I have MTH's Mel's Diner Drive In I use on our modular layout. It is quite loud, to the point of being obnoxious when played multiple times. Is there any way to reduce the volume? I am running it on 12 v ac. My buddies are ready to throw it in the nearest river.

Dick Richard
Original Post

Have you asked the manufacturer? Not being familiar with the product, I would say to look in the instructions, or ask MTH, or take the cover off and see if there's a volume control inside. If not, it's easy to reduce the volume with a couple of resistors or a potentiometer.

There are things to ask MTH, if there's no built-in way to reduce the volume. You need to ask what impedance the speaker is, for starters. I'm sure that they have an engineer at their HQ who can give you the answers.
The speaker is sure to have a red and black wire just get a rotary volume control from the shack and wire it in to the red wire.

David
Like I said, you need to do this scientifically. You need to find out the impedance of the speaker circuit. The speaker may be marked, or you can ask MTH. Then you need to use a potentiometer, wired as such, (three connections) not wired with two connections...that's a rheostat...

Using a potentiometer that has a high impedance wired as a rheostat, will not significantly reduce the speaker signal, and you will probably not even notice any reduction in volume.

You need to create a voltage divider circuit---that's what a pot does...and you will then have a linear volume control that will allow you to do an infinite adjustment.

Once you know the impedance of the speaker, we can continue and you'll be satisfied.
Trying to drive a low-impedance loudspeaker in a potentiometric configuration isn't a good idea. The potentiometer value would need to be lower than the impedance of the loudspeaker, and that would add additional load to the amplifier.

If you make the potentiometer value high, you essentially wind up with a rheostat because not much of the current will flow through the bottom leg of the pot.

A potentiometer with a resistance of about 20 ohms connected as a rheostat would give at least a 10 dB control range with an 8 ohm speaker. The pot must have enough power handling rating to carry the speaker's current - probably a minimum of 1 watt.
Non-essential discussion triva:
Whats needed is an L pad which is 2 pots ganged and wired such that it presents a steady impedance to the amplifier as the volume is decreased/increased. Unfortunately, thay are quite large compared to Mels diner because they can handle large power.
Sam, I doubt that the amplifier cares what the load impedance is as long at it is no lower than the original speaker load.
quote:
Originally posted by Dale Manquen:
Sam, I doubt that the amplifier cares what the load impedance is as long at it is no lower than the original speaker load.
True Dale, just the engineer in me musing over what it should be over reality. Doubt the amp chip really cares what the impedance is unless shorted wires and even then probably has some protection. So any low value pot would work as a voltage divider.
For those of us without a degree in Electrical Engineering, is there a simplified answer... like maybe a Radio Shack part number for a volume control?
quote:
Originally posted by Chessie:
For those of us without a degree in Electrical Engineering, is there a simplified answer... like maybe a Radio Shack part number for a volume control?

Will check Rat shack online if I can get past the cell phone Direct Dish etc ads popups.
Thanks for all the responses. I had the diner out at a show this weekend, and haven't had a chance to unpack it and check out the suggestions. I will let you know how it works out.

The simpler, the better. I learning a lot from the discussion. Even though some of it is well over my head, I appreciate the clarity of the messages.
25-Ohm 3-Watt Rheostat Model: 271-265 | Catalog #: 271-265
I installed the
quote:
25-Ohm 3-Watt Rheostat Model: 271-265 | Catalog #: 271-265
Dale Manquen suggested, and it did let me reduce the sound by about 1/2.

Thanks to everyone for their help.

If I may extend this thread in a different direction: I purchased A Mel's Diner at York and am just now trying to wire it up. The "directions" seem redundant/puzzling for the five wires. Where can I find a schematic? I just don't want to damage the mechanisms. Please excuse if this has been covered before.

Wally

Wally,

I hope this helps

Connect A - to transformer AC (Positive)

also Connect A - to one side of activation button (NOTE: you need 2 wires on A)

Connect B - to transformer AC (Ground)

Connect C - to other side of activation button

Connect D - to transformer AC (Positive)activationbutton

Connect E - to transformer AC (Ground)

D & E control the lighting

A-B-C control the mechanism

Thanks so much Dennis. Is there a difference on different transformers (ZW,1033, etc.) as to which posts are "positive" vs "ground"/"common". I remember reading a chart somewhere that this is the case. Thanks again.

Wally

Wally,

When using Lionel type power supplies the terminal marked - U - is usually the common or ground terminal.

Originally Posted by Dennis S:

Wally,

When using Lionel type power supplies the terminal marked - U - is the common or ground terminal.

That's not universally true. Specifically, for the 1033, the U terminal goes to the center rail.  If not, the whistle will ring the bell instead.  There are a couple of other PW transformers that are wired that way as well, but the numbers escape me right now.  I happen to have a couple of 1033's here, so I know that one for sure.

Originally Posted by gunrunnerjohn:
Originally Posted by Dennis S:

Wally,

When using Lionel type power supplies the terminal marked - U - is the common or ground terminal.

That's not universally true. Specifically, for the 1033, the U terminal goes to the center rail.  If not, the whistle will ring the bell instead.  There are a couple of other PW transformers that are wired that way as well, but the numbers escape me right now.  I happen to have a couple of 1033's here, so I know that one for sure.

Another one is the TW.  (Happened to have one under the desk from when I updated a sound file recently )  U is the center, A is common.

-Dave

That's the one, I knew that I had seen another one that did that, couldn't remember the model.

On the Lionel postwar transformers, generaly if the transformer has controls for one train the U post goes to the center rail. If the transformer controls two or more trains the U post goes to the outside common rail.

Al

Interesting Al, I never made that connection.  Perhaps the connection scheme did have some reasoning behind it.  OTOH, why in the world didn't they make it consistent?

Based on my experience...put a piece of tape over the speaker opening. Cover as much as you want to reduce volume. That is how the old Victrolas did it. Open the door to increase sound, close as much as you want to make quieter. If the other guys hate it just cut the wire. Keep it simple. Chances are no trips for parts, you most likely have a piece of tape.

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