el cheapo DAC

[ramdog2004]

I'm making a cdplayer from a cdrom - but wanted to use the cdrom digital out so I can connect it to a dac.

[insomniac]

Ramdog

The info in thread below may be helpful in what you are planning:

rockgrotto.proboards39.com/index.cgi?action=display&board=talk&thread=3328&page=1

Reply #10 has links to CD-ROM TTL level > S/PDIF conversion circuits.

[rickcr42]

looking at the diagram the power supply is a little cheap and cheerful no seperation between digital and analogue likely worth a look at.

even when you do see this "separation" you rarely see it done RIGHT.

for instance the DAI section (Digital Audio Interface better known as the "receiver").It is rare to see the powering and grounding seprated into the analog and digitl sections yet if you look at the CS8412 (for example) it is CLEAR there is an analog section of this "digital" chip.

My personal take,one that has proven to be suitable in my own attempts is to use a single DC power bus as the overall DCdistribution point (usually a regulated +8 volts unless the chips need both polarities in which case +/- 8VDC regulated) then "post" regulation for each stage in combination with decoupling networks.

If you think of thsi as a "DC Grid" much like your power companies "AC Power Grid" you get the power feed from a central point which is then split off to each "building" (circuit module) and like with all the crosstalk and crap on your mains which requires you to isolate and filter various componants in your system,each "block" with it own needs (amps different from premps different from digital etc) you provide each section with the power it needs,clan it up (coupling/bypassing) and iolate it from other sections (decoupling).This keeps down cost but more importantly complexity which more often than not causes more problems than it cures.At least for me it does

[leo]

Jan 27, 2009 13:08:46 GMT robertkd said:

Hi Leo,

whats the concern with the i/p selector jitter/clock recovery?

looking at the diagram the power supply is a little cheap and cheerful no seperation between digital and analogue likely worth a look at.

Robert

Hi Robert,

I missed out capacitors regarding the PLL filter.
The receiver is also an important part, using poor quality/wrong type components can add an unpleasant signature.

All these little things can add up if done poorly resulting in bad sound

Leo

[Deleted]

I personally can't stand those green and blue Wima FKP caps, I've used those before in filtering and found them to have issues in the high frequencies, low inductive film types are better.
- Leo

This morning I replaced the 2 x green Wima 2n2, and the 4 x Wima 1n0, with Wima MKP capacitors. The sound is quite a bit improved. I am still using the 12V SMPS at this stage. You may need to carefully use something like a .8mm PCB drill bit (manually,not high speed !) to clear the residual solder out of the holes. Could also be that this particular roll of Gootwick hasn't got quite as much flux as normal.
SandyK

[robertkd]

Well the price you pay living so far from civilization, yes it arrived!

pressed into service with an old nokia 12V (and yes a SMPSU!) phone charger and surprisingly not to bad using optical in, it's definitely not better then the Onkyo AV receiver or even as a source for the SCHA I don't think it's as good as the Macs analogue out (I'm using the Mac's optical out to feed it!) but now it's time for fun

Robert

[pagan]

Jan 28, 2009 1:20:01 GMT @sandyk said:

You may need to carefully use something like a .8mm PCB drill bit (manually,not high speed !) to clear the residual solder out of the holes.
SandyK

Alex
I use a small plastic hand drill, got it from Altronics. IIRC

Allan

Don't remember where i got it
But it looks like this.
listings.maplin.co.uk/cheap_uk_dnsty/Buy_this_Miniature_Hand_Drill_cheap_online_219907.htm

[Deleted]

Allan
I use a PCB Drill Chuck with a .8mm drill bit. (Jaycar) It's slow, but much safer.
Alex

[robertkd]

Hey Guys and Girls there back

cgi.ebay.com/Mini-SPDIF-OPTICAL-DAC-Board-PCM1793-DIR9001-OPA2134_W0QQitemZ290293551672QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item290293551672&_trksid=p4634.c0.m14

I think there pretty good out of the box, rolled opa2604 into output op amp , Alex and I have some mods in mind to do with PSU, Leo has some good advice for PLL and other tweaks, but you gotta start somewhere if your looking for a spdif/toslink DAC this is a reasonable starting point. worth a look

Robert

[robertkd]

Well how low can they go?

cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWNX:IT&item=180324780197

with a case well okay but this is getting cheaper

very much the same from the photos some (maybe) different caps in the analogue output stage.

Also be aware the module will only handle up to 96Ks/sec due to the receiver limitation.

ATM I have RF out of my sub $20 DVD/CD (Palsonic DVD2040) into the module then into SCHA (the only one without LJH it woud seem ) and seriously great bang for buck factor


PS
also note the case orientation, whops wrong way around ,.. mm screwdriver 30 seconds fixed

[robertkd]

As I say cheap and cheerful also be aware the module is limited to only 96K due to the DIR9001.

Whilst a wall wart will work for PSU both Alex and I are considering modifications to PSU and other improvements as well Leo has suggested other modifications such as capacitor swap outs all of which should inch some improvements form the beast

Robert

[robertkd]

Well finally making a start on this unit

[Deleted]

Robert
All I have done on mine so far is fit polyprops around the I.C, where appropiate.
Try removing the RCA sockets !
Alex

[robertkd]

Ok now running on a dual rail PSU sounding Ok need to let capacitors form for a few days. currently running +/- 8V supplies



Alex as for the RCA's

no problemo,... surgical application of this, just don't expect to use the RCA's after

[robertkd]

Well it's certainly working very well despite my best efforts to the contrary

so far the spoils of war



mmm the i/p select switch didn't make it

changes thus far

set to work with dual supply @ +/- 8V draws 75mA on + and 10mA on - supplies

replaced
VCO filter caps with PP's as specified in DIR9001
VCOM with PP 1Uf

supply bypass
470uF 16V
100uF 35V

Buffer/Filter now sports an OPA2604 still need to look at filter (slight tweak on i/p filter caps so far!)

10uF Tants on +/- of op amp


the unit is locked to 128fs via PSCK1 && PSCK0 = Low, so be interesting, all I need to do is be able to see the tracks so I can attack this to see what effect reduced jitter might have

one outstanding item to complete, add additional series R with that pesky blue power indicator LED ;D

a very similar unit is available for $49USD with a case this one sports a blue PCB and some differences in PCB details the red PCB seems to have made a little more effort in ground plane layout and some different "better" components, they both sound quite good but I think I perfer the red PCB version albeit at $67USD without a case and $80USD with case,...

mmm blue pill, red pill your choice, I'd go the red


and the cases the silver unit is slightly better finished vs the black (cheaper) unit which is a little poor in metal work and only two out of four screws in the front panel



out of the box at 44.1 they both sound reasonably good, even with a 12V SMPSU aka Nokia 2110 charger

Robert

[Deleted]

Robert
I am not surprised at your choice of +-8V rails.
Any higher than +-8v and the 3.3V and 5V regs could get too hot. I am surprised that the 5V rail was actually regulating (?)with a 12V input. The series diode would have dropped the input to 11.4V. The rail splitter would have supplied it with around 5.7V. That is LOW, even for a LDO regulator.
Mine will be built into a small case with toroidal transformer and dual reg PCB set to +-7.5-8V.
I need to get a lower voltage toroidal as the regs (317/337) will run too hot with a 12-0-12 or 15-0-15 toroidal.
Alex

[robertkd]

Alex,

well they are LVD but

yes +/-8V is more then twice peak output swing and fits nicely with the transformer

ok on the transformer, I have gone the DSE M2854 12-0-12 @150ma

neg supply would disparate sod all and pos less then .75W ;D

and a sign of the times these little transformers are a "clearance" items

Robert

[Deleted]

Feb 22, 2009 10:42:11 GMT robertkd said:

Alex,

well they are LVD but

yes +/-8V is more then twice peak output swing and fits nicely with the transformer

ok on the transformer, I have gone the DSE M2854 12-0-12 @150ma

neg supply would disparate sod all and pos less then .75W ;D

and a sign of the times these little transformers are a "clearance" items

Robert

Robert
It might be a sign of the times in slooooow moving north Queensland, but DSE has been out of electronic components supply in Sydney for quite a while. ;D
Alex

P.S.
I just rediscovered a small 12-0-12 15VA toroidal.

[robertkd]

Feb 22, 2009 10:51:03 GMT @sandyk said:

P.S.
I just rediscovered a small 12-0-12 15VA toroidal.

[robertkd]

Alex

mmm well yes and no, both the SPDIF and TOSLINK get remote mounted also allows the use of pulse transformer to totally remove any galvanic connection.

the switch is a simple ground to select SPDIF i/p

the DAC is currently running on it's newly conceived PSU and sounding gorgeous and detailed listening to Diana Krall

Robert

[Deleted]

Robert
I have mine as I described, but haven't got around to finishing the PSU in the box yet to let the smoke out. I wanted to retain input selectability, as I have previously found
that SPDIF appears to have a slight edge over Toslink.I can shove a proper 1:1 SPDIF transformer on a bit of perf board or similar at the rear of the case.
Alex

[robertkd]

Mar 12, 2009 10:44:33 GMT @sandyk said:

Robert
I have mine as I described, but haven't got around to finishing the PSU in the box yet to let the smoke out. I wanted to retain input selectability, as I have previously found
that SPDIF appears to have a slight edge over Toslink.I can shove a proper 1:1 SPDIF transformer on a bit of perf board or similar at the rear of the case.
Alex

Alex,

agreed but alas I only have toslink from Mac so the transport likely an onkyo or pioneer ATM.

yes it's the DSE almost look alike strip board to mount the optical receiver and transformer, I suspect the addition of some local decoupling on the optical rx will improve eyehight slightly by reducing noise on the supply I read that somewhere

PS
oh yes I have also replaced the chip ceramics with PP's waiting on some inductors to modify the i/p filter to the buffer

Robert

[robertkd]

Well grovers it's been a while so today Mr PCM1793 DAC got a case to call it's own nothing to flash in fact it's pretty cheap and cheerful

so here is the new digs



yes I know I need to do something with the on board regulators but hey they work ;D

next is the rear panel, I have SPDIF and TOSLINK, as well as "Aux" Analogue in and output as well as an IEC 240VAC 50Hz interface



Alex what was so hard about the RCA's ?



next the source selector switch and an LED for "data error" indication

Robert

[Deleted]

Mar 14, 2009 21:02:42 GMT mrarroyo said:

I have been meaning to ask for a long time why so many here build the PSU in the same enclosure as the amp or dac w/o putting a piece of metal in between the psu section and the board for the amp or dac. Many builders make a big deal of placing the psu on a separate enclosure to reduce "issues" from the transformer and the rest of the psu w/ the amp or dac board. Other builders if they use the same enclosure put a piece of metal as done above.

I know I am not a technical kind of guy so if my question is silly please disregard it.

Miguel
It has partly been answered previously in several different threads.
The main reasons for a separate PSU comes down to making the unit more compact, supposedly for the SQ benefits too. In many cases this is simply just an excuse to cut costs by using a cheap plugpack sourced from Asia. Toroidal transformers have a radiated field about 1/8th that of a typical open frame transformer, so provided that care is taken with internal layout, there is little advantage, and a disadvantage or 2 by using external PSUs. The main disadvantage of many toroidal transformers is that the doughnut shape often eats into available internal space. Even when using the type of transformer that Robert has used, additional reduction in the effects of it's radiated field can be achieved by orientation of the transformer at an appropiate angle. I think that Robert's construction is more likely to do with physical support of the transformer, as unless the screening plate is made from mumetal or other ferrous material , the screening advantages of the internal plate are small. The case chosen also has special slots that facilitate the mounting of vertical PCBs etc. which can often help to conserve space and permit a modular construction.
With some larger Class A power amplifiers and preamplifiers, and low level signal amplifiers such as phono and microphone etc. , there is often a real benefit to having the PSU separate.
SandyK

[robertkd]

Alex is correct and and what I have achieved using the aluminum angle is to orientate the transformer so I have "about" the minimum magnetic field towards the signal area in this case the DAC PCB.

Gone are the days of getting shielded transformers for anything this side of ludicrous money.

indeed the metal work for my SCHA will have a full depth and height steel divider within the case with PSU and rectifier and the larger filter capacitors in that section and the analog/signal stuff on the other.

As for separate Amp/PSU there are times when it makes sense there are however times when it's a PIA or even funnier when the PSU and device a stacked one on top or beside the other and you end up with more hum then you would if the PSU was thoughtfully incorporated in the same enclosure

ah the fun of it