How important is impedance matching.

[DANGERDAN]

Preamps were designed in their original days as a first stage
amplification as all or most sources were a low line level output of
around 10mv and were amplified to a more acceptable voltage of 1v+, this
would ensure that the Power amp which is the second stage amplification
delivers the current sufficient enough for a acceptable output.

So the first stage and second stage phase were important for a sufficed
power output, but this is not all that the preamp was made for, it has
to also adjust the impedance to match with the power amplifier because
the low level line output is not the same and can cause distortion so
its important to match the signals as best as possible to avoid this.
There are other things a preamp does but i dont think its relevant in
this discussion as they are too minor.

So impedance matching how important do you think it is ?, do you think
pre amps are still needed because of this requirement or should it be
nothing to worry about (from a audiophiles perspective). What is a good rule of thumb when matching impedance between equipments ?.

[JJkizak]

Impedance mismatches can cut transfer by 50% if you mismatch it enough. There is also at higher frequencies the reflected component called VSWR. Pure resistive pads (20db) can reduce the VSWR to almost nothing. At audio frequencies I would just personally use good cables designed for interconnecting units. Units of the same brand will be better off (most/some of the time) than different brands. In the real world you can spend $5.000.00 for interconnect cables which in my opinion are $4,950.00 overpriced. There are many threads on cables on this forum with just as many opinions. Some claim if you use a coat hanger you can't tell the difference in the sound. You never know however what other high frequencies are bouncing/floating about between units of cheap design. And don't use 50 ohm cables when 100 ohm are required.

JJK

[Arkytype]

In the good ol' days of telephony and radio, impedance matching (using transformers and passive filter networks) was the norm as one wanted the maximum transfer of power from one device to another. 600 ohm source and load impedances were common.

With today's gear, one is only intereseted in impedance bridging and we want the maximum transfer of voltage between devices. As a rule of thumb, a 1:10 relationship between the output impedance of say a preamp and the input impedance of a power amplifier will ensure flat frequency response and minimum signal degradation especially if you have a long cable run.

Lee

[Don Richard]

High impedance sources need to go into very high impedance inputs, 10X to 20X greater. This could eliminate a recommendation to use certain vacuum tube preamps with certain power amplifiers, usually solid state power amps. Check output and input impedances to be certain of compatibility.

[Edgar]

And as for concerns about standing waves, even if the signal travels through the wire at only 50% the speed of light (it's typically faster than that), at 20 kHz the wavelength is 7500 meters, or about 4.66 miles. Until the length of your interconnect is a signifcant fraction of 1/4 wavelength, transmission line effects don't even exist.

Greg

[Marvel]

High impedance sources need to go into very high impedance inputs, 10X to 20X greater. This could eliminate a recommendation to use certain vacuum tube preamps with certain power amplifiers, usually solid state power amps. Check output and input impedances to be certain of compatibility.

The best reply yet!

I cannot use my JM Merlin preamp fed into most SS amps. The combination works like a filter and I have almost NO bass. One of the Blueberry models had a low impedance output, which took care of the issue if you had that problem.

Bruce

[DANGERDAN]

Ok so a preamp with say 100ohm connected to say 10-30kohm poweramp is a preferred matched impedance ??.

[Edgar]

Ok so a preamp with say 100ohm connected to say 10-30kohm poweramp is a preferred matched impedance ??.

It's not so much that it's "preferred", and it's certainly not "matched". It's a situation in which poor matches can be identified (high impedance driving low impedance), but just about everything else (low impedance driving high impedance) qualifies as "OK". So 100 Ohm driving 30 kOhm is not intrinsically better than 100 Ohm driving 10 kOhm -- both are just fine under most circumstances.

[DANGERDAN]

roger i get ya.

[DANGERDAN]

In saying that does that indicate at all that we still need pre amps, with the equipment technology that we have today a lot of source devices like blu ray players, computer sound cards, external DAC's all can put out around 1v+. Would we not benifit today by removing this possible useless link in our chain of audio connections, unless the preamps are still good for something else i dont see what could be of optimal use.

[Edgar]

There are still the issues of source switching and volume control. Many DACs can switch between multiple sources, but not all of them can drive passive volume controls very well. In such cases, the buffering provided by a preamp can be beneficial.