Noise floor on Heritage systems

[3dzapper]

I just measured the HF-81 I am listening to now. With the volume control set for normal listening volume there is 2mV at the speaker outputs and no audible noise from the aux (CD) input. this noise floor did not move when the volume knob was moved. From the phono section at the same setting there is 3mV and it is just audible. The voltage and hiss did increase with gain setting on this input(I'm not suprised) to 12mV and is quite appearant at that level.

At a setting that would equal 90db SPL this would be around a 27db SNR at 105mW. It is possible that your amps are working within their design limits. Idling SS devices which are biased on (class A or A/B) will amplify any upstream noise reaching them with higher odd order harmonics at such a low power.

Rick

[Klewless]

Hey Guys,

Technically a passive device (like a speaker without powered sub-woofer built-in) does not have a noise floor. It does however have a sensitivity.

Active devices (amps, preamps, tuners, CD players, etc) have a noise floor which is documented in it's signal-to-noise ratio.

What is going on in highly sensitive speakers (like horns) is that with no signal applied to the amp (the input is often shorted for this test) any idling currents in the output are reproduced by the speaker because speakers are supposed to turn currents into sound. A perfect amp would of course not have any currents in the output with its input shorted. If you remove the input short and now get the hiss, then the amp is generating the noise internally.

If still no hiss with the amp's input open now add the preamp. No hiss at this stage means you have a good system so far (no excessive internal noise being manufactured by your electronics at idle). Crank up the preamp volume control way up there and you are just about guaranteed to get that hiss (produced by the preamp and dutifully passed on by the power amp in all its glory). No hiss at this stage means you should be rejoicing right now.

I am not talking about the sonic characteristics of the electronics. Only the noise (or lack thereof) generated internally.

SS or tube matters not, the speaker does not know why the current is there; it just does its thing with whatever comes in.

I have had both tube and SS (lots of both) and got varying amounts of hiss from ALL OF THEM. Most however were quiet enough to not be a problem.

I am using LaScalas, Cornwalls, and Heresies currently and my discussion is based on them. I have also had many inefficient speakers which of course do not have the hiss. But if they are not reproducing the idle currents, then what else are they not reproducing?

Not trying to be argumentive here, just trying to explain that IMO hiss is nothing more than idle currents which are always present to some extent and are easily reproduced by highly sensitive speakers.

[Rudy81]

Well,this is the good news bad news scenario. Parasound has been extremely helpful at working with me on this issue. Here is the deal we found. I am currently using BALANCED cables for my pre/pro amp connection. They suggested I try unbalanced cables for the connection.

That change took care of the problem. I am not good at EE, so I don't quite understand why the hiss would go away with unbalanced cables and come back with the balanced cables. Regardless of which balanced cable I connect to the amp, the hiss returns to the speaker connected to that cable.

Very weird.

[Rudy81]

I have been told that my system is set up for THX Ultra2 standards with in the unbalanced section. Then, the balanced section has a 6dB gain on top of that! Perhaps you EE whizzes can tell me why a balanced section has that much gain.

Have any of you used quad shielded coax to make rca unbalanced cables? Just wondeing. This place is such a wealth of knowledge, I have to ask.

[D-MAN]

I have run both tubes and solid state gear for years. Back in the late seventies, my Khorns used to hiss; seems to be a natural condition of the EV tweeter. All of the amps I've ever used hissed to the same degree.

I am now using a Mac solid state setup and no longer use the EV tweeter; I have not noticed the hissing at all even with my ear up to it.

I do get thumps at turn-on, just like the "old" days. Some things just don't change...

[PAR69]

Rudy81:

To make unbalanced audio cables using coax, you will need the following:

4 RCA male jacks - preferably color-coded so you can match left to left and right to right

2 pieces of coax cable of equal and suitable length for your application

1 pair of "dikes" (diagonal wire cutters)

1 pair of wire strippers

1 sharp knife

1 soldering iron, solder and the skill to use it

So, start with 1 end of the coax cable and strip off approximately 1" of the outer casing, leaving the shield intact.

Slide the shell of the RCA down the cable about a foot

Using the dikes, cut into the shield either once or a second time on the other side of the center conductor

Peel back the shield

Use the wire strippers to cut the dielectric to the center conductor and strip away the dielectric

Solder the center conductor of the coax to the pin of the RCA (center) and solder the shield to the outer clamp of the RCA

(If you split the shield into 2 halves, only solder one to the outer clamp of the RCA and cut of the other half)

Close up the RCA

Repeat 3 times

Install

Enjoy good music

Paul

[peterbwreal]

I ran my Belles with a Hafler DH-500 power amp and Hafler DH-110 preamp with absolutely no hiss - dead quiet. I switched to a Dynaco PAS-3 preamp and picked up a hiss, and also kept blowing fuses on my ALK networks when switching from Tuner to Auxiliary. I figured I was just putting too much power to the speakers (255w/channel!) and switched to a Dynaco ST-35 with 17.5w/ch. That cured the fuse problem, but the hiss remained. It has to be the preamp, so my next guess is to test tubes and go from there. Incidentally, everything you hear about tubes is true: the Belles sound much richer with the Dynaco equipment. The ALK networks allows me to attenuate the squawker level, and I had set them way down as the speakers were too bright with the Hafler. I returned them to the "normal" setting with the Dynaco tube equipment.

[Rudy81]

Thanks for the information. I had found a few sites with great information on DIY cables. This one in particular is very good. I should receive the Canare cables, RCA connectors, shrink tube and flextubing tomorrow. I also found some decent "Proflex" cables on eBay for $15 for 5 cables. I had paid much more than that for my original Proflex cables a while ago.

I already made a Canare cable for my sub and it worked out really well.

I also decided to use their 4S11 cable for my speaker cables. That should arrive tomorrow also.

To show you how stupid I was, I had modified my original Proflex component video cables a while ago to change one of the ends from RCA to BNC terminations to better connect to my HALO gear. Having never made BNC connectors, I was not aware that the center pin is a crimp pin. So, i just put the connectors on without crimping the pin. Amazingly, the cables worked, but it would just have been a matter of time before I would have had video problems. I'm sure I would have started fearing projector, dvd, or processor problems.

Having researched the DIY cable issue, I now have a nice crimp tool, coax cutter, etc.

I am looking forward to making some nice cables.

[Rudy81]

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On 10/27/2003 10:00:15 PM peterbwreal wrote:

I ran my Belles with a Hafler DH-500 power amp and Hafler DH-110 preamp with absolutely no hiss - dead quiet. I switched to a Dynaco PAS-3 preamp and picked up a hiss, and also kept blowing fuses on my ALK networks when switching from Tuner to Auxiliary. I figured I was just putting too much power to the speakers (255w/channel!) and switched to a Dynaco ST-35 with 17.5w/ch. That cured the fuse problem, but the hiss remained. It has to be the preamp, so my next guess is to test tubes and go from there. Incidentally, everything you hear about tubes is true: the Belles sound much richer with the Dynaco equipment. The ALK networks allows me to attenuate the squawker level, and I had set them way down as the speakers were too bright with the Hafler. I returned them to the "normal" setting with the Dynaco tube equipment.

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My hiss is due to using the balanced section to connect the amps. I have no hiss when using the unbalanced section. I have really appreciated the ability to attenuate the squawker level also. However, I have found that the normal setting is most to my liking. That's probably because I always have listened to the Belles in "normal" setting when I had the AB crossovers. Good luck with your hiss.