SET Amps HUM

[George Roland]

I am considering getting a pair of SET amps for K-horns, probably Bottlehead or Welborne. I am REALLY sick and tired of hiss, hum, etc. coming through my speakers from every amp I try on my system. Could any of you with experience with the currently available forms of either of these mfg's amps comment on how QUIET they are--both mechanical and audio hum?

Thanks,

George

[Guest " "]

it would be intresting to see signal to noise ratio ratings.

[pauln]

George,

I have 2004 LaScalas and Wright 3.5s with the Wright preamp. With the original Sovtek tubes, the system is deadly dark quiet no hum, no hiss. With the volume at minimum I can place my head against the front of the LS and hear the most faint sound (what is called blow in amp-speak) that sounds like one is just gently exhaling a breath. From a few feet in front this is totally inaudible. With EH Gold tubes, there is a very slight hum, but from the listening position this also becomes totally inaudible.

I have been doing some listening experiments with old 70s SS lately, and the first impression I have is that the Wrights are much quieter than the SS at all volume levels. The SS amps dont hum, but the overall background hiss and rumble are surprisingly there, whereas the SETs are so quiet.

In terms of noise, with the Wrights I use phono (I only play records). I have to take the volume passed half way (way too far for music listening) to get a background level of noise (no signal), but with the other inputs selected there is absolutely no noise with the volume all the way up!

You are correct to be concerned about SET matching to big Klipsch as far as noise. The big Klipsch will find and portray any noise in the system with full fidelity. Since the musical dynamics are almost entirely within the first watt, it is critical that this listening range be clean, clear, and free of any noise that might mask the details and low level sounds that make SETs so enjoyable for music.

Others here can speak to the Bheads and Wborns I have not heard them, but I can recommend the Wrights. If possible, listening to the ones you are considering would be due diligence.

Pauln

[LarryC]

Also some other info, please.

Turn off your stuff and disconnect the leads to your amps [edit:] and turn the amps back on [end edit] -- do you still get the hiss and hum? If not, a little further look-see is in order, to detect where it's really coming from. The hiss could be from your preamp (the usual source IMHO), and the hum could be from your preamp, signal source, or a loose connection in one or more interconnects. Amps are usually quiet by themselves.

Your amp has moderate gain (1.7 v in for 100 watts out), so it's not a high-gain situation which can magnify preamp noise and is difficult to solve with K-horns. Your preamp apparently has 26 db line-stage gain, which is on the high side (many pre's have only 20 db) and could present a little higher hiss level to your amp to send to the K-horns. My previous CAT pre had 26 db, and I had to be careful with amplifier gain choices. I don't know what the gain or sensitivity is of the SET amps.

lc

[Wardsweb]

Have you ever checked your AC outlets for DC? DC on the line can cause

some transformers to oscillate. Also don't forget to check your preamp

for noise. For the longest time I thought I had an amp issue when it

turned out my pre was noisy.

As for kit amps, they vary greatly in their noise levels due to all the

factors that are important; solder joints, power and signal line

separation/isolation, grounding, build technique. I know this all

to well while running some 104dB efficient horns. At that level, they

are very unforgiving. My amps run the gamut from DIY to kits to

off the shelf. My Bottlehead S.E.X. amp is dead quiet while my $2500

Shanling monoblocks have a very slight hum when the gain is 100% and

you're less than a foot away from the speaker. While my one off

2A3 stereo amp is quiet.

I agree you really need to audition in your own home to be sure. That

is unless you want to spend some stupid money and get amp(s) that are

always quiet.

[JBryan]

George,

Noise has been the bane of many around here and its certainly a pet-peeve of mine. Both amps you mention are good choices although I don't have much experience with the Bottlehead amps. I did have a modified BH preamp a while back and it sounded fine and their kits are considered a great value. The Welbourne amps also offer tremendous value with good-quality parts and excellent designs.

Noise is a big issue with high-efficiency speakers and I wish more manufacturers would listen and tweak their equipment through a decent 100dB speaker. They must realize that noise destroys low-level transients and microdynamics which contribute to the overall detail and articulation. Of course, you also need to consider that noise is also coming from your home's electrical system as well as the compatibility of your audio components, wires and cables. We can't blame mismatched sensitivity, gain and impedance on anyone but ourselves and a bit of research can save a lot of aggravation and grief.

Having said that, I had a pair of Welbourne Labs 300b Laurels a few years ago and they were very nice-sounding amps although I could hear a little hiss through Khorns and the trannies had a slight mechanical hum. I tried power conditioners, better cables and tubes - with no improvement. A couple of years ago, I picked up a pair of the DRD45 amps and they are one of the quietest amps I've had in my system. I will say that my system has changed quite a bit since the Laurels and the DRD45s are running more efficient drivers than those in the Khorn.

Another amp that I've found to be very quiet is the Transcendent Sound SEOTL amp (1.5w). It is a very dynamic amp with excellent bottom end and it gets close to the sound of SET. Two amps can be used as monoblocks with an easy mod to produce 4w/channel and double the damping factor (a big plus for the Khorns woofer). The only drawback is that I had to deal with a bit of hum but I was able to get rid of it eventually.

If noise is a prime consideration, you could also look at some of the digital amps as they are extremely quiet. I have a pair of Hypex amps (100w) running the Khorn bass bins and I leave them on all the time. Aside from the green LED, there is no way of knowing that they are on unless music is playing. They put out a modicum of heat and use about as much energy as a flashlight bulb.

Have fun, Bryan

[kev313]

My Moondogs hummed. This could be controlled - to an extent - by the hum pot. Never could hear it with the music playing, though, so I didn't consider it to be much of an issue. It might have been, however, if I wasn't firmly in the "turn off my amps when not in use" camp.

[leok]

Tube amps, SET or otherwise, are not generally the quietest amps available. Many ss amps are much quieter (they may not sound so great). My Crown D-45 creates no audible hum or hiss and sounds great. My tube amps create a small amount of hum (not audible at listening positions) and also sound great.

I suspect you have a system issue and until you solve it anything will hum and hiss. SET certainly isn't going to solve a system hum problem. Another possibility is you have simply had a series of noisy amps and what you want is a quiet amp. Again, SET or any tube amp is probably not the quietest.

Leo

[steve]

My Assemblage 300B SETs are dead quiet..they are mated with a SS Adcom preamp, the GFP565 (although I'm always considering another tube preamp)

I have had SS amps/integrated amps in the system that definitely exhibit hiss (but no hum so far) and an old Scott 130 tube pre that was the most full sounding pre I have ever owned..but I couldn't get rid of the annoying hiss at idle!

I agree with others here..it may be something else in your system..that turntable grounded OK? Your AC on the up and up?

Best of luck..

Regards

Steve

[mike stehr]

Cornwalls+50C5 amp=death buzz......

[Cut-Throat]

I am considering getting a pair of SET amps for K-horns, probably Bottlehead or Welborne. I am REALLY sick and tired of hiss, hum, etc. coming through my speakers from every amp I try on my system. Could any of you with experience with the currently available forms of either of these mfg's amps comment on how QUIET they are--both mechanical and audio hum?

Thanks,

George

My Welborne DRD45 amps are Dead Quiet! - When I first powered them up, I thought something may have been wrong because I could hear nothing at all in my speakers. They are as quiet as any Solid State amp that I own also.

[Daddy Dee]

My experience with Wright 2A3's has been happy.

[TommyK]

Have you ever checked your AC outlets for DC? DC on the line can cause some transformers to oscillate.

How does one check AC outlets for DC?

Thanks in advance.

TommyK

[Mark Hardy]

DHT amps hum, and that's pretty much the way it is. They're also not too amenable to DC on the filaments, due to the potential -- pun intended :-) for cathode stripping.

You have to be a bit philosophical and/or masochistic to use low-power SE amps :-) I think it's sort of like surf fishing -- you either get it or you don't. It's OK if you don't.

As a point of reference: a Marantz 8B I recently recapped is dead quiet on Cornwalls and sounds magnificent. Absolutely magnificent.

[DRBILL]

My Mark IIIs had a faint hum through the Khorns even with the proper grounding of all the equipment. You couldn't hear it with music, but it was there if you listened in expectation of hearing it.

The first thing I did was remove the cap between the center tap of the heater supply and ground and run the center tap directly to ground. This made a significant improvement.

One afternoon with too little to do, I lifted my whole system from the power line. I used two Isotaps. I was astounded with the positive difference. Through the speakers there was no hum or blow. (OK, maybe it IS funny -- try to get over it.)

I could still hear something. By crawling around on my hands and knees I discovered that one of the power transformers had a whine. It was not 60 Hz, but (in musical terms) a third above 120 Hz.

Again, I don't hear it unless I listen for it. This has something to do with the laws of diminishing returns.

DRBILL

[LarryC]

Dr Bill, what's an isotap? Thanks,

Larry