Raspberry Pi streamer DAC builds

Thermionics said:

OK. So if I don't care about DSD (sorry, I'm a heathen), is there anything else gained by his FIFO?

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Of course, DSD compatibility is not the raison d’être for these items by any stretch of the imagination, it's an added bonus for those that want it. All of the design is applicable to straight PCM too, whether that be 16-bit Redbook or 24-bit "hi-rez" files.

The FIFO you allude to is not a brand new type of design, it was pioneered by Wadia 2+ decades ago. Many of the best sounding CD players and DACs of the last 20 years employ a similar design, a FIFO is utilized to remove jitter at the input by briefly storing the data (in first in first out fashion) in a memory buffer and then precisely re-clocking it using ultra-spec clocks (oscillators) and very tight local power supply voltage regulation.

That simply sounds better regardless of the playback format, and prior to the last few years was something completely unimaginable as available for use on low-ticket tech like the Raspberry Pi. Previous versions of this offered by Ian had the FIFO buffer, clocks, and isolator on 3 separate boards.

This latest group buy will offer all 3 of those functions combined onto one HAT, this new incarnation is called FifoPi, pictured below with the DAC HAT on top, and an optional hardware controller board too for those that want to use the DAC's built-in ESS hardware volume control:

Are the green 2-pin connectors on both boards 5VDC? Is it required you power it separately from the Pi board? Would there be any benefit of the FIFO for a non-DAC HAT scenario (e.g. I just want S/PDIF out to an outboard DAC)?

Would this work with Raspbian / SqueezeLite, or do you think I'd have to jump to a different playback client?

[EDIT: found this nugget: "By default, my design works at hardware mode. So, theoretically can work with any software."]

Sorry for all the dumb questions. I'm at work and unfortunately don't have time to read through nearly 300 pages of DIYAudio to try and glean the answers. I appreciate your patience as I think I need to decide sooner rather than later about the group buy.

Thanks!

Thermionics said:

I appreciate your patience as I think I need to decide sooner rather than later about the group buy.

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No hurry just yet, right now all he is asking is for interested parties to use the sign-up list on DIYaudio so that he can properly gauge the production run quantity. That's all, currently there are no prices and as such no commit to buy, but it's going to be coming pretty soon, and that will be the actual Group Buy offering complete with the prices.

Right now there is no obligation, he just asks that only those truly interested sign-up. I think he will wrap this phase at the end of January or so, so another week or two, then officially announce the group buy.

Thermionics said:

Are the green 2-pin connectors on both boards 5VDC? Is it required you power it separately from the Pi board? Would there be any benefit of the FIFO for a non-DAC HAT scenario (e.g. I just want S/PDIF out to an outboard DAC)?

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This one is not a fast answer.

MikeyFresh said:

This one is not a fast answer.

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Perhaps I should just ask the DIYAudio thread and hope that Ian sees it. I'm guessing the short answer on the FIFO-sans-DAC-hat is 'no benefit' as you'd want the re-clock on the DAC end of the house, not on the Pi end.

-D

Thermionics said:

Are the green 2-pin connectors on both boards 5VDC? Is it required you power it separately from the Pi board?

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Yes they are both 5VDC, if I'm remembering it correctly they don't both need to be powered, I believe he said the DAC can be powered by the FifoPi, or the FifioPi can be powered by the DAC. The RPi needs it's own separate power however.

What isn't pictured above is the DAC's analog output stage, that too is a HAT, worn by the DAC, and can either be an actively driven opamp board, or a passive board with transformer based output, I don't remember anymore if he will offer multiple different transformer options as he had at one time hinted, or did he settle on Lundahl LL 1674 as the choice.

Thermionics said:

Perhaps I should just ask the DIYAudio thread and hope that Ian sees it.

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Not a bad idea, and even if Ian doesn't see it there are others there who might be able to chime in with their experience on that configuration. I'd imagine there would still be a benefit, contingent on things like which specific SPDIF HAT is in use, does it have a master clocking arrangement (i.e. Digi+ Pro) and what kind of power supply is in use.

But yes the larger benefit would likely come from using a DAC HAT I'd imagine.

I will have an extra of the original IsolatorPi (sans FIFO and clocks) if you conclude the new version is overkill for an SPDIF arrangement.

What SPDIF HAT do you have, and which DAC do you use with it?

Forthcoming IanCanada set-up with passive Lundahl transformer-based output:



Active I/V stage with OPA861 opamp instead of passive transformer-based output:



The list of items in the IanCanada GB2019 are as follows:

1. FifoPi 768KHz I2S/DSD/DoP for RPi with built in isolator
2. LiFePO₄ pure battery power supply
3. ESS controller
4. Dual Mono ES9038Q2M DAC HAT
5. ES9028Q2M DAC HAT
6. STD opamp I/V stage
7. Transformer I/V PCB mini KIT

So based on the above there is a choice of two slightly different DACs, one using the ES9038Q2M chip in a dual mono configuration, the other using the similar but not identical ES9028Q2M in a single chip (stereo) configuration.

Also a choice of 2 different analog output stages, the standard one uses an actively driven opamp for I/V conversion, while the other is a passive transformer based design and apparently will be a kit, meaning some assembly required (and probably bring your own transformers too as that's a super expensive part for Ian to preorder/stock).

The power supply option at this point is a battery based unit that employs LiFePO₄ cells (probably bring your own cells there to avoid shipping hassles), though any existing/quality 5 volt supplies can be used. There is also a supercapacitor (EDLC) based power supply in development, however it is not ready for this particular GB and may or may not be offered in the near future.

I'm stoked for the dual mono DAC, the FifoPi, battery supply, and transformer I/V stage, however until the prices are set I won't be sure if I can swing all of that, as well as actually assemble the transformer output kit with my brand of knowledge and skill. I'm hoping I can tap the wisdom of @Redboy on such matters so that I don't muck up any expensive parts!

One other interesting photo from the development stage, this is the RPi3, with FifoPi, DAC, and opamp output stage, powered by the "Pure Power" LiFePO₄ multi-voltage rail battery supply:

I am following this with intrest.
I have to make a server decision in the near future.
My issue is computer knowledge.
I like simple easy implementation ... I am not a tech geek

MikeyFresh said:

What SPDIF HAT do you have, and which DAC do you use with it?

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I have a HiFiBerry DIGI+PRO HAT and currently I'm using a transformer-coupled Gigawork LM-DAC3 v9 as a DAC.

Thermionics said:

I have a HiFiBerry DIGI+PRO HAT and currently I'm using a transformer-coupled Gigawork LM-DAC3 v9 as a DAC.

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I would say that set-up is certainly going to benefit from something like a FifoPi, however just how much of that would be due to the galvanic isolation from the RPi's noisy ground vs. the FIFO buffer and re-clocking is tough to say, and the only real way to know would be to directly compare using the new FifoPi with the older IsolatorPi in that set-up.

No question the most important clocking occurs just before the DAC's input as you said, so some (but probably not all) of the FIFO buffer and re-clocking benefit would be squandered or obscured by the imperfect "is what it is" SPDIF transfer protocol.

So right now you power the entire thing from the Pete Millet supply? Use of an isolator would yield the additional benefit of powering the Digi+ Pro separately from the RPi, so you'd use the high quality supply to power the isolator/Digi+ Pro, and a lesser supply can then be used on the "dirty" RPi side. That benefit would be present using either the old or the new version isolator.

MikeyFresh said:

So right now you power the entire thing from the Pete Millet supply? Use of an isolator would yield the additional benefit of powering the Digi+ Pro separately from the RPi, so you'd use the high quality supply to power the isolator/Digi+ Pro, and a lesser supply can then be used on the "dirty" RPi side. That benefit would be present using either the old or the new version isolator.

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Hmmm...given the output of the Millett supply has plenty of amperage, I wonder if I use some sort of custom USB splitter on the output and power both the Pi and the isolator / Digi+ from it?

[EDIT: something like this, perhaps?]

Thanks.

Thermionics said:

Hmmm...given the output of the Millett supply has plenty of amperage, I wonder if I use some sort of custom USB splitter on the output and power both the Pi and the isolator / Digi+ from it?

[EDIT: something like this, perhaps?]

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You could do that, and yes the linked product would work, but I'd be concerned that the wire itself isn't up to snuff as compared to the quality of the power supply, you'd hate to think a cheesy generic wire was holding back that performance.

Separate of just that wire quality, the gauge on the one you linked is meant for USB 2.0 500mA maximum, and one leg also has data "sync" conductors that are entirely unneeded in a power supply umbilical, you only need the VBUS.

I would make that out of a piece of Canare 4S6 star quad, and a Type A USB head shell like this one. Rather than power the RPi through it's micro USB port, just connect two of the wires in the 4S6 to the Pi's GPIO pins like @gable did in Post #1 of this thread, and connect the other wire pair in the 4S6 to the isolator's power input.

MikeyFresh said:

Rather than power the RPi through it's micro USB port, just connect two of the wires in the 4S6 to the Pi's GPIO pins like @gable did in Post #1 of this thread, and connect the other wire pair in the 4S6 to the isolator's power input.

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I think it would be even easier than that with the Digi+ PRO - there's a power header on the board that I could use to power the Digi that includes a pass-through via GIPO to power the PI (unless the FIFO isolates the power pins of the GPIO).

I think I'm gonna sign up for the FIFO.

Thermionics said:

I think it would be even easier than that with the Digi+ PRO - there's a power header on the board that I could use to power the Digi that includes a pass-through via GIPO to power the PI (unless the FIFO isolates the power pins of the GPIO).

I think I'm gonna sign up for the FIFO.

Click to expand...

The isolator aspect would prevent the RPi from being powered through the Digi+ Pro in that way, however the effect would be that the FifoPi would receive it's power from the Digi+ Pro. Unclear whether that would be better/worse/preferential to powering the FifoPi and letting it power the Digi+ Pro, my guess is the latter would be preferred.

I'm already signed up on the so-called "interested" list, the real question now is price. The original IsolatorPi was just $49, however it was only an isolator, it lacked the FIFO memory buffer and reclocking that are part of the FifoPi. I'm hoping it will be closer to $100 than $200, but that's probably wishful thinking.

Thermionics said:

Hmmm...given the output of the Millett supply has plenty of amperage, I wonder if I use some sort of custom USB splitter on the output and power both the Pi and the isolator / Digi+ from it?

Click to expand...

One final thought on this is a vague memory that Ian advised against it, because in effect you then defeat the isolation between the RPi and the DAC/SPDIF HAT.

So even though this works, it is only advisable for two pieces each of which are on the "clean" side of the isolation moat. The RPi is on the dirty side, it has a noisy ground plane and a switching regulator on the board, tying that back to the same power supply as something on the "clean" side of the isolator effectively defeats that isolation.

This question came up with the previous incarnations of these products because they were on separate boards. so you could power the isolator, and anything above it (FIFO, reclocker, DAC/SPDIF) with the same supply assuming enough available current, but you did not want to power anything on that clean side with the same power supply as the one feeding the "dirty" RPi.

MikeyFresh said:

One final thought on this is a vague memory that Ian advised against it, because in effect you then defeat the isolation between the RPi and the DAC/SPDIF HAT.

So even though this works, it is only advisable for two pieces each of which are on the "clean" side of the isolation moat. The RPi is on the dirty side, it has a noisy ground plane and a switching regulator on the board, tying that back to the same power supply as something on the "clean" side of the isolator effectively defeats that isolation.

This question came up with the previous incarnations of these products because they were on separate boards. so you could power the isolator, and anything above it (FIFO, reclocker, DAC/SPDIF) with the same supply assuming enough available current, but you did not want to power anything on that clean side with the same power supply as the one feeding the "dirty" RPi.

Click to expand...

So...two Millett USB 5v boards then?

And am I understanding correctly that the ES9028Q2M and ES9028Q2M DACs are current-source output, hence the I/V stage(s)? So if you want to go with the DAC hat you have to get either the IC I/V or transformer I/V stages?

Thermionics said:

So...two Millett USB 5v boards then?

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Now you're talkin'!

Thermionics said:

And am I understanding correctly that the ES9028Q2M and ES9028Q2M DACs are current-source output, hence the I/V stage(s)? So if you want to go with the DAC hat you have to get either the IC I/V or transformer I/V stages?

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That's correct, and he was also working on offering an adapter board that would allow connection of those DACs to the Twisted Pear Audio I/V stages, which are not HATs, but many people want to use them in more elaborate set-ups that they will put in a larger case. I have not seen any further information on that adapter however so it appears it won't be a part of this group buy: