Topic: Schoeps - Nbob Actives - Tinybox - M10 & Distortion Problems

[Datfly]

Schoeps MK5 - Nbob Actives - TinyBox with Low-Mid-High Standard Gain & Trafo Out & Dir Out - Sony M10

My normal settings with this set up so far for clubs up front & concerts from mid floor have been Tinybox on Mid Trafo Out and the Sony M10 record knob around 3-4-5.
I get good levels and the recordings once normalized sound great. I use the MID gain as the low will not give me the levels I need without pushing the M10 past 5.

Then came Rush. I had front row seats in front of the stack and it was LOUD and the levels were slamming.
The first error was that setting on the M10 was set to Auto Rec. I fixed that 1 song in
and then put the Tinybox to Low and then everything looked great. Smooth even levels and life was good....
until I got in the car. The recording is nothing but distortion & major pops throughout, well actually the first song that had auto levels came out pretty good!

The second time this happened was even more of a shocker as I just recorded one band on my normal settings of
Tinybox set to MID with Transfor Out & M10 on 3 and they came out great but the next band I did that was a little bass heavy
came out distorted & pops like Rush, though not as severe, and I was 30 feet away from the main stack and again the levels looked right.

Has anyone pulled a stack tape with this set up? What setting do you use? Should I have not used Transfo out in
a super loud scenario?

The Schoeps can handle a head in the major concert stack tape right?
What exactly does Trafo out do again? Just add color? (embarrassed to ask that but.....)

Sample Below.

Any thoughts or ideas would be great.
Thanks,
Datfly

RUSH



Stiletto Red

[hi and lo]

I don't think it would be possible to clip a TB on the low setting (+4dB). Looks more like an intermittent connection.

[Datfly]

If you click the image it should take you to Photobucket & a larger image.
Obviously the spikes are the pops and even though the wave looks good the bass is distorted.

Sample provided Below.

[it-goes-to-eleven]

Only thing I've seen similar to that is a diaphragm physically bottoming out and hitting the backplate.  That's extremely loud though, typically 150dBSPL or more--or an air blast.

I have overloaded Schoeps, however this is not that (Dino Jr).  Especially not given the OP's description of the circumstances of the second overload.

Maybe Nick will offer some suggestions.

[schoepsnbox]

PM sent!

[cashandkerouac]

did this issue get resolved? 

i was having a similar issue with my Naiant AKG active set-up and Jon is currently evaluating my Tinybox to identify the problem.  in my situation the spikes did not seem to be the result of a bass-heavy band or loud volume from the PA.  in fact, i couldn't identify any pattern to it at all.  cables and caps were tested with another Tinybox and everything is good.  any feedback about the resolution to your issue would be greatly appreciated.  thanks.

[Datfly]

Upon further experimentation with a dual out tinybox, I think it was probably severe clipping of the output transformers.  Generally, the OTs are going to give up (20% THD below 100Hz) at +8dBV, that is 5dB below the direct out headroom.  When I got to +10dBV on the transformer out, I was able to produce clicks as in your recording.  Note that the rated transformer output is +8dBV, and saturation is already prominent at 0dBV.

In such cases, if you have a dual box I would use the direct out as that has more headroom.  However, in the dual boxes the outputs interact somewhat, which limits the headroom of the direct out to +10dBV at 100Hz (down from +13dBV in a transformerless box).

The volume where you hit maximum level depends on your microphones.  For flat-response (omnis, typically) -40dBV/Pa mics, that is 138dBSPL at minimum gain (4dB).  Note that A-weighted SPL (the measurement of earbleed) can be much lower than peak unweighted SPL, because the volume at low frequencies at a rock concert is typically much higher.  So a concert that is 120dBSPL-A could exceed headroom at low frequencies.

To cope with that, again use the direct out if you have that, or select capsules that have limited low-frequency response.  Other options are padding the mics (tinybox can be configured to do that as a option), and specifying 0dB as minimum gain.  Another option in a dual box is to have the transformer out level padded down from the direct out, -6dB should make the two outputs have the same headroom.

Generally, watch the clip LED on tinybox, if it's flashing red you could be exceeding the rating for the transformer output.

Is there a option to send the Tinybox in and have it reconfigured or does it require a new Tinybox?

I plan on doing some heavy testing this weekend. I have two Paul McCartney shows in a couple of weeks & do not want to lose them
and one is once again from the front row.

Thanks for your research.

Datfly

[brad.bartels]

If I'm reading the original post right, the Tinybox was set to the mid-gain setting on both recordings with the noise? So, I would think for loud shows, you should set it to low and compensate by raising the record level on your M10 and that might do the trick. I don't think I have the output transformers on mine, but I know I've run the gain on low several times for louder shows. I'm pretty sure I've ran the M10 as high as 7 or 8 on the record level and I don't remember having any audible issues (it looks like you are tying to keep it below 5). Not sure what gain levels you have configured on the tinybox, I think standard is +6 / +16 / +32 or something along those lines, so that would buy you 10 dB between the mid and low setting if it's standard (or whatever the difference is between your mid and low gains).

Or maybe I'm not thinking about this the right way, but seems like lowering the input gain on the Tinybox would lower the output hitting the output transformers by the same amount.

[Datfly]

I'll change the transformer input level or minimum gain for return shipping charge only; also I can make the clip meter more sensitive (lower trigger).  Those changes are just a few resistors on the bottom side PCB, very fast & easy change to make.

OK. Thanks.

For just about every show I have done I HAD to have the Tinybox on MID just to get the levels to 12 on the Sony M10. So the MID setting is what I
will need most. I do not do classical or anything soft so I do not think I would need the Max gain.
That said, the odd thing was the second time it happened was at a show that was not as loud as a few I have done bit it did have more bass.

I believe unity is at 3 to 5 on the M10 so I try not to go over that.

Datfly

[Todd R]

OK. Thanks.

For just about every show I have done I HAD to have the Tinybox on MID just to get the levels to 12 on the Sony M10. So the MID setting is what I
will need most. I do not do classical or anything soft so I do not think I would need the Max gain.
That said, the odd thing was the second time it happened was at a show that was not as loud as a few I have done bit it did have more bass.

I believe unity is at 3 to 5 on the M10 so I try not to go over that.

Datfly

Had to have the TB on mid setting to get to -12dbFS on the M10 with the M10 set to 3 or set to 5, or couldn't get to -12dbFS on the low setting on the TB with the M10 set to 9-10?

IME, unity gain is a pretty useless concept for what we do, and is totally over-emphasized on ts.com, and for little good, solid reasons.

From the specs, the minimum input level on the M10 line inputs (I assume to get to 0dbFS recordings) is 500mV.  500mV is a -6dbV signal, which is far under the problem area of the TB and the output transformers.

I'd run the TB at the low setting and if you can't get to -12dbFS to -6dbFS with the M10 set at 9 or 10, then bump up the gain to the mid setting on the TB.  I haven't seen any published information on the M10 showing that it has significantly, or any, more distortion or noise when run at a setting of 9 than it does at a setting of 3.  Running it at 3-5 looks like it is causing problems for you, and the "need" to run at 3-5 is just some unsubstantiated ts.com rumors.

Sorry for the hard come-down on this, but the unity gain mantra drives me nuts, and even worse when it is leading to failed recordings.

[brad.bartels]

Right, but in this case there was a tinybox set on low with clipping transformers.  That has to be fixed before the recorder.

If you only do moderate-to-loud shows, then gain settings of 0/10/20 might be more useful.

If I read the original post correctly, the Tinybox was not set to low gain, but mid gain when the problem occurred. My thinking is that using low gain and a higher recording level on the M-10 is the answer for louder shows (or at least would help greatly). But just my 2 cents. To Todd's point, I am pretty sure I've run the M-10 up close to 8 or more without any discernible issues.

But, I don't have output transformers on my tinybox, I don't think.

[Todd R]

Right, but in this case there was a tinybox set on low with clipping transformers.  That has to be fixed before the recorder.

If you only do moderate-to-loud shows, then gain settings of 0/10/20 might be more useful.

Ok, that makes total sense, and it looks like a gain revision is in order. I'd just hate to see anyone give up on their gear combo or do potentially unnecessary revisions just to hold to the unity gain theory.

The unity gain thing just baffles me, esp for concert recording where the venue noise floor even without music going through the PA is probably 70-80db, maybe more. Add to that unity gain settings are not published, and people are basing them on when the output signal on the line out equals the original input level (when we have no info on what level of gain or attenuation is applied on the line out).  And then on top of that, there is an assumption that the noise or distortion of the gain stage inamps, or op amps, or discrete front end or whatever the manufacturer is using is in fact lower at 0 gain than it is at a gain of 20db or whatever.  Man that is a whole lot of assumptions and guesses that are being made to lead people to be afraid to run their recorders outside some narrow gain setting on the dial.

[Datfly]

Right, but in this case there was a tinybox set on low with clipping transformers.  That has to be fixed before the recorder.

If you only do moderate-to-loud shows, then gain settings of 0/10/20 might be more useful.

Ok, that makes total sense, and it looks like a gain revision is in order. I'd just hate to see anyone give up on their gear combo or do potentially unnecessary revisions just to hold to the unity gain theory.

The unity gain thing just baffles me, esp for concert recording where the venue noise floor even without music going through the PA is probably 70-80db, maybe more. Add to that unity gain settings are not published, and people are basing them on when the output signal on the line out equals the original input level (when we have no info on what level of gain or attenuation is applied on the line out).  And then on top of that, there is an assumption that the noise or distortion of the gain stage inamps, or op amps, or discrete front end or whatever the manufacturer is using is in fact lower at 0 gain than it is at a gain of 20db or whatever.  Man that is a whole lot of assumptions and guesses that are being made to lead people to be afraid to run their recorders outside some narrow gain setting on the dial.

Yes, I thought that if I cranked the dial past the unity gain that I would be open for distortion & crackling popping noises......oh wait.

Seriously. I thought that going past that would let the deck amp over ride the TB pre-amp and distort, or something along those lines.
So my thought was set the M10 to no more than 5 and use the Tinybox to fill in the rest and I was afraid of 5 thinking that was near the distortion zone.

Learn as we go. I will be more open but I don't want to waste a recording to find out as if I am recording them I want the recording.
Maybe we need to start a poll & see where people set there M10 recording dial?

Thanks for all the tips.

Datfly

[DSatz]

At the risk of jumping in when I haven't had time to read everything carefully: The overload limit of audio transformers--particularly miniature ones and/or ones with a substantial voltage step-up--depends greatly on the frequency of the audio signal. A transformer that can perfectly well handle (say) -10 dBu input at 100 Hz might overload at -20 dBu at 50 Hz and at -30 dBu at 30 or 40 Hz. Those are made-up numbers, but I hope the point is clear: When you're trying to determine the maximum safe input level for a small audio transformer (even the very best), a bass-heavy signal (and I mean really low frequencies, not just mid-bass) will cause overload far sooner than a signal with its energy concentrated in the midrange, and the curve becomes markedly steeper, almost cliff-like, the lower you go in frequency, so that a very unforgiving limit can be reached.

This is more likely to occur with pressure-gradient transducers (generally, directional microphones) as the result of solid-borne sound (physical vibration, handling noise) or gross air motion (wind, air conditioning) and even proximity effect to some extent. With pressure transducers (pure omnis) the sensitivity to these sources of infrasonic noise is much lower. Some people prefer omnis because they can have flat response to very low audio frequencies--and perhaps ironically, they can also be the cure for low-frequency overload in some situations, because they don't pick up nearly as much low-frequency garbage. Much more of whatever a cardioid or other pressure-gradient microphone is putting out at, say, 40 Hz is noise rather than legitimate response to acoustical input.

BTW, when an audio transformer saturates, it doesn't only distort the low frequencies that caused the saturation. Depending on the severity of overload at the given moment, it produces distortion across the whole audio spectrum.

--best regards

[Todd R]

Seriously. I thought that going past that would let the deck amp over ride the TB pre-amp and distort, or something along those lines.

BTW Datfly, by no means did I mean to give you grief for what you did -- makes total sense given all the info around here on what levels to run the M10.  I'm just exasperated with the prevailing conventional wisdom on this board about unity gain and how important it is.  I think it leads people to the false conclusion that there is some narrow range that recorders can be safely run within.

I've used my M10 from 2 on the dial up to a fully cranked 10 on the dial, and have never noticed any ill effects.  Which isn't to say that controlled testing might show more or less noise if run at the extremes, but there don't seem to be any glaring issues running across a pretty full range (still not sure what happens if you get into the 0-1 range).