Impedance Mismatch ???

I am currently running an amp that has 600 ohm input transformers. This tube amp does not match up well with anything but a linestage that also has 600 ohm output transformers (I have such a linestage). A friend has a different amp that also has input transformers (also 600 ohms) that is hard to match with linestages. None of his tube linestages work well with that amp, and even solid state linestages that do not have an extremely low output impedance is not ideal; he runs that amp with a Levinson No. 32 preamp which has a very low 20 ohm output impedance into unbalanced lines (10 ohms into balanced). This is another example of rare, special requirements.

Viridian, thanks for the link - very interesting. Current loops like 4-20mA became at one point industry standard for their inherent immunity to noise or resistance of the cable especially on very long runs. Current source has very high output impedance making more difficult to induce currents in the loop.

usually impedance is measured at 1000Hz signal that may show different values.

It would be a good question to ask Jeff Rowland. I'd be interested in the answer.

There are always tradeoff issues in designs. I'm sure Rowland know what his are for each particular product.

Larryi, that might be the case but when he designs whole amp (instead of using Icepower modules) most likely he has option of setting 10k or 40k input impedance without extra stage. It might be electrical noise issue since higher impedance input is more likely to pickup interference. Preamp side is low output impedance, but not at the radio frequencies where it might be tens of kiloohms. It is tradeoff between performance of the best amp and convenience of matching for lower end amps. It is feasible that, as you suggested, he targeted class D amps for use with tube preamps while his new model 625 is class AB.

Could be.

I would probably not be concerned with most any amp input impedance 10K or higher for use with SS mainly. Use of higher output impedance tube pre-amps is the scenario that is more problematic. Tube pre-amps are popular with audiophiles these days but are probably still a very niche market overall. Many amps including stock Icepower have only 10K input impedance. That may just be the most practical approach with the most appeal.

I love the sound of my ARC tube pre but I am sure there are similarly good sounding SS pre-amps out there for reasonable cost as well. My next pre-amp I buy and keep someday will likely be SS as long as it is not a step backwards from teh ARC.

I say that because even my 30+ year old SS NAD 7020 receiver that I am using in my family room system today as a pre-amp only with the TAD Hibachi amps and OHM 100S3 speakers sounds very good, although it is guilty of a touch of that warmer sound that NAD can be known for. Its' my long time spare unit that I put it in to replace my similar older Carver pre-amp in that system when the Carver developed a problem needing repair. I would like to try a newer good quality SS pre-amp in there sometime soon when I can come up with a good justification at which time I might try a shootout for my ARC pre-amps place in my main system.

Adding an extra stage to increase input impedance to 40k probably degrades sound a little bit, so not doing so would be an improvement. The trade off is less compatibility with tube linestages which can have fairly high output impedances. Rowland may have decided that the tradeoff is worthwhile, either because of the performance gain and/or because tube linestages are unlikely to be used with that particular amp.

Strangely, Jeff Rowland increased ICEpower module input impedance from 10k to 40k by adding extra amplifier board on my model 102 amplifier but released brand new all his design model 625 that has only 10k input impedance. Does he know something we don't?

Well Thank you Gentlemen for the quick reply and the analogy of the drumhead being struck helps nicely !
From now on, the impedance rating will be part of any amp and preamp that I might ventue on to.
Actually been looking around for a little while now and that`s how I stumbled across this subject !
Thanks again guys !

Agree with Viridian that on paper you are in good shape.

FWIW, vendors that design amps to match well with most any pre-amp, including most higher output impedance tube pre-amps, may go even higher with their amps input impedance as an insurance policy, in that actual impedance varies with frequency. So, for example 100 ohm output impedance is a genralized measure across all frequencies. Impedance at some frequencies may be much higher, thereby lowering the ratio and potentially impacting sound.

My rule of thumb is 30K SS amp input impedance is towards the low end I would use to have a decent insurance policy against issues that specs may not reflect accurately,like actual impedance at specific frequencies.

FOr example, in researching Class D Icepower amps, 60K input impedance is designed into the Wyred amps to help assure optimal results with most tube pre-amps. The BEl Canto ref1000m amps I use have 100K (unbalanced) input impedance. Balanced is double that even as I recall.

My TAD amps have similar 30K or so input impedance as I recall. I could hear a difference in sound with those versus my BCs that might be attributable to input impedance. Hard to say for certain with two different overall amp designs.

So its possible you might hear some difference with say a similar SS amp with 60K or higher imput impedance.

Higher amp input impedance can often result in a relatively leaner sound. That may or may not sound best to an individual, depending on personal preference and synergy with system overall including speakers and room acoustics.

SO a lot depends. Regardless, being aware of impedance matching considerations is a best practice IMHO that might lead to some useful and perhaps even predictable comparisons of value over time.

Better impedance matching should deliver better dynamics and lower distortion. For example, the difference is analogous to the difference striking a drum with a proper tightly drawn drumhead versus one that is less so.

Impedance matching of output to input matters between each pair of components, from source to speakers. Pre-amp to amp and amp to speakers (refered to as "damping")are the two that get the most attention. Wires/ICs can also have impedance characteristics that matter and can be used to "tweak" the sound, but meaningful specs to chose wires based on this are hard to find and usually involves more trial and error.