La Scala II and Tubes

[mikebse2a3]

Thanks for the feedback deadlift...!

 

I would love to hear the Manley Labs Neo-Classic 300B preamplifier and especially the Manley Labs Neo-Classic SE/PP 300B Monoblocks.

 

To be able to offer either SE or PP in the amplifier without compromise to either would require some excellent transformers and design efforts/implementation.

 

Shoot some pictures when you get a chance and share with us.

 

miketn

[deadlift]

Sure there you can see the 300 SE/PP glowing away....  Despite the initial noise issues these things sound really sweet with the la scala's incredible sound stage.

 

 

[alzinski]

This is fantastic!! There is a tube and a SS section here     I do prefer tubes myself but I am old and grew up with them so  I am biased.

 

It is not unrealistic to have a hum free amp. The Quicksilver amps may have had regulated DC filaments along with a better power supply compared to the Manley. I am not familiar with either but unless you get under the hood you won't know until you start comparing the two internally.

 

[deadlift]

hello aalzinski,

 

The quicksilver was specifically built and designed for very efficient speakers from the web page: " 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. The amplifier is designed to sound good at the extremely low levels (milliwatts) that horn loudspeakers require. Many amplifiers actually have higher distortion at these low levels. " 

 

comparing the input sensitivity:

Quicksilver:

Input Sensitivity

6 volts

 

Manley:

Input Sensitivity with 5db FB SINGLE ENDED: 700mV for Maximum Power

Input Sensitivity with 5db FB PUSH-PULL: 450mV for Maximum Power

Input Sensitivity with 5db FB SINGLE ENDED: 165mV for 1V output into 8 Ohms

Input Sensitivity with 5db FB PUSH-PULL: 160mV for 1V output into 8 Ohms

 

[richieb]

I owned the 'Horns a couple times and just recently sold a pair. The amps themselves are very quiet through KHorns and Jubes. If you sense/hear a high noise floor it's most likely the preamp. Noisy preamp with Horn Monos negates the Monos design.

[deadlift]

Hi richieb

 

The Manley preamp was dead quiet when hooked up to the Qucikailvers only when switching over to the Manley amps did the noise begin, this has since been corrected with an attenuator.

 

 

[alzinski]

I too have La Scala's and is how I found this forum.

 

It appears the quicksilver amp has a gain of 7db. The 6v sensitiviity means there still has to be gain somewhere in the chain to achieve full output power. Where was this gain coming from? Most likely a preamplifier. If you had no hum when using a preamplifier then the preamp was designed well.

 

To acheive the sensitivity the Manley amps have they are most likely using a VAS with more gain which is akin to you using a preamp to acheive the 6v input for your quicksilver amps. The Manley amps must have skimped out on PSRR or something in the VAS stage which is common. It's hard to get good PSRR from a VAS since they usually share the same supply as the output stage, the higher current draw from the output stage creates a larger ripple which in turn needs more filtering.

 

My current amp for my La Scala's has a gain of 10db and there is zero hum. A modern source of 2vrms gets me to full output power of 5 watts.

[deadlift]

hi alzinski,

 

here's a link to the specs etc of the Manley amps if you would care to look over....

 

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

 

Thanks

 

[alzinski]

I am not a fan of gimmicks so I don't like the functions of swtiching from one topology to another or variable negative feedback. I like amps that are optamized for a specific topology.

 

From briefly reading throught their literature I surmise that they do use DC on the filaments which is good. They use tube rectifiers which limits the amount of capacitance you can use for filters and pretty much forces you to use heavy expensive chokes in the power supply, which I don't think they used. Resistively loaded gain stages don't offer the best PSRR which I don't know if they use or not but I would guess they do. Hum is hard to diagnose over a the internet so layout and ground loops could be a cultprit too. 

 

Is the amp any quieter in PP mode? If not the noise is most likely generated by the 6SL7 gain stage. The 6SL7 has an internal impedance of ~40k and when loaded by a 100k resistor doesn't offer much ripple rejection. 

 

Feel free to take a picture of the guts for us, there may be room for modifications and or at least further assesment.

 

 

[deadlift]

Perhaps a bit gimmicky but Sam liked their sound http://www.stereophile.com/content/manley-labs-sepp-300b-monoblock-power-amplifier#yA3PI8DKY86Iwxfm.97

As do I. As for the original noise issue I have solved that by placing a Goldpoint Attenuator in the path and now I have to press my ear up to the speaker to hear the slightest of noise which I can live with.

 

 

 

[alzinski]

A gimmick to me is an option for someone else and options are good so long as it doesn't compromise the performance. If you like the amp that's all that matters, I am happy for you.

 

So you have an attenuator between the preamp and the amp now? Is the attenuator passive? i.e. a resistive divider?  It seems that the Manley having more gain was amplifying the preamp noise and so attenuating the output of the preamp helps to reduce the noise going to the power amp. The problem with that is you are not just attenuating the noise but also the signal from the preamp. It seems that you have enough gain from the preamp and the power amp is sensitive enough for you to reach the desired output power. The only downside is now the preamp is swinging more output and you are probably getting a bit more distortion, but hey it's a tube amp so it's pleasant distortion.

[deadlift]

Hi alzinski,

 

     I was not offended in the least (just hope Eveanna Manley does not read these posts would not want to mess with her!!!) in fact I enjoy picking at your in depth knowledge of the topics at hand.  Yes it is passive and up o this point I have not noticed any distortion but I will at some point listen with and without the attenuator and assess whether dealing with the noise or using the attenuator is the better sound.

 

Thanks

 

[alzinski]

I don't know how in depth my knowledge is, I am  just a tinkerer that is passionate about music and audio.

 

The specs say THD .08% @ 1kHz 1vrms, I don't know what it would be at 5vrms out. If it's mainly second harmonic it might be hard to detect by ear but if third and higher harmonics start creeping up at higher outputs then it could add coloration to the signal.

 

It also says THD+N .01% but isn't specific about what frequency or what amplitude (into what load). And which output?

 

If the hum was bugging you I would just stick to using the attenuator, the distortion is most likely the lesser of two evils.

 

Picking gear is a bit more strenous when you have speakers like ours, trust me I know. Low noise is my #1 priority, I hate hum and noise from my speakers.

[tube fanatic]

On 4/27/2017 at 2:46 PM, alzinski said:

I am not a fan of gimmicks so I don't like the functions of swtiching from one topology to another or variable negative feedback. I like amps that are optamized for a specific topology.

 

 

 

Hi Albert- in reading your posts, and noting your depth of understanding of tube electronics, I have the sense that you are an old tube-head like me (please don't be offended if you are a young guy!).

 

In regard to variable negative fb, I recently used a successful implementation of it in a little SEP design in which I found that the amount of fb wasn't terribly critical. So, by making it variable, I was able to create a fb filter for pseudo bass boosting which allows the corner frequency to be moved around between about 38 and 65 Hz.  It's very useful for tuning the bottom end response for a particular system or listening taste.

 

Here are some measurements of the Horn Monos which you may find informative:

 

http://www.stereophile.com/content/quicksilver-audio-horn-mono-monoblock-power-amplifier-measurements#PRG5vD59SK2kyiJ8.97

 

Hope you become a frequent contributor.  There aren't too many guys on here who are into the technical side of tube electronics as you seem to be.  Beware though- I'm an old, crabby, guy who likes to argue about technical matters although I only have time to be on here occasionally this time of year.

 

Maynard

[alzinski]

Hi Maynard, you build amps? That is really great. I am an old 'tube head' as you so elegantly stated, I have nothing against solid state it's just the tubes seems to remind me of being a kid. In all honesty these old ears don't really need the .0001% THD and I find with my La Scala's  aren't sloppy with a mediocre damping factor. I actually think they shine with tube gear. It's been a while since I have built an amp, I have restored some old classics from time to time when I get the itch to tinker. My new project was going to refresh my crossovers but to be honest I don't know if they need it.

 

As for variable feedback I guess it depends on the implementation, I never thought of it as an effect as you have done with your design. I would just worry about stability but if it's only 10db or less around 2-3 stages there shouldn't be any issues provided decent output iron.

 

Thank you for link on the amps I will read through it with my coffee.

 

I am old and crabby too so we may get along just fine. Probably a lot of old crabby guys on audio forums so we are in good company.

[alzinski]

hi wdecho, I agree, tubes are still king with the heritage models. I hope to participate here when I have time.

[Kalifornian]

Picked up a McIntosh Mc275 VI and am running them on Crites/Volti modded Belles and have ZERO noise floor.  I did notice when I switched to some older NOS GE 5751 blackplates that there was some initial noise until the tubes heated up.  On new production tubes it has absolutely no noise whatsoever when nothing is being played....Just FYI from a different type of amp...

[NOSValves]

On 4/24/2017 at 9:47 AM, deadlift said:

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

 

Yeah Mike at Quick Silver played a nice one with those horn mono amps. I bet the amplifiers have just as much "amplifier" noise as any other decent tube amp. Raising the input sensitivity to 6 volts will make any preamp a top notch performer in the noise department. 

[tube fanatic]

Most noise in tube amps originates in the gain stages which precede the output stage.  Mike's approach in using a very low input sensitivity is a wonderful way to deal with the noise issue when the amp is to be used with very high sensitivity/efficiency speakers.  And, the measured performance of these amps is truly outstanding and far better than the majority of tube amps out there (including my own).

 

Maynard

[deadlift]

I could not agree more in regards to the Quicksilver's and for the price one is getting a very big bang for the buck.