THE END ALL TO TURN ON/OFF NOISE PAGE
Because of their age and design my amps did have an issue. On turn on/off there is a pretty good DC voltage sweep causing a noise. Its not really a pop but its still there and not good for the speakers or your scores when competing. To eliminate this I designed a pretty simple circuit that would delay the output on the amps for about 5 seconds. This is a last resort measure in most cases but if you have run out of options trying to get rid of turn on/off noise but dont want to buy new amps this is for you.
Basically the way it works is it has constant power, remote and ground. When it sees the remote and the amp turn on but relay is still open disconnecting the speakers from the output of the amps. After 5 seconds the delay circuit applies +12v to the relay, closing the relay and reconnecting the output to the speakers. With this delay the amp has time to settle in and the speakers are connected well after the DC sweep, AKA noise. The delay is just a little shorter then it take an Alpine CD player to power up, spool up a CD and start playing so the delay is not even noticeable.
OK, below it the schematic of the circuit, parts list and a more detailed description of how it works. If you don't really understand it that's ok, you can still make this thing. Just take your time and follow the schematic carefully and you will be OK.
Parts List:
R1,R3 = 10K
Q1 = 2N3906, or equivalent
R2 = 680K (see text)
IC1 = CD4001, or equivalent CMOS
R4,R5 = 6K8
D1,D2,D3 = 1N4001, or equivalent
C1 = see text
Ry = Relay, 12V
C2 = 0.1uF (100nF), ceramic
This circuit is a delayed turn-on relay
driver and can produce time delays for up to several minutes with reasonable
accuracy. For my purpose I set the delay to around 5 seconds. The 14001 (or
4001) CMOS gate here is configured as a simple digital inverter. Its output is
fed to the base of a regular 2N3906 (PNP) transistor, Q1, at the junction of
resistor R5 and capacitor C2. The input to IC1 is taken from the junction of the
time-controlled potential divider formed by R2 and C1. Before power is applied
to the circuit, C1 is fully discharged. Therefore, the inverter input is
grounded, and its output equals the positive supply rail; Q1 and RY1 are both
off under this circuit condition. When power is applied to the circuit, C1
charges through R2, and the exponentially rising voltage is applied to the input
of the CMOS inverter gate.
After a time delay determined by the RC time constant values of C1 and R2, this
voltage rises to the threshold value of the CMOS inverter gate. The gate's
output then falls toward zero volts and drives Q1 and relay Ry 'ON'. The relay
then remains on until power is removed from the circuit. When that occurs,
capacitor C1 discharges rapidly through diode D1 and R1, completing the
sequence.
The time delay can be controlled by different values for C1 and R2. The delay is
approximately 0.5 seconds for every uF as value for C1. The delay can further be
made variable by replacing R2 with a fixed and a variable resistor equal to that
of the value of R2. Taken the value for R2 of 680K, it would be a combination of
180K for the fixed resistor in series with a 500K variable trim pot. The fixed
resistor is necessary.
Now onto how I used this simpy circuit in my system. In my system I have 2 four channel and 1 two channel amps that needed to be hook up to this thing somehow, thats 10 channels each needing is own relay. There was no forseable way I was going to use 10 standard "Bosch" automotive relays. One with 10 of then turning on and off at the same time that would be pretty loud. In IASCA you would get counted off in the judge could hear then inside that car. Two their size and the fact that if would be a little more challenging to mount then to a PC board pretty must ruled then out. So now I was off to find a better solution. After a visit to my local electronics surplus store I found a bunch of nice, small, PC mounted relays. They were rated up to 5 amps which would be more the I would need in this case. I bought 14 of then. I also found some nice screw clamp connectors for the speaker in/output and a small one for power and bought enough to do what I have planned out in my head. I then bought all the other parts and bit I thought I might use including a few extras just in case. All together I spend under $30. Next stop was Radio Shack to pick up a PC board etching kit. This actually turn out perfect becuase the kit comes with two double sided boards of about the size I needed. I think that was around $30 also.
Now that I had everything I needed it was time to plan out just how I was going to make it all work for my system. I came up with a master/slave plan. Basically I would make a master board that had the delay circuit and the relays for the left side of the car and then make a copy of that board minus the delay curcuit for the right side. This board would be the slave and would get its power for the relays from the master board. To make this whole project much easier I used a program called ExpressPCB to help design that schamatic, board layout and trace locations. Its FREE and really is a cool tool to have for projects like this. Also for make the boards even and allow for future expantion is needed there are actually enough relays on each board to switch 6 channels even thought I only needed 5.
As you can see from the schimactic above that master board has a main relay powered by the delay circuit. In turn that relay powers all the other relays on the master board and the slave board. The main relays gets its power straight from the constent 12V input on the board.
Above is a diagram of the parts layout for the master board using ExpressPCB. The slave is the same minus the delay curcuit
Above are the two blank board from the etching kit from Radio Shack. These are double sided and just the right size for what I needed.
Here the boards after I marked and drilled all the holes for the components. The kit does come with a small drill bit but I found it was to big for things like resistors, caps, ICs...... and to small for bigger things like the connectors. Good thing I have a set of very small drill bits laying around.
In order to make the board with the etching solution to must first draw out all the traces on the boards using a perminent marker. Using the design I made using the software I carefully draw out all the traces on the boards. For the most part all the positive traces are on the bottom and the grounds on the top. It was pretty tricky to get everything that way I needed it in order for it to work but again the software makes it super easy. After you are sure you have all the traces drawn out correctly then you poor half the etching solution into the small pan it comes with and then place one of the boards in to the pan for about 15 minutes. After that pull the board out, clean it off and you now have a custom PC board that you made yourself.....pretty darn cool I think. Do the same for the second board.
After the boards were etched it ws time to stuff the boards with all the parts following the schimatics closely to make sure everything is put in the right place and the right way. Above are pictures of the finished master board. Here you can cleanly see the main relay off by itself to the upper right side of the board right next to the power inputs. The connections along the top and bottom are the speaker in/outputs. Just to make things easier the boards are design so that both positive and nagitive sides of the speaker wires get connected to the board. On the board the nagitive is simply past throught to the other side while the positve is switched through the relays.
After testing both board I installed them right behind the right and left crossover boards in the trunk after wrapping them in carpet to help insolate the sound of all those relays turning on and off, 13 in all. All I can say is this has work perfectly. There is not even a hint of turn on/off niose anymore. You also cant hear the relays from inside the car which was one of my worries. I have had this in my car now for a few month with not one problem. Once its installed you will not even know it is there.