Reviewing what I wrote, turns out its neither
The Intersil uses 15uH coils (through hole type) and the STA board has 22uH (SMT). So I should have suggested 33uH to you for the Popa amp. But a filter designed for 16ohms load can be used with either of the designs.@JP more than happy to have this thread split up by board. And I agree with what you're saying about it being the future - based on SQ it'll have no competition provided the power supply makes the grade. Because digital end to end solutions have to be compelling unless one wants to sell 'audiophile' cables at hefty mark-ups
@irribeo - Is your estimation of quality based on listening or numbers? If the former which have you listened to?
To avoid further confusion I suggested the mods to call the subcategory: "Full Digital Amplification". Not a name I really like (thinking of 0's and 1's going to a speaker) but I think it covers best what is meant and it seems a kind of standard name in the market.
@Abraxalito: please make a new thread for the other board and rename this one (or have it renamed) to a thread name that covers the first board or simply start a new one and let this one be (deleted). Can't help you as I am not a moderator.
Hope you are not doing this on purpose: of course the FDA technology itself is broadly meant not a variety of just one chip manufacturer. A new subcategory "Full Digital Amplification" will also separate standard Class D from FDA meaning more clear sight in the threads. You can try to fight FDA but I think you won't win Let's see where we will be in a year from now OK?
@Abraxalito: please make a new thread for the other board and rename this one (or have it renamed) to a thread name that covers the first board or simply start a new one and let this one be (deleted). Can't help you as I am not a moderator.
Hope you are not doing this on purpose: of course the FDA technology itself is broadly meant not a variety of just one chip manufacturer. A new subcategory "Full Digital Amplification" will also separate standard Class D from FDA meaning more clear sight in the threads. You can try to fight FDA but I think you won't win
Let's see where we will be in a year from now OK?
Last edited:
OK, answer from the moderator team is that this type and topology of design (FDA) fits well under the current Class D brief and that an additional forum or subforum is not at this time warranted.
No separate subcategory for now. Well, I tried
I suggest keeping FDA topics under "Digital Line Level" as that fits better than "Class D". FDA have SPDIF/USB/I2S inputs in general (so digital line level). Modifications probably will be in that field too.
No separate subcategory for now. Well, I tried
I suggest keeping FDA topics under "Digital Line Level" as that fits better than "Class D". FDA have SPDIF/USB/I2S inputs in general (so digital line level). Modifications probably will be in that field too.
Last edited:
Here's another listing that has a diagram of the various controls which might be useful.
HIFI 20W+20W USB Pure Digital Stereo Audio Amplifier Board USB Sound Card/DAC PC | eBay
Ray
HIFI 20W+20W USB Pure Digital Stereo Audio Amplifier Board USB Sound Card/DAC PC | eBay
Ray
Obviously without a board to inspect I can't be sure but I suspect the tracks I've scribbled around on the image below deliver I2S data from the USB section to the STA chip. If I'm right it should be simple enough to solder I2S connections to the vias in front of the chip, though clearly we will need to work out which connection is which. I'll have a more detailed look at the datasheet a bit later.
An externally hosted image should be here but it was not working when we last tested it.
Here's a link to the STA chip datasheet;
http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00166760.pdf
Page 10 includes a pin allocation table that shows I2S inputs on pins 28 (BCLK), 29 (LRCLK) & 30 (DATA). Table 13 (Page 24) confirms internal operation as 88.2/96KHz, higher sample rates get down-sampled (and lower rates up-sampled). Lots more to digest but it does look like it will be possible to improve on the onboard USB input.
As abraxilato has shown, there are benefits to be had with a good power supply so what's the thinking on the optimal approach to a power supply for this sort of device?
Ray
http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00166760.pdf
Page 10 includes a pin allocation table that shows I2S inputs on pins 28 (BCLK), 29 (LRCLK) & 30 (DATA). Table 13 (Page 24) confirms internal operation as 88.2/96KHz, higher sample rates get down-sampled (and lower rates up-sampled). Lots more to digest but it does look like it will be possible to improve on the onboard USB input.
As abraxilato has shown, there are benefits to be had with a good power supply so what's the thinking on the optimal approach to a power supply for this sort of device?
Ray
These amps (as irribeo has hinted above) have no PSRR so what you hear is the power supply.
The switching output stage has no feedback in this technology so its just a multiplier of the supply rail - the volume can be controlled simply by reducing the supply volts. This extreme sensitivity to the supply is the challenge - the reference is found when feeding headphones as the SQ is the most dynamic I've heard from any amp/DAC combination to date. With headphones the current demands are very low hence not taxing of the supply, but with speakers as a load it becomes much more of a challenge to create a low impedance throughout the whole audio band. I go for arrays of smaller caps as single larger caps tend to have higher ESR and ESL.
The switching output stage has no feedback in this technology so its just a multiplier of the supply rail - the volume can be controlled simply by reducing the supply volts. This extreme sensitivity to the supply is the challenge - the reference is found when feeding headphones as the SQ is the most dynamic I've heard from any amp/DAC combination to date. With headphones the current demands are very low hence not taxing of the supply, but with speakers as a load it becomes much more of a challenge to create a low impedance throughout the whole audio band. I go for arrays of smaller caps as single larger caps tend to have higher ESR and ESL.
If only it were that simple!
Thanks for the pointer (and the link in your follow on post).
What are you using as your supply currently, I get the capacitor bank aspect but are you still using a SMPS brick or have you gone for a ground up power supply? Just trying to tap into what you've learned so far.
To my simple thinking a shunt supply would seem like a good option, though I'm not aware of any designs with sufficient current for a loudspeaker solution. I do have a Twisted Pear Placid HD (which will deliver upto around 800mA I believe) that I could perhaps try for headphone operation?
Ray
On the STA333 board I'm feeding the 'powerbase' cap bank underneath from my adjustable bench supply - a cheapo Chinese unit which does the job fine. On the Popa amp I'm still using the supplied 24V brick. But on that I'm going to experiment with higher voltages as I'm not quite satisfied with the sound yet, good though it is.
A shunt supply might be good though it hard to imagine its going to achieve the impedance of an optimized cap bank (comfortably below 10mohm above 1kHz). Besides a shunt rather negates the efficiency of the switching output does it not? For headphones if you're using a step-down transformer then the supply becomes far less critical - my headphone version of the Popa amp has an effective load impedance around 1kohm. So the supply impedance is 100X less critical.
A shunt supply might be good though it hard to imagine its going to achieve the impedance of an optimized cap bank (comfortably below 10mohm above 1kHz). Besides a shunt rather negates the efficiency of the switching output does it not? For headphones if you're using a step-down transformer then the supply becomes far less critical - my headphone version of the Popa amp has an effective load impedance around 1kohm. So the supply impedance is 100X less critical.
Hi, how do you feed your headphones from class d amplifier, since I know the GNDs of the 2 channels must not be tied together? have you made a custom headphone jack with separate grounds to each channel, so instead of 3 wires you have 4 wires?
All new Nad amps are Hypex so it seems and they all are more or less immune to speakerload because of feedback. A very small amp can be made filterless maybe, that would be a future for digital input devices. But really, come on, requiring a very good psu to get to this ??? blue line. How bad a dac do we need to attach to TI analog input new series tpa32xx 40-700 watt that also will be less speakerload sensitive with second external feedbackloop ?? Red line is with postfilter feedback added.
Attachments
great idea @abraxalito, can you give me a link to a readily available transformer which does the job? i'm not interested in some very expensive "audiophille" ones, just a cheap one that does the job right in this scenario, strictly for headphone use; are these transformers universal type, I mean they match to any class D amplifier or only to some specific chip? thanks