Any chance of a diagram Leo.
just in case i get bored one evening.
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Any chance of a diagram Leo.
just in case i get bored one evening.
http://i374.photobucket.com/albums/o.../WithTants.jpg
Hi,
Legs a little shorter.
Considering the components have had very little burn-in time its sounding rather good. Its a little bit bright at the moment but I guess this will settle down with time. Bass is still a little shy.
Richard
Richard.
The surface mounts are the bypass caps, in most cases anyway.
Most of the electrolytics are already bypassed with an adjacent surface mount cap. Its these we are trying to improve, on as much as anything.
http://www.lampizator.eu/LAMPIZATOR/...RA/schemat.jpg
I 've bypassed the surface mounts with a variety of 0.1uf poly caps which are hopefully better quality. This now means the lytics have bypass caps of 0.22. I could have added some 0.01uf as well, but space is tight.
I can't remember much about the burn in except that it didn't seem to change much after a few hours constant use. It's quite some time since i first fired it up.
I have a few questions…
I intend to house the DAC pcb and transformer/power supply in separate aluminium enclosures. I have some 4 pole Speakon connectors and five core mains cable for the umbilical. Can I combine the analogue and digital grounds together?
http://i374.photobucket.com/albums/o...nconnector.jpg
http://i374.photobucket.com/albums/o...connector2.jpg
http://i374.photobucket.com/albums/o...owersupply.jpg
I also have some light weight coax for connecting a coax socket to the pcb. Will this be ok?
http://i374.photobucket.com/albums/o...photo/coax.jpg
Leo said the LM4562 needs a lot of tweaking for it to sound half decent. Will it sound better than the stock opamp without tweaks?
Thanks
Richard
p.s I am available for hand modelling if anyone is interested ;)
It was cobbled together from various circuits so I'll have to try and draw it outQuote:
Originally Posted by alb
Basically a centre tapped transformer, centre tap as ground, both the secondaries go to a MBR20200 double schottky, 2200uf- 1R resistor - 2200uf- cap multiplier-shunt
Cap multiplier is based on this http://www.pinkfishmedia.net/forum/s...ad.php?t=39990
Shunt uses a transistor as a current source
I might seperate the 3.3v supply on the dac board and feed it its own shunt, I don't like the layout of this dac, also the fact that the main 5v is too far away from the circuit
The LM4562 is a double edged sword, it offers good performance but only when used with care, its also crap at driving capactive loads, it needs a really good clean low impedance supply to work its best , ideally regulation needs to be close not run from lengths of cable which will likely result in a thin sterile sound.Quote:
Originally Posted by Tripmaster
Basically a slower lower spec op-amp may be better and easier to use
The dacs analogue and digital grounds are all on the same ground plane on the dacs pcb, normally best to keep the ground impedance as low as possisble , I'd personally run them all separate from the regulated PSU to the dac board, you can try running all together but it may sound worse
I don't have one of those supplies, do the ground wires from that supply have separate grounds or are they just fed from a ground plane same way as the dac board? if the regulated psu has a single ground plane for both supplies multiple/separate ground wires to the dac probably won't make any difference, if that makes sense:)
Nice pics BTW, pin sharp on my monitor!
Hi LeoQuote:
Originally Posted by leo
Thanks for your reply.
Here is a picture of the rough layout I am proposing. Please ignore the cables in the picture.
http://i374.photobucket.com/albums/o.../DACLayout.jpg
I plan to run all signal cables along the top and power along the bottom of the picture. In your previous reply you suggested keeping the power supply close to the DAC pcb. Am I going to suffer any RFI with this configuration? If this is OK I intend to mount the transformer in a separate enclosure with mains umbilical between the two.
Which opamp do you think works best for this project?
Picture not so good this time ;(
Thanks
Richard
It should be ok, try not to have the lead from the transformer too long either if possible, its normally a transformer when run too close to signal that causes noise pick up, toroidals radiate more crap
What I'd do if possible is before drilling holes etc in the case try to run it as you intend to lay it out first, obviously you have to be careful not to short anything etc, if it sounds ok then you can then start bolting things together.
Using shielded cables for the signals should also help prevent unwanted noise pick up, having unshielded signal cable running close to supply cable as you know can give hum
Regarding the best op-amp, I've honestly no idea, they tend to be a personal taste thing, I mainly use AD826 because of its good output drive, its also much harder to implement than the LM4562 though
OPA2111 sounds ok and usually behaves, some people like OPA2107, opa2132 AD8066 and AD8620, the last two are smd so need to be fitted on brown adaptors, they also have a max voltage of +/-12v
The fet input based ones sound smoother if thats what you want
I have now added leads to allow using optional valve output stage, something I'm still messing about with:)
Hi Tripmaster, just wondering what are those 2 black caps for? Could you explain your setup basically? I have done similar job, but still waiting to get Vishay for c9 . My board's analog part is intact, all I will be doing is remove those e-lytes after digital and steal signal for my lampizator tube stage.Quote:
Originally Posted by Tripmaster
Just interested in your approach...and those 2 black caps :)
Hi!
I just want to thank for all the great help I found here.
Just for fun I did a measurement of my Lawrence DAC before I started modding.
This is the frequency measurement before doing anything.
http://img.skitch.com/20080924-pp4n2...nsg4npqr64.jpg
As you can see, the -3db point is at 13.000hz!
After changing out the resistors to the same value and then changing C32, C33, C34, C35 to 150pF it now looked like this!
http://img.skitch.com/20080924-kjb48...ftc4srp1et.jpg
And it sound great! My wife said that it sounded better than my extensivly modified Zero DAC. And I have to agree. Next step, better opamp and modify the power supply.
Thanks guys for the help!