GK MB210 Tweeter Replacement

rockinroller · #1 09-30-2011, 09:59 AM

I am on my third GK MB series combo amp (two MB210s and an MB212) with tweeter issues. I'd like to replace the OEM Piezo with something more "durable". Any recommendations?

I have an approximate 2" diameter insertion hole for installation purposes, although I suppose I could enlarge that if needed, if it meant being able to accommodate a "super" tweeter!

Thanks in advance.

Windreaper · #2 09-30-2011, 11:10 AM

What do you mean by durable? Piezos can take a ton of power and naturally reject low freq due to high impedance. Besides, if you were to swap in a compression driver, you'd have to build a crossover network. Not worth the trouble, if you ask me. Does the Piezo look like this?

You could try to source a CTS/Motorola piezo, I've heard they're still available, should sound a lot better than a Chinese copy. Put a 4-10ohm resistor (10W should be fine) in series with the plus lug and it should work just fine.

rockinroller · #3 09-30-2011, 12:24 PM

"Durable" as in something that weighs more than a couple of ounces and is all-plastic. Seems to be a cheap component in an otherwise "sturdy" system. Here's a pair on Ebay right now: DJ PA Professional Boom Box Piezo Tweeter Speaker Pair | eBay

lowendblues · #4 10-01-2011, 06:51 AM

The weak link in the MB series in my opinion. I cant use the one on my MB115, its nothing but a hiss generator.

rockinroller · #5 10-13-2011, 09:21 AM

Apparently the former Motorola/CTS 1165a tweeter is an ideal replacement for GK's Piezo OEM tweeter, if you want to go heavy duty. They are becoming increasingly hard to find due to being out of production for a few years but there's an occasional surplus seller or two on Ebay that has them for around $30-$35 with shipping.

It's probably an easy switch-out as there's only 4 small screws holding the OEM tweeter in place (and the replacement's hole location is not critical as you can simply start new holes into the plywood backing), plus the OEM's install hole is similar in size to the replacement tweeter.

Doug Parent · #6 10-13-2011, 09:24 AM

I made a larger hole, installed an actual tweeter with 4khz cross-over and never looked back.

billfitzmaurice · #7 10-13-2011, 09:31 AM

Quote:

Originally Posted by Windreaper

What do you mean by durable? Piezos can take a ton of power and naturally reject low freq due to high impedance. .

Not really. Piezos are voltage limited, not power limited, to about 25 volts on average. That's a bit shy of 100 watts at 8 ohms. To be safe they must be used in series wired pairs, or series wired pairs of parallel arrays, which doubles the voltage limit to 50V, corresponding to almost 400 watts at 8 ohms, almost 800 watts at 4 ohms.
As for rejecting low frequencies, they do, but not effectively enough for pro-sound use. They greatly benefit from a 2nd order high-pass filter. But it must be one specifically created for use with piezos, those made for use with compression drivers won't work.
There's always been a bad rap against piezos, but they actually work quite well when properly used. The problem is that they almost never are.

Quote:

The weak link in the MB series in my opinion. I cant use the one on my MB115, its nothing but a hiss generator.

Tweeters don't hiss. Amps do.

Doug Parent · #8 10-13-2011, 10:19 AM

The tweeter GK uses in the MB series is the Le Son piezo. Same one that SWR and Ampeg uses in some of their lines. It's a higher output than the motorola based on my experience, and you gain nothing by putting essentially a similar unit in there.

It hisses because the amp puts out audible signal in the range it can reproduce it, like Bill was saying. The Le Son is pretty effective if you want a slap tone out of that combo, but it's up there around 6-7khz. whereas a tweeter would give you more in the 3-4 khz region.

lowendblues · #9 10-13-2011, 11:04 AM

Ok,,, so the amp hisses when I engage the tweeter. What can I do to at least cut the hiss by say 50%?

If I crank the treble down it helps a little, but its still annoying.

will33 · #10 10-13-2011, 11:09 AM

Quote:

Originally Posted by lowendblues

Ok,,, so the amp hisses when I engage the tweeter. What can I do to at least cut the hiss by say 50%?

If I crank the treble down it helps a little, but its still annoying.

If the amp hisses, it hisses, you just have speakers that reproduce the hiss. Make sure the outlet you're plugged into is grounded, bass is shielded good, etc. Other than that, not much you can do aside from getting a 31 band eq and finding the one or two sliders that kill the hiss.

Doug Parent · #11 10-13-2011, 11:18 AM

Quote:

Originally Posted by lowendblues

Ok,,, so the amp hisses when I engage the tweeter. What can I do to at least cut the hiss by say 50%?

If I crank the treble down it helps a little, but its still annoying.

If the hiss is in the 5-8khz range, turn the tweeter off. Or get a different amp altogether.

billfitzmaurice · #12 10-13-2011, 11:32 AM

Quote:

Originally Posted by lowendblues

Ok,,, so the amp hisses when I engage the tweeter. What can I do to at least cut the hiss by say 50%?

If I crank the treble down it helps a little, but its still annoying.

Get a rig that doesn't hiss. Ideally that would mean speakers that use a midrange driver, to give you the mids you want to hear, and no tweeter, so you don't hear the hiss that you don't. When you get down to it running woofer/tweeter rather than woofer/midrange for electric bass doesn't make much sense. But woofer/tweeter is a lot cheaper to produce than woofer/midrange, so...

lowendblues · #13 10-13-2011, 11:36 AM

Quote:

Originally Posted by billfitzmaurice

When you get down to it running woofer/tweeter rather than woofer/midrange for electric bass doesn't make much sense..

Agreed. I usually just turn it off anyway.

Doug Parent · #14 10-13-2011, 12:13 PM

Quote:

Originally Posted by billfitzmaurice

Get a rig that doesn't hiss. Ideally that would mean speakers that use a midrange driver, to give you the mids you want to hear, and no tweeter, so you don't hear the hiss that you don't. When you get down to it running woofer/tweeter rather than woofer/midrange for electric bass doesn't make much sense. But woofer/tweeter is a lot cheaper to produce than woofer/midrange, so...

Us slippers might disagree ...its a preference thing.

Doug Parent · #15 10-13-2011, 12:14 PM

Slappers not slippers. Damn spell check.

billfitzmaurice · #16 10-13-2011, 01:26 PM

Quote:

Originally Posted by Doug Parent

Us slippers might disagree ...its a preference thing.

I slap, with no tweeters. Fully half the frequency bandwidth of tweeters lies above where even slappers go, while they don't go low enough to meet where woofers top out. If bass cabs were loaded with tweeters that went down to 2.5kHz they'd make sense, but they aren't, so they don't.

Windreaper · #17 10-13-2011, 02:02 PM

Quote:

Originally Posted by billfitzmaurice

Not really. Piezos are voltage limited, not power limited, to about 25 volts on average. That's a bit shy of 100 watts at 8 ohms. To be safe they must be used in series wired pairs, or series wired pairs of parallel arrays, which doubles the voltage limit to 50V, corresponding to almost 400 watts at 8 ohms, almost 800 watts at 4 ohms.
As for rejecting low frequencies, they do, but not effectively enough for pro-sound use. They greatly benefit from a 2nd order high-pass filter. But it must be one specifically created for use with piezos, those made for use with compression drivers won't work.

True that. Just curious, but exactly how is the XO design different? If you insert a parallel resistor the XO network should see the piezos as current driven, no? Add a HPF (if you just want to protect the piezo, a simple cap for 6dB/oct should do) and you've just increased the power handling (as the piezo is voltage limited like you said). What am I missing?

Windreaper · #18 10-13-2011, 02:13 PM

Quote:

Originally Posted by Doug Parent

The tweeter GK uses in the MB series is the Le Son piezo. Same one that SWR and Ampeg uses in some of their lines. It's a higher output than the motorola based on my experience, and you gain nothing by putting essentially a similar unit in there.

If it is a LeSon, I was truly giving bad advice in my first post. I'm a bit fuzzy on the details but I recall they come with a coil inside the piezo and the user needs to add a cap (to select XO frequency). In other words the MB piezo should be properly crossovered already. If that is the case, I can't understand why the MB-series combos have taken so much flak for using a piezo. Listening with eyes maybe?

billfitzmaurice · #19 10-13-2011, 02:47 PM

Quote:

Originally Posted by Windreaper

What am I missing?

6dB of insertion loss using an 8 ohm resistor. I use a 30 ohm resistor to eliminate insertion loss, and a high Q Chebyshev alignment to bring the useable response down to 2kHz.

Doug Parent · #20 10-13-2011, 02:56 PM

Quote:

Originally Posted by billfitzmaurice

I slap, with no tweeters. Fully half the frequency bandwidth of tweeters lies above where even slappers go, while they don't go low enough to meet where woofers top out. If bass cabs were loaded with tweeters that went down to 2.5kHz they'd make sense, but they aren't, so they don't.

Yeah but this slapper "likes" the hole in between the tweet and the woof. Less clank and more slice in my soup please.

(My own preference of course, not saying it should be right for anyone else)