Closing the G-A-P

Like the look. The only caution I would give is against parallel connecting the speakers as it cuts the impedance in half. That may not be good for the amplifier. In the case of a locomotive equipped with a single 4-Ohm speaker, I'd put two 8-Ohm speakers in parallel (+ to +/- to -) to provide the proper 4-Ohm impedance. I have an FT set I'm looking at re-working for close coupling and drawbar connection on the A/B pairs. 

Thanks for the tip Matt.  How about a resister before the 2nd speaker?  

S.F.Jim; nice job.

Doesn't quite work. The math formula is kinda cumbersome.

 

Impedance = 1/(1/R1 + 1/R2 +...+1/Rn). So in the case here, the impedance would be 1/(1/4 + 1/4) = 1/(1/2) = 2 Ohms. Adding a resistor to the second speaker could actually reduce the impedance unless you put that same resistor on BOTH speakers. Also be concerned about having resistors of sufficient wattage.

 

What I've been shopping for is good 8-Ohm speakers so I can put two in parallel for 4-Ohm loads (3-volt Proto-2) and two in series for 16-Ohm load requirements (5-volt Proto-2). Haven't found ones I like yet.

For my money, the MTH PA body is as good as it gets, so long as you like plastic models. I have converted three to metal (one A in nickel silver), and am pleased.  I use CLW trucks and gearboxes.

 

My compliments on that spacing - you need to show that to a few 2-railers.  I am seeing videos posted on the 2- rail forum with passenger cars spaced like your original photo.  They tell me it is an optical illusion, but it sure looks like a six foot jump for the miniature passengers to me!

 

 

Matt, I need to make sure I understand you explaination before I proceed.  Are you saying that if the factory unit contains a 4-Ohm speaker and the speaker that I placed in the dummy B-unit is 8-Ohms, that I should go back and replace the factory installed 4-Ohm speaker with an 8-Ohm speaker?

 

Question #2.  If the factory installed speaker in the lead unit is 8-Ohms I leave it in place can I then install 2 more 8-Ohm speakers (in series with each other) in the dummy B?

 

The last thing I want to do is damage the amplifier.

 

Thanks in advance,

 

 

 

Nice job there Jim.

 

I'm impressed to see you diving in so deep to get what you want. I like the look of the speaker wires as "MU hoses" too. As long as they're not in the way, I say let 'em hang.

 

- RICH

 

 

OK Jim. Here you go. The three diagrams would keep your sound amp from seeing too little resistance. Keeping in mind that the standard for Proto-2 is 4-Ohms, you need that as a minimum.

 

If you get an Ohm meter and tinker with the combinations, you'll see how the resistance changes.

 

The first example replaces the single 4-Ohm speaker in the lead unit with an 8-Ohm speaker in the lead unit in parallel with an 8-Ohm speaker in the B-unit. The net impedance is 4 Ohms.

 

 

This next one puts two 8-Ohm speakers in parallel inside the B-unit and retains the 4-Ohm speaker in the Lead unit. To keep at or above the 4-Ohm minimum, the 4-Ohm speaker is wired in series with the 8-Ohm pair for a net impedance of 8 Ohms.

 

 

 

 

This is one I was looking at for my ABBA F unit sets. It puts each AB pair in series, then connects the two AB sets in parallel for a net of 4 Ohms. The beauty of this configuration is that if you just ran the lead AB pair, the amp would see 8 Ohms and not suffer from insufficient impedance.

 

 

Matt -

 

This is GREAT.  Next week I will open up the units, get out my meter check the Ohms on the currently installed speakers and figure out a combination that will work for me.  

 

These drawings make is very easy to understand.  I am sure that there are more than a few Forum members that will benefit from your drawings.  You already have got me thinking about now adding sound to the other B-unit as well.  

 

Your motto sure sums it up:  "The best service you can provide for the hobby is to pass on what you have learned." 

 

Thanks-a-million.  

 

Jim

 

 

No problem. My dad's hobby was HiFi and he showed me some literature of a speaker called the "Sweet 16" which had 16 speakers of various sizes within the enclosure. They were wired in combinations of series/parallel connections to yield an 8-Ohm impedance at the connection for the amp. The purpose was to take advantage of the sound characteristics of each speaker to provide clean full-range sound and strong bass. He was interested in building one of his own from scratch. Never built it but seemed to have a lot of fun designing it...much like me and layouts.

Santa fe Jim,

 

Great article. I just bought a legacy ABA Santa Fe Alco PA set from a member and that is exactly what I want to do regarding the lash up. For sound in the dummys I'm wondering if the ERR mini commanders driving separate railsounds would work ?

 

Are you going to fix the pilots? I've got to find some plan drawings to see if adding a pilot spacer would yield a prototypical pilot depth or be too long.

 

Thanks for sharing.

Would really sound cool with sound eminating from all the units.

 

Not sure the MTH Alco's have the same pilot issues the Lionel ones do.
(Though they do have that funky cord which must thread from A to A unit through the B units...)

Pilots for PAs are so easy to make it is almost trivial.  But the anti- climber is in the wrong spot on the MTH - it is the only flaw in the body I am aware of, and I have not tried to make a new one.

How do the Lionel and these new MTH PAs compare for level of detail and fidelity to prototype?

Someone I trust said the Lionel shell is very very good.

Jim:

 

What a super modification. Sure looks very good and appreciate all of the details in your conversion project.

According to Bob Turner (bob2 here on the forum), the MTH PA model has the most correct nose & cab. Since Bob is a well nown O Scale scratch builder, I thus assume he measures every single dimension & detail, in order to make such a statement of opinion.

I can not speak for the overall accuracy of the MTH vs Lionel PA's.  But I can tell you this, MTH nailed the red color of the war bonnet.