A NOS 192/24 DAC with the PCM1794 (and WaveIO USB input)

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#2,583
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#2,587
dwjames said:
They were saying that their mk2 and mk3 rakk dac just used a jfet, whereas their mk4 uses their new secret recipe, which they claim is a further improvement.
I think their "just use a jfet" advice was a way of helping me (and stopping me asking direct questions about their design in a public forum) without giving away their latest secret, which all seemed fair enough to me.

It's a shame that no high res pictures seem to exist on the net for their mk4 board...
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My money is on a BJT-based CCS... kind of kidding, but it really doesn't matter to me.

Not only that I'd be personally interested if this group could come up with something original for this (and then I'd like to hear some tests, putting together some CCSs, listening to improvements - or not -, etc.), but I do respect their work and design and all that. Not that I'd hold back from espionage activities where we'd try to figure out what they did by looking at pictures - which is also fair enough... -, but it's just that their work is their work and if they want to share, great, if they don't, equally fine and it's perfectly fair. If we also get something put together I'd feel great about that.

I personally am unable to try any CCSs in the next couple of weeks (but can and will test after), but I also don't (yet) have a DDDAC 1794. So I'd like to hear from anybody getting ahead with this.

Radu.
 
#2,589
dwjames said:
Are you not concerned about the mixing of audio channels running this way or do you have an amp setup with separate channel grounds?....
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Here’s an interesting one. Even though I don’t use an output cap I still had the 100k resistor sitting parallel across the RCA output connectors of the DAC, as per the diagrams. Yesterday when upgrading the RCA connectors I removed these.

Now my channel bleed problem is gone, I can no longer reproduce it (by muting left or right channel at the source). So both NEG channels output connected via common ground in a single ended amp is working fine in my case. I have no idea how this is possible (yet ;-))

So, might be worthwhile testing without these 100K’s in place.

Also I can report back that after two weeks of burn-in of the OSCON’s (they really take some time and patience) at the Vcom&Vcc positions (and Vdd's), I can definitely say they sound extremely well here, and still improving, very smooth and accurate tonality.
 
#2,590
stijn001 said:
Here’s an interesting one. Even though I don’t use an output cap I still had the 100k resistor sitting parallel across the RCA output connectors of the DAC, as per the diagrams. Yesterday when upgrading the RCA connectors I removed these.

Now my channel bleed problem is gone, I can no longer reproduce it (by muting left or right channel at the source). So both NEG channels output connected via common ground in a single ended amp is working fine in my case. I have no idea how this is possible (yet ;-))

So, might be worthwhile testing without these 100K’s in place.

Also I can report back that after two weeks of burn-in of the OSCON’s (they really take some time and patience) at the Vcom&Vcc positions (and Vdd's), I can definitely say they sound extremely well here, and still improving, very smooth and accurate tonality.
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Peculiar... Do you still register continuity across the outers of your L&R rca plugs with the leads plugged into the amp?
 
#2,594
Someone feel free to correct me, but I thought the main job of this resistor across the rca socket was as a bleeder to discharge the output capacitors after use.

Now I think about it, when I tested my system for crosstalk across the channels, I also still had a 10k bleeder across the RCAs.

I'm happy with the Cinemags for now and am going to try a jfet buffer soon in between the main board and the output transformers. This should drive the transformers better from my single dac deck and also mean that the DAC has some level of separation from the transformers and the amp stage afterwards.
 
#2,596
The suggested 10K resistor is to load the transformer.

Are you saying you have output caps AND a transformer? Only one or the other is needed.

An output capacitor does not store energy, it is a coupler, nothing to bleed.

Better to place that resistor at the transformer secondary instead of at the RCAs.

Brian Lowe says his smallest regs can be configured as current sinks. Still do not possess a working DAC (phono stage still takes priority) but should have it working by the weekend and then to experiment with the sink.
 
#2,600
nige2000 said:
Tried one of these
E-301 Semitec | Mouser

Immediate increase in bass weight and definition
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Great. Now we know it's worth it (though we had the K&K testimony). A packaged current source is a pretty good option at around 120dB rejection in the audio band.

[/QUOTE]Anyone know why that would be[/QUOTE]

If my interpretation is correct, the quality of the voltage reference internal to pin 20 becomes of lesser relevance when a high quality current source is being placed on that pin (a resistor can only be as good a current source as the voltage reference that sets its current). Unless somebody finds out more on the internal workings of the DAC chip, I think listening tests (and measurements where possible) are the avenues to take here.

Radu.
 
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