Does anyone know of a way to stop Motor hum with Soundtraxx low cost Decoders?
In a word, no way. Okay, two words…nope.
The decoder will allow you to control the pulse width modulation (PWM) in one of the CV’s, can’t recall which, but you can download that decoder’s manual from Soundtraxx’s site. I could not get my Heritage 0-6-0 to stop growling, no matter which of about 20 settings I tried.
I finally gave up and had a Tsunami put in it. Wow! What a difference.
-Crandell
two more words Low Cost!! They didn’t build any BEMF or silent drive into them to keep the cost down.
Ken.
It’s marketing, not to keep the cost down. It wouldn’t have actually ‘cost’ anything to put the silent drive code into the chip (assuming it fit). They already had the code.
Either replace with a new Tsunami, or use a different decoder for the motor drive and the LC for sound - or use a DSX with another brand of decoder for motor control. Nothing really can be done to make a non-silent running decoder into a silent running one.
–Randy
I’ve heard the LC before and was dissappointed. A friend of mine uses the DSX in conjunction with a Digitrax motor control decoder. Sounds much better and there is no buzzing or humming. .
Actually, I don’t really think this is true. The first Soundtraxx motor decoder with silent drive and BEMF is the Tsunami. Any decoder prior to that has had a low frequency drive circuit and no BEM, including the more expensive DSD-150.
The humming you hear isn’t actually the 20Khz motor drive frequency, but rather the harmonics below that frequency. Open frame motors and three pole motors seem to be more susceptible to this problem. Digitrax and several other companies have gotten around this by using a variable frequency, and others use a higher starting point frequency such as 32 or 40 Khz to avoid the harmonics problem.
The quick solution would be to install a separate motor decoder in the locomotive that has silent drive. You would be using the Soundtraxx DSD as a sound only decoder at that point, and assuming you install the resistor across the motor leads as per Soundtraxx instructions, it should operate and program just fine in that installation.
Good luck!
Jeff
Actually, the PWM frequency of a LC decoder is adjustable from 19.1 Hz to 195.3 Hz, which is much lower than the average modern decoder. The following formula is used:
period = (255-CV9) • 204.8µs (note divide by 1000 to get cycle time in ms)
invert the value in ms ( Milliseconds) to get the frequency.
For example, if CV9 = 55:
255-55=200
200 x 0.0002048 =0.04096
1 divided by 0.04096 = 24.4 HZ (this is the PWM frequency value).
adjusting this value also affects the motor torque; lower frequencies result in greater torque at low speeds but cause more noise; higher frequencies lower the noise volume while increasing its frequency, but starting motor torque is reduced. Adjust CV9 for best balance between the two.
Why not get a silent drive decoder in the first place? Then you don’t have to go through all the song and dance of installing a second decoder to do the first ones job.
I have five LC decoders installed in various locos and I don’t recall any of them humming. I am just thinking out loud here but possibly you don’t have your Capacitor wired up to your speakers or it is bad??? I thought the function of the SPeaker cap was to filter out DCC signal hum and of course I may be full of you know what][:D][:D][:D]
Terry[8D]
I guess its all a matter of perspective. If you’ve been into DCC since 1993 like me, then you know the silent decoders are a relatively recent innovation (last 5 years or so). I’ve got a lot of older “noisey” decoders so the motor hum with the LC decoders is just par for the course.
Since I mainly use the LC decoders in dummy units, the motor hum isn’t much of a problem. In cases where the hum could be a problem, using a silent decoder for the motor is a reasonable solution.
Just connect the red and black wires on the Soundtraxx LC decoder to the track power, leave the orange and grey wires disconnected. You’ll need to program the LC decoder to be the same address as the motor decoder, or give it a unique address and consist it.
The one thing to watch out for with this dual decoder arrangement is accidentally reprogramming the LC’s CV settings while you are trying to program the motor decoder’s settings. Consisting is a better way to go since you can give the sound decoder it’s own address … just remember what it is!
It is not a speaker-type sound to which this person has been referring. It is motor groan due to non-BEMF circuitry.
I had two LC’s, one in a 0-6-0, and another in a FA2/FB2 set, both by Life Like. The diesel was whisper quiet and smooth, the steamer was a real groaner…and smooth.
The motor’s characteristics affect the amount of noise you get from the decoder. I have also noticed P2K E units are quiet; using the LC in a Proto 1000 RS-11 produces a considerable amount of motor hum. Until recently, LC decoders were widely used where cost and/or sound choices are a factor.
I have several LC decoders in locomotives. Steam and diesel. Only one of them ever gave me any problem with ‘motor hum’. It was installed in a PK2 E8. I couldn’t figure it out but it was annoying. I finally came to the conclusion that I had some how shorted the sound outputs during installation and testing. I sent it back to Soundtraxx, it was still under warranty, and they replaced it. The new decoder works fine.
Was my diagnosis right? Who knows? All I know is the loco and the decoder are fine the second time around.
If the noise came from the speaker, this is a condition known as motoboating. If the noise came strictly from the motor, it is possible the bridge rectifier circuit used to convert the DCC track current to steady current for the decoder’s circuits may have been damaged by the amplifier’s short circuit condition - sorry for the technical answer, but in electronics, the answers to these questions are usually in this space.