Topic: Somewhat newbie questions about preamps/A-D converters (and other stuff)

[crazyfish]

This might be somewhat long, I apologize.  I've read the FAQs and archives for answers and got some good ideas but I still didn't find answers to these.

I used to tape for a while a few years ago, I wound up putting together a decent entry level rig for the time.  My rig was (and still is) a set of omni CSB clones with a custom battery box, going into a Sharp MD-MT90 portable minidisc recorder.  A few weeks ago, I was wondering to myself why I had stopped taping, and went to record a friend's band with my rig.  The NiMH rechargable battery came dangerously close to dying near the end of the 35 minute show.  Not only that, I have to deal with lossy masters, media that is expensive and hard to find, and a battery that dies in 40 minutes (and if it would have died, I would have lost the entire show because of the MD's marvelously wonderful requirement to write out the TOC before anything recorded is valid).  No wonder I lost interest.

Lately, I've become significantly more interested in taping shows again (both stealth and non-stealth), and wondered if hard drive or solid state recorders had shown up at a reasonable price range yet.  Well, reading about the JB3, it seems to be a dream come true for me.  A unit with space for two internal batteries for long periods of recording, no worry about changing discs, lossless recording, sub-realtime uploads, and no hard to find media to deal with!  I'll most definitely be picking up a JB3 soon.

Now, if you enjoyed my long preamble, I'll finally get to my questions.  Basically, I plan to buy the JB3 as a trial concept, if I tape some shows with it and they turn out well enough for me, I will most definitely keep the unit and probably upgrade my rig further.  I've been researching mics, and I've pretty much settled that my future rig will be based on a set of AT853Rx mics, which I know require phantom power.

My questions are, since I'm not extremely knowledgeable about the tech specs behind audio gear in general:

1) Does a mic preamp mean that it provides phantom power?  If not, what exactly does a mic preamp do in the signal chain? 
2) If the AD-20 does not in fact provide phantom power, would I be able to use the AT853Rx mics with a PS-2 and JB3 only (while waiting to be able to afford an AD-20 to go with this rig), possibly with some adapter cables?  I ask because I'm not sure what kind of levels the AT853Rx+PS-2 would produce, whether they be too high or too low for the JB3 to make decent use of them.
3) What sort of battery life do these two units get under real-world circumstances?  I saw a figure on the PS-2 that said anywhere from 4-35 hours, which seems to be an enormous range, so I figured I'd employ people who actually used these things for a figure.
4) I'd probably be interested in getting a second battery for the JB3 (correct me if I'm wrong, I'm under the impression that it can hold two internal batteries at once, and that only one is required for normal operation), is the three hour constant record time (which I've seen thrown around here) a quote for one internal battery at once or for two?  I'm trying to see if a second battery is a nice luxury or an absolute necessity. 

Thanks a lot and I'm looking forward to your replies.

[Sanjay]

1) Does a mic preamp mean that it provides phantom power?  If not, what exactly does a mic preamp do in the signal chain? 

Not always, many of them do however.  The preamp acts to boost the signal on the recording, allowing you to adjust the right and left channels

2) If the AD-20 does not in fact provide phantom power, would I be able to use the AT853Rx mics with a PS-2 and JB3 only (while waiting to be able to afford an AD-20 to go with this rig), possibly with some adapter cables?  I ask because I'm not sure what kind of levels the AT853Rx+PS-2 would produce, whether they be too high or too low for the JB3 to make decent use of them.

The AD-20 Does not provide phantom power.  So you would need to run PS-2 > AD-20.  You can run simply a PS-2 however you will need to buy a pair of line transformers (XLR>1/4" adapters) to step down the signal to line level.  Before or after that you can add switchable gain attenuators to boost the signal if you feel the need to.  They are cheap, clean gain.

3) What sort of battery life do these two units get under real-world circumstances?  I saw a figure on the PS-2 that said anywhere from 4-35 hours, which seems to be an enormous range, so I figured I'd employ people who actually used these things for a figure.

I have never run the PS-2 but people usually run them for one show and then switch the batteries, phantom power tends to drain 9v's quick.  I would expect 6 hours safely though.  The AD-20 probably gets about the same, but as I said before i never have used them.  For open taping situations you can build a cable and use a dvd player battery to power them.

4) I'd probably be interested in getting a second battery for the JB3 (correct me if I'm wrong, I'm under the impression that it can hold two internal batteries at once, and that only one is required for normal operation), is the three hour constant record time (which I've seen thrown around here) a quote for one internal battery at once or for two?  I'm trying to see if a second battery is a nice luxury or an absolute necessity. 

Three hours can be expected of a single battery if it is newer and has a good charge.  I would invest in two simply for the comfort of not having to worry and the occasional longer show.  It is worth it.

[crazyfish]

1) Does a mic preamp mean that it provides phantom power?  If not, what exactly does a mic preamp do in the signal chain? 

Not always, many of them do however.  The preamp acts to boost the signal on the recording, allowing you to adjust the right and left channels

2) If the AD-20 does not in fact provide phantom power, would I be able to use the AT853Rx mics with a PS-2 and JB3 only (while waiting to be able to afford an AD-20 to go with this rig), possibly with some adapter cables?  I ask because I'm not sure what kind of levels the AT853Rx+PS-2 would produce, whether they be too high or too low for the JB3 to make decent use of them.

The AD-20 Does not provide phantom power.  So you would need to run PS-2 > AD-20.  You can run simply a PS-2 however you will need to buy a pair of line transformers (XLR>1/4" adapters) to step down the signal to line level.  Before or after that you can add switchable gain attenuators to boost the signal if you feel the need to.  They are cheap, clean gain.

3) What sort of battery life do these two units get under real-world circumstances?  I saw a figure on the PS-2 that said anywhere from 4-35 hours, which seems to be an enormous range, so I figured I'd employ people who actually used these things for a figure.

I have never run the PS-2 but people usually run them for one show and then switch the batteries, phantom power tends to drain 9v's quick.  I would expect 6 hours safely though.  The AD-20 probably gets about the same, but as I said before i never have used them.  For open taping situations you can build a cable and use a dvd player battery to power them.

4) I'd probably be interested in getting a second battery for the JB3 (correct me if I'm wrong, I'm under the impression that it can hold two internal batteries at once, and that only one is required for normal operation), is the three hour constant record time (which I've seen thrown around here) a quote for one internal battery at once or for two?  I'm trying to see if a second battery is a nice luxury or an absolute necessity. 

Three hours can be expected of a single battery if it is newer and has a good charge.  I would invest in two simply for the comfort of not having to worry and the occasional longer show.  It is worth it.

This all seems like good information, thanks for the reply.  I'm definitely glad to hear about the JB3's battery life, I can finally go to shows and tape without wondering if my battery is going to die on me and kill off my entire recording (argh I hate you minidisc).

If the JB3 works out for me, I think my initial rig update will be AT853Rx->PS-2->JB3, because I know I can use the XLR->1/4" for board patching.

I'm not even going to think about how someone like me with a relatively small frame (5'10", 125lbs) is going to stealth a pair of AT853Rx, a PS-2, AD-20, and all the necessary cabling (the JB3 can of course be "just an mp3 player" ).

[eman]

Hey, I haven't read too much about this unit I did a few searches to see if it had been written up here, but I didn't find too much. Perhaps I am totally wrong and it has been fully discredited already. Or maybe it is too big for you.
http://www.fostex.com/index.php?file=products/digital/mr8hd
Maybe you could test drive one and write a review for us. It has the features of a preamp/A->D/phantom power unit/ hard disk recorder all in one, plus FX and 8 channels. They seem to be going for about $400 or so.
It would certainly be nicer if it could also record 24/96 and have a 200 Gig hard drive.

[crazyfish]

Hey, I haven't read too much about this unit I did a few searches to see if it had been written up here, but I didn't find too much. Perhaps I am totally wrong and it has been fully discredited already. Or maybe it is too big for you.
http://www.fostex.com/index.php?file=products/digital/mr8hd
Maybe you could test drive one and write a review for us. It has the features of a preamp/A->D/phantom power unit/ hard disk recorder all in one, plus FX and 8 channels. They seem to be going for about $400 or so.
It would certainly be nicer if it could also record 24/96 and have a 200 Gig hard drive.

Definitely too big, as I plan to use my JB3 (which I just bought) in stealth situations too.

[ivory88]

Thanks 'fish for posing many of the same questions I had on my mind, and to Sanjay for the great answers.  I was hoping to get a few similar questions answered here rather than starting a new thread.

I plan on doing some stealth taping in late October.  Already have a JB3, and will be upgrading from Giant Squid mics to the SP CMC-8's.  Venues will be smaller (~2000 or so), and I expect SPL's to be pretty hefty.  That being the case, I'm going to opt for SP's Phantom Power Kit, and I have an account with an area A/V rental place that rents out the Shure FP-24.  My questions then are:

1.  What do I need to go from the FP-24 into the JB3?  Would it be 2 XLR's that terminate into a mini-plug?  (Sorry if the terminology is off. )
2.  I've read up on the CMC-8's here ALOT, and the one problem that seems to pop up is bass being distorted.  Others have commented that supplying them with phantom power basically eliminates this problem.  The band is Jamiroquai, and I expect bass to be prevelant.  Would "stack" recording be OK in this situation, or something more FOB & centered?  (While we're at it, is there ever decent sound to be had from the balcony?)
3.  Finally, is it typical to set the levels on the JB3 around "0" mark, and then adjust the levels on the FP-24 until a nice, solid signal is registering on the JB3?

Didn't mean to hi-jack the thread, but had these similar questions on my mind.

And crazyfish:  I just recieved a back-up JB3 battery from Creative Labs.  Last week they had a limited (read = 4!!) amount of refurbished batteries available for $50.  I called them directly after getting the tip here that this was the only means of ordering them, since they wouldn't be listed online.  Might want to give them a call, just for peace of mind.

[Sanjay]

To answer your questions:

- DO NOT JUST SOLDER ON TWO XLRS, DO NOT DO NOT DO NOT.  You will fry your mics the minute you plug them into phantom power.  I run mine with the Shure FP-24 and It is imperative you use a phantom adapter, either the Samsom PM-4, Audio Technica 8533, or the Audio Technica 853x.  This Steps down the voltage (48v > 5v) so it doesn't fry your mics.  The reason it is better is that it is a 3 wire powering system and therefore allows ground and power to be sent through seperate channels instead of the same one as in a 2 wire (stereo miniplug) system.  If you look at the thread in the microphone section entitle "small and compact AT853 as your only mics" there is a diagram for a 3 wire battery box, this should in theory do the same thing as phantom power, except in a small package.

- With a regular battery box and any AT mic chances are your bass will be distorted, this is a factor of the two wire system I talked about above.  I have taped bands that are bass heavy and not had it distort but that did not happen as much as it did distort.  Phantom power will eliminate distortion. 

-As for where to run, that depends on two thing 1. where you are comforatable and can access in the crowded venue.  2.  Does the band mix in stereo or mono.  If the band mixes in mono (same noise coming out of each speaker) then you are fine to stack tape.  If in stereo you will miss out on quite a bit stack taping, you may not hear some musicians at all.  For this reason I usually stand in the center FOB.  Yes there can be decent sound from the balcony, it is completely venue dependent though.  Speaker type, direction, balcony and stage location all come into play.

-What you do with the FP-24 is leave it on zero, and adjust the meters ont he FP-24 so they are to your liking.  The meters in the JB3 are not worth 2 shits in a bucket so I don't bother them.  However make sure your JB3 is calibrated closely to the FP-24 so peaking on the FP-24 is not way past the peak line of the jb3.  Keep in mind the numbers on the meters of the FP-24 are NOT decibels.  So peakign will be at the end of the row.  Also bring along electrical tape as you can't turn the meters off on the FP-24 and you may want to black them out a bit.

Hope that helps.

[leegeddy]

To answer your questions:

- DO NOT JUST SOLDER ON TWO XLRS, DO NOT DO NOT DO NOT.  You will fry your mics the minute you plug them into phantom power. 

have you ever done it, sanjay?

i can tell you from personal experience that nothing happens.

This Steps down the voltage (48v > 5v) so it doesn't fry your mics.  The reason it is better is that it is a 3 wire powering system and therefore allows ground and power to be sent through seperate channels instead of the same one as in a 2 wire (stereo miniplug) system.  If you look at the thread in the microphone section entitle "small and compact AT853 as your only mics" there is a diagram for a 3 wire battery box, this should in theory do the same thing as phantom power, except in a small package.

first, not trying to be an ass and pick on your posts.  but from reading some of your replies in regards to AT mics, i really think you should fully understand the role of the P48 adaptors before you give out less-than-accurate advices. they serve a much bigger role than simply convert a P48 down to a 5v supply voltage. there's an entire (and more important) separate function that goes on inside the modules that takes place, mainly converting an unbalanced signal > a balanced signal to interface with P48 preamps.

pls. take my post for what it's worth.

marc

[Sanjay]

As for the frying of the caps:  I haven't had that happen to me, however I do believe that when I posed the question last year or the year before on how to mod them, you and several others told me that if I plug in XLR's it would fry them when connected.  I think even last week someone had said they had fried a pair of capsules doing that.  I will try and find it.  I would test your claim nothing happens but I don't think I am gonna risk a pair of elements.  Either way it won't work to record a show.

I don't claim to understand them as much as you, and i realized there is the whole balanced to unbalanced issue to deal with preamps.  However he asked about distortion, and if you are not using a p48 preamp the balanced unbalanced deal at least to my knowledge isn't a big deal.  Poorlyconditioned and I have used the same circuits on that page we have both built battery boxes that we've tested against a phantom and appears there is no distortion in either.  Granted the At8533 adapter sounds a bit better, but that could be because I am running it with a colored preamp.  However there is no distortion sound, they seem to both be getting the maximum spls. 

I know your not being an ass, thanks for the correction.  I'm always learning myself, but I wasn't trying to mislead anyone here.

[leegeddy]

As for the frying of the caps:  I haven't had that happen to me, however I do believe that when I posed the question last year or the year before on how to mod them, you and several others told me that if I plug in XLR's it would fry them when connected.

sanjay;

i'm more than happy to eat my words if i have EVER posted that mics would fry if directly connected to a P48 source w/o the adaptors.  as far as i can recall, i would have never made that claim since i have connected my AT853 directly to my pre in the past.... and nothing happened. no signal and no frying of capsules.

I don't claim to understand them as much as you, and i realized there is the whole balanced to unbalanced issue to deal with preamps.  However he asked about distortion, and if you are not using a p48 preamp the balanced unbalanced deal at least to my knowledge isn't a big deal.  Poorlyconditioned and I have used the same circuits on that page we have both built battery boxes that we've tested against a phantom and appears there is no distortion in either.  Granted the At8533 adapter sounds a bit better, but that could be because I am running it with a colored preamp.  However there is no distortion sound, they seem to both be getting the maximum spls. 

I know your not being an ass, thanks for the correction.  I'm always learning myself, but I wasn't trying to mislead anyone here.

thanks for understanding my POV. the point i'm stressing is that the modules do MUCH more than simply converting P48 down to 5v supply voltage. two voltages are totally different from one another.  i wouldn't want a newbie or a DIY'er to misinterpret P48 vs. 5v supply voltage and modify their gear based on what they read here.  we should be careful to pass along correct information based on facts and not someone's "understanding".  that's all i'm saying.

marc