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New FIFO buffer for RPI/SBCs
New FIFO buffer for RPI/SBCs
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Old 11th March 2018, 08:10 AM   #1541
cdsgames is offline cdsgames  Canada
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Quote:
Originally Posted by Dimdim View Post
That sounds excellent.

I was just asking because the previous figures that you quoted were "THD+N" so I just wanted to be sure that we were comparing apples to apples.
Apple to apples its the right way..however a lot of the N in the THD+N comes from actual PSU and some (in testing) from the Gdn of the RPI.

THD is more from the dac design and analog stage.
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Old 11th March 2018, 01:33 PM   #1542
soundcheck is offline soundcheck  Germany
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Quote:
Originally Posted by cdsgames View Post
I think that Ians took a different route with his design
No question!

However.

I'm not talking about tweaks here!

Ian introduced a seperate HAT for the outputstage.
This way it can easily get swapped. This is what you IMO should look at at.

Many people appreciate output transformer stages. They prefer them over
opamp stages. I'm just saying...

And then there will be people who'd love to see a tube-HAT-stage.

It's about future options.

All that doesn't mean opamp stages - if done right - are a bad thing.
It's a good option to start with.
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Old 11th March 2018, 03:07 PM   #1543
chris14 is offline chris14
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Quote:
Originally Posted by cdsgames View Post
Apple to apples its the right way..however a lot of the N in the THD+N comes from actual PSU and some (in testing) from the Gdn of the RPI.

THD is more from the dac design and analog stage.
Does the power/control board act as an isolator between the Pi and the rest of the stack, or would you need to use the isolator board in addition to the 3 board stack to remove noise coming in from the Pi?
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Old 11th March 2018, 05:15 PM   #1544
Greg Stewart is offline Greg Stewart  United States
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New FIFO buffer for RPI/SBCs
Quote:
Originally Posted by soundcheck View Post
No question!

However.

I'm not talking about tweaks here!

Ian introduced a seperate HAT for the outputstage.
This way it can easily get swapped. This is what you IMO should look at at.

Many people appreciate output transformer stages. They prefer them over
opamp stages. I'm just saying...

And then there will be people who'd love to see a tube-HAT-stage.

It's about future options.

All that doesn't mean opamp stages - if done right - are a bad thing.
It's a good option to start with.
@Soundcheck,

I'm a bit confused by what you wrote. Allo has had a separate output stage board in the Katana design from the beginning:

Quote:
Originally Posted by cdsgames View Post
Hello DimDim

yeap we had to do it 3 story high. The DAC is connected to i2s so no DSD..checking for DOP (I assumed its compatible)

In any case the design was very complicated , we used lots of LDOs and filtering on both 3.3v , 1.2V and + - 15V (for opamps) . Placement was difficult , but by using 3 decks we separated dirty grounds from clean grounds (not isolated)..and we placed the powers on proper places. Like I said...difficult. <SNIP>
Quote:
Originally Posted by Greg Stewart View Post
Ioan,

I for one am eagerly awaiting this. While there are other R-Pi-based DACs with pretensions to high-ish-end (I'm thinking fo the Terra-BerryDAC2 & the TauDAC as ones that appear to actually have made it to release), none combine the array of features, flexibility, & reasonable cost that you're projecting in this DAC.

I'm excited by:
<SNIP>
2. Multiple-board stacking. One of the biggest issues with getting great performance out of an RPi DAC is the limited board space. Stacking gives you much more flexibility to the manufacturer do great things (such as better output stages and better power) by providing more circuit board real-estate... along with...

3. Flexibility. By separating the main board, output board and power board, you provide for a level of flexibility in options, upgrades, and meddlesome tweaking and modifying like I am wont to do.
<SNIP>
Quote:
Originally Posted by cdsgames View Post
3 board stack

1.ess sabre , 2.analog board output with discrete opamp , 3.control and voltages.

I'd say the difference between Allo & Ian's approaches is that:

- Allo's DAC is intended to give you the best SQ they can manage in a R-Pi DAC HAT-sized set of boards that can be easily by a single 5V supply, but provides some flexibility for tweaking.

- Ian's approach is to give you very good sounding DAC base and one (or maybe eventually more) output board(s) where you can roll your own.

The 1st is great for a product that can be used by a wide swath of consumers, the 2nd is great for many of us DIY'ers here in DIYAudio.

I'm happy that both are out there and intend to use both when they are available.

Just my 2 cents.

Greg in Mississippi

P.S. For a DAC HAT with a separate transformer output stage already available, you can go buy a TauDAC at about 650 Euro.
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Last edited by Greg Stewart; 11th March 2018 at 05:24 PM.
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Old 12th March 2018, 09:43 AM   #1545
cdsgames is offline cdsgames  Canada
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Hmmmmm....we found out that our AP machine has a noise of 6uV on RCA and 10uV on XLR by default ( using loop back).

Our noise in RCA is of 13uV right now and 25 of XLR (removing base noise thats 7uV on RCA and 14 on XLR)

THD+N is solved. I don't have the exact calculation but its better than -105 THD+N on both RCA and XLR (1Khz). :-)

Final version of PCBs (after measuring and tweaking every power rail , about 45 different ones) is being worked on and will sent to PCB house for mass production.

Also as a side note , we have developed the 5V SMPS that goes along with it. 10 days to new prototype. We expect to set a new record in 5V SMPS ( low noise) in both input (towards mains) and output (towards your DAC/RPI) . Special attention was directed towards "leakage currents" on output and EMI reduction at the source. (diode and mosfet)

Its hard to explain how many hours we slaved in reducing loop area on mosfet (imagine a tetris game) we changed the mosfet 3 times , last time to gain about 4mm sq (less) of loop area . Also ferrite beads were strategically placed in gate driver , drain and r2dc snubber (+ 2 on source resistors)

Along with less EMI , we have as a side effect that we need less Y capacitance to pass EMI test and less Y capacitor = less leakage .
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Old 12th March 2018, 09:46 AM   #1546
cdsgames is offline cdsgames  Canada
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Quote:
Originally Posted by soundcheck View Post
No question!


All that doesn't mean opamp stages - if done right - are a bad thing.
It's a good option to start with.
Its done right :-) Handmade. (rather checked manually for offset). Only film caps on the path (or LPF) analog side.
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Old 12th March 2018, 09:52 AM   #1547
cdsgames is offline cdsgames  Canada
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Quote:
Originally Posted by chris14 View Post
Does the power/control board act as an isolator between the Pi and the rest of the stack, or would you need to use the isolator board in addition to the 3 board stack to remove noise coming in from the Pi?

No it does not. This week we have scheduled to test the isolator board as well to see whats the reduction in noise. However when you arrive at 6-7uV its hard to see the improvement.
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Old 13th March 2018, 04:08 PM   #1548
cdsgames is offline cdsgames  Canada
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Default Opamp board

Discreet stage .
Attached Files
File Type: pdf OPAM 03.pdf (370.0 KB, 406 views)
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Old 13th March 2018, 05:16 PM   #1549
absolutk is offline absolutk
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XLR?!
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Old 13th March 2018, 06:22 PM   #1550
Dimdim is online now Dimdim  Greece
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New FIFO buffer for RPI/SBCs
This looks very nice.. very nice indeed..
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