2. amps-preamps
  3. 1090350165

Impedance Question: Tube Preamp with SS Power Amp

Having researched this issue with the archived threads, I am still having difficulties understanding the problems of impedance mismatch between Pre and Power amps. As a budding audiophile moving onto my first separates Pre/Power, I want to know more about impedance matching. I have several questions that I hope veterian audiophiles can help me out with.

1)Is the 10:100 ratio between the output impedance of preamp and input impedance of the power amp an absolute rule?

2)What would happen if impedance mismatch do occur? Will the sound be any less satisfying?

3)I understand that Tube preamps generally have higher output impedance values compared to SS, so does that make it problematic to use it with a SS power amp even though tubed preamps are often priased over their SS counterparts?

I ask these questions because I recently purchased a tubed Preamp (Musical Design SP-2B)that has an impedance of 2K Ohms. I want to match that with a SS power amp with an impedance value of 20K Ohms. Am I cutting it too close? (exactlly 10:100 ratio) Or are all of these issues irrevalent and I should just listen to that setup and hear for myself if it would work or not? Thanks in advance for the answers.
speedracerucr
morbius396c
134 posts
 
John,

The Krell amps are "direct coupled" - that is they don't put
capacitors in the signal path. This is an advantage since
"coupling capacitors" can have a negative impact on the quality
of the signal.

Krell amplifiers also have DC protection circuitry which will
shutdown the amp if too much DC signal is seen at the input.
Too much DC can be damaging.

Unfortunately, many tube amps output a signal with a DC
component above that which will trigger Krell's protection
circuitry.

In order to use a tube preamp with a Krell amplifier - Krell
advises that the normally inactive coupling capacitors in
the Krell amp be activated by a Krell dealer.

Dr. Gregory Greenman
Physicist
johncusick
10 posts
 
So where do I go to find out if my AR Ref One MK2 is one of those tube preamps that puts out too much DC ???
morbius396c
134 posts
 
John,

I'd contact either Krell or Acoustic Research or both.

I'm sure you're not the first to hook an AR pre to a
Krell power amp.

Perhaps the two manufacturers have some experience - either
directly or garnered from their customers.

Dr. Gregory Greenman
Physicist
johncusick
10 posts
 
Just to follow up - I spoke to Leonard at ARC and he clarified for me the fact that the Ref One has DC capacitors in it's output to filter DC from the Amp. So unless a tub blows or some such crisis the Krell's should be ok. He thought it to be a reasonable gamble to leave the jumpers in the Krell so as to keep the capacitors out of the signal path.

Thanks all
John
vladimir
346 posts
 
Impedance mismatches in this way affect (diminishes) the very low bass; some of those who say they don't have any problems may be due to the fact that they don't own really full range speakers.
More to discover