Self-contained LIMP jig.

[Pete Basel]

Re: Self-contained LIMP jig.

Thanks, its been a while since I've read that and most do consider using a power amp to
measure at a more reasonable level. I see that they show headphone out as a minimum so
the question I'd have is if this "line out" is really a headphone out capable of driving 100 ohms.
Many line outs have trouble with less than 600 ohms, some less than 2000 ohms.

I just want to point out that high distortion in the output stage is not good for the measurements.
Under 1% is probably ok, more not so good.

[Pete Basel]

Re: Self-contained LIMP jig.

I just got an E-MU 0202 used on ebay for well under $100 that I plan to use with ARTA and LIMP:
http://www.prodj.com.ua/img/img2b/20...0514134836.jpg

Some comments here:
http://techtalk.parts-express.com/sh...and-LIMP-Setup

[JasonP]

Re: Self-contained LIMP jig.

I notice that your diagram shows line out driving the 100 R to the driver. Many OP amps
cannot reasonably drive 100 ohms, do you know what OP amp is used or is it on chip?
Most OP amps have trouble driving below 1K ohms.

Have you tested to see how many volts you can get undistorted? I use a power amp in
that path so that I can test at higher levels.

I had posted the chip's documentation to answer just this question Pete. This is a single chip solution for line out and headphones, and has an "earphone buffer" built in. If you look at Page 33 of said chip documentation sheet, you can see AudioPrecision tests on its output into a 32 ohm headphone load. It has less than 0.01% THD+N across the 20 to 20khz spectrum, and less than 0.4db ripple.

In addition the youtube video review is essentially about the reviewer explaining how well it drives his headphones...

[Pete Basel]

Re: Self-contained LIMP jig.

Just took a look at that but none of the jacks are headphone out or am I missing something.
It is possible that the headphone signals are not wired up.
And the line outs were tested with 10K load.

[JasonP]

Re: Self-contained LIMP jig.

Just took a look at that but none of the jacks are headphone out or am I missing something.
It is possible that the headphone signals are not wired up.
And the line outs were tested with 10K load.

It is a multiple layer PCB, took me a bit to trace the lines manually. The Front Out 3.5mm jack has two inputs from an interior PCB layer, which I can only conclude is a switch to toggle between headphone and line out connections.

[Pete Basel]

Re: Self-contained LIMP jig.

I'm not quite following you because I don't see any switch but at least we are on the
right track. If you can make one jack headphone out then you should be good.
There are some pads for a connector or something and a location for an OP amp or
some chip that are unpopulated. I wonder if the headphone outs are on any of
those pads.

[Pete Basel]

Re: Self-contained LIMP jig.

I'm not quite following you because I don't see any switch but at least we are on the
right track. If you can make one jack headphone out then you should be good.
There are some pads for a connector or something and a location for an OP amp or
some chip that are unpopulated. I wonder if the headphone outs are on any of
those pads.

[Whitneyville1]

Re: Self-contained LIMP jig.

P-E's little Behringer's UFO202 USB/Audio Interface Phono Pre-Amp for 29.95 does a great job. It has a headphone output that will drive 32 ohm headphones to 350-500 mW (guesstimated). I patched it together like Johnnie and got more consistent readings than my ultra-precise Wallin-jig (ahem!). I was very seriously considering buying a DATS V2. Not so much now.

[JasonP]

Re: Self-contained LIMP jig.

I'm not quite following you because I don't see any switch but at least we are on the
right track. If you can make one jack headphone out then you should be good.
There are some pads for a connector or something and a location for an OP amp or
some chip that are unpopulated. I wonder if the headphone outs are on any of
those pads.

I am not sure how its wired honestly. I lack AudioPrecision so I was only left with one option: hooking up my 60 ohm headphones to the front out jack and seeing how loud I could go. Well, there was no audible distortion driving my 'phones to levels that made my ears bleed.

[Pete Basel]

Re: Self-contained LIMP jig.

That's sounding hopeful.

You could load that output with 100 ohms, and then loop it back to line in and run RMAA:
http://audio.rightmark.org/products/rmaa.shtml

[JasonP]

Re: Self-contained LIMP jig.

That's sounding hopeful.

You could load that output with 100 ohms, and then loop it back to line in and run RMAA:
http://audio.rightmark.org/products/rmaa.shtml

I hooked up my limp jig to the card tonight and ran through two RMAA tests. Here are the results, nothing stellar (as expected) but fine for this kind of testing IMO.



Results on the left are at 50% output, and 100% output on the right. As you can see, nothing special here. The FR is pretty horrible, it starting to roll-off at 100 hz. It is -4 db at 40 and -8 db at 20. However, since LIMP is measuring the difference between channels, FR level isn't an issue at all. Channel matching between right and left is, and this card excels at that. LIMP calibrated with a channel difference of 0.02db, perfect. Tests I made conclude this to work just as well as my ASUS Xonar DX for low level measurement of T/S and impedance. I will not that even at 100% output, my DMM told me it was putting out 0.5 Vrms which isn't all that high. It did not seem to reflect in my measurements comparison in anyway however.

[djkest]

Re: Self-contained LIMP jig.

So if I understand this correctly, this is a low-cost alternative to DATS using LIMP software which is free?

So a piece of hardware to use LIMP on a PC and come up with T/S parameters for drivers?

[r-carpenter]

Re: Self-contained LIMP jig.

So if I understand this correctly, this is a low-cost alternative to DATS using LIMP software which is free?

So a piece of hardware to use LIMP on a PC and come up with T/S parameters for drivers?

Correct. LIMP has been around for a while and to build the jig cost peanuts.
You can also use various voltage to excite DUT if needed.

[donradick]

Re: Self-contained LIMP jig.

Correct. LIMP has been around for a while and to build the jig cost peanuts.
You can also use various voltage to excite DUT if needed.

I tried to use (unlicensed) LIMP recently, and was unable to access the menu entry for T/S params.
Of course, it may have been my error, but it looked like LIMP for T/S params had been removed
for the unpaid version.

[rhodesj]

Re: Self-contained LIMP jig.

REW supports measuring impedance and T/S parameter calculations. Here's some of their documentation on it:

http://www.roomeqwizard.com/wizardhe...ement.html#top
http://www.roomeqwizard.com/wizardhe...small.html#top