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Bottlehead Kits => Legacy Kit Products => Stereomour => Topic started by: Montigne on March 03, 2014, 04:56:55 AM

Title: Recently Completed Stereomour - Hiss in Right Channel
Post by: Montigne on March 03, 2014, 04:56:55 AM
Bottlehead,

I recently completed my first amplifier kit, your Stereomour, and couldn't be happier. The quality, sound, and fun of it all for under $900 is very satisfying. You have made me a believer, and I truly feel that DIY vacuum tube-based Hi-Fi is the purest path to audio magic.

One problem: I have used it for about two weeks every night for a few hours and weekend days, and am getting a small hiss in the right channel only. I've tried swapping source component cables at the outputs, swapped the 2A3 tubes from L-R, and it's not the hum pots either. Not a buzz or hum, definitely a soft hiss. I'm using higher efficiency speakers and the noise is very subtle, but definitely audible when I get close to the driver and I'd like to have it perfect or remedied if possible. There's the usual turn on hum for a few seconds at power up that goes away, but I don't hear the hiss right away until the hum goes away and then the hiss kicks in like a switch. I am planning on getting another 12AT7 to swap and see if it's the NOS tube that came with the kit, but I wanted to get the question out into the forum first.

Any suggestions? Thanks in advance Bottleheaders.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: fullheadofnothing on March 03, 2014, 06:16:45 AM
This could be many things. A different 12AT7 is certainly a good place to start.

How efficient are your speakers? You may simply be dealing with the noise floor. Can you hear the hiss with the input shorted? Is it volume dependent or not? What impedance setting did you use? What impedance are your speakers?

It seems that this noise is not audible from the listening seat. Is that correct? You will drive yourself insane tracking down noises you hear with your head pressed to a speaker, but they don't effect anything in the real world.

Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Montigne on March 04, 2014, 04:26:23 PM
Thank you for the reply. Yes, the hiss in the right channel is slightly audible from the listening position when the program material is soft or completely quiet. I know it'll drive me crazy trying to track it down, but I feel there could be a solution because it's something in the circuit making it manifest in the right channel only.

I've wired the OTs of the Stereomour kit to 16ohms, and my speakers are 16ohm as well. They are RCA LC-1Bs and are about 97db efficient I think. I tried a different NOS 12AT7 and also a new JJ tube, but the hiss still remained, leading be to believe it's source is in the circuit somewhere. I even tried shorting the inputs (which actually quieted them down vs. having a source cabled in), but it didn't't change the hiss. Conversely, the left channel is dead quiet.

Anything else I could try? Thanks for the feedback so far, I appreciate it.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: triode on March 04, 2014, 10:13:43 PM
Hi
I have the same problem with Stereomour hiss in my horn speaker.
I changed the 431 in 12AT7 cathode with resistor and the hiss is gone

See toward the end of the thread : http://bottlehead.com/smf/index.php/topic,4521.0.html

Hope this helps

Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Paul Joppa on March 05, 2014, 11:01:53 AM
If this works, please post about it - I'm gathering data.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Montigne on March 05, 2014, 12:54:17 PM
Thank you for the suggestion, I had also read that thread but the swapping of parts and mentions of it affecting the frequency response of the amp deterred me honestly. If possible, I'd like to avoid deviating from the stock kit with modifications to try to solve this. The left channel is dead quiet, why would only the right channel exhibit this symptom? If I understand it correctly, the 431 is a shunt regulator that controls cathode bias voltage of the 12AT7 tube? I assume this is done in each channel, correct? Would trying a replacement 431 be worth it, or would I somehow have the same issue? I have read about the resistor replacement solution you said worked Triode, but what value of resistors should I use and how would I replace the three leads connection points on the 431 with just the two on a resistor?

Sorry if I'm asking redundant questions found in other threads, I'm still learning and really trying to understand. Thank you for the continued help.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Paul Birkeland on March 05, 2014, 01:42:42 PM
You could indeed just pop in a different TL431 and see if that helps.

-PB
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Paul Joppa on March 05, 2014, 05:38:36 PM
Before I get into details, there is always the possibility of a poor connection, solder or tube socket or corroded tube pin.

That aside, PB is right. The reason I want more data is a suspicion that we have acquired some bad, possibly fake, 431s - there are a LOT of fake everythings coming out of [country names withheld], not just Rolexes. We seem to have had this problem only recently, or at least mostly.

A proper 431 should meet the specification. The most complete specification is that for the ON semiconductor product, which is what I used in the original design. It includes a very complete description of the noise character, which is better than most of these "adjustable Zener equivalent" chips - that's why we use that chip. You can swap the 431s to check - swap the connection from 12AT7 pins 3 and 8 to their respective kreg  connections, at one end or the other. If the noise moves then it's the 431.

If you don't want to unsolder the 431 and replace it (I wouldn't want to, my hands are too shaky these days) you can replace the chip with a resistor as described in the referenced thread. I'm not checking that thread while posting this, so let us know if it's unclear. The C4S current is about 3.8mA and the chip drops 2.5 volts, so the perfect resistor is about 660 ohms; 680 ohms is close enough and widely available. This will be quieter than even the best 431, if it is metal film or wirewound or bulk metal foil. It raises the driver's effective plate impedance by about mu times the resistance; mu is nominally 60 so about 55K total. The 2A3 Miller capacitance is about 70pF giving a corner frequency of 41kHz. At 20kHz that 1dB reduction, so probably not audible unless you have bat ears.

I think that same thread mentions substituting an LED for the resistor. The problem is, we don't know much about LEDs other than the one we use which is noted for both low noise and a low dynamic impedance. That LED, the HLMP-6000, runs about 1.57 volts, significantly less than the target 2.5 volts. It should work, we've used it in previous incarnations of this circuit, but I moved to 2.5 volts for a reason, I think it's a more reliably good sounding operating point, given the variety of 12AT7s out there. (This has to do with differences in grid-cathode contact potential, if anyone cares.) My compromise would be to use an HLMP-6000 in series with a 240 ohm resistor, which moves the corner frequency to over 100kHz.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Montigne on March 06, 2014, 06:41:33 PM
Paul,

Thank you for the detailed response. This weekend I'll begin by checking solder joints, but then will likely want to swap out the 431 if it's not a connection joint. Is it something I can order from Mouser, and if so, is there a specific model or part # I should be looking for? Or, can I order one from you guys? If that doesn't work I'll be dong the resistor substitutions if I can find a 660 ohm (or 680). If I do that, where would the two leads of the resistor go instead of the three of the 431, and what direction should the resistor be pointing?

Thanks.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: ffivaz on March 07, 2014, 01:48:01 AM
That is good news. I have an audible hiss (from my seat, 3 meters away) in both channels since the beginning. I replaced the 12AT7, reducing the noise only a little. I also was reluctant to change the 431s with resistors since it would affect the sound of the amp. But given PJ's exaplanation, I'll give it a try.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Paul Joppa on March 07, 2014, 02:32:04 PM
The "previous referenced thread" is http://bottlehead.com/smf/index.php/topic,4521.15.html and my most current note is reply number 18.

I see there are no detailed descriptions, sorry! I'll try remotely (I don't have a Stereomour at hand).

You'll want to unscrew the PC board over the 12AT7 socket, first, so you can get access to the socket. This is going to be fussy work, sorry! In the link I mention 499 to 720 ohms as workable, with 660 the one that best matches the original design. I'll call it a 680 in the instructions below.

There is a black wire that goes from B3 to kreg on the board. Remove it at both ends (* see note). Do the same with the black wire from B8 to the other kreg.

Take a 680 ohm resistor  and solder it to B3 at one end, and terminal 6 at the other end. Yes I know, T6 is crowded, if T8 is easier then you can use it - 6, 8, and 10 are grounds.

Take another 680 ohm resistor and solder it from B8 to T10 (or T8 if that is easier)

*note that if the socket is impossible to get to, you can use the wires already soldered to B3 and B8, merely removing them from the kreg terminals on the PC board. Connect the resistor between the wire and T6, and the other between the other wire and T10. Rather than cut the wire to length, you can fold it to shorten it if that is easier - pinch a piece and twist the loop to minimize magnetic pickup. I'll try to do an ASCII picture here:

      _       pinch
      X
      X       twisted section
      X
______X_____ wire


This will require that you connect the resistor to the wire without a terminal to solder both of them to. Bend both 180 degrees to make a solid mechanical connection before soldering, and make an apologetic sacrifice to the solder gods for bad practice!
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Montigne on March 10, 2014, 08:23:12 AM
Paul,

Thank you for the step-by-step response, this will be very helpful. I have a few more questions before I attempt the fix:

- I'd like to try replacing the 431 in the right channel first, so is there a specific part # I need to order one from Bottlehead or Mouser?
- I've also found 650 ohm metal film resistors, but what power rating, tolerance, and voltage rating should I get?
- in your previously posted instructions, are your steps of adding the resistors after removing the 431's, or do I leave those in and just bypass them with the resistors in your steps?

Thanks again.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Paul Joppa on March 10, 2014, 02:43:11 PM
Go to the Mouser site. It's under semiconductors > power > Power management > voltage references, then restrict the search to ON semiconductor. It's a TL431 in a TO-92 package. There are several variants, you want some in bulk (not on a tape or a reel of 2000 or an ammo box full of them...) and that are in stock. Other suppliers have similar search engines - now's a good time to learn to use them, they are quite handy.

I'm specifying ON because they have the best data sheet (you can download it from Mouser; the noise specification is in Figure 13 FYI) which is what I've used for all my designs to date. I believe it may have been a TI design originally, and they are a reliable manufacturer as well. Other variants may have different specs, I have not (obviously?) gone around reading and comparing all the available data sheets!
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Montigne on March 17, 2014, 08:08:52 PM
Paul,

So I called last week and Eileen sent me three new 431s to try. I tried all three in the channel with the hiss, and it still remained. Also, I even tried one of these new 431s in the silent channel and guess what: hiss was introduced where it wasn't before. I took a closer look at the markings on each and found that the original two that came in my kit were different: fKB31 LM431 ACZ (silent channel) and WS TL431A 12427 (hiss channel). Also, the three that were sent as the replacements were all the WS TL431A 12427 as well. My conclusion: I agree with your previous assumption that these different 431s are the hiss problem possibly due to manufacturing.

My next step will be to bypass the 431s with resistors as instructed in your previous reply, but what tolerance, voltage, etc. of 680 ohm resistors should I get? What specs on those very resistors should I stick to to have a successful outcome?

Thanks, I feel we are close.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Paul Joppa on March 18, 2014, 11:10:33 AM
Wow! Thanks so much for doing such careful work and reporting it! Now we're getting somewhere ... :^)

For the 680 ohm replacement, the power is tiny so any size is fine. Use metal film for preference - I like the Dale RN series metal films but most brands are very quiet. A really good carbon film can be quiet but given the origin of this thread I would not use one to start with. Wirewound would be good as well; non-inductive or not should make no real difference in this application but they are likely to be bulky and inconvenient to install.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Montigne on March 18, 2014, 12:13:09 PM
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!
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Paul Joppa on March 18, 2014, 02:39:30 PM
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.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: borism on March 19, 2014, 05:21:22 AM
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). 
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Paul Joppa on March 19, 2014, 12:19:15 PM
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.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Dr. Toobz on March 19, 2014, 12:29:35 PM
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!
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Doc B. on March 19, 2014, 12:47:23 PM
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.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Dr. Toobz on March 19, 2014, 02:12:29 PM
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.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Montigne on March 23, 2014, 06:38:03 PM
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
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Grainger49 on March 24, 2014, 12:05:58 AM
    .  .  .    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.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: ffivaz on March 28, 2014, 11:58:33 AM
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.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: borism on March 31, 2014, 04:17:46 AM
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)?
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: ffivaz on March 31, 2014, 08:46:37 AM
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.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Paul Birkeland on March 31, 2014, 09:04:49 AM
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
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Grainger49 on March 31, 2014, 09:32:48 AM
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!  ! 
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: bjorgens on March 31, 2014, 10:08:42 AM
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
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Paul Birkeland on March 31, 2014, 12:36:03 PM
Hello Bryan,

I'd look for Fairchild or ON Semiconductor TL-431 ACZ. 

-PB
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: bjorgens on March 31, 2014, 01:11:37 PM
thanks Paul !

is there any pre-install measurement I can make to determine if one part is potentially quieter than another, or is it simply a listening test only?
bryan
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Paul Birkeland on March 31, 2014, 01:17:30 PM
Nah, smoke it and see!
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: bjorgens on March 31, 2014, 01:33:03 PM
:)
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Paul Joppa on March 31, 2014, 04:22:14 PM
To be clear - the TL431 and LM431 are supposedly the same and meet the same specifications. We seem to have acquired a batch that don't meet specifications (i.e. they are very noisy).

I think this may have happened in the past as well; I recall a time period where we suddenly had a number of noise problems with Foreplay upgrades. At the time we were not aware that the parts may be out of spec, but we found a modification which helped. Now I am wondering if we got another bad batch. (The mod is not applicable to the Paramour or Paramount.)
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: borism on April 08, 2014, 12:26:22 PM
A brief update. After stating in a post before that my WS 431s were quiet and reading Docs note that hiss comes in degrees I went back and realized that there was a soft noise from my speakers audible from within 2 feet.
 
Then Fabien reported that he had replaced his noisy WS 431s with some FKA48 LM431 ACZ (I believe Fairchild) to good effect and he graciously offered to send me some extras.

So, I accepted his offer and replaced the WS ones in my amp. The result was eye opening. The soft noise that I originally attributed to tube rush is completely gone. The speakers are dead quiet now.

Thank you Fabien.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: ffivaz on April 08, 2014, 08:57:20 PM
I'm glad I could help.
Fabien
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: johnsonad on May 16, 2014, 04:58:06 AM
I wanted to add a little something to this.  I too received these WS marked 431's in my soft start kits.  I replaced them this morning with two different brands of LM431ACZ regulators.  Both are equally quiet with a slight difference in noise that they make but both are significantly quieter than the WS marked regulators.  Before I could here the noise in my listening chair and through the quiet passages of music.  Now I hear nothing at the listening position.  Thank you for the heads up on this.  I'm no longer chasing noise through my amps.
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: Jim R. on May 16, 2014, 10:05:04 AM
I just got a couple dozen fairchild lm431 aczs and will replace any of the ws ones I find in my amps. Thanks all for doing the detective work.

-- Jim
Title: Re: Recently Completed Stereomour - Hiss in Right Channel
Post by: DesignTaylor on January 16, 2019, 05:22:43 AM
Also wanted to add a note here since I found this thread helpful in my search. I had a lot of background hiss (especially noticeable when I added some bullet tweeters) and after reading this I checked and sure enough, I had the WS marking on my 431s. The BH folks kindly sent me some replacements and I swapped them out (not super easy on an assembled unit for someone with my soldering capabilities).

The replacements cut the noise in half if not more. There is still some low hiss present but you need to be less than a foot or two from the driver to really head it.