Jocko Homo Audio

Audio Topics => Digital Audio Stuff => Topic started by: Gen. Dreedle on June 06, 2010, 09:07:32 AM

Title: The ol' I/V and op-amp controversy
Post by: Gen. Dreedle on June 06, 2010, 09:07:32 AM
I ran across this, somewhere. Won't say where, as it is not somewhere any people with any intelligence are found.

(No, it is not Greaser's Palace. A few steps below that. Maybe several.)

Anyway, it was posted a few years back, so no need to post the trivial details of who, when or why. Just putting it here, just to see who it sucks in!

"Andy_c's analysis is fundamentally flawed in that not only does 8x oversampling not reduce slew requirements to 1/8, but a Sigma Delta modulator like the pcm1794 that he mentions could actually slew full scale more than once per sample received from the 8x FIR filter.

That said, I'm not saying that people's ears are broken and that all opamp I/V automatically sounds horrible. But there is really no way ir can compete, and there's hardly reason to use opamps when alternatives are not that much more expensive. Except I guess in portables."

(I left in the typos! Just to be accurate.)

Anyway, the analysis he was referring to was at Greaser's Palace. You can read it here:

http://www.diyhifi.org/forums/viewtopic.php?p=5091#p5091

OK, your turn to comment.

Jocko
Title: Re: The ol' I/V and op-amp controversy
Post by: seagreen on June 06, 2010, 01:59:11 PM
I commented the first time.  Got excoriated.  Learned my lesson, more or less.

Slightly OT...  Oddly enough, I've been working on a somewhat higher speed DAC system of late.  2.5 GHz sampling rate.  Anyway, guess what one of the challenges is?  Making sure the various bypassing arrays don't have resonant points. 

Come to think of it, I was excoriated this time as well by a different set of guys.  I tell ya - I don't get no respect.
Title: Re: The ol' I/V and op-amp controversy
Post by: Gen. Dreedle on June 06, 2010, 04:19:40 PM
I need to extend the "courtesy edit time", to about one day. I keep finding typos I missed the first time. Grrr.........

And you worry about being excoriated.

Jocko
Title: Re: The ol' I/V and op-amp controversy
Post by: seagreen on July 30, 2010, 04:05:06 PM
Note the surface mount parts not in the "signal path".  (How many things were wrong with that sentence?)

http://www.psaudio.com/ps/products/description/perfectwave-dac?cat=audio (http://www.psaudio.com/ps/products/description/perfectwave-dac?cat=audio)
Title: Re: The ol' I/V and op-amp controversy
Post by: Gen. Dreedle on July 31, 2010, 12:54:12 PM
Why are you kvetching? It has 7 inputs, including I2S. What else can you possibly want? Uses mostly through hole................it has to be good!

Plus, this gem:

Quote
The PerfectWave series is assembled, programmed and tested at our new production facility in Boulder Colorado.  Instead of the typical production line process, each PWD is hand built by one person from beginning to end.  There is a measure of pride of workmanship that goes into every one of these PerfectWave products and it shows from the moment you open the unit up and plug it in.

Translation: We only have one guy building these, in his garage. At least, that is how that would be translated if any of us had a their own stereo company. No farming it out to fancy assembly houses, who make a big pile of them, all at once. No, just one guy, hunched over the PCB, doing it all by himself.

Sure sounds that way to me.

Hmmm................that gives me an idea..............if I took...............

Jocko
Title: Re: The ol' I/V and op-amp controversy
Post by: seagreen on July 31, 2010, 06:23:00 PM
Guess no ball grid arrays then.

Those itty bitty parts, like the DAC for example, sure look like surface mount parts to me.  But I've certainly been wrong before.

I could also swear that I read somewhere that the DAC was somehow in the signal path.  It may have been in the same article that I read that the DAC was an integrated circuit, too.

Title: Re: The ol' I/V and op-amp controversy
Post by: Gen. Dreedle on August 03, 2010, 06:20:35 AM
Signal path = stuff connected to the output jack.

Right?

Jocko
Title: Re: The ol' I/V and op-amp controversy
Post by: seagreen on August 09, 2010, 06:19:24 PM
You mean like the cabinet?

I was wondering... How hard would it be to build a more-or-less discrete R2R ladder DAC (I really mean the converter itself)?  I bet with the right FPGA programming, some very good tolerance resistors, and some really good modern CMOS switches it's probably doable.
Title: Re: The ol' I/V and op-amp controversy
Post by: MystereoN on August 10, 2010, 03:45:47 PM
yeah, with tight layout and super cooling 64 bits is possible  ;D ;D ;D
Along with 64 bit OS like Vista this should be a sonic killer  ;)
http://www.sonicillusions.co.uk/discrete_dac.htm (http://www.sonicillusions.co.uk/discrete_dac.htm)

Cheap source of energy needed for cooling
http://www.wonderhowto.com/how-to-run-home-fusion-reactor-64450/ (http://www.wonderhowto.com/how-to-run-home-fusion-reactor-64450/)

How it sounds...
"World's first 64 bit R2R DAC coupled with fusion reactor"
Title: Re: The ol' I/V and op-amp controversy
Post by: seagreen on August 10, 2010, 05:12:10 PM
Or...

http://www.msbtech.com/oem/oemHome.php (http://www.msbtech.com/oem/oemHome.php)

http://www.msbtech.com/products/dac4home.php?Page=platinumHome (http://www.msbtech.com/products/dac4home.php?Page=platinumHome)



Title: Re: The ol' I/V and op-amp controversy
Post by: Gen. Dreedle on August 11, 2010, 06:55:42 AM
MSB, eh...............

Back when I was active in the world of building high-end stuff, probably my most famous "claim to fame" was my feedback-less transimpedance I/V. I 'splained some of it, to a guy who worked at our dealer, in Chicago. About 6 months later, he told me they had a new MSB unit in, and it also had a similar I/V.

He proceeded to tell me he 'splained what I 'splained to him to Mark Brasfield. Aka, MSB Technologies. And apologized for opening his big mouth to a competitor.

And some folks still don't understand why I am stingy with what I know, sometimes.

Jocko
Title: Re: The ol' I/V and op-amp controversy
Post by: seagreen on August 11, 2010, 07:55:51 AM
"Imitation is the sincerest form of flattery."

Jackal barf...
Title: Re: The ol' I/V and op-amp controversy
Post by: Gen. Dreedle on February 09, 2012, 08:40:01 AM
Oh, dear...................they are at it...........yet again..............

Quote
Folks have resorted to high distortion high bjt count open loop transimpedance I/V that really never caught on.

So............I guess anything over 0.001% distortion is considered high. Yeah..........never seemed to worry that much about 0.01% distortion. Now I know what my basic problem is!

"You mean your personality disorder?"

Other than the obvious.

All I can say is "Thankfully, it never caught on." That is why you hobbyists will always remain hobbyists.

"You rack disciprine!"

No, you lack finesse! (Ha! Two times, for the same pun, in the same day. Should I go for the trifecta?)
Title: Re: The ol' I/V and op-amp controversy
Post by: seagreen on February 09, 2012, 06:08:50 PM
Personality distortion...
Title: Re: The ol' I/V and op-amp controversy
Post by: MystereoN on February 09, 2012, 08:23:26 PM
same situation as with Japanese audio in '80
"Look at this new amp with 0,001% distortion...."
"Nah, look at new Sony Vollverstärker, even better with 0,00001%..."
 ;D
Title: Re: The ol' I/V and op-amp controversy
Post by: Gen. Dreedle on August 06, 2012, 12:04:44 PM
Another guy who believes everything his simulator tells him.

http://www.diyaudio.com/forums/digital-source/217459-dac-i-v-convertion-very-low-distortion.html#post3116901 (http://www.diyaudio.com/forums/digital-source/217459-dac-i-v-convertion-very-low-distortion.html#post3116901)

Of course, I can not see the schematic, so I am not judging its performance. Just the silly notion that a simulator can predict distortion, to this level.

Translation: build the friggin' thing, pal, and then tell us about its distortion.
Title: Re: The ol' I/V and op-amp controversy
Post by: MystereoN on August 06, 2012, 01:01:35 PM
Quote
Of course, I can not see the schematic...
Title: Re: The ol' I/V and op-amp controversy
Post by: Gen. Dreedle on August 07, 2012, 07:32:57 PM
I still don't see anything magical about it. Common-base folded cascode. Guess I am too stupid to see anything magical about how the cascode stage is biased.  I just know it is a place that can make the HF do weird things.

Maybe that is what I always failed to do............simulate it first!

"You don't have a simulator, and if you did, you would be too stupid to make it work."

Yeah..................right on both counts.
Title: Re: The ol' I/V and op-amp controversy
Post by: Gen. Dreedle on January 26, 2017, 09:57:16 AM
Real long story short..................

Someone made a private reference, to a certain poster, over at The Pub. Seems to be a sharp guy, that has posted lots of good stuff. Took a look at his site, and one thing stood out.

He has a section on I/V stages.

One of the circuits was a discrete gizmo, similar to what I came up with, back in '89 (or whenever). One thing curious about it: it only had 0.25 V out, for 2.5 mA in. So, it needed a 20 dB amp, after it. Well, to my convoluted way of thinking, that kinda sorta defeats its purpose. This chap felt that raising the gain hurt distortion.

Well, ok................his circuit, not mine, and since it is a free world............

Now, by pure coincidence, I came up with a newer version of the I/V. Around 30 years to think of a better way to do it, maybe better parts (unless you want to make a JFET version, which I never would, despite my heavy reliance on JFETs), SMT, CAD PCB s/w, and a lot of other stuff, here is what it looks like:

(http://jockohomo.net/data/jocko%20ivy.gif)

(Yes, that is a Beavis and Butt-head mouse pad. Yes, there are mistakes in the layout. Yes, I left off the rail bypass caps. Stop carping!)

So, how does it work?

Well, here is the distortion. First, in % THD, and next in dB down:

(http://jockohomo.net/data/nu%20jocko%20dist1.gif)

(http://jockohomo.net/data/nu%20jocko%20dist2.gif)

So, with a 1 mA input (like you would get from that nasty old AD1862), and you want 2.5 V, it is less than 0.02% THD, and all the harmonics are down 80 dB. Good enough to use, without any tweaking.

And the input impedance............

(http://jockohomo.net/data/nu%20jocko%20imp.gif)

Roughly 1.75R, and it is flat. OK, I did not calibrate the measurement, but so what.......................good enough to use.

Draw your own conclusions.

If enough folks ask, maybe I will make some more PCBs.

Not for sale to Ireland. (Not sure where that came from, but someone accused me of that before. So, why change now?)

Oh...............did this on +/- 12 V. Designed it to work on higher voltages, which is why some of the LEDs were passed over. Ran it on the designed 18 V rails, and it measured the same. (Because the gizmo it is going to get stuck in has 18 V rails.)

All for now................
Title: Re: The ol' I/V and op-amp controversy
Post by: MystereoN on January 27, 2017, 06:48:50 AM
Looks nice and I belief it sounds nice too....is this dark violet color?
Yes, this older gentleman know what he is talking about.
A lot of opamp based I/V on his site and other interesting circuits, too.
Title: Re: The ol' I/V and op-amp controversy
Post by: Gen. Dreedle on February 06, 2017, 08:59:12 PM
The guys who make it call it purple.

Picky, picky, picky.......................

oshpark.com (http://oshpark.com)