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Class D Switching Power Amplifiers and Power D/A conversion

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Old 13th May 2014, 08:57 PM   #1
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Default Noob all-in one digital audio

I am ready to embark on a first DIY audio expedition, which is supposed to replace my age old Marantz PM4xxx amp, my harman/kardon CD player (that I use as an external DAC) and my media center with a single all-inclusive digital box driving my once-famous Kef cresta 2 speakers (100W RMS).

So, the main component of this system is a Class D amplifier module. What I need is a module (or a combination of modules) that takes one i2s input from a system-on-a-chip board (like raspberry or beagle bone black) and amplifies it, attaining a SQ beyond my current entry-level audio system. I also need a coaxial and an optical SPDIF input to connect other devices (but no analog needed). Finally I need the whole system to be remote controllable.

First I had settled on DDX320 from hifimediy that has received a number of good reviews and seems to fulfill all the criteria. But the kit has been out of stock for a while and hifimediy seems unsure of its future.

I then decided to upgrade my plans, for instance by combining hypex amps with USB/digital audio receivers and a sabre DAC. But this costs several times more than the initial setup and still doesn't provide all I need: I will need to add a separate DSP and a control board to make remote controlled switching between inputs possible. Plus, I do not want to create too much complexity for this first project (although I know that the difference in SQ will probably justify all the hassle...).

I wonder if you have any alternative for ddx320 in mind, or any suggestion that can simplify/complete my project without compromising the requirements/outcomes.

Thanks in advance for your help!

Last edited by retrography; 13th May 2014 at 09:24 PM.
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Old 15th May 2014, 01:34 AM   #2
thommy is offline thommy  United Kingdom
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I do not know of any amps with built in dacs which sound anywhere near what you would call hifi.

B&O ICEPower amps are convenient with an onboard power supply and sound very good considering their price ($250 for the 90wpc RMS 125ASX2 module).

You will need either to take the I2S directly from the Pi and feed it into a DAC, or use a suitable USB -> I2S interface.

Next you need a DAC with switchable I2S and SPDIF inputs. Getting TOSLink and RCA SPDIF might also be difficult and you are unlikely to be able to select one of the three types with a single switch. It's most likely going to be one for I2S / SPDIF and another for TOSLink / RCA.

After the DAC you might need an attenuator or buffer unless you are happy with using a software only volume control.

Some idea of your budget would be useful.
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Old 20th May 2014, 02:20 AM   #3
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Thommy,

Thanks for your constructive response. I just looked up B&O's ICEPower amps and it seems your suggestion is one of the best choices I have. My main question is how can one buy ICEPower amps, given that the website explicitly stipulates that the company is not interested in end consumers (for this product line)?

I found out that there is a Ghent Audio anodized aluminium enclosure that is designed for this amp and comes with an optional passive pre-amp ALPS volume potentiometer. That should (I assume) be sufficient to take care of the volume until my next upgrade...

I have also found a second-hand Cambridge Audio DacMagic for a reasonable price that can take care of D/A conversion. It has TOSLINK, Coaxial, and USB inputs, so it should solve the input-switch issue. It doesn't have a remote control, but that is a fair compromise given the price.

I am wondering, though, whether I will be better off with a pair of Hypex UcD 180s instead of the B&O. I have never used any of the two. Both power supplies and transformers matching with UcD 180 are currently on promotion on Hypex website... That makes it an interesting deal: The set of two UcD180HG + HxR + 2 separate transformers + two separate power supply modules can be had for 280 euros.

Concerning the budget, I really don't have one. The aim is to 1) get rid of the old equipment with their lifeless sound 2) start a DIY audio system that I can gradually tweak later 3) make a nice-sounding space-saving little hifi that when I move to my own condo I can use as the bedroom hifi. But for now it will be used as the main hifi for about a year or so. I just don't want to spend too much on it, because it is a rather temporary solution, but I don't want to get to a similarly lousy sound as I have today...

Btw, I don't think DDX320 has an integrated pre-amplification DAC. As far as I know it converts the PCM input from I2S directly to PWM, amplifies it, and then transforms the digital signal to analog audio only at the output stage... As such it completely bypasses D/A conversion at the line level.

Last edited by retrography; 20th May 2014 at 02:49 AM.
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Old 25th May 2014, 03:51 AM   #4
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Default Here are a few ideas....

Have you considered MiniDSP?They sell DSP and amp modules. I myself own a 2x4 DSP and use it for EQ and crossover duty.

Recently I saw this web site and their Genius DSP and amp combos. The prices are good but I have no personal experience with them.
DSP+CLASS D AMP+SMPS 2.1 OR THREE WAY HI FI AMP WITH ANALOG/SPDIF/USB SOURCE SELECTOR-in Consumer Electronics on Aliexpress.com

The co. is "Sinewave'. You can google the home site. They sell a more powerful box too. I'd buy the cheapie for lower power uses. I believe this product would be competitive with nearly anything.

Let me also add my prejudice that, beyond some point, much of the sound quality you think you hear is hallucinogenic Not saying there is never a difference but those who most resist (double) blind tests usually have a paycheck (= dealer) or ego ( = builder or gullible buyer) at stake. For people like me, my ego is not too big and takes pride in our ancient Bose 901s, Behringer amps and other unspeakable things

Duh, here is an old thread recently active, dealing with the same Co. different product

csinewave T400D

I have no idea of Sinewave's availability, but I am a new happy customer of AliExpress.I got a huge (12" screen) Android tablet under $200 deliverred in like two days. They have a credit card security process that takes some trouble but seems to be legitimate. And bless my bank...they approve an internet sale in China and the next night decline my grocery store purchase (5 miles from my home) as a "fraud alert"
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Last edited by Soldermizer; 25th May 2014 at 04:04 AM.
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Old 25th May 2014, 05:13 AM   #5
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There is also the extraordinary G36D: Genius 36D

Yet, I don't know what to think about these products. As much as I hear about their sound, I also hear about their low build quality and subsequent problems.

And I won't pay a penny for a product that leaves me indifferent in real (blind-tested) performance. But there are changes that one does notice: I have been using a pair of highest-end Monster RCA cables to connect my DAC and my amp. These were bought about 6 years ago for a considerable amount of money. But they are pretty heavy and keep putting too much pressure on RCA connectors of my devices. My local audio shop suggested that I take home a pair of RCA cables at about 80$ price point and test them, before the RCA connectors break. I did so, and even without doing A/B tests I immediately knew I was hearing a huge loss in low frequencies... I mean, 80$ is still supposed to be quite decent, but turns out that not really.

I also had the opportunity to compare several Moon amps with some more regular sells such as mid-range Rotels, NADs and Cambridge Audios a couple of months ago. I can tell you the 2-3k difference in price was very well justified!

So, for now I am looking into Abletec, Hypex and B&W ICEPower amps for amplification. I have also been looking into Dac Magic, MiniDSP and Twisted Pair (Twisted Pear Audio) for DSP and DAC. Twisted Pair seems to be in process of making an external audio masterclock cape for Beagle Bone Black in order to make it possible to fetch I2S signal directly from BBB's audio controller...

But I am eager to hear if anybody has experience using Sinewave products.

Last edited by retrography; 25th May 2014 at 05:19 AM.
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Old 25th May 2014, 08:25 PM   #6
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A pair of 36Ds are even more enjoyable
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Old 25th May 2014, 10:46 PM   #7
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Quote:
Originally Posted by retrography View Post
...
Btw, I don't think DDX320 has an integrated pre-amplification DAC. As far as I know it converts the PCM input from I2S directly to PWM, amplifies it, and then transforms the digital signal to analog audio only at the output stage... As such it completely bypasses D/A conversion at the line level.
Err, sort of.

The DDX320 has a wm8805 that switches between 4 spdif: 2 rca, 2 optical (and has a switch that enables 4 more spdif in). The 8804 outputs I2S to the STA320 (there's also some control signals on the side). The STA320 converts the I2S to amplified PWM which is filtered and goes to the speakers ... yep no DtoA and AtoD!



The DDX320 accesses some of the STA320's cool features: 2 vs 3 ch, xover 80-360Hz, eq settings ...

DDX w cllk, digital ps, 15 000uf on ps.jpg

from
Another project, all digital DDX amplifier


The STA320 is a cool chip (from spec):

FEATURES:
■ 2.1 Channels of 24-bit DDXTM
■ >100dB SNR and Dynamic Range
■ Selectable 32kHz-192kHz Input Sample Rates
■ I2C control with Selectable Device Address
■ Digital Gain/Attenuation +48dB to -90dB in 0.5dB steps
■ Soft Volume Update
■ Individual Channel and Master Gain/ Attenuation
■ Dual Independent Limiters/Compressors
■ Dynamic Range Compression or Anti-Clipping Modes
■ AutoModesTM:
– 7 Preset Crossover filters
– 32 Preset EQ Settings
– Auto Volume Controlled Loudness
– 3 Preset Volume Curves
– 2 Preset Anti-Clipping Modes
– Preset Nighttime Listening Mode
– Preset TV AGC
■ Individual Channel and Master Soft and Hard Mute
■ Independent Channel Volume and DSP Bypass
■ Automatic Zero-Detect Mute
■ Automatic Invalid Input Detect Mute
■ 2-Channel I2S Input Data Interface
■ Input and Output Channel Mapping
■ 4 28-bit User Programmable Biquads (EQ) per channel
■ Bass/Treble Tone Control
■ DC Blocking Selectable High-Pass Filter
■ Selectable De-emphasis Post-EQ User Programmable mix
■ User Programmable 2.1 Bass Management
■ Sub Channel Mix into Left and Right Channels
■ Advanced AM Interference Frequency Switching and Noise Suppression Modes
■ Selectable High or Low Bandwidth Noise Shaping Topologies
■ Variable Max Power Correction for lower fullpower THD
■ 3 or 4 Output Routing Configurations
■ Selectable Clock Input Ratio
■ 96kHz Internal Processing Sample Rate, 24 to 28-bit precision

Attachment 420446



But DIYer implementations rarely give you access to all that.

...

...

Even less implemented is the Hifimediy UDA20 (20W) and UDA80 (80W).

They have all the same capabilities (and more) but have been reined back to just digital volume and full range 2-ch! the STA must be sooo bored ....

Attachment 420448

STA533BW
Features
■ Wide supply voltage range (5 to 24V)
■ 4 Power Output Configurations – 2 channels of ternary PWM (stereo mode)
(2 x 20 W @ 8 Ω, 18 V) – 3 channels - left, right using binary and LFE
using ternary PWM (2.1 mode) (2x10W + 1x20 W @ 2 x 4 Ω, 1 x 8 Ω, 20 V)
– 1 channel PWM output (parallel-mode) (1 x 40 W) – 2 channels of ternary PWM (2 x 20 W) + stereo lineout ternary
■ 2.1 Channels of 24-Bit DDX®
■ >94dB SNR and Dynamic Range
■ Selectable 32 KHz to 192 KHz Input Sample Rates
■ I2C control with Selectable Device Address
■ Digital Gain/Attenuation +48 dB to -80 dB in 0.5 dB steps
■ Soft Volume Update
■ Individual Channel and Master Gain/Attenuation
■ Dual Independent Limiters/Compressors
■ Dynamic Range Compression or Anti-Clipping Modes
■ AutomodesTM
– 15 Preset Crossover filters
– 2 Preset Anti-Clipping Modes
– Preset Nighttime Listening Mode
■ Individual Channel and Master Soft and Hard Mute
■ Independent Channel Volume and DSP Bypass
■ Automatic Zero-Detect Mute
■ Automatic Invalid Input Detect Mute
■ 2-Channel I2S Input Data Interface
■ Input and Output Channel Mapping
■ 4 x 28-bit User Programmable Biquads (EQ) per channel
■ Bass/Treble Tone Control
■ DC Blocking Selectable High-Pass Filter
■ Selectable De-emphasis
■ Sub Channel Mix into Left and Right Channels
■ Advanced AM Interference Frequency Switching and Noise Suppression Modes
■ Selectable High or Low Bandwidth Noise Shaping Topologies
■ Variable Max Power Correction for lower fullpower THD
■ Selectable Clock Input Ratio
■ 96 KHz Internal Processing Sample Rate, 24 to 28-bit precision
■ Thermal Overload and Short-circuit Protection embedded
■ Video Application: 576 x fs input mode supporting
■ PSSO-36 Slug Down package.

Last edited by AudioLapDance; 25th May 2014 at 11:12 PM.
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Old 26th May 2014, 06:21 PM   #8
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Quote:
Originally Posted by AudioLapDance View Post
...The 8804 outputs I2S to the STA320 (there's also some control signals on the side). The STA320 converts the I2S to amplified PWM which is filtered and goes to the speakers ... yep no DtoA and AtoD!



The DDX320 accesses some of the STA320's cool features: 2 vs 3 ch, xover 80-360Hz, eq settings ...
...
Err, sort of! Its 2op+2coax spdif in, WM8805 to STA320

Then STA320 to:

STA510A (2x100W@6ohm) for stereo
STA510 stereo.jpg
STA510A.pdf

and sta508 (160W@4ohm) for bass channel.
STA508 BTL 160WTHD10%VCC35V4Ω.jpg
STA508.pdf

Wow, forgot how powerful it is ... hmmm, with 3 SLAs 3x12.8V=38.4V maybe I'll put it in the car ....
















Last edited by AudioLapDance; 26th May 2014 at 06:26 PM.
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Old 1st June 2014, 09:17 AM   #9
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Here's what I did: http://www.minidsp.com/forum/diy-hif...lt-in-nanodigi
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Old 3rd June 2014, 01:42 PM   #10
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Thanks AudioLapDance for the comprehensive explanation! That is exactly why I am searching for a ddx320. Despite all its SQ limitations, it seems to be a great kit to start exploring no-feedback d-class amps. It seems it is the only DIY kit available that exploits at least some of the DSP and control capabilities of STA320.

cookiemonster77, do you mind sharing a bit more with us? Maybe a simple diagram that makes visualizing the whole system easier? I am really interested in your assembly.




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