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