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pete0  
#1 Posted : Thursday, August 6, 2015 10:29:03 AM(UTC)
pete0

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Hi,

bought in 2011 a Buffalo III with trident regulators V1.1. Since I already have an Buffalo II (no Tridents and ZAPfilter 2 as I/V-Stage) and I am very pleased with the performence I left the Buffalo III unused.

But now, with some spare time I started to build a stand alone DAC based on BUFFALO III.

After installing the Trident regulators I powered up the BIII with clean 5V. All LEDs are lit and I meassured following voltages and currents.

Input Voltage: 5.1V

VDD:1.18V Current (R7):57,6mA
VDD_XO: 3.24V Current (R7):44.73 mA
DVCC: 3.25V Current (R7):49.68 mA

So far nothing special, but I couldn't resist and switched on my scope to check for any ripple/noise..

To my supprise all voltages show ripple/oscillation d'oh! Please see the attached Meassurements.

Meassurement of the output voltage
Trident_V1.1_1.2V_VDD.png
Trident_V1.1_3.3V_DVCC.png
Trident_V1.1_3.3V_VDD_XO.png

Meassurent of the OP output (Pin 6)
Trident_V1.1_1.2V_VDD_OP_out.png
Trident_V1.1_3.3V_DVCC_OP_out.png
Trident_V1.1_3.3V_VDD_XO_OP_out.png

I can't believe that this is normal for the Tridents. I know the hint for getting rid of the AVCC ripple, since I faced the same probleme with my AVCC regulator too. Soldering 47pF Cs fixed it. But I have not found a fix for the Tridents and without a circuit diagramm I can't look for myself how to fix this.

Any hints?

Kind Regards
Peter

pete0 attached the following image(s):
Trident_V1.1_1.2V_VDD.png (51kb) downloaded 17 time(s).
Trident_V1.1_3.3V_DVCC.png (46kb) downloaded 13 time(s).
Trident_V1.1_3.3V_VDD_XO.png (60kb) downloaded 14 time(s).
Trident_V1.1_1.2V_VDD_OP_out.png (52kb) downloaded 14 time(s).
Trident_V1.1_3.3V_DVCC_OP_out.png (43kb) downloaded 15 time(s).

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pete0  
#2 Posted : Thursday, August 13, 2015 7:38:47 AM(UTC)
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Ok,

found a cure for the oscillations.

Solderd to each Trident a electrolytic capacitor to OUT & G

VDD: 47uF
VDD_XO: 2.2uF
VCC: 10uF

These are minimum values to stop the oscillation.

Question is, are there any negative side effects since the tridents do not have any output buffer C's and I think this is not because of reducing production costs.

Kind Regards
Peter
igy137  
#3 Posted : Tuesday, August 18, 2015 7:10:33 AM(UTC)
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Hi,

That would be interesting for me, too.
I had the same problems with Trident 3.0, and the oscillations actually caused nasty noises at the amplifier output (I think it was caused by DVCC mainly). I also had 12-13MHz oscillations on VDD_XO.
Both places I added 22uF (I did not experiment finding the minimum values) which solved the issues, at least the stuttering noise at the output.

igy
pete0  
#4 Posted : Tuesday, August 18, 2015 6:20:33 PM(UTC)
pete0

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Hi,

oh, bad news to hear that the Trident 3.0 still have this problem!

I have ordered a complete set of Tridents Rev 3.0 because I thought that with the new, improved design the problems with oscillations are gone!

:-(

To repeat the question from my #2 post.

@Twisted Pear Audio: Are there any negative side effects adding buffer Cs to the Trident output ?

Any other prefered way to increase the stability?

Regards,
Peter
avr300  
#5 Posted : Tuesday, August 18, 2015 6:42:49 PM(UTC)
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I just checked my BII with Tridents 3.0 and current AVCC.

NO sign of oscillation what so ever.


avr300  
#6 Posted : Tuesday, August 18, 2015 6:44:23 PM(UTC)
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And just being curious.

You were seeing oscillation at what magnitude ?

edit: question aimed at igy

.

Edited by user Tuesday, August 18, 2015 6:46:59 PM(UTC)  | Reason: question aimed at igy

igy137  
#7 Posted : Tuesday, August 18, 2015 7:10:32 PM(UTC)
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I posted a capture of the vdd_xo here: http://www.twistedpearau...nt-3-0-supplying-XO.aspx
Others had this with the 3.0, too: http://www.twistedpearau...nce-at-Tridents-out.aspx

On my side, for dvcc and vdd were much nastier, at much lower frequency (few kHz).
I don't remember exactly the numbers, I can post some pics tomorrow when I'm back at work :)

All those with the Placid HDs already modified to ged rid of the ripple on their output (http://www.twistedpearaudio.com/forum/yaf_postst3005_Ripple-at-output.aspx).

I also had to AVCC ripple, too, but I rather ordered the most recent version there.
igy137  
#8 Posted : Wednesday, August 19, 2015 6:33:37 AM(UTC)
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As promised, here're some pics from my Trident 3.0 regs, before adding extra caps at output, but after fixing placid hd ripple. This created some stuttering noise at the amplifier outputs, too.

Edited by user Wednesday, August 19, 2015 6:36:21 AM(UTC)  | Reason: Not specified

igy137 attached the following image(s):
1.2v.png (24kb) downloaded 21 time(s).
3.3v.png (28kb) downloaded 13 time(s).

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Russ White  
#9 Posted : Tuesday, August 25, 2015 9:07:08 PM(UTC)
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Hmmm - can't replicate this - with a normal load I have almost immeasurable ripple on the output of the trident 3.

Cheers!
Russ
Russ White  
#10 Posted : Tuesday, August 25, 2015 9:07:46 PM(UTC)
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You may have some EMI or an HF ground loop?
Russ White  
#11 Posted : Tuesday, August 25, 2015 9:13:50 PM(UTC)
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One thing to note - if your AVCC is oscillating it can cause some pretty horrible ground bounce - which will show up everywhere.
igy137  
#12 Posted : Wednesday, August 26, 2015 5:48:58 AM(UTC)
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Hi Russ,

thanks for jumping in :)
I'd be happy to take further measurements/scope captures if you'd like to look into this issue, just tell me what/where to check.

I started looking into this, because I got some stuttering noise at the amp outputs. However, it's sure was not caused by AVCC. Although it was also not clean, replacing the older AVCC (SRA2 1.0) with the most recent version (SR_1.0) did not solve this stuttering noise issue (even though the AVCC output is much better looking).

The stuttering noise was gone when I added the 22u cap to DVCC and VDD_XO. I guess it was DVCC causing that noise. Their output is clean now, and the noise is gone. (I attach a wav with the stutter recorded, just to hear what it was like).

Regarding EMI/HF ground loop. I'm not sure what/how to check for these. Everything was assembled simply on my desktop table, no case, no output connected, not connected to safety earth, stock trafo wired to placid hd (modified to remove the output ripple as described here in the forum, output clean), which is connected to buffalo iii dac with a ~10cm cable. The buffalo iii is v1.0.1, got the microcontroller removed, no other mods. I observed the same results at home and at my workplace, too. As input I use a dsp board (TI OMAP LCDK), but then to check I replaced it with a Papilio Pro FPGA board only outputting clock (no other lines connected), to make the buffalo locking. (I heard the noise at the dac output only when the dac locked). Nevertheless, the trident oscillaton was there without any input connected.

Summing up, let me know if you'd like me to make some further measurements.

Thanks,
igy
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__amp_out_-69.2db__.wav (143kb) downloaded 26 time(s).

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Russ White  
#13 Posted : Wednesday, August 26, 2015 11:40:01 AM(UTC)
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Trident expects a load. You should use a dummy load when measuring it.
Russ White  
#14 Posted : Wednesday, August 26, 2015 11:52:34 AM(UTC)
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BTW DVCC and VDD-XO are not directly involved with the analog side at all. This is why I think what we are seeing is some ground bounce.

Also be sure VDD (1.2V) trident is putting out enough juice - it is actually the most taxed reg on the board. You can add say 27R at R4 to bolster it's output current. The demand of that supply goes up substantially at high sample rates.
Russ White  
#15 Posted : Wednesday, August 26, 2015 11:54:38 AM(UTC)
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That noise in the wav sounds like the analog side picking up EMI from the digital inputs. It is very low freq (khz). how are you wiring the analog output? Pics?
igy137  
#16 Posted : Wednesday, August 26, 2015 12:48:49 PM(UTC)
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I always measured the Tridents assembled in the BIII.
The oscillation/ripple on Tridents were there without anything connected to BIII input/output, just installed in BIII and powered as ususal.

On the output stuttering noise, there were two conditions needed to be met to reproduce it:
1. bit clock / lock (with/without actual i2s data lines connected noise was the same), until no lock, output was silent as expected
2. connected to amp, in my case Hypex NC400

I tried directly connecting the amp to BIII output, and also in BIII-IVYIII-AMP setup, the result is the same.
Wire to amp had length of 10-20cm, stock cabling supplied with amp (shielded Mogami mic cable).

I tried many things, isolating i2s input lines, output caps on IVY to break DC, etc.
Nothing helped. Then I started measuring trident outputs and found the ripples.

I just installed the 22u caps on VDD_XO and DVCC, and then the output noise was also gone, so was the ripple.

I can try to add/change (I guess rather replace? it's not in front of me) 27R to R4, though I'm not sure I've it lying around (especially in SMD), so it'll take some time to source it. BTW, I have had the noise issue with just the 2.8MHz bitclock fed in, so no higher bitrates at all...

Anyway, I'm not sure what are we looking with this now:
- the oscillation on the Tridents
- or the noise on the output when connected to amp

Do you think that if I increase VDD 1.2V current supply by changing R4, that would probably solve the output noise issue, which is currently "solved" with adding caps on the other two regs on VDD_XO and DVCC?
Russ White  
#17 Posted : Wednesday, August 26, 2015 3:31:38 PM(UTC)
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Tridents themselves do not oscillate - so I think what we are seeing is some external effect. Testing them in-situ does not really tell you much about the trident - just that you have something that is cause large supply spikes. I am wonder if some rapid mute un-mute activity is happening.

You cannot just supply the bit clock - you must also supply a word clock. Otherwise the DAC does not know your word length.
Russ White  
#18 Posted : Wednesday, August 26, 2015 3:34:32 PM(UTC)
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You actually should supply a true I2S signal - so that the data pin is not floating but you are truly sending silence.

in other words - sending only a bit clock is nothing close to sending PCM slience. :)

Edited by user Wednesday, August 26, 2015 3:36:16 PM(UTC)  | Reason: Not specified

igy137  
#19 Posted : Wednesday, August 26, 2015 7:52:00 PM(UTC)
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Russ,

I tried many-many combinations regarding the output noise. As I said, it's necessary and sufficient to connect the bitclock to reproduce the output stuttering. It is the same if I connect proper I2S input with bit- and frame clock and data lines. The stuttering noise is there, once there's bit clock, I guess that enables the dac output.

Also, let me clearly state it. My Trident 3.0s _do_ have a ripple as the scope captures show in post #8. This is the case with all stock transformer, Placid HD, BIII, AVCC and Tridents, but no other components connected (here I mean without clock, I2S input or output stage, amp, etc.).

Whether the Trident ripple/oscillation causes the stuttering noise when the source and amp are actually connected, I cannot definitely tell.

However, what I can again definitely state, that both Trident ripple and the output stuttering noise goes away with the caps added to the Tridents.

igy
Russ White  
#20 Posted : Wednesday, August 26, 2015 8:49:07 PM(UTC)
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igy - not arguing with you - just trying to find the cause. Ripple != oscillation. What you are describing is nothing close to normal operation - so I am just trying to help you find the cause. :)

If you run a trident on it's own - with a dummy load - you will see it is self-stable. What I think is happening is you are seeing massive ground bounce (which of course local decoupling at the measuring point will remove)

The why is a head scratcher - i can't duplicate it. Still thinking.
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