Tried looking this up, the closest I found was that Naim amps are classified as Class B amps, but could not find any conclusive info… What are Naim classic amps and 500 series amps considered to be? Class A, Class AB, Class B, G, D?
The Class B reference was here:
Naim Audio amplification - Wikipedia
And in case of interest, I believe the NAP500 is a bridged design, and for this unique among the Naim power amps (edit: also the Statement S1)
Bridging is a way of getting more power: a pair of power amps bridged give twice the voltage output and hence 4 times the output power into the same impedance compared to each amp alone, but typically limits the lowest impedance the amp is happy to drive to twice the impedance that could be powered by the separate power amps. It also means neither of the speaker terminals is at ground potential, unlike more common single-ended designs.
Some stereo power amps (though to the best of my knowledge none of Naim’s) can readily be converted to have the two channels paired to run in bridged mode, turning the amp into a much higher power but mono amp.
Don’t forget the NAP S1 which is also a bridged design.
I keep trying to forget it😉
Very interesting… Where on earth did you find this information?
I can see you edging closer…I think there will be a whisky glass sitting on one…in your abode next year!!!
So in my case, my speakers are 4 Ohm nominal impedance and the NAP500 is rated at 140W/8 Ohm, Is there something that I am missing out on compared to a non-bridged separate scenario?
Not as long as the speakers’ lowest impedance (as opposed to nominal impedance) is above the lowest the 500 is comfortable with. If it sounds good and the 500 doesn’f become stressed (e.g turn its fan on continuously) I doubt there’s anything to be concerned about.
As for where I learnt, that was originally over 40 years ago when I needed more power headroom than my Sinclair Z50 modules gave alone, so I rebuilt my amp with bridged modules. More recently I found most Bryston amps have a switch to change them into mono bridged amps, while, like Naim’s, their highest power amps are bridged already.
Seriously an S1 if I had the cash … and didnt have to compromise…I would do it in a heart beat. I would probabky buy a SH … statement system and sell the 552/500dr to put towards it… I have seen a couple atcaround 1/2 price…
I believe tho that the THD doubles in bridged mode, which doesn’t help the SQ. (As far as I know).
I don’t know whether or not THD increases - though on the one hand the outputs of two amps being added suggests it would double compared to one of the amps on its own, I believe the voltage gain is also doubled which suggests that percentage wise THD would be unchanged. I guess other factors will have an influence, so it may not be as simple as that - however whether any difference would be audible in real life with high quality amps is another matter… Perhaps someone from Naim can comment?
Bryston quote the same THD for their bridged amps as for the single-ended on which they are based, but as they are “less than” figures any difference would be not be evident if still below 0.005%
Yes, good points. Maybe @Richard.Dane knows more details.
I seem to recall that the reason Naim chose to go with a bridged design for the NAP500 was because they wanted a lot more power but wanted to avoid using paralleled output devices to achieve it - bridging gave them just that. Naim speakers were a benign load, rarely dipping below 6 ohms, so current into very low impedances wasn’t seen as such an issue.
Going way way back here … didn’t Linn originally use bridged 250’s to power their cutting lathe?
As lnnocent_bystander goes on to say, its a characteristic of the generic ‘bridged configuration’, and typically applies to all amplifiers which adopt this method to achieve higher power output, you end up with more transistors in series in the output stage which with all other things being equal leads to higher output impedance.
There are compromises in all design topologies. It was particularly popular in early 70’s and 80’s in car stereo systems where you only had a 12V supply to play with. No doubt that has changed with the advent of low cost DC to DC converters and class D amps but I expect they still bridge class D amps for "even More Power!’
Could not find out this info, trying to find it from the manufacturer, all they state in the tech specs is the nominal resistance…
Yes, not many manufacturers publish the minimum impedance. You may bd able to find from test results by a reviewer that conducts electrical as well as listening tests.