See Vunce...I told you this was something special. 
I knew you would have to hear it for yourself. In fact, I also said, "WOW" the first time I heard it. I might add that for a little while I listened to it with the 9th-order filter jumpered out, and I can say that the good sound also comes from an excellent I/V stage. Of course, the sound improves a step with the filter back in.
As far as the output caps, normally you can get by with about 10 uF to 22 uF caps if going to a 10k pot as my preamp has. But your iron pre has a multi-tapped autotransformer (it might first go through a diamond buffer, I can't remember), and abraxalito said a large cap value is needed going to a transformer. So putting a little film cap in parallel is about all you can do, instead of replacing it with all film caps. For me, I am not sure it would be worth the effort, but I imagine someone will try it eventually. This is diy. I once replaced the 10 uF Silmic 2 elko cap on the input of my ACA amp with a nice film cap, and I could not really tell a difference.
I imagine soon there will be several more people posting "WOW's" in this thread.
I knew you would have to hear it for yourself. In fact, I also said, "WOW" the first time I heard it. I might add that for a little while I listened to it with the 9th-order filter jumpered out, and I can say that the good sound also comes from an excellent I/V stage. Of course, the sound improves a step with the filter back in.As far as the output caps, normally you can get by with about 10 uF to 22 uF caps if going to a 10k pot as my preamp has. But your iron pre has a multi-tapped autotransformer (it might first go through a diamond buffer, I can't remember), and abraxalito said a large cap value is needed going to a transformer. So putting a little film cap in parallel is about all you can do, instead of replacing it with all film caps. For me, I am not sure it would be worth the effort, but I imagine someone will try it eventually. This is diy. I once replaced the 10 uF Silmic 2 elko cap on the input of my ACA amp with a nice film cap, and I could not really tell a difference.
I imagine soon there will be several more people posting "WOW's" in this thread.
Yep, Dark I/V is a keeper for sure . The Iron Pre is a slimmed down Iron Pumpkin, so no transformer volume control, just a standard 20K ALPS. I could play around with the output caps but not feeling it's necessary at this time. Did you try a different psu yet? I have the transformer's two 9V secondaries wired in series to power Abrax's psu, very convenient.
. The Iron Pre is a slimmed down Iron Pumpkin, so no transformer volume control, just a standard 20K ALPS. I could play around with the output caps but not feeling it's necessary at this time. Did you try a different psu yet? I have the transformer's two 9V secondaries wired in series to power Abrax's psu, very convenient.Yes, the transformer arrived, so I am using just one transformer now. The two 9 V secondaries are wired in parallel to supply the 18 VAC output to the PS I purchased from abraxalito.
Another thing...when I first listened to the dark LED I/V, I found myself inadvertently listening to the cleaner sound louder than before and started to clip my 14 watt amp. Now I keep the volume down to proper levels. If I do go too loud, eventually my wife will let me know. Yes, I know, seems I should start another amp project with more power.
Another thing...when I first listened to the dark LED I/V, I found myself inadvertently listening to the cleaner sound louder than before and started to clip my 14 watt amp. Now I keep the volume down to proper levels. If I do go too loud, eventually my wife will let me know. Yes, I know, seems I should start another amp project with more power.
Hi JP
The last six days I was investigating the I2S line RF spread using many I2S line configurations.
If both the sender and the receiver PCBs were made with guarded traces and designed to accept each of the three (or four) lines with their grounds plus an overall shield, then the corresponding (GSGSGS)/S cable would be of no concern, regardless of line length.
Lack of such proper connection of the I2S lines, invalidates the EMI superiority of the best cable configurations, as RF evidently leaks from these two 5mm-long improper cable end connections.
As to the line itself, GSSS flat line is the worst possible. Twisted to itself is only a tad better.
Flat GSGSGS ribbon is better. More so if twisted to itself.
Then twisted pairs unshielded (UTP).
Good mic cable (four conductors+good copper braid)
3xRF coaxials (e.g. mini RG59, RG174)
Twisted pairs shielded (STP, S/FTP, S/STP)
George
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Designed and made tens of DACs when it was still possible for an experienced DIYer to outperform ready made DACs.
Not so anymore, one has a nearly impossible task to outperform recent cheap single board DACs. Add to that the way higher costs to DIY and the difficulty to find a unrealistic expensive (for private persons) DAC chip to that.
Not so anymore, one has a nearly impossible task to outperform recent cheap single board DACs. Add to that the way higher costs to DIY and the difficulty to find a unrealistic expensive (for private persons) DAC chip to that.
No separate DAC at all. A music player with good internal DAC and no external interfaces suits me best. Still searching and trying. Some devices tried out have not really outstanding DAC chips but more often than not outperform external top notch DACs. Hence the wish to avoid SPDIF, USB, external I2S etc. The flexibility of interfaces may be nice but but does one really need it? What is gained, what is lost?
Just a personal observation, nothing more nothing less.
Just a personal observation, nothing more nothing less.
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https://www.diyaudio.com/community/threads/ljm-mini-usbdac.379014/post-7092006
Real cheap also.
Cheers,
Patrick
It's been some time so better to resume. Abraxalito kindly designed a pair of Celibidache filters that work with 150 ohm output resistor to fit my PCM1794 DAC. I'm going to use them in a completely passive I/V scheme without the Dark LED. I had to build a "motherboard". The filters are on the bottom side and on top are the output caps and a few relays to select output mode including an option to bypass the filters. It was quite an exercise to squeeze all these in a very crowded chassis thus the awkward layout.
150 ohm is very hot for PCM1794 but there were no issues with DC offset or clipping. Distortion is typical for this DAC fitted with 150 ohm, nothing added by the filter. However, I was used to better figures with 22 ohm but this also was a compromise for dynamic range. So, I came up with solution that seems to work but it's always possible I'm missing something and your comments are welcome. What I did was to put another 150ohm resistor right at the chip output in front of the filter. Now, DC offset, Vrms and distortion is like I have a 150||150=75 ohm resistor and the frequency response is not affected.
I have it all installed and I like how it seems in measurements. But I won't be able for a critical sonic evaluation before I readjust the gain of my preamp for the much higher signal level from 200mV to 850mV now. I'll report when it's done.
Abraxalito, once again thank you very much for your help!
150 ohm is very hot for PCM1794 but there were no issues with DC offset or clipping. Distortion is typical for this DAC fitted with 150 ohm, nothing added by the filter. However, I was used to better figures with 22 ohm but this also was a compromise for dynamic range. So, I came up with solution that seems to work but it's always possible I'm missing something and your comments are welcome. What I did was to put another 150ohm resistor right at the chip output in front of the filter. Now, DC offset, Vrms and distortion is like I have a 150||150=75 ohm resistor and the frequency response is not affected.
I have it all installed and I like how it seems in measurements. But I won't be able for a critical sonic evaluation before I readjust the gain of my preamp for the much higher signal level from 200mV to 850mV now. I'll report when it's done.
Abraxalito, once again thank you very much for your help!
Attachments
Hi Abrax,
your project looks like pure magic. And is what I am looking for, for a long time. But it seems, I have to rebuilt my NOS project.
I am using Juaneda receiver unit, followed by 4 pcm1704 (because I am using symmetric signal for the diy pass X150) followed by Nelson Pass I/U-Stage.
So far, I was very dissapointed with the project because everything above 15 kHz looks like minecraft and not like music. And it sounds this way even. So what you offer is nothing more, than the holy grale for me. Well almost, as the pcm1704 unforunately don't deliver the +/-1mA. So I need a new idea for the NOS DAC-Chip. But anyway I want to make sure, to get the Dark LED passive filter stage for the coming project. As I am working with balanced signal, I will have to order 2 of them - right? Are you still selling them? Please be so kind to contact me: zippo999@web.de
Thanks Matthias
your project looks like pure magic. And is what I am looking for, for a long time. But it seems, I have to rebuilt my NOS project.
I am using Juaneda receiver unit, followed by 4 pcm1704 (because I am using symmetric signal for the diy pass X150) followed by Nelson Pass I/U-Stage.
So far, I was very dissapointed with the project because everything above 15 kHz looks like minecraft and not like music. And it sounds this way even. So what you offer is nothing more, than the holy grale for me. Well almost, as the pcm1704 unforunately don't deliver the +/-1mA. So I need a new idea for the NOS DAC-Chip. But anyway I want to make sure, to get the Dark LED passive filter stage for the coming project. As I am working with balanced signal, I will have to order 2 of them - right? Are you still selling them? Please be so kind to contact me: zippo999@web.de
Thanks Matthias
