Can I do away with a pre amp?

Tonymerritt

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Can anyone help with whether a preamp is really needed in my set up?

I've got a Mac mini into a Cambridge audio DAC (no preamp in the DAC). I'm using itunes for my digitised music that is all on an external drive. If I connect my DAC to a power amp without a volume control can I use itunes to control input to the power amp?
 

tino

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A pre-amp or at least an attenuator of some sort is always desirable, but I recommend you read the following article, which even though it applies to Logitech Squeezebox, contains a lot of useful information.

http://wiki.slimdevices.com/index.php/Connecting_directly_to_a_power_amplifier
 

Overdose

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It would be best to use some form of volume control after the DAC, mainly to provide a level of protection for your equipment should you have an accidental full scale volume incident.
 
If your chosen power amp has a sensivity level that matches then all you need to do is have much more luck than I do in controlling volume smoothly using your Mac. Personally I would never rely on a computer control for such an important function. Too many chances of it lurching the wrong way, sticking, or changing in uncomfortable leaps for my liking.

I would always use a proper preamp.
 

Vladimir

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No.

You need a preamp or a power amp with volume controls for each channel.

Power amps without attenuation operate by default at 100% gain. AKA a very large pop and then you may use the speaker cones as hats.
 

andyjm

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Tonymerritt said:
Can anyone help with whether a preamp is really needed in my set up?

I've got a Mac mini into a Cambridge audio DAC (no preamp in the DAC). I'm using itunes for my digitised music that is all on an external drive. If I connect my DAC to a power amp without a volume control can I use itunes to control input to the power amp?

Of course you can do away with a pre amp. Ignore the muddled headed thinking in the thread above.

As a general rule, the less links in the chain, the better. No pre-amp has zero distortion and zero noise, so including a pre amp in the chain will have a negative effect on the sound quality. Most users trade this off against the input switching and volume control features of a pre-amp - but if you dont need them, why have them?

Back in the glory days of Squeezebox, the software on the 'Transporter' streamer did have the worrying tendency to occasionally flip out and produce white noise at full volume. As a result, those driving power amps direct from their streamer would include passive attenuators (fancy name for a couple of resistors) to make sure that full output on the streamer didn't damage the speakers. This depends on the sensitivity of the power amp and the max output of the DAC / streamer - it may be that even at full output, the power amp would not be able to damage your speakers.

These days, streamers / DACs are much more stable - I have never had a 'full output event' in the 10 years or so I have been using a streamer. Personally, I wouldn't worry about it and would just connect the DAC to the power amp.
 

Gazzip

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This may be a dumb statement, but isn't your PC, (or in the case of the squeezebox, the squeezebox), acting as a digital pre-amp in the situations you describe? So you would be using a pre-amp in both situations, no?
 

Gazzip

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Forgot to add the important point that it takes a clever box of tricks to prevent loss of resolution during digital attenuation so a good quality sound card in an absolute must if using the solution you describe.
 
andyjm said:
Of course you can do away with a pre amp. Ignore the muddled headed thinking in the thread above.

As a general rule, the less links in the chain, the better. No pre-amp has zero distortion and zero noise, so including a pre amp in the chain will have a negative effect on the sound quality. Most users trade this off against the input switching and volume control features of a pre-amp - but if you dont need them, why have them?
Andy, surely you are overlooking the impedance matching benefits of a proper preamp? I realise minute amonts of distortion may be introduced but the benefits usually outweigh the disadvantages. DACs without volume controls rely on flaky pcs to control them, which is far from ideal.
 

steve_1979

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andyjm said:
Tonymerritt said:
Can anyone help with whether a preamp is really needed in my set up?

I've got a Mac mini into a Cambridge audio DAC (no preamp in the DAC). I'm using itunes for my digitised music that is all on an external drive. If I connect my DAC to a power amp without a volume control can I use itunes to control input to the power amp?

Of course you can do away with a pre amp. Ignore the muddled headed thinking in the thread above.

As a general rule, the less links in the chain, the better. No pre-amp has zero distortion and zero noise, so including a pre amp in the chain will have a negative effect on the sound quality. Most users trade this off against the input switching and volume control features of a pre-amp - but if you dont need them, why have them?

Back in the glory days of Squeezebox, the software on the 'Transporter' streamer did have the worrying tendency to occasionally flip out and produce white noise at full volume. As a result, those driving power amps direct from their streamer would include passive attenuators (fancy name for a couple of resistors) to make sure that full output on the streamer didn't damage the speakers. This depends on the sensitivity of the power amp and the max output of the DAC / streamer - it may be that even at full output, the power amp would not be able to damage your speakers.

These days, streamers / DACs are much more stable - I have never had a 'full output event' in the 10 years or so I have been using a streamer. Personally, I wouldn't worry about it and would just connect the DAC to the power amp.

While you're technically correct I don't think that this is very good advice. Depending on the output sensitivity of the DAC and input sensitivity of the amplifier it is likely to be much too loud.

I recently tried using my DM5 active speakers plugged into the fixed gain output of a DAC without using a pre-amp. I was hoping to use the Windows volume control on my PC to control the volume. It does work, kind of. But I needed to keep the Windows volume turned down below to between 3-5% or it was too loud. At 3-5% digital volume the noise floor is audible and there was very noticable background hiss whenever the music stopped playing. Not only that but I was in constant fear that if I slipped with the volume slider or something happened with PC or DAC and a pop or crackle got through to the speakers at full volume they could have been damaged.

My advice would be to use a pre-amp. It's no worth the risk of damaging your speakers and depending on the input sensitivity of your amplifier using a digital pre-amp below 5% volume is likely to introduce background hiss.

Fostex sell in-line volume controllers for £25, Genelec for £60 and TC Electronics for £70.

http://www.studiospares.com/speaker-spares+accessories/fostex-pc1ex-monitor-volume-controller/invt/229290
 

Overdose

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steve_1979 said:
andyjm said:
Tonymerritt said:
Can anyone help with whether a preamp is really needed in my set up?

I've got a Mac mini into a Cambridge audio DAC (no preamp in the DAC). I'm using itunes for my digitised music that is all on an external drive. If I connect my DAC to a power amp without a volume control can I use itunes to control input to the power amp?

Of course you can do away with a pre amp. Ignore the muddled headed thinking in the thread above.

As a general rule, the less links in the chain, the better. No pre-amp has zero distortion and zero noise, so including a pre amp in the chain will have a negative effect on the sound quality. Most users trade this off against the input switching and volume control features of a pre-amp - but if you dont need them, why have them?

Back in the glory days of Squeezebox, the software on the 'Transporter' streamer did have the worrying tendency to occasionally flip out and produce white noise at full volume. As a result, those driving power amps direct from their streamer would include passive attenuators (fancy name for a couple of resistors) to make sure that full output on the streamer didn't damage the speakers. This depends on the sensitivity of the power amp and the max output of the DAC / streamer - it may be that even at full output, the power amp would not be able to damage your speakers.

These days, streamers / DACs are much more stable - I have never had a 'full output event' in the 10 years or so I have been using a streamer. Personally, I wouldn't worry about it and would just connect the DAC to the power amp.

While you're technically correct I don't think that this is very good advice. Depending on the output sensitivity of the DAC and input sensitivity of the amplifier it is likely to be much too loud.

I recently tried using my DM5 active speakers plugged into the fixed gain output of a DAC without using a pre-amp. I was hoping to use the Windows volume control on my PC to control the volume. It does work, kind of. But I needed to keep the Windows volume turned down below to between 3-5% or it was too loud. At 3-5% digital volume the noise floor is audible and there was very noticable background hiss whenever the music stopped playing. Not only that but I was in constant fear that if I slipped with the volume slider or something happened with PC or DAC and a pop or crackle got through to the speakers at full volume they could have been damaged.

My advice would be to use a pre-amp. It's no worth the risk of damaging your speakers and depending on the input sensitivity of your amplifier using a digital pre-amp below 5% volume is likely to introduce background hiss.

Fostex sell in-line volume controllers for £25, Genelec for £60 and TC Electronics for £70.

http://www.studiospares.com/speaker-spares+accessories/fostex-pc1ex-monitor-volume-controller/invt/229290

+1.

Whilst additional connections and stages will induce additional distortion, the effects are likely to be inaudible and the benefits are a reduced noise floor and the ability to use full scale digital signal, so no loss of resolution, even if this were inaudible too.

The cost for volume control is minimal, the downsides are likely as not inaudible and with the benefit of a level of safety for the equipment. No matter how small the risk, it still exists unless there is a backstop in the form of additional attenuation.

The best way to set it up is to back off the volume and max out on the digital level, then increase the volume on the external volume control to a level that is as loud as you are likely to listen to.

The result will be a fully controllable volume by the computer software without audible losses and a guarantee that the speakers/amp will have protection from a full signal input.
 

andyjm

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nopiano said:
andyjm said:
Of course you can do away with a pre amp. Ignore the muddled headed thinking in the thread above.

As a general rule, the less links in the chain, the better. No pre-amp has zero distortion and zero noise, so including a pre amp in the chain will have a negative effect on the sound quality. Most users trade this off against the input switching and volume control features of a pre-amp - but if you dont need them, why have them?
Andy, surely you are overlooking the impedance matching benefits of a proper preamp?

There is no impedance matching on single ended (unbalanced) RCA line level connections. The source usually has a relatively low impedance (a few hundred ohms), the sink has a high impedance (around 10K ohms or so). There is no attempt to match characteristic impedance of the cable or connectors.
 

andyjm

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steve_1979 said:
andyjm said:
Tonymerritt said:
Can anyone help with whether a preamp is really needed in my set up?

I've got a Mac mini into a Cambridge audio DAC (no preamp in the DAC). I'm using itunes for my digitised music that is all on an external drive. If I connect my DAC to a power amp without a volume control can I use itunes to control input to the power amp?

Of course you can do away with a pre amp. Ignore the muddled headed thinking in the thread above.

As a general rule, the less links in the chain, the better. No pre-amp has zero distortion and zero noise, so including a pre amp in the chain will have a negative effect on the sound quality. Most users trade this off against the input switching and volume control features of a pre-amp - but if you dont need them, why have them?

Back in the glory days of Squeezebox, the software on the 'Transporter' streamer did have the worrying tendency to occasionally flip out and produce white noise at full volume. As a result, those driving power amps direct from their streamer would include passive attenuators (fancy name for a couple of resistors) to make sure that full output on the streamer didn't damage the speakers. This depends on the sensitivity of the power amp and the max output of the DAC / streamer - it may be that even at full output, the power amp would not be able to damage your speakers.

These days, streamers / DACs are much more stable - I have never had a 'full output event' in the 10 years or so I have been using a streamer. Personally, I wouldn't worry about it and would just connect the DAC to the power amp.

While you're technically correct I don't think that this is very good advice. Depending on the output sensitivity of the DAC and input sensitivity of the amplifier it is likely to be much too loud.

I recently tried using my DM5 active speakers plugged into the fixed gain output of a DAC without using a pre-amp. I was hoping to use the Windows volume control on my PC to control the volume. It does work, kind of. But I needed to keep the Windows volume turned down below to between 3-5% or it was too loud. At 3-5% digital volume the noise floor is audible and there was very noticable background hiss whenever the music stopped playing. Not only that but I was in constant fear that if I slipped with the volume slider or something happened with PC or DAC and a pop or crackle got through to the speakers at full volume they could have been damaged.

My advice would be to use a pre-amp. It's no worth the risk of damaging your speakers and depending on the input sensitivity of your amplifier using a digital pre-amp below 5% volume is likely to introduce background hiss.

Fostex sell in-line volume controllers for £25, Genelec for £60 and TC Electronics for £70.

http://www.studiospares.com/speaker-spares+accessories/fostex-pc1ex-monitor-volume-controller/invt/229290

If there is a vast difference in output level from the DAC and input sensitivity to the power amp for full volume, then this approach makes sense. I would note that the product linked to is not a pre-amp, but an adjustable passive attenuator, of a similar type to the one described in my original post.
 

Vladimir

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Only takes someone to unplug a cable, electricity to go down or some sound from the PC at 100% and your speakers will blow up. Not to mention the risk of human error.

Get cheap PC speakers, have them at 100% volume on their internal amp and just use the PC as volume control. Live with that for a week and you will see how practical it is.
 

steve_1979

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Vladimir said:
Only takes someone to unplug a cable, electricity to go down or some sound from the PC at 100% and your speakers will blow up. Not to mention the risk of human error.

When I first plugged in my DM5's without using a pre-amp I made a dumb mistake and accidently had music playing at 100% full volume for a few seconds. They went very loud with minimal distortion thanks to their built in soft clipping protection. I dredd to think what would have happened if I'd been using an amplifier/speakers that didn't have any sort of protection. It would have been a very silly and expensive mistake which is all to easy to make.
 

unsleepable

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andyjm said:
There is no impedance matching on single ended (unbalanced) RCA line level connections. The source usually has a relatively low impedance (a few hundred ohms), the sink has a high impedance (around 10K ohms or so). There is no attempt to match characteristic impedance of the cable or connectors.

That is true. On the other hand, for the specific case of connecting preamp and power amp, there has traditionally been a matching impedance of a 1,000 order—that is, a power amp with a 50 kOhm input impedance would be matched with a preamp with 50 Ohm output impedance. This doesn't seem to be so often the case with modern gear, though. But good preamps will still typically have an output impedance < 100 Ohm.

I suppose this sort of matching would apply when connecting a DAC directly into a power amp.

This is by the way something I tested, connecting my irDac directly into my P38 power amp, and was surprised by the overall good results. Less background noise and pretty much perfect cross-channel separation in comparison with using my A19 as a preamp.

Functionally it didn't work so well, though. For example, since volume is controlled at the source, you need to be careful with devices plugged to other ports of the DAC—and if using something like an Airport Express, with all devices that your friends bring home. To play music at low volume, you'll want a volume control that can do some dithering/noise-shaping, or least with a decent bit-depth headroom in respect to the bit-depth of the music you are playing. Also, if playing from OS X, as it doesn't control the volume—OS X doesn't do digital volume control, so this needs to be adjusted at the source application—, any dings that for any reason go out to the DAC will play at full volume. A lesser concern could be that some power amps need a higher voltage to achieve full gain, and since the DAC only produces line-level voltage, with one of these it wouldn't be possible to obtain the maximum volume that the power amp could produce.
 

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