Transformer Based A to D Converter with No Active Electronics in Path

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Not sure what they are bragging about...  Of course there are active electronics in the path, or else it couldn't work.

A/D convertors like to be driven from a low source impedance...

The implication is that the active electronics inside the A/D convertor are OK, but any active electronics outside the convertor are suspect.  Perhaps if designed by somebody who thinks like that.  :eek:  Sounds like marketing voodoo to me.

JR
 
judging by description, "PEP" just sounds like a fancy proprietary acronym for an FFT filter.
on another note, 2k8 seems like a rather arbitrary input impedance?
JohnRoberts said:
The implication is that the active electronics inside the A/D convertor are OK, but any active electronics outside the convertor are suspect.  Perhaps if designed by somebody who thinks like that.  :eek:
or for somebody who thinks like that...
at least one of their distributors would make me inclined to wonder whether they aren't just casting bait in the "high end" sub-forum of a certain site.
 
I'm not trying to judge this guy's motivations or whether it is marketing BS. In fact I am trying to cut through that stuff and get to the hardware itself. I think it is interesting that he is doing something a bit different and it seems like something that may be cool to DIY. Any info out there on this type of setup or similar DIY projects?
 
JohnRoberts said:
Not sure what they are bragging about...  Of course there are active electronics in the path, or else it couldn't work.

A/D convertors like to be driven from a low source impedance...

It's possible to connect the secondary right to the A/D input.  It's not going to be as clean as a active low-Z buffer but I've certainly seen it done before.  The Slam! A/D boards had this approach, iirc.

Josh wouldn't tell me exactly what the PEP DSP code does, but then again I wouldn't tell him what out PMT code does either.  So we all have our little secrets.


DC
 
So we all have our little secrets.

Yeah, secrets suck, especially when you're selling designs based on the hard work of others that DID share their ideas.
I think if you borrow, you share. Plain and simple.
 
dcollins said:
JohnRoberts said:
Not sure what they are bragging about...  Of course there are active electronics in the path, or else it couldn't work.

A/D convertors like to be driven from a low source impedance...

It's possible to connect the secondary right to the A/D input.  It's not going to be as clean as a active low-Z buffer but I've certainly seen it done before.  The Slam! A/D boards had this approach, iirc.

Josh wouldn't tell me exactly what the PEP DSP code does, but then again I wouldn't tell him what out PMT code does either.  So we all have our little secrets.

I couldn't find a description of this "PEP" anywhere.

But I don't understand the motivation behind a transformer input, especially since now the ADC input is wholly dependent on the driving device, which may be tens of feet away. As JR says, an ADC chip really wants a low-Z driving source.

-a
 
i guess i was going more off the acronym than anything.
when i dissect "power equalization processing," i expect to see something change on a spectrograph when looking at output vs. input.  how this is being achieved depends entirely on what they mean by no net change in frequency response.  if there is actual frequency manipulation then this must mean across multiple tracks, because for a single track the gross and net would be one in the same... unless i've gone daft?
i suppose it could also incorporate phase shifting.
images

;) ;) ;)

 
xfmr said:
So we all have our little secrets.
Yeah, secrets suck, especially when you're selling designs based on the hard work of others that DID share their ideas.

When you spend time and money developing and implementing a proprietary signal processing technique, is it really so bad to keep it to yourself? 

Granted there is little new under the sun, especially in audio..........

I think if you borrow, you share. Plain and simple.

I share some aspect of my knowledge every day on the Internets.


DC
 
I don't mind not knowing your secret sauce, or his.... but understand that many are skeptical of grand claims about vaguely described "secrets inside".
-----
Back on topic I find the introduction of a transformer in series with the input of an A/D questionable design practice, to put it as kindly as I can. I can not imagine any good coming from introducing series impedance there.
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Off topic, I am a little embarrassed by people complaining that they can't access other people's original work.

I joined here for the open dialog about how to design, not how to copy.  While it is possible to describe a technology or technique without giving away the blue prints.

So back on topic, to design an A/D convertor, buffer the input with a low impedance driver. Modern A/D convertors use a sample and hold at their very input that is connecting and disconnecting at a very high frequency, so this low impedance driver is not trivial and needs to be low Z at HF.

JR


 
JohnRoberts said:
I don't mind not knowing your secret sauce, or his.... but understand that many are skeptical of grand claims about vaguely described "secrets inside".

I'll post before and after FFT's of our Top Secret Proprietary Mystery Process, if you like.  I've never seen any comparisons of the PEP system in Josh's converters.

Back on topic I find the introduction of a transformer in series with the input of an A/D questionable design practice, to put it as kindly as I can. I can not imagine any good coming from introducing series impedance there.

Yes, I agree it's a bad idea.  Didn't stop it from being a highly regarded A/D, in some circles.  It had the 2.5V A/D bias in the center tap of the transformer and, if things weren't bad enough, 600R and series chokes.

You know what's a great part to run here?  The OPA-1632.  Actually designed for this application.  Even then you have to be careful with the implementation.


DC

 

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To be honest I don't do much high end audio path design these days so do not follow the popular uber opamp du jour.

I would be inclined to try a few and look at their output pin in use. I have been surprised enough times making decisions based on spec sheets.

I don't have any personal interest in seeing your FFTs but others may.. They can say so if they are..

=====

I am impressed with how much work the IC makers already do for modern engineers. At some point they say, not my job mon. Any cost they put in that isn't needed or wanted by all their customers makes the part less price competitive. 

Some consumer codecs can accept relatively high impedance mic outputs directly and even have gain or pad capability built in.

To some extent you can deal with A/D S/H source impedance interaction with a C termination to ground at the input pin (C just needs to be large relative to S/H C), but this requires care too (for drive opamp stability etc).... I use the cap termination for one  difficult case where multiple inputs are multiplexed into a single A/D... this sharing can cause all kinds of crosstalk errors between inputs, but I am dealing with a lower bandwidth and lower resolution non-audio path applications.  YMMV

JR
 
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