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La Scala II and Tubes


deadlift

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I have a pair of these along with a Manley Labs Neo-Classic 300B preamplifier and a pair of Quciksilver Horn Monoblocks. I have replaced all the tubes with Brent Jesse parts and when turned on there is dead silence at he speakers no matter how close you put your ears.  I know that Mike at Quciksilver had designed these amps specifically for high efficiency speakers so I'm not entirely surprised.  Then along comes a pair of Manley Labs Neo-Classic SE/PP 300B Monoblocks and now the noise.  It's not horrible, but perhaps I had gotten spoiled  with the Quicksilvers?

Is it unrealistic to throw 6 300B's 18 tubes in total to a pair of 105DB speakers and expect complete silence?

 

 

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Glad it's not just me I have noticed that by staying in SE mode and cranking the negative feedback to 10 - it does quiet the buzz a bit.  Just yesterday I rolled all the tubes with Brent Jesse stuff and biased but alas still that buzz.

 

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I agree with Schu no noise is the ideal, I have read that some people feel its acceptable to say move 3 or 4 feet away from the speakers and if the noise can no longer be heard that's OK.  What I have noticed is that friends and family who are listening never seem to notice, but in between tracks I hear it and it annoys.  I also wonder with these tubes being so new after burning on for a bit will they start to quiet down.

 

 

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5 hours ago, deadlift said:

Then along comes a pair of Manley Labs Neo-Classic SE/PP 300B Monoblocks and now the noise.  It's not horrible, but perhaps I had gotten spoiled  with the Quicksilvers?

Is it unrealistic to throw 6 300B's 18 tubes in total to a pair of 105DB speakers and expect complete silence?

 

No it's not unrealistic...... it just requires good design with attention paid to minimize noise with high-efficiency 105db loudspeakers.

 

What is the manufacture year of your amplifiers..?

 

Do you have noise when the signal mute switch is activated..?

 

Is the noise more Hum or Hiss or both..?

 

Have you optimized the bias settings of the 300B output Tubes...?  This is critical for minimum noise.

 

I have attached the owners manual for the version with 5U4 rectifiers.

 

Manely NEO-CLASSIC SE-PP NSEPP.pdf

 

http://www.manley.com/products/view/nsepp

 

Interesting design,

miketn

 

 

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5 hours ago, deadlift said:

Glad it's not just me I have noticed that by staying in SE mode and cranking the negative feedback to 10 - it does quiet the buzz a bit.  Just yesterday I rolled all the tubes with Brent Jesse stuff and biased but alas still that buzz.

 

 

The buzz is less because in SE mode the balance of the 300Bs is less critical and as negative feedback is increased the amplifiers gain is reduced.

 

Have you experimented with lifting the AC plug ground on one or both amplifiers as suggested in the manual..?

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Hi Miken,

 

I just purchased the Manley's a few months ago - so I would say very recent.  When the mute switch is on there is dead silence.  When I first powered these them on even after checking the bias they were very noisy more of a hiss then a hum.  I noticed after more time the noise was getting less noticeable. Just 2 days I rolled the tubes with Brent Jesse suggestions and while the noise did not go away it did not get any worse.  I'm hoping as these tubes age and I keep checking the bias the noise will disappear because when the music is playing - the sound is truly sweet!!!

 

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23 minutes ago, deadlift said:

When the mute switch is on there is dead silence.

 

This pretty much eliminates the amplifiers as the source of your noise and is probably more likely due to noise floor from the pre-amp relative to the amplifiers input sensitivity.

 

Does the noise change when the pre-amp's volume control is adjusted...?

 

21 minutes ago, deadlift said:

Yes the left channel was noticeably nosier then the right so I did add a cheater plug for the left amp which did make a difference

 

I would suggest trying a cheater plug on the right amp also if you haven't to see if that reduces noise any more..

 

 

miketn

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17 minutes ago, deadlift said:

I will try that but having the Manley neo-classic preamp I thought these guys would play nice together.  The Manley preamp seems to love the Quicksilvers zero noise with those amps.

 

Second cheater plug probably want help much but worth a try...

 

You would think they would play nice but the pre-amp does have a fairly high noise floor specification [ manual quotes: Noise Floor: typically -70 dB (1 Hz - 100 KHz) ] making amplifier input sensitivity critical with High efficiency speakers(105db) but less critical with loudspeakers with efficiencies in the 95db or so range.. ie: this would be like reducing the noise floor of the system by 10db.

 

The quick silvers probably have a lower input sensitivity ie: takes more voltage to drive them.

 

You could experiment with adding an attenuator in front of the Manley Amplifiers for a better system S/N floor.

 

 

For those wanting to read more about the Manley 300B Pre-Amp:

 

Manely NEO-CLASSIC 300B Preamplifier NEO3BR_manual_2016.pdf

 

http://www.manley.com/products/view/neo3br

 

 

miketn

 

 

 

 

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5 minutes ago, mikebse2a3 said:

You could experiment with adding an attenuator in front of the Manley Amplifiers for a better system S/N floor.

dluoC

Quote

 

Hi Miken

Could you elaborate more about this? I find this very interesting and would love to give it a try.

 

Thanks

 

Tom

 

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The attenuator would simply reduce the voltage applied to the input of the Manley Amplifier and your goal would be to attenuate the Manley Preamp's noise floor signal while still retaining enough drive signal to reach full output power from the Manley Amplifier.

 

A few questions that might tell us if an attenuator will work in your situation.

 

Questions (1) and (2) below are with no music playing and the system is just turned on and idling..!

 

(1) Does the noise level change with the volume control position..?

 

(2) How loud is the noise level in your room:....  ie: roughly how far away from the speakers can the noise be heard with no music playing..?

 

(3) Do you have plenty of preamp volume control range....?

ie: for example If you typically have the volume control at the 9:00 o'clock position for reasonably medium to loud listening levels then an attenuator is a good option.

ie: for example If you typically have the volume control at the 3:00 o'clock position for reasonably medium to loud listening levels then an attenuator is probably not a good option.

 

 

miketn

 

 

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An attenuator for our purposes is simple a voltage divider used to reduce signal level.

They can be fixed or variable and designed with different impedance values.

The impedance value of an attenuator can interact with the drive source output and thus affect the sound so this should be taken into account.

 

Examples of fixed and variable attenuators.

note: so called passive preamps are attenuators and they would be a very good option in many situations.

 

https://www.parts-express.com/cat/line-level-attenuators/1916?utm_source=google&utm_medium=cpc&utm_campaign=L_Cats_BP&utm_group=line-level-attenuators_1916_BP

 

http://www.goldpt.com/prices.html

 

 

266-242_HR_0.jpg

 

 

sa1.jpg

 

 

 

 

 

No longer in production but I have found this to be a very good sounding and flexible piece of equipment. 

50K Impedance

 

e.jpg

 

 

miketn

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Hello Miken,

 

   First thank you for taking the time to reply, much appreciated .  Please forgive my brain fart in regards to attenuators I actually own a few pairs of Harrison's 12db which i had been using when I was experimenting with the Rogue Audio M180 mono blocks.

 

As to your questions

 

1. Yes the hiss does get more pronounced with the volume cranked up

 

2. I would say the noise is noticeable at least to me from 15 to 16 feet away from the speakers.

 

3. Although not as ridiculous as with the Rogue Audios I did fee that the volume was getting too loud too sound which surprised me a bit with what 11 watts in SE mode.

 

So I added the 12db Harrison's into the mix and ...  I now had to be within a foot maybe a foot and 1/2 in order to hear any noise.

 

I will actually listen to some music on Monday and let you know how it goes.

 

Thanks

 

 

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Just a follow up Miken was right on with this issue - I compared the specs for the Manley amp and the Quciksilver and the one spec that jumped out at me was the input sensitivity the Manley is with 5DB FB Push Pull 160mV for 1V output into 8 ohms the Quciksilver on the other hand is 6 volts and as described

" The Horn Mono Amplifier is designed specifically for use with very efficient loudspeakers. It has extremely low noise and distortion and approximately 18 db less gain than Quicksilver's standard amplifiers.  This avoids the noise and gain problems that normally appear when using horn speakers. :

 

So no wonder all is quiet with the Quciksilvers, however I have found as Miken suggested that the attenuators have taken care of the excessive noise with the Manley amps.

 

Live and learn as they say.

 

Thanks

 

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