Hacks Output

Submitted by cmcook22 on Wed, 08/22/2012 - 15:45

Haven't yet received my kit yet so might be putting the cart before the horse, but wanted to get some info on the Hacks Output before I order more parts for my amp build.

What I'd like to do is use the Hacks Output to run into a VU Meter. I've never used one in anything I've built, and the info I've googled on wiring up on an amp just confuses me. The VU meter is the cheap chinese version on eBay for ~$8 and has 4 leads on the back. Two + and two -. One set feeds the meter, second set is for powering the meter's light (or so it would seem). Can the +/- outs of the Hacks Out wire into the VU meter? Doesn't need to be accurate, just looking for some eye candy to bounce around. Here's the link

http://www.ebay.com/itm/500-A-Panel-VU-Meter-Warm-Back-Light-Recording-A...

If it can be wired up, what resistor value do I need for R14? What about RPD2? I've also seen full on circuits to be wired to vu meters. is this something that I'd need? Any suggestions on how I can wire this up? I'm limited on space, this isn't going in a full head or cab, it's going to be in a hammond enclosure. Oh, and I intend on using the 4 AA battery for power, if that matters.

(sorry for the mispost on the High Gain thread. Didn't mean to put that there or hijack anything).

Member for

11 years 5 months

John

Wed, 08/22/2012 - 22:34

Wow, that looks like a great little meter! I just picked one up for myself.

For this application, you don't need to change Rpd2. Just leave it at 2.2M.

Here is what I would do. After you assemble the Stella Amp, solder wires to the meter, to the pads on R14, and to the hacks output.

Grab a 100k or 50k pot (not less than 50k!). Crank the pot all the way down, and hook up one R14 pad to pin 2 of the pot, and the other R14 pad to pin 3. Use a breadboard or alligator clip to connect the - on the meter to the - on the hacks output.

With the Stella Amp powered on, lightly touch the + meter wire to the + hacks output. Make sure the needle doesn't slam all the way to the right when you do that! Slamming the needle is bad for the meter. If it doesn't slam, then twist those two wires together (or clip them with a clip or use a breadboard.)

Keep the meter pot cranked down, and slowly crank the Stella. The meter shouldn't move much. Once you have the Stella cranked, hit a chord, watch the meter, crank the meter pot a teeny bit, hit a chord, etc, until the meter goes all the way into the red when the Stella is fully cranked. Again, don't go to far, and try not to let it slam all the way to the right.

When you get it where you want it, disconnect the pot, and measure it with a multimeter. Round UP to the nearest standard 5 percent (or 1 percent) resistor value.

(Obviously, while you are doing this, never turn the meter pot all the way up, because then the effective resistance is zero, and you will probably burn out your meter!)

For that meter, I think the value should be around 6k, more or less (@ 6 volts). But that's just a guesstimate, I could be way off, it could be lower, or it even could be as high as 12k, it depends on the meter's internal circuitry, and whether it is ACTUALLY a VU meter or if it is just a regular meter labeled as a VU meter.

At any rate, let me know what you get for a value!

Member for

10 years 3 months

cmcook22

Thu, 08/23/2012 - 10:11

So if I understand correctly, I use the 2.2M on Rpd2 regardless. 100k pot is simply for testing purposes to determine the proper resistor value? Once I come up with that value, would I need 1/4w or 1/8w? I apologize, I'm a newbie to electronics and learning as I go.

If we find that the value < 10k (close to your guess at 6k), would it be safe to just use the included 10k resistor for R14? I understand that getting close to 100% value on the meter is the goal, and that using too high a resistor value might keep the needle lower - say 75% at full volume. I'm ok with this, again it doesn't have to be totally accurate. Just don't want it pegged, and possibly fry the meter, OR just barely moving on the bottom end.

Thanks for the quick and detailed reply, can't wait to start the build.

Member for

10 years 3 months

cmcook22

Thu, 08/23/2012 - 10:19

also forgot to ask another question....

This meter does have a backlight. Now this is totally optional, but would really be icing if i could include that as well. But I have no idea how to tie that into the power. I know that it'll eat batteries, so i would probably cut a switch in to turn the light off if not needed. But where in the circuit would i pull power from? OR would it be better to have a second battery inside and just give it's own source? I don't want to sacrifice amp quality or sound for this.

Member for

11 years 5 months

John

Thu, 08/23/2012 - 18:03

1/4 watt is fine.

After you determine the value, if it is less than 10k, set the pot to 10k and see if you like how the response looks. If the needle barely moves, then you know you need to go down, but if it looks "good enough" then you're good to go.

As for the backlight, is it an LED or an incandescent bulb?

Anonymous (not verified)

Thu, 08/23/2012 - 22:47

The listing says "filament" so I'm assuming it's incandescent. Power says 6-12v. Didn't know if it could be tied into the power of the amp or if I'd need it's own source.

Member for

11 years 5 months

John

Sat, 08/25/2012 - 09:05

I think you can tie it to the amp power supply just fine. It will suck down the batteries though.

I'll put it this way. I've had the same set of batteries in my stella for the past month. I don't use it every day but I have left it on by accident overnight a couple of times. With that filament running, that's basically acting like a flashlight. You wouldn't want to leave a flashlight on overnight, because you'd have a dead flashlight in the morning.

Member for

11 years 5 months

John

Fri, 08/31/2012 - 20:33

I don't know what you mean by "pigtail" off of. I would just put it in parallel with the Stella amp.

So, off the + of the battery pack, I would wire a switch, and then from the switch go to the filament, then from the other side of the filament go to ground. Then you have your switch in there for flipping the back light on and off.

If you want to get fancy, you can go battery pack to the main Stella amp power switch, and from that switch run one wire to the Stella Amp, and one wire to your back light switch, then connect the backlight switch to your filament as mentioned above.

That way when you power off the amp, you power off the backlight as well, no matter what the backlight switch is set to.

Member for

11 years 5 months

John

Tue, 09/18/2012 - 22:31

I picked up one of these, and it looks like powering it with 6v is pretty dim. Looks great with 12v.

Right now for my commuting amplifier I just use a 4xAA powered basic Stella amp. I think I'll get a 12v regulator for my car, and build an amp with that as the power source. That way, I can just power the filament, because it's running off the car and not off batteries.