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Greetings, I have been purchasing and gathering items for my dual mono single legato build for the past year. I have not purchased everything all at once since this is an expensive build. so this is what I have so far: 1 buf3 version 1.01 1 buf3 version 1.02 1 legato 2 5.25 shunt power supplies 1 _-15v shunt supply 3 transformers now that I have everything, I started assembling and measuring the devices. 1 - I set se and balanced dc offset on legato to 0 v --- ok 2- checked se dc offset with b3 plugged into legato v1.02 --- ok 3- removed version 1.02 and checked with v 1.01 --- measured oscilation at dc offset reading of legato. --- does not seem to be ok. there seems to be oscilation on the b3 v1.01 outputs. Note: this is the first time powering the units and I have not yet hooked any input nor output to the device. I have not setup the dual mono configuration either. all is setup for stereo operation and under assmbly and measurement mode. Legato has no output buffer Is there a way to fix this? is the device defective and if so, what is the process for replacement. regards. ps: I have a pdf showing scope output attached Edited by user Sunday, December 9, 2012 9:32:35 PM(UTC)
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1.0.1 and 1.0.2 are virtually identical. The only change is some fixes to silk and a couple of convenience pads. The DAC itself can't oscillate. If you are seeing the signal common mode, it may not even matter - as they will cancel in the balanced signal. You might try swapping the AVCC modules. If you find one of the AVCC modules is not stable for you - then you can add 100-200pf or so from each opamp output to the inverting input. Cheers! Russ Edited by user Sunday, December 9, 2012 10:47:47 PM(UTC)
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thanks for feedback russ,
We can agree that oscilation is not the proper word, noise is more appropriate and I would like to figure out where the source is coming from.
I did try to swap out the avcc module and also the shunt power supplies but the noise is still present on one of the "noisy" BIII. The measurements were taken on the single-ended legato output. Did not try meauring the bal output though. The pdf shows both bufalos with one distinctly showing some kind of noise at the se output of the legato. I cancelled out problem from power supply and legato since these wre common in both tests and are not producing any noise when in use with the "good" BIII. The noise appears only when the other "noisy" bIII is in the build. Not sure how to isolate such a problem.
would it be a good idea to swap out the other 3 regs (one at a time) and see if the noise source is from one of them?
Do you think I should try it in a full input/output circuit. I'm not at ease with this since I am direct coupled after the output of the legato in se configuration.
regards.
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The problem could be in I2S wiring (noise from crosstalk).
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havn't yet connected i2s nor i2c.
I merely measured with power supplies, legato and vanilla b3
no input/output
if it is crosstalk, what can be done to resolve?
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Continued trying to isolate source of noise.
I swapped out all the tridents from one b3 to the other and the noise is still present (see pdf attached on first post).
With all my testing, it appears that the noise source is in fact from the noisy buf3 board.
Its been confirmed that all common components perform perfectly with the other buf3 board.
Perhaps its a defective clock, sabre dac or other component from the buf3 board.
I don't know where to look anymore.
any help or hint from experts is more than welcome.
regards.
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The other regs wouldn't come into play. and if swapping AVCC module made no difference then it is not that either.
It could however be something like a missing output jumper making the analog section not symetrical. Check solder joints there.
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resoldered 0r resisters on both dacs
same problem persists.
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Do you have the controllers installed?
Have you tried swapping controllers and changing switch settings?
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Pictures of the setup may help too.
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greetings,
I swapped out the controllers and tested both boards individually.
I am still having the same issue: one noisy board and one is ready to go to the next step.
The switches are factory defaults on. I didn't even remove the tape on the switches. These devices are new and never been used. This is the first time I have been testing and measuring them.
don't know where to go from here.
kind regards.
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All switches on is - not - default configuration. You must manually set them all to off.
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Also for the test you really should be using some input signal. Even silence is fine.
Once again - pictures would help.
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The factory default is in fact on. its says so in the manual (shipped with all switches on). I did not even touch those yet. The tape is still on the switches.
Nonetheless, its still disturbing that in my current test configuration, that one board is silent and the other one is noisy with all other components common.
I'll try with switch settings off and report back.
what kind of pictures do you want me to upload?
Is there anything specific you want to see?
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The switches come from the factory all switched on - but the DAC default config is designed for them all to be "off". :)
Just a general tour of the test rig would be fine - but first lets try things with a live signal and see what happens.
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Greetings
Here's the latest test:
1- set all switches to off except sw2:123478
2- hooked up ian's reclocker with i2s signal
3- tested in stereo mode
4- tested with 1 board and then swapped the other board so tested one at a time (ie: not in dual mono)
4- sent 2k sine wave on spdif from computer hooked up to reclocker input
results:
both boards output the 2k signal but the scope still detected the noise on the v1.01 board.
then, I sent 96khz music file and hooked output to DCB1/forplay/F5 and I could not detect an audible difference but the scope still showed noise on the v1.01
Still don't know where the source of the noise is from.
I think I'm ready to go dual mono but I'd really like to resolve this issue.
ps: in dual mono, am I right to say that:
1- the switches on both boards must be set to mono
2- one of the 2 boards jumpered address
3 the i2c connected between the 2 boards
4 one of the atmels removed from one board
regards.
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Originally Posted by: necplusultra 
ps: in dual mono, am I right to say that:
1- the switches on both boards must be set to mono
2- one of the 2 boards jumpered address
3 the i2c connected between the 2 boards
4 one of the atmels removed from one board
No. Please read the procedure on page 21. You also need to look at R7 or L5.
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If you have the older AVCC modules you could try putting say 47-100uf low ESR at the outputs of the AVCC modules.
I think there may be some small difference between the two version in terms of size of bypass caps.
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Greetings,
well, I gave up on fixing the noise issue on one channel since I do not hear an auduble difference. So I've been listenning to the dac for a while now. everything very good. Its hooked up to ian's reclocker in i2s asynch mode.Then, yesterday, as I was listenning to music, all of a sudden, no more sound.
I verified the B3's and legato and all seems fine in terms of voltages. I verfified the I2s source with another dac and all ok there. All regs light up ok. I've isolated the problem to the buf3/ legato.
Anyone know where I can troubleshoot? I really don't know where to look at this point.
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