Topic: Waveform problem - PLEASE HELP

[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