Active vs Passive Pre amps

David12: The passive seemed more neutral and detailed, the ARC a little rich and lush. I know you are supposed to lose dynamics with a passive pre.

Hi David, first off your system as you have found just by listening, is a perfect impedance match for passive preamps as are most others out there.

Your ARC Ref 75 has a great 300kohm input impedance, 1.5v input sensitivity for full output and your Resolution Audio Resolution Audio Opus 21 has 2.5v output at 100ohms absolutely perfect for any passive.
And your speaker are 96db, efficient no need for extra active preamp amplification.

As for passive and dynamics, if I can explain, this belief is a total "furphy". If a passive preamp is a good impedance match as you have, they are more neutral have better detail and more dynamics than any active preamp.

The only way an active preamp can have better dynamics than a properly implemented passive as you have, is if the active preamp has a "dynamic range enhancer" (DBX) built into it, which sound like rubbish.

An active preamp cannot make better dynamics than what the source is giving, if anything they can only diminish dynamics, as all active components have losses when compared to source to amp direct in, like a well implemented passive can mirror.

Read Nelson Pass's quote on passive preamps.
" Nelson Pass,
We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp."

Cheers George

You are correct David12, this isn't a new subject here at all, in fact, it's quite old. It seems to come up once every week or two.
Just as any debate here on these forums, tubes vs. solid state, digital vs. analog, etc., there will be proponents of both sides. In the end, all that matters is what you think.

Thanks for your comments everyone. As to the dynamics issue, if there is one, some of you dispute that, I thought there was a difference between resistor and transformer based passives. My unit uses the same transformers as the MFA Baby reference. Again, my understanding is that transformer based units have less limitation on dynamics and headroom.

It sounds like I am going to have to spend a lot to improve on my passive unit, which only cost me about $1400 second hand, less than the cost of the transformers themselves.

Has anyone any comments on the quality hierachy of the ARC pre's. My understanding is that it would be in this order LS27>Ref3>LS26, I may be wrong.

I would just replace the pots in your passive with 42 Stepped Ladder type.....or you might try the more recent smd type pot. I'm using one now and prefer it to ALPS. With a resistor based stepped ladder you can choose the type of high end resistor you like....Dale tend to be faster while Takman seem to be more romantic. I think from what you have described you'll prefer Dale.

So, keep your passive and just replace the pots......you'll save a bundle while upgrading your preamp and providing you the gain control you desire. This is a simple solder job...if you are not comfortable your local repair shop should be able to do it for under $35. The cost of the pots should be around $70.00. Remember to order the correct impedance for you pots to match your amp.

Thanks me later!

Oops.....I should have done my research on this passive before wading into these waters. Your pre is transformer based and pot replacement is not as simple as a non transformer based pre. There are other passives that have 48 gain settings...you might try them. Akustyk is a great option....and can be customized to your needs.