Low output gain amplifier for ZU 101db Efficient speakers

I’m actually quite happy with the first watt. Thanks for all the suggestions

The Art Audio PX-25 is 5w and is brilliant with Zu speakers.  The PX-25 is an interesting sort of "goldilocks" tube which is in the middle between a 2A3 and 300B.  It is not quite as detailed as a 2A3 and the midrange is not quite as lush as a 300B but it is more detailed than a 300B and has a midrange that is more lush than a 2A3. 

Is $8499 above your budget?  

Yes, Thanks for the update. 

If only every thread was updated by the op like this. Congrats and thanks for finishing it out.

Almost 2-1/2 years later:

1. I ditched the Rogue RP-5 in favor of a BHK Pre (PSAudio). The difference was major. The pre was quieter with my old NuForce amp.

2. I sold the NuForce and purchased a Firstwatt j2. This amp is beautiful and will run you out of the room when cranked. Smooth tube like flavor with a really deep low end. Right now I could not be happier. 

Thanks for feedback. 

Hi , now I’m here . Thanks for the info on Cryo Tubes, I’ll be shopping there soon . I have the Rogue RP-1, Schiit Bifrost Uber Analog DAC, Musical Fidelity’s transport and a Dennis Had Inspire with a 9 pin driver tube . I also have Zu Omens . So we have quite a few similarities. Dennis Had just shipped back my amp after replacing the self bias components on the left channel that blew due to a bad GL KT-77 that was new . As I said on the other thread , I put fresh tubes in the Rogue and Dennis just went through the Inspire . I run Silnote power cords , Morrow MA5 interconnects and Anti-Cables level 3 speaker cables . Yesterday I turned the pre to max volume with the source on pause . It was dead quiet at 8”, no hum and no hiss . The hiss was really bad when I had the Rogue hooked up to a vintage Marantz SS amp. I could hear it from a distance like you can . The Inspire matches up very well with the Rogue and the Omens . My system is very modest compared to others, but I am very pleased with the sound quality . I have 6 or 7 sets of power Tubes , about 8 driver Tubes ( It takes a single E88 ) and 5 rectifier tubes . It’s been a total blast to play with . Also regarding the driver tube discussion , In regards to brightness , I find that certain Tubes in the pre or the driver in the Inspire make the treble image out front further then the lower 2/3’s of the sound . I also experience this when I run a higher voltage rectifier tube . Depending on the Rectifier / Power combo, it goes from about 7 to 12 WPC. Also I have a 10 year old pair of lower tier Zu speaker cables and I like the Anti-Cables more    ( I have level 1 & 3 ). Best to you and Happy Listening , Mike. 

If you want a great sounding amp that is dead quiet check out one of the offerings from Linear Tube Audio. These are David Berning designed amps that are simply fantastic.

Thanks. I will , however, shop for a new amp (my original plan) after New Years. 

Hiss at the tweeter is normal for any system of that efficiency. Glad you got it sorted!

Can I say quiet as a mouse? I got the RP-5 back from Rogue and no hiss (unless I press my ear up to tweeter). I'm thrilled I can hold off on an amp purchase and enjoy what I have for the time being. Thanks everyone for the suggestions. I will be shopping after the new year. 

My Rp-5 is on its way back. The preamp needed to get some "op amps" replaced, LED display needed firmware re-install and a ground wire, and they installed new tubes. Rogue did hear the excessive hiss and now its quiet on their system. I'll be curious how much quieter the RP-5 is now in my system. I'll report back

It was the strangest sound , i initially thought it was serious 

My citcuits are dedicated,  they have their own breaker....that scent thing was in another room

oddiofyl, that's exactly why many people run a separate dedicated line/circuit for their audio gear. Dimmers in particular are the worst offenders.

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

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...

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

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.

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.

I wonder if a company could manufacture a pre with a switch to change gain settings. I know I can change phono gain on my RP-5

Of course he did, that’s one of his bread and butter items, he’s not going to shoot himself and his company in the foot, left himself an "out" by saying "an unexplained phenomenon" BTW Where is this quote?

It was a video interview. When pressed further he basically said that he doesn’t design preamps and that they are a completely different animal. He said to talk to the Pass Labs preamp designer and gave his name. 

Some of his amps have very low input impedances.

Yes granted, this is the reason why an active pre is needed, if they were >50kohm then a low impedance active pre is not needed, remember the Industry Standard for input impedance was 47kohm or higher, but sometimes if the input stage is bi-polar this not achievable, but it is with fet input, then it’s up to the designer to make it so.

Classic example of a high end poweramp here in Australia having only 1kohm input impedance, only their own preamp with 10ohm output impedance would drive it, all others especially tube sounded like crap, so no need to say they also sold many premaps with that poweramp.
But here the crux, inside that poweramp was a secrete link that when pulled made it 68kohm input impedance, which I exposed online, then owners were free to use all different preamps with it including passive. It’s called shady marketing, good if you get away with it as it makes sales for their preamps.

Cheers George

He qualified it by saying that his amps sound better with an active preamp. He basically said that it’s an unexplained phenomenon.

Of course he did, that’s one of his bread and butter items, he’s not going to shoot himself and his company in the foot, left himself an "out" by saying "an unexplained phenomenon" BTW Where is this quote?

Cheers George

I have read a couple of faverable reviews with the J2 paired with ZU speakers. RENO hi fi has a couple demo j2s for sale

With speakers that are over 98dB there's really no advantage in having a preamp with gain, as you've found it's a diadvatage, you'll find many now are starting to go for passive preamps as per this Nelson Pass quote:

George I heard Nelson say basically the same thing in an interview but then he qualified it by saying that his amps sound better with an active preamp. He basically said that it’s an unexplained phenomenon. 

"   One thing I could also do is go to a high end passive preamp. "

which I offered to you to try and sent you a message, but you never got back to me.     would have been really no money out of your pocket except for return shipping.....

My RP-5 arrives at Rogue today. Hopefully, they can fix the super loud white noise (plus buzzing in headphone section). My goal is to keep the RP-5

I'm updating my power amp by the end of the year regardless how quiet the RP-5 comes back. I'm keeping my ZU omen defs. I really want a tube power amp. I also understand the firstwatts are fantastic.

Anyway, here are the specs for the RP-5:

- Tube complement: 4 x 12AU7/ECC82 tubes
- Frequency response: 1Hz – 100KHz +/- 1 dB
- THD: <0.1%
- Gain line stage: 10 dB
- Rated output: 1V
- Maximum output: 27V RMS
- Output impedance: 500 Ohms
- Gain phono stage: 40dB, 50dB, 55dB, 60dB
- RIAA accuracy: +/- 0.1 dB
- Dimensions: 18.5 ”W X 4.5 ”H X 14.5” D
- Weight 30 pounds
- Shipping weight 45 pounds
- Power requirements 115/230V – 50/50Hz

For reference, the specs of my current amp:

-GeneralPower output80W x2Ch @ 8 Ohm
-Input impedance51k Ohm
-Output impedance30m Ohm*
-Gain34.8dB
-Frequency response20Hz - 80kHz
-Sensitivity0.45Vrms
-Signal to noise ratio100dB
-Total harmonic distortion<0.03%
-Power supply115 / 230V
-Power consumption3.15A/ 1.57A
-Nominal input level0.6V

Now, with the above specs in mind, along with buying blind (I'll make sure there's a good return policy). What amp specs should I be looking at for low noise and good matching with the RP-5 and Zu's? I'm not looking for brands...just specs where I can at least narrow down my choices. I'm not worried about having high power. The 80 (SS) watts I currently have is more than enough for my speakers. 

I know my current amp does have high gain (34.8) for my system, however, with my old Peachtree Nova, the amp hiss was only audible if I placed an ear on tweeter.

Here are the Nova Pre specs:
Variable RCA Stereo Output: 7V rms/11.2V peak •
Pre Out 1 Output Impedance: 50 Ω (discrete class A) •
Pre Out 2 Output Impedance: 15 Ω •
S/N at the Variable Analog Output: 96db •
Jitter Measured at the Master Clock: < 3.0ps •
Power Supply: 8700µF of filtering •
Stereo Separation: 94db • Maximum Power Consumption:
60W, standby less than 1W


Thanks for your help. Looking forward to responses. Once I hear back from Rogue, I will report their findings

Last week one buddy loaned me his First Watt M2, another loaned me his Schiit Freya preamp. Using both now on my Zu. Dead quiet. And I can open the volume all the way (with some quiet ditties) with the louder gain tube option, ergo has a built in governor of sorts. The combo btw sure is tasty.

Can you compare and describe the sound characteristics of both amps with your zu's?

:+1: on the Decware amps for high efficient speakers. They're dead quiet (especially the Torii/Torii Jr/MiniTorii) and sound amazing!

well it's not sub worthy but with the de capos good for me

the decware has a line out for a sub or use it as a preamp


We’ll see how the pre comes back from Rogue. I really like the combination tube pre and ss amp due to the deep bass. The firstwatts may be what i need. I love my amp, however, i planned on changing it out anyway and use it for a second system. I love my zu’s too much to get rid of. 

there's plenty of people that have tube amps and Zu’s with great satisfaction. 

One thing I could also do is go to a high end passive preamp. 

There is something not right with my R-5. There should not be beyond normal hiss, along with buzzing thru headphones. Buzzing and hiss are boyh loud thru my AT phones, grado and iphone pods. We’ll see

Look at things logically, a horn speakers worst friend is noise, and you have too much gain from the pre and the amp, maybe even the source.

Get rid of the one you think has more noise, the tube pre or the ss amp.
And replace it with a lower or zero gain item that is quiet.

Or you could be back where you started, if you replace a quiet high gain item with noisy low gain item.

Cheers George

well it's not sub worthy but with the de capos good for me

the decware has a line out for a sub or use it as a preamp

Hows the low end of the decware?

I will second the Decware amps.  My mini torii is powering some 92db Ref 3A de Capos  plenty loud and the best sound for 4 watts

I also have a Grommes PHI26  2 watts in triode and 6 in pentode and have used it on the de capos and some klipsch Quartets  great sound and it drives them well even at low volumes

+1 Dennis Had Inspire

Dennis Had "Inspire" Fire Bottle…best amp I've ever heard.

Wow. The Finale/triode amps are beautiful. 

Take a look at FInale Audio / Triode labs

made in North America. Very high sound quality for dollar. 

That still does not explain the loud hiss  and buzz  thru headphones. If the amo comes back with everything “ok”, ill just sell it and move on 

That Nuforce amp has a real low input sensitivity of only .45 volts. The amp is the problem, not the preamp!

Last week one buddy loaned me his First Watt M2, another loaned me his Schiit Freya preamp. Using both now on my Zu. Dead quiet. And I can open the volume all the way (with some quiet ditties) with the louder gain tube option, ergo has a built in governor of sorts. The combo btw sure is tasty. 

Not sure whether these would work for you, but there are a pair of Sophia Electric 300b monoblocks for sale on Audiogon. Good price.

You can hear the hiss on the video at link below. The hiss is much louder in person. The phone mic is quite sensative to overall environment. Thus, the overall video sounds a bit hissy. You’ll want to listen closely in a quiet area

https://www.dropbox.com/s/wgdbtqzhqf3nn1n/File%20Oct%2013%2C%204%2044%2055%20PM.mov?dl=0

Yes, the First watts have got my attention. Plus, they supply a great low end wheras the pre can add smoothness to highs and mids. The RP-5 did sound great ontop of all the freaking hiss. I took an iphone video of me muting and unmuting the preamp. Ill post it later