Topic: Greetings... my new mic preamp.

[flipp]

I really like the layout of the Fostex FR2's power and phantom switches*, both on the right side with the XLR inputs. Since they are only used at the beginning and end of recording, they don't have to be readily accessible like rolloff, hp, meter switches etc. Perhaps put the power and phantom switches on the side with LEDs on the front (perhaps under one of the handles?) to indicate their state.

Appreciate your taking our input into consideration. Most of us have specific likes/dislikes that you won't be able to cstomize without actually building each unit custom. I hope you do offer a kit. That way those who purchase a kit can customize to their individual desires.

* http://www.fostexinternational.com/images/product_img/mid/fr2_right.jpg

[fivefishdiy]

Okay, before I get in too deep into this project, I want to test first if my PSU can handle 2 channels. I haven't tested the DC-DC PSU with 2 channels + 2 VU meters.  So it was a little nerve-wracking to see if it will work or not.

  Happy to say it works just fine. I have it powered for several hours now and it just barely gets warm. Touch with your finger the PSU chip and the little heat dissipates away, sucked away by your finger.

Did some load testing and measurements of current consumption.
Baseline: Power ON LED indicator ON. LED still using low-value Resistors, so LED current consumption is a little on the high side.

1 Channel Pre = 117mA  @ 12VDC   (1.4 Watts)  <--- on our earlier 9V battery testing, we got the same numbers (117mA)
2 Channels Pre = 180mA @ 12VDC   (2.1 Watts)
2 Channels + 48V Phantom Power ON for both channels (no mic load) = 200mA @ 12VDC  (2.4 Watts)
2 Channels + 48V Phantom Power loaded with 2 condenser mics =  230mA @ 12VDC (2.7 Watts)
2 Channels + 48V Phantom Power loaded with 2 condenser mics + 2 VU Meters running = 240-250mA @ 12VDC (3 Watts)





As I have no idea if this 250mA is good or bad, so I looked around the net for comparables. I found the V3 with a listed spec of 600mA with phantom power OFF, and AD converter OFF (and 1000mA PP ON, AD ON)

So I think the 250mA consumption running fully loaded is not bad at all.

Using an ordinary 9V toy battery, 580mAh, this gives us 2 hrs and 20 minutes running fully loaded.

Using a beefier 3000mAh Li-Ion battery, this gives us 12 hours. And with some DVD batteries, 6000mAh, this gives 24 hours of operation time.

Ok..I feel better now, and we shall continue.

[PH]

Wow, that's virtually no power consumption. Since many of us use the 6000 dvd batteries to power our gear, that would mean we could run an entire festival on one battery.
Huge bonus.

[illconditioned]

Nice work!!!

Would you be willing to share your Phantom power generator circuit with us?   I'm wondering what chip you use to get 48v?

Thanks for any insight...

 Richard

[Chuck]

Will this be available in kit form? Please?

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

Another vote here, for a kit.

[fivefishdiy]

DUHHHH I am so Embarassed by this.... 

Let me explain.

A few days ago, I did the 9V battery test. Remember?
http://taperssection.com/index.php/topic,105112.msg1409154.html#msg1409154

I even remarked:

The current consumption ranges from 109 to 117mA. I'm a little surprised about this, since the preamp board is supposed to use only 17mA... and add 5mA for the PSU LED.

And then today I did the 2 channel test and measured current consumption. I got 250mA for 2 channels, full loaded, Phantom, VU, 2 mics connected, etc..

Guys... I am terribly sorry... the current consumption I wrote a few days ago and earlier today are ALL  WRONG. (The 9V voltages from a few days ago are correct though.)

What happened?

So out of the blue, I decided to check if I'm getting 48Volts with 2 preamps connected and powered. I put the same tester I used for my current measurement, set it to voltage, move the jacks to the proper holes and I get a 63 Volts reading!    So I kinda panic and tried to adjust it down the trimmer... then I decided to use another meter... I measure and now I'm getting 35Volts reading.... okay... what's going on?   One of these meter is lying. But which one?

So I turned on my bench multitester and got 35V too. AHHHH!!!! That means, the first tester I've been using for current measurements these past few days is defective and giving me wrong readings...i.e. it's giving higher readings for voltage and current! 

I am so mad I chuck the thing in the trash! 

So now I repeat the measurements using a working meter.

Here are the NEW and CORRECT current consumption readings:

2 Channels, No Phantom Power =  130mA @ 12VDC = 1.56 Watts
2 Channels, with +48V phantom power, loaded with mics, plus VU Meters = 170mA - 190mA @ 12VDC = 2.2 Watts

So there you go... using a 9V toy battery, 580mAh, we'll get 3.0 hrs!
Using a 3000mAh battery, we'll get 15.75 hrs!
And using a 6000mAh DVD battery, we'll get 31.5 hrs! 

So there you go....

As for me, I am going to treat myself and buy a real nice meter. Maybe a Fluke.

[OOK]

So what do you all think of this face plate for starters.........


Peace OOK

[fivefishdiy]

I like the centered text, maybe make a tad bit smaller.
Maybe a different and smaller font for "The Tapers Edition"... or even drop the "The" word
I don't like the quote symbols.
I really like the dB numbers in between the LEDs.  That's good. I like that. (Arial font for clearer text.)
I don't know where I'm going to stick my logo. The brackets take up some of the room.

Thanks!

[rowjimmy]

I like the centered text, maybe make a tad bit smaller.
Maybe a different and smaller font for "The Tapers Edition"... or even drop the "The" word
I don't like the quote symbols.
I really like the dB numbers in between the LEDs.  That's good. I like that. (Arial font for clearer text.)
I don't know where I'm going to stick my logo. The brackets take up some of the room.

Thanks!

I think it's dead sexy.
I don't disagree with your critiques on the text, though.

[rich]

where can i buy one and how soon can you deliver it to me?

rich

[boojum]

"As for me, I am going to treat myself and buy a real nice meter. Maybe a Fluke."


The work you are doing deserves FLuke.  You will never be disappointed.

[fivefishdiy]

where can i buy one and how soon can you deliver it to me?
rich

Rich, It's not available yet... but will be available direct from my website. Thanks for looking.

[fivefishdiy]

The work you are doing deserves FLuke.  You will never be disappointed.

I called in the order yesterday... so I should get my Fluke next week.   

I don't know about the *DESERVE* part, but I know I WANT it and after the wasted hours of work because of wrong readouts, I now know I NEED it . 

[fivefishdiy]

Starting the design of the switchboard. Still need to add the 48V converter schematic on this board.

Screenshot:



Here's my dilemna. So we'll have (6) switches...



1st :
2nd: 48V CH1
3rd: Polarity Reverse CH1
4th: Polarity Reverse CH2
5th: 48V CH2
6th: POWER ON

I know you guys didn't ask for the polarity reverse, but I'm trying to see if I can design the switchboard for the homestudio users as well.  Either way, if you *really* don't want it, I can just remove the switch and short the connection inside. 

My *problem* is Switch #1.  What could it be?

[eric.B]

My *problem* is Switch #1.  What could it be?

a few suggestions..

on/off switch for vu meter/lights
switch for m/s decoding...   and have the switch work!   
have a peak hold reset button?  then of course youd need a peak hold to begin with..