Regulated / Unregulated Amps

Looking at the 3 posted, I can see clear detail differences between each of them. The Cap size clearly, but also the wiring. The ‘Choc Block’ is missing from No.3 (the small Cap version) and the wiring routing is different in each example.

From what I can make out there is a ceramic resistor by the fuses that then feeds the fan?

In the last photo you’ve posted it looks like 2 resistors and a switch at the other end of the back panel for “two stage” cooling

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Hi Richard,

I can’t be sure, as I haven’t looked inside a NAB300 for many years, but I think the thing(s) by the fuses are mains filter capacitors & the switch modification looks to be in the earthing - possibly to alleviate a hum loop?


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Okay I think I know the difference between regulated and unregulated PS in theory but what’s the difference in audio terms?

I can’t comment on the modern and Olive series but have compared 32.5/HICAP/160 against 32.5/HICAP/250 driving late Isobariks, all chrome bumper and serviced. Not sure how true but read that the 250 is a 160 redesigned with regulation.

The 250 sounded better with improved grip, control and detail. The 160 was more musically coherent and engaging for me, but it’s very subjective and I’m sure many folks would prefer the 250. The 160 might have been a bit more dynamic too but can’t recall for sure. I think some folks find the unregulated amps more tiring. The other 110s and 160s I’ve heard (all serviced) had broadly similar strengths / weaknesses.

How do other members hear the differences?

Open question and depends on who you ask.

A regulated amp, recovers faster from transients like a drum that drain a lot of power. So in theory a regulated amp does run out of steam as much when things get hectic and is better equipped to deliver hard hitting attack. As a result, low frequency notes following a transient can continue to follow through with the power they require to sound sharp and solid.

However, they are much harder to design well and do have their drawbacks. Having a regulated power amp can add another layer between you and the music which some manufactures claim leads to unacceptable loss of midrange clarity where the most important action is. For this reason, non regulated amps are often described as sounding more transparent and clean but with softened rolled off bass notes on hectic tracks.

An argument you hear quite often is that regulated amps are fine for (and necessary in) a pro audio studio context but not suitable for the demands of domestic hifi replay.

As with everything in the world of hifi, you pick your poison. There are no absolutes. Most manufacturers decide against regulated amps for the sonic reasons described above.

As a tangent, you can think of tube amps as “super unregulated”. The regulation aspect of an amplifier is really tied to rectification (conversion from AC to DC) stage, not the amplification stage. A tube rectifier can only be followed by small value capacitors which leads them to run out of steam faster and smooth off bass notes even more, not to mention leave a minor 50/60Hz wobble on the DC - which is part of the tube sound people like. Rectification, and therefore regulation (or lack of it) have a massive impact on the flavour of sound - perhaps more than the amplification stage that follows.


As I’m no electronics engineer and prefer things explained to me in layman’s terms, this is how it was once explained to me; A regulated amp is in essence effectively two amplifiers in one - one that regulates the other. It means that the amp is held to operate within very tightly controlled parameters and performance won’t be allowed to “sag” or “slide” like an unregulated amp when great demands are made of it. They’re not easy to do and quite tricky to get just right, which is why you don’t see them very often except from Naim and maybe one or two others in the past, like Exposure of old.


Didn’t realise they were that rare.

Very interesting - thanks!

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