own LClock XO3 is perfect for the job

Michael.

 

BTW, do you have a copy of the ZAPPulse "cookbook"? It has loads of useful information on using the modules, tech. specs etc.

I have the version for the 2.1 modules but most of it is the same (as for the newer modules). I was just looking for a link on the site and it looks like they've pulled it because they are about to release the English version of the updated (for 2.2) manual. If you can read Danish then the Danish version is here: http://www.lightball.dk/download/dk/pdf/zp22mat.pdf

Michael.

 

No Danish here I'm afraid. I had read the 2.1 cookbook, but obviously not closely enough.

"Our V4P power Supply board is perfect for multichannel amplifiers, as it has connection for up to 8 channels. For
normal use one 500 VA transformer is enough to drive 5 channels of 200 Watts RMS (total 1000 Watts Audio Power) because there is no thermal loss in the amplifiers, and even if the power at clipping level is 1000 Watts total, the average power cointent of a
signal integrated over a period of ½ hour (thermal time constant of the transformer), is only less than 50%. A complete 5 ch. 200 Watts can be built for around 1500 USD."

To my amature eyes;
5x200W = 1000 /0.95 = 1052W supply.
But factoring in their <50% average music power is how they get the 500VA to roughly fit.

4x200W = 800 /0.95 = 842W supply.

Bearing in mind these are reported to be about about 2.7x more efficient than Class AB, i.e. 800VA is similar to 2160VA for Class AB?

It gets more tricky, as my Linn Keilidh bass drivers pair to 4ohm loads while the trebles are 8ohms.

Lets face it I won't be running at max 230W+438W in to each speaker when I'm in the room. It's just balancing peak v.s. average power needs I guess.

[Edit:]
Just noticed on the zap zp2 page:
"(Recommended transformer for
2 x 200 Watts RMS: 2 X 42 V AC 400 VA,
or for
2 x 290 Watts RMS: 2 x 50 V AC 600 VA). "


regards,
Rob.

 

I think if I was to have a go at building one of these I would probably NOT buy the LCAudio psu and go for monoblocks. Probably use a 200 VA transformer per channel and simple hexfred rectifier with 2 biggish (47,000 uF) caps bypassed by Black Gate 'N' and then silver mica and that's it.

What is great is that with boards like the LC and Tripaths own eval boards it is easier to make one of these than any other amp I know of.

Again well done Michael for showing it is possible with a very nice looking example. Mine would look a lot more 'industrial'

 

Thanks Lee I tried to get mine to look as much like a "professional" product as I could.

Having listened to it for a few days now I think it's safe to say that this amp is easily the biggest improvement in my system since I got the DAC64. The overall sound is just so much more lively and believable than it was before. I'm very happy with it and the satisfaction you get from looking at your amp and thinking "I made that" is unbeatable

Michael.

 

That's what DIY is all about.

I may check out some of the cheaper boards from profusion, which with the addition of a 5v supply and a couple of bigger caps would virtually slot into my Gainclone box.

 

Michael,

how would you rate the relative merits of your pre and power amp? I'm alittle surprised you put so much emphasis on the merits of the power amp.