Mono Block Power supply

[Hemmo1969]

Hi,

Could someone explain the workings of the NVA power supply in the range..... I notice as you move up the range components move from (let’s say) a 100va power supply to then 160va input / 160va output.

How does this improve the sound, is the 100va model just sharing the 100va between input and output?

Total nupmty on the internal workings of an amplifier just interested to understand a little more please.

Chris

[Dr Bunsen Honeydew]

I am inclined to ask why do you want to know. The benefits are musical that is all you need to know. BUT it is all explained in old posts just search the archive.

[CN211276]

Into is in the NVA power amplifiers thread. The Doc explained the difference between the A70s and A80s in May this year.

[Hemmo1969]

Thanks both..... nothing underhand about my asking, just wondered how moving up the range changed in terms of the power supply used, also didnt grasp the need for having one for input and output?
I’ll go and have a search.

[Dr Bunsen Honeydew]

I saw nothing underhand just the time to do it when I have done it before, more than once. Can I ask members to search the archive before asking questions.

[karatestu]

My take on this (not nva related) is that bigger power supplies are better.

Power supply consists of ac power cable to on/off switch to transformer to rectifier to smoothing / reservoir caps

In a stereo amp both amplifer boards share (left & right channels) a single transformer, rectifier, smoothing caps and regulator (if used) Saying that, i have seen stereo amps with one transformer and then split off to rectifier and caps for each channel. Also sometimes the transformer may have twin secondary windings with a psu on each one.

Mono blocs have totally independat psu's obviously, as there is only one channel in the box. This is better in my view.

Front end and output stage is where it gets interesting. Front end is voltage amplification and the output stage is current amplification. Alot of amp boards have the facility to split the positive and negative voltage supply so they can be powered independently. This is a good thing because the demands on the psu from the output stage can detrimentally affect the supply to the front end.

The front end can be viewed as a sort of preamp or an extension of your active preamp. As such it benefits (imo) from as clean a dc voltage as you can give it. So a regulator on the front end can be a very good thing. If no regulator is used the front end still benefits from its own psu because the ripple imposed by the demands of the output stage are separated.

Regulating output stage is not a good idea altough naim did it in the nap250 and nap135. They sound lifeless compared to unregulated output stage where music is allowed the freedom to soar as required.

Bigger transformers and smoothing caps are better musically because their impedance drops as they get bigger ( VA gets bigger and secondary voltages stay the same) and also with caps they reduce ripple on the supply as they get bigger. VA = voltage x amps so if the voltage stays the same as the va gets bigger then the transformer can potentially supply more curent before over heating. Curent output is still limited by transistor choice and heat sinking though.

The output and input stages could possibly be further divided and given more independent psu's. The output transistors could be powered separately from the driver transistors and in the input stage the LTP (long tailed pair) transistors could probably be powered independently from the rest. Input stages typically draw very little current (compared to the output stage) so smaller transformers can be used but bigger ones sound better here too.

Increasing voltage supplied will allow for more power from the amp but is limited to what voltage the transistors and caps will take before failing and of course heat sinking.
All in my opinion of course, from the experiments i have done in the past

[hillsanddalesrover]

Regulating output stage is not a good idea although Naim did it in the nap250 and nap135. They sound lifeless compared to unregulated output stage where music is allowed the freedom to soar as required.

Just because the way Naim did it in those amps did not work does not necessarily mean it's a bad idea.

[Dr Bunsen Honeydew]

I agree with Stu. It is as all things swings and roundabouts. Regulated - that is all you get don't ask for more. but completely stable in voltage drift. Unregulated - you want more here you go take it, but not for too long please, may have some voltage drift, but so what you wont hear it.

In the swings and roundabout stakes, voltage gain stages, especially low voltage gain more than they lose. Current gain stages, especially power amp output stages they lose more than they gain by regulating.

And yes I have tried all way with the NVA circuit, what I do sounds best for me.

[hillsanddalesrover]

Well, shunt and series regulation can both have differing effects, and using thermionic devices can also achieve good results.

As in most things, it's not always simple or clear cut which is best.

[karatestu]

I never liked the idea of shunt regulators. Seems like a lot of power wasted as heat and more ripple on the raw supply due to increased demand. I tŕy to keep things as cool as possible - it can only help lengthen the life time of components within an enclosure