Topic: Waveform problem - PLEASE HELP

[morningdew]

I've recently changed two things.  I had my UA-5 receive the Busman mod and I switched to new mics.  I made my first recordings with both new pieces of equipment at Summercamp and now I have a problem.

The wave forms for all four bands that I taped have what I believe to be phase shift.  The + part of the wave is going higher than the minus part of the wave.  It is not DC offset.  The wave appears to be centered.  Before I left for Summer Camp, I calibrated my SVU level meter using a sine wave as a test tone.  I didn't really pay close enough attention when I did but now looking back both these test tones have the problem as well.  This rules out anything to with the location I recorded at.  I have also looked at several recordings before I made the changes and none of them have this problem.

I am suspecting the busman mod right now.  I have a PM in to him to look at this thread.  I still have my old mics and tomorrow night I will run a test with both set of mics to see if I can eliminate the mics as the problem.

Actual field recording.


sine wave made at home and stretched:


Same sine wave compressed:

[Geoff G]

Did you rule out your capture program? 

[morningdew]

I assumming you mean the program that opens the wav?  Only by default.  Soundforge 8.0 is the only program I've ever used and it has never opened a waveform like these until I made my changes.  I've only changed 2 things (actually 3 if you count mic cables, but it is happening in both channels so I doubt that it is the cables).

Tonight I plan to run a different set of mics and a different set of cables and capture a sine wave.  If the problem repeats it only leaves the recent mods busman performed as the culprit.

To help him, I'll then run the following.  All in 16 bit.  I have no way of capturing in 24 bit.  Also, I checked last night and rechecked this morning.  My ADV/OFF switch is definately in the OFF position, so I wasn't sending 24 bits to the JB3.

1. XLR mic in - 48 kHz
2. RCA in - 48 kHz
3. 1/4" in - 48 kHz
4. XLR mic in - 44.1 kHz
5. RCA in - 44.1 kHz
6. 1/4" in - 44.1 kHz

[terrapinj]

i've had similar issues with my bmp+ ua-5 - problem was not able to be duplicated at home - only seemed to occur in the field - pretty much flattens everything over -6db range

reallt curious to see what you find out.

[morningdew]

Thanks terrrapinj.  I found your old thread.  Others can see it here.

http://taperssection.com/index.php?topic=63084.msg843200#msg843200

You say you weren't able to reproduce it at home but YOU DID reproduce the exact same thing when you recorded your speakers, you can clearly see it.  You can see it even more clearly in my sample sine waves.

I made these sample sine waves by having Soundforge generate a sine wave and then placing my mics right next to the speakers.

Looking at my over 7 hours of wavs from Summer Camp I believe it isn't capping at some specific level (i.e. - 6db) but it is rounding/or flattening off the (-) side of the wave relative to the amount of gain I produce on the UA-5.  You can also see that is clearly worse in the right channel than the left channel.  I'll swap channels while recording sine waves tonight to verify that it always much worse on the right channel.

I'm also going to PM poorlyconditioned because he seems to enjoy troubleshooting as well.

Finally, I found another thread where someone had a similiar issue with a cheap pre-amp.  He emailed the company and an engineer replied that it was because they use low tolerance resistors (5%) and it can cause this type of waveform.  I didn't think his reply had any validity when he proceeded to say that it made no difference whatsoever on the sound.  If you put a sine wave IN you should get a sine wave OUT.  Therefore, I'm not even going to post that link but I could dig it up if anyone needed it.

[poorlyconditioned]

I've recently changed two things.  I had my UA-5 receive the Busman mod and I switched to new mics.  I made my first recordings with both new pieces of equipment at Summercamp and now I have a problem.

The wave forms for all four bands that I taped have what I believe to be phase shift.  The + part of the wave is going higher than the minus part of the wave.  It is not DC offset.  The wave appears to be centered.  Before I left for Summer Camp, I calibrated my SVU level meter using a sine wave as a test tone.  I didn't really pay close enough attention when I did but now looking back both these test tones have the problem as well.  This rules out anything to with the location I recorded at.  I have also looked at several recordings before I made the changes and none of them have this problem.

I am suspecting the busman mod right now.  I have a PM in to him to look at this thread.  I still have my old mics and tomorrow night I will run a test with both set of mics to see if I can eliminate the mics as the problem.

Actual field recording.


sine wave made at home and stretched:


Same sine wave compressed:

Hmm.  Sounds to me like an opamp problem (bias/offset voltage?).  I know I had this type of thing when I tried to put some hot-shot bipolar opamps (LT6233, LT6203 I think) in my UA5.  They went away when I replaced them with FET input opamps (AD712, AD8620).  I think all opamps can be made to work, but need some tweaking of the surrounding components, and I'm too lazy to figure this out.

Sounds like Busman2 should take a look.  Either the opamp(s) are bad, or should be replaced with a different variety.  Of course, feel free to correct me if this is another problem.

  Richard

[terrapinj]

Thanks terrrapinj.  I found your old thread.  Others can see it here.

http://taperssection.com/index.php?topic=63084.msg843200#msg843200

You say you weren't able to reproduce it at home but YOU DID reproduce the exact same thing when you recorded your speakers, you can clearly see it.  You can see it even more clearly in my sample sine waves.

I made these sample sine waves by having Soundforge generate a sine wave and then placing my mics right next to the speakers.

Looking at my over 7 hours of wavs from Summer Camp I believe it isn't capping at some specific level (i.e. - 6db) but it is rounding/or flattening off the (-) side of the wave relative to the amount of gain I produce on the UA-5.  You can also see that is clearly worse in the right channel than the left channel.  I'll swap channels while recording sine waves tonight to verify that it always much worse on the right channel.

I'm also going to PM poorlyconditioned because he seems to enjoy troubleshooting as well.

Finally, I found another thread where someone had a similiar issue with a cheap pre-amp.  He emailed the company and an engineer replied that it was because they use low tolerance resistors (5%) and it can cause this type of waveform.  I didn't think his reply had any validity when he proceeded to say that it made no difference whatsoever on the sound.  If you put a sine wave IN you should get a sine wave OUT.  Therefore, I'm not even going to post that link but I could dig it up if anyone needed it.

i didn't conduct the tests with proper samples so there were variables in there that shouldn't have been. i couldn't duplicate the exact same results but they were similar - bottom line though I know there's something not quite right with my ua-5. i would like to run tests in the field but haven't been able to get a spare set of mics. i think it may have something to do with the way an op-cap or capacitor handles the SPLs but that's my very unscientificly based hypothesis.

[morningdew]

I just wanted to update this thread.

Chris has PMed me and is attempting to help me resolve this situation by trying to fix the box.  As of right now I'm very happy with his reply and response time.  I have high hopes we can resolve this issue.

[jeromejello]

I just wanted to update this thread.

Chris has PMed me and is attempting to help me resolve this situation by trying to fix the box.  As of right now I'm very happy with his reply and response time.  I have high hopes we can resolve this issue.

busman is definately on the level.  that said, i just recieved box #29.  i am going to try it out tonight at a free jazz thing just to 'break it in' - and in all honesty, to make sure that i am not having a similar issue.
to the two that have had issues (mikey and morning dew) what are your box numbers?  also, with you two, was this problem immediate, or did it develop after some use.
any info would be appreciated, even from busman, if there is something that he finds out in his poking around.

[morningdew]

I believe I'm box #28.  I would definately check it out.  Busman mentioned he might have had a bad batch of Op Amps. I'm concerned it might be something else but I'm waiting for that verdict.

You can easily check it out at home.  Make sure you run the mics into the UA-5 without the MP-2.  Set up your mics right in front of your computer speakers.  Have your software spit out a 10 second sine wave at 0.1 dB (I use Soundforge 8.0) get your levels so they are running nice (just under clipping..like -1dB) and then record it.  The transfer to your computer and open it up, stretch it out a bit to see what it looks like.

I believe you should just have a nice sine wave, just like in Geometry in HS.  I don't get this at all.  I get a sine wave similar to what is pictured in this thread.

Edited to add that my problem was immediate.  I didn't realize it at the time but the very first thing I did with the box was recalibrate my level meters by recording a sine wave.  I didn't notice at first.  It's much more obvious if you stretch out the sine wave a bit.

[Busman Audio]

One thing you must remember is that the Ua-5 stock showed signs of slight clipping starting at -3db also. Yes this is the op amps that are the problem and yes I will fix it. If it was something else in the circuit it would do this as a stock unit also.

[terrapinj]

I just wanted to update this thread.

Chris has PMed me and is attempting to help me resolve this situation by trying to fix the box.  As of right now I'm very happy with his reply and response time.  I have high hopes we can resolve this issue.

no doubt. chris's customer service is top notch. i have no doubt in my mind that the issues will be resolved. anyone thinking about getting a mod done should not have hesitations because of this issue - chris is a good man no worries dealing with him.

[stirinthesauce]

One thing you must remember is that the Ua-5 stock showed signs of slight clipping starting at -3db also. Yes this is the op amps that are the problem and yes I will fix it. If it was something else in the circuit it would do this as a stock unit also.

Thanks for the quick reply addressing this issue, Chris.  After thinking about this all morning I remember a thread where Richard(Poorlyconditioned) noted that his testing on the stock unit noticed some issues at around -3 or -2db.  Don't have a link to the exact thread but I'm sure it can be found easily enough
 
Still loving my bm2p+ though having to sell it here shortly  

Echoing terrapinj's comments, turnaround time was great in getting this mod, clear communication, top notch work.  Have made many great recordings in the past 8 months with this box.  I think this community is really priveleged to have someone offering these mods to us at such reasonable prices.
-Jon

[Tye]

hmmm
 I have been real happy with my Bm2p+ mod I have not noticed this problem with mine. I don't recall which # mine is .
Mine is #13 ( just for refrence )
I have not run any full tests on it I will have to try and run some for a comparison but everything has been real clean for me, with the exception for some crackling which I am 99% sure it is my left mic cable.

 note to self get some decent cables

[morningdew]

Just to reiterate.  I am by no means calling Chris out are trying to even pretend for one second that I know more than him.  I have been very pleased with how he is handling this particular problem and I'm just trying to keep an open lines of communication to help resolve the issue.  I have heard some nice recordings done with his mods.  This is why I choose to take my business to him in the first place.  If his level of service continues at this level and the issue is resolved he will receive nothing but the utmost and truthful praise from me.

In a seperate issue,  I wasn't aware that a stock UA-5 shows signs of clipping at -3 dB.  I realize the light is programmed to light up at -3 dB per the manual but does anyone have a stock mod UA-5 that they've verified this on and could show some wav captures?  I've looked at a lot recordings made with my stock UA-5 and never noticed.  I always try to keep my levels high.  I easily could have missed some rounding of the peaks in the -3 dB to 0 dB range.  I'll go through  a few of my stock original wavs tonight to see if I can spot it.