There are five standards and of course lots more.... In no particular order:
1) Placette passive - very highly regarded, excellent support - resistor based as opposed to transformer based - this is the big decision you get to make
2) Sonic Euphoria - PLC for passive line controller - transformer based
3) Bent TAP is the new generation product using autoformers - design change was required when the transformer provider stopped providing, the previous version is also highly sought after
4) Promitheus TVC - for transformer volume control preamps - quite a full line - built offshore so high price/performance ratio
As far as I know all these suppliers will build balanced or single ended, multiple inputs and remote volume control
5) Probably the simplest units out there are by Channel Island Audio - they have a passive/active unit and a two source passive - small form factors and very clean
Full disclosure - I run my Keces 151 DAC into my Sonic Euphoria passive and then onto my Graaf. As the Brits like to say, "brilliant".
Don't underestimate the Channel Island passive preamps, they are very good.
I have tried most of the 5 recommended above, and a few others. They ALL left me with great detail but no warmth or body to the music, though the TVS types were by far the most natural sounding.
I am now using a Raysonic 168 CD player, which has a terrific variable tube output stage. I run it via the balanced output. It equalled a $3K preamp, so I sold it. Also, the output stage can be modified by Underwood HiFi. Something I am considering, thinking it is my weakest link. BUT, I just replaced the power cord to my amp with a new Tek Line Cable Reference power cord, the sound is much more organic. I need another one for my 168. After that I'll decide whether I need the mod.
Hello, You can also add Goldpoint attenuators http://www.goldpt.com/
to your list of candidates. They come complete/built or as a kit. Several versions including balanced XLRs. Comes with one, two or four inputs along with other options available.
Two others that you can try the McCormack TLC-1 and the McCormack Micro Line Drive. The TLC offers a passive and a buffered output while the Micro L/D offers a passive and an active output, the active output has an adjustable output of +/-6bd of gain. This will give you the option of deciding weather you like active or passive preamp's. Plus if you so chose you can have it upgraded at SMC Audio. I have a TLC and 2 Micro's one upgraded to Gold and the upgrade was well worth the money. For less than $1K the upgraded Micro gives the TLC a run for its money. I use the TLC because it has more inputs that I need. I'm scheduled to have the TLC upgraded with all the goodies after the new year, if you were curious.
Thanks everyone for the thoughtful responses! I'll start checking into these options.
There is a long thread on DIY forum on the Lightspeed passive attenuator, which is sold commercially by georgehifi (indentified throughout the thread.) His design is based on optocoupler resistors, as formerly used in the Melos photentiometer volume control and more recently, apparently, in a Dart Zeel $20K preamp. The design is not easily adaptable to a balanced system, but if you are running single ended, this may be the most transparent(and inexpensive) passive.
I think all the information above is very good, not mentioned (unless I missed it) is the music forst which is a TVC and is very nice
I recently did something of a passive shoot out using the Music First copper, Promitheus Ref with Double C-Core, Placette, and both balanced and unbalanced EVO nude attenuators.
I could have lived with any of them happily preferring the Promitheus.
Ultimately I have choosen a tube distinctions soulmate and a TRL battery unit as the ones I will keep. But this is not purely for sonic reasons but some convenience and aesthetics as well.
IMO, the use of passives is very system dependent....if you have the right output from your front end and the right gain structure throughout, can keep the IC's short and preferably use unshielded IC's so capacitance is not an issue the results can be terrific. Now these are important conditions and not easy to meet without other issues popping up.
I run a Canary Audio CA-200 Passive Preamp between a modified Music Hall Maverick CD player and a Spectron Musician amp. I have experienced none of the negatives you usually hear about using a passive preamp. There is nothing fancy about the design and I run it using very short Wireworld gold/silver Eclipse cables.
Are you still using the Paradigm Reference Active 40 speakers? If so and I read the amp specs correctly the line in input impedance is 15k ohms. That is something to take into consideration when selecting a passive preamp. That being said the other posters have covered the gamut on the different brands. Personally I prefer the TVC models over the resistor models as impedance matching is less of an issue.
Another consideration would be the new Pass B1 buffer preamp. It is a zero gain design with a buffer output that offers all the benefits of a passive but eliminates impedance matching issues. It's listed here on Audiogon for about $875 new IIRC.
With that 15kohm inout impedance I would only go with the Pass B1 Buffer, not quite passive, but awfully close. For some reason the GON consensus seems to be that TVC and AVCs (I've owned both from Bent and K&K, as well as the Placette Active and RVC)are always better than resistor based passive. With my Cardas GR IC (very low capaitance) and Music Reference RM9 Special Edition I find the Gold Point Volume Attenuator SA1 works just as well to my ears. Plenty of soundstage, dynamics, and clarity. The technoids can proabably explain it better, but I get the sense that TVC and AVCs are also problematic, though they do provide a partial solution to impedance mismatches. To my ears, with properly matched source and amps, the resistor-based attenuators are undeniably simpler, purer, and capable of even lower distortion - but they do have to be in the "right" system for them to perform their best.
Incidently, toward the end of the above Lightspeed thread, Nelson Pass contributes schematics for a buffered passive that employs optocoupler resistors. I don't know whether he is currently selling product based on this design. My read is that sonics of the AU$500 Lightspeed passive should equal or surpass the optical volume control in the $23K DartZeel NHB-18S.
I believe Nelson Pass already posted the schematic on the Pass DIY site as well. I saw a couple built by Audiogon member Rawsonte fly out of here of late.
As Pubul57 says the rsistor based design is much simpler. I'm tempted to break out my EVS nude attenuators and give them a test run in my new set-up. I looked at the Lightspeed thread and am curious about those attenuators as well. Anyone know a way to contact the manufacturer?
He keeps a low profile; emailing him through that forum is probably the best way.
One more I forgot to mention is from ElectraPrint marketed by their Electra-Fidelity subsidiary. Three versions (at least) all very reasonably priced.
Jack Elliano, ElectraPrints guiding light is considered to be one of the industries gurus when it comes to building audio output transformers, chokes, and power transformers.
After reading 63 pages on the DIY Audio forum and speaking to George I decided to pull the trigger on the Lightspeed. Also, I figure if Nelson Pass got into the mix on LDRs it is worth checking out.
Dave, did you ever get them implemented in the active preamp. I can't remember if you posted the outcome on DIY Audio.
Clio, I acquired the LDR piece parts, but abandoned the project due to problems getting LDRs to track closely in a high-impedance volume control for a balanced tube preamp. I've been waiting on Unixman from that thread to complete a rather complex digital control system that would resolve this issue. But assuming you need a single-ended passive of around 10K impedance, the Lightspeed should do fine. Looking forward to your findings.
Actually I would have preferred balanced, but the cost was prohibitive due to the added parts and work involved. George wasn't excited about tackling the project either. I was able to get him to build me one with dual volume controls so I could have a balance option.
My DAC has an output impedance of 50 ohms and my amps an input impedance of 100k ohms. The Lightspeed should be fine I imagine.
To find eight closely matched LDRs as needed for a balanced passive, requires measuring & sorting through many dozens of pieces. The task is much simpler with a single-ended passive. Only two matched pairs of LDRs are necessary for a two channel SE passive, and variation in matching between L and R channel LDRs is noncritical. In contrast, in a balanced configuration, even small variations in LDR matching will produce poor common mode noise rejection. George understands these devices well and has probably been wise to steer clear of balanced configurations.
For those unfamiliar with the technology, an LDR is a photosensitive variable resistor, whose resistance is controlled by an adjacent LED. The volume pot on the passive preamp sends a variable control voltage to the LEDs, which determines the light intensity applied to the variable resistors. Two LDR elements per channel in a series/shunt arrangement, provide all the functionality of an expensive ladder-type attenuator based on conventional resistors. Apart from being simpler than a conventional ladder attenuator, the LDR attenuator is better insofar as there are no switch contacts in the signal path. Moreover, the sound of LDR resistors is reportedly as transparent as the best conventional resistors. Finally, as the control pot is not in the signal path, the chosen pot may be of the cheapest variety and have no impact on sound. So it's a win-win of simplicity, economy, & performance as seldom found in audio.
Received the Lightspeed and have had a chance to listen for a bit. This little piece is pretty amazing. Dead quiet and excellent dynamics. Better than my previous K&K TVC that used S&B transformers and better than any other resistor based passives I have heard. I've always been partial to transformer based passives, but the Lightspeed is quickly changing that opinion.
How about the Adcom preamps. Are they as good as Stereophile makes them out to be???
Clio, where did you buy Lightspeed? I've been thinking of getting a Bent Tap-x (again) with the autoformers, as I've decided to stay passive with the Music Reference amp.
Pubul57, I'm traveling on business but I can get you George's email address when I get home Wednesday. Go over to DIY.com (do a search with "lightspeed") and read the thread as well. Very interesting stuff. Also, if you'd like to try one out first let me know. I'm not using mine right now and I'm happy to lend it to you.
Higuys,I am the manufacturerof the"Lightspeed Attenuator" in Australia that has been mentioned in these posts. If you need info and pics of the unit you can (PM)from here or email me ( georgehifi at optusnet.com.au ) and supply your email address and I'll send out the info and pics and circuit diagrams to you.
Just to correct the price of the "Lightspeed Attenuator" it is $398usd posted and insured.
Cheers George from Oz.
And Clio09, glad your loving the Lightspeed Attenuator, told you you were in for an ear opening experince.
George, you were indeed right. Also, I appreciate the fact you went out of your way to build me one with dual volume controls.
I'm picking up these to compare to the Lightspeed as they are comparably priced and I always wanted to hear the Slagle's.http://intactaudio.com/module.html
I'll post comparisons when I get around to it.