Topic: What's up with this waveform?? (pic inside)

[travelinbeat]

not sure what caused this. it could be a weak battery. That is my only guess here. I recommend 9.6v maha batteries for my preamps. Because you can charge them every time you go out and have a good voltage. My preamp will run fine down to 7.6 volts. Thats a pretty dead 9v.

I do use the Powerex 9.6 rechargables.  The 9V I used for this show was fully charged then run for about 3hr at a different show, then used for this show.  How long would you expect a 9V to last?  Would I be able to charge it and run it in the preamp without being at a show and take hour to hour readings with a voltmeter or would the draw be different with a high SPL signal running through it?

[Church-Audio]

not sure what caused this. it could be a weak battery. That is my only guess here. I recommend 9.6v maha batteries for my preamps. Because you can charge them every time you go out and have a good voltage. My preamp will run fine down to 7.6 volts. Thats a pretty dead 9v.

I do use the Powerex 9.6 rechargables.  The 9V I used for this show was fully charged then run for about 3hr at a different show, then used for this show.  How long would you expect a 9V to last?  Would I be able to charge it and run it in the preamp without being at a show and take hour to hour readings with a voltmeter or would the draw be different with a high SPL signal running through it?

Honestly you should be able to run that preamp for atleast 20 + hours with out having to worry about voltage drop at all. So I would say it was not a voltage issue.

[SparkE!]

not sure what caused this. it could be a weak battery. That is my only guess here. I recommend 9.6v maha batteries for my preamps. Because you can charge them every time you go out and have a good voltage. My preamp will run fine down to 7.6 volts. Thats a pretty dead 9v.

I do use the Powerex 9.6 rechargables.  The 9V I used for this show was fully charged then run for about 3hr at a different show, then used for this show.  How long would you expect a 9V to last?  Would I be able to charge it and run it in the preamp without being at a show and take hour to hour readings with a voltmeter or would the draw be different with a high SPL signal running through it?

Honestly you should be able to run that preamp for atleast 20 + hours with out having to worry about voltage drop at all. So I would say it was not a voltage issue.

Sure looks like a low battery voltage issue.  However, you'll get the same thing if the source is really loud or if the PA in the venue is badly over-driven (or both).  Either way (low battery or loud source), the result is even harmonic distortion (which looks exactly like what you've shown, compressed on one side of the waveform).

How does the recording sound?  If it sounds OK, I wouldn't worry about it too much.

[dnsacks]

Again, this waveform looks identical to the waveforms I saw when my preamp batteries were on their way out.

You could try to duplicate the situation by first recording loud music with freshly charged batteries and then repeating the circumstances leading up to this recording (run them for 3 hours plus, etc) and compare the resulting waveforms.

Years ago, I tried using powerex 9v batteries to run a ps2 providing phantom to some mbhos and ended up needing to go with another solution after having inconsistent performance from the batteries.

[travelinbeat]

not sure what caused this. it could be a weak battery. That is my only guess here. I recommend 9.6v maha batteries for my preamps. Because you can charge them every time you go out and have a good voltage. My preamp will run fine down to 7.6 volts. Thats a pretty dead 9v.

I do use the Powerex 9.6 rechargables.  The 9V I used for this show was fully charged then run for about 3hr at a different show, then used for this show.  How long would you expect a 9V to last?  Would I be able to charge it and run it in the preamp without being at a show and take hour to hour readings with a voltmeter or would the draw be different with a high SPL signal running through it?

Honestly you should be able to run that preamp for atleast 20 + hours with out having to worry about voltage drop at all. So I would say it was not a voltage issue.

Sure looks like a low battery voltage issue.  However, you'll get the same thing if the source is really loud or if the PA in the venue is badly over-driven (or both).  Either way (low battery or loud source), the result is even harmonic distortion (which looks exactly like what you've shown, compressed on one side of the waveform).

How does the recording sound?  If it sounds OK, I wouldn't worry about it too much.

I've posted a sample song from the recording on the previous page of this discussion-- overall I'd say I'm happy with it for a stack-tape.  Just wondering for my own edification what could've caused this and how I could avoid repeating this sort of waveform.   

[bombdiggity]

See DSatz' comment at the (current) end of related thread over here:

http://taperssection.com/index.php?topic=160298.0

If it doesn't sound like something wrong there probably isn't... 

[Church-Audio]

Again, this waveform looks identical to the waveforms I saw when my preamp batteries were on their way out.

You could try to duplicate the situation by first recording loud music with freshly charged batteries and then repeating the circumstances leading up to this recording (run them for 3 hours plus, etc) and compare the resulting waveforms.

Years ago, I tried using powerex 9v batteries to run a ps2 providing phantom to some mbhos and ended up needing to go with another solution after having inconsistent performance from the batteries.

I wonder were you using the 9.6v powerex or the regular 9v Just out of curiosity?. So far so good for me, but I only really use them for testing as I dont have time to record very many shows. They also have a new 8.6v 350mA battery that looks interesting.

[SparkE!]

not sure what caused this. it could be a weak battery. That is my only guess here. I recommend 9.6v maha batteries for my preamps. Because you can charge them every time you go out and have a good voltage. My preamp will run fine down to 7.6 volts. Thats a pretty dead 9v.

I do use the Powerex 9.6 rechargables.  The 9V I used for this show was fully charged then run for about 3hr at a different show, then used for this show.  How long would you expect a 9V to last?  Would I be able to charge it and run it in the preamp without being at a show and take hour to hour readings with a voltmeter or would the draw be different with a high SPL signal running through it?

Honestly you should be able to run that preamp for atleast 20 + hours with out having to worry about voltage drop at all. So I would say it was not a voltage issue.

Sure looks like a low battery voltage issue.  However, you'll get the same thing if the source is really loud or if the PA in the venue is badly over-driven (or both).  Either way (low battery or loud source), the result is even harmonic distortion (which looks exactly like what you've shown, compressed on one side of the waveform).

How does the recording sound?  If it sounds OK, I wouldn't worry about it too much.

I've posted a sample song from the recording on the previous page of this discussion-- overall I'd say I'm happy with it for a stack-tape.  Just wondering for my own edification what could've caused this and how I could avoid repeating this sort of waveform.   

After listening to the sample and realizing that it's still asymmetric in the quiet (crowd noise only) sections of the recording, I highly suspect the battery was low.  Fortunately it was not low enough to cause clipping distortion.

As DSatz pointed out in the other thread, "If it doesn't sound like something wrong there probably isn't..."

My advice is to make sure you always charge the battery before recording and if you see the problem gradually getting worse over time, it's time to replace the battery.

[Gutbucket]

I'm With SparkE on this, replace the battery.

Years ago, I tried using powerex 9v batteries to run a ps2 providing phantom to some mbhos and ended up needing to go with another solution after having inconsistent performance from the batteries.

The Maha 9.6V batteries are now available as Low Self Discharge type, under their Imedion brand name (Imedion LSD has a black and grey casing verses Powerex with a white case with yellow lettering).  The Imedion LSD type hold charge far longer and are more predictable.  When my original non-LSD Maha Powerex 9.6V batteries started going wonky it drove me nuts tracking down the cause of distortion and similar asymetrical waveforms.  I would take them out of the CA-UGLYs after a session and they would measure ~9V.  It wasn't until I started measuring them in the preamp while under load that I realized they were dropping to 6-7V in use, but would measure 9V on a voltmeter out of the device.  Replaced them with the Imedions and have had no more problems.

[travelinbeat]

So that's been a couple people now leaning towards a weak battery-- I've just gone ahead and ordered a pair of those Imedion 9.6V's.  I'm using the "POWEREX MH-C490F-DCW Stealth Two Hour Compact 4 Bank 9-Volt Charger," how do you guys feel about this charger?  Should I be looking into getting a new charger as well or was that battery just getting old?  I bought 4 of these Powerex 9.6V's about 2 years ago and I've been using them pretty regularly (taped about 120 shows since I got them).  How long should one expect these types of batteries to last?

[Gutbucket]

Your experience is identical to mine- 4 powerex 9.6V, same charger, 2 years of similarly constant use before they developed problems sometimes causing similar wavefrom symtoms as yours, and sometimes loss of headroom and audible distortion of high level signals. Once I understood the source of the problem and decided to replace them I found the then new Imedion version, was happy with the Imedion AAs & AAAs I'd been using for a number of years and have since been using these for the past 2-1/2 years in the same charger.  I now check voltage on them after they have been on for 6+ hours and while still in the powered-up preamps and they measure ~9V.  I recharge them and don't worry about using them for 2 weeks.  Longer than that and I'll pop them back in the charger the night before.  When they eventually begin to drop significantly below 9V after 6+hrs I'll replace them, before I get similar end-of-life problems.

[Church-Audio]

I'm With SparkE on this, replace the battery.

Years ago, I tried using powerex 9v batteries to run a ps2 providing phantom to some mbhos and ended up needing to go with another solution after having inconsistent performance from the batteries.

The Maha 9.6V batteries are now available as Low Self Discharge type, under their Imedion brand name (Imedion LSD has a black and grey casing verses Powerex with a white case with yellow lettering).  The Imedion LSD type hold charge far longer and are more predictable.  When my original non-LSD Maha Powerex 9.6V batteries started going wonky it drove me nuts tracking down the cause of distortion and similar asymetrical waveforms.  I would take them out of the CA-UGLYs after a session and they would measure ~9V.  It wasn't until I started measuring them in the preamp while under load that I realized they were dropping to 6-7V in use, but would measure 9V on a voltmeter out of the device.  Replaced them with the Imedions and have had no more problems.

Well that's good to know I will stop recommending them.

[Gutbucket]

Well, the Powerex worked great for a couple years of heavy use.  It's just that now I'd recommend the Imdeion version over them.  I expect the Imdedions will eventually succumb to the same fate, but they have already lasted longer and show no signs of getting weaker this far with the benefits of slower self discharge. I check voltage on them afterwards to make sure they aren't starting to drop for peace of mind . 

I still like to charge them the night before I know I'll use them but if even if they were charged a week or two prior, I check voltage on them before using them and they are usually fine. 

[travelinbeat]

Your experience is identical to mine- 4 powerex 9.6V, same charger, 2 years of similarly constant use before they developed problems sometimes causing similar wavefrom symtoms as yours, and sometimes loss of headroom and audible distortion of high level signals. Once I understood the source of the problem and decided to replace them I found the then new Imedion version, was happy with the Imedion AAs & AAAs I'd been using for a number of years and have since been using these for the past 2-1/2 years in the same charger.  I now check voltage on them after they have been on for 6+ hours and while still in the powered-up preamps and they measure ~9V.  I recharge them and don't worry about using them for 2 weeks.  Longer than that and I'll pop them back in the charger the night before.  When they eventually begin to drop significantly below 9V after 6+hrs I'll replace them, before I get similar end-of-life problems.

Could you recommend a good, cheap voltmeter for 9V's and AA's?

[Gutbucket]

Could you recommend a good, cheap voltmeter for 9V's and AA's?

The dollar store across the here usually has cheap multimeters in hardware isle for.. $1
Good?, umm well no, but I imagine they meaure DV Voltage accurately enough, and only cost a dollar.

The multimeter I use is a $20 Harborfreight special and is a Cadillac in comparison, but measuring battery voltage is a Yugo level job.