Soekris DAC Build

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Ray P
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#46 Re: Soekris DAC Build

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TJF wrote: Sun Dec 06, 2020 9:44 am @Ray
Thank you, too! It is very interesting to know in advance! I am amazed that JB publishes it like this ...
Even when I think of my own power supply units ...
It's a good circuit and I think some people don't have the problem, it's more down to bad luck with mis-matching of caps in the power supply I believe - remember that electrolytics will typically be +/-20%.
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TJF
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#47 Re: Soekris DAC Build

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You could measure them and use some parallel caps to get it very equal. Better foils: I.e. JB uses https://www.avx.com/products/film-capac ... fe-series/
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Nick
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#48 Re: Soekris DAC Build

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I thought the point of the Akido was its PSRR. Also a shame that the name he chose clashes with the earlier (1957) Augmented Cathode Follower by McaDonald that has no such problems with PSRR. The JB circuit seems to rely on the power supply for balanced hum cancelation.

https://jrossmacdonald.com/jrm/wp-conte ... llower.pdf

Also looking at the Broskie circuit, the DC offset from the output is set by assuming symmetrical DC lines which seems to be set by assuming equal leakage in the 220uf caps. I would have added a couple of 220k 2W resistors across them to set the centre point voltage.
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Ray P
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#49 Re: Soekris DAC Build

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Sorry, I couldn't resist!
TJF
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#50 Re: Soekris DAC Build

Unread post by TJF »

I see, that I cannot use the buffer. I need more gain (> 10V RMS output) to drive the amp. The balanced Aikido would be a good solution. Does anyone have experience with that? Soekris outputs voltage with all models. Is that right? In case of voltage output, the basic aikido (high resistance -> input) could be used. And I would prefer dam1941.
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Ray P
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#51 Re: Soekris DAC Build

Unread post by Ray P »

TJF wrote: Mon Dec 07, 2020 1:53 pm Soekris outputs voltage with all models. Is that right?
Yes, the Soekris doesn't require any I/V stage.
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#52 Re: Soekris DAC Build

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Thank you, Ray!
les24preludes
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#53 Re: Soekris DAC Build

Unread post by les24preludes »

I have a Soekris related question, but it may or may not apply to R2R DACs in general. I just got a DAM 1021 0.05 board working with a Wave IO input USB board. In comparison I have a basic Chinese AK4490 DAC with op-amp output. The big differences I hear are:
Soekris - very smooth, detailed and instrumental tonalities are "natural" but with one exception - dynamics. The dynamics are rather "flat" meaning I'm not getting a proper attack on the leading edge of notes. Like if you enter a flat tone to notes in Logic/Garageband rather than using a touch sensitive keyboard which gives you the proper attack and decay. This is most obvious with a Steinway piano which sounds flat rather than percussive and steely as it should, and does on the AK4490.
AK4490 - detailed and proper attack and decay. Not as refined as the Soekris but more involving because of the dynamics.

I don't know if this is a characteristic of R2R DACs in general, or just my implementation of the Soekris. The PSU is 3.3V and 5V DC from bench supplies and +-12V DC from a regulated supply with LM317/337.
The other salient feature is that the guy who set it up for me downloaded a different filter which was popular in threads, will have to ask which filter it was.

Input is a Mac Pro. Output is a 2a3 amp configured Hammond 1:4 SUT 1140-LN-C > 10Y > 2a3. These both work fine for dynamics with the AK4490. I believe the output of the Soekris is 1.4V straight off the board.

I need to solve this problem to be happy using the Soekris. There are some very clever guys on this thread, so could I please have some idea of where to look for answers to this question?

1. I can make a different +-12V supply if you think that's the issue. e.g. CLC
2. If you think the filter is the issue I can look at downloading another filter
3. Or could it be something else?
4. Or might it be a characteristic of R2R DACs?

I'm a musician and this is really bugging me.
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Nick
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#54 Re: Soekris DAC Build

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AK4490 - detailed and proper attack and decay. Not as refined as the Soekris but more involving because of the dynamics.
I wonder if you are using "refined" as a synonym for "less dynamics", it may be that if you make the R2R more dynamic you may also make it less refined. YMMV.

I would certainly look at the choice of filter, but it sounds to me that you prefer the AK4490 DAC, so why not use that, or consider playing with the op amp and power supply on that to see if you can fix whatever you like less about that.
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les24preludes
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#55 Re: Soekris DAC Build

Unread post by les24preludes »

Wise words. I've been wondering about exactly this - upgrading the AK4490. Many ways to do that. I have the WAVE IO board for USB input though that's wired to the Soekris at present.
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Ray P
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#56 Re: Soekris DAC Build

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Coming to this late but I would still investigate the Soekris filter options as well as exploring tweaks to the AK4490. There's a whole lot more information and experience of the Soekris DAC over on DIY Audio, including a whole thread on brewing different filters.
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