2. amps-preamps
  3. 1080847496

Understanding impedence matching

I am a psychologist and my eyes start crossing when the conversation gets too technical, but that being said, I am beginning to wonder what impedence matching means and what I should pay attention to as I upgrade my setup.

The two pieces in my system that are likely here to stay for a while are my SF Electra Amator II, that evidently don't drop below 6 ohmns, making them receptive to an OTL amp, and my Cary pre, that has phono impedence @ 47K (evidently this can be adjusted) and output at 800 ohms. I am in the process of upgrading my amp and TT.

What does this mean in terms of how I think about these two acquisitions?? Are there specific numbers I need to pay attention to, and/or formulas for these, or is it all in the listening?

As always, thanks for your help. This community is amazing.
ccryder
subaruguru
1,369 posts
 
Still with us, Cc? Just be careful to home-demo ANY amp you try with a relatively high output impedence, like many tube amps. Simple.
ccryder OP
45 posts
 
Thanks for asking, Subaruguru. I am tracking, except for when I'm not! The main upshot of all of this is that I am going to want to find some coherent, organized introduction to these issues, as I would like to pull back the veil a little. Any suggestions? The links people have provided seem to start in the middle, given my starting position.

And, I also understand that there is the same kind of impedence issues with the TT/cartridge and the pre-amp. I assume the same principles are involved. Is that right?

But, whether I understand it all or not, I am really enjoying reading and appreciate people's input.
morbius396c
134 posts
 
Ccryder,

The interface between the TT/cartridge and the preamp does
have to be impedance matched. However, cartridge makers and
preamp makes have standardized this interface to be a 47k ohm
transmission line - so you don't have to do anything special.

Likewise, all your interconnects are 75 ohm transmission lines
which is also standardized - and therefore impedance matched.

However, for the power amp to speaker interface there is an
intentional mismatch - so as Sean states - the speakers
can't feedback to the amp and modulate it.

For this interface, you check the specs of the power amp
or receiver - that will tell you the minimum load impedance
that the particular amp will handle properly.

Best wishes.

Dr. Gregory Greenman
Physicist
subaruguru
1,369 posts
 
...if it's a tube amp ask for the oftentimes dirty little secret of it's output impedence. This will give you a hint as to how much relative frequency response trampolining can occur compared to another amp. Again, you have to home-demo WITH your speakers. Don't make a career of reading about this...it'll come down to how the amp mates with your speakers. If you become obsessed with amplifier output impedence just get a nice ss amp....
ccryder OP
45 posts
 
Hi Subaruguru,

The only problem is that I am probably going to buy it over audiogon, so home audition may not be an option.... I had another thread earlier asking people who have the same speakers what amps they have found works well, and of course, got several differing opinions! I got a book by Robert Harley that explains some of the electronic basics, so I am learning, slowly. Thanks again for your help and input.
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