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.

[Busman Audio]

Thanks for your support guys. There is always more to learn. I am happy to provide this service and I would not let a few issues get in the way. Things happen and those things will get fixed. We will overcome these issues and move on in our quest for great sound at a price that is affordable.

Thanks and +T  to all of you.

[stirinthesauce]

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.

Here is the thread I was referring to.http://taperssection.com/index.php?topic=57630.0Never run a stock unit so I can't comment and have never done any testing with sine waves on my unit.  Maybe Richard can chime in with some of his experience with the stock units.

[poorlyconditioned]

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.

Here is the thread I was referring to.http://taperssection.com/index.php?topic=57630.0Never run a stock unit so I can't comment and have never done any testing with sine waves on my unit.  Maybe Richard can chime in with some of his experience with the stock units.

Yep, that's me

OK, *I believe* there are two separate issues here.
- the UA5 shows significant distortion (eg., 1% THD), when driven above -3 or -6dB.  I *believe* this is due to the ADC and not the opamps.
- the observed distortion (clipped/assymetrical sinewaves) is different.  I *believe* this is an opamp problem.

I think the first is a *defect* in the design of the UA5, but I cannot explain why or how to fix it.  For comparison, driving something like a Minidisc with the same signal (line in, up to -1dB) does *not* produce the same distortion.  This unit it *broken* in my opinion!  A cheezy workaround is to run at -6dB always.  Never let the clip light turn on and you will get better sound out of it, even if you have to add that 6dB back in post.

The second is *probably* an opamp problem.  I've experienced this before on swapping various opamps.  It could be defective amps, connections broken, or just the wrong opamps.  I hope Busman2 can track this one down.  I would not even know where to start!

OK, +T to all of you for isolating and tracking down these problems.  It is not easy!  And +T to Chris for great service.

  Richard

[beanstalk]

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 .
 
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

Same here. No problems at all. #11 (I believe)

[jeromejello]

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.

QFT

i also went ahead with my bm2p+ due to the overwhelming kudos for the sound and service busman delivered.  i have no intentions on putting chris on the spot, i was just trying to facilitate a dialogue with some of the other users of this box to see if there was anything in the commonality that could help everyone with one of these things.

+t to the bm2p+ team 

[morningdew]

Stirthesauce,

Excellent link, I just learned a ton.

Poorlyconditioned,

Thanks for chiming in!  Learn me something though  .  Throughout the thread you seem to be assumming that the JB3 does nothing to manipulate it's line out?  Is this true?  And this also leads me to the question, why do we trust the soundcard?  I'm assumming you go straight from your sound card to line-in on the JB3 to line-out of the JB3 to the RCAs or the XLRs of the UA-5.

Aren't soundcards from computers notoriously crappy?  Could the soundcard or the JB3 be introducing this harmonics?

This is why I have been actually recording the sound (sine waves) coming out of my speakers.  I thought I would be eliminating a lot of signal processing by doing it this way.

[beanstalk]

Stirthesauce,

Excellent link, I just learned a ton.

Poorlyconditioned,

Thanks for chiming in!  Learn me something though  .  Throughout the thread you seem to be assumming that the JB3 does nothing to manipulate it's line out?  Is this true?  And this also leads me to the question, why do we trust the soundcard?  I'm assumming you go straight from your sound card to line-in on the JB3 to line-out of the JB3 to the RCAs or the XLRs of the UA-5.

Aren't soundcards from computers notoriously crappy?  Could the soundcard or the JB3 be introducing this harmonics?

This is why I have been actually recording the sound (sine waves) coming out of my speakers.  I thought I would be eliminating a lot of signal processing by doing it this way.

JB3 has Harmonic Distortion Output 0.1%

[bgalizio]

My UA-5 is busman #8. Never seen anything like that in my recordings. I'd be interested in the root cause, once that gets figured out!

[poorlyconditioned]

Stirthesauce,

Excellent link, I just learned a ton.

Poorlyconditioned,

Thanks for chiming in!  Learn me something though  .  Throughout the thread you seem to be assumming that the JB3 does nothing to manipulate it's line out?  Is this true?  And this also leads me to the question, why do we trust the soundcard?  I'm assumming you go straight from your sound card to line-in on the JB3 to line-out of the JB3 to the RCAs or the XLRs of the UA-5.

Aren't soundcards from computers notoriously crappy?  Could the soundcard or the JB3 be introducing this harmonics?

This is why I have been actually recording the sound (sine waves) coming out of my speakers.  I thought I would be eliminating a lot of signal processing by doing it this way.

I generate sinewaves/testpatterns in a program (like Audacity), transfer *via firewire* to the NJB3, then use line-out on the NJB3 to the test device.

Line out on NJB3 is pretty good.  Unlike headphone out, which is "scooped" (accentuate highs and lows), NJB3 is flat.  I've measured it.  Distortion might not be great, but it is certainly good enough to find 1% or more distortion in other gear!
By the way, not all line out are flat.  For example, line out on my MD is just the same shape as headphone.

Moral of the story: Assume nothing works as advertised.  Even if it sounds OK, there can be big problems.  Test everything.  I haven't got a distortion meter or other fancy audio gear, so this is all I can do.  But I can still find big/obvious problems that seem to be overlooked.  Who the hell designs this stuff with bugs in it?  Well, we know M-audio does

  Richard

[stirinthesauce]

OK, so let me see if I get this straight.  Richard, Chris or anyone, please feel free to set me straight, just seeing if I'm following correctly to what I talked a little bit with morningdew this morning via pm.

Because of the stock adc/design of the ua-5, there *will* be some distortion at under -3db or -2db.  Maybe soft clipping So this distortion will be apparant with any mod, whether oade or busman2 or anyone elses as the adc is not changed, just the opamps.

Does that statement stand to reason or am I completely missing the mark?

Great discussion folks!  

-Jon

[poorlyconditioned]

OK, so let me see if I get this straight.  Richard, Chris or anyone, please feel free to set me straight, just seeing if I'm following correctly to what I talked a little bit with morningdew this morning via pm.

Because of the stock adc/design of the ua-5, there *will* be some distortion at under -3db or -2db.  Maybe soft clipping So this distortion will be apparant with any mod, whether oade or busman2 or anyone elses as the adc is not changed, just the opamps.

Does that statement stand to reason or am I completely missing the mark?

Great discussion folks! 

-Jon

Yes, that sounds right.

- The ADC has got maybe 1% distortion (instead of 0.1% what it should be).  It *should* not have this.  Probably some setup of the ADC is at fault.  It is a defect, but I don't know how to fix it.  So, drive at -6dB or so to avoid this.

- the other problem (very obvious assymetry/clipping of inputs) is probably due to the opamps, either incorrect opamp, or some defect in the opamp or connections.  All of us (Busman, Oade, etc) are only changing opamps (and capactors, and maybe power supply, phantom parts).  As far as I know noone is changing the ADC, so the 1% distortion will persist.

  Richard

[morningdew]

Poorlyconditioned - Thanks! Great explanation I think I have it now.

Just so we are all on the same page, here is what busman has claimed his mods provide:

This is why I was worried my problem was cause by the "new" phantom power" caps but busman assurred this is not the case:

So here we go.
  First I have taken many hours of time and tons of research to figure out how to do this and what parts to change out and what parts should be the replacements. There are tons of great op amps out there to change the sound of a pre amp and all there is to go by is the data sheets to figure out what is the best for the application it is being used for. So to start I found a high speed low noise op amp that had a relatively fast settling time for quick dynamic changes.  Once I found a good sound I found that those didn't meet my gain requirements so I found another op amp to drive the A/D converter that would give a better gain at the  point at which it enters the ADC. The difference in noise is amazing I can crank the gain pots up to the 5 o'clock position before noticing any noise to my ears. After finishing this part of the mod I figured why not go all the way and do the capacitors like Oade does to really clean up the signal. So I went to work researching capacitors used in high end audio upgrades and decided on the brand I wanted to try. These are not film capacitors like Doug uses they are caps made specifically for audio applications and are used in high end audio amplifiers to give a totally transparent but non fatiguing sound. Again going for lower noise higher signal pass through. First I tried changing the input caps and this was very pleasing to my ears. It lent a smoother sound in all frequencies and gave the soundstage a little more clarity. Next I changed out the phantom power capacitors which there are a total of 10 this goes along the same lines as before in cleaning up the signal and gives the phantom supply a better more consistent voltage to power the mics.  I also now change out the op amp in the analog RCA input path to improve that sound for matrixes or analog patchers. These mods are done by ears for ears not specs.
     I don't claim to be an electrical engineer so don't pick me apart. I have merely provided a service that a lot of people have found useful. Also I don't claim to know exactly what Doug does to his but I am pretty positive I am on the right track. Anyone who gets this mod I hgihly doubt will be dissapointed with the results. I also don't want to claim a flavor of pre but this does lean to the transparent end of the spectrum. Please don't attempt these mods at home if you are not prepared to ruin a good pre it is not easy and does require special soldering tools other than a typical soldering iron.
   If you are interested in prices PM me and I will let you know. I hope everyone that has a stock non-Oade unit will consider this mod as it really does make a huge difference to you recordings and I know your ears will thank you, mine did.
  Thanks to all that have paid for this service I am very happy to see my handy work out there in the field.
I hope this answers most of the questions everyone has about my mods.

You hit the nail on the head.
 Mine started
  BM2 mod = op amp replacement
  BM2+mod = op amps and input capacitors replaced
  BM2p+mod= phantom power caps, input caps and op amps are replaced

I have rolled all of it into one from now on it is all the BM2p+ mod because I feel the price is right and I might as well do all the work to make this thing sound as good as it can in one shot.
 
The reason for the 3 different mods was I was slowly working on getting the right components and yet wanted to offer what I could as I went along. I am offering good prices to those that don't have the full BM2p+ mod so they can get it upgraded the rest of the way if they like. Otherwise they can run them like they have them.

I do have a serial# system to keep track of them and what each one unit has as far as mods go.

[bgalizio]

I just wanted to confirm that my UA-5 does NOT have this problem, assuming my method was valid. It is serial number 8, if that helps Chris figure out which batch of op amps had problems. I created a sine wave, ran it from my iMac into the 1/4" inputs. Set it for when the peak light came on. The recording peaks at -2.2dB and shows a smooth sine wave when zoomed in.

[morningdew]

bg,

 .  I would say no you do not have that problem.  Did you see my sine wave on the first page?

The only thing holding me back is that I haven't used the 1/4" inputs.  I don't know how all that works.  I have always used the XLR in's.  Obviously the 1/4" inputs work, I thought they were disabled with the mods.  I tried them briefly when doing the testing and couldn't get them to work but I only tried for a second and it was probably an error on my part.

I'd try again but my unit is out for repair.

[bgalizio]

bg,

 .  I would say no you do not have that problem.  Did you see my sine wave on the first page?

The only thing holding me back is that I haven't used the 1/4" inputs.  I don't know how all that works.  I have always used the XLR in's.  Obviously the 1/4" inputs work, I thought they were disabled with the mods.  I tried them briefly when doing the testing and couldn't get them to work but I only tried for a second and it was probably an error on my part.

I'd try again but my unit is out for repair.

Yup, I dunno if the 1/4" inputs would cause anything to be different from the XLR inputs. I don't have a way to send a line level signal to the XLRs without hooking up my mics, which obviously wouldn't create a perfect sine wave since there would be some outside noise.

I believe the 1/4" input is disabled with Oade mods, but busman told me from the get-go that they were active with his mod.

[SparkE!]

Reading with interest.  Has anyone paged SparkE! and asked his opinion?  I want to say I've read something similar and that he's commented on it but I can't remember when.  Just a thought.  I'll have to check my Bm2p+ soon.

Yeah, I've commented previously on a few threads:

http://taperssection.com/index.php?topic=60987.msg811250;topicseen#msg811250
http://taperssection.com/index.php?topic=57630.msg761070;topicseen#msg761070
http://taperssection.com/index.php?topic=64184.msg859775;topicseen#msg859775

The problems can be due to op amps that don't go rail-to-rail on their input or on their output or it can be due to use of polarized coupling caps or due to even harmonic distortion in the acoustic signal you are recording or due to using crappy electret mic elements with an internal common source JFET amp.  In order to figure out what it is, it would probably be easiest to probe various points in the signal path with an oscilloscope probe and try to identify where the distorted waveform first appears.

If you don't have an O-scope, then you'll have to be a bit more creative to figure out what's going wrong.  One thing you could do is use your audio editor to generate a test tone, then use your soundcard to play it back into your UA-5 at different amplitudes and see if the distortion varies with signal level or if it is even present at all.  If it's not present, then your problem is probably your mics.

[terrapinj]

Reading with interest.  Has anyone paged SparkE! and asked his opinion?  I want to say I've read something similar and that he's commented on it but I can't remember when.  Just a thought.  I'll have to check my Bm2p+ soon.

Yeah, I've commented previously on a few threads:

http://taperssection.com/index.php?topic=60987.msg811250;topicseen#msg811250
http://taperssection.com/index.php?topic=57630.msg761070;topicseen#msg761070
http://taperssection.com/index.php?topic=64184.msg859775;topicseen#msg859775

The problems can be due to op amps that don't go rail-to-rail on their input or on their output or it can be due to use of polarized coupling caps or due to even harmonic distortion in the acoustic signal you are recording or due to using crappy electret mic elements with an internal common source JFET amp.  In order to figure out what it is, it would probably be easiest to probe various points in the signal path with an oscilloscope probe and try to identify where the distorted waveform first appears.

If you don't have an O-scope, then you'll have to be a bit more creative to figure out what's going wrong.  One thing you could do is use your audio editor to generate a test tone, then use your soundcard to play it back into your UA-5 at different amplitudes and see if the distortion varies with signal level or if it is even present at all.  If it's not present, then your problem is probably your mics.

no oscilloscope - hopefully chris has one?

i know for a fact it wasn't my mics or cables, many clean recordings since then with other gear perhaps its the case for morningdew though, i can't comment there

[poorlyconditioned]

Reading with interest.  Has anyone paged SparkE! and asked his opinion?  I want to say I've read something similar and that he's commented on it but I can't remember when.  Just a thought.  I'll have to check my Bm2p+ soon.

Yeah, I've commented previously on a few threads:

http://taperssection.com/index.php?topic=60987.msg811250;topicseen#msg811250
http://taperssection.com/index.php?topic=57630.msg761070;topicseen#msg761070
http://taperssection.com/index.php?topic=64184.msg859775;topicseen#msg859775

The problems can be due to op amps that don't go rail-to-rail on their input or on their output or it can be due to use of polarized coupling caps or due to even harmonic distortion in the acoustic signal you are recording or due to using crappy electret mic elements with an internal common source JFET amp.  In order to figure out what it is, it would probably be easiest to probe various points in the signal path with an oscilloscope probe and try to identify where the distorted waveform first appears.

If you don't have an O-scope, then you'll have to be a bit more creative to figure out what's going wrong.  One thing you could do is use your audio editor to generate a test tone, then use your soundcard to play it back into your UA-5 at different amplitudes and see if the distortion varies with signal level or if it is even present at all.  If it's not present, then your problem is probably your mics.

Hey, that's exactly what I've been doing.  I used an editor (Audacity) to create a 1600Hz sinewave, and a sweeped sinewave (20Hz-20kHz).  Then I exported to a NJB3 using Firewire.  Then I played line in from the NJB3 into the UA5, both mic and line in.  (I saved various attenuations 0dB, -20dB, etc in my audio editor.)  Then I "recorded" with the UA5>NJB3, and compared to the original signal on my computer.

I discovered that the NJB3 line out is pretty good, and pretty flat as well.  I also discovered that both the stock and Poorly-modded UA5 had significant distortion (approx 1% THD) at levels between -3 and 0dB.

But the problems described in this thread are much more severe than 1% THD.   They are crazy distortoed.  Anyhow, I hope you guys sort it out.

  Richard

[poorlyconditioned]

the UA5 shows significant distortion (eg., 1% THD), when driven above -3 or -6dB.  I *believe* this is due to the ADC and not the opamps.

I think the first is a *defect* in the design of the UA5, but I cannot explain why or how to fix it.  For comparison, driving something like a Minidisc with the same signal (line in, up to -1dB) does *not* produce the same distortion.  This unit it *broken* in my opinion!  A cheezy workaround is to run at -6dB always.  Never let the clip light turn on and you will get better sound out of it, even if you have to add that 6dB back in post.

- The ADC has got maybe 1% distortion (instead of 0.1% what it should be).  It *should* not have this.  Probably some setup of the ADC is at fault.  It is a defect, but I don't know how to fix it.  So, drive at -6dB or so to avoid this.

has anyone contacted doug oade to see if he is aware of this?  I'm very intrigued to see what his comments would be.

I don't know Doug, but I'd love to hear his comments.  My guess is that noone has systematically tested this.  Also, since he isn't working on this unit anymore it doesn't matter.  But if anyone knows Doug go ahead and ask his opinion.

This is a prime example of the pitfalls of just "using your ears".  You'll never notice unless there are huge waveform patterns like in this thread.  Damn, I hate companies that sell broken products!

  Richard

[jeromejello]

bump... looking to see how things panned out... whats the GOOD word, yo!

[morningdew]

Sorry for the delay but I have been busy.

Saturday, June 10th I picked up my repaired box from the post office.  Chris had return shipped it priority mail so I had it just in time for a Disco Biscuits/Umphrey's show.  I ran it that day and the tapes sound nice and the wave forms appear to be normal but I didn't get a chance to test the box until late last night because my sister got married this past weekend.

I played back a sine wave through my computer speakers, amplified it through the UA-5 to 0.2 dB and recorded it on a JB3.  I opened it up on Sound Forge 8.0b and it looks just fine.  So it appears that every thing is just great.

Tonight, I have Derek Trucks and ABB so it will get another work out.  Right after that I'm off for four days camping with my family so I won't get a chance to listen to the recordings for a week.

But so far it looks real promising and the communication with Chris and turn around time were great.

[gmm6797]

Can Chris chime in and let us know what the "hardware" issue was?  Just curious.

My box #30 is working like a champ.... and would be better if the DMB Warehouse seats were not so nice and the PA not so loud LOL