Peavey Kosmos

[jtubbs6117]

 I am shifting from prefab Subs to the big fun of  picking drivers and amps etc. I have 3 Adcom GFA 555 MK ii's these should do about 800 each bridged mono.  I was looking at the stereo integrity 24's for 1299.99 Picking up a pair and seeing if I could have some fun. But Talking with a electronics guy he told me that using a regular amp not a sub plate amp would not yield the output i am looking for because the plate amps take the RCA or balanced signal and increase it in the preamp section. Is this consistent with what you guys have run into?  I used a Peavey Kosomos in college to DJ parties and to have independent control of the subs it worked great and sounded incredible.  Just throwing this out there to see how you guys are getting over this hurdle. Thank you all.  

[wstrickland1]

Probably several things to consider like the driver impedance and the stability of the amp at 2 ohms when bridged. A lot of amps don't like seeing less than 8 ohms when bridged as I think the driver impedance is halved. Not sure how the adcom acts when hooked up that way.

[CECAA850]

37 minutes ago, wstrickland1 said:

Probably several things to consider like the driver impedance and the stability of the amp at 2 ohms when bridged. A lot of amps don't like seeing less than 8 ohms when bridged as I think the driver impedance is halved. Not sure how the adcom acts when hooked up that way.

I believe you can get a dual 2 Ohm driver which can be wired to a final load of 4 Ohms.  You're right though, a lot of amps are only rated 8 Ohms bridged.  I'm not familiar with the Adcom he has.

[wstrickland1]

36 minutes ago, CECAA850 said:

I believe you can get a dual 2 Ohm driver which can be wired to a final load of 4 Ohms.  You're right though, a lot of amps are only rated 8 Ohms bridged.  I'm not familiar with the Adcom he has.

I was assuming a 4 ohm load, which a lot of bridged stereo amps would see as 2 ohms. Might be a bit of a strain but who knows it might be fine. I kinda doubt it though.

[wstrickland1]

I just read the manual and it states you can use 4 ohm speakers when bridged. It does say that you shouldn't use a speaker that dips much below 4 since the amp is seeing 2 ohms. Sounds like you might be good. 

[wstrickland1]

https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.adcom-usa.com/userguides/gfa-555ii-ug.pdf&ved=0ahUKEwjonbfd963YAhUqQt8KHYu2AfsQFgggMAI&usg=AOvVaw3-2HONqPEJkHjnW-GG_UYA

 

Link to the manual

[CECAA850]

53 minutes ago, wstrickland1 said:

I was assuming a 4 ohm load, which a lot of bridged stereo amps would see as 2 ohms.

Not following you there.

[CECAA850]

16 hours ago, wstrickland1 said:

https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.adcom-usa.com/userguides/gfa-555ii-ug.pdf&ved=0ahUKEwjonbfd963YAhUqQt8KHYu2AfsQFgggMAI&usg=AOvVaw3-2HONqPEJkHjnW-GG_UYA

 

Link to the manual

According to that it's rated at 600 watts bridged at 8 ohms, 850 watts @ 4 Ohms with the fan option.  Don't put it on a sub driver.

[wstrickland1]

23 minutes ago, CECAA850 said:

Not following you there.

You said he could series a pair of 2 ohm drivers to get 4 ohms. I was saying that I had already assumed he would use a 4 ohm driver, which on a bridged amp is actually 2 ohms. Wasn't sure if that amp could handle it, but reading the manual see it does appear to be good down to 2 ohms but no less. That actually speaks to the quality of that amp, many won't do it.  

You can do it, just have to know exactly what your driver is. The manual says 4 ohm loads bridged.  It will probably run a little warm. I'd give it a whirl and keep an eye on it. You can always get a sub amp later.

Also it looks like it needs less than 2 volts to reach rated output so you shouldn't have to worry about driving it.

 

[jtubbs6117]

thank you for all the information guys we will see how bonus time works out.

[jtubbs6117]

I my just end up going with pro amps I would rather not chance killing the adcoms

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[CECAA850]

11 hours ago, wstrickland1 said:

You said he could series a pair of 2 ohm drivers to get 4 ohms. I was saying that I had already assumed he would use a 4 ohm driver, which on a bridged amp is actually 2 ohms. Wasn't sure if that amp could handle it, but reading the manual see it does appear to be good down to 2 ohms but no less. That actually speaks to the quality of that amp, many won't do it.  

You can do it, just have to know exactly what your driver is. The manual says 4 ohm loads bridged.  It will probably run a little warm. I'd give it a whirl and keep an eye on it. You can always get a sub amp later.

Also it looks like it needs less than 2 volts to reach rated output so you shouldn't have to worry about driving it.

 

That's the part I didn't get.  I don't see how the amp sees double the load.  The manufacturer already takes that into account when they list the specs.

 

 

I think a pro amp is definitely the way to go.

[wstrickland1]

42 minutes ago, CECAA850 said:

That's the part I didn't get.  I don't see how the amp sees double the load.  The manufacturer already takes that into account when they list the specs.

 

 

I think a pro amp is definitely the way to go.

I'm not sure the exact "technicalities" but I believe it has something to do with the fact that when bridging 2 amp channels, each one shares the load, so when using an 8 ohm speaker, each "amp" sees 4 ohms and so on. I'm sure we have some technical people here that can explain that better (I can't really splain it at all  ).  The manual does say that the amp is good down to 2 ohms, which is impressive. You could do it but there are definitely better options for subs.

[CECAA850]

53 minutes ago, wstrickland1 said:

I'm not sure the exact "technicalities" but I believe it has something to do with the fact that when bridging 2 amp channels, each one shares the load, so when using an 8 ohm speaker, each "amp" sees 4 ohms and so on. I'm sure we have some technical people here that can explain that better (I can't really splain it at all  ). 

That makes sense now that I think about it, thanks.  That's why they only rate it bridged with an 8 Ohm load as the amp will see 4 Ohms.

[wuzzzer]

9 hours ago, jtubbs6117 said:

I my just end up going with pro amps I would rather not chance killing the adcoms

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I'm going to be selling my Crown xti 1000.  Awesome amp.  Interested?

[avguytx]

And aren't most plate amps some form of high speed Class D which are far more efficient than Class AB amps like the Adcom?  Efficiency alone will make a big difference....80%+ versus 40% or so.  The AB amps will generate a lot more heat which equates to less "power to the pavement".  At least in my past experience that held true.

[CECAA850]

22 minutes ago, avguytx said:

The AB amps will generate a lot more heat which equates to less "power to the pavement".

If they put out their rated wattage it's a moot point.  They may consume more current and give off more heat but a watt is a watt.

[wstrickland1]

2 hours ago, CECAA850 said:

That makes sense now that I think about it, thanks.  That's why they only rate it bridged with an 8 Ohm load as the amp will see 4 Ohms.

Yes but although it is not the right tool for the job, it will work. If you read through it it says you can indeed run a true 4 ohm load when bridged. The amp is good down to 2 ohms. As mentioned it would be inefficient and would probably be a great amp to run in the winter  

[babadono]

Think about it. When an amplifier is used in bridged mode both channels are driving the same load but in opposite polarities. So when one output is say at +10volts the other is at -10 volts. So what does the output that is at +10 volts see? Given a 4 ohm load it sees it has to drive 5 amps into the load because the total voltage across the load is 20 volts. So effectively the output has to drive twice the current than the 4 ohm load would suggest if driven to ground. So effectively the loads impedance is cut in half.

[rockhound]

Hey Jeff what do you have up your sleeve? Buy pro amps if you can, you still need to make the trip to Murfreesboro and hear my 684 and the THTLP.