Passive preamps - suggestions / advice

Warren, get well soon. Life is best lived with optimism and a generosity of spirit. Where disagreements occur, that can't be resolved, acknowledge them and just move on. Your life is way more important than the fluff that happens in a hifi forum.

I wish you and your loved ones well, am sure it'll be a successful procedure and hope you're back and fighting fit on here soon.

 

I have a Superphon SP100 by Stan Warren. It's a buffered passive design but might be something else for you to consider.

Pat

 

This post interests me, because about 2 years ago, I bought one of these. I thought it was really mediocre (sonically), in the three audio systems I tried it in. So, I was very disappointed. An old Conrad Johnson PV-4, that I also had, sounded MUCH more alive and revealing of subtle detials. I feel the SP100 is a well constructed preamp, deserves a prominant place in audio history (being a very simple design from a VERY repected designer), but sonically, just nothing special at all.

So, the choice of preamp REALLY depends on the rest of the system's price level, and level of audio quality that it is intended to complement.

 

I tried the Promethius but found it a bit veiled. The Sonic Euphoria I ended up with I love. It gets out of the way of the music. It is more open and detailed. Sadly they are no longer in business but you might find one in the secondary market.

By the way Emotive also sells a passive volume control similar to the TC Electronics for about $50.

 

As Robin L said, I think the quality of the potentiometer makes a hugh difference in sound quality, whether the pre is active or passive.

My favorite preamp for a decade and a half was the Melos SHA Gold. It used light dependant resistors for volume control, but not the modern LED driven ones that we have now. When my volume board died, the "photentiometer", I couldn't find anyone to fix it without swapping out the volume control for a conventional potentiometer or stepped resistor potentiometer. I was not interested in this solution. The parts needed for repair had stopped being manufactured even before the SHA Gold had been built!

(BTW-Many of the folks who worked on Melos products in the past have either ceased to do so, died, or disappeared. HiFi is full of wonderful, sad, and mysterious characters!)

The Melos sat broken in the closet for two years, until Tortuga Audio made their LDR boards available to the public. I replaced the broken "photentiometer" with the Tortuga unit, and my Melos that everyone said was unrepairable was making music again. I liked the Tortuga board so much that I purchased one of their passive LDR preamps.

I like it very much. The LDR's are software controlled, and can be auto calibrated at any time. The LDR's can be user replaced, so there's no worries if a LDR should fail in the future.

My Tortuga Audio LDR replaced a popular tubed unit that used a pair of 6SN7's & a 5AR4. I still have the Melos SHA Gold with the Tortuga board & it sounds great, but the Tortuga Audio LDR3.V2 is seeing daily duty now.

 

I have two Melos 333R preamps sitting in storage. They are 3 chassis each: power supply, line stage and phono.

Does anyone know someone who would work on them for me?

 

If you're in the UK, try NVA. They are on ebay and do a sale or return and if you wish to upgrade, will do so for just the difference in price. He does potentiometer or stepped-attenuator volume controls in stereo or dual mono. I have a P90SA

 

Good shout. I like their designs. He's down in Peterborough I think (Nene Valley Audio) and been going for years. Good call that man!

 

The AVI player—does it have a variable output, does the Cambridge? I ask because you might not need a passive pre, just a source selector box. I've had one of those for 30 years, very simple solution to your problem.

 

I'll check. The 752 is fine but the AVI I'm not sure about. No volume function on the remote, but will check with AVI directly.

 

Sorry about getting you upset, Warren. My disappointment was more about the message than the messenger. You don't need to get your BP up now; you know that. I have been through your situation myself, so I know how hard that can be. I am wishing you many more years of joy and many fewer days of stress!

That is what I was disappointed about. I felt it detracted from the OP's stated goal. I also saw lots of pros but no cons on the transformer solution. It isn't for everyone, especially those within budget range of most users. Even when it is, I still prefer top notch active units to passives of any design type. In any case, it's not worth losing any sleep over. It's just audio...
-Bill

 

I have had two of Luminous Audio's Axiom attenuators. Version one and two. I first used them with Martin Logan "purity" self powered hybrid electrostatics. http://www.luminousaudio.com/axiom2.html I have since moved on but I do miss the ML purity. I think the Axiom works best in its simplest form. One input only.

 

Cheers, prices are from £200 to £640 but it looks like there's a new entry level preamp coming that will be around £100, that would allow you to dip your toe in the water and upgrade if you're happy

 

Cool, that's good to hear. The P50sa looks like a good candidate. £300. Excellence Audio are another.

 

It's too bad Creek doesn't currently make a passive. I used an OBH-12 for years before upgrading to a Tortuga. You may be able to find a used OBH-12 or OBH-22 to dip your toe into the passive waters. They have a couple of inputs as well as remote. That, with an ifi as buffer cited earlier in the thread, would give you a good idea as to whether passives are to your liking.
As with most things in audio you will get 85% of the quality with a moderately priced component when compared to components that are multiples of the cost that squeeze out that last 15%. That applies to transformer and resistive based passives equally. This might be a gross generalization, but when first considering passives it seemed to me that those who prefer tubes and vinyl favored the transformer and those who preferred solid state favored resistor based passives. Hope this helps.

 

The Tortuga and similar can't be sold in the EU as apart from some commercial exceptions LDR's are banned due to Cadmium content. They must be disposed off very carefully if you have a broken model. BTW NVA are now based in South London.

 

If your speakers have a built-in amp with 10k input impedance I would not even try a passive. It's not a question of whether it will work, there's no doubt it will, it's a question of how much compromise there will be. Every source will perform differently depending on it's output impedance and ability to deliver current as well. IMO your best bet is to look for a used active preamp, that way any source you use will not be affected by the low input impedance of your amp.

 

10K is not a low input impedance. 5K is common and I have amps with 1.5 Kohm. This low you do need a buffer stage or active pre with preferably 100 ohm output impedance or lower. A passive will likely work OK with 10K but it's usually a try it and see situation. It's best to use power amps that are designed for use with a passive.

 

10k is low enough to degrade the sound quality of many sources. Low output impedance is not enough information to know if a source will work properly either, it also depends on ability to deliver current. Output impedance IS NOT a measure of current drive ability! Personally, I would not like to be in a situation where this is going to be a factor in selecting a source. And 10k is low relative to the 100k input impedance of many other amps, and also low relative to the average input impedances of most hifi consumer amplifiers. 5k is not common at all and 1.5k is ridiculous.

 

The question of economics and system priorities can be a big factor with passives. I have a DIY preamp that uses a TortugaLDR board. Compared to my modded Acurus RL11, the transparency is stunning. I would bet that there are active that would make my system sound great but they probably start at $2k. That is a big chunk of change for me.

 

Probably more, I'm building a preamp with a Tortuga LDR volume control and Aikido tube buffer, it's going to run close to $2k just in parts. A really good active preamp that sounds better than your passive could easily run $5k.

 

If I had the capability to build a preamp, this is exactly what I would want to try to do.

 

How's the LDR coming along?

 

For inexpensive solutions, the Promitheus TVC was a nice upgrade from my Adcom GFP-565 (generally well regarded) in my system, and I think I got it for $175 used since it had a busted input selector (don't care since I just use one source ).

I went that way first to inexpensively check out the concept, then I got a Music First mark II later that year, which sounds even better, has better handling of grounds, is balanced, and has a remote for the volume (yes!)

 

Balanced and a remote you say...??