Bridging Nord amps

[LApstrE]

Hi,
I've read the benefits of Bridging being discussed/recommended in this forum.

I'm driving a Revel M16(6ohm rated) with a single nc122mp based hypex amp(fed by a minidsp ddrc-24). I've two of these amps and am looking to use each in a bridged config for each channel. I was looking to do this to add more volume as well as wondering how this will change the response of the speaker.

Based on the documentation(attached pg. 16) for nc122mp, I can see that you can bridge both channels by plugging both speaker terminals to +ve and +ve of either channel, there is no need to connect the negative terminals to each other as the hypex amps are designed with the negative terminals bridged together. There is talk about output signal being inverted across left/right so this configuration should be fine. I assume the signal will need to be split from source and same signal fed to both terminals? The amp will invert the signal across L/R. Am I reading this right? Appreciate any advice/guidance.

 

[DonH56]

Search the Buckeye Amp thread for the special XLR cable you'll need to provide an inverted input to one channel. Inversion is performed at the input of the amp.

 

[LApstrE]

Search the Buckeye Amp thread for the special XLR cable you'll need to provide an inverted input to one channel. Inversion is performed at the input of the amp.

Thanks for the quick response. Given I've a minidsp ddrc-24, I assumed I can invert the signal at source if required, but given the additional DIRAC processing layer after I wasn't too sure. My IOM built amp also comes with a special cable that allows you to split a single input signal to both channels, but I suspect that is just splitting, not inverting it. Will check this thread out. Thanks!

 

[NTK]

Please see this post for the bridging cable schematic. In this case, channel 2 is driven with inverted input.

Buckeye Amps: New US based Hypex multichannel amplifier builder, line-up announcement!

Me too!! :D

www.audiosciencereview.com

 

[DonH56]

Thanks for the quick response. Given I've a minidsp ddrc-24, I assumed I can invert the signal at source if required, but given the additional DIRAC processing layer after I wasn't too sure. My IOM built amp also comes with a special cable that allows you to split a single input signal to both channels, but I suspect that is just splitting, not inverting it. Will check this thread out. Thanks!

Yes, you need to invert one side, not just split the signal. See @NTK's post above.

 

[LApstrE]

Thank you both. I'm already running an RCA to XLR converting cable(monoprice), if I manage to find a RCA to dual XLR and add an XLR inverter plug to one of the splits, I assume that might do it, or I could put one together. (I'm assuming this is not available to buy prebuilt).

Just so I'm clear, What is the consequence of getting this wrong?

 

[RayDunzl]

If you don't invert one input to the bridge, then both amplifiers output the same phase of signal across the speaker, which would result in no sound, or very little, if the amplifier outputs aren't well matched.

I don't see that causing damage.

The inverter on one channel creates opposing polarity, one channel of the amp goes positive while the other goes negative across the speaker.

That would be normal.

Short circuit on the input side won't damage the amp. The source may not like it, but probably won't be harmed.

---

You'll double the voltage available across the speakers.

That gives about 6dB additional available loudness, but only at the very top of the loudness range.

What's the point?

You listen wide open now and it's not enough?

 

[DonH56]

Thank you both. I'm already running an RCA to XLR converting cable(monoprice), if I manage to find a RCA to dual XLR and add an XLR inverter plug to one of the splits, I assume that might do it, or I could put one together. (I'm assuming this is not available to buy prebuilt).

You can rewire an XLR connector per the instructions linked earlier -- see the post after @NTK's first post. You need to flip pins 2 and 3 on one connector relative to the other. You can also use two RCA outputs from the miniDSP with one inverted internally, or the balanced outputs if it has them, or buy a single-ended to balanced converter (active or transformer).

Just so I'm clear, What is the consequence of getting this wrong?

What @RayDunzl said.

 

[Buckeye Amps]

Blue Jeans Cable would likely make custom cables as well if you ask them, so you could go from RCA to split XLR with one out of phase.

I would try to do it in an all in one cable and avoid any unnecessary extra connections/adapters in the chain

 

[LApstrE]

What's the point?

You listen wide open now and it's not enough?

Good question, It appears, that for a few sources the volume is very low after ddrc dirac calibration. Seems good, loud and clear enough for music (Chromecast via TV -> Optical out -> Minidsp), but audio from TV direct is sometimes not as loud as I Getty it to be. I've worked around by using different presets for source, but I'm limited to 4 presets in total with my minidsp.

I know I'm just trying to brute force the problem by bridging the amps here, but I've a spare amp and I've always heard Revels need a little the more juice to open up, the question has always been bugging me so finally going down this route.