Markbass Mini CMD 121P - simplest of upgrades

[alanbass1]

I bought this amp earlier this year for rehearsals and thought it a nice little amp which had a big sound. However, I was always troubled by the piezo tweeter which sounds 'spitty' and can't be adjusted. Well, yesterday I had enough of it and took off the front grill and removed the 12" speaker - I then plugged the amp speaker lead direct to the 12" speaker and plugged the lead from the crossover to speaker on the spare lugs of the crossover (i.e. where the lead to the amp used to connect) to keep them from being loose. This effectively took both the crossover and the tweeter out of the equation and boy what a difference. It's quite amazing how well the 12" handles the treble - very smooth and not at all dull. Even at volume the high's have a nice presence without sounding spitty or clanky - and had me thinking again about the quality of Markbass speakers which I previously thought of as average and overpriced. The piezo is not good but I reckon the crossover was sucking the life out of the 12" speaker as well.

Edited November 28, 2009 by alanbass1

[zzaass]

[quote name='alanbass1' post='668549' date='Nov 28 2009, 07:01 PM']The piezo is not good but I reckon the crossover was sucking the life out of the 12" speaker as well.[/quote]



Good Post. I think I will try this

[dannybuoy]

Me too, if it's easily reversible and doesn't require a soldering iron!

[Beedster]

I'm never quite sure how tweeters got into bass cabs anyway?

[Moos3h]

...especially, you would think, with a 12" speaker on board?

I've never much liked the tweeter sound, but in my experience they are sometimes useful in just helping you cut through enough to hear yourself. Can't comment on the Markbass stuff though, as I've never owned one!

[alanbass1]

[quote name='dannybuoy' post='826677' date='May 3 2010, 06:15 PM']Me too, if it's easily reversible and doesn't require a soldering iron![/quote]

Yep, no soldering iron, just swapping over two pairs of wires that are held in place by spade connectors. Takes about 20 minutes - remember to unscrew the speakers with the combo lying on its back and the speaker facing upwards. That way there is no strain on the last bolts and the speaker will not 'topple' out when all the screws are removed.

[PaulKing]

Very interesting that.
I'm getting the 121H extension this weekend, so pesumably will be able to dial in the (better) horn on that in place of the piezo on the combo.
I've only gigged it once and didn't find it too offensive, but there was definitely a brightness to the click (I play slap upright ... Willie Dixon / Larry Taylor style) which I was tempted to tame, but without losing top end of the tone.

Think I'll try this little experiment too then.

A fellow poster over on doublebasschat.com was enquiring about the distinct hiss that comes from the piezo too, thought there was trouble there, but seems it's just normal.

[alanbass1]

[quote name='PaulKing' post='830157' date='May 6 2010, 10:55 PM']Very interesting that.
I'm getting the 121H extension this weekend, so pesumably will be able to dial in the (better) horn on that in place of the piezo on the combo.
I've only gigged it once and didn't find it too offensive, but there was definitely a brightness to the click (I play slap upright ... Willie Dixon / Larry Taylor style) which I was tempted to tame, but without losing top end of the tone.

Think I'll try this little experiment too then.

A fellow poster over on doublebasschat.com was enquiring about the distinct hiss that comes from the piezo too, thought there was trouble there, but seems it's just normal.[/quote]

You will be surprised how good the single 12" speaker is without the piezo - it does have decent treble extension

[mart]

Does this mod change the impedance of the cab at all? It seems to me that it might reduce the impedance, risking damage to the amp, but a multimeter will quickly tell you whether or not that's the case.

[machinehead]

I find my CMD121P a useful tool for rehearsals and gigs in small pubs.

I do agree though, that the tweeter can sound a little harsh, especially if you drop in a little pop on the G string during a 99% finger style song.

The harshness seems to jump out at you in contrast to the quite warm sound from the amp generally.

Frank.

[machinehead]

[quote name='mart' post='830532' date='May 7 2010, 12:00 PM']Does this mod change the impedance of the cab at all? It seems to me that it might reduce the impedance, risking damage to the amp, but a multimeter will quickly tell you whether or not that's the case.[/quote]


Multimeters aren't really the tool for a reliable measurement of impedance.

I should think the speaker would be 8 ohms though and the amp can handle a 4 ohm load so all should be well. It's definately well worth checking carefully.

Frank.

[alanbass1]

[quote name='mart' post='830532' date='May 7 2010, 12:00 PM']Does this mod change the impedance of the cab at all? It seems to me that it might reduce the impedance, risking damage to the amp, but a multimeter will quickly tell you whether or not that's the case.[/quote]


Nope - speaker is 8 ohms and the amp can cope down to 4 ohms

[PaulKing]

[quote name='alanbass1' post='831106' date='May 7 2010, 11:06 PM']Nope - speaker is 8 ohms and the amp can cope down to 4 ohms[/quote]

I've been wondering this too. I've bypassed the piezo as you describe (took 5 minutes...).
Sure the main speaker is 8ohms. Is the piezo impedance relevant? Or does the crossover somehow make it irrelevant? Or is it so high it's irrelevant ... or something? Piezos are high aren't they?

I looked at an alternative horn that one guy has used to replace his MB piezo. It was rated at 8ohms.
So I got thinking ... the combo is rated at 8ohms, allowing you to link to an 8ohm extension cab.
But are there 2 8ohm speakers already inside the combo? And if not, would replacing the piezo with an 8ohm horn make the cab 4ohms?
I guess the speaker and piezo are not strictly in parallel because of the crossover unit ... so I'm left thinking do 2 speakers connected by crossover still represent 8 ohm load? Therefore removing one leaves the load still at 8 ohms.

In other words ... now I've disconnected the piezo, I'll still be running it into 4ohms when I hook up the extension.
Am I making sense?

[Pkomor]

I think the frequency response of the tweeter is soo high its irrelevant!

[booboo]

Replaced the Le son piezo tweeter in mine with a Stage Line HT-30 Minature Horn Tweeter. £12-13 online, remove (4xphilips screws) grill, remove (3x philips screws) tweeter. Use a large file / small saw to enlarge the cutout at the bottom until HT-30 drops in. The wires are push fit, blue + black - .
Test and enjoy clearer more 'airy' sound without the hiss of the piezo unit. Bear in mind this will invalidate any warranty and make what was a great combo almost perfect. i plan to do the same with an NY121 cab when funds permit.

Edited July 13, 2013 by booboo

[Lozz196]

I`ve never worried about the sound from the tweeter, but I would like a control for it the same as the NY121 cab has.

[booboo]

In a gig situation I've had no probs either, but when recording with a big band at lower volumes the 'noise' from the tweeter was noticed by anyone nearby and was a pain to be honest. I was Di'd so didn't affect the recording but it's dead quiet now with the HT-30, with an even more open top end without the noise or any harshness. as an upgrade I think it's a no-brainer to be honest, and I was a fan of this combo to start with.

[Fionn]

I've just disconnected the tweeter on my CMD121P.

I didn't have any of the "hissy tweeter" issues that some folk describe, although I did find the tweeter to sound a bit crude and spitty at high volume.

I've disconnected the tweeter by the means described in the original post, and upon immediate impressions I would echo everything that Alanbass1 wrote. It sounds rich and complete. I've still to hear it in the band mix, although I expect good results. Perhaps the eq will need a wee tweek? We'll see.

Being such a fast, easy, and reversible operation, I would recommend this experiment to any of you CMD121P users who don't like the harshness of the piezo. I've had the combo CRANKED LOUD today, and it sounds sweet. So much nicer. I might try the HT-30 horn in there at some point, but for now I can't imagine that it's necessary.

For now, I'm surprised and happy. I'll report my thoughts again, after Thursdays band practice.

[Fionn]

The combo sounded amazing at practice, with the tweeter disconnected. To my simple ear, I'd most succinctly describe the difference as the smoothing of a harsh edge. It's best perceived when popping a high note, or in the string-clang when heavy digging. There's a quality to that smoothness, and no more need to compromise by eq.

IMHO, It's a better sound, and a better piece of kit for the sake of a 10 minute procedure that's as simple as crossing a couple of wires over.

It baffles me, why a tweeter was put there in the first place.

Remarkable.

[steve-bbb]

slightly off brand butstill on topic - i just did the same to a hartke vx115 - the pesky tweeter had no off switch and was bright enough for a dog to hear it in the next county - so i disconnected the tweeter and bypassed the crossover

much pleased

[JapanAxe]

In response to some of the questions about impedances, the crossover shares out the frequency range between the speaker and the tweeter, so the amp still 'sees' an 8 ohm load.

[Phil Starr]

Don't worry about the impedance of the tweeter, Piezos work in an entirely different way and they have a very high impedance which falls with frequency. They usually have a very high value resistor in series so they make very little impact on the overall impedance. they don't need a crossover and I suspect the crossover here is simply to filter the high frequencies from going to the main driver. Hence the effect when you remove it from the circuit. I suspect this mod is a very good call.

[Jus Lukin]

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Edited February 28, 2022 by Jus Lukin

[edpirie]

Old thread I know, but thanks for the tip. I've been struggling to get a decent sound out of my 121P as a practice cab at home with my Roadworn Jazz, and couldn't understand it as it sounds great through a Korg PX4D with cans. Disconnecting the piezo instantly gave me the rounded highs I was trying in vain to coax out.

[BassManGraham]

Only just seen this thread - like 5 years on Doh! I am going to disconnect piezo from my CMD Mini121P today, I use it with a TRV121H so I can retain a controllable top end). I recently sold my beloved CMD102P as the tweeter was irritating at times.

I love Mark bass gear but to my ears their compression drivers are so much better than their piezo tweeters particularly on the cabs you can adjust them. Belated thanks for this tip! The best ideas are often the simplest, just kicking myself I hadn't seen this thread or even thought of it earlier!

Marco needs to offer all his combo versions (other than the Jeff Berlin Players 115 ) without Peizo or ideally with controllable Compression driver.