Pre amp/ power amp

[Garett]

Can someone please explain to me the advantages of having a pre amp and power amp combination? Waht is the pre amps job and what is the power amps job and why is having amps dedicated to each job better?

I have a Rotel RA02 and know it can be used as a pre amp to go with a power amp. If I was to use a power amp a couple of price points ahead of it would I hear much difference or would it have the RA02 character?

Feel free to be as techincal as you want in your explanation, I have a reasonable understanding of audio electronics!

 

[Rethep]

I think that if you don't use a recordplayer, you don't need a poweramp. The signal of a recordplayer is very low and needs much amplification. The higher amplification can influence the low signal. A cd-players sound is high enough to be amplified by just an integrated amp. I never had a pre/power, nor will ever have one.

 

[gramps23]

As far as I understand it, the main reason behind seperate pre and power amp stages is having a dedicated power suply for each. When the power amp is taking big glugs of current, it can effect the amount of voltage going to the more sensitive pre stage, which can obviously have a detrimental effect.

Strangely, I've been in a similar position to you with amps, and have just bought a seperate power amp (Rotel RB971 mk2) to go with my integrated amp (Rotel RA971 mk2). At the moment I'm using it to bi-amp my B&W's, which sounds fantastic. Next move, I'm hoping to be able to get another of the power amps, and do a bit of experimenting using both in bridged mode, or bi-amping without using the integrated's output stage, simply using it as a pre-amp until I can afford a dedicated unit.

Anyway, blah blah blah... In answer to your question about the RA02's character - it's difficult to know which bit of the amp is having the most impact on the character of the sound, without seperating the two parts and listening to them as individual components. I would imagine that being a Rotel, the Pre stage would be well designed, so figure that there's no reason it shouldn't be used with a better power amp - you'll always have the option to upgrade the RA-02 when funds allow.

Hope that helps.

 

[Garett]

I do use a record player, but my amp has a phono amp in there to bring it upto line level. What I mean is a power amp to drive my speakers fed by a pre-amp that controls volume and switches between inputs.

 

[gramps23]

I think that if you don't use a recordplayer, you don't need a poweramp. The signal of a recordplayer is very low and needs much amplification. The higher amplification can influence the low signal. A cd-players sound is high enough to be amplified by just an integrated amp. I never had a pre/power, nor will ever have one.

Erm... Sorry for being picky, but an integrated amplifier is a pre-amplifier and power-amplifier in one box. Also, regardless of whether you're using a record player, CD or other source, you always need a power amplifier to create enough electrical signal for speakers to turn into sound.

 

[Garett]

Thanks for the input gramps I posted my previous post before i'd seen your first reply, hence it doesn't follow!

It sounds like you have an intresting and affordable experiment there. Unfortunately my speakers are not bi-wireable, but is it advisable to run 2 power amps in mono for R and L? As I believe most people running 2 power amps use them for high and low.

 

[Rethep]

Erm... Sorry for being picky, but an integrated amplifier is a pre-amplifier and power-amplifier in one box. Also, regardless of whether you're using a record player, CD or other source, you always need a power amplifier to create enough electrical signal for speakers to turn into sound.

Ok, just add the word "seperate" to "pre/power" in my story.

 

[Al ears]

It's better because it makes upgrading easier!

 

[davedotco]

Generally speaking modern amplifiers have four separate sections. They are,

Phono stage. Takes the very low output from a moving magnet or moving coil cartridge, applies RIAA equalisation and amplifies it to line level, anywhere between 500mv and 2volts, depending on the design.

Digital stage. This takes a digital input, spdif rca, toslink, hdmi for example, converts it to analogue then amplifies it to line level. Essentially a built in dac.

Pre amp stage. This is the bit that takes all your inputs, organizes them so that you can switch between them and provides other functionality such as eq (tone controls) and separate outputs such as record, pre out etc. it also has the volume control to match the level of the inputs to the power amp amd adjust playback level.

Power amp stage. This is usually a fixed gain amplifier that delivers the power to the speakers in such a way that it is a match for the low impedence of all loudspeakers.

Virtually any of these stages can be combined together or built as separate units, a 'full function' preamp for example may contain both a digital and a phono stage, add a power amp and you have an integrated amplifier. Performance wise there are a number of good reasons to keep these different sections separate but this is invariably more expensive, so is something of a balancing act.

 

[bluedroog]

The main advantage is having separate power supplies for each unit, also more insulation between electronic components. That said there is nothing to say just because it is a pre / power set up it will be better than an intergraded but the higher end you go the more likely it will be pre / power and so they often are better. You can find some very high end integrated that will trounce some pre / power combinations of course.

There isn’t a right or wrong or better solution, it just depends really. With integrated you don’t have issues with matching impendence or synergy and of course you’ve got a nice neat solution, pre / powers allow greater flexibility for future upgrade, ability to tailor the sound and of course I could split my system if I wished. I quite fancy trying active speakers at some point so may well pair my pre with them and use a DAC direct to my power amp for a second system.

Personally I have used integrated in the past and have moved to a pre / power set up as I wanted to try a tube amp with solid state power and it has given my the results I was looking for.

 

[gramps23]

Thanks for the input gramps I posted my previous post before i'd seen your first reply, hence it doesn't follow!

It sounds like you have an intresting and affordable experiment there. Unfortunately my speakers are not bi-wireable, but is it advisable to run 2 power amps in mono for R and L? As I believe most people running 2 power amps use them for high and low.

No worries, I guessed that was probably the case!

Yep, I'm very pleased with how the system is growing just now, and it's been very cheap indeed - amazing what you can pick up decent second hand gear for.

Using mono power amps for each channel can work very well, and isn't uncommon (I've had a couple of systems in the past running in that configuration). Apparently the Rotels sound much improved in bridged mode, but unfortunately won't drive loads below 8ohms when bridged (as with modern models like the RB-03, and mostly all sensibly priced amps), so not suitable for speakers like your Zensors.

 

[CnoEvil]

Most of the reasons have been well covered above, though I would make a couple of points:

- A Pre/Power is not automatically better.

- A Pre/Power can give greater flexibility eg. A Tube Pre with a SS Power, or indeed the other way round.

 

[davedotco]

The advent of cd players has made a big difference,before their introduction most hifi sources outputed about 500mv, tuners, tape players and pretty much everything you could plug into an amplifier put out around that level.

To get the output up to the level that you could use to drive speakers required quite a lot of gain, which was done in stages. In those days even integrated amplifiers would have some gain in the pre amp section, so it was simple to split the too. Phono stages were still pretty much universal and having one in a separate pre amp could keep it 's delicate, high gain circuitry away from the noise of the big power supply needed for the power amp.

This all changed with the arrival of the cd player with it.s 'Red Book' standard 2 volt output. Gain stages in the pre amp were now redundant and it was easy to make the power amp a little more sensitive so that the cd player drove it more or less direct, just via the input attenuator, (volume control).

A lot of modern integrateds are just that, a power amplifier with reasonably high gain, input selector and volume control. In fact that has become pretty much the purist approach with the phono stage and dac as outboard devices.