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Hi Guys, I was one of the lucky ones to manage to get an order in for the Buffalo (actually a mate ordered it for me) Because I have 80% of parts already to build a IVY I decided on a bare pcb for that, only main thing I need to order from Farnell is the differential op-amps, I was just wondering which is the preffered device, OPA1632 or the THS4131? specs look almost the same, Farnell stock both I'll add some impressions soon as it all arrives and playing music Also would like to congratulate Brian and Russ for sorting out the Godaddy fiasco, things would have been hectic already without that place adding problems  Cheers, Leo Edited by user Sunday, September 14, 2008 11:07:51 AM(UTC)
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Hi Leo, Thanks! Brian did a great job managing the site during the problem. The two opamps are virtually identical. They sound and measure the same. Many think they are actually the same device rebranded. You will notice in the datasheets that the performance is pretty much the same, its the tests/charts that are different. The opa1632 datasheet has most of its specs stated in the audio frequency range. The THS datasheet is targeted at much higher frequencies, but if you extrapolate down to audio frequencies the graphs look the same. The OPA1632 tends to cost a bit less, so I would go with that device. Cheers! Russ Edited by user Sunday, September 14, 2008 11:33:08 AM(UTC)
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Rank: Advanced Member
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Hi Russ,
Thank you for the quick response, thought I'd ask before ordering just to be sure
I'm really looking forward to hearing this thing, got a few other dacs to compare against so it should prove interesting
Cheers,
Leo
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Buffalo arrived safely,a couple of Leds missing but this was no problem, I mean't to post the other day but didn't get much time. Anyway thanks a lot guys for making it all possible for us to own one of these dacs this past few weeks must have been bloody hectic! I'm currently using it with a SB3 feeding the SPDIF input, the output stage is the IVY using Buffalo1 setting. Theres some odd noises with a lot of music(only really noticable through the headphone amp and cans) it sounds like low distortion on the edges of some instruments, a sort of low crackling sound on the decay of piano etc Playing a sinewave into the scope gives a good response up to about 15k, 15k and higher the waveform gives some slight ringing so I'm not sure whats causing the stange noises/distortion BTW its not really bad, just something I noticed with the headphones Switch 3 high or low makes no difference Apart from the above I must admit I'm very impressed with the Buffalo dac so far, it gives a very detailed and 3d sense of realism, depth is also very good indeed!
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Hi Leo, I am not sure what is causing this distortion above 15K. I must admit I am puzzled... Does this happen without the IVY(with the DAC operating in voltage output mode)? Keep in mind there will be 1.65V DC offset on the outputs, so you may only want to check this on the scope. Cheers! Russ Edited by user Monday, October 6, 2008 4:19:47 PM(UTC)
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Hi Russ,
Thank you for your reply.
I may have found the cause, the wire from the Buffalo to IVY seems to be picking up RF, I have tried very short wires, short twisted wires and also short braided wires but the noise can still be heard.
It seems to be only noticeable with music playing and at certain frequencies , like the sound of screwed tracing paper
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Can you post a picture of your layout? It would help to see what it's neighbors are.
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Hi Brian, This is a temp set up until I can get a nice case The Left and Right +/- gnd wires go straight down to the IVY board, they are now plaited (I've tried single wired and twisted so far) the green and white twisted wire is the spdif input, the black and white wire is the IVY output The regulation for the IVY is a pair of stacked ALW super regs, the Buffalo regs are separate LT1086. I also tried the standard regulated PSU's with same results Cheers, Leo  Edited by user Tuesday, October 7, 2008 6:44:01 PM(UTC)
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BTW guys apart from small noise issue this dac sounds brilliant! certainly one of the best I've tried so far
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Ok, I tried a pair of very short screened cables, so far (its been running about 20mins) the noise is no more :d/
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Is there any details or threads for the Counterpoint and Placid Russ? I'd like to have a read of those if theres anything posted yet
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I'll be posting pages with details in the next few days.
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Thanks Brian, I'll look forward to it.
The standard regs are good but the Buffalo and IVY don't half sing with super regs:-)) the sound goes 3D!
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Placid should have even better load regulation and less noise than the super regs. :) Counterpoint is something completely new (at least I have never seen any I/V stage like it). It has undergone a metamorphosis since last I posted about it. :) I am very excited to try it. Cheers! Russ Edited by user Wednesday, October 8, 2008 8:41:19 PM(UTC)
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Excellent stuff! I'll look forward to the seeing details for the Placid and Counterpoint. The ALW's are a worthy upgrade over standard regs but if the Placid is even better, exciting times ahead guys be great to compare and post results
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Well "better" is relative. :)
All I can say is placid should be nice and quiet, with excellent load and line regulation.
Cheers!
Russ
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Hi Guys, I want to try a separate regulated 80mhz XO, on the pair of pads marked disable before C4 I soldered a pair of through hole pins and fitted a small jumper (same as the ones used on ATA hardrives for setting the pins) With these pins shorted 3.3v still supplys the onboard crystek XO and 1.65v is still measured on the pads after the onboard crystek, is this normal? Also with the pair of disable pins shorted the lock led still lights up  3.3v is measured from the now shorted disable pins Cheers, Leo
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Hi Leo, I see the problem. The top most(with the "Buffalo DAC" test oriented correctly) pin of the disable jumper should be connected to GND. This appears to be a problem with the gerber export not connecting that pad to the GND plane. Luckily for you there are several GND pads clos by to which you can run a jumper. :)
Personally, the added length of the signal from any external clock is liable to swamp and benefits it might have. But, don't let that stop you from giving it a go! :-)
Cheers!
Russ
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You guys are quick! the support on here is great! I first tried a external regged 80mhz XO without realising the disable pins wasn't working, it made a loud whining noise  thinking about it now I guess the Sabre didn't like having a pair of 80mhz's XO's feeding it  The funny thing is swapping the 80mhz XO to a Tent 24mhz on the external regged one and plugging that in worked fine without any noise so the Sabre was having its onboard 80mhz + external 24mhz Anyway I'll try running a jumper to one of the grounds as you suggest and see how it goes, its getting late here so I'd better try it tomorrow after work Thanks again Leo
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