LightSpeed Passive Preamplifier/Attenuator for my OB Set-Up

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-Richard-

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My simple 2-way Open Baffle set-up, which is bi-amped, consists of a pair of Lowther PM5A Alnico/Ticonal on top played ‘full-range’ (it has a ‘secret' ingredient of Titanium added to the metallic soup of the Alnico magnet) driven by the 2-watt Yamamoto A80S 45 Single Ended Triode amplifier, and a pair of Eminence Alpha 15A’s on the bottom, passively high-passed at around 250-300 Hz (using a coiled inductor) and driven by the Millenia TBI integrated Class BD 8 watt amplifier.

I split the streaming signal from Spotify on my iPad mini to both amplifiers.

I was using an inexpensive ‘passive’ preamplifier to attenuate the signal to the Yamamoto SET amplifier. That allowed me to stream the signal from the iPad mini at full volume. The TBI has a volume control. I was reluctant to use the iPad mini to attenuate the signal, although it does have a control for volume, because I read that a digital volume control strips-out detail. I became convinced after careful listening to my set-up that the passive preamplifier was holding back the performance of my OB’s.

So I switched-out that passive preamplifier and sent the signal directly from the iPad mini to both amplifiers using the volume ‘controls’ on the iPad mini and was greeted with much more detail and an obvious jump in the sense of ‘presence’ and ‘immediacy’. Thus began my search for a preamplifier that would not limit the ‘fidelity’ of the streaming musical signal.

In my past experiences with Single Ended Triode amplifiers I had experimented with several ‘passive’ and active preamplifiers, and every SET amplifier sounded more alive, more magical when I used a passive preamplifier, except for one SET which needed an active preamplifier to come fully alive. The Yamamoto already sounded wonderful and magically alive so thankfully an active preamplifier was not necessary.

A ‘passive’ preamplifier, often referred to as an ‘attenuator', has no ‘active’ stage to boost the initial 2-volt signal generated from either a CD player, or as in my current set-up, streamed from the iPad mini, to the amplifier. It ‘attenuates’ downward from the peak volume of what 2-volts delivers from source.

I did my usual ‘research’ which is to try to read everything one can find on the web, written by ‘professional’ reviewers like Srajan of 6-moons, and members of audio-related circles, like our community here at Audiocircle, Audiogon, and what the products themselves suggest on their websites. As you might expect there are differing opinions about the various circuits that are being offered by manufactures world-wide. At one point I narrowed the search to two offerings, Bent Audio’s version using the Slagle’s autoformer, and George Stantscheff’s LightSpeed Attenuator. Alas, John Chapman of Bent no longer offers a ‘finished’ passive preamplifier, only parts for a DIY project. Dave Slagle offers a passive version that is expensive and aesthetically unappealing to me.

I wrestled my way out of the usual paralysis that prefigures one’s audio choices by calling a fellow who writes honestly about his observations on Audiogon’s forum and who has tried almost ‘everything’. He wrote enthusiastically about his experiences with the LightSpeed Attenuator and felt it was the best he had ever heard, even compared to some highly-rated and expensive active preamplifiers. Speaking to him helped me to make my decision to purchase George Stantscheff’s special LightSpeed Attenuator by answering all of my questions honestly.

George is a pleasure to work with. He is honest, knowledgable, generous and extremely helpful. It cost me $400 shipped directly to my door from Australia.

His ‘Attenuator’ uses LED light transmitting optocouplers instead of metal contacts. Here is a brief explanation of this ‘revolutionary’ approach from the website, DIY Audio Projects: http://diyaudioprojects.com/Solid/DIY-Lightspeed-Passive-Attenuator/

"What makes this passive preamplifier interesting is that there are no contact points in the form of a "wiper" as in the case of a potentiometer or "switches" as may be with a discrete stepped attenuator. The key components in the Lightspeed Attenuator are Silonex NSL-32SR2 Optocouplers (PDF - 34kB). The optocoupler device is a sealed unit which consists of a high performance LED that shines on a light dependent resistor (LDR). The operating principle of the optocoupler is fairly simple. As the intensity of the LED varies, so does the internal resistance of the LDR (resistance decreases with increasing light). So in the case of the Lightspeed Attenuator, we change the volume (resistance) by changing the intensity of the LED. By using a series and shunt combination of optocouplers the attenuator can be configured to produces a constant input and output impedance, regardless of where the voltage control setting is.”

George’s LightSpeed Attenuator needs an AC to DC converter to light the LED optocouplers and can stay on all of the time with the volume controls set at half, or lower, as in my case, with an estimated LED optocoupler ‘life’ of 50 years. I wish the tubes used for the Yamamoto could last 50 years!

I plugged it in and waited the 15 minutes that George recommends before engaging it. What I heard immediately confirmed that the volume control on the iPad mini was stripping vital detail and ‘presence’ from the musical signal when the volume was lowered, which was necessary in order to not be blown out of my house at full volume.

Now I was able to use the iPad mini at full volume using the LightSpeed Attenuator to raise or lower the volume of the Yamamoto with absolutely no compromise of important detail and ambient spatial presence, no matter what volume I played the music. Also, and just as helpful, the volume of both amplifiers can be adjusted for a seamless musical presentation that is completely convincing.

The fact that I can play the LightSpeed Attenuator at much lower volumes without losing the magical sense of ambient detail, immediacy and presence, that is the pure delight of the Open Baffle presentation, allows Deborah and I to listen to music late at night without fear of bothering neighbors. Everything sounds more transparent, with more of a sense of ‘air’ around voices and instruments. As it turns out the Yamamoto SET is more crystalline and transparent than was apparent before using the LightSpeed. And beyond that, what we are hearing now is a deep resonate sense of any instruments materials, like a cello’s wood and the rosin on the strings, or a flutes metal mixed with the vibrating reed, or the deep warmth and emotional complexity of the human voice.

Deborah and I have never been as thoroughly happy with our Open Baffle set-up as we are now. I cannot express the joy Deborah and I feel listening to music come to life played through our home stereo.

Oh yes... I almost forgot to include that while reading about Spotify recently, there was a reference that Spotify has now included an EQ function within it. I opened up the EQ option and choose Bass Boost, which has a curve that could be adjusted within a nice range of lower Hz gamuts. That has made a huge difference in how low the 15" Alpha 15A's can go, also the 'boost' in the bass around 60Hz to 120Hz has made up for any cancellation inherent in the Open Baffle paradigm. Absolutely no need for an additional dedicated bass driver now. Fantastic feature for us DIY Open Baffle designers! Every music streaming service should have this feature and hopefully one that is even more sophisticated in the not-to-distant future. If you use Spotify and have designed your own Open Baffle speakers, please give the Bass Boost a try and let us know what you think!

Happy ThanksGiving & With Warmest Friendship ~ Richard
« Last Edit: 27 Nov 2015, 03:50 am by -Richard- »

nicoch

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Re: LightSpeed Passive Preamplifier/Attenuator for my OB Set-Up
« Reply #1 on: 2 Dec 2015, 03:27 pm »
HI Richard the ligthspeed work nice but your system is so good that you need two mod:
avoid the ipad mini at last use Pono or hifi spotify device and  an active xover x the 15" that coil slow down your alpha that are not soo fast ;) a small caps at the input of Yama to cut some bass out
Ciao

-Richard-

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Re: LightSpeed Passive Preamplifier/Attenuator for my OB Set-Up
« Reply #2 on: 2 Dec 2015, 11:28 pm »
Hi Ciao ~

Your sense of where the 'improvements' need to be worked out seems correct. The iPad mini should be replaced with a more sophisticated product, and Stereophile does feel that the Pono is excellent at its price-point, I think around $400. An 'active' cross-over would probably help to make the Eminence drivers respond more quickly as well. Several knowledgable DIY designers here at the OB forum also think that 'cutting some base' from the Yammie would help the Lowther's as well.

I am moving slowly into 'refinements' or 'upgrades' with this set-up. Deborah and I are really listening to different recordings through Spotify every day to get to know what the set-up needs next to further release the 'magic' of the music.

In the meantime, the 'core' musical experience is quite good, so that I don't actually feel I am missing anything yet. The top-end, higher frequency 'resolution' and 'detail' is not comparable to my memory of the newer Magnapan panels. But the Maggies did not reveal this level of intimacy or textural 'presence' in the mid to lower mid-range. It really is a 'trade-off' isn't it? But what we are hearing is deeply satisfying for now.

Has anyone in our community heard the much talked-about (at least a few months ago) Auralic Aries mini, since it began shipping at the end of November? If so, what do you think? Has anyone compared it to the Pono?

With Warmest Friendship ~ Richard


gilbodavid

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Re: LightSpeed Passive Preamplifier/Attenuator for my OB Set-Up
« Reply #3 on: 7 Dec 2015, 09:07 pm »
Hi again Richard.

I have been using a diy paradise eva 2 as preamp in my system for 2 years. It uses diodes and has 3 inputs and a remote control. It has been better for than passive preamp and like the light speed attenuation seems to maintain dynamics at all volumes. The best preamp I've had in my system for me

Cheers David

-Richard-

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Re: LightSpeed Passive Preamplifier/Attenuator for my OB Set-Up
« Reply #4 on: 15 Dec 2015, 12:43 am »
Hi David ~

I just returned home after being away for a while. Sorry that my reply comes a little late.

I looked up your diy paradise eva preamp and it looks like a very good candidate for an effective passive.

George Stantscheff who makes the LightSpeed Attenuator makes the point that many of the LED Optocouplers he purchases do not stand up to tests he puts them through to test their stability and reliability. He rejects quite a lot before selecting 'matched pairs' for his LightSpeed application. Apparently that is the fly-in-the-ointment of using LED Optocouplers. So hopefully diy paradise uses similar practices of stringently testing them. Also, George has mentioned that he has tried a remote option on the LightSpeed but claims that it always reduces the resolution a little.

Interestingly, I am not a fan of remote controlled volume control devices, although admittedly they are sought after by many audio aficionados for their ease of use. The simple reason is that I like to be in 'touch' with the controls directly. The precision of control offered by the LightSpeed is remarkable. The 'feel' of the controls are more like you would find on expensive audio gear; the 2 controls, one for each channel, have a wonderful smoothness to them that is seductive. Also, I find myself adjusting the sound to suit various recordings, which I dial-in just after I have selected something on Spotify, so I am already where my audio set-up is.

The one device that I definitely would want remote control on is a CD player, it really does make it easier to select a particular musical offering using a remote controlled device. Irregardless, the diy paradise seems like a bargain given its included remote control device and more options for inputs.

Thanks for mentioning it to our AudioCircle community. It seems worth checking out.

With Warmest Friendship, and Wishing Everyone a Wonderful Joy-Filled and Music-Filled New Year ~ Richard

georgehifi

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Re: LightSpeed Passive Preamplifier/Attenuator for my OB Set-Up
« Reply #5 on: 15 Dec 2015, 10:18 pm »
Hi David ~

George Stantscheff who makes the LightSpeed Attenuator makes the point that many of the LED Optocouplers he purchases do not stand up to tests he puts them through to test their stability and reliability. He rejects quite a lot before selecting 'matched pairs' for his LightSpeed application. Apparently that is the fly-in-the-ointment of using LED Optocouplers. So hopefully diy paradise uses similar practices of stringently testing them. Also, George has mentioned that he has tried a remote option on the LightSpeed but claims that it always reduces the resolution a little.

With Warmest Friendship, and Wishing Everyone a Wonderful Joy-Filled and Music-Filled New Year ~ Richard


Hi Richard, just have to correct a couple of points you made above using words that can be misconstrued by some.

The Lightspeed Attenuator uses "matched quads" not matched pairs as other do, this allows for not only better sound but for a more progressive feel to the volume control, and better low level min volume.

As for where you used the word the "remote" the first time, that should be "a active forced matching circuit". I don't believe in these, as they can and will over (safe) current the LDR's that need more mA put into them to keep up with the others, which can and will over stress them and cause failure in the long term.
As well as this type of circuit can be detrimental to the sound as they are attached to the signal output just like an active feedback network is, and need to constantly sens re-adjust each time the volume is changed. So in effect these types of Lightspeed cannot be called passive, as they have this active network attached to the signal output.

As for the use of remote controls for volume adjustment, I have no problem with this, but it is almost impossible to find after market ones of very good quality, that will last the distance, so I prefer not to, because those types of suppliers for Asia are here today gone tomorrow, and I know they will go faulty sooner or later mainly the remote buttons go first.

BTW: here is the circuit if someone with the skills wants to make one for themselves. Please ask any questions here, if you need help building this.

 

Cheers George and to all have a Merry Xmas and happy New Year.
« Last Edit: 20 Dec 2015, 07:23 pm by georgehifi »