|
|
Joined:
June 2004
Posts: 271
Location: Ft. Lauderdale, Florida | A buddy gave me a 50 watt Yamaha Amp w/a blown speaker... we lucked out and found a Bazooka El1204 12" Woofer, at a Salvation Army tent sale, that dropped into the SAME mounting holes... for $5.99
The sound needed some mid and hi-end so I made one phone call and found a brand new pr. of Bazooka EL6502, 6-1/2" mid and tweeter combo, for a closeout price of $8.99 at Brands Mart...
Sounds great hooked up in the Yamaha box, couple hours with the saber saw and a router and all was mounted... Some people say I need a crossover to protect the speakers...
The 12" Woofer is 20-900Hz, 4 ohms recommended RMS 200 watts.
The 6-1/2" mid/tweeter combo HAS a built in crossover already (6db per octave) the freq range is 56-20kHz, 4 ohms also, rated at 120 watts.
Not to worried about the gap in coverage between 900 Hz and 56 kHz... For what I have in it this thing cranks...
What I need to know is what exactly the crossovers should be and HOW to wire them...
I have 2 wires and a ground coming out of the amplifier.
Three speakers shoe-horned into the cabinet:
1) Woofer
2) midrange/tweeter combos
ALL with 2 terminals (+ and -)
A tech at Parts Express, recommended 2 parts, is installed, after we told him what we had. Here are the parts he recommended:
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=027-...
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=266-...
But my "friend" who called Parts Express left town w/o telling me how to finish this...
Are these the right parts???
How many of each do I need???
How do I wire them, in series or parallel ???
Ab |
|
| |
|
Joined:
May 2003
Posts: 4389
Location: Capital District, NY, USA Minor Outlying Islands | Damned if I know, but I love those yamaha amps |
|
| |
|
Joined:
August 2004
Posts: 604
Location: Tampa, FL | Caveat Reader but here is my suggestion:
(BruDev will likely have the definitive response)
Since your mid/tweeter already has a crossover you only need to deal with the woofer. Here's what you do. Put the inductor (2nd part) in series with woofer. Put the capacitor in parallel with the woofer. If you might get confused, wire it this way.
1. wire from amp to one end of inductor
2. wire from other end of inductor to woofer
3. connect one end of capacitor to one woofer terminal
4. connect other end of capacitor to the other woofer terminal.
5. connect 2nd wire from amp to the woofer terminal that is not connected to the inductor.
Power it up and watch for smoke. Accordinhg to the specs, the parts you have should handle the power. The one I would worry about is the capacitor. In any case, crank it up to a reasonable sound level and play for a minute or so. Then shut the amp down and see if either part is hot. Hot is when you lose your finger prints from touching the part. Warm is not hot. There are some parties nearby that I would recommend having a couple of pounds of solder on hand for this project (oh my! you would hate to run out in the middle). Any one else could probably get by with about 6 - 10 inches of .020.
If this doesn't work:
1. you shouldn't damage any speakers
2. you will prove that electronics work on smoke (cause once you let the smoke out, they stop working).
Good luck, let us know how this little adventure turns out. |
|
| |
|
Joined:
March 2005
Posts: 1421
Location: Orange County, California | Was that Yamaha amp designed for a 4Ω load, worse yeat, a 2Ω load if he wires the separates (mid & tweet) in parallel with the woofer. Smoke will definatley come out. The crossover's don't so much "protect" the speakers as only allow them to see (mostly) the frequencies they are capable of reproducing best. If you over power them, or the crossover or any of the x-over components (voltage rating of the capacitors, or current rating of the coil), bad stuff will happen to them, which is stinky, but fun!!. My biggest concern though would be the power supply in the amp though. If an amp is rated at 50 Watts into an 8Ω load, it might only make 35 Watts into a 16Ω load, but it will make about 100 Watts into a 4Ω load, for a very short period of time. Usually until the power supply ceases to provide the neccessary current to keep the whole mess going. If it has a really beefy power supply, it'll last until the "finals" go all "liquid sounding" then die. Spectacular to actually hear!! Mind you, at low volumes everything will probably sound OK, but if you are running 1/4 of the rated load on the output, "2 1/2" on the volume dial is like "10" to the power supply. I suggest experimenting with something that you don't care about. Save up and get a decent 12" 8Ω LOUDSPEAKER, not woofer, repair the cabinet, and it'll sound right!!
Something like this |
|
| |
|
Joined:
December 2004
Posts: 1116
Location: Keller, TX | Adding my $0.03 (inflation, of course).
I agree with Fred's resistance calculation and concern.
If the speaker is 8 ohm, then the easy way to do this is to go down to your local RadioShack (they used to have them) and pickup a passive crossover. You connect your amp on the input and put the speakers on the correct output. It is all labeled and makes it easy.
Here is a site that explains it all. here |
|
| |
|
Joined:
August 2004
Posts: 604
Location: Tampa, FL | Ok boys, before we gat all technical here consider the following.
The mid/tweeter already has a network so I figure you can approximate that as a lump of 4 ohm impedance. The woofer is already spec'd at 4 ohms. I suppose if you are concerned with overloading your amp (check the output specs, if it has a rating for 4 ohms you are going to be ok) you could get a second cap (double the value ~ 10uf) and place that in series with the mid/tweeter assembly. This will result in a quasi highpass into the midrange (3 db somewhere between 700 and 2K Hz) and a low pass into the woofer (the cap across the woofer is probably not necessary).
Otherwise, you could do what is suggested above.
Keep in mind, you are not going to end up with a Genz Benz high tolerance well spec'd amp but you will likely end up in a smoke free environment, making loud noises. |
|
| |
|
Joined:
June 2004
Posts: 271
Location: Ft. Lauderdale, Florida | OK... Thanks guys for the input... I checked the Amp it says in big letters on the back panel 8 ohms minimum !!!
Questions:
Currently the speakers are wired in parallel... If I wired the speakers in series would the amp "THINK" they were a higher resistance... And if so would that be 6, 8 or ???
Can I add resistors to the speakers to make this fly ??? (ie make the amp "think" the speaker(s) resistance, is higher than 4 ohms ???)
The reason I say that is the more I play, this rig, the more it smells, like toasted electroncis... In fact it smells REALLY BAD, after a 1/2 hour or so... Even smells a bit when it has cooled down... Nothing dripping anywhere yet...
I think Chatman has nailed it... Amp is defintely being toasted by three, 4 ohm speakers, in parallel... which may be "seen" as 2 ohms or less... by the amp.
Ab |
|
| |
|
Joined:
December 2001
Posts: 10583
Location: NJ | I was going to send you to www.crossingover.com
but that's no help to you |
|
| |
|
Joined:
June 2002
Posts: 6202
Location: Phoenix AZ | Al, your link disappointed me. I was expecting to find something on cross-dressing. Maybe next time. Dave |
|
| |
|
Joined:
August 2004
Posts: 604
Location: Tampa, FL | Sorry on two counts,
First I believe it was MBFred that first suggested a drive problem. I was just riding the wave.
Second, the only minimally efficient way drive your speakers from this amp would be an matching transformer (which I don't even know for certain exists) that would match the output from your amp to your speakers.
Resistors will work :rolleyes: but you will end up with a 25W amp at best. If you try this route, you need to know they will get HOT. Fingerprint removing hot. So they must be located away from every thing inside the amp. You can think of them as a little 25W light bulb that doesn't glow but consumes all the heat in a tiny package.
The toasty smells you notice coming from the amp usually come from one of a few places (by the way the toasty smell is actually a smoke leak so the operational goodness of your amp is slowly leaking out). First and likeliest are the output transistors (assuming solidstate). Another is favorite is the input power transformer, if you overdrive the output you, by definition, overload the input. Last, and least likely, is an output transformer if it exists. They are most common on tube amps but I'd think they might find some application in solidstate.
If you can see the circuit you can look around for parts that 'don't look right'. This description generally includes discoloration, changes in the surface appearance, stuff like that.
Sometime today I'll do a quick look around the net to see if I find any impedance matching transformers. I'm not too hopeful though. |
|
| |
|
Joined:
June 2004
Posts: 271
Location: Ft. Lauderdale, Florida | I talked to a tech at Parts Express and my guess at putting the speakers in series was correct... That should ease the load on the amp...
I just rewired it a played for 20 minutes no smoke, no smell... Volume was down but I put the preamp on and it still cranks... I 'll see if this will last a week, before I invest anymore $$$ in it...
Thanks to all, for the heads up on the "smoking gun" I was playing...
Ab
PS Now to get thru HURRICANE WILMA... At least when the power goes out I can play w/o the amp... |
|
| |
Crossover Advice needed for rebuilt Amplifier...
