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Re: Using Power Amps without a Pre Amp
Posted: Mon May 17, 2021 11:01 am
by Vinyl-ant
Volume pot position is completely irrelevant. It is completely dependent on the output voltage of the source, and the initial gain of the power amp.
Think of it this way, full volume from a system is not attenuated at all, all a volume pot/attenuator does is to reduce the voltage that the first stage of a power amp sees.
If using an amplifier with an input sensitivity of say 1v, and all the source can output is 1v, at full volume the power amp will make its full power. The volume at that point is then dependent on the sensitivity of the speakers
If using an amp with a 500 millivolt input sensitivity, and a source with a 1v output, the amp will make its full power at a point on the attenuator where 500millivolts comes out of the attenuator. Turn it up louder and eventually the input stage of the power amp will start to distort as the voltage it sees on its input is higher than its input stage is designed for
The taper of the pot or attenuator is not linear (usually) so this does not mean that it will be at the same volume half way around when compared to the first power amp.
Pot position is not an indicator of power output or volume from one system to another.
My nva a20 puts out 20w or whatever it is, my f5 puts out 28w. There is much less gain in the f5 circuit compared to the a20 circuit, so to match volume, the pot on the f5 would need to be turned further for the same volume compared to the a20. Two amps with similar power outputs, same source, completely different pot positions because one requires a different input voltage to the other for a given volume.
The a20 is difficult to get to work well with my speakers because they are 101db efficient, so its high gain input stage needs very little input voltage to get them to go very loud indeed. Most pots/attenuators are not very fine adjustable at the bottom of their travel, so using the a20, one minute its too quiet, and a tiny adjustment has it blowing the windows out. The f5 has the pot in a different part of its travel where it is fine adjustable, so is much more useable.
All input sensitivity is is a measure of the input voltage needed for the amp to make its full power. The higher the number, the further around the dial the pot will be. The lower the number the less far around it will be.
Look at old 60s and 70s amps and you will see the quoted sensitivity as high as 200 millivolts
Re: Using Power Amps without a Pre Amp
Posted: Mon May 17, 2021 11:05 am
by savvypaul
Vinyl-ant wrote: ↑Mon May 17, 2021 11:01 am
Volume pot position is completely irrelevant. It is completely dependent on the output voltage of the source, and the initial gain of the power amp.
True, but it's a basic frame of reference for those with NVA systems...
Re: Using Power Amps without a Pre Amp
Posted: Mon May 17, 2021 11:08 am
by savvypaul
Vinyl-ant wrote: ↑Mon May 17, 2021 11:01 am
The a20 is difficult to get to work well with my speakers because they are 101db efficient, so its high gain input stage needs very little input voltage to get them to go very loud indeed. Most pots/attenuators are not very fine adjustable at the bottom of their travel, so using the a20, one minute its too quiet, and a tiny adjustment has it blowing the windows out. The f5 has the pot in a different part of its travel where it is fine adjustable, so is much more useable.
The attenuator we fit in the P50SA has half volume at 3/4 travel, for easier fine adjustment.
Re: Using Power Amps without a Pre Amp
Posted: Mon May 17, 2021 11:13 am
by Geoff.R.G
Vinyl-ant wrote: ↑Mon May 17, 2021 11:01 am
Volume pot position is completely irrelevant. It is completely dependent on the output voltage of the source, and the initial gain of the power amp.
Think of it this way, full volume from a system is not attenuated at all, all a volume pot/attenuator does is to reduce the voltage that the first stage of a power amp sees.
If using an amplifier with an input sensitivity of say 1v, and all the source can output is 1v, at full volume the power amp will make its full power. The volume at that point is then dependent on the sensitivity of the speakers
If using an amp with a 500 millivolt input sensitivity, and a source with a 1v output, the amp will make its full power at a point on the attenuator where 500millivolts comes out of the attenuator. Turn it up louder and eventually the input stage of the power amp will start to distort as the voltage it sees on its input is higher than its input stage is designed for
The taper of the pot or attenuator is not linear (usually) so this does not mean that it will be at the same volume half way around when compared to the first power amp.
Pot position is not an indicator of power output or volume from one system to another.
My nva a20 puts out 20w or whatever it is, my f5 puts out 28w. There is much less gain in the f5 circuit compared to the a20 circuit, so to match volume, the pot on the f5 would need to be turned further for the same volume compared to the a20. Two amps with similar power outputs, same source, completely different pot positions because one requires a different input voltage to the other for a given volume.
The a20 is difficult to get to work well with my speakers because they are 101db efficient, so its high gain input stage needs very little input voltage to get them to go very loud indeed. Most pots/attenuators are not very fine adjustable at the bottom of their travel, so using the a20, one minute its too quiet, and a tiny adjustment has it blowing the windows out. The f5 has the pot in a different part of its travel where it is fine adjustable, so is much more useable.
All input sensitivity is is a measure of the input voltage needed for the amp to make its full power. The higher the number, the further around the dial the pot will be. The lower the number the less far around it will be.
Look at old 60s and 70s amps and you will see the quoted sensitivity as high as 200 millivolts
Indeed, but if people insist on saying that they listen at 11:00 on the volume control we might at least know they are all meaning the same position.
My comment that my pre-amp doesn't have a conventional volume pot should have been a clue that I think volume control position is meaningless. Volume pots are usually logarithmic not linear.
https://www.google.com/imgres?imgurl=ht ... egUIARDyAg
This is what I use more often than my Hi-Fi.
Re: Using Power Amps without a Pre Amp
Posted: Mon May 17, 2021 11:17 am
by Vinyl-ant
Not really imo paul, because its dependent on what the output voltage of their source is and the efficiency of their speakers is
Yes the power amp is going to do the same in each system, but the ancillary components are not, your cubes, magnums and the heresys are a case in point, im sure that the volume control is in a different place dependent on which speakers are in the end of your amps, and wether you are using one source or another (vinyl notwithstanding, it will always need turning up further unless you have a phono stage with a particularly hot output)
Just my opinion though, it should be taken with a pinch of salt
Ps, i know volume pots are generally log, sometimes you will also see the use of a linear pot with a law faking resistor to approximate a log taper, and some conductive plastic pots are not log at all, but a pair of linear tapers with something of a 'flat' in the middle rather than a smooth logarithmic taper
Re: Using Power Amps without a Pre Amp
Posted: Mon May 17, 2021 11:36 am
by savvypaul
Vinyl-ant wrote: ↑Mon May 17, 2021 11:17 am
Not really imo paul, because its dependent on what the output voltage of their source is and the efficiency of their speakers is
Yes the power amp is going to do the same in each system, but the ancillary components are not, your cubes, magnums and the heresys are a case in point, im sure that the volume control is in a different place dependent on which speakers are in the end of your amps, and wether you are using one source or another (vinyl notwithstanding, it will always need turning up further unless you have a phono stage with a particularly hot output)
I know. I'd assumed folks would automatically work that bit out.
Re: Using Power Amps without a Pre Amp
Posted: Mon May 17, 2021 2:56 pm
by Daniel Quinn
Some of you are being a bit anal about it
The clocks analogy is a rough and ready device for comparing volume.
Re: Using Power Amps without a Pre Amp
Posted: Tue May 18, 2021 12:09 am
by BadgerBeerIsBest
Geoff.R.G wrote: ↑Mon May 17, 2021 10:35 am
(quiet at the back I like having a remote control)
Me to, I am in agreement with the need for a remote control, You get nice and comfy and relaxed, in the zone for some serious listening only to break the spell by getting up to adjust the volume.
Adding other manufacturers equipment in the chain to do this surly goes against the NVA way of less is more in the signal path, would we not be happier to let an NVA preamp do this?
Could NVA not re-introduce the P20 preamp with just a motorised Alps volume control. would this not also make it more inviting for new NVA users to get on the bottom rung of the ladder.
Enjoying the learning process from this post & others, again a big thank you to the tech savvy posters making it easier for a electrical numpty like myself.
Re: Using Power Amps without a Pre Amp
Posted: Tue May 18, 2021 8:02 am
by CN211276
I am very acustomed to controlling everything from my phone and don 't see the lack of a remote as an issue. On the second system where the tablet is connected directly to the P20 I use the DAC remote to control volUme.
Re: Using Power Amps without a Pre Amp
Posted: Tue May 18, 2021 8:20 am
by Geoff.R.G
Vinyl-ant wrote: ↑Mon May 17, 2021 11:17 am
Not really imo paul, because its dependent on what the output voltage of their source is and the efficiency of their speakers is
Yes the power amp is going to do the same in each system, but the ancillary components are not, your cubes, magnums and the heresys are a case in point, im sure that the volume control is in a different place dependent on which speakers are in the end of your amps, and wether you are using one source or another (vinyl notwithstanding, it will always need turning up further unless you have a phono stage with a particularly hot output
I said some pages back that on of the functions of a pre-amp is to, as nearly as possible, match the levels of the various sources. A passive pre-amp can’t do that, unless you have a high sensitivity power amp, but all that does is to require attenuators on the higher level sources. The same thing applies to a phono stage, it should provide sufficient gain to drive the power amp properly (assuming a passive pre-amp), if you have to turn the volume up a lot when playing records the phono stage needs more gain, in my opinion.
Modern active source components, with their high level outputs, are well suited to being used with passive pre-amps. Unfortunately many older sources aren’t. The current trend is for low sensitivity power amps to match the high output of the source. That the lower gain required of the power amp also results in lower measured noise is something most manufacturers don’t mention.
The point is that if the volume control has to be set quite high for one source and much lower for another, to achieve a comfortable listening level, something isn’t “right”. Probably it is simply that the source that requires the high volume setting is older than the other. In hi-fi there is no “standard” line output level, manufacturers tend to do their own thing. Likewise there is no “standard” sensitivity for power amps. Guess why putting a system together is such a minefield?
Meanwhile I will keep using my active pre-amps to match my low output sources to my, by current thinking, over sensitive power amps. Clearly I am spending too much time with the “pre-amp” I linked to above. Oh, by the way it does have a remote control.
