That is interesting... Not sure if the large electrolytic caps are for decoupling though, the smaller 1000uf ones on each rail don't have safety valves and I assume are polymer?
Soren, are the changes an enhancement?
What changes ? and compared to what ?
On the dam1941, the electrolytic capacitors on vrefs are polymer.
Major differences of 1941 compared to 1021?... Sorry "changes" was not the right description.
Or fake polymers that are actually electrolytic and ready for a really big bang when it fails.
Quick question... Where should I insert caps at the oscillator...? Thanks so much!
Sorry if that was insensitive... I meant where/how to best install an additional cap at the oscillator without completely destroying the board, if I were to venture such a mod...
I think it was maybe sometime last year that I realized none of this would be recommended by Soren anyways... There’s no right or wrong here only trade offs. I believe Soren’s judgement has made possible such an interesting and financially accessible project for everyone here, and inspired a bunch of other (very similar) products. As to whether I’m taking too much risk and also wasting my time, I’m not sure... but I hope not...
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That was the plan... just have a couple of tweaks and fixes that I need to make to the build and I probably won’t open it again for a while, hopefully. The decision to do the vref mod was only made yesterday with the info from living sounds and a re-evaluation of other available info. I bought the caps but might give up if it’s too risky (two 1021 not well stacked to allow easy disassembly). I was searching for output filter and vref stuff and came across jacklee’s report on oscillator cap. I figured my 1500uf polymer cap might work for that too and shouldn’t be that much extra work so why not...
Replacing LDOs with regs $50 a pop is probably too far for me, as tempting as it obviously is...Plus my build is probably too compact for it to work well.
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Well - after downgrading to 1.16 the problem seems to be gone - I cannot say for sure, but I have now had five hours without the noise. @Soekris, if you are interested in a board that apparently creates problem with 1.19 I have one, in Roskilde, Denmark that I can offer you to play with. It is version 3 - I also have a version four that gives no problem with 1.19.
PM me if you are interested in that.
PM me if you are interested in that.
henrylarsen;5640958i said:
I Repeat:
I can only recommend to supply any power on J1, the diode bridge used on the input is a low noise schottky type.
J2 is NOT for supplying power, it's for testing or for sourcing small amount of power for external input circuits. Applying power will probably blow the board.
If you insist to improve the onboard power supply, try replacing the 6 electrolytic capacitors with aluminum polymer types, 1000u 16V exist in same 10mm smd footprint and t.ex. digikey stock them at $2.20 each. Should be easy to replace.
You can also add a small polymer electrolyt on the 3.3V output, but please note that the clock oscillator power already have a filter, so I doubt it will make any difference.
But on the other hand, just go ahead, I'll be happy to sell you a couple of new boards
Decided not to go for the 3.3v cap mod - no vias for it on rev4 which multiplies the risk and difficulty. Also the section seems, to a layman, much less important than the vref, at least in r2r. I take the SI514 and no vias to be hints from Soren that vref mod is more important, though he would certainly deny that he recommends it. (hope no one is offended...)
Theoretically, are the electrolytic caps (and regs) polluting good DC power? Or are they more or less harmless and provide extra AC input functionality as I assumed...? Just ever so slightly concerned after reading comments claiming AC input measures better and cascading regulators is an evil. Thanks!
So to the sound. I have to admit, that I have not listened to my other modifications a) as I had not always enough parts lying around to modify all rails. b) I was very tight in time and only did the full modification for the most promising version. So I compare only with the unmodified DAM.
I currently only can listen with my headphone (an "vintage" Stax Lambda Pro + SRM1 Mk2). First observation is, with high sample rate recordings, the unmodded DAM and this headphone I sooner or later got some kind of headache. With the modded version this seems to be gone! I suspect that either that 39kHz noise hump either caused distortions it the head phone amp or this high frequency junk in the signal wereas transmitted to well to the ear and although inaudible caused some pain. So good point
This reminds me of my experience with dam1021 last year (before I shorted my PSU...) - with an adapted sigma22 PSU the system gave me “headaches” (harsh sounding?). Everything else equal, Salas UltraBiB gave me no such impression and I’ve been listening for a couple of weeks. Didn’t think much of it at first since there’s a lot on my mind but maybe this is useful information for some.
That sounds kind of worrying. It’s not specific to this device (though modding could damage components). Some components can fail silently and this means that all we really can rely on to keep our equipment well-functioning is our ears... and statistical intervals...
Right maybe that was the problem... I was kind of assuming that Soren might help you diagnose the crackling noise. The worry, which is much more general and maybe excessive, is that of inevitable and sometimes premature component failure. Polymer caps in particular seem more like to fail without any apparent symptom...
You don't need to add caps directly where the clock is, just clean up the 3v3 rail with a capacitor installed in the FPGA jtag header pins (gnd and 3v3 is there), and upgrade the 3v3 ldo regulator. As for how it sounds, it certainly didn't make anything worse, but unfortunately I did some other mods at the time, yes there was a noticeable improvement, but I also removed the buffers+lowpass cap at that point. I have never used the buffers in the dual-mono build but only now got around to removing them.
Thanks for the recommendations! Your build is a dream to dual-mono users...! Is there a recommended capacitance for this, could a 1500uF polymer cap be too large? Also, is there a possible drop-in for the LDO or only external options are available/significant as an upgrade?