Recently Completed Stereomour - Hiss in Right Channel

[Montigne]

Paul,

Thank you again for the response. I have found a Vishay / Dale 665 ohms Metal Film Resistor on Mouser. It's specs are here (http://tinyurl.com/nlfscru), but basically it's: 665 Ohms, 125 mW (1/8 W), 1 % tolerance, 50 PPM / C, 300 V, Axial, and operatimng temperature of -65 C to +175 C. Will this work then?

Also, just to be sure I complete your previous instructions correctly: I add the resistors after removing the 431's, or do I leave them in and just bypass them with the 665ohms resistors in your steps?

Thanks, I'm getting excited to finish!

[Paul Joppa]

When you remove the black wire going to kreg, the 431 is disconnected from everything except ground and can do no more harm to anything. Much easier to leave it in place!

The resistor you described is an excellent choice.

[borism]

After reading the issue with the WS labeled 431s, I went back to check the make on the ones in my kit. I just completed my build and sure enough both are labeled WS. However, I haven't noticed any hiss in either channel. I should add that my speakers have a sensitivity of 92 (don't know if that matters). 

[Paul Joppa]

This noise will be louder on more sensitive speakers.

We'll be trying a variety of 431s to get to the bottom of this. Yesterday I noticed that of the many manufacturers of this chip, only two have actual specifications for the noise, and they are about 10dB different from each other. It makes no sense to me, yet.

[Dr. Toobz]

I was one of those unlucky persons whose 431's hissed like snakes on my 99dB speakers, so I went to cathode resistors. Would be happy to go back to the 431's (just for the sake of sticking to the intended circuit) if we can figure out which ones are consistently quiet!

[Doc B.]

There is a pattern. The guys with high sensitivity speakers are hearing the hiss. Owners of lower sensitivity speakers don't seem to be noticing it. Noise issues are not all or none, it's more a matter of degree. So what we can say is that we will do what we can to find a chip with a consistently lower noise level. But if you have really sensitive speakers and you hear noise that bothers you, you may have to use the alternative approach we have offered here anyway. That is the one of trade offs - along with reduced bandwidth - that you have to deal with when you go to very sensitive speakers.

[Dr. Toobz]

I can confirm that the resistors don't sound noticeably worse or different than the 431's with my speakers, so the upside is that the alternative arrangement, when needed, still results in a wonderful-sounding amp.

[Montigne]

Dearest Bottlehead,

Success. Hiss=gone. There is slightly more ground buzz than before with the 431s, but it's only when I have my ear right next to the driver and is completely unnoticeable when listening. Thanks for all the help so far Paul.

-Chris

[Grainger49]

    .  .  .    only when I have my ear right next to the driver    .  .  .  .   

You would probably find this in multi-thousand dollar commercial products, tubed and solid state.

[ffivaz]

Hi,

I finally managed to get a new pair of 431s. Mine where noisy and read WS 431 on them. I replaced them with some FKA48 LM431 ACZ I found on the bay.

They are quiet as hell. My hiss is gone.

Thanks guys for finding the problem.

[borism]

A naive question out of curiosity. Do you have to take off the small board to change the 431s (if a consistently less noisy type becomes available) or can it be done with the board in place (and how)?

[ffivaz]

I had not too short pins, so I just cut the regulator out. Then with desoldering pump, I carefully removed the solder out of the holes, applying some heat. I finally was able to put the new regulator in and resolder it in place from the top, without removing the board. I was careful that the pins in the holes do not fall towards the socket and make some bad shorts.

BTW, I can send you some 431s. I received a handful. Just PM your address.

[Paul Birkeland]

I thought I'd let everybody know that we quarantined the WS-431's that we had in our inventory, and have switched over to a quieter part.

-PB

[Grainger49]

I thought I'd let everybody know that we quarantined the WS-431's that we had in our inventory, and have switched over to a quieter part.

-PB

Just what I would expect from Bottlehead. 

Awesome!  ! 

[bjorgens]

PB, PJ,
Can you share the vendor/ PN for the quieter part you mention above?

Am wondering if its worth experimenting with different 431s on my paramounts (in hopes that I might remove the 10000uF caps I have across -reg and Kreg.

bryan