4 Ohms and 8 Ohms.

[beerdragon]

Hi, Excuse my ignorance on this subject, I have a Trace 300watt 1715 Combo which i think is 8 ohms, i would like to pair a cabinet which sold then bought back off a friend, it's one i made up of Two 10inch Celestion 300 watt BN10X 4 ohms. is this possible without doing any damage, am i right in thinking this will just cut down the amp 150 watts? Thanks.

[neepheid]

Not sure this sounds right. The amp more than likely has a min impedance of 4 ohms. If the internal speaker is 8 ohms, the extension speaker must be 8 ohms min - combined in parallel that will give 4 ohms impedance. If you connect the 8 ohm internal speaker in parallel with a 4 ohm cab you'll end up with a total impedance of 2 2/3 ohms - probably too low, unless the amp goes down to 2, but that's not common.

[Marc S]

Yes, check the minimum specified load for the amp
If it's 8 ohms you should not lower that, or you risk damaging the amplifier
Connecting 2x 8ohm speakers in parallel with give you combined impedance of 4 ohms

It should tell you on the plate at the back of the amp
Does it have an extension speaker socket? If so, it should tell you the recommended impedance of extension cabs

Good luck

[beerdragon]

Hi, Thanks for the replies, it does have a extension socket, but no info on the back, It's really what i expected. these celestions i think are over a hundred quid now, i might try and see if i can swap them for 8 ohms.

[SubsonicSimpleton]

If your cab contains two drivers which each have a nominal impedance of 4 ohms, you can wire them in series to make the load that the amp sees 8 ohms, if they are wired in parallel they will present a load of 2 ohms to the amp.

[beerdragon]

[quote name='SubsonicSimpleton' timestamp='1461671207' post='3036583']
If your cab contains two drivers which each have a nominal impedance of 4 ohms, you can wire them in series to make the load that the amp sees 8 ohms, if they are wired in parallel they will present a load of 2 ohms to the amp.
[/quote] Right that's what i thought. Thanks.

[4stringslow]

[quote name='beerdragon' timestamp='1461668633' post='3036545']
Hi, Excuse my ignorance on this subject, I have a Trace 300watt 1715 Combo which i think is 8 ohms, i would like to pair a cabinet which sold then bought back off a friend, it's one i made up of Two 10inch Celestion 300 watt BN10X 4 ohms. is this possible without doing any damage, am i right in thinking this will just cut down the amp 150 watts? Thanks.
[/quote]

I can't find a manual for a 1715 combo. Closest are 1215 or 715 combos. Are you certain of the model number? Does the combo have a socket for an extension cab?

In general, amps work down to 4 ohms and cabs (or combos with external cab sockets) are 8 ohms. Amp ratings are specified into their minimum ohm loads. Thus, a 300W amp will drive 300W into 4 ohms and somewhat less into 8ohms (typically about 2/3rds, so 200W in this case). So, a 300W combo with an extension cab socket will likely be an 8ohm speaker and will develop about 200W when used alone. Adding an 8 ohm extension cab will create an overall load of 4ohms and the amp will then deliver its full 300W.

BUT, all that is general and there will be exceptions. We can only be sure by knowing the full details of your combo, which should be stated in the operating manual.

[Marc S]

[quote name='4stringslow' timestamp='1461673371' post='3036608']
I can't find a manual for a 1715 combo. Closest are 1215 or 715 combos. Are you certain of the model number? Does the combo have a socket for an extension cab?
.....
[/quote]

I was just going to ask if you had a manual, or if there was one available online....
Might be a good idea to search for one, or ask a friendly BC member might have one?
Worth a try - so many BC members are helpful, maybe they can scan or photocopy a manual, or know of a link....

[SubsonicSimpleton]

Bunch of trace manuals can be found here
http://www.britishaudioservice.com/#!trace-manuals/c1mt9

[LewisK1975]

[quote name='4stringslow' timestamp='1461673371' post='3036608']
I can't find a manual for a 1715 combo. Closest are 1215 or 715 combos. Are you certain of the model number? Does the combo have a socket for an extension cab?

In general, amps work down to 4 ohms and cabs (or combos with external cab sockets) are 8 ohms. Amp ratings are specified into their minimum ohm loads. Thus, a 300W amp will drive 300W into 4 ohms and somewhat less into 8ohms (typically about 2/3rds, so 200W in this case). So, a 300W combo with an extension cab socket will likely be an 8ohm speaker and will develop about 200W when used alone. Adding an 8 ohm extension cab will create an overall load of 4ohms and the amp will then deliver its full 300W.

BUT, all that is general and there will be exceptions. We can only be sure by knowing the full details of your combo, which should be stated in the operating manual.
[/quote]

This is the 100% correct answer to the OP's question.

[beerdragon]

Thanks for the Manual link, I removed the drivers and they are wired series so i should be ok. i thought it best to ask before i use them.

this what the manual says, [font=Optima][size=2]The 7210H and 7215 combos produce around 200Watts into their respective internal speakers which provide an 8-Ohm load in both cases. There is an additional output socket on the rear of both combos to allow an additional 8-Ohm cabinet to be used. They will then produce the full 300Watts into the combined 4-Ohm load. If you want to run the combos with a single 4-Ohm speaker cabinet, (or indeed two 8-Ohm cabs), then the internal speaker must be disconnected. This is achieved by the removal of the jack plug in the rear socket. [/size][/font]

Edited April 26, 2016 by beerdragon