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I have assembled the Buffalo III, Ivy III set up in stereo mode I have a Placid powering the DAC and seperate high quality PSU for the IVY. The only issue I have - so far - is that on power on the DAC is unstable. I get large DC offsets on both channels almost instantly and or HF oscilation. If I power off then re-apply power after a second or two it stabilises and bingo works beautifully. I have checked reg outputs and appear in order. Of significance is that I do not see an issue until the mute is released - once I apply digital input that is and then the instability is outputted through the IVY. I have tried powering off the ivy and checking the inputs to the IVY and still see the issue here.
So I'm confident this is an issue regarding the DAC. Anybody come across this issue before ?
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Where are you measuring the DC offset? In your power-on test, are you switching on the power to the Buffalo only, or both the Buffalo and the Ivy?
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This sounds like a problem at the output stage, not the DAC. There is not feedback involved at the DAC itself so it can't really "Oscillate". It could however be configured incorrectly. Can you show some pictures and give more details? How do you have the DAC switches configured? Edited by user Saturday, December 10, 2011 7:56:18 AM(UTC)
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Thanks for getting back to me, appreciated. Ok, I will follow up with further detail. But I usually power up both Dac & IVY simultaneously but also get the same result if I power up the DAC or IVY first. If I drive an amplifier by either output balance or single with a digital source connected I get no audio but get a thump as the offset DC offset kicks in. If I do not apply the Digital input signal the mute does not come off and I hear nothing and get no offset. When I apply the dig input Spdif signal the mute drops off and the the DC offset appears. I measure the offset from the IVY outputs.
I have an array of measuring equipment, HP digital scope included so I can take measurements whereever you want.
Please note that at present I have set the dac up on my workbench and is not cased as yet. This is because I'm halfway through building a pre/line driver and wanted to integrate this into it. Photo's with pleasure, would you like them E-mailed ?
Russ - my initial thoughts were the same as yours....
I have set the DIP switches as follows:
Sw1 , 1 & Sw2 , 8 on all others off.
I have tried connecting up to my stereo getting the same results using a logitech touch source and driving balanced to my Hypex amp. Sounds fine on this system also, when the offset settles.
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Hi, not much time to work on this but I have split the DAC and IVY Boards. Loaded one of the Voltage outputs with a 1k resistor and used the scope to take a look at the output. I have the same result. If I power up I get a signal could be oscilation, re-power up and I then get the audio signal. So definetley DAC board issue, or super reg instability (not noticed this as yet). Any ideas?
Simon.
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Once again photos would help. Also - try using the DAC all by itself with only coupling caps at the output. Edited by user Sunday, December 11, 2011 4:04:03 PM(UTC)
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Hi Russ, I have some pictures, not sure how to attach / get them to you so I will try and e-mail them to you. Along with a dialog.. I have compressed the images as they enormous file sizes... Thanks .. First picture shows the how I'm doing a functionality test. The DAC is powered by the Placid, the SPDIF input comes from a spare DVD player. Edited by user Monday, December 12, 2011 1:19:59 PM(UTC)
| Reason: Not specified S.Ward attached the following image(s):  DAC TEST.jpg (50kb) downloaded 260 time(s).You cannot view/download attachments. Try to login or register.
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Just click the attach button(upper right of the post) on the last message you posted.
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Next three pictures show board details note these are highly compressed images I could try larger file sizes.. S.Ward attached the following image(s): DAC TOP VIEW.jpg (50kb) downloaded 254 time(s). UNDERSIDE - CONNECTION.jpg (39kb) downloaded 253 time(s). DAC SIDE VIEW.jpg (44kb) downloaded 252 time(s).You cannot view/download attachments. Try to login or register.
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1st observation is that ribbon cable from the SPDIF input board is far too long. Keep it to a couple inches or less if you can.
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You can easily double the image size.
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Next three show the following: The output across one leg of one channel which is loaded with a 1k resistor. Would a cap be better ? This ultimately appears almost as a sawtooth waveform. Second one shows that applying a SPDIF input does effect the output but only slightly. Third shows what happens when I remove power wait a couple of seconds then re apply power. Also if interest is that if I switch off wait 15 seconds then reapply power I'm back to square one as the second image. S.Ward attached the following image(s): START NO INPUT.jpg (40kb) downloaded 244 time(s). ADD SPDIF SIGNAL.jpg (40kb) downloaded 242 time(s). SWITCH OFF WAIT 2 SECS REAPPLY SUPPLY.jpg (44kb) downloaded 244 time(s).You cannot view/download attachments. Try to login or register.
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I only see one end of things clipped on your probe. Where is the prob GND ref? You should definitely use a coupling cap at +OUT and measure from +OUT to GND. You will alsways see noise in this case though because of the way the DAC works. To see a clean signal you need to be putting the scope on the OUT+ to OUT- and measuring the differential signal. Edited by user Monday, December 12, 2011 1:35:46 PM(UTC)
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Try doing these same measurements w/o the S/PDIF module connected.
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Shot of underside - more clarity S.Ward attached the following image(s): UNDERSIDE - MORE DETAIL.jpg (120kb) downloaded 238 time(s).You cannot view/download attachments. Try to login or register.
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Switch Positions - changed sw1 ,1 Hope this clarifys - got to go she who commands and all that  Edited by user Monday, December 12, 2011 1:44:51 PM(UTC)
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Two things you need to do right way.
First thing you need to do is measure either after BAL/SE conversion, or differentially.
Second. Shorten up that ribbon cable to 1-2" max.
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Also Brian and I have been talking and it may be good to also test with the SPDIF input module completely removed. You will still get some HF junk on a single ended DAC output but it should be small magnitude, if you measure differentially(or after BAL/SE conversion) the DAC should be nice and quiet.
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Hi,
I connect the scope gnd at the SPDIF oV. Measuring across the outputs presents a couple of hurdles (the usual) as my sscope chassis is earthed. The DAC etc was in effect earthed through the scope. The source actually isnt earthed and is isolated from the DAC by the input transformer as well I guess. But it does mean that if I connect the scope earth to one of the DAC outputs I may get an earth current flowing (could be bad news) so I have two other approaches one is to measure by sum of two channels on the scope (my prefered approach) and the other is I have access to a Fluke scope multimeter which whilst is state of the art and has isolatedinputs its display is a piece of junk in comparison to the display on the HP.
Anyway I've made a shorter ribbon, and will have a go at something a bit later measuring the sum of the outputs.
Thanks,
Simon.
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Hmm that is far from the ideal place to connect the probe GND ref. You should be connecting it to the GND right at the analog output. If you AC couple the outputs (as I suggested a bit earlier) then the DC offset will not matter in the least. :) You don't have any choice but to connect the GND. Even if you sum. Edited by user Tuesday, December 13, 2011 1:00:07 PM(UTC)
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