Understanding pairing pre amp with the optimum power amp.

[Thomas savage]

plenty of audiophiles wax lyrical about synergy when it's just a numbers game imo.

Please help me and these guys by explaining what one should be concerned about when putting together these two components.

What's going on between the two, the pre amp drives the amp?

Please in lighten and help folks avoid expensive mistakes and prevent them from having to rely on nonsense about synergy but instead rely on knowledge about issues such as input and output impedance and gain in individual components and how they relate to each other as a whole.

Feel free to include source component and the effect ( potentially) of 'loud' dynamically compressed music recordings on the gain structure. ( tipping your amps over to clipping and distortion)

 

[Thomas savage]

this is the kind of thing I am hoping for..

https://www.audioholics.com/audio-amplifier/amplifier-voltage-gain

 

[DonH56]

Yah.

"Synergy" is usually about getting the sound you want and so technical rules rarely apply. Someone who likes tube sound but wants deep bass and has relatively inefficient low-impedance (or widely varying impedance) speakers may go with a tube preamp and big SS amp. It provides the sound (distortion) that the listener desires. I did that for years but understood what and why I liked it. Synergy to audiophiles is often about complementary, often contradictory, goals for the sound they want to hear.

There is a technical basis for some synergies, like impedance matching for particular loads (source/preamp/power amp/speakers) through the chain, and the usual distortion vs. noise trades made to optimize the gain structure, but except for hiss when high-gain amps are paired with very sensitive speakers, that has not how synergy has been explained to me by audiophiles.

IMO - Don

 

[Thomas savage]

Yah.

"Synergy" is usually about getting the sound you want and so technical rules rarely apply. Someone who likes tube sound but wants deep bass and has relatively inefficient low-impedance (or widely varying impedance) speakers may go with a tube preamp and big SS amp. It provides the sound (distortion) that the listener desires. I did that for years but understood what and why I liked it. Synergy to audiophiles is often about complementary, often contradictory, goals for the sound they want to hear.

There is a technical basis for some synergies, like impedance matching for particular loads (source/preamp/power amp/speakers) through the chain, and the usual distortion vs. noise trades made to optimize the gain structure, but except for hiss when high-gain amps are paired with very sensitive speakers, that has not how synergy has been explained to me by audiophiles.

IMO - Don

Thanks don, I was driving at impedance matching and over all gain. What measurements to look for to make sure we stay on the right side of that?

So technically correct synergy if you like, want to avoid the BS mystical audiophile synergy.

 

[DonH56]

I usually just use the dictionary definition:

syn·er·gy
ˈsinərjē/
noun

1. the interaction or cooperation of two or more organizations, substances, or other agents to produce a combined effect greater than the sum of their separate effects.

The debate begins with how one defines "greater than". If I have a circuit and add another that cancels some distortion terms in the first without adding more distortion, that is synergistic. Feedback can do that. If the second circuit adds different distortion (and/or noise) but masks the distortion of the first, it may be synergistic if masking the original distortion is more important in the application. Dither can do that. If the second circuit adds more distortion without otherwise improving anything I would not consider it synergy. Adding a tube preamp can do that. In all cases please note that "can do" does not imply "will do".

You can analyze any cascade of gain stages for noise and distortion to optimize the output with respect to those parameters. You need to know the gain, noise (input referred and noise bandwidth in the RF world), and distortion curves (or intercept point in the RF world) of each component in the chain, then it becomes a tedious but straight forward optimization exercise. That is usually not too bad for audio until you get to the speaker, then it may be hard to find the transfer curves as few manufacturers publish distortion vs. input voltage (or power) curves. For audio, impedance matching usually doesn't really matter until the power amp meets the speakers unless you have a gross mismatch (which does happen, usually when a high-impedance tube output drives a low'ish-impedance SS amplifier input; I have added tube or SS buffers in some such cases). Again not usually an issue until the amp/speaker interface, and again finding amplifier output impedance and speaker input impedance curves can be challenging. I'd guess the manufacturers know far more than they publish, and in the past was able to either measure it myself or in some cases the manufacturer provided data at my request. Currently I do not have access to audio-frequency test gear, alas.

As usual there is not a single pat answer. In general low SNR, high amplifier gain, and high speaker sensitivity leads to hiss but low distortion. An amp with lower gain and/or higher SNR will work better. If you have speakers that vary widely in impedance, with high phase angles and low magnitude dips, chances are a low-impedance amplifier that stays low over the audio band and beyond is a better match than one with high output impedance. And so forth and so on...

FWIWFM - Don

 

[tomelex]

unless you have over say 3 feet of normal interconnect from your source to your power amp, pre-amps, as amplifiers are sort of worth less. Now, if you pramp does switching duties, perhaps phone amp or tone controls but absolutely a very high quality volume control, then it has some value in general. Electrically, the preamp job IMO is to ensure that the signal coming in is what is presented to the power amp input, without any alteration (if you want some sort of tone device then of course its a preference thing) the primary alteration due to longer interconnect lengths which can distort phase and amplitude FR to some degree when interacting between the pre amp and power amp.
A pre amp with a strong current output drive is a good thing. Like a mini power amp when you need to drive long cables to your power amp(s)

 

[Sal1950]

Being of the old school purist/minimalist audiophile camp I bought into the passive preamp idea early on. My first was a homemade diy rig using a Noble level control with some RS switches and RCA plugs, later to be replaced with a Mod Squad (Steve McCormack) Line Drive that was to remain at the systems head for the next 20some years. The passive approach has the big positive of being near straight wire like with little if any distortion or sound of it's own. But the issues of the input/output impedance of source/load components has to be taken into account if a roll off of the high end is to be avoided. Also of import will be the source components output level and the loads input sensitivity. My VTL power amps of the time were the perfect match with a high input impedance of 137k and very high pro level input sensitivity of 775mV. I don't remember the numbers on some of my source components of the day but they were all chosen carefully for a low output impedance and high output level. One was the PS Audio PS III phono amp which Paul McGowan had designed to work well with his own passive pre so it had the required numbers.
For short if you do want to go the passive pre route you want to look for low output imp. values of less than 1k and a high load imp of at least 10k of more. Keep your interconnects as short as possible and maybe look at something with a rated low capacitance like BlueJeans LC-1's
Semi obsolete info today but thought I'd include it in any case.

Today I satisfy my minimalist leanings by using my Emotiva DC-1 DAC straight into my power amp connected to the L & R front speakers. This is a very popular setup in today's market as many DAC's are designed to run double duty as a remote controlled preamp.
A very neat approach to get as little gear as possible between your source and the power amp. Many of these DAC's also offer at least one analog input and you can run a stand alone phono amp into it too if desired.
Less really is more.
Sal

 

[RayDunzl]

I built a passive with a pair of 10k pots and used it for a long time.

The pots were mounted to a piece of discarded curtain rod hanging hardware, and then those were mounted on a nice used discarded round wooden base that already had some felt on the bottom of it.

Cost: Couple of bucks, plus some discarded coaxial cable and some new RCA plugs from Radio Shack.

But it wasn't pragmatic any more as the system expanded to include more than one source.

 

[Purité Audio]

Low output impedance into higher input impedance is the general rule, usually looking for a 10x ( I believe) input impedance, but as has already been stated usually not an issue unless you are using valve gear passive preamp , highly capacitive long cable runs.
Keith.

 

[Fitzcaraldo215]

Low output impedance into higher input impedance is the general rule, usually looking for a 10x ( I believe) input impedance, but as has already been stated usually not an issue unless you are using valve gear passive preamp , highly capacitive long cable runs.
Keith.

I agree. Impedance issues seem to be virtually nonexistent with solid state gear these days at reasonable cable lengths. Tubes and passive preamps can have special problems, though, and be much more variable.

I know we are not talking cables in this thread, but it is a directly related issue, including cable length. I much prefer keeping amps close to speakers allowing short speaker cables, using longer, low capacitance interconnects as necessary, preferably balanced. In my experience subjectively, speaker cable length may tend to have a bigger effect on sonics than the length of good interconnects. But, maybe that is not true with tubes or a passive preamp. Some DIY experiments with unbalanced (actually quasi-balanced 2 conductor plus shield with RCA connectors), high capacitance, bulk Belden interconnects of different length revealed substantial HF rolloff at 10 meters in my all SS system. They sounded fine at 1-2 meters, though, and I used them that way for years.

Low capacitance, balanced interconnects need not be expensive. Pro studios use them all over the place for mikes, etc. I use 4 balanced XLR pairs each at 10 meters obtained from bettercables.com for the surround and back amps and speakers in my 7.1 setup. They have excellent electrical specs, especially capacitance, and they passed the listening tests against shorter lengths and against some hyperexpensive, 2 meter Cardas I was using at the time with flying colors. So, I switched and used them for all 8 channels, even the short lengths, now all coming directly from my small footprint Exasound DAC to my amps and sub. (There is no preamp in my system.) I am quite happy sonically, and I saved a big bundle vs. "audiophile" cables.

 

[Thomas savage]

Low output impedance into higher input impedance is the general rule, usually looking for a 10x ( I believe) input impedance, but as has already been stated usually not an issue unless you are using valve gear passive preamp , highly capacitive long cable runs.
Keith.

If you don't think understanding overall system gain is nessersary, just strap whatever to whatever read this!

It's a all to common happening!

http://www.hifiwigwam.com/showthread.php?135756-Help-Gain-from-XLR-over-RCA&p=2331562#post2331562

That is what guys need to avoid and understanding simple measurements will enable them to do this..albeit his speakers might also be a issue, not sure.

 

[Ethan Winer]

The article is about being aware of gain in your system... When putting pre amp and power amp together Not simple turning the volume knob down...

But that's exactly what volume controls are for. If I were presented with two pieces of gear that both had very large gain ranges, I'd set the preamp's gain so it outputs about 1 volt while playing a loud passage, then adjust the power amp's gain to play about as loud as I'd ever want. Boom, all done! Then you use the preamp's gain as the main volume control. This is not rocket surgery!

So even a hifi dealer is ignorant in this instance.

Impossible! That never has happened!

--Ethan

 

[Thomas savage]

Another guy having the same issue but with vinyl..

http://www.hifiwigwam.com/showthread.php?135823-Gain-on-Vinyl

A useful reply to that thread from a member there but I want to inform folks so this never happens !

Originally Posted by freefallrob
The 834P is a high gain phono stage. In my experience with it, it some circumstances it can overload the inputs on some integrated amplifiers/pre - amps.
Indeed. 2.2mV or 220uV input for 1V out is about 12dB more than normal. With a 5mV MM cartridge on a hot LP, output could be 20V!!!

I'd go for a 20dB attenuator rather than the 15dB I suggested earlier.

S