The Simplest Pre-Amp

[hermanv]

Posted by anatech
Your comment about distortion is completely unfounded. You are looking at it in isolation away from the inevitable interactions with some input circuits. There are times you need some current, not directly related to input resistance. As far as noise is concerned, that's a very dangerous viewpoint. All I said was that you have a reasonably high impedance source driving a cable. There is a reason why we don't run turntable leads very far, and your low levels for good S/N run about the same magnitude.

You are starting to grasp at straws, if there is some kind of magic, undefined and unknown interaction you can not rule out that this same interaction will not happen with an active unit.

Turntable signals are in the humdreds of microvolts to 5 millivolt range. Large gains are required as well as extensive frequency shaping to amplify them. This just has nothing to do with discussions about passive pre-amps operating at 2 VRMS.

This site is not only for those just starting out, but that is irrelevant. It will be a rare case where the passive encounters the problems you imply are legion, it is just not so.

As a repair person is it possible that you only see the worst equipment because the good stuff never makes it to your lab leading you to conclude that all equipment is equaly represented by your work samples?

An engineer would agree with this I think.

I am an electronic engineer, I think it's kind of clear I don't agree.

[anatech]

Hi Hermanv,
Groan. What are the levels at the input to the amplifier for the finer details? That's my point. You are looking at the wrong end of the gun.

I am not looking at "magic", or grasping at straws. I merely stated that the reason for the effect was unknown to me. I was brave enough to report it honestly. Others have noticed this effect as well. I did give you a test you could try yourself. With your hearing acumen, you should be able to hear this easily.

Yeah I work on junk. Conrad Johnson, Nakamichi, Marantz, McIntosh .. on and on. Oh yeah, it's new. I modify units to solve problems that escape the lab - while talking to the design engineers. Yup, we're working together. Shocking to you I'm sure. I solve basic engineering errors that were created by engineers. Not true but I'll say it. Engineers design the stuff, technicians make it work.

I didn't ask you to agree with me, I know some that do. That's enough for me. I think that you should do some experimenting.

-Chris

[hermanv]

I did not mean to get personal, a passion for musical truth is good.

I have done many experiments and find that my conclusions dissagree with yours. I know the math allows one to fall near the middle ground of the discusion but I haven't heard a passive have problems like the ones you are concerned about. Have I heard all possible passives in all possible circuits, of course not.

I like short cables, because I think they sound better and since I like good cables they cost less too.

I worry about grounds so my equipment collection might be more immune to problems with passives, but the grounding I use is not extreme or weird just common sense. I have taken my passive to other's homes where they too marvelled at what was possible and set about "fixing" what was wrong with their pre-amplifier chain.

The passive may not be for everyone, but I encourage a trial in your personal system because you will be hard pressed to find a solution at any price that beats this nice simple idea. So I will repeat myself: I have heard nothing at any price that outperforms a well made passive pre (and no, I don't sell them or work for anyone who does). And even though I accept that there might be problems in some systems I personally have never heard these problems.

[carlosfm]

Originally posted by hermanv
Without opening commercial products for which many of us paid big bucks, the well made passive pre offers exceptional bang for the buck.

Are you afraid to open it?
Don't be, you don't know how huge improvements you can make inside, incompetence is everywhere, at every price.
I once opened an integrated Krell.
It was more the parts that I removed than the ones I changed inside.
Input buffer stage=out, next: electrolythic DC coupling caps = out, dac volume control (let it be), electrolythic DC coupling caps (again!!!) = out, OPA2604 op-amps = changed.
Input of power amp: electrolythic DC coupling caps (!!!!) = changed for better ones.

PSU, etc, etc, etc...

Yes, the deam Krell sounded very bad to me in original form (I don't understand the hype), and hey, it was a 6000 Euro amp!
I just made a service to an unhappy friend, he loves the amp now. Not because it's pretty or because it's a Krell. It's because it sounds good.
But a modded Pioneer A400 also sounds good.

[anatech]

Hi Hermanv,
Fair enough. I have tried this.

I have tried some passives with varying results depending on the amplifier. Generally, I find they work best with tube or J-fet based first stages. Some bipolar diff pair type amps will not sound as good without a higher drive current.

If you get a chance, have a listen to a Nakamichi PA-7. They are quiet. Another preamp you may want to listen to is a Marantz SC-9. I am sure there are others.

Funny story. Nakamichi came out with "HTA" series amplifiers. New technology they said. The Marantz 500 used it years earlier. It was simply a class A buffer in front of a bipolar differential pair.

-Chris

[carlosfm]

Originally posted by anatech
I have tried some passives with varying results depending on the amplifier. Generally, I find they work best with tube or J-fet based first stages. Some bipolar diff pair type amps will not sound as good without a higher drive current.

Yes, that's exactly my point, that's why I said one has to know the insides.
It is related to the first stages' input impedance, it's not just a question of what value resistors are there shunting the RCA inputs.

[anatech]

Hi Carlos,
So true, and on that we totally agree.

-Chris