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franjam's κDCX build for non-engineers & the inexperienced

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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby amb » February 6th, 2018, 2:56 am

I doubt that it's a JFET problem, and I think you were measuring some the voltages with the red/black probes flipped. For these measurements the black probe should always be on 1, or on 3 for the "3+2" column.

Anyway, try reflowing all solder joints of U2[D-K]. Several of them exhibit higher than normal differential DC offset. Be careful not to melt the Wima capacitors with your iron tip. Also, make sure you make these measurements are done with nothing connected to the inputs or output XLR jacks.
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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby franjam » February 6th, 2018, 3:19 am

-I thought it might be a ground problem :

I took out the board, sanded the bottom screw hole for each XLR output and sanded the main earth connection from chassis to mains and put it back together. The results were inconclusive but different to those of yesterday :

Output,pin 3,pin2
1) 7, 0.3
2) -32, 38
3) 14, -7
4) 9, -3
5) -24, 30
6) 24, -18

I have also installed the switch SW1 which I hadn't in the vague hope it might make a difference and tested the resistances between the fets, (Q2,Q1) and pins 4 and 8 of U2, all is correct around 145 to 148ohms :) .
In conclusion, output 1) seems to be "cured"compared to last night, although both measurements are +ve which is curious :? , and output 4) is also within spec, as for the rest....

I don't know how to begin to explain these readings :o ...help!

EDIT: didn't see the above reply, I will try to improve U2 joints ; nothing was connected to any jacks.
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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby franjam » February 6th, 2018, 4:30 am

Ok, reflowed all U2 legs and other op-amps while I was at it,( scarred 2/3 Wima's but not badly), job looks better, no shorts I checked carefully :

Results are MUCH WORSE!! :shock: :o :roll: :cry:

Output, pin2, pin3
1) 35, -26
2) 77, -68
3) 233, -215
4) 49, -38
5) 72, -63
6) -38 45

polarity is now inverted on 6) :?

Given the incredible and impressive consistency in the measurements on all the previous test points, what on earth provokes these apparently chaotic and changeable readings? Could the problem come from a bad ribbon cable..?
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franjam's κDCX build for non-engineers & the inexperienced

Postby amb » February 6th, 2018, 7:56 am

Did you let the opamps cool completely after soldering before making these measurements?

Btw, any of the two outputs of the OPA1632 can exhibit positive or negative DC offset relative to ground. So the result of #6 is not “inverted”.

But all of the offsets are too high. Make sure the Vcom pins are all well soldered and measure 0mV on all six of the output channels.

The ribbon cable shouldn’t influence this.

Oh and of course, check to make sure they are all indeed OPA1632, not OPA1612 or OPA1611 for other positions.
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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby franjam » February 7th, 2018, 12:29 am

Ok, the problem was definitely the cable J13. Somehow the plug was not compressed straight and the the teeth were largely bent backwards. The clip was cracked but it seemed ok, however when I took it apart it was a mess. This was on kDCX side, so I was able to plunder a cable from a computer A drive and refix a plug although it was longer. All readings went to within spec except ouput 6, (which I don't use), so its probably out slightly again as it is a bit of a bodge job. I am awaiting new plug/clip today from Farnell to do the job properly.

I remember fiddling around trying to hold the clip in place and the cable perpendicular while trying to tighten the vice, I got it right 3 times out of 4 ; the video makes it look so simple but things can go wrong ; so my advice is that once you have taken the time to align clip, plug and cable, wrap a length of tape around it to keep it all tight and in place and make sure it is nice and flat against the pads of the vice on both sides before tightening. ;) .

Anyway it is up and running at last despite the various setbacks, (I have muted ouput 6), and it's the dog's bollocks, (this is a quaint English substitute for "awesooome"), I'm a happy man, :D :P :lol: ;) ;

So lots to to say, including a couple of possible adjustments/ problems to talk about, so I will go back and talk a little about this build from my point view.....

EDIT: The plug arrived from Farnell, got it right this time, with a bit of tape ;) ; all readings are well within spec at +/- 4mV! :D
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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby jrhill » February 7th, 2018, 3:17 am

Hi, newby here and wondering about the total cost of the whole set of the projects with the new 01 master clock, 78 & 79 regs, etc for a standard DCX2496
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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby amb » February 7th, 2018, 5:45 am

Great stuff franjam, I’m glad it’s all fixed.
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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby franjam » February 7th, 2018, 6:07 am

jrhill wrote:Hi, newby here and wondering about the total cost of the whole set of the projects with the new 01 master clock, 78 & 79 regs, etc for a standard DCX2496


Hi there and welcome,

The first answer depends on where you are : If you are in the US, postage is cheaper and so is Digikey which currently are the only ones to stock certain caps for the o1clock and possibly also the 078/79. Digikey cost me a bloody fortune as I had to pay tax on top plus UPS charges which they neglected to mention or I "missed".

I am in France and I paid roughly 100 euros for the kDCX, o1, o78 and o79 pcb's including postage. I got most of the initial parts from Mouser, which does free postage to europe over 50 euros, for about 200 euros. Digikey parts plus tax plus postage cost me another 100 euros but I got extra for another o1 clock, ( for the DAC section), and 5 o78s;
So the total job probably cost me close to 400 euros including a couple of extra orders from Farnell for other bits, (read my posts). I think it could probably be done for 300 euros if you're in the States and don't make too many mistakes and don't have to buy too many extra tools. ;-) .
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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby franjam » February 9th, 2018, 3:10 am

Ok i'd like to go back and go over the actual bulld which I left off on page 2 of this topic.
As I was saying , after the various SMD's came a lot of resistors, (BTW, the flux pen is indispensable and I discovered later on that if actually you press the knib the flux flows :shock: miracle! :shock: ,at least on mine , so I think the job may have been easier if i'd realised this earlier :| ). Any way for me the resistors were the tedious part, bending all the leads with the pliers, turning the pcb over without them falling out, reheating and pushing the ones that were too high off the board, (at least the worst ones), etc. Do make sure you are methodical or it will be easy to get lost. Also I was soldering at 315°C, when I turned up the heat as Ti suggested, the job got easier and a little quicker ;) .

condenser and resistors resized.jpg


I then happily moved on to the caps feeling, at least psychologically, that the job was nearly done :) . As I was following my parts printout I completed all the caps including the electrolytics ; mistake!! :|, because I then had to tape the relays to the board to solder them, even then I cocked up and soldered all the legs on the first one before realising it was off the board! :roll: So out came the solder-sucker but it wasn't easy to get it down again and it still isn't perfect. The 2 others I soldered the diagonally opposite legs until the part was flush with the pcb before finishing the rest. Moral is check sizes of parts , don't be in too much of a hurry and read /re-read Ti's instructions, he hasn't missed very much and is very complete.

resized 2.jpg


After the caps and relays the job is really nearly done, but do wait until just before the input/output sockets to solder the 6 electrolytics, as they do get in the way if you don't, I couldn't be bothered to de-solder them but I did fart around a bit with tape to get stuff done. :lol:



So once the pcb is done you have to make the cables ;) If you've read my earlier posts you will know that I had fun with this part :) ; it took me a while to realise the problem was coming from a bad cable plug, so pay attention while doing this! The video makes it look oh so simple ;) , which it is, when you don't cock it up as I did :lol: . Again my advice is use tape to hold everything in place so nothing moves when you squeeeeeeeze, ;) .

So job done, All tested good once the cable was fixed, what does it sound like? Which after all, apart from tearing your hair out when things go wrong, is the point of the exercise yes?

out with the old in with new.jpg


First I have to be honest I didn't hear instantaneous mind-blowing tears to your eyes change as I have done with certain,(but few), other mods/changes.
Things were definitely better however : one of the best changes was the absence of the high gain hiss in my tweeters. Words like : more clarity, space, cleanliness come to mind and then yes, listening more : more tuneful bass, more separation and more detail. greater breadth in the soundstage. Overall I could say that there was a general impression of more refinement in the overall sound.

This job cost me a lot more than I'd anticipated initially for various reasons , non of them the fault of AMB. Is the overall improvement worth that? That is frankly difficult to quantify, but I have also just added the o1clock to my CD player, (sic. relevant post) and the sound from my system is exquisite, so I have to say that I am very pleased with the result and with all I have learnt doing this. Especially soldering SMD's which I'd not done before. If you live in the States you will manage this job for at least 25% less than I did , so don't hesistate if you consider yourself competent , or just game :lol: It's a great design and fun to do, (apart from the resistors :P )

I'd like to thank you Ti for a great design ; you are a talented chap, and also for unfailing patience, reactivity, service and good advice, nice one man ;) .

Next will be the DSP board : o78 regulators,o1 clock and caps so watch this space, :)
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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby jrhill » February 20th, 2018, 3:00 am

Thanks franjam for your detailed reply about the costs in your post #72 a few weeks ago - the notification was delayed a bit and I missed the link - sorry, didn't intentionally ignore your efforts

We don't do too badly for freight costs out of the US - Digikey isn't so good as there's usually an excessive handling fee involved but .... Mouser's pretty good and Farnell's are their usual high prices like RS - I was guessing about the A$600 for the lot of the boards plus maybe a separate supply board for the new clock so this is currently about your 400Eu mark.

I have the Selectronic version here (phono jack on outputs 1 - 6) that has a problem with selecting the inputs A & B (the input C works okay and the unit/programs are functioning okay) so in my ignorance, dropped it off to our local tech to check - in the meantime, I'm learning about the unit and this new series of pcbs

I have some studying to do yet but I think I might get a new/2nd hand basic unit and develop the full set of upgrades from scratch, plus do the adc/dac changeups as well.

There is a relatively new device here in Oz called the Audio Precision (from Sydney) that has a basic set of modules for somewhere in the vicinity of A$3k (about Eu 1800) - in comparison, the new AMB boards/kits plus the stock Berhinger is much more viable plus learning thru building the unit from the ground up

Thanks for your posts - very clear at showing your progress and your 'mistakes' are invaluable. ... James
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