Topic: Greetings... my new mic preamp.

[digifish_music]

So that +17dB on the VU meter is still a good 5dB away from clipping.

EDIT: So I guess using a RED LED for the 5th LED in the VU meter might be confusing... maybe I should just change the 5th LED to Yellow instead of RED?

Would having 5 dB of headroom at the point the user starts to worry about gain be a bad thing? I am thinking most people everyone will be recording into digital recorders and any signal hot enough to light the +10 dB LED will be more than capable of delivering a clean level for a digital recorder to deal with?

What I am saying is 5 dB safety margin on an analog device that is aimed at recording mainly concert material (with unpredictable max volume) is probably a good thing. I know on my MixPre maxing the peak meter does not = audible distortion, but still keep well away from it.

digifish

[fivefishdiy]

Ideally, one should record at an average of 0dB analog (which corresponds to -18dbfs (or lower) on your digital scale A/D).  Any peaks in the sound would be covered well by the analog headroom (where you have +18 to +22dBu above 0dBu, which then corresponds to 0dBFS on the digital scale), thus there is no danger of clipping the A/D.

If you record HOT that your average level is +10dBu, you run into clipping the AD more likely than someone recording at 0dBu average. (Because the former has 10dB less headroom to work with.)

Maybe this diagram would show what I mean.

[Todd R]

EDIT: So I guess using a RED LED for the 5th LED in the VU meter might be confusing... maybe I should just change the 5th LED to Yellow instead of RED?

I think you should keep with red, and that overall the green>yellow>red scheme will work great.

Not meaning to place this on O-canis, but I think there is some confusion on this board between dBu, which is simply a representation of voltage, and dBFS for digital recorders.  That is, many know you cannot go above 0dbFS without digital clipping and therefore assume that something like 17dBu must be bad (when all it means is you are putting out a signal at a level of about 5.5v).  The dBu output level of the preamp really only has meaning in regards to point at which the preamp can no longer provide output without distortion, and also the maximum level the ADC or recorder can accept without itself clipping. 

The gain structure of the ADC/digital recorder creates a relationship between the dBu output of the preamp and dBFS of the digital recording, but there is no inherent relationship between dBu and dBFS (i.e., any relationship defined within the preamp itself).

[fivefishdiy]

Just for clarification... for the VU meter, the 5th LED denotes:
+17dBu = 5.48 Vrms  = 15.51 Vpeak-to-peak

The preamp's max out is about
+22dBu = 9.7 Vrms = 27.5 Vpeak-to-peak

So even if the 5th LED lits up, the pre is still far away from actual clipping.

That said, nobody should be recording at +17dBu average... but it's okay to have peaks at that level. You want your signal chain setup just so when your pre is peaking (for loud material) at +17dBu or above, your A/D converter should just be showing maybe -3dB below the 0dBFS clipping point.

[strangetapes]

Excellent explanations guys +t

[digifish_music]

Just for clarification... for the VU meter, the 5th LED denotes:
+17dBu = 5.48 Vrms  = 15.51 Vpeak-to-peak

The preamp's max out is about
+22dBu = 9.7 Vrms = 27.5 Vpeak-to-peak

So even if the 5th LED lits up, the pre is still far away from actual clipping.

That said, nobody should be recording at +17dBu average... but it's okay to have peaks at that level. You want your signal chain setup just so when your pre is peaking (for loud material) at +17dBu or above, your A/D converter should just be showing maybe -3dB below the 0dBFS clipping point.

Perhaps you could mill an analog to digital meter calibration table on the base of the unit

digifish

[PH]

Shake, and Bake!

[Gutbucket]

Mmmmm, chicken.


"And I helped"

[fivefishdiy]

Nothing exciting to show yet....

but making slow progress with it...



It's going to be tight... but everything still fits so far. 6" wide, 4" deep for the motherboard PCB. I wonder if I should switch to SMD parts.

Check out the 2 vertical VU meters. And we also got some transformer mojo going on here.

[OOK]

Nothing exciting to show yet....

but making slow progress with it...



It's going to be tight... but everything still fits so far. 6" wide, 4" deep for the motherboard PCB. I wonder if I should switch to SMD parts.

Check out the 2 vertical VU meters. And we also got some transformer mojo going on here.

Simply Awsome.......I bet the pre is going to sound amazing.........

Peace OOK

[F.O.Bean]

count me in for one

[Chuck]

What's it going to weigh with those transformers in there? We may have to come up with an appropriate nic name. "The brick" is already taken.

[Chilly Brioschi]

   What are those funny round things that look like squat capacitators?          

[bugg100]

Flux capacitors...

[willndmb]

back after a week away - still looking good