Preamp Impedance

Harmon · « **on:** 17 Aug 2003, 07:59 pm »

Hey guys, is it good sonically for a preamp to have a big disparity between its input impedance and its output impedance. For example, 33.5k ohms input impedance and lets say 100 ohms of output impedance.
Thanks

john curl · « **Reply #1 on:** 17 Aug 2003, 08:26 pm »

Yes, it is one of the main reasons that we make active preamps. Just a volume control will actually do most of what a preamp needs to do, BUT it will have a fairly high output impedance, up to 1/4 the input impedance. Lower output impedance that stays the same with different volume settings is best.

John Casler · « **Reply #2 on:** 18 Aug 2003, 12:11 am »

Hi John,

Good to see you over here.

It's funny, I was posting just the other day about the "Good Ole Days" (before there was an internet, and you, myself, Cory Greenburg, Saul Marantz, Jonas Miller, the guy who started NHT (whose name I always forget), and many, many others frequented a "bulletin board" called TAN or The Audiophile Network.

This must have been in the early/mid 80's. Well times have changed but passions haven't.

Welcome

shokunin · « **Reply #3 on:** 18 Aug 2003, 12:51 am »

Yo John (casler) ... psst.. "Ken Kantor". BTW, it's nice to see Mr. Curl and Crump over here on audiocircle! Welcome!

KevinW · « **Reply #4 on:** 18 Aug 2003, 02:10 am »

As John Curl says, active preamps are designed to have a high input impedance, and low output impedence. You always want the "upstream" component in the audio chain to have a lower output impedance than the "downstream" component's input impedance. Otherwise sound quality will suffer significantly.

In fact, impedance matching is one of the reasons people talk about system synergy. If various components don't have complementary impedance profiles, bad things will happen to the sound. That's how one component can sound great in one system, and poor in another. There are other factors of course, but impedance matching is one of the less obvious reasons.

EDS_ · « **Reply #5 on:** 18 Aug 2003, 01:58 pm »

Quote from: john curl

Yes, it is one of the main reasons that we make active preamps. Just a volume control will actually do most of what a preamp needs to do, BUT it will have a fairly high output impedance, up to 1/4 the input impedance. Lower output impedance that stays the same with different volume settings is best.

Wow!
When Mr. Curl speaks........I will listen. I've never seen this topic explained in five lines before.

Paul L · « **Reply #6 on:** 18 Aug 2003, 06:23 pm »

I think that is too generalize. Does an active preamp must have an input stage before the volume? Not all of them have. If so, if this stage can be incorporated in the source if the source output is implement correctly. Does an active preamp must have an output stage after the volume control, I think all of active does. But this stage again can be incorporated into the driver stage of the poweramp. A high input impedance in the poweramp driver stage and low impedance to its next stage is just like the active preamp. That leaves the volume control alone like a passive controller. Why spend money to buy an active preamp to introduce another variable or "system synergy". Isn't it more cost effective by buying a properly designed poweramp that does the job an eliminate the another active stage.

Curt · « **Reply #7 on:** 19 Aug 2003, 10:24 am »

Yes, an active preamp will perform best with the first active stage coming before the volume attenuator. This is how IRD preamps are designed.

No, putting the first (preamp) active stage into the source or the last (preamp) active stage into the amp will not work, essentially that is the same thing as using a passive attenuator volume control. It's the interconnect cables and connectors that cause the problems and demand an active preamp be self contained.

A well designed active preamp will sound better than a well designed passive volume control in almost every system.

MaxCast · « **Reply #8 on:** 19 Aug 2003, 12:13 pm »

Those specs up there are pretty close to a Purist

This is a good post with responses by some knowledgeable people. Would someone care to explain how these in/out impeadances effect each coponent as each "sees" these impeadances along the signal chain?

Impeadance is resistance, correct? Does a higher number offer more resistance or less?

Paul L · « **Reply #9 on:** 19 Aug 2003, 01:59 pm »

Maxcast,
I have a post in audioasylum explaining how the source see the volume, i/Cs control and poweramp, and how the poweramp see the source, I/Cs and volume control. It is not unlike the active line stage that see the first stage of the and volume control. You can do a search there using Paul L as author and the subject is about x-coupler. Don't want to turn this post into passive vs active thread. Just use your ears to decide which is better for your system.

Sa-dono · « **Reply #10 on:** 19 Aug 2003, 06:27 pm »

Quote from: Curt

A well designed active preamp will sound better than a well designed passive volume control in almost every system.

Curt,
Let us please leave gross generalizations out of here. If that is your opinion, then fine..but please avoid stating your opinion as fact.

From my own experiences, I have actually found passive preamps to greatly excel over active preamps in the price to performance category (and even in just the performance category quite a number of times).

Quote from: Paul L

Maxcast,
Don't want to turn this post into passive vs active thread. Just use your ears to decide which is better for your system.

Completely agreed. As always, this will be system dependent (as we want that synergy) and based on personal tastes.

Curt · « **Reply #11 on:** 19 Aug 2003, 08:15 pm »

Sa-dono and Paul,

No offense intended, it is my opinion and my experience with passives. And, I was talking about high performance units (well designed) not best buy units.

When I read Paul's post it was against every experience I've had in electronic design, so I put in my 2 cents.

Many people choose a passive to save money, that's OK, but I believe there is a trade-off for the savings. It's not often you get a free lunch.

I don't believe I'm alone in this opinion, but I cheerfully agree to disagree. I wasn't looking for a lengthy discussion either just chatting.

This is what makes audio stimulating, all the different possibilities, and opinions. Each to their own.

Sa-dono · « **Reply #12 on:** 19 Aug 2003, 11:42 pm »

Quote from: Curt

Sa-dono and Paul,

No offense intended, it is my opinion and my experience with passives. And, I was talking about high performance units (well designed) not best buy units.

When I read Paul's post it was against every experience I've had in electronic design, so I put in my 2 cents.

Many people choose a passive to save money, that's OK, but I believe there is a trade-off for the savings. It's not often you get a free lunch.

I don't believe I'm alone in this opinion, but I cheerfully agree to disagree. I wasn't looking for a lengthy discussion either just chatting.

This is what makes audio stimulating, all the different possibilities, and opinions. Each to their own.

No worries Curt. We're just definitely getting into opinion territory, and I just want to make sure everyone is aware of such.

I will also state that I am not just talking about best buy units, but the very high-end units as well. I know of numerous people that have compared some of the top passives against top active units from Levinson, Pass Labs, and the like (meaning as much as $18K or more)..with them preferring the passive.

I agree to each their own..as that is what makes audio fun. There's a million routes..and all that matters is reaching a point where you can be happy with your system.