# MRC 312 speaker upgrade



## kix662003 (Mar 8, 2013)

I've seen suggestions to increase the volume on the digital MRC Sound Station 312, but never anyone saying that they've upgraded the speakers to have more volume. The one that I have needs a little more volume even using a small layout in a medium size bedroom. Has anyone here actually modified this sound system successfully? As shown in the photo, it doesn't appear to be over-engineered judging by the thin wiring and lack of a strain relief on the controller cord. It works well, but needs more amplification. I also have the 'matching' MRC City and Country Sounds for the grandchildren when they visit.


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## gunrunnerjohn (Nov 10, 2010)

One would think you could feed to audio to almost any amplifier if you wanted to do that.


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## kix662003 (Mar 8, 2013)

gunrunnerjohn said:


> One would think you could feed to audio to almost any amplifier if you wanted to do that.


Like re-amplifying through a stereo receiver.... the input will be pre-amplified or perhaps not with the volume know at zero? Both units have a volume knob. I'd take the screws out, but I wouldn't know how to describe what I'm seeing. Maybe post some photos?


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## gunrunnerjohn (Nov 10, 2010)

Photos are always good.


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## kix662003 (Mar 8, 2013)

gunrunnerjohn said:


> Photos are always good.


Hey GRJ. I just put my two MRC sound boxes side by side. The AA552 City and Country unit is a lot louder than the aging 312 train sounds box. It is designed differently. Both speakers play the same sounds on the AA552, so sounds can come from different places on the layout. In a volume scale of 1-10, it's loud enough at 2 or 3. The 312 plays half of the sounds through one speaker and half through the other. The volume is set to max. Do you have any idea who the Mid-Atlantic authorized repair center might be? I want to see if I can obtain a schematic for both units. There may be something in Sam's Photofacts, but I don't know where RR sound boxes would be found. The 312 was used when I got it but I purchased the AA552 new and it's still under warranty. I'd love to find that there's a more powerful amp in the new one that has the same pin configuration of the 312 unit. Any thoughts or input? Am I dreaming? I'll still take the 312 apart soon to take photos, but I don't want to take the AA552 apart yet and void the warranty. Thanks again for your help in this matter!


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## gunrunnerjohn (Nov 10, 2010)

I don't have any idea where the repair center would be, I'd probably contact MRC and ask. I haven't seen the Sam's stuff in years, when I was a young sprout I worked in a TV repair shop and used the Sam's stuff. I'd be a bit surprised if they had info on something this specialized, but you never know.


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## kix662003 (Mar 8, 2013)

Here are the photos that I promised. Sorry for the delay. John, there isn't much on the components that can't be seen in the photos, but I'll try using a magnifying glass if you need numbers off the transistor or other parts. Thanks for the help. I think it looks pretty simple, and need a nudge to amplify the sounds using the four speaker wires. I'd appreciate any cautions and/or suggestions!































































Perhaps if I can't amplify the sound for each speaker (each produces half the sounds from the system) it looks like I can mount the speakers on the bottom side of the board and have them closer to where the train runs. This would keep the speaker boxes out of the way too. Again, any cautions or thoughts? I doubt that using larger auto speakers would increase volume and would probably make it worse. No impedance values on the speakers. Smaller speakers would probably sound tinnier or worse?


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## gunrunnerjohn (Nov 10, 2010)

Looks simple, hard to say what would improve it without seeing it in person.


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## kix662003 (Mar 8, 2013)

Think I'd risk much if I just cut the speaker wires and tried hooking them to powered PC speakers, and cautiously switch on the power? My other thought was to use an amp for autos, but I think that would be overkill. Someone else may chime in, but I'd hate to fry the board. These things are hard to find in like new condition like this one. Thanks for the reply and glad you enjoyed the York show. I lived there when our oldest son was born in '77.


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## rrgrassi (May 3, 2012)

You could amp up the sound from the speaker leads using "high" input leads instead of line out leads.

Over kill? Nah, not if you use some good car speakers!


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## gunrunnerjohn (Nov 10, 2010)

I doubt you'll have a problem connecting to amplified speakers. I'd use a load resistor of say 16 ohms to replace the speaker, the little amp might not work right without it.


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## kix662003 (Mar 8, 2013)

Thanks, John. I was thinking the little speaker was probably 8 Ohms. Is using a 16 to help reduce the noise and/or distortion since the signal will be amplified again? Just asking to know, not questioning your recommendation. I took electronics classes in the mid-60s when power tubes were still used.


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## gunrunnerjohn (Nov 10, 2010)

I specified the 16 ohm as that's typically the highest impedance value speaker you would see. It's not a problem to have too much resistance, but it will increase distortion and potentially overload the amplifier to have too low a resistance. Hence the 16 ohms.


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## kix662003 (Mar 8, 2013)

gunrunnerjohn said:


> I specified the 16 ohm as that's typically the highest impedance value speaker you would see. It's not a problem to have too much resistance, but it will increase distortion and potentially overload the amplifier to have too low a resistance. Hence the 16 ohms.


That makes a lot of sense. It's good to have knowledgeable members who are willing to share with other members. I'm probably up to the minimum Digikey purchase amount now. I'm also going to buy some resistors for my LED lights that are less than 12-Volts, and some to reduce the Voltage to my new overhead lights. I can smell the heat from the incandescent bulbs. Maybe I can reduce down to 9 or 10 Volts without reducing everything fed off of the 12-Volt transformer. Thanks again for the good advice, suggestions and schooling! George


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## norgale (Apr 4, 2011)

TUBES? Hey I remember tubes. Mostly we were always looking for replacements for them. I have a six volt 1952 Packard radio here with tubes and stuff in it and it works great. Pete


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## kix662003 (Mar 8, 2013)

We used to find more powerful (solid I think) tubes to plug into our CB radios to "walk the dog". We used crystals that plugged into the front of the base station, one to transmit and one to receive. We'd talk and listen on different channels so we didn't get caught. It provided some privacy too, in a day when people sat around searching for someone to talk to. If there was an Uncle Charlie, we didn't want to meet him! One Summer I worked for Sylvania Electric in Williamsport, PA pulling and packing tubes for shipment. Hot job with lousy pay, but it was a job!


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## rrgrassi (May 3, 2012)

Those MRC speakers are the same cheapies as low end computer speakers. When I had that set up, and after the warranty expired, I used some older Bose shelf speakers that used the single star driver. I just cut the wires that ran to the speakers, made the wires longer and connected the Bose speakers. That was a huge improvement!!


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## gunrunnerjohn (Nov 10, 2010)

I've actually designed real circuits with tubes! I prefer solid-state, but that was long ago and in a place far away, and transistors were new and very expensive!


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## rrgrassi (May 3, 2012)

IC's are now cheap and tubes are quite spendy!


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## gunrunnerjohn (Nov 10, 2010)

That's why I don't use tubes any longer.


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## kix662003 (Mar 8, 2013)

Well, the upgrade is finished and it sounds great. GRJ provided good info and values, and there's no distortion or unwanted frequency noise. Supplemental power is from a JBL computer speaker system amplifier and an old IBM subwoofer. The JBL amp has a plug prewired for the sub and even headphones. Volume was way too loud when first tested so I put the 15-Ohm 5-Watt resistor inline on the (+) side of the speaker wire instead of going across the speaker leads. This, and upgrading the locomotive sound speaker (upper set of sound buttons) for 2 digital Jensen speakers did the trick. The sub has it's own on/off button and volume control, and the second (MRC 312) speaker for the lower range of sounds had a dedicated volume control. Now, the four speakers can be arranged so the sounds are like home theater and not just in one spot. Thanks for all the help and ideas! Since the M.T.H. F-3 HO diesel set I just bought with DCS and Proto-Sound 3.0 is getting returned to the store (as advised by MTH), it will be nice to continue to have a digital sound layout. 



















Looks like some kind of weird gizmo from the Back-To-The-Future movie to me...










I posted the last photo to show the difference in original speaker and the speakers used in the upgrade. That magnet on the original speaker looks like it was made as lightweight as possible for some reason. Not what I'd use in home or auto sound.


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## DonR (Oct 18, 2012)

John

Old tube type amps usually had a high impedence input
for phonos etc. Don't solid state amps have low
impedence inputs of 50 ohms or so?

I know there's really too much power but couldn't a
resistance circuit make possible plugging into an
old amp of some sort and have it drive the existing
speakers to get a louder sound?

Don


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## gunrunnerjohn (Nov 10, 2010)

You can drive most amplifiers from a sound source such as the one discussed here by simulating the speaker with a power resistor. That provides the proper impedance match for the sound source, then the amplifier just works with that signal.


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