Bridging amps and 4 ohm loads

[kgveteran]

What is it about a 4 ohm load that gives the amp a hard time in bridged mode ?

What if the amp has enough power and the 4 ohm load really only goes from 100hz on up.

Is it that no matter what I do, the amp will be stressed out by this load ?

This is my project for the summer as movie watching falls off the edge.I'm buying three Ashly FET-200's.My plans are to transplant all three under one chassis.Why...I'm not sure. I have owned them in the past and they are a nice class AB mosfet design and if the amp is beatup real good I can get it cheaper.it's the insides i want.This will give me three mono channels that only share the 120vac/20a electrical connection.They are a fan cooled design, so the heat sinks will be mounted on the outside of the chassis.I'm figuring about 385 watts mono into 8 ohms (X3) and i'll be driving three RS center channels from the DIY thread. I can get each one for anywhere from 120.00 to 150.00 dollars. There is a used audio store in town, I'll be going there to find them.Thats where I got the idea.Why not just plop down each one and be done with it ? Good question !

[David Meek]

What is it about a 4 ohm load that gives the amp a hard time in bridged mode ?

I wasn't aware that this was a regularly occurring issue. Is it? If so, that's a good question.

Shoot, there's nothing wrong with building a better (read "less expensive") mousetrap - or amp. If you can get three mechanically sound amps, replace their damaged casing with a good one of your own and come up with a good performing unit for less money then more power to ya! :yesnod:

[Glen B]

What is it about a 4 ohm load that gives the amp a hard time in bridged mode ?

When an amp is bridged, it "sees" half the normal load impedance, Therefore, an 8-ohm load appears like 4 ohms and a 4-ohm load appears like 2 ohms. That is because in bridged mode the amp delivers twice the voltage and current (as in unbridged mode) to the speaker.

[Kal Rubinson]

Yes, and how 'stressed' the amp is will depend on its design and how much current it can deliver into low impedances. Some have the capability and some do not.

Kal

[kgveteran]

Yes, and how 'stressed' the amp is will depend on its design and how much current it can deliver into low impedances. Some have the capability and some do not.

Kal

I guess what I can do is integrate them into the system one at a time, if all goes well, the project can continue.

I would like to get a hold of one of those Cello amp cases.They are huge.It would match my huge Outlaw 990.

Thanx for the input!

[Kevin P]

You'll be ok if you use an amp that can drive 2-ohm loads unbridged, in bridged mode with a 4 ohm load.

[kgveteran]

You'll be ok if you use an amp that can drive 2-ohm loads unbridged, in bridged mode with a 4 ohm load.

I think I'll email the tech guys at Ashly and see.They should have some idea.Tha t makes a world of since about driving a 2 ohm load.

[alebonau]

When an amp is bridged, it "sees" half the normal load impedance, Therefore, an 8-ohm load appears like 4 ohms and a 4-ohm load appears like 2 ohms. That is because in bridged mode the amp delivers twice the voltage and current (as in unbridged mode) to the speaker.

jsut one thing too, I've found bridging an amp can completely change its chrecter. a rotel 1066 6ch amp for instance that we bridged once for a demo made it coarse, forward hard to listen to, hardly the rotel charecter I'm familiar with. I believe briding amps double its distortion as well. Perhaps somethign impacting on sound as well. there are some awesonme bridged amps though the mightt elctrocompaniet nemos that abbey road used to drive their reference B&Ws I think from memory were two electrocompaniet amps bridged to form the monoblocs. So yeah guess theres always excepetions ?

[kgveteran]

jsut one thing too, I've found bridging an amp can completely change its chrecter. a rotel 1066 6ch amp for instance that we bridged once for a demo made it coarse, forward hard to listen to, hardly the rotel charecter I'm familiar with. I believe briding amps double its distortion as well. Perhaps somethign impacting on sound as well. there are some awesonme bridged amps though the mightt elctrocompaniet nemos that abbey road used to drive their reference B&Ws I think from memory were two electrocompaniet amps bridged to form the monoblocs. So yeah guess theres always excepetions ?

More food for thought, after a great lunch of sushi. Thanx guys.I will take all this in concideration.Ashly also made a FET-500. 250 watts perchannel.I've seen them around also.Same design but more output transistors.I think they used Toshiba mos-fets...I think