I ask as a friend bought a stereo power amp then added a 2nd one recently - to have them both fail within hours of each other. He reports no obvious mains issues. Am not sure what the nominal impedance of his speakers are though. These amps are designed to optionally be used this way so have a switch on them. He tends to listen at moderate volumes. The dealer has checked for blown internal fuses - all were fine. They have been sent off for repair. These amps were being driven straight from a NAD M51 DAC.
Bridging stereo amps a good idea?
- Thread starter busb
- Start date
Darth Vader
From the Dark Side
What are the amps?
If designed to be bridged then they shouldn't fail. Mine are bridged and work very well indeed.
Cheers,
DV
If designed to be bridged then they shouldn't fail. Mine are bridged and work very well indeed.
Cheers,
DV
wow&flutter
pfm Member
You don't mention the make of power amps but it's not uncommon for the manufacturer to specify a minimum impedance for bridged mode or an amp running two pairs of speakers. Certainly worth looking into.
Robert
Tapehead
Which amps?
No amps should fail when used at moderate listening levels unless the load is really abnormal or their is a fault in the loudspeaker perhaps causing short, or near short.
Most amps will simply clip or fire their protection circuits if fitted, or blow fuses if those are fitted.
Bridging can be done in two ways - using each channel of the stereo amp to handle half the waveform (series) or connecting both outputs in parallel to increase current capability. The former can often provide more voltage swing but each channel sees half the load impedance so often there is no benefit, and sometimes the result will be worse if the amp has relatively weak current limits. The parallel option can work better if more current is required but it requires balancing components to match the channel precisely.
I'm not a fan of either method TBH unless the amplifier is designed with this mode of operation in mind from the outset and has sufficient current capability (like the Meridian mentioned). Often better to change the amplifier for something designed for the intended load and expected SPLs.
No amps should fail when used at moderate listening levels unless the load is really abnormal or their is a fault in the loudspeaker perhaps causing short, or near short.
Most amps will simply clip or fire their protection circuits if fitted, or blow fuses if those are fitted.
Bridging can be done in two ways - using each channel of the stereo amp to handle half the waveform (series) or connecting both outputs in parallel to increase current capability. The former can often provide more voltage swing but each channel sees half the load impedance so often there is no benefit, and sometimes the result will be worse if the amp has relatively weak current limits. The parallel option can work better if more current is required but it requires balancing components to match the channel precisely.
I'm not a fan of either method TBH unless the amplifier is designed with this mode of operation in mind from the outset and has sufficient current capability (like the Meridian mentioned). Often better to change the amplifier for something designed for the intended load and expected SPLs.
Barrymagrec
pfm Member
Surely connecting the outputs in parallel is not strictly bridging, it is just a parallel connection, and requires precise balancing of the amplifiers for equal load sharing?
In fact, thinking about it, if you connect the amps in parallel and switch the inputs to bridge you effectively short the outputs.
In fact, thinking about it, if you connect the amps in parallel and switch the inputs to bridge you effectively short the outputs.
Robert
Tapehead
Strictly no. It's a method used to get more current from some amplifiers, with and without the manufacturer approval depending on the design. It does require very precise matching and the addition of balancing resistors on the output. It can be shown to help with low impedance loads and is often referred to as bridging. I don't recommend it.
linnfomaniac83
I bet you can’t wheelie a unicycle!
Not many amp manufacturers design amps to be used in parallel configuration, in fact the only ones that I can think of off the top of my head are the old crown macrotech amps which are heavy commercial amps. If you try and parallel the outputs of most amps you can expect smoke and an unpleasant TCP like odour.
Arkless Electronics
Trade: Amp design and repairs.
Several Musical Fidelity amps had the channels paralleled.
linnfomaniac83
I bet you can’t wheelie a unicycle!
I think when done properly it can be very reliable. A great deal of commercial amps the difference between lower and higher powered amps in the same range is the number of output devices and the size of the PSU components, are essentially the same circuit and they just add more devices in parallel to achieve a higher power capacity.
I remember once when a mate was running two matrix 1600 power amps on bass and mid duties and a matrix 1300 for HF in a 3 way active PA setup, one of the 1600s went pop and let out some magic smoke. I managed to save the night by cutting out the damaged devices and reassigning it to HF duties.
Michael J
pfm Member
QUAD valve amps could be used that way, iirc, if 12W wasn't enough then you were allowed to parallel as many as you needed to get sufficient power.
Bryston 7B has this as an option for loads that dip to 1 Ohm.
The older models had a switch for it.
linnfomaniac83
I bet you can’t wheelie a unicycle!
Yes, the whole idea is to achive more current to drive heavier loads as opposed to the higher voltage output that bridging provides. I have never liked bridging amps to be honest.
Nice to know which amp manufacturers provide the facility, I'd say that those who do provide it mean business, it shows that their amps are designed to be workhorses.
To the OP, if two amps have failed in quick succession then they are being used outside of their design limits (driving too heavy a load) or they were not designed to be bridged and they have failed because the channels have been shorted into each other.
The amps have been sent off for repair by the dealer for hopefully warranty repair. The 2nd identical amp was sold on the basis it was going to be bridged as would be the existing one. I prefer to not reveal the manufacturer but the speakers are a pair of oldish Gradients, not sure of the model but have a single dual concentric in each frame - they are designed to work against walls. If they are nominally 4 Ohms, I'd be suspicious of that being the issue.
As an asside - I presume these amps have a switch on the rear to switch to bridge mode & be supplied with a short jumper for the speaker terminals, my single Primare A34.2 does/did.
As an asside - I presume these amps have a switch on the rear to switch to bridge mode & be supplied with a short jumper for the speaker terminals, my single Primare A34.2 does/did.
Barrymagrec
pfm Member
Parallel running of valve amplifiers is relatively straightforward since the highish output impedance forces more or less equal power sharing.
Arkless Electronics
Trade: Amp design and repairs.
Only for paralleled channels I hope!?