Low output gain amplifier for ZU 101db Efficient speakers

A Solid State option is the Benchmark AHB2. Most quiet amp on the planet. Don't know how it sounds, however...

I own a pair of Zu Omen def with a Line Magnetic 219ia. This is an expensive amplifier, but even the cheaper ones (518 and 508) are excellent.
Another good option is a relatively new amplifier from Hong Kong - KingKo Audio. The designer is a friend of mine (he was previously selling Rogue Audio, Line Magnetic and Zu, so he decided to create his product based on his own ideas and also the best from each brand he was selling).
His amplifier is small and perfect for high efficiency speakers. Top quality parts, extra care with the transformer and even a very high quality headphones tap. Also very affordable valves and gorgeous meters. 
Can work as integrated or power amp. 
The sales are exceeding his previous expectations and there is a very good review on the audio website DAGOGO. 
Here are the links:
http://kingkoaudio.com/en/pages/KINGKO-AUDIO.html

https://www.dagogo.com/kingko-audio-ka-101-integrated-amplifier-review/

Note: although friend of the owner of this brand, I have no interest or profits from his sales. I'm just giving a very personal and honest suggestion. 

Thanks for the kingko link. I would have never found unless I posted here

I've got both Decware and Quicksilver Horn Monos.  The Quicksilvers are really dead quiet amps and they sound superb.  They'd be a great match in your setup. 

Well, I did some more testing. I have a defective pre-amp. I had time to kill. I went and purchased some new JJ 12au7's and the loud Hiss is still audible from back of room. Another audiophile from another forum told me that, even with my amp's gain and speakers, the hiss should not be that loud. Plus, I tried headphones, the hiss is loud WITH buzzing. Again, I'm not expecting SS quiet, especially with my speakers. I plugged in my class D ceiling speaker amp (along with  ceiling speakers)---hiss is loud as can be. Same with my older B&K amp and different speakers. Plus, I did all the usual (cables, outlets, power conditioner, power cord, etc).

So I am boxing the amp and sending off to Rogue today. Hopefully, I can get back in the next week. This was my 50th Birthday gift from my wife  I'm taking a couple of days off late next week and I hope I get the unit returned by then. Very disappointed :(

I've got both Decware and Quicksilver Horn Monos. The Quicksilvers are really dead quiet amps and they sound superb. They'd be a great match in your setup.


Which do you prefer and what are the sound charactoristics of each?

Sorry to hear that about your preamp.  Mine is dead quiet and although my speakers are only 93.5DB efficient, with the gain cranked up to max on my RP-5 and connected to a Conrad-Johnson 250wpc amp, it is dead quiet.  I can't hear anything from the speakers even with my ear right against the grills.  The JJ tubes supplied with your preamp should be dead quiet as that is one of the reasons Rogue uses them.

aberyclark
 Low output gain amplifier for ZU 101db Efficient speakers

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:

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.

You could always trial a Schiit Freya preamp it has virtually no gain (unity gain) itself, in all of it’s modes tube, solid state, or passive output, got remote 3 inputs and balanced or rca, and sounds from reports very very good.

Cheers George

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

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

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

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. 

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

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 

Take a look at FInale Audio / Triode labs

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

Wow. The Finale/triode amps are beautiful. 

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

+1 Dennis Had Inspire

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

Hows the low end of the decware?

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

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


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

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

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?

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

"   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.....

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. 

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

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

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

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. 

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

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

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

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

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

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

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. 

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

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

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.