Zimo MX645 speaker - how many ohms?

[Chamby]

I was chatting with the Youchoos guys at Warley, and was warned against my current practice of installing their ‘double dumbo’ speakers with an MX645 chip because the impedance was incorrect. The double dumbo features two 8ohm speakers wired in parallel, so a combined 4 ohm impedance. I was advised that this would work for a while but burn out the chip in time because it required a 8 ohm speaker. I was advised to use the single dumbo with 3D printed chamber instead.

 

Upon checking the technical data on Zimo’s website, apparently the MX645 requires a speaker of 4 ohms, which is different to (for example) the MX646-8 and MX649 series which require 8 ohm speakers.

 

(I normally use Loksound v4 which seem to be standardised at 4 ohms but have recently acquired a few Zimo chips with pre-programmed Locoman sounds).

 

This conflicting info about Zimo’s chips is confusing at best! Can anyone ‘in the know’ provide some definitive clarification please?

 

Phil

Edited December 1, 2017 by Chamby

[tractor_37260]

I was chatting with the Youchoos guys at Warley, and was warned against my current practice of installing their ‘double dumbo’ speakers with an MX645 chip because the impedance was incorrect. The double dumbo features two 8ohm speakers wired in parallel, so a combined 4 ohm impedance. I was advised that this would work for a while but burn out the chip in time because it required a 8 ohm speaker. I was advised to use the single dumbo with 3D printed chamber instead.

 

Upon checking the technical data on Zimo’s website, apparently the MX645 requires a speaker of 4 ohms, which is different to (for example) the MX646-8 and MX649 series which require 8 ohm speakers.

 

(I normally use Loksound v4 which seem to be standardised at 4 ohms but have recently acquired a few Zimo chips with pre-programmed Locoman sounds).

 

This conflicting info about Zimo’s chips is confusing at best! Can anyone ‘in the know’ provide some definitive clarification please?

 

Phil

 

According to the (ZIMO) paperwork that comes with a Zimo MX645 it states : all Zimo sound decoders are designed for use with 8 ohm speakers, but the MX645 can also power 4 Ohm speakers.  So either 2 x 8 Ohm wired in Parallel OR 2 x 4 Ohm wired in Series.  Most sugar cubes and Dumbo's are 8 Ohm.

 

One of my 26's uses a MX645 with a 3D Zimo twin dumbo speaker, and it sounds excellent..................a similar set up is used in the SLW sound fitted Class 24.........although in this application the speakers have individual sound chambers.

 

The twin Dumbo's sound far better than the single versions, if using the single version the overall volume has to be reduced, else the sound clips, especially on using the Horns etc 

Edited December 1, 2017 by tractor_37260

[Chamby]

Thanks Tractor.  Wish that resellers who pre-load and repackage chips could pass on the technical leaflets too!

 

I am left wondering why the guys at YouChoos gave other guidance?  The guy seemed very assured on this point though, maybe their experience is otherwise???

[tractor_37260]

Thanks Tractor.  Wish that resellers who pre-load and repackage chips could pass on the technical leaflets too!

 

I am left wondering why the guys at YouChoos gave other guidance?  The guy seemed very assured on this point though, maybe their experience is otherwise???

 

Perhaps the Zimo Guru (Paul Chetter) will be along shortly, and add some of his extensive knowledge on Zimo's ............

[mkrob]

I recently fitted Digitrains sound to my Dapol class 22 & verified with them that a 4 ohms double speaker was OK with the MX644D.

The technical info that came in the decoder packaging said 4 ohms could be used also.

 

It makes sense that if a 4 ohms impedance load is used, the audio output will be louder but the audio driver of the decoder will be driven harder & use more current. This obviously could cause the decoder temperature to get warmer.

It may be prudent to reduce volume CV, as a precaution.

 

The question is why would Zimo sell 4 ohm double speakers if their decoders couldn't handle it. THEY WOULDN'T!!!!

 

http://www.zimo.at/web2010/products/lokdecoder_EN.htm

[Bowie]

As someone who uses Zimo MX644 & 645 decoders with Twin-Dumbo Speakers (Beauty of O-Scale)

and as someone who lives on the other side of the world (Australia)

 

I'm very cautious when it comes to installations due to obvious reasons...Decoder & Freight Costs plus Travel time *Cough Cough

 

I'll say the gentlemen were giving OVERLY cautious advice for the reasons of.

 

Possibly not being 100% certain of the answer due to product knowledge and giving you a safe response.

Possibly as modellers themselves, you wouldn't want to give out bad advice that could potentially damage a 100 Pound Decoder/Speaker or worse a locomotive worth hundreds of pounds.

 

You have referenced the Zimo instructions but you could try the Youchoos website itself. (You wouldn't publish the following on the internet if there were serious consequences)

 

Here are two links from their site. One about Zimo Decoders and Speakers and the other an install using a MX644,

which in my option is basically an MX645 without the PLUX interface and uses the MTC interface Minus 2 functions without capacitor connections per-wired (*I am more than happy to be corrected as I'm always willing to listen and learn)

 

http://www.youchoos.co.uk/Index-QuickHelps.php?L1=SolderingSpeakers

 

http://www.youchoos.co.uk/Index-Resource.php?L1=Guides&Item=ODapolJinty

 

As I said in this long winded explanation... Treat it as overly cautious advice looking out for your modelling needs and the model themselves.

 

No connection to Youchoos other than using their Custom Speakers for my P4, HO and O-Scale models...Yes I'm a very sick puppy.

Edited December 3, 2017 by Bowie

[Chamby]

Thanks for the above responses.

 

The Youchoos guy at Warley did say that the MX645 would work for an indefinite period with the 4ohm double dumbo, but at some point would likely overheat and blow the chip... he also thought it strange that they sold these speakers that were best used with Loksound chips! I can only assume that he was additional staff taken on for Warley, or he maybe had personal experience of one blowing.

 

I’ll go with the published advice on Youchoos own website over the verbal advice then. It is consistent with Zimo’s own technical sheets and other suppliers views as well, so I’ll stick with my double dumbo installations - but be mindful of the volume. Should be fine for home use and I’ll be careful about tweaking up the volume for exhibitions or club use.

 

Phil.

[John YouChoos]

Sounds like a misunderstanding... MX645 can drive from 1W to 3W and between 4ohm and 8ohm speakers, which includes the dual-speaker Dumbos.

I recall the conversation at Warley and we were talking about MX648, which must use 1W and 8ohm speakers.

 

If you split the Zimo range into these 2 groups (forget large scale for a moment), then the rules are:

 

MX645, MX644: 1 to 3 W and 4 to 8ohm

MX648, MX649, MX658: 1W and 8ohm only

 

Hope that clears it up!

John

[Chamby]

Sounds like a misunderstanding... MX645 can drive from 1W to 3W and between 4ohm and 8ohm speakers, which includes the dual-speaker Dumbos.

I recall the conversation at Warley and we were talking about MX648, which must use 1W and 8ohm speakers.

 

If you split the Zimo range into these 2 groups (forget large scale for a moment), then the rules are:

 

MX645, MX644: 1 to 3 W and 4 to 8ohm

MX648, MX649, MX658: 1W and 8ohm only

 

Hope that clears it up!

John

Thanks John, I understood we were talking about MX645.... explains it then.

 

Phil