Thank you Abraxalito for the input,
Of course I'll use the "balanced" version of the headphones instead of trannies, since they most often color the sound. Anyway, I guess that we can obtain a very nice sound through headphones with these chips !
I haven't found the link of the STA333BW Boards on Taobao... Any link welcome !
Perhaps I'll better understand your mods as explained in the blog after having a close look to the board.
Of course I'll use the "balanced" version of the headphones instead of trannies, since they most often color the sound. Anyway, I guess that we can obtain a very nice sound through headphones with these chips !
I haven't found the link of the STA333BW Boards on Taobao... Any link welcome !
Perhaps I'll better understand your mods as explained in the blog after having a close look to the board.
When not using trafos you'll find high impedance headphones (e.g. DT880s in the 600ohm incarnation) are better suited than lower impedance ones. In fact if you're running at 12V supply the DT880s in 600R are close to a perfect match (provided you liberate the commoned 0Vs of course!). You'll then want to choose filter components (L,C) to suit a 300ohm loading (half the 600ohm across the bridge).
The link to the Taobao vendor is here : https://item.taobao.com/item.htm?spm=a230r.1.14.19.4wjcvg&id=526018865372&ns=1&abbucket=13#detailhttps://item.taobao.com/item.htm?spm=a230r.1.14.19.4wjcvg&id=526018865372&ns=1&abbucket=13#detail. The same board's available on Ebay - check out the thread about it where a couple of links have been posted - http://www.diyaudio.com/forums/class-d/299007-modding-taobao-digital-amps.html
The link to the Taobao vendor is here : https://item.taobao.com/item.htm?spm=a230r.1.14.19.4wjcvg&id=526018865372&ns=1&abbucket=13#detailhttps://item.taobao.com/item.htm?spm=a230r.1.14.19.4wjcvg&id=526018865372&ns=1&abbucket=13#detail. The same board's available on Ebay - check out the thread about it where a couple of links have been posted - http://www.diyaudio.com/forums/class-d/299007-modding-taobao-digital-amps.html
Thank you for the links... I found the Ebay link of the STA board myself in the interval and the thread you opened on DIY Audio on the subject. As stated by Jean-Paul these boards are limited to 44.1-48 kHz sampling rate, even if internal processing is made in 96 kHz.
I understand that, as usual, the higher the load, the better the adaptation with the amplifier output... But some guys argue that this is untrue with the ST chips... They aren't explaining always the reasons why it's like this.
Please, can you recall me how to compute the L-C components to suit the load ? Since I've a bunch of headphones, I suppose that I've to make several adapted interfaces with the correct L-C cells for every headphone...
I think it's a really nice project provided the boards with ST chips are available with other than the limited 333 DDX.
I understand that, as usual, the higher the load, the better the adaptation with the amplifier output... But some guys argue that this is untrue with the ST chips... They aren't explaining always the reasons why it's like this.
Please, can you recall me how to compute the L-C components to suit the load ? Since I've a bunch of headphones, I suppose that I've to make several adapted interfaces with the correct L-C cells for every headphone...
I think it's a really nice project provided the boards with ST chips are available with other than the limited 333 DDX.
I'm not sure its necessary to have perfect damping on all your headphones, for the reason that the peaking of the filter is normally beyond our hearing range.
This paper from TI deals with the calculations for the filter - http://www.ti.com/lit/an/sloa119b/sloa119b.pdf
This paper from TI deals with the calculations for the filter - http://www.ti.com/lit/an/sloa119b/sloa119b.pdf
Thanks Abraxalito for this reference. Not sure that one can derive the correct values for any situation, since it seems the calculations are valid for 4, 6 and 8 ohms loads both for the AD and the BD modulations.
May be I'm wrong and I didn't catch the method...
Any additional explanation will be welcome !
May be I'm wrong and I didn't catch the method...
Any additional explanation will be welcome !
Yes the TI paper discusses filters for going between classD amps and speakers. On that particular blog post I'm showing a filter for going between a digital amp (i.e. a digital input amp) and an analog power amp. The extra orders are there because amplifiers hate ultrasonics. If you'd like to follow up on that theme, check out Audio Precision's use of a passive high-order filter when doing measurements of a classD amp.
Hi abraxalito,
I come back to your idea of using trafos with the STA3XX boards for headphone use purposes. I think there are at least two main drawbacks in this project :
- firstly, I didn't never achieve a "neutral" sound with trafos, even high-quality inputs or/and outputs units, and as a passive volume controller (TVCs).
- then, we loose 3 dB in the balanced to single-ended transformation.
The level reduction can easily be made through resistors bridges and the filter, as you explained, can be modified with a few passive components.
What is your opinion on these points and can you suggest a simple solution with a few components to derive an headphone amp with this cheap STA333 board (I already acquired a couple of them for this project).
I come back to your idea of using trafos with the STA3XX boards for headphone use purposes. I think there are at least two main drawbacks in this project :
- firstly, I didn't never achieve a "neutral" sound with trafos, even high-quality inputs or/and outputs units, and as a passive volume controller (TVCs).
- then, we loose 3 dB in the balanced to single-ended transformation.
The level reduction can easily be made through resistors bridges and the filter, as you explained, can be modified with a few passive components.
What is your opinion on these points and can you suggest a simple solution with a few components to derive an headphone amp with this cheap STA333 board (I already acquired a couple of them for this project).
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How would you then describe the sound that you got with your high-quality units?
In my experience transformers give a more neutral sound than solid state circuits, even discrete ones. TVCs to my ears sound more transparent than volume control pots. I also find digital volume controls (such as implemented in the digital amps I've tried) effectively transparent.
On your second point, I don't recognise the '3dB loss' that you mention. Would you please spell it out in more detail, giving numbers of a specific example so that I can follow along?
In my experience transformers give a more neutral sound than solid state circuits, even discrete ones. TVCs to my ears sound more transparent than volume control pots. I also find digital volume controls (such as implemented in the digital amps I've tried) effectively transparent.
On your second point, I don't recognise the '3dB loss' that you mention. Would you please spell it out in more detail, giving numbers of a specific example so that I can follow along?
How would you then describe the sound that you got with your high-quality units?
Coloured... In the best way. But not close enough to the original sound. For example, I made several recordings live with good mikes (Schoeps CMCC6 with cardioïde caps in both analog and digital) using an artist I perfectly know, since it's my daughter, thus I can compare the original to the reproduced versions using several volume controlers (TVC, High precision resistor matrices, and a lot of other systems) and Genelec active monitors. I agree with you : best results have been achieved in digital domain, and this discover has stopped my quest for the best volume control. With the 3 or 4 different TVCs I built, the sound always took a specific colour depending of the transformers used... And even the best transformers add a bit of distortion. But of course, this is my personal experience.
On your second point, I don't recognise the '3dB loss' that you mention. Would you please spell it out in more detail, giving numbers of a specific example so that I can follow along?
Well, please forget the "loss" I mentioned, this isn't an issue, because you're using a 7:1 reduction ratio... Whatever the topology of the balanced to unbalanced, the induced "loss" is small compared to the reduction factor. But, it remains that to unbalance a transformer output, one compromises the common mode noise rejection by grounding one side of the transformer, you don't think so ?
Coloured... In the best way. But not close enough to the original sound. For example, I made several recordings live with good mikes (Schoeps CMCC6 with cardioïde caps in both analog and digital) using an artist I perfectly know, since it's my daughter, thus I can compare the original to the reproduced versions using several volume controlers (TVC, High precision resistor matrices, and a lot of other systems) and Genelec active monitors. I agree with you : best results have been achieved in digital domain, and this discover has stopped my quest for the best volume control. With the 3 or 4 different TVCs I built, the sound always took a specific colour depending of the transformers used... And even the best transformers add a bit of distortion. But of course, this is my personal experience.
On your second point, I don't recognise the '3dB loss' that you mention. Would you please spell it out in more detail, giving numbers of a specific example so that I can follow along?
Well, please forget the "loss" I mentioned, this isn't an issue, because you're using a 7:1 reduction ratio... Whatever the topology of the balanced to unbalanced, the induced "loss" is small compared to the reduction factor. But, it remains that to unbalance a transformer output, one compromises the common mode noise rejection by grounding one side of the transformer, you don't think so ?
Strikes me that the largest colouration you may have in your system will be the amplifiers of the Genelecs?
On transformer grounding, I'm not grounding anything on the transformers. The outputs are remaining floating, there's no need to ground the common sides of the two windings (L and R).
On transformer grounding, I'm not grounding anything on the transformers. The outputs are remaining floating, there's no need to ground the common sides of the two windings (L and R).
Do you try some studio monitors one day or another ? Colored is probably the last characteristic of a studio monitor. But forget it, you ask me why I do prefer to avoid a transformer, I explained what I observed and measured. But again, this is my personal opinion.
If you don’t ground the low (pin 3) side of an output transformer, but instead leave it floating, your receiving device will see a very low-level signal that is lacking in low frequencies. This is because there’s nothing but stray capacitance between the transformer windings and ground to complete the circuit. But may be I'm wrong about this point.
Anyway, if it's possible, I'll avoid the use of transformers at inputs or outputs of my audio systems.
And I thank you very much for your help in this project.
If you don’t ground the low (pin 3) side of an output transformer, but instead leave it floating, your receiving device will see a very low-level signal that is lacking in low frequencies. This is because there’s nothing but stray capacitance between the transformer windings and ground to complete the circuit. But may be I'm wrong about this point.
Anyway, if it's possible, I'll avoid the use of transformers at inputs or outputs of my audio systems.
And I thank you very much for your help in this project.
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Yeah I have tried, I used to have a day job working for a studio console manufacturer in UK. So perhaps we mean different things by 'coloured'?
My output transformers don't have pin numberings, sounds rather like you're talking about XLRs? The circuit most certainly is complete without any ground or no sound would come out.
My output transformers don't have pin numberings, sounds rather like you're talking about XLRs? The circuit most certainly is complete without any ground or no sound would come out.
May be we aren't speaking of the same thing and I apologize because my English isn't good enough to perfectly translate what I have in mind. Anyway, I compared the TVCs and a bunch of other volume controllers to the digital volume control of the DACs just in front of my 1032A+1094A system : the digital was, by far, the best , i. e. the more neutral, of all.
Anyway, as I tried to explain, I just want to modify the output of the STA333 board or to add the less components possible to reduce the gain and adapt the impedance to my IEMs and Headphones. If I'm correct the outputs of the STAs are differential, then a balanced use of the cans is allowed. I do prefer to keep this facility in the mods if it's possible.
Anyway, as I tried to explain, I just want to modify the output of the STA333 board or to add the less components possible to reduce the gain and adapt the impedance to my IEMs and Headphones. If I'm correct the outputs of the STAs are differential, then a balanced use of the cans is allowed. I do prefer to keep this facility in the mods if it's possible.
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