How do I connect XJ300ST power amps in bridged mode??

Forums › Home Theatre (including HTPC and EPG Collector) › How do I connect XJ300ST power amps in bridged mode??

nicknick

27 posts

Geek

#257366 29-Sep-2019 11:29

Having trouble getting the Amps to work at the moment I have the preamp RCA left going to left amp mono connection and the RCA right going to the right amp mono connection I then have used the top mono outputs left + right - out to speaker is this the right way to connect??

I have 2 XJ300ST amps one for each speaker bridged to get 170w

1 | 2

9075 posts

Uber Geek
+1 received by user: 2499

ID Verified

Trusted

Subscriber

#2326638 29-Sep-2019 11:42

Hi that sounds correct basically use the left input rca and the speaker across te L+ and R- but I would expect a manual switch somewhere purhaps inside to finish the signal routing.

Cyril

cyril7

9075 posts

Uber Geek
+1 received by user: 2499

ID Verified

Trusted

Subscriber

#2326641 29-Sep-2019 11:47

OK found the manual, you need to connect the left preamp out to both l and r inputs of the power amp, so a Y splitter

Cyril

nicknick

27 posts

Geek

#2326647 29-Sep-2019 11:57

Awesome thanks am yet to try this so will let you know how it goes I wasnt getting any sound at all how it was

cyril7

9075 posts

Uber Geek
+1 received by user: 2499

ID Verified

Trusted

Subscriber

#2326648 29-Sep-2019 11:57

Also you say you want 170w if that the case just feed the L channel and speaker to just L channel terminals, but to get 300w, ie Bridge connect as I mentioned above.

Cyril

nicknick

27 posts

Geek

#2326672 29-Sep-2019 12:28

I am using them for 8 ohm KEF Q950 speakers. XJ300ST specs says 170w 8 ohm mono and 4 ohm mono which is 300w will this give the speakers 300w or does it somehow know they are 8 ohm

cyril7

9075 posts

Uber Geek
+1 received by user: 2499

ID Verified

Trusted

Subscriber

#2326680 29-Sep-2019 12:49

Hi, power is an ability, not an imposed delivery, in bridge mode you are technically able to deliever around 600w into an 8ohm load, but something will break before you get there, most likely the voice coils and crossover.

Cyril

Mighty Ape

Shop now at Mighty Ape (affiliate link).

nicknick

27 posts

Geek

#2326726 29-Sep-2019 13:53

Cool thanks so I just tried splitters and still no sound what am I missing something simple? The green light is on the amps so there is power there really strange it all seems good but the amps just wont go???

1101

3141 posts

Uber Geek
+1 received by user: 1143

#2327013 30-Sep-2019 09:55

When I bridged my homemade amp years back.....
For bridged mode, the input has to be mono & the input into one of the channels needs to be inverted.
I made a inverting opamp circuit for that
Then put the speaker across the L+ and the R+ (from memory)

Your digital amp may be wired differently than usual . -R and -L are usually the same connection , so I cant see why you would use -R for the spkr in bridge mode. May being something strange
with the design of your amp .

also , if you have a 8ohm speaker, each ~amp~ (channel) will see a 4ohm load . So check the max rating into 4ohm for the amp.

Regardless , you'll blow the ring out of the speakers
Speakers are often rated for max power of the voicecoils , not rated for the max the speaker can mechanically cope with.

even 170W is far to much in any home.
100W is ear bleeding volume ... IF you speakers can actually cope with that power . And they cant , not mechanically.

Power & logrithms . Means you need 10x the power to double the volume as we hear it. Your speakers wont cope .
10w is plenty. Thats all you need in the av home.

cyril7

9075 posts

Uber Geek
+1 received by user: 2499

ID Verified

Trusted

Subscriber

#2327020 30-Sep-2019 10:03

Hi, if both channels are driven in phase, then using L+ and R- will make up for that.

I have a set of Kef 700Q's driven from a 100w/ch Yamaha, could not imagine it pushed to full throttle, so yes not sure why so much power is needed.

Cyril

ilovemusic

1469 posts

Uber Geek
+1 received by user: 307

#2327084 30-Sep-2019 12:42

to add to the above...

bridged amps usually sound worse.

nicknick

27 posts

Geek

#2327251 30-Sep-2019 18:44

Thanks. the speakers say 15w to 200w I would of thought you could give them 200w and not blow anything?

Samsung

Shop now on Samsung phones, tablets, TVs and more (affiliate link).

richms

29099 posts

Uber Geek
+1 received by user: 10210

Trusted

Lifetime subscriber

#2327258 30-Sep-2019 18:56

1101:

Your digital amp may be wired differently than usual . -R and -L are usually the same connection , so I cant see why you would use -R for the spkr in bridge mode. May being something strange
with the design of your amp .

Usual is that one channel is inverted and the red terminal is ground, black terminal is driven on that side. Means that when in stereo the 2 channels are pulling from opposite rails most of the time and can be bridged without any additional parts.

Richard rich.ms

cyril7

9075 posts

Uber Geek
+1 received by user: 2499

ID Verified

Trusted

Subscriber

#2327273 30-Sep-2019 19:10

Hi yes you could give them 200w, but if this is in a suburban setting I think you have got the formula wrong.

Cyril

nicknick

27 posts

Geek

#2327292 30-Sep-2019 20:12

Just wanted a slighty more powerful amp as preamp is only 80w probably enough at lower volume but was hoping these amps would get them rocking a bit more

RunningMan

9186 posts

Uber Geek
+1 received by user: 4840

#2327296 30-Sep-2019 20:36

Preamp would normally be in milliwatts, not 80 watts. If you've fed 80 watts into the input stage of that amp, it may be cooked.

1 | 2