Members NathanSPhillips Posted February 28, 2007 Members Share Posted February 28, 2007 Hi- I recently bought a used crate limo because I wanted a small amp for acoustic guitar and vocals that runs on batteries. The features are nice but I'm not fond of the speakers. The piezo tweeter has a hiss as soon as I turn it on. I saw a 2 inch replacement piezo tweeter on the peavey web site and would like to know if it would work with the amp and if it would help the hiss problem. Here are the amp specs from the manual output power rating: 50W RMS @10%THD, 4 Ohms Woofer: Crate Custom Design 10" 4 Ohm, 100 Watt 1.5" Voice Coil, 16 oz MagnetTweeter: 2" Piezo, 4 Ohm, 150watt network This is the tweeter I saw online http://www.peavey.com/products/browse.cfm/action/detail/item/1400/number/00050100/cat/233/begin/1/Piezo+Tweeter.cfm The peavey is listed at 8 ohms. Would I lose a lot of volume going from a 4 ohm tweeter to 8 ohms? I don't know anything about piezo tweeters so I'm lost. For the woofer can anyone recommend a cheap 10" woofer that might sound better than the stock one from crate? Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted February 28, 2007 CMS Author Share Posted February 28, 2007 Welcome to the forum Nathan, Sounds as if the piezo is faithfully reproducing the hiss that's generated somewhere in the amp. Replacing the tweeter is not going to stop the hiss, but upgrading to a compression tweeter with a very small horn might be an improvement in the overall HF sound. It would require some modification to fit whatever you use into the cabinet. You may have trouble finding a 4 ohm compression driver that's relatively inexpensive, but I honestly haven't looked recently. Typically 8 and 16 ohm comps are used. Try partsexpress.com for a lot of choices. You're looking to upgrade the 10" but want it to be cheap. Those are mutually-exclusive requirements. But I don't know what cheap is to you. A typical Eminence Beta 10A would be about $60. There's no guarantee that even a more-expensive speaker would actually improve things, so it's a bit of a risk. You need to determine the internal size of the cabinet and the size of the port, and then figure out what driver best fits that acoustically. Link to comment Share on other sites More sharing options...
Members boomerweps Posted February 28, 2007 Members Share Posted February 28, 2007 There's no guarantee that even a more-expensive speaker would actually improve things, so it's a bit of a risk. You need to determine the internal size of the cabinet and the size of the port, and then figure out what driver best fits that acoustically. Isn't the Crate Taxi an open back amp? If so, cabinet loading is gone and the woofer depends on what kind of guitar amp speaker breakup you want. Emminence has a couple different guitar amp specific lines, one they call classic british and one classic american sound, some fairly inexpensive. Yah, check www.partsexpess.com for a great selection. If anything you might want to check for a similar sized, ohm, & wattage rated speaker with a better listed effeciency since that is a small battery powered amp. Boomerweps Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted February 28, 2007 CMS Author Share Posted February 28, 2007 Isn't the Crate Taxi an open back amp? If so, cabinet loading is gone and the woofer depends on what kind of guitar amp speaker breakup you want. Emminence has a couple different guitar amp specific lines, one they call classic british and one classic american sound, some fairly inexpensive. Yah, check www.partsexpess.com for a great selection. If anything you might want to check for a similar sized, ohm, & wattage rated speaker with a better listed effeciency since that is a small battery powered amp.Boomerweps The Taxi may be open-back, but the Limo is a ported cab. Link to comment Share on other sites More sharing options...
Members agedhorse Posted February 28, 2007 Members Share Posted February 28, 2007 Welcome to the forum Nathan,Sounds as if the piezo is faithfully reproducing the hiss that's generated somewhere in the amp. Replacing the tweeter is not going to stop the hiss, but upgrading to a compression tweeter with a very small horn might be an improvement in the overall HF sound. It would require some modification to fit whatever you use into the cabinet. You may have trouble finding a 4 ohm compression driver that's relatively inexpensive, but I honestly haven't looked recently. Typically 8 and 16 ohm comps are used. Try partsexpress.com for a lot of choices.You're looking to upgrade the 10" but want it to be cheap. Those are mutually-exclusive requirements. But I don't know what cheap is to you. A typical Eminence Beta 10A would be about $60. There's no guarantee that even a more-expensive speaker would actually improve things, so it's a bit of a risk. You need to determine the internal size of the cabinet and the size of the port, and then figure out what driver best fits that acoustically. This pretty much sums it up! Link to comment Share on other sites More sharing options...
Members NathanSPhillips Posted March 1, 2007 Author Members Share Posted March 1, 2007 Welcome to the forum Nathan,Sounds as if the piezo is faithfully reproducing the hiss that's generated somewhere in the amp. Replacing the tweeter is not going to stop the hiss, but upgrading to a compression tweeter with a very small horn might be an improvement in the overall HF sound. It would require some modification to fit whatever you use into the cabinet. You may have trouble finding a 4 ohm compression driver that's relatively inexpensive, but I honestly haven't looked recently. Typically 8 and 16 ohm comps are used. Try partsexpress.com for a lot of choices.You're looking to upgrade the 10" but want it to be cheap. Those are mutually-exclusive requirements. But I don't know what cheap is to you. A typical Eminence Beta 10A would be about $60. There's no guarantee that even a more-expensive speaker would actually improve things, so it's a bit of a risk. You need to determine the internal size of the cabinet and the size of the port, and then figure out what driver best fits that acoustically. Thank you for the information. So you mean the hiss is coming from the power amp - because of the 10% THD? and the piezo is passing it along and not making it itself because it's a bad one, right? I read something online that I can't find right now about adding a resistor to the existing piezo tweeter to and that is supposed to cut down on the hiss frequencies a bit at the cost of 2 or 3 db. Do you know if that is true and would going from a 4 ohm tweeter to an 8 ohm do the same thing by adding more resistance? I checked out parts express and searched the web but I couldn't find any 10 inch 4 ohm woofers. Everything was 8 ohms except things that were meant for car stereos. That eminence speaker is in a good price range for an experiment. I have to take it apart to change the battery so I will measure the port then. How can i figure out what speaker will work best acoustically once I know the size of the port? Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted March 1, 2007 CMS Author Share Posted March 1, 2007 Thank you for the information. So you mean the hiss is coming from the power amp - because of the 10% THD? and the piezo is passing it along and not making it itself because it's a bad one, right?I read something online that I can't find right now about adding a resistor to the existing piezo tweeter to and that is supposed to cut down on the hiss frequencies a bit at the cost of 2 or 3 db. Do you know if that is true and would going from a 4 ohm tweeter to an 8 ohm do the same thing by adding more resistance?I checked out parts express and searched the web but I couldn't find any 10 inch 4 ohm woofers. Everything was 8 ohms except things that were meant for car stereos. That eminence speaker is in a good price range for an experiment.I have to take it apart to change the battery so I will measure the port then. How can i figure out what speaker will work best acoustically once I know the size of the port? There's software available to estimate cabinets, and sites like partsexpress have some project plans for specific drivers that could be useful. It's not the high THD spec that causes hiss, but usually it's a 'noisy' component(s) in the circuitry. As you can see, it can be pretty hard to find components that will work. Even if you find a 10" 4-ohm, it's a longshot that it'll work well in that small cab. IIWY I'd leave it be. The Limo's a pretty neat idea, and it's about as good as it'll get without spending a bunch more. Link to comment Share on other sites More sharing options...
Members W. M. Hellinger Posted March 1, 2007 Members Share Posted March 1, 2007 I read something online that I can't find right now about adding a resistor to the existing piezo tweeter to and that is supposed to cut down on the hiss frequencies a bit at the cost of 2 or 3 db? If you stick the combo amp in the attic and leave it there for... oh, about 20 years, and then start playing it again, you'll notice most of that nasty hiss will be gone (just like that annoying raster whine has disappeared from most TV sets in the last 20 years from what I can tell). Seriously though: As far as the resistor thing goes: You can achieve the same results with some sort of physical attenuation. Also, the higher the frequency of the hiss, the more directional it will be. You might try a piece of gaff tape in a cross hatch pattern across the piezo... basically making a sound blocker for the center area of the horn flair. You could also experiment around with different materials stuffed in the throat of the horn flair. I'm thinking some cotton balls or foam tastefully stuffed down in the throat would work fine. Maybe even a shot of hair spray down the throat would dull the hiss down about right. Or just disconnect the piezo altogether... the combo amp might sound just fine without it. Link to comment Share on other sites More sharing options...
CMS Author Craig Vecchione Posted March 1, 2007 CMS Author Share Posted March 1, 2007 Or perhaps an appropriately-sized choke coil to act as a LPF, essentially lowering the upper end of the piezo's response. ....or yeah, disconnecting it altogether..... Link to comment Share on other sites More sharing options...
Members agedhorse Posted March 1, 2007 Members Share Posted March 1, 2007 The hiss has nothing to do with the distortion of the power amp, it's purely due to the gain (at in the offending frequency spectrum) and the choice of components in the amp's design. Try a resistive pad in front of the piezo, something like 5 watts in series with the piezo and 8 ohms in parallel across the piezo should tame it down a bit. Use 5 watt resistors. Link to comment Share on other sites More sharing options...
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