Low output gain amplifier for ZU 101db Efficient speakers

The Aric Audio full-tube (rectifier, voltage regulator, signal) Unlimited preamp that I just bought has a knob in the back to control the output gain. Its really handy since I switch between amplifiers and speakers and it allows me to keep the volume control within the sweet spot(s) of they amps and the speakers with different sensitivity. I think every preamp should have this feature. Take a look at his products. He offers several models of tube preamps and tube amplifiers and they are all point to point wired and reasonably priced. He will even make one to your specs. I really like mine.

Any time you have a high efficiency speaker combined with a high gain amplifier of 30 db or more you are asking for noise problems.

As George points out, you simply don't need all that gain.

I do not agree with him however that getting rid of preamp gain is the solution. The Rogue has a very reasonable 10 db of gain in its linestage, which is helpful if you plan to use a low output cartridge with the phono stage.

Our preamps have about 16 db of gain in the line stage and we don't have noise problems with high efficiency speakers **provided** the user has made a sensible choice with the amplifier, one which does not have too much gain. Pass Labs amps for example have about 25 db of gain, which makes this a lot easier. Our amps have similar gain, and we offer a jumper plug to replace one of the voltage amplifier tubes so as to reduce the gain further (to about 12-15 db). This can be really helpful with horn speakers since you can get much lower noise floors with a low gain amp!!

One simple solution would be to place a volume control at the input of your amplifier (perhaps with a passive volume control using extremely short interconnect cables between the amp and the PVC; I would not allow the cables to be over a foot long....) to simulate a lower gain amp. You will still have the noise floor of the amp itself, but this will help you with the noise floor in general. This technique is known as 'gain riding' and will allow you to run higher volume control settings on the preamp.

Another thing to consider is that the Nuforce makes far more power than you will need unless you have a very large room! It has the extra gain because it is meant to drive speakers with less efficiency that will need both the gain and the power. In your case, the extra power is actually a liability and here's why:
The Nuforce is a traditional solid state amp, and like all traditional (not class D IOW) solid state amps, there is a certain power level at which it makes the least amount of distortion. That power level is typically about 5-7% of full power. This is a 150 watt amp, so we're talking about somewhere around 10 watts. Below that power level distortion *increases* quite a lot- and its in a form that is audible as harshness, brightness and lack of detail (distortion can mask low level information).

This is not a malfunction of the amp so much as its a simple mismatch of equipment. You would be far better off with a solid state amp of less power (30 watts or so would do nicely) and of course even better than that if you ran a tube amp, also of lower power. Our S-30 would be plenty on that speaker and I bet you could get by easily with only 15 watts (although IME, the ZU speakers are a couple of db shy of their ratings). You would not be having any noise issues with such lower powered tube amps as they tend to have less gain since they are intended to be used on higher efficiency speakers.

Ralph, thanks so much for the info. Of course, one of your amps would be perfect, however, above my budget :(. My brother n law runs one of your amps and pre with his ZU Souls and loves the combo. Ive heard it a couple of times and it sounds fantastic. If my pre comes back still noisy, i may try the passive volume control at the amps input. I really love the Rogue for its remote and input capabilities. Again, i always like hearing your input

I’m driving a pair of ZU Druid mk5 with a ~1 watt Yamamoto 45 SET amp and no preamp. The amp is driven directly from my PS Audio DirectStream.
Scary realism.
Give one a chance...

Hi

The Quicksilver Horn Monos are great for sensitive speakers.  They have much less gain so your volume range on your pre will be normal   All of Mikes gear offers a lot for the money.  

I understand the OP has very sensitive speakers but i wanted to share my experience with "noisy tubes" .   I have a preamp that is tough on tubes,so i am familiar with what they can sound like.....

Also a dirty socket can be the problem... anyway i was chasing a noise , i couldnt tell where it was coming from.  Replaced the 6922 in my pre with Gold Lion.    Still noise.   Pulled my amps out, cleaned all sockets... replaced tubes with like new spare tubes, cleaned pins before installling.    

Noise was still there.  It sounded like a bug zapper, but at a really low level, and every few seconds.  I doubt most people would have heard it but it was driving me crazy.....

I thought i had removed every potential source of electronic noise, as only these outlets are on the breaker.  The source of the noise was one of those air fresheners that plug in to warm up the gel

Once unplugged the system was dead quiet