luigi Posted June 14, 2009 Share Posted June 14, 2009 I have already alluded to this new Optocoupler preamp design in a thread entitled "OB Designs" in the D-I-Y section, but to be brief, if you are messing with passive preamps, ditch them now and check out what Optocouplers and LDRs can offer. This is akin to CDs taking over from records, so as an analogy, it is poor (!) but the physical or mechanical contact (like a needle) is no longer necessary (replaced by a laser). The only difference being the result is better, not worse. Instead of having a wiper physically touching a track, as in a pot or stepped attenuator, this varies resistance using the output of LED picked up by an LDR (light dependent resistor) so no physical contact is made in the attenuation circuit . The result is a passive preamp that not only knocks any stepped attenuator for six as far as transparency (also imaging, and truth of timbre) is concerned, but also betters traditional passive preamps for drive and dynamics. You can tell because the bass is no longer missing in action. In fact, the unit I have (supplied by Georgehifi - George Stantscheff [georgehifi@optusnet.com.au] is rendering the best bass I have ever had in my system. The augmenting 15-inch drivers aren't used any longer, at least for music, at any rate. I am certainly not the only one to comment favourably on this form of passive preamp. Check out the 80-odd pages on its design and implementation here: http://www.diyaudio.com/forums/showthread.php?threadid=80194 Pretty much everyone rates it. Especially for the money. Now Optocoupler devices are also being made that you can use to replace your volume control if you have an integrated amp. see here: http://www.ska-audio.com/ Optivol. Link to comment Share on other sites More sharing options...
Antipodes1553552706 Posted June 15, 2009 Share Posted June 15, 2009 I will have a read thanks Luigi. I remember that Melos did this many years ago but some problems were experienced. I was always a little surprised this promising idea wasn't developed further. Was there a patent getting the way perhaps? Link to comment Share on other sites More sharing options...
luigi Posted June 15, 2009 Author Share Posted June 15, 2009 Antipodes: Not sure whether patent was involved, but think really that this was a question of the technology being immature. Clearly, from the (almost total) lack of comment, it is apparent almost no-one messes with passive preamps anymore! Which is kind of understandable -the impedance mismatches, and the resulting lack of dynamics, can mess with your head. But truly this new system of attenuation is a revelation. Moreover, it is simple, and evidently extremely reliable - the LDRs last for 25 years, and 50 years if the volume control is left at rest in the 12-00 position, according to George. Like, who cares? I'd be happy if it lasted without fault for just a few years, considering its cost. A bit of history on these devices. One of the best preamps of yesteryear, according to those in the know, and we're talking 15 years or so back, was the Melos SHA Gold Ref preamp. Evidently it sung sweetly but was unreliable, and probably contributed to the demise of the firm. But people swore by them for their sonics, when they weren't crashing and burning. This was the first implementation of LDRs for volume attenuation. As is often the case, there is a time when technology improvements lead to new products that might not have been possible a decade earlier. Guess this is the case with the new LDRs which are evidently pretty bulletproof. The one rider is that lots of these cheap devices have to be purchased to find two that actually match. Not a problem if you're buying one built up. The point then of this thread is not necessarily that these preamps are available, and relatively inexpensive ($400 landed here for Eva, with remote control for heaven's sake; $600 odd for Lightspeed Attenuator) but that this form of volume attenuation will likely be at the forefront of all moderately priced to insanely expensive high end gear and anyone can get purchase it for relative beans. Did I mention that these units have bested TVC-based preamps? (transformer volume controls) which typically cost thousands rather than hundreds of dollars. Already volume pots with this technology (admittedly, first generation) can be bought for $Au40. Link to comment Share on other sites More sharing options...
Antipodes1553552706 Posted June 16, 2009 Share Posted June 16, 2009 I have never liked the TVCs, and would prefer the grunge of a wiper pot than the strange phase irregularities of inline transformers. I prefer to use digital attenuation (much understood and unfairly maligned) if possible, but the problem is you need to get the gain structure of your system right for it to work well, and avoid the end to end system dithering more than once. What is the unit you recommend? I am always up for trying something new. Link to comment Share on other sites More sharing options...
Jon1553552729 Posted June 16, 2009 Share Posted June 16, 2009 luigi;94219 wrote: Antipodes: Not sure whether patent was involved, but think really that this was a question of the technology being immature. Clearly, from the (almost total) lack of comment, it is apparent almost no-one messes with passive preamps anymore! In my case it is more that of absorbing all of the info you have given and then trying to make sense of it. Passive preamps are a known and well understood technology and have a lot of fans. The octo-coupler has been around for a long time, it has taken this long and George's commitment (!) to making this work. You will note that the thread in Diyaudio started in 2006 -and currently has 90+ pages. As you say the cheapness of the technology is amazing! I still need to get my head round all the info! So at this stage all I can say is thank you for drawing this to my attention! Link to comment Share on other sites More sharing options...
Robocop Posted June 16, 2009 Share Posted June 16, 2009 I concur with Jon certainly interesting reading. I've been down this road with Alps, Bourne's and Electronic Visionary Elnas with Black vishay resistors and nearly Dact. Currently using active preamp for all the regular reasons. Always had a cleaner sound with passives but lacked some dynamics although compared to some preamps this was a big improvement in sound overall ie: early Perreaux preamps SM2 and SM3 which I once owned but left for passive devices which I ran for about 10 years. The old story less is best should work but in Hi-Fi there are forces at work which we still don't understand. Link to comment Share on other sites More sharing options...
luigi Posted June 16, 2009 Author Share Posted June 16, 2009 Antipodes: Only know of those two units for sale commercially. In essence, one is manual and the other has remote control, which looks a bit nasty (thin, tiny, easily lost Blaupunkt, from car audio I think) if Im honest. I should think there will be no real difference in the sound quality, as both likely use the same optocouplers, though George does use double regulation for the cheap regulated power supply. The pot he uses is neither here nor there because it is not part of the circuit that carries the signal anyway. Just beware you dont run into problems with excess gain because the lowest zero setting (back at the stops) still lets a "whisper" of music through. Which means with 94dB speakers, it is louder than desirable for late night listening, at least with my source. It outputs 2v where most CDPs are more like 1v, Im led to believe. Other than that, I'd probably still go with George's one, as it has had more time in the market place, and doesn't seem to break, at least that I know of. The other rider: one set of inputs and one set of outputs only. So most people would need something like a QED splitter for multiple inputs. Or somesuch. Link to comment Share on other sites More sharing options...
luigi Posted June 16, 2009 Author Share Posted June 16, 2009 Robocop: this is the first passive that seems somewhat more immune to impedance mismatches than any Ive tried before. And yes, I went down that passive path for a long time too, ending with Goldpoint stepped attenuator linked to a 12v tubed buffer circuit. It worked well..ish. Not a patch on the LDR unit though. If you read some of the DIYaudio thread, it is surprising what the LightSpeed Attenuator bests. Lots of it expensive and tubed. I just love what this does with piano, voice, guitar and awesome bass, something Ive never had in spades before with a passive. Cheers Luigi Link to comment Share on other sites More sharing options...
Owen Y Posted June 16, 2009 Share Posted June 16, 2009 I understand from another audio pal that Optocoupler attenuators are pretty GOOD. As I have opined here before... I have found that I prefer a wiper pot to resistor attenuators &, whilst all passive devices all tend to have sonic signature, to my ear I prefer the mix of compromises of a transformer. Power transfer (dynamic headroom, ppp to fff) without strain, being the most appealing trait (but then, I like horns too!). But like all audio TXs, bandwidth (resp/phase) is not unlimited, less so in the better designed ones. PS. The SMD resistor attenuators seem to be much better performed than the old type resistor types. Link to comment Share on other sites More sharing options...
Owen Y Posted June 16, 2009 Share Posted June 16, 2009 Of course, most R attenuators tend to be Series attenuators, rather than a Ladder attenuator... the latter with one series R + a shunt, would be (technically) much closer to an LDR Optocoupler... in principle anyway. Link to comment Share on other sites More sharing options...
Owen Y Posted June 16, 2009 Share Posted June 16, 2009 The LDR Attenuator is a VERY simple build. Just some sockets, a dual gang pot, 4 x LDRs, a couple of LEDs & R's.... & the costliest part would probably be the 5v PSU. A good DIY project for someone, volunteers? Link to comment Share on other sites More sharing options...
Luckiestmanalive Posted June 16, 2009 Share Posted June 16, 2009 Owen Y;94287 wrote: The LDR Attenuator is a VERY simple build. Just some sockets, a dual gang pot, 4 x LDRs, a couple of LEDs & R's.... & the costliest part would probably be the 5v PSU. A good DIY project for someone, volunteers? Yes! I'd be happy to chip in (given I have no skills or experience) for parts if I got a lend of the finished article when it was done... then I could determine whether it was somewhere I'd like to go. Link to comment Share on other sites More sharing options...
gortnipper Posted June 16, 2009 Share Posted June 16, 2009 luckiestmanalive;94299 wrote: Yes! I'd be happy to chip in (given I have no skills or experience) for parts if I got a lend of the finished article when it was done... then I could determine whether it was somewhere I'd like to go. Ditto - I would think as added incentive, the "doer" wouldnt have to pay at all for his part of labor. :rolleyes: Link to comment Share on other sites More sharing options...
Owen Y Posted July 1, 2009 Share Posted July 1, 2009 Luigi, That diyaudio.com Lightspeed thread is absorbing reading. Have only had time so far to get a quarter thru the 90-odd posts(!) & counting. Not sure where it's headed but there's a load of DIY info in there & George has done all the hard work already. This one will go on my audio to-do list. Link to comment Share on other sites More sharing options...
Owen Y Posted July 1, 2009 Share Posted July 1, 2009 Edit: That thread is 90-odd pgs, >2,000 posts! Link to comment Share on other sites More sharing options...
Antipodes1553552706 Posted July 1, 2009 Share Posted July 1, 2009 Yes, I gave up looking for something that summed it up succinctly. But will try again when I can find the time. Link to comment Share on other sites More sharing options...
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