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Old 3rd July 2012, 09:15 PM   #961
NicMac is offline NicMac  Italy
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Ok. Here are a couple of photos. As you can se it looks like s...
What you cannot see with your ears is that it sounds divine despite the fact that this is so very much an alpha build
First photo show the "off" situation where the batteries are getting charged and some amber power LED's light up. They actually serve the purpose of dumping the charging voltage to what I wanted. They also dim in accordance with the degree a charge (can't really take the honor for this useful feature).
Second photo show the "on" state. There are some blue LEDs on the pre-regulated side to indicate that the rails are powered.
The rest should be pretty obvious as I have posted it before in this thread.
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File Type: jpg DSCF0013.jpg (226.2 KB, 532 views)
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Old 4th July 2012, 12:51 AM   #962
EUVL is offline EUVL  Europe
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Shining example.
Thanks for posting.


Patrick
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Old 5th July 2012, 07:21 AM   #963
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thank you Nic

what have you connected to output connectors where Sen out go
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Old 5th July 2012, 10:53 AM   #964
NicMac is offline NicMac  Italy
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The I/V-resistors and filter caps.
This is a very convenient configuration as you don't need to route the DAC ground to the SEN boards.
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Old 5th July 2012, 11:16 AM   #965
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Quote:
Originally Posted by NicMac View Post
A very naive and basic question: with the SEN9018 I am doing the I/V-conversion using resistors connected on the XLR output pins.
Why not do it on the pre-amp input, or even in the power amp if the pre-amp is a current amplifier?
Is current coupled signal transmission more prone to interference than potential coupled?
Forgive me my ignorance and sorry for the OT - just trying to learn here
Cheers,
Nic
I find this an interesting topic, could we discuss it here? Any input Patrick?

Normal practice is to have a low impedance source and a high impedance load, to minimize interference and cable effect (filtering). So the I/V resistor should be right at the converter board.

Any further thoughts?
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Old 5th July 2012, 02:36 PM   #966
regal is offline regal  United States
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Originally Posted by Alexandre View Post
I find this an interesting topic, could we discuss it here? Any input Patrick?

Normal practice is to have a low impedance source and a high impedance load, to minimize interference and cable effect (filtering). So the I/V resistor should be right at the converter board.

Any further thoughts?
See Audio-gd ACSS based on an old Krell technology. With the Audio-gd the I/V resistor replaces the volume control either with a potentiometer or relayed attenuator (higher models.) Even on V-out DAC's the analog stage is is current steering or current mode (needing an I/V resistor.)

What I found with an ACSS integrated DAC-headamp is that the measured distortion was constant up to clipping, IOW's the FFT looked the same with 2vrms into 10k load on the rca (dac out) as it did swingin 6V's into 38 ohms (1W). So the advatage was unlike most gear the sound did't "change" as you moved the volume up/down. The problem I had with it is the DAC analog section wasn't the greatest and started with fairly high distortion (.01% THD) which for a modern wolfson based DAC (I know this isn't a current out DAC but the analog stage was) wasn't good enough for sensitive phones. For orthos it was great because pushing 1W it had the same .01% THD and distortion profile (not easy to achieve .01% THD swinging 6V into 38 ohms without NFB.)

But if you go this route the only real advantage is turning the "buffered" I/V into your volume knob using one of the relay based attenuators or a stepped attenuator with the amp in the same chassis. I believe there are proporetary tricks (powerful transimpedance analog stage) to use interconnects which most have found to be not as good as old fashioned balanced cables.
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Old 5th July 2012, 06:15 PM   #967
bcarso is offline bcarso  United States
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Quote:
Originally Posted by regal View Post
[snip] The problem I had with it is the DAC analog section wasn't the greatest and started with fairly high distortion (.01% THD) which for a modern wolfson based DAC (I know this isn't a current out DAC but the analog stage was)...[snip]
The terminology we commonly use to distinguish among DAC outputs is rather confusing.

Voltage-output DACs are pretty easy to understand: as long as the output current limits are observed, they produce code-dependent output voltages more-or-less independent of loading.

Current-output DACs usually require a rather low resistance load to meet their specifications of properly code-dependent output current. They are not usually per se current generators of anything approaching an ideal sort, where, in analogy to voltage sources, the current delivered is independent of the loading, i.e., the voltage burden.

A better description of most "current-output" DACs would be "DAC which requires a low resistance load to output the proper current". Philips for example mentions the maximum voltage that can be produced by the output current flowing in the load for some of their "current-output" DACs.

One cited reference a while back in this thread shows some of the errors that can arise for a simple R-2R ladder network DAC if not terminated in a low resistance. Granted that most modern audio DACs are not as simple, for the majority there is still a need to make the voltage swings small.

Patrick assures this in his minimalistic way by using common-gate high-transconductance JFETs running at Idss. The usual default in stock equipment is I-V converters with transresistance-configured opamps, which tend to have their own sets of problems.

Brad
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Old 5th July 2012, 06:23 PM   #968
EUVL is offline EUVL  Europe
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If you were to build your entire audio chain (like me), and you wanted to operate in current mode, then you should go 100% current mode.

That means no R_iv, but that you use a (variable gain) current amplifier to drive the speakers in open loop.
Malcolm Hawksford has a couple of papers on the topic.

e.g. http://www.essex.ac.uk/csee/research...nt%20drive.pdf

It of course gets somewhat complicated when you want to use a multi-way speaker with crossovers, either before or after the current amplifier.
But then if you use the ES9018, you have 8 channels which can give you 4-way stereo.
And then you can also do all your cross over filters in the digital domain.

BIGGGGG project.


Patrick
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Old 5th July 2012, 06:33 PM   #969
EUVL is offline EUVL  Europe
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Jan Didden has a new website for Linear Audio, and here is the link to the online article.

http://www.linearaudio.net/images/on...0-vol2euvl.pdf

I cannot thank Jan enough for his generosity to make available the article to all, free of charge.
I hope some of you would in turn support Jan and his brave undertaking, so that we can have many many more interesting articles in the future, at Linear Audio.


Cheers Jan,
Patrick
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Old 6th July 2012, 07:43 AM   #970
regal is offline regal  United States
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Ok for the modulating DAC's we have accepted servoe IC's for offset.

What about a leap foward and create a balanced Sen and sum the phases with an opamp. The simulations are amazing, real benefit by summing the balanced output phases, pushing distortion will below -100dB with PCM1704 current levels (including the weak 1704's output impedance.)

Also as non-linearities due to the circuits input impedance cause 2H distortion, that gets canceled as well.

Summing a balanced Sen gives THD numbers nearly as good as the new NPD1 but with Jfets which are designed for low-noise applications (i.e. the uV 20th LSB.) I mean you wouldn't design the input to a phono preamp with a mosfet.

Granted it seems counter intuitive using an opamp at all in this NFB free I/V, the summation (rather subtraction) of differential into single end is one area the opamp has been perfected for (there are better choices than showed in he sim).

There are other options but ever look at a transformer's THD below 100 hz? And I haven't seen a low distortion discrete open loop option to sum differential to unbalanced. So here is the sim to play with.
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