Topic: Greetings... my new mic preamp.

[illconditioned]

Nice work on testing.  This is cool.

  Richard

[bluegrass_brad]

I *think* I will ditch the VU Meter function and opt instead to use a signal and over/clipping indicator, using low-power opamps to do the job. Hmmmm.....

I hope you leave it in, good metering IMO is a huge bonus. With the batteries we have available to us power isnt much of a problem when we are talking about the consumption of VU meters.  Especially when you are getting almost 4 hours on a normal 9v w/ everything on. Whatever you do though, thanks for keeping us in the loop.

[Todd R]

From my standpoint, it seems hard for a taper to calibrate an analog preamp (metering in dBu) to a digital recording device or A/D (metering in dBFS).  So you can't really use meters on an analog preamp all that well for setting levels -- you need to use the meters on your A/D or recorder.

That said, to me it seems basic metering (albeit 2ch metering) is all that needed.  I don't know the circuit ramifications or whether in the end it would save in current draw, but you could use bicolor LEDs.  Something like this:

http://www.vishay.com/docs/83056/tluv5300.pdf

If you use 2 of these per channel, you'd only have 4 LEDs total, but could set them up so that you had for each channel one of these bicolor LEDs could show signal present at ~-24 (eg, Red) and stronger signal at ~-12 (change to Green), and the other LED could show near peak levels of ~-6db (Green) and approaching clipping of ~-2db (change to Red).  [Sorry these db suggestions are my interpretation of dBFS, I'm not sure how this would play out with preamp.  I guess you could start with the clipping point of your design and work backwards.]

[bugg100]

Will this be available in kit form? Please?

If so, definately leave the option of metering in but switchable.

[fivefishdiy]

Todd, I'm thinking of using those kind of LEDs actually. But haven't thought of it for use in a VU. That's a novel way to use it. But it could be confusing if used as a VU as the user will see green/red, green/red.

What I'm thinking is show GREEN for signal present, and light up the RED for "pre-clip".  Whatever is the exact level in between, I guess doesn't matter.

But the VUs do sure look pretty... makes me want to keep them.

bugg100

>>Will this be available in kit form? Please?

I don't know yet. We'll see.

[Javier Cinakowski]

Most of us agree that VU are not critical for a preamp.   BUT, we all know that pretty lights do sell well. 

"It is all about the lights!"

[willndmb]

pretty lights do one thing thats a huge plus
they let you know fasssssst if there is a signal
they saved my ass once when i forgot to turn on phantom and i am looking down saying why am i showing a recording being made but i have no lights on showing there is an actual signal being recorded
i kept my svu1 for this reason (although now i don't really need it because the fr2le has lights on the side)

[fivefishdiy]

but what does it  take to make an LCD display do what every one is asking for in lights and meters?

A LOT!

Well, you'll need a microprocessor (like a PIC or Atmel). A clock. Or pick a microprocessor with a built-in clock.  Need a A/D converter, or a built-in one. Then the LCD display (usually a HD4480 compatible display).  If the LCD does not use LED backlights, and uses the older style EL panel, then you need a high voltage DC converter too.  And the chips will have to run either on 3.3 or 5V.

May be more trouble than it's worth if it's just going to be used as a VU.  (Plus the clock circuitry, and digital data zipping by could induce RF which you'll hear as a whine in your amplified mic pre signal. )


Okay, I'll rethink the VU meters. I do like them... makes the unit "alive" instead of just sitting there.

[halleyscomet8]

i don't think meters should be a huge necessity. the lights also might not help in not so friendly situations. i personally like the look of the blue box with just xlr and knobs. but, i am just 1 of the 100's giving input.

[spyder9]

I agree that metering is not a big need on a analog preamp.  My Aerco has no lights.  I've relied solely on the recorder's ADC and metering to get the job done.  The results have been satisfactory as far as good clean unobstructed recordings go.  Knowing your equipment is the key.

However, a single peak light would be nice.

+T fivefishdiy on your creation.    

[eric.B]

Sure metering lights are great and all, but IMHO you dont need anything more than what the grace designs V2 had.

from the grace manual.. 

PEAK INDICATOR The LED peak indicator, which monitors the signal between the input
and output amplifiers, illuminates the green LED at -14dBu and illuminates the red LED at
+16dB (10dB before clipping).

plenty for a purely analog standalone portable microphone preamp..

[fivefishdiy]

PEAK INDICATOR The LED peak indicator, which monitors the signal between the input
and output amplifiers, illuminates the green LED at -14dBu and illuminates the red LED at
+16dB (10dB before clipping).

Eric.B! Hey thanks for that tidbit of info!

Guess what?!  My existing VU meter's 5 LEDs denotes
–13dB, -7dB, 0dB, +10dB, +17dB

I can basically just use the 1st and 5th LED... and I basically have an instant -13dB and +17dB indicator... similar enough to the -14dB and +16dB indicators of the Grace.

If I'm going to do that, might as well put in the VU. (just thinking out loud)

[Kindguy]

Sure metering lights are great and all, but IMHO you dont need anything more than what the grace designs V2 had.

from the grace manual.. 

PEAK INDICATOR The LED peak indicator, which monitors the signal between the input
and output amplifiers, illuminates the green LED at -14dBu and illuminates the red LED at
+16dB (10dB before clipping).

plenty for a purely analog standalone portable microphone preamp..

I agree... Love the avatar BTW

[silentmark]

Nice work ...

[fivefishdiy]

Parts arrived, Switchcraft mini-XLRs, locking DC jacks, mini-switches, knobs, spacers, stainless steel nuts and bolts to replace the cheapie screws that came from the factory... I think everything is starting to fit together.

Finished designing my VU meter last night, made it smaller. 1.25" tall x 1.6" wide.



Sending it out for prototype manufacturing.

This is how I plan to use the VU meters on the panel. (Artist rendition )



Check out the knobs... I sorta like it... kinda gives it a vintage look.

The buttons will probably end up being round, instead of square... we'll see.

Next step: Designing the main motherboard.