How quiet is quiet?

[arveedub]

My system consists of an Eros phono stage, a base model Foreplay III, first generation Paramours & 96dB speakers. Can somebody give me an idea about how much noise I should expect to hear from the Eros at a reasonable volume level? From the replies to my other posts I understand that there is no real way to meaningfully measure the noise, but can you suggest any comparisons? As loud as a whisper? A hummingbird's wings? A downshifting eighteen wheeler?

Perhaps a comparison with the surface noise of a record.

A question without a real answer, I know. I'm just looking for a gauge on how much effort I should expend on trying to quiet the amp.

Just to be clear: the amp is quiet, but at higher volumes I do hear a hiss. It's not a problem I'm trying to fix so much as a metric I'm looking for.

Thanks!

 

[Paul Birkeland]

Hiss may have a lot more to do with specific tubes than anything else.  Generally, hum and buzz are the big annoyances.  Is the hiss there with the inputs to the Eros shorted?

 

[Grainger49]

After you answer Paul PB Birkeland's question ...  

There are a number of variables that haven't been addressed.  How loud do you listen to your music?  How big is the room?  How close to the speakers do you sit (that makes quite a difference)?  And maybe a couple of others that don't come to mind right now.

For instance, I have a 13.5 'X 21.5' room sit 9.5' from the speakers.  My speakers are a little less sensitive, 94dBW.  I listen to peaks in the high 80dB range.  Edit: I am using a recommended 5mV output cartridge.

I have some experience with the Eros, a lot with the Seduction.  The Seduction has very low noise in my listening situation, but I can barely hear it at my chair.  That is, I notice the difference when it is on with no music playing, between cuts, versus the CD player.  The Eros caused me to turn the volume down a quarter of a turn (90 degrees) and was noticeably quieter.  I hear surface noise on LPs but the noise in the Eros is lower than that.  That was with the stock, Bottlehead supplied tubes.  The Russian 6J32P can be variable.  Some are just noisy, others can be incredible sounding and very quiet, but they are a very low cost alternative to NOS European tubes.  As always, YMMV.

 

[Doc B]

AS PB says, it's tube dependent. The number one thing we need to know is what the nominal output level of your phono cartridge is. With that info we can give a rough idea of what level of noise to expect. If it's 5mV cart trying different tubes might help. But if it is, for example, a 1mV cartridge - that is below the recommended output level and you may be pushing up against the S/N floor regardless of the tube type.

 

[tbbenton]

I have the DV 20xH (2.8mV) eros, extended foreplay 3, paramounts and 99 dB speakers (4 pi).  From my listening position, I can not hear any noise when my digital source is selected and not playing anything.  Switching to the phono, there is definitely audible noise - not much hum, mostly white noise, but with a solid bottom end.  This noise just barely looses out to groove or surface noise from the needle.  So before lowering the arm, the noise is clearly there, but not so obvious.  Once the track begins, forget about the noise, until the album is over and I lift the arm.  My guess is that you should be okay with your setup, but not if you are a quiet freak (like I am.)  I'm working on it though.

 

[Grainger49]

tbbenton,

I wonder if padding the output of the FP III or the Paramount input would help with the noise.  Your speakers are very sensitive.  That makes the system susceptible to any tube noise or low level hum.  

I'm assuming you have all kinds of gain, meaning you can play it really loud without using much of the volume control.

 

[tbbenton]

Thanks Grainger, you are right about having plenty of gain, the system will play about as loud as I like.  And I do use a padded FP3 input for the phono.  While it gives me better resolution on the volume control, it doesn't really get rid of noise. 

BTW, I did experiment with different drivers (12AY7 instead of 12AT7) in the Paramounts to reduce the gain.  It worked but then my (old, used) tubes got noisy and started glowing purple.  When I swapped back in my 12AT7s I liked the sound better.

 

[arveedub]

tbbenton,

Thanks. I'm in the same boat. There is definitely noise, but only a little & it really doesn't get in the way. It's nothing more than white noise. I do know that I should expect some. I'm just trying to get a handle on when I have to stop blaming the noise on the amp. Today I got a set of dutch made amperex ef86's in the mail & they are quieter than anything else I have. Perhaps that's the answer right there: if it's only the tube I'm hearing, then the amp can't get any quieter. It's not its fault.

I am having quite a time finding good tubes. In a separate thread I'm going on about that. The string of bad tubes I'm having is probably making me paranoid about noise in general.

 

[Grainger49]

IIRC somewhere on the Foreplay III file Doc posted about a noise floor improvement on the FP III.  I asked if it were applicable to the other products but didn't get an answer.  If the problem is similar the fix, a change in capacitor or a bypass capacitor, I don't remember, might help.

Edit:  This, as seen below, is a bad idea.  The bypass doesn't work for the Eros.

 

[Paul Birkeland]

IIRC somewhere on the Foreplay III file Doc posted about a noise floor improvement on the FP III.  I asked if it were applicable to the other products but didn't get an answer.  If the problem is similar the fix, a change in capacitor or a bypass capacitor, I don't remember, might help.

If the problem is simply tube noise, no fix on the regulator board will help at all.

Just a thought.

That noise tweak was to minimize noise in the cathode follower half of the extended FP-III, but I don't see that it would hurt anything in the Eros. You would just want to bypass the two 110k resistors in each channel with a 2uf @400v cap. 

 

[Grainger49]

Paul,

Thanks !  

Edit:  The rest removed as this doesn't work. 

 

[Paul Birkeland]

In the Eros would that be R4A and R4B for each channel?  Is that 4 resistors to be bypassed; 2 for left and 2 for right? 

Yes, you would bypass each pair in each channel.  I would do this with a single cap across each pair, although you could split the job up between a pair of caps for each channel. 

How is that Seduction coming along? 

 

[Grainger49]

This is me laughing at myself.  I was thinking 4 caps.  D'oh!  (insert smack on head here)

Thanks for the clarity.

I should plug in the PS this afternoon and make some checks.  There are 3 different kinds of transistors on the reg. board (one is probably a 3 pin regulator) mirror imaged to each other.  I didn't think you could have made a mistake.  You didn't of course.  Now I need to verify the wiring I did afterward.

 

[tbbenton]

DANGER DANGER

I don't see that it would hurt anything in the Eros. You would just want to bypass the two 110k resistors in each channel with a 2uf @400v cap.  

It looks like it could definately do some harm:
Bypassing the 110 k resistors leads to a turn on transient current of 90 mA.  This would put instantaneous power on the 2.49 k resistor (R3) at about 20 W.    I think each channel needs a zener across R3 to protect it at start up.

I guess the 431 IC will need the protection of the zener too, since it's rated for something like 36 v, much less than the 225v it will see at start up.

 

[Paul Birkeland]

DANGER DANGER
It looks like it could definately do some harm:
Bypassing the 110 k resistors leads to a turn on transient current of 90 mA.  This would put instantaneous power on the 2.49 k resistor (R3) at about 20 W.    I think each channel needs a zener across R3 to protect it at start up.

I guess the 431 IC will need the protection of the zener too, since it's rated for something like 36 v, much less than the 225v it will see at start up.

I do see your reasoning, but the current available to charge that cap will be 23.5ma, 90ma won't pass through the top CCS.  Also the cathode voltage and anode voltage are both zero until the shunt regulator starts conduction, so the reference terminal is free to vary a bit.  This has worked on the shunt regulators in many Extended Foreplay III's.  If we had a fet in there instead of a tube, then I might be pretty worried. 

 

[tbbenton]

I do see your reasoning, but the current available to charge that cap will be 23.5ma, 90ma won't pass through the top CCS.  Also the cathode voltage and anode voltage are both zero until the shunt regulator starts conduction, so the reference terminal is free to vary a bit.  This has worked on the shunt regulators in many Extended Foreplay III's.  If we had a fet in there instead of a tube, then I might be pretty worried. 

Good point on the current source.  How much current does the tube sink?  Assuming worst case that 23 mA runs through the 2.49k R3, then there's about 60v on the 431, which is way above maximum rating of 37v.  This capacitor bypass is bad news.  I tried it and fried my Eros.

 

[Paul Birkeland]

Hmm, that is not good news!  PM me and I can ship you another board.  I will have to take some measurements in my FP-III and Eros related circuit to see why this might happen...  What was the exact failure in your Eros?

 

[Paul Joppa]

Just a note - the Eros does not have any cathode followers, all the stages are isolated from power supply noise by current sources. Making the shunt regulator even quieter won't affect the noise, which comes from other sources - mostly the EF86's thermal noise floor.

 

[tbbenton]

Hmm, that is not good news!  PM me and I can ship you another board.  I will have to take some measurements in my FP-III and Eros related circuit to see why this might happen...  What was the exact failure in your Eros?

Snapping sound and a flash of light, not in that order, of course.  All LEDs dead.  The resistors all still measure good, but replacing the 431s alone (from above - didn't remove the pc) didn't bring it back to life.  I will need to perform further tests.

 

[tbbenton]

Follow up:  My TL431s were indeed toasted and the LEDs on the shunt reg board were all shorted by the event.  Thanks to Paul, I received and installed a new shunt reg board and my Eros is back in fine form.  I am happy to have things working again and I have no plans to monkey any further with the power supply.