Do you really need a preamp?

[scoran]

Forget for a minute all the obvious reasons for having a preamp (boosting signal strength, noise reduction, switching, etc.): is a preamp must-have sonic component for 2-channel listening? If so, why?

I recently auditioned a vintage solid state Japanese Class A/AB dual mono solid state amp with "direct" and "subsonic" inputs plus gain adjustments for each channel. It sounded great listening to CDs using the direct input - like a silver-face Pioneer receiver

If I only listen to CDs, why should I gum up the works with a preamp?

Could I plug a turntable with no phono stage into the subsonic channel?

Maybe I'm missing something?

 

[tcdriver]

No, you do not really need a preamplifier as long as your source has enough output to drive your amplifier to full output.

 

[whoaru99]

Could I plug a turntable with no phono stage into the subsonic channel?

Maybe I'm missing something?

Apparently there are some types of phono cartridges that don't need RIAA equalization to sound right but, generally speaking, you need a phono preamp for a turntable. Three fold reasons -

1. RIAA equalization
2. Proper cartridge loading
3. Sufficient gain (phono cartridge is typ. MUCH less output, needing on the order of 40-50dB gain above and beyond the preamp/amp).

 

[slimecity]

No. I have driven my pioneer M22 straight from my computer's outputs totally fine. I'm only of the mind to add and use a preamp if it "adds to" the sound - as I've recently found with my Accuphase C200. Otherwise yes, use one if you need a phono stage.

 

[scoran]

Apparently there are some types of phono cartridges that don't need RIAA equalization to sound right but, generally speaking, you need a phono preamp for a turntable. Three fold reasons -

1. RIAA equalization
2. Proper cartridge loading
3. Sufficient gain (phono cartridge is typ. MUCH less output, needing on the order of 40-50dB gain above and beyond the preamp/amp).

Good point. I would expect to use a dedicated phono preamp with a turntable.

Can an amp with subsonic inputs take care of that instead, or is subsonic for connecting a traditional preamp?

 

[scoran]

No. I have driven my pioneer M22 straight from my computer's outputs totally fine. I'm only of the mind to add and use a preamp if it "adds to" the sound - as I've recently found with my Accuphase C200. Otherwise yes, use one if you need a phono stage.

Thanks. The M22 is on my list. I can only imagine how it would sound with vinyl or a decent DAC.

 

[slimecity]

Hi Scoran. The M22 quite simply sounds num num num num.

I haven't used it enough tho. I did have the C21 preamplifier as well but it was no match sonically. Both amps had been reconditioned too.

Re: you "subsonic" question. I think you may be getting issues confused. A subsonic filter is something you may see on an amplifier/preamplifier that allows you to filter-out very low signals, to prevent rumble and the amp's power being chewed up with sound that you cant hear. If you are amplifying a turntable you need a standalone phono preamp, or an amplifier/preamplifier with a phono input.

 

[ZOOM]

Noise... Reduction? That's impossible. A pre amp can only (and will) ADD noise. This is why it should be avoided whenever possible. It's been an obsolete component since the late 70s.

 

[JURB]

Well, I fed my PC directly into my PL 400/2 and it would not drive it to full output. Other than that it sounded good, but it just didn't have enough output.

 

[savatage1973]

The advantage to no preamp is the "line direct" input into the amp from the source --provided that the source has sufficient output to drive the amp (as already mentioned), and that either the source and/or the amp has some sort of volume control. The drawback is that this configuration generally (almost always) limits you to a single source.

My amps and most of my sources have volume controls, so I could get away with no preamp, but I need a preamp as a "switching center" since I run 5 different sources.

 

[Rex Aeterna]

no, not really. as mention above too, preamps will most likely add noise instead of reducing it cause most likely the power amp always will have a higher s/n and of course better filtering...

most sources will have enough output especially digital sources. avg cd player will put out 2v rms on its outputs which is more than enough. even lot of mobile phones will output up to 1v out of it's headphone jack by itself and lot of home power amps usually have input sensitivity of below 1v or around 1v for full output. i only use a mixer/preamp cause i always run more than one source usually. i do have a passive volume controller as well but, haven't used it lately due to my amps being balanced and using xlr jacks. i know jbl made/makes a balanced passive volume attenuator for their powered studio monitors so i might try theirs one day but, for now my mixer works fine for my purposes.

 

[MacPhantom]

Voodoo-blah blah aside, here's a list of technical reasons why you would need a preamp (and when):

• You are using a power amp (ok, then you could use an attenuator in line before it)
  
• You want to have multiple inputs and/or a record selector circuitry (alternative: use an attenuator with a selector before)
• You want a better signal to noise ratio (carefully designed preamps have better specs than a simple potentiometer; e.g. by using variable gain circuitry)
• You want a phono equalizer (and don't want to use an external one)
• You need basic tone controls

Here's all reasons why not:

• You have an integrated amp which does everything you need
• You have a mixer that does the job

 

[E-Stat]

If I only listen to CDs, why should I gum up the works with a preamp?

It's all about matching. Some sources drive power amps well while others don't. I successfully used a GamuT CD-1 to drive VTL amps through a DIY box using DACT attenuators for about ten years. The GamuT had an exceptionally low output impedance (75 ohms) and high output (4V) driving 10k attenuators into 137k amps using low capacitance JPS Labs cabling.

When I replaced the player with an Audio Research DAC7, that route no longer was optimal and now use an SP20 preamp with better overall results. While passives do typically excel at resolution, they usually compromise low level dynamics.

I started out by building a simple attenuator box using $15 worth of Radio Shack parts. Might as well give it a try.

 

[scoran]

You want a better signal to noise ratio (carefully designed preamps have better specs than a simple potentiometer; e.g. by using variable gain circuitry)

Interesting. Can you elaborate on this a little? Why would a potentiometer have signal-to-noise issues, and what way(s) would carefully designed preamp do a better job with this?

 

[sqlsavior]

My guess is that the "subsonic" input on the amp places a subsonic filter on the input, to save the power amp from useless work, and the speakers from excess cone excursion, probably mostly for use with vinyl records, as subsonic noise with considerable energy can be present with vinyl.

You always need a phono preamp to play records. Equipment with jacks labeled "Phono" has one built-in.

Most people need a means to control volume. If you have that means, a traditional, line-level, active preamp with gain is not usually needed with other sources..

 

[MacPhantom]

Doesn't have anything to do with a subsonic filter.

Instead, the problem is the following: if you are using a potentiometer, the analog signal is dampened by the volume setting and then amplified again by the power amp (resp. also the preamp if you don't have a variable gain circuit) with a fixed factor. Every amplification induces some noise into an analog signal.
The better way of doing it is using a variable gain amp: here, the signal is not attenuated but directly amplified by the setting of the volume knob.

Example: you are feeding an amp a signal (e.g. from a tuner) with 500mV. A conventional preamp would then attenuate this to e.g. 200mV (potentiometer), then amplify it again by a constant of, say, 1V (resulting in 1.2V output). This signal would then be fed into the power amp (stage). A variable gain preamp instead doesn't bother attenuating the signal, instead it directly to 1.2V from 200mV. This means that there is less to amplify (and hence a higher signal-to-noise ratio).

 

[audiomagnate]

I've put together several systems consisting of just an Android/iOS controlled streamer/DAC, a power amp and a pair of speakers. The phone/tablet controls the volume and selects the music. But if you play records and/or have more than one source (remember FM?) you pretty much need a preamp.

 

[hnash53]

The advantage to no preamp is the "line direct" input into the amp from the source --provided that the source has sufficient output to drive the amp (as already mentioned), and that either the source and/or the amp has some sort of volume control. The drawback is that this configuration generally (almost always) limits you to a single source.

My amps and most of my sources have volume controls, so I could get away with no preamp, but I need a preamp as a "switching center" since I run 5 different sources.

Wouldn't a passive switcher like this http://atariage.com/forums/topic/179972-hooking-another-rf-into-a-2600/ work in place of a preamp? That's assuming that all your sources connect via RCA.

 

[Northwinds]

The preamps I use have as low a s/n ratio as my amps. Not all preamps add noise, this is why it's good to use equipment that matches up. I don't feel preamps are obsolete and many people who run big monster amps don't have sources with their own volume controls. I for one would never run my system off a computer. Sort of defeats the analogness

 

[sqlsavior]

Doesn't have anything to do with a subsonic filter.

Instead, the problem is the following: if you are using a potentiometer, the analog signal is dampened by the volume setting and then amplified again by the power amp (resp. also the preamp if you don't have a variable gain circuit) with a fixed factor. Every amplification induces some noise into an analog signal.
The better way of doing it is using a variable gain amp: here, the signal is not attenuated but directly amplified by the setting of the volume knob.

Example: you are feeding an amp a signal (e.g. from a tuner) with 500mV. A conventional preamp would then attenuate this to e.g. 200mV (potentiometer), then amplify it again by a constant of, say, 1V (resulting in 1.2V output). This signal would then be fed into the power amp (stage). A variable gain preamp instead doesn't bother attenuating the signal, instead it directly to 1.2V from 200mV. This means that there is less to amplify (and hence a higher signal-to-noise ratio).

Very, very few preamps use variable gain circuitry. Most are fixed gain, which is then attenuated. Attenuation via resistance also adds noise.

What do you think it means when an input to a power amp is labeled "subsonic"?