[BrokenEnglish]

my integrated harman/kardon amp is getting weak in some parts (balance-pot etc.) and i'm searching for a solution to replace it in the nearer future. so i thought of asking some of the diy-manufacturers to build me a passive preamp. all it has to have are 3 switchable inputs (cdp, tape, reserve), 2 paralleled outs (poweramp & tape-in/ppa) and some decent volume-regulation (alps blue?). i don't need all these bass-, treble- and balance-pots at all.

for listening through speakers i want to combine it with an used rotel-poweramp (eg. rb951). the phones are going to be feeded with the ppa. my main source currently is a sony scd-xe670 (entry level cdp/sacd)

do you think a passive preamp would be enough to power one of the smaller rotel-poweramps? or should i just purchase an (low-cost) active preamp?

 

[nilanjan]

It depends on your speakers. You shouldn't have any problems with highly sensitive speakers. If your speakers are not sensitive, you may need the additional gain from an active preamp.

 

[drewski]

Most of the complaints about passive preamps are about bass and dynamics. I had the McCormack TLC-1 which is highly rated in the passive mode. I thought it had a really sweet top end, but I couldn't get any dynamics out of it and eventually the soft sound got old. I've been told by others here on this forum that they've had success with the McCormack and I could have had problems with impendance matching between my amp and preamp.

But I did end up getting another passive- a Dact attenuator. This only had a single in and a single out with a dact attenuator in between- so it was basically a volume control. This sounded much better with my system- it had bass, dynamics, nice imaging, and great highs. It costs about $200US to put together and I'd compare it to any $1000 preamp out on the market today- it just didn't have any component switching capabilities.

There are also some prebuilt solutions- building something like this may be more expensive than actually buying new- the Placette remote volume control gets raves although I've never heard. Also, the Goldpoint controls http://www.goldpt.com/ are supposed to be decent as well.

Good luck!

 

[BrokenEnglish]

thanks for your suggestions so far, fellows!

nice idea, drewski... the dact attenuator attracted me more than once. put a switcher in front and it should do a fine job, right?

nilanjan, well.. i really don't know if my speakers (magnat vector55) are sensitive/insensitive. the little harman (hk6150) is able to drive them well, but most likely not at their best. actually i thought dynamics and bass depend solely on the poweramp. but i never had a pre-/poweramp-combination before. thanks for your statement!

 

[Joe Bloggs]

Not speaking from personal experience here, but I hear that the main problem with passive preamps is that you can't do long cable runs with them (from the source to the power amp).

 

[kentamcolin]

I use an Adcom SLC-515 (passive pre) in a system at home. You can find these in great condition for around $100. They "sound" good, absolutely black background and have a tape loop so I believe you can connect your headamp as well as power amp. I can test mine that way if you'd like to know for sure. No tone controls, just volume. I powered 89db speakers through it with a 60 wpc amp with great results. Didn't seem to be lacking any dynamics.

 

[nilanjan]

I hope you find this article helpful:

http://www.stereophile.com/reference/917/index.html

 

[Large4mat]

nilanjan is right. I once used a McCormack Micro Line Drive in passive mode with a Sound Valves tubed amp (Glorified ST-70). It sounded wonderful but it wouldn't reach satisfying levels when some of my music collection called for it. I don't have very efficient speakers, and that may have made the difference. I ended up buying a Fisher 400 receiver and never looked back. It killed the aforementioned combination and had a dynamite headphone jack to boot.

 

[gerG]

imho passive is the best sound quality. The only risk is if your amp does not have enough gain to play loud enough from your source. A simple test is to connect the source directly to the amp. This will be the max level that a passive will achieve. If the level is high enough for you, then a passive is the answer. If not, then you need more gain, either from a different amp, or an active preamp.

I am quite impressed by the PSAudio preamps. They will work in either passive or active mode.

btw, the only difference is an additional gain stage. Dynamics are unchanged, but the extra electronics of an active preamp will introduce extra distortion.

gerG

 

[Nick Dangerous]

If I tried that, my speakers would explode unless I played very, very soft music.

 

[kentamcolin]

I would NOT recommend connecting your source directly to your amp unless your source has a variable output (volume control).

 

[gerG]

Oh come on, what is a little extra ozone when the smoke escapes frome the tweeters

Anyway this is how I tested to see if a passive preamp would be sufficient. The DC hookup gave me just exactly the right sound level, but I did approach it with more caution than abandon. Sneaking up with soft music is a given. Hey, the 1812 overture starts out soft, right?

A more sane approach is to disconnect the amp, match the voltage output of your praemp to that of your source, and mark the volume control. Then you can hook the preamp back up and carefully ramp the volume control up to the mark. That is equivalent to the max that you will get out of a passive.

btw, the direct hookup sounds cleaner than any preamp possibly can, passive or otherwise.


gerG

 

[BrokenEnglish]

thanks a lot for your feedback, fellows!

nilanjan, the 1:10 ratio between output impedance of source and input impedance of poweramplifier they recommend in your linked article is hard to obtain: my (sa)cdp has >10kOhm, the rotel rb951 32kOhm. may it would be necessary to adjust values via certain resistors that have to be installed in the passive preamp, if possible?

furthermore this could explain different sound-experiences with different passive preamps some of you reported...

for the moment i tend towards a diy-manufactured passive switchbox with stepped attenuator as pre"amp". well... for the moment...

first of all i have to save up some money, then i have to talk with fiddler...

 

[JaZZ]

BrokenEnglish...

...are you sure your SCD-XE670 (?) has an output impedance of 10 kOhm? I really doubt it. The common values go from 100 to 1000 ohm. 10 kOhm would exclude a passive operation, at least in cooperation with a 32-kOhm load.

In my own system I have a Bel Canto DAC2 with 20 ohm and a Philips DVD 963SA SACD-player with 200 ohm output impedances; they are connected to a passive pre with an Alps 10-kOhm potentiometer, which controls a Metaxas Solitaire with its 100-kOhm input. That's a very uncritical combination. But it also works with my Hitachi tuner and its 2 kOhm, and it also did with my former Rotel RB 880 with its 25 kOhm input impedance.

The 1:10 ratio is a good rule of thumbs. A ratio of 10:32 most likely won't work though. But as I said, I doubt the 10 kOhm. But I might be wrong.

Apart from such problematic cases I agree with gerG: there's no other way to reach such a low signal degradation than with the passive solution, as long as the electrical values allow it. Even the potential frequency-response degradation by certain capacitance effects (with relatively long cables) may have a minor sonic effect than the additional amplification stages an active preamp puts into the signal path. So if it's sonic purity you're after, go passive! But take care to clarify your source's output impedance... or get yourself a better source, if you're at it!

 

[BrokenEnglish]

thanks, jazz...

...the user-manual of the sony scd-xe670 specifies a "load impedance" of "over 10 kiloohms" (!). couldn't believe it myself. maybe "load impedance" refers to peak-values? no other specs available...