PC audio test set

[Tubetec]

I was able to improve the measured noise floor of my SSL2 interface by 13db with a few minor modifications and separating off analog and digital PSU rails .
I find the balanced Hi-Z input useful where you want to minimise any loading on the device on test .

REW doesnt know when I switch my interface from mic to line to hi-z ,
obviously the gain changes , that means the reference level needs to be reset or the numbers are off.

A midi controlled external attenuator , under the control of REW would be nice , so it automatically re-calculates .

 

[jp8]

In a similar way, I improved the performance of the UMC202HD that I use in my "Audio Analyzer" setup. The major improvement came from changing the internal Vdd level from 4.5V (!) to 4.9V. At the same time, I raised the USB voltage from the USB Isolator to 5.15V, btw. The Codec chip required at least 4.75V according to the datasheet, but Behringer decided it could also run from 4.5V... The low Vdd caused huge distortions above -6dBFs, but also at lower levels distortion can be improved with a higher Vdd. I also bypassed the input and output circuits, except the AD input filter section and the DA output buffer. This essentially leaves you with a clean Codec with USB interface, to which you can then connect your own front end.

In the tables below, you can see what improvements can be made and how the Analyzer with a modified UMC202HD rates against a cheap Mackie ProFX12 mixer.

A midi controlled external attenuator , under the control of REW would be nice , so it automatically re-calculates .

How about the other way around? I.e. when you design your own frontend, you know the input sensitivity. The most important thing for REW to know is the calibration level of each gain setting on your frontend. Is there any way to interface to REW and send calibration levels from an external program or through a file or whatever?

Jan

 

[abbey road d enfer]

For what it's worth, here's the schemo of my "front end".
Of course, if I had to do it again, I wouldn't repeat the mistakes I made at the time...

 

[jp8]

Would you mind elaborating on those mistakes...? And perhaps on what you do like about your design and what might be useful for us to know? As I said, I'm not going to do build a frontend again, but I'm shure there are forum members who like to learn from your design choices.

Jan

 

[abbey road d enfer]

Would you mind elaborating on those mistakes...?

I would duplicate the meter output on a buffered BNC (connected to one channel of oscilloscope) and lose the reconfigurable optional filter for a basic A-weighted. I would also lose the 10dB attenuator on the Gen input.

And perhaps on what you do like about your design

I like the 100kohm input Z and its large gain/attenuation range, the output Z management and the 22-22k filter, all of which are essential in a good test set IMO.

 

[blue_luke]

I would duplicate the meter output on a buffered BNC (connected to one channel of oscilloscope) and lose the reconfigurable optional filter for a basic A-weighted. I would also lose the 10dB attenuator on the Gen input.

I like the 100kohm input Z and its large gain/attenuation range, the output Z management and the 22-22k filter, all of which are essential in a good test set IMO.

Taking note !
Right now, even if I don't make much noise here, I read everyday comments and advices that people share..
I am not trying to make an Audio Precision killer here, just a "comfortable" interface to test pretty much any audio device in and out, within the limitations of a modern sound card, which are pretty remarquable devices nowadays, even the cheapest ones are quite sum'thin!
Remember, I started building audio stuff in the late 60's where a S/N ratio of 74db was deemed fantastique!
Walt Jung, John Roberts, Don Lancaster and a few others were considered gurus in the days of Audio Amateur, electronic, world, popular electronic and some other magazines!
I have learned so much from these!

 

[JohnRoberts]

Taking note !
Right now, even if I don't make much noise here, I read everyday comments and advices that people share..
I am not trying to make an Audio Precision killer here, just a "comfortable" interface to test pretty much any audio device in and out, within the limitations of a modern sound card, which are pretty remarquable devices nowadays, even the cheapest ones are quite sum'thin!
Remember, I started building audio stuff in the late 60's where a S/N ratio of 74db was deemed fantastique!
Walt Jung, John Roberts, Don Lancaster and a few others were considered gurus in the days of Audio Amateur, electronic, world, popular electronic and some other magazines!
I have learned so much from these!

Not a guru but back in the 80s I designed a piece of semi-pro test equipment (TS-1) and that was harder than I expected.

I have much respect for the guys who designed Audio Precision and lab grade audio test gear.

JR

 

[Matt Syson]

I find it curious how some excellent designs miss out on the 'bleeding obvious' such as my AP Portble One won't sit on it's back because the power cord (plug) is too long unless you find the right angle variant AND the BNC outputs cannot be used for the same reason. The headphone out should be easily configurable to balanced or unbalanced (headphones OR an external amplifier). I love my System One with Windows software but it was a pig in DOS. Neutrik mini (Minirator) boxes won't handle plus 21dBu input balanced or unbalanced, what were they thinking? The mini sig gen is OK considering it runs on batteries and is otherwise 'acceptable'. The Neutrik Brown test sets were reasonable but the oscillator relays weld together if you accidentally have phantom power on, or the output stage burns. I believe the predecessor to these was from Theatre Projects (??) in the UK which was good but did not have the autoranging meter (1980 era).

 

[blue_luke]

I have much respect for the guys who designed Audio Precision and lab grade audio test gear.

So do I!

My first "real job" (before I was 'only' a musician with a B Mus) was at Canadian Marconi in Montreal as a 'bench' technician.
My job was to test pretty much all PCBs from the assembly lines.
All mil spec, all very serious and all very fussy!
I was, by definition, the first one to put power on a new assembly for the first time and had to calibrate, confirm specifications and give it the nod for service.
Some days it was VERY interesting!
Magic smoke a'puffin', smell of dying semiconductors and loud sound effect galore made for a rather exciting job!
Some of the test engineers there where absolute genius.
Not only they had to design the stuff, in 'K' and 'U' band and nav-aid, and maritime radar, but they had also to design the test jigs and write the test procedures for 'the bench'.
I happen to have a certain talent for writing, and also I am very curious.
In those days, manuals were typed from manuscripts by a secretary in the office on Trenton av. while the plant was on Canora street (blvd?)
Working there I had 2 immense luck.
There was a huge library, the size of a city library, full of technical magazines, scientific books, Phd thesis, documents from Guillermo himself and many. many writings from the engineers that worked for him.
And there was an engineer, who was a real genius but despised writing technical notes.
I was a beginner, with no diploma as of yet, and still going to night courses in electronic (Institut Teccart, if someone here is interested)
In those times, a design engineer was able to 'borrow' a tech from the plant to help him put together new stuff, or revise test procedure, build test jigs etc... You see the line.
Ian, I've forgotten his full name, came to see the super, Mr. Bennett (who hired me during a snow storm the day I learned my wife was pregnant of our daughter!) and asked for an 'aide'.
I was affected to him and wen he found that not only I did not mind writing lab notes, but that I was quite good at it, he insisted that I was the only tech working for him when needed.
Oh can I go at length here!
So much memories....
And those who think such a post is really inappropriate or off topic, think of it as if we were a bunch of guys in a brasserie on a Friday night , having beer, shooting **** and pool, and of course discussing audio circuitry!

Back to the subject, I am working on quite a few issues at the same time so for the moment I don't have much to discuss, but the subject and it's thread are far from closed!
Some very good ideas were given here, and valid points were made.
I have to digest and absorb quite a bit.
Luc

 

[JohnRoberts]

So do I!

My first "real job" (before I was 'only' a musician with a B Mus) was at Canadian Marconi in Montreal as a 'bench' technician.
My job was to test pretty much all PCBs from the assembly lines.
All mil spec, all very serious and all very fussy!
I was, by definition, the first one to put power on a new assembly for the first time and had to calibrate, confirm specifications and give it the nod for service.
Some days it was VERY interesting!
Magic smoke a'puffin', smell of dying semiconductors and loud sound effect galore made for a rather exciting job!
Some of the test engineers there where absolute genius.
Not only they had to design the stuff, in 'K' and 'U' band and nav-aid, and maritime radar, but they had also to design the test jigs and write the test procedures for 'the bench'.
I happen to have a certain talent for writing, and also I am very curious.
In those days, manuals were typed from manuscripts by a secretary in the office on Trenton av. while the plant was on Canora street (blvd?)
Working there I had 2 immense luck.
There was a huge library, the size of a city library, full of technical magazines, scientific books, Phd thesis, documents from Guillermo himself and many. many writings from the engineers that worked for him.
And there was an engineer, who was a real genius but despised writing technical notes.
I was a beginner, with no diploma as of yet, and still going to night courses in electronic (Institut Teccart, if someone here is interested)
In those times, a design engineer was able to 'borrow' a tech from the plant to help him put together new stuff, or revise test procedure, build test jigs etc... You see the line.
Ian, I've forgotten his full name, came to see the super, Mr. Bennett (who hired me during a snow storm the day I learned my wife was pregnant of our daughter!) and asked for an 'aide'.
I was affected to him and wen he found that not only I did not mind writing lab notes, but that I was quite good at it, he insisted that I was the only tech working for him when needed.
Oh can I go at length here!
So much memories....
And those who think such a post is really inappropriate or off topic, think of it as if we were a bunch of guys in a brasserie on a Friday night , having beer, shooting **** and pool, and of course discussing audio circuitry!

Back to the subject, I am working on quite a few issues at the same time so for the moment I don't have much to discuss, but the subject and it's thread are far from closed!
Some very good ideas were given here, and valid points were made.
I have to digest and absorb quite a bit.
Luc

No worries... From my decades in the trenches I have been lucky enough to find multiple mentors to give me a hand understanding new material.

That is the nature of engineering and there are many people here capable of paying the assistance that they received forward. Enjoy...

JR

 

[Rob Flinn]

So do I!

My first "real job" (before I was 'only' a musician with a B Mus) was at Canadian Marconi in Montreal as a 'bench' technician.
My job was to test pretty much all PCBs from the assembly lines.
All mil spec, all very serious and all very fussy!
I was, by definition, the first one to put power on a new assembly for the first time and had to calibrate, confirm specifications and give it the nod for service.
Some days it was VERY interesting!
Magic smoke a'puffin', smell of dying semiconductors and loud sound effect galore made for a rather exciting job!
Some of the test engineers there where absolute genius.
Not only they had to design the stuff, in 'K' and 'U' band and nav-aid, and maritime radar, but they had also to design the test jigs and write the test procedures for 'the bench'.
I happen to have a certain talent for writing, and also I am very curious.
In those days, manuals were typed from manuscripts by a secretary in the office on Trenton av. while the plant was on Canora street (blvd?)
Working there I had 2 immense luck.
There was a huge library, the size of a city library, full of technical magazines, scientific books, Phd thesis, documents from Guillermo himself and many. many writings from the engineers that worked for him.
And there was an engineer, who was a real genius but despised writing technical notes.
I was a beginner, with no diploma as of yet, and still going to night courses in electronic (Institut Teccart, if someone here is interested)
In those times, a design engineer was able to 'borrow' a tech from the plant to help him put together new stuff, or revise test procedure, build test jigs etc... You see the line.
Ian, I've forgotten his full name, came to see the super, Mr. Bennett (who hired me during a snow storm the day I learned my wife was pregnant of our daughter!) and asked for an 'aide'.
I was affected to him and wen he found that not only I did not mind writing lab notes, but that I was quite good at it, he insisted that I was the only tech working for him when needed.
Oh can I go at length here!
So much memories....
And those who think such a post is really inappropriate or off topic, think of it as if we were a bunch of guys in a brasserie on a Friday night , having beer, shooting **** and pool, and of course discussing audio circuitry!

Back to the subject, I am working on quite a few issues at the same time so for the moment I don't have much to discuss, but the subject and it's thread are far from closed!
Some very good ideas were given here, and valid points were made.
I have to digest and absorb quite a bit.
Luc

You may well have read some work by my great uncle James Moon who was a chief engineer who worked with the great man Marconi himself.