Passive preamps - suggestions / advice

Thinking about getting a preamp now that I'm using active speakers. I've seen some passive preamps and wondered what issues, if any exist. Also general opinions from users if possible?

Thanks in advance.

 

Well, you need to pay attention to impedance matching between source and the amp/active speakers, and cable capacitance, and voltage output of the source shouldn't be too low. You can google for the specifics.

My general opinion is passives can be quite nice, but i prefer my active pre. But I haven't heard any of those very expensive transformer based passives.

 

Your speakers (as listed in your profile) appear to be sensitive enough for a passive, but their input impedance, 10K, is a bit low for a conventional passive. 20K and above is generally recommended, with higher numbers being better.

You could use a buffer with a passive, but it kind of defeats the reason for using a passive.

A lot of folks running the Crown XLS's have been using the Ifi Itube with good results, using it as a buffer or a one input preamp with gain.

I don't miss using an active pre at all. However, my amps are very low input sensitive & have high input impedances.

 

Well, I sell the "expensive tansformer based passives", made by Music First Audio. I am NOT answering this thread merely to try selling one. I AM answering to inform all that the trade-offs of typical resistive passive premaps (that use resistor networks or potentiometers) are TOTALLY different than the transformer passives.

Any passive preamp EXCEPT the transformer based ones create a high output impedance which interacts with cable capacitance and amplifier input impedance in such a way that sound is very often compromised. The primary reason that most preamps are active is to deal with this high output impedance coming out of the resistive volume control. The second reason is to provide gain, which is usually not required. Thus active preamps usually have their volume control set at 9 or 10 o'clock, and all that active gain is just not beneficial at all. The biggest problem with any resistive passive preamp is that as volume is turned down, it's output impedance rises, which causes an even worse interaction with cables and amp. Thus sound degrades as volume is turned down.

Transformer based passives are considerally more expensive to manufacture. The advantage is that when at maximum volume, its output impedance is just a transferance of the source component's output impedance. The preamp does not add any increase in output impedance. Then as the volume is turned down, the output impedance gets LOWER, not higher.

The result is extremely compatible electrical properties into any amplifier. Sound has full dynamics, impedance incompatibilty does not exist, and the sound does not change as volume is changed.

As with all passive preamps, a transformer based passive does not provide gain. The transformers can be wound to provide some gain, in the neighborhood of 3 to 6 dB, but not much more than that. Occasionally, an amplifier with very low sensitivity into low efficiency speakers can result in the passive preamp just not providing enough gain to play the system loud. So, it is best to test in the system.

Of course, before buying any preamp, its best to audition it.

This is no problem at all for a transformer based passive preamp.

 

I guess another advantage of the passive pre is they should last a damn long time. You won't have failing caps or anything. Even the resistor based ones should be pretty bullet proof (not sure about the type that uses light dependent resistors though).

For what it's worth, I have one of these:

http://softone.a.la9.jp/english/Model5/m5-1.htm

a resistor based passive pre. It's very well made, as is typical for most stuff built in Japan, pretty inexpensive, and sounds good. However, it is sensitive to the equipment it is used with, so system matching is important.

 

I have used a Creek OBH12 for many years, with a number of SS amps, where it has worked flawlessly. I should try it with a tube amp, now that I think of it.

 

yawn...

 

How helpful.

 

Thanks for the replies guys. Currently out on the last weekend of the Edinburgh Festival Fringe but appreciate the many detailed responses. I'll read them in detail when I get home.

 

Get one of these:

http://www.tcelectronic.com/level-pilot/

-Bill

 

Sorry; it was way too full of holes and painful to read to even begin to rebut. Have at it...
-Bill

 

Hello Bill, this item looks quite inexpensive. If it indeed sounds as good as our transformer passives (for thousands $ less), I would like to own a couple and recommend them to my customers. Of course I am skeptical, but I wrote a private message to you to discuss in detail.

I hope you will repond privately to me and tell me your experience.

--Warren

 

That looks like a neat solution Bill. I'd need selection capability to switch between my 752BD and AVI Lab Series CD player though. Neat though and just under £60 in the UK.

 

I agree, this is a cute little volume control, for under $100. With the XLR connections, I could use one between my Otari open-reel tape deck and some kind of compact monitoring power amp and speakers

This is definitely not an audiophile product, but for a cheap and small pot, I'm gonna buy one just to have.

 

Yeah, it's basically a cheap 10k volume pot and a very nice, very heavy knob. The thing feels good to turn, is heavy enough to stay put fairly well, and best of all perhaps is that it comes hard wired with cables included. That is a bit of a pain for those who need longer lengths but a huge cost savings and sonic benefit to those who just want a compact desktop monitor controller. This is one of the cheapest solutions available that has these benefits. You'll need at least one and maybe a couple of XLR extension cables if you are running your monitors 8' apart, etc.

For a unit that also includes input switching, you are going to lose the cables included at that price. This unit is the cheapest that I can think of which has input selection and is a passive attenuator: http://www.smproaudio.com/index.php/en/products/monitor-controllers/m-patch-2


High frequency roll-off isn't going to be an issue with a 10k pot and reasonably short cables. Start running 25' and using a higher impedance pot and you'll lose a bit but it might not even be such a bad thing considering how brutal some studio monitors can sound in the top octave. In any event, nothing beats a really good active stage IME. at some price point, you might as well go active if you need the inputs, etc. The trouble comes only as the cheap active units don't sound that nice either...
-Bill

 

Bill,
I understand that the OP is not in the market for a multi-thousand dollar passive preamp, and that you suggested items more practical for the price range he wishes to spend. So your recommendation for the Level Pilot was very good, and now even I want one. My post was targeted to "inform all" about some technical advantages of transformer passive vs. resistor passive. You chose to critisize me with no detail of what mistake you think I may have made.

Since you have not answered my friendly private question, about what technical faults you found in my post, I choose now to publicly expose your ignorance and selfish arrogance.

This is a detailed technical article about the frequency response and output impedance of a transformer vs. passive volume control, at various volume settings.
http://www.diyhifi.org/forums/viewtopic.php?f=15&t=2908

I request that you read this article, understand that it supports every point I expressed, and apologize to me that you were wrong. If you cannot do this, after your unexplained criticism of my knowledge, then you have no right to sell a Bryston or Jolida preamp, just for your shallow profit, when in truth you find consideration of a Music First Audio preamp "painful" compared to your <$100 pot recommendation.

Warren

 

As it happens, I didn't give a price range, but my speakers are in the £1000 range. I'd guess I'd want to keep it in the bracket, or at least no more than that. Lower priced always welcome!

Edit: some examples of the ones I've seen so far include Tisbury Audio, Promitheus TVC, and a couple of others. Prices from £130-500.

 

I understand there are many passive preamps to consider, at many price levels. And I'm glad to know there are some affordable transformer based options for you to explore.

I'm just insulted by KT88's disrepectful and unexplained criticism of my post. I don't think his curt comment was appropriate in the friendly and supportive environment of Steve's website.

 

My two cents. I remember taking the Alps pots out of my Stax headphone amp, replacing with a resistor network of fixed value. I would change the level of whatever DAT recorder or phono pre I was feeding to the Stax energizer at the source. That pretty expensive Alps potentiometer in a pretty expensive circuit turned out to be an audibly weak link. The Stax amp [J-fet to triodes, direct-coupled to the electrostatic 'earspeakers'] is most 'transparent' playback device I've owned, so far. Point being that the audibility of something like a passive attenuator depends a lot on the resolution of the rest of the system, along with paying attention to electrical values/equipment compatibility. For someone with a home studio and powered monitors, the t.c. electronics doo-hickey is just fine. For someone into single-ended triodes, maybe not.

 

Please keep us informed here about any passive you try, buy, or decide you like.

 

Hi Brother,


Firstly......Congrats on the active AE's......nice move.

I listen to my OPPO 105 connected DIRECT to my actives and have no SQ issues with it's volume control whatsoever.

Why don't you try hooking up your CA 752 that way and have a listen?

I would expect it to sound excellent........ and you can also adjust the AE's input sensitivity if required.

Just remember to LOWER the CA's volume via the remote BEFORE you start listening!!!!!

You could run another set of I/C's for your AVI Labs and switch between them at the speakers or just use one set and switch at the sources if access is easy.

That volume control knob thingy looks cool but apart from not offering source switching it also doesn't come with a remote.

Good luck
Cheers

 

Hey mate! I prefer the AVI for CD playback. The actives makes the difference between sources more obvious. While the Cambridge is fine, I think the upsampling is the difference as the underlying chipset is the same.

I'd prefer bit too swap cables out, so I want a suitable pre. Equally, I might well stick with Onkyo, and get one of their AV pre amps. Nothing set in stone yet!

 

I will. As you gather from my reply above, there's a few options to mull over!

 

I am still fumimg about KT88's rudeness and weakness of character, claiming to know enough about transformers to call my post "full of holes", then not explaining himself.

I am in the hospital now, awaiting open-heart surgery this week. So, I admit this forum is the only distraction I have to think about... except TV.

So I found one sentence in my post-in-question that wasn't written quite right. Here it is expanded for absolute correctness:

The advantage (of transformer based over resistor/potentiometer based) is that at unity gain (this is typically max volume for a passive) the preamp's output impedance equals the source component's output impedance. Never higher. By definition of a transformer's basic function, at a 1:1 winding ratio, impedance out equals impedance in.

Unlike every other preamp type, a transformer cannot create its own output impedance. It simply "transforms" the input component's output impedance into a "transformed" output impedance, dependant simply upon the transformer's winding ratio.

 

Seems to be constructed on the same idea:

http://audio-zone.ca/pre-T1.html