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Disabling or replacing piezo tweeter in MarkBass CMD121P combo?


mcnach
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I have a MarkBass CMD121P combo, which I love for many reasons and I've been using it a lot since I bought it last May.

What I don't love is the harsh tweeter. Blergh.

I am considering disconnecting the tweeter and see what it sounds like. I imagine that it would not be difficult to open the thing and disconnect a couple of wires. I am also considering replacing the tweeter with something else that sounds better.

Would it be bad to simply disconnect the tweeter?
I suspect the impedance of the internal speaker will change... The amp is designed to run at 4ohm minimum, and I often add an 8ohm cab to the combo... will disconnecting the tweeter be bad for the amp when using an extension cab?

In another thread a couple of weeks ago or so I found some people disconnected the piezo tweeter just fine, and someone even replaced it with another type... It seems simple enough, but there was no reference as to how long they've been running the amps that way, or whether they used extension cabinets.

The replacement tweeter mentioned was this one:

[url="http://www.bluearan.co.uk/index.php?id=MON100190"]http://www.bluearan.co.uk/index.php?id=MON100190[/url]

which is an 8ohm tweeter...

I'm a little lost here, so I'd appreciate any help/suggestions. I don't want to damage this combo that I love just to remove something that bothers me but it's not a deal breaker.

Cheers!

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Disconecting the tweeter won't harm the amp, you can either leave the driver going through the x-over or connect it directly to the amp output if you find you need a bit of highs on the sound.

Personally, i would invest in replacing the tweeter for one i like better and add a L-Pad to be able to defeat the tweeter or attenuate it to a more pleasant mix. It would be more expensive but i believe the final result would pay off.
I would start with just the L-Pad first, who knows if lowering the existing tweeter a little won't be suficient (and less expensive).

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I would be wary of replacing a piezo tweeter with a dynamic one without also installing a new crossover, as piezo tweeters have very high impedance and the existing crossover is unlikely to be suitable. There would be no harm in disconnecting the tweeter and crossover board entirely and running the amp output straight to the 12" though, and it's easily reversible if you don't like the results.
Or for the absolute lowest tech, least invasive approach you could cut a bit of dense foam to sit in between the tweeter and grille to cut the high end somewhat!

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Yep, you can't replace the piezo with a dynamic one, they work entirely differently. the piezo has a high impedance that rises at low frequencies to the extent that it doesn't need a crossover. Put in a 8ohm dynamic without a crossover and it will blow at the first loud note.

Disconnecting the piezo is just a matter of cutting a wire or pulling off a spade connector but you need to make sure the wire ends are insulated so they can't short out accidentally.

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[quote name='Ghost_Bass' timestamp='1389181448' post='2330911']
Disconecting the tweeter won't harm the amp,
[/quote]Disconnecting a tweeter can harm an amp, if the tweeter uses a crossover. Most piezo tweeters don't, but one must be sure of that before cutting wires.
[quote]I would start with just the L-Pad first, who knows if lowering the existing tweeter a little won't be suficient[/quote]LPads don't work with most piezos.
[quote]I would be wary of replacing a piezo tweeter with a dynamic one without also installing a new crossover, as piezo tweeters have very high impedance and the existing crossover is unlikely to be suitable. [/quote]True. This is not a job that should be attempted by someone not totally familiar with what they're doing.

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I saw a thread a long time ago where someone removed the tweeter and crossover entirely, hooking up the speaker full range. I think that'd be your best bet, you'd probably get a bit more high mids that way.

You could look out for a 121H instead which has a better tweeter and a slightly larger box for more low end!

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[quote name='Bill Fitzmaurice' timestamp='1389186310' post='2331007']
Disconnecting a tweeter can harm an amp, if the tweeter uses a crossover. Most piezo tweeters don't, but one must be sure of that before cutting wires.[/quote]
It can? How? Will the x-over present a diferent impedance to the amp?

[quote name='Bill Fitzmaurice' timestamp='1389186310' post='2331007']
LPads don't work with most piezos.[/quote]
MB has the NY121 cab that is made to be the best extention cab for the CMD, from looking at it (never owned or opened one) they seem to have a very similar tweeter, if not the exact same one. They are fitted with an L-Pad so i guess it's possible to fit one on the CMD, isn't it?

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[quote name='Ghost_Bass' timestamp='1389197267' post='2331214']
It can? How? Will the x-over present a diferent impedance to the amp?[/quote]It can make the crossover appear as a dead short. Read this:
http://www.bcae1.com/xoorder.htm

[quote]MB has the NY121 cab that is made to be the best extention cab for the CMD, from looking at it (never owned or opened one) they seem to have a very similar tweeter, if not the exact same one. They are fitted with an L-Pad so i guess it's possible to fit one on the CMD, isn't it?
[/quote]An Lpad will only work as it should with a resistive load, piezos are a capacitive load. To use a piezo with either an LPad or a crossover additional components are required.

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Must admit, I have the CMD121P combo and NY121 and although when playing on my own I notice the tweeter a bit, I don`t when the band is going. I`ve also not noticed much difference with the tweeter off on the NY121. I do use dead roundwound strings though - maybe it`s only really noticeable with newer strings?

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Your'e right, the VLE does kill the hiss by chopping the top end but also fundamentally changes the eq/voicing of the amp much more than just a bit of noise reduction.
I've replaced the tweeter in mine with no ill effects and now not only his free, but with (IMHO) a sweeter, refined and more open top end.

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[quote name='Lozz196' timestamp='1389210917' post='2331492']
Must admit, I have the CMD121P combo and NY121 and although when playing on my own I notice the tweeter a bit, I don`t when the band is going. I`ve also not noticed much difference with the tweeter off on the NY121. I do use dead roundwound strings though - maybe it`s only really noticeable with newer strings?
[/quote]One of the reasons why tweeters and electric bass are not a match made in heaven is that most tweeters don't do much below 4kHz, while added zing is really needed above 2.5kHz. That's with rounds; with flats there's no need for any assistance, even at 2.5kHz. But tweeters capable of going to 2.5kHz, and the crossovers that are necessary to go with them, are more expensive, so they're seldom employed. I wouldn't use tweeters with flats, and when shopping for a cab for rounds I'd be sure that the 2.5kHz range is covered by the tweeter or a midrange driver.

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OK to make it clear, there probably isn't a crossover, it's the main cost saving you get by using a piezo. There probably will be a couple of big white resistors and maybe a capacitor just to match the output of horn and bass unit. To be safe remove the wires that run from either the main speaker or probably the amp itself to the horn and any associated components leaving just two wires going to the two terminals on the speaker itself. Don't leave any loose wires to touch anything and it should be safe enough. If there is a problem then put up a photo and we will advise.

Bill is right though about the tweeter, There is virtually no energy at all above 5kHz where the horn you suggested using starts, so little or no point in adding it unless string noise is something you look for!

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I'm probably going to just leave it as it is, you're all scaring and confusing me :P

And I thank you :)

But, I'm still curious about the consequences of what others have done by replacing the tweeter.
The Markbass combo does appear to have a crossover (at 3.5 KHz). I found a post where someone had looked into this combo and an extension cab rated at 8ohm that contained a tweeter (non-piezo, not sure what type, but that tweeter was rated at 8ohm too, apparently, like the one in the link I posted). The crossover was -allegedly- the same in both the extension cab and the combo, suggesting swapping tweeters was ok... but then, people who know about these things are saying here that it *may* cause harm. That is alone for me to leave the combo as it is. It's only a minor complain of mine.

I use the VLE control a bit. It is true that it tames the harshness of the piezo a bit, and that with the amp at volume and everything else going on, nobody but me (when I'm close to it) can hear that annoying zing. It puts me off slightly, specially when slapping ("that's the problem right there! And the solution: don't slap!" I hear some of you say :P), but I know it does not get heard very much out there, especially since most times I'm DI'd anyway, so I learn to ignore it. I'd love to tame it at source *if* it were as simple as disconnecting or replacing the tweeter... but it seems there are a number of things to consider that I am not knowledgeable about, so I might as well leave it as it is.

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[quote name='booboo' timestamp='1389211721' post='2331507']
I've replaced the tweeter in mine with no ill effects and now not only his free, but with (IMHO) a sweeter, refined and more open top end.
[/quote]

oh, you have?

What did you use?
Do you use the combo on its own or with an extension cab?

Tell me more, please.

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I replaced the Le son piezo with that HT-30 that you put in the op. 10 min job - I'll post instructions if you like, and the difference is night and day as far as noise goes. I'd used the combo for recording, and people around me found the hiss from the tweeter during quiet sections annoying although it didn't bleed into any mics and I was DI'd.
Using the VLE as a tweeter atenuator does work to kill the hiss, but also chops off some highs. the foam in front of the tweeter is not a bad idea if you want to leave it as is, it does work ,and the hiss is only an issue if you are not doing a loud gig tbh.
I've not needed to use an extension yet, but plan to get the matching NY121 cab used on here when funds permit. If it has the same tweeter I'd be tempted to put an HT-30 in that as well.
I'm not slagging off the combo - far from it, its a great bit of kit and I think this mod is well worthwhile.

Edited by booboo
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[quote name='booboo' timestamp='1389311264' post='2332857']
I replaced the Le son piezo with that HT-30 that you put in the op. 10 min job - I'll post instructions if you like, and the difference is night and day as far as noise goes. I'd used the combo for recording, and people around me found the hiss from the tweeter during quiet sections annoying although it didn't bleed into any mics and I was DI'd.
Using the VLE as a tweeter atenuator does work to kill the hiss, but also chops off some highs. the foam in front of the tweeter is not a bad idea if you want to leave it as is, it does work ,and the hiss is only an issue if you are not doing a loud gig tbh.
I've not needed to use an extension yet, but plan to get the matching NY121 cab used on here when funds permit. If it has the same tweeter I'd be tempted to put an HT-30 in that as well.
I'm not slagging off the combo - far from it, its a great bit of kit and I think this mod is well worthwhile.
[/quote]


The hiss is only noticeable at low volume, say at home, for instance. I can imagine that if you're recording and have microphones around it can be a little undesirable.

Eliminating the hiss would be nice, but I'm more interested in removing what I can only describe as harsh high end, that I blame on the piezo tweeter. Turning down treble or using the VLE works to some extent, but it also removes too much top end if I want to remove the harshness entirely.

It's not a huge problem. I've been using this combo since May and I love it. But I'd love it more if there were a simple and safe way to address the treble harshness.

You are probably the 4th or 5th person I found that has replaced the CMD121P piezo driver for that unit I linked to in my OP and likes the result.
What worries me is that it's labelled as 8ohm, same as the internal speaker... How would that affect my amp if I were going to add an extension cab? Should I continue to treat the combo as an "8 ohm unit", or would that be wrong now? I often use my combo with an extension cab, so it's an important question for me. I suppose the amp will shut down itself if the resulting impedance is too low, and that way I would know... but I don't want to rely in the built-in protection system in the amp to find out ;).

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The clue is in the word .A crossover splits the signal so that below the crossover frequency the sound goes to the bass unit and above crosses over to the tweeter. The system will be 8ohms all the way but you can only do this with a crossover and it has to be the right one.

Using the horn you suggest will still make little or no difference to the sound compared to not having a horn, it simply doesn't cover any of the frequencies important to bass. The piezo probably comes in at around 3.5kHz so it does cover some of the top end and will contribute a little to the sound.

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  • 6 months later...

I have replaced the stock tweeter with an HT 30 and it's killed that annoying hiss and doesn't spit and ring like the original. Sounds much much better. The top end is now the same as my other horn fitted MB cabs. Best £11 upgrade you can make on a £600 combo IMO.

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[quote name='Sparky Mark' timestamp='1405589057' post='2503261']
I have replaced the stock tweeter with an HT 30 and it's killed that annoying hiss and doesn't spit and ring like the original. Sounds much much better. The top end is now the same as my other horn fitted MB cabs. Best £11 upgrade you can make on a £600 combo IMO.
[/quote]

Hmmmm, you're going to make me do it! :)

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[quote name='Sparky Mark' timestamp='1405590599' post='2503280']
£10.94 including delivery from CPC Farnell. Just do it.
[/quote]


erm... I already have one in my drawer!
I've just been too scared to try it. I meant to simply disconnect the original, as I hear enough to make me a little scared of replacing it... But I did buy one, and it's sitting in my drawer.

;)

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I haven't actually looked at what crossover is used in my traveller 121H cab but others have said it is the same as the one in the CMD121H and CMD121P combos. If that is the case then this crossover works with 8ohm loads. The stock tweeter is so bad that I just don't understand why MB fit it. The small ht horn is much more refined and just adds a nice level of clarity to the top end. I haven't had the opportunity to use it at full volume yet to see if anything fails but I will report back when I have. I'm sure that if any of the other people who have fitted an ht30 had a problem they would've told us.

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