how to bridge 4ch to 2ch?

[Nathan2]

Hi,
I have a PowerAcoustik HMR240-4 240 watt (max) 4ch 2 ohm amp and was wondering if I can bridge it to 2ch? and how to bridge it?



P.S. The speakers are Blaupunkt RL6937 6x9 4ohm 170 watts (peak) 85 watt (RMS)



Thanks,
Nathan

 

[AndrewT]

Hi,
if you add on a phase inverter to a channel then the outputs from the inverted and the normal will be out of phase.

The power available from the two out of phase channels will be double the power into double the impedance.

If you start with 240W into 2ohm load, then bridged will give you 480W into 4ohm.
That's a lot of overdrive for a 75W speaker.
The 240W into 2ohm amp will give about 120W into 4ohm and probably a bit extra (about 130W to 150W) and at lower distortion.

The answer is yes, invert two channels and your 4channel have become 2 bridged channels.

However an amp that is already bridged cannot be bridged again.

 

[Nathan2]

Ok,
the output side looks like this
L R L R
+ - - + + - - +
CH1 CH2 CH3 CH4


So if I do this it will work?


+ - - + + - - +
| \ | /
\ \ / /
\ \ / /
\ \/ /
\ /\ /
\ / \ /
CH 1 CH2
Left Right

 

[Nathan2]

well that didn't come out right

so if i tie CH1 & CH3 together, and CH2 & CH4 together that will work? L L R R




Thanks,
Nathan

 

[leadbelly]

You haven't answered the question yet as to what you are doing on the input side of things.

EDIT: I found this link which basically says that your amp isn't bridgeable: http://www.bestamp.com/electronics/car_audio/amplifiers/power_acoustik/hammer/hmr500_2_hmr800_4.htm

 

[Nathan2]

Input side
can't I just take the left out of the stereo and splice it into two and same on the right?

 

[clem_o]

No you can't. If it were that simple then anyone would have advertised their amp as bridgeable. Read leadbelly and AndrewT's posts again...

Cheers!

 

[Nathan2]

Ok,
what is a phase inverter?
and so basically what you all are telling me is, no it can't be bridged.




Thanks

 

[AndrewT]

Hi,
yes, it tells you that in the spec sheet.

It drives 40W into 4ohm. It is unsuitable for 2ohm speaker duty.
The spec says it is stable into 2ohms, presumably resistive only. Check the power into 2ohms the voltage is down by -2.03db.
A good amp would be down -0.5db, reasonable -1db and poor -1.5db. This model is bad into 2ohm.

 

[JWZ]

Your amp is still possible to bridge although there is no built in
facility to do that as stated in the spec. You can add external phase inverters in between the signal source and the input terminals to the amp. and also need to reassign the meaning of the speaker out terminals of the amp. If you need any schematic to do it, I will email to you.

 

[AndrewT]

But NOT if the topology is already bridged. It states floating ground probably indicating the same.

 

[Nathan2]

How expensive are phase inverters?
(I am trying to do this as cheap as posable since the amp was free)

Can I make one myself?
I know how to read a schematic and have a basic knowledge of electronics.

 

[Nigel Goodwin]

How expensive are phase inverters?
(I am trying to do this as cheap as posable since the amp was free)

Can I make one myself?
I know how to read a schematic and have a basic knowledge of electronics.

Just an opamp and two resistors, assuming you have a split supply to power it from?.

However, I agree that it sounds like it's not possible, you can't bridge bridged amplifiers - and it sounds like they are probably bridged already?.

Easy way to check, a simple ohm check from the speaker terminals to the -ve supply (with the unit completely disconnected from power and speakers) - if they are already bridged neither speaker terminal will read short to -ve supply, if it's NOT bridged one of each four should read, usually the negative speaker wires.

 

[cpemma]

Easy way to check, a simple ohm check from the speaker terminals to the -ve supply (with the unit completely disconnected from power and speakers) - if they are already bridged neither speaker terminal will read short to -ve supply, if it's NOT bridged one of each four should read, usually the negative speaker wires.

Should that be 0V ground rather than -ve?

Sorry, spotted it's a car amp so same difference.

 

[Nigel Goodwin]

Should that be 0V ground rather than -ve?

Sorry, spotted it's a car amp so same difference.

I was trying to keep it simple 😎

 

[JWZ]

Here I have the schematic to bridge your amp. its size is big (2.3 MB) so I will email to you. Please give me your email adderess.
The bridged amp will ouput about 80 watts at 8 ohm load and 100watts at 4 ohm load, you don't get 160 watts because the amp could not supply so much current as the spec. says 50 watts into 2 ohms.

Talking about the cost: NE5532 cost less than a dollar, you can build the whole thing for under 5 dollars.

 

[JWZ]

Floating ground does not mean that the amp has been bridged, the easy way to find out is to measure the continuity of the -ve terminals of the speaker outputs, if they are shorted, the amp has not been bridged.
Here is the schematic, I managed to convert it to jif format so it is much smaller.

 

[AndrewT]

Hi,
I feel like giving up.
I will just wait to see the posted results of placing the inverting circuit in front of one channel and then bridging the outputs of a nomal channel and the inverted channel.

I promise not to say "I told you so".

 

[Nigel Goodwin]

I feel like giving up.

I know what you mean!.

And I didn't know you could now get a squeezy lemon graphic format?.

 

[AndrewT]

What's this

squeezy lemon graphic format