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Old 18th February 2018, 08:51 PM   #281
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
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ES9038Q2M Board
And if it is true, then
should be:
Jumpers_actual.png
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Old 18th February 2018, 11:44 PM   #282
Lo_Tse is offline Lo_Tse  Canada
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Quote:
Originally Posted by bisesik View Post
It is true. Transformer can not cost less than OPs - it is mostly handmade thing. But for me personally there is no any chances for any OPs to make i/v conversion better than current transformer. In terms of current transformers... It is very important not to confuse current transformers with voltage transformers. Current transformer must have as lower DC resistance of the primary coil as it can, to become really current-mode transformer. In other words, the curernt of the DAC's signal must be shorted to the ground to provide best SQ. And only the inductance as a reactive resistance should transform that alternating current from the primary coil to secondary. In real world it is very difficult task to get low windings (and DC resistance) with enough level of inductance. Browse yourself and try to find out similiar to "mine" transformer specs? I'm afraid that Lundahl transformers are totaly going out of that specs - it is pure voltage transformers. In this case mostly all the conversion happens inside active resistance of primary coil (or even separate resistor in parallel with primary coil of the transformer). Sound is forming outside of the transformer in this case. To safe the output of the DAC from the voltage applied to it during i\v conversion almost forever is used a small value resistor in parallel with primary coil (small voltage of signal as result) and then to make the signal louder, a huge amount of turns ratio (10-20 times!) is applied in transformer. It simply kills the sound. In that case it is really better to use OPs I guess. As far as I know there is only one model in the market at all that can be compared with "my" transformers, but "my" are better at least by specs. I mean Sowter 9545 model, which is captured by AudioNote and not presented on ready for sell market at least for now. Again: DC=5Ohm, Inductance=16H, FR: -0.5dB 20-100k, output level ~8Vpp, turns ratio 1:3.5
Forgive my ignorance, I do not quite understand what exactly are "voltage transformers and current transformers" . When a voltage is applied on the primary side of a transformer, an induced voltage will appear on secondary side. When a load is placed on the secondary side, a current will flow. That's the the whole idea of a transformer. Both voltage and current will be induced on the secondary side of the transformer.

For a real world transformer, there are three kind of losses, copper loss, iron loss and loss due to eddy currents. The DC resistance of the coil is mainly responsible for the copper loss. Higher the copper losses, more signal is "wasted". More turns in the secondary coil of the transformer, higher the inductance. Higher the inductance, higher the reactance ==> higher the impedance. For efficient energy transfer (the signal), the impedances of the output of the secondary coil and the input of the device (which is connecting to the secondary coil) should be within a certain range. Definitely that's something one has to watch out. What exactly is this range, it depends on the transformer and the device it connects to and can be determined experimentally.

Regards,
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Old 18th February 2018, 11:49 PM   #283
Markw4 is offline Markw4  United States
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Agreed, transformers are transformers. The term current transformer usually refers to a transformer that is optimized and characterized for current measurements, such as described here:Current transformer - Wikipedia

But, they are still transformers and standard transformer models apply to them.

EDIT: Corrected Link

Last edited by Markw4; 18th February 2018 at 11:52 PM.
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Old 19th February 2018, 12:04 AM   #284
Lo_Tse is offline Lo_Tse  Canada
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Originally Posted by Markw4 View Post
The AVCC+ power rail is +3.3 volts. I can't measure anything on my board right now as it is all apart. Can't be more than around 3 volts though.

More important is probably how much current it can put out. The sound quality is higher if the DAC outputs are run into a short to ground. That means the secondary of the transformer should be a short and you should have a current stage there to convert to voltage. Otherwise, if you connect the transformer to a high impedance input that means the DAC is still working in voltage mode. If that's what you want, you may as well use it without any modification at all. Well, unless maybe you like the sound of transformers added in. Some of them can make a little distortion that some people like the sound of.
The output current of the DAC is part of its design parameter and not much we can do about it, am I right?

I am baffled by this current/voltage mode thing. There are always voltage and current present at the DAC output. I guess one can manipulate the amount of current wrt voltage. How does one know how much current output is good, how little is bad? It seems to me (correct me if I am wrong) that matching the output impedance of the DAC with the input impedance of the device to which the DAC is connected to is more important.

Regards,


Regards
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Old 19th February 2018, 12:19 AM   #285
Lo_Tse is offline Lo_Tse  Canada
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Quote:
Originally Posted by Markw4 View Post
Some info on the Sowter transformers:
Sowter Type 9545 DAC INTERFACE TRANSFORMER
1465 DAC Interface Transformer
DAC OUTPUT TRANSFORMERS

Looks like 1465 is the closest to the 9545, and it's only about 110 British Pounds for one. They say it is the 100 ohm or 200 ohm resistor that does the IV conversion, and the transformer provides galvanic isolation. They also say the IV resistor can be attached at the secondary, but with it's value increased according to the impedance ratio of the transformer.
Thank you for the link. Useful information!

Regards,
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Old 19th February 2018, 05:09 AM   #286
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
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Transformer is transformer, you are right. Transformer - is a device that transforms impedances. But the source can be current or voltage, right? Let's going away for a minute from this kind of DAC with its "hybrid" output (ES9018, I don't really understand how it can provide pure current mode) but let's refer to the old one R2R DAC. PCM63 for example (http://www.sowter.co.uk/dacinfo/PCM63.pdf). It has only current output of +/-2mA, there is no voltage mode at all. Say, if you will short the current output to the ground, you will not get any Voltage, right? But the current of signal is still there, at full scale it is +/-2mA with the best SQ. Question - is how to grab it and bring to the consumer device without affecting to the output of DAC. It is necessary to force the DAC to work on the ground but it is still necessary to take somehow the whole signal. 1465\9545 is a good choice I guess. But. The more pure (without noise in small signals) dynamic range or the higher the volume of the signal at the output, the better. In this regard, to save small signals from the noise of PSU, I prefer to get the maximum possible volume level from the DAC. Compared to Sowter's transformer I have better choice I hope. But to be honest, if it will be possible in future, I would like to get possibility to compare SQ with such branded devices like LL or Sowter...
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Old 19th February 2018, 06:14 AM   #287
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
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One more thing about this board\DAC. It is may be some kind of joke... But I can not force it to play square signals lower than 7kHz within 384k SR (through I2S). I have a file with the squared signals swept from 0 to 24kHz. And the DAC simply keeps silent untill the freq get up to ~7kHz. After that point it plays without problems till the end of file, till 24kHz. There is no problems when it's playing similar sinusoidal signals from 0Hz and higher. But for square signals lower ~7kHz (for 384k SR) DAC periodically loses the sync (Lock led starts "flashing"). But everything is OK with 192k SR.


Last edited by bisesik; 19th February 2018 at 06:30 AM.
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Old 19th February 2018, 11:01 AM   #288
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
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Another common measuring of this board (with OPamp). 16-bit monotonicity of code of signal conversion. At least, I can not find such measurements in public access.

16bit_monotonicity.jpg

It seems that this DAC can provide 16-bit accuracy (plus/minus)

Last edited by bisesik; 19th February 2018 at 11:03 AM.
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Old 19th February 2018, 12:32 PM   #289
TNT is offline TNT  Sweden
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ES9038Q2M Board
Quote:
Originally Posted by Markw4 View Post
Also, looks like AVCC might be powered by a 3.3V 3-terminal regulator that also provides some power for the 100Mhz oscillator. Appears that the 3.3 volt bus is RC filtered then used for AVCC.

In addition, found another post from back in 2009 saying the ESS DACs outputs can either run into a Hi-Z input buffer buffer for voltage mode, or into a virtual ground IV for current mode operation. The DAC doesn't care which, but SQ is better with IV.
It seems that you have other things going on on that boards that probably has much more effect than I or V out.... ?

My bet is that of you do two implementation identical except for the I & V thing, you don't have much aural difference left... I have done my share of testing with a 9016...

//
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Old 19th February 2018, 01:24 PM   #290
janos_904 is offline janos_904  Hungary
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There is a 10k pot doing better job

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Originally Posted by bisesik View Post
It's funny to regulate Volume by fingers. First finger of one hand is on VOL pin, and second finger on +15V for decreasing or on the GND pin to increase.
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