Instructables

Help with Circuit Board

The effect light below is supposed to sequence the lights on and off, one at a time, in response to music (sound). Well it does that, but not until the input is around 95 - 100 DBs. I'm trying to figure out what to replace so that it responds to sounds at lower DB levels. The left knob on the rear is for sound adjustment (worthless at this point), the right knob is the chase (sequence)speed. The sound is set to max and the lights still doesn't respond until you really crank the music up. CN2 is where the sound and chase controls connect. It's wired, left to right as follows 1 - red from chase knob 2 - yellow from chase knob 3 - red from sound knob 4 - yellow from sound knob 5 - blue from sound knob The pin block in front of CN2 is power and the other block goes to LEDs on the rear of the unit. I'm trying to figure out what I can replace to make this more sensitive to sound input. The mic isn't the issue, I've tried several and even directly wired headphone input into it and still had to crank it up before it would respond. No comments on my soldering butcher job on the back. The red wire is the positive to the mic (which should be in the burned out hole to the left, but it works there - no better, but no worse) Any thoughts at all on what I could play with to make this thing respond to sound a lower levels would be greatly appreciated.

Picture of Help with Circuit Board
\\Brad\SharedDocs\My Pictures\circuit board\EPSON2007.06.28-08.21.10.jpg
\\Brad\SharedDocs\My Pictures\circuit board\EPSON2007.06.28-08.26.30.jpg
gmoon7 years ago
I have a couple simple transistor amps ripped from toys--'spy telescopes' that only cost a couple bucks. You might try scavenging something like that.

You can also use a very simple amp design, like this one transistor preamp. (found it by searching for 'one transistor amp'. ;-) )

You won't need a very clean amp for this application, as you would for recording audio.
BradWhite (author)  gmoon7 years ago
That does look simple enough for even me!!! I'll build one and see what happens - in the mean time I'm going to purchase a couple of inexpensive mic preamps that will give me control over gain and output also. I've got my one preamp wired directly to the mic input on two of the units right now and they respond great. Hell, I can get them sensitive enough to respond to a normal conversation at this point. Thank you very much for your thoughts and time. I'm a happy camper.
gmoon BradWhite7 years ago
Any recommendations for an unbalanced mic preamp? I have a couple vintage (late '50s, early '60s) mics, but they are just signal & gnd. Hopefully something that's not too expensive (maybe two channel, also?)
BradWhite (author)  gmoon7 years ago
Look at the Berhinger MIC100 http://www.musiciansfriend.com/product/Behringer-TUBE-ULTRAGAIN-MIC100-Preamp?sku=182482

but it does say they're balanced input and output -
gmoon BradWhite7 years ago
I have looked at ART units, but not closely at Behringer. Looks like both balanced and unbalanced inputs & outputs. I definitely don't need any modeling (since they are already vintage mics.) Not two channel, but for that price I can afford two.... @ nachomahma: I still need the preamp part, at least for one of the mics. I understand really good mic transformers aren't cheap, but a balun might work well enough with a balanced preamp.
. A balun may work for use with a balanced input. Usually pretty cheap.
LasVegas7 years ago
You might also consider using a condenser mic. It's very inexpensive and might just give the boost you need.
BradWhite (author)  LasVegas7 years ago
Thanks for another idea. I do know that the preamp idea from gmoon works. I own a mic preamp, gee never thunk to use it though, and wired it in. Worked great! Only problem, I'm not buying $70 preamps for five $40 effect lights. I found an article on the internet for a $5 preamp but have no idea how to go about making it. http://www.record-producer.com/learn.cfm?a=3080
Basically, they've removed everything they didn't need for a known input and battery power. The result is that only R4, R5 and R6 are kept with the preamp A1. I've greyed out what they removed from the schematic for the $5 pre-amp.
ina217-edit.gif
BradWhite (author)  LasVegas7 years ago
Thank you so much for your time. I'm a total novice to this, but it's very interesting and I'll find someone around here that can help me. Again, thanks for your help.
gmoon7 years ago
Possibly the original input was a direct line-in? Rather than alter the board, try adding a preamp after the mic.
BradWhite (author)  gmoon7 years ago
The original input is a mic element. I like the idea of a preamp. I just wouldn't have a clue what to buy or where to install it. Sorry, total novice. I'll be researching that though. Thanks for the idea