Hi Ben, from the responses, it seems the sound of a preamp is quite dependent on the system and personal preference. I tried something yesterday that I have tried at least 20 times previously, with the same result. I know, the definition of insanity, right? I replaced my unity gain buffered preamp with a Goldpoint passive. At first, I really enjoyed the quiet background, nice tone, clarity, and purity, but after about 5 - 6 songs, I had the familiar sense that something was missing. I reinstalled my active/buffered preamp and.....Technicolor! The preamp had the same attributes as the passive but added tremendous body, dimensionality, and tonal density that made the music sound more "real." Since you asked about what level of quality it takes to improve the sound over a passive, here are my thoughts. - The passives I own, have owned, or have tried on an extended basis include, Goldpoint balanced passive, Endler Attenuators balanced, Adcom GFA-750 (mentioned in a previous post), and a Bent Tap type preamp using autoformers - Acoustic Imagery’s JaySho.
- My active/buffered preamp discussed above is a custom pre from Steve McCormack of SMc Audio, based on the TLC-1 platform modified with many improvements from Steve’s VRE-1. While it does not provide gain (unity gain) the signal is buffered and the preamp uses the VRE-1 choke power supply, a custom attenuator with AN Tantalum resistors, special Lundahl transformers (for a balanced signal), and more.
- I have tried more than 20 (tubed and SS) preamps in my system and the SMc preamp is the best I have heard. Several of the preamps had a list price north of $10K. My second and third preferences were Tom Evan’s Vibe and Pulse and Lamm’s LL2 Deluxe, both single-ended units.
Like you, I also own (but don’t currently use) one of Steve’s upgraded amplifiers that you can see on my system page. If you can stand not having remote control, I would recommend discussing options with Steve. IMO, the preamp is really that good and would match well with your upgraded DNA-1. If desired, Steve can design the preamp with +6dB gain from the transformers. You can mention my preamp, which is pictured on his website. He also has other options he has more recently developed. |
As George points out, suitable impedance matching and adequate voltage gain are critical to achieving good results with a passive. Other considerations, depending on the type of passive, are the potential for changes in impedance with changes in volume, and the effect of cables on impedance and capacitance. Passives seem to work best in situations where there are short cable runs after the passive. You can read a lot about this in these forums. Active buffering helps control impedance so that it stays low and consistent, and to help with consistent current delivery.
One thing you should consider is that while the stock DNA-1 has an input impedance of 100K ohms, if Steve's upgrade of your amplifier included adding transformers the resulting input impedance was likely changed to only 10K ohms, which would significantly affect your compatibility equation for use with a passive. BTW, the amplifier I used for my passive comparison described below has input impedance of 100K ohms. |
Source output impedances in the typical range of about 100 - 500 ohms should easily drive preamps with input impedances of 10K or up....as long as the cables are kept reasonably short. However, it must then be considered what happens between the passive preamp and the amplifier, how long are the cables, and what is the input impedance of the amplifier? All of these are factors contributing to the successful use of a passive preamp IMO.
I believe it is to simplistic to simply say that if you have enough voltage and reasonable impedances, then a passive will sound good. I have heard it go the other way too many times. Based on comparisons between passives and my unity gain buffered preamp, the active buffering (but not necessarily gain) does lead to improved dynamics and bass, even when voltage and impedance rules are met between partnering equipment. |
The $699 Freya from Schitt seems like an amazing bargain for the price.
If I didn't already have something great, and were on a tighter budget, I would definitely be interested.
For passives, the only one remaining that interests me is
Townshend’s Allegri+ which uses autotransformers that are wound using Townshend’s own Fractal wire and coated in ultra thin Mu foil.
Unfortunately, it does not match my system well since it is single-ended only. |
Good point George, I haven't tried a preamp made from light dependent resistors yet. I did try Tortuga Audio's tube buffer as part of their "tour" last year. It was pretty good and I suspect putting that buffer in-line with their LDR passive would probably sound good, although probably not as neutral as a SS buffer.
I have sometimes thought about constructing a version of NP's B1 buffer but modified to be balanced and to have a high quality attenuator and other high quality parts, but that is actually what my preamp consists of. I have not had a single instance where I used a passive and found it to be the sonic equal of my buffered preamp. |
I do not believe "gain" to be the main issue here. IME, the reason some hear improvements in dynamics and bass when moving from a passive to an active preamp is due to improved impedance matching through the volume control and consistent current delivery. An active buffer (with or without added gain) can make the source's job of driving an amplifier easier by allowing the source to see a high input impedance into the volume control and the amp to be fed a consistently low output impedance following the volume control. With the high'ish output of
today's
sources (i.e., CD players at 2V and
DACs at 2V to 6V) gain is probably not the main reason people hear improvements due to active circuitry.
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From Nelson's B1 Buffer paper; Is impedance matching an issue? Passive volume controls do have to make a trade-off between input impedance and output impedance. If the input impedance is high, making the input to the volume control easy for the source to drive, then the output impedance is also high, possibly creating difficulty with the input impedance of the power amplifier. And vice versa: If your amplifier prefers low source impedance, then your signal source might have to look at low impedance in the volume control. This suggests the possibility of using a high quality buffer in conjunction with a volume control. A buffer is still an active circuit using tubes or transistors, but it has no voltage gain – it only interposes itself to make a low impedance into a high impedance, or vice versa.
A lot of this is system dependent....i.e., electrical values of the source upstream, amplifier downstream, and amp-speaker interface, as well as which cables are being used and how long they are. I agree there is a purity to the sound of a passive but there are more than a few of us who continue to believe something is missing when inserting a passive into our systems.
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@mrdecibel , IME, impedance matching (not matching as in "equal" but rather low to high as you move down the chain) is more important than gain. If it were not, you could simply increase the output of your source...to 4V or 6V, but that alone doesn’t seem to cut it for many listeners. Most sources (even those with sufficient voltage gain) cannot suitably handle the impedance changes that occur as the signal passes through the volume control and through the interconnects. Aball does a nice job of discussing the benefits of buffers a couple of post ago. There are trade-offs, and personal preferences, as always. Having less circuitry can sound better to some, but only if the ancillary consequences are not deal-breakers.
BTW, Steve McCormack (SMc Audio) makes one of the best sounding buffered preamps you can buy - the VRE-1C. That unit is the culmination of a career’s worth of research and trials going all the way back to his early Mod Squad/McCormack days with the Mod Squad Line Drive, TLC- 1 (Transparent Line Control), and Micro Line Drive units. You can order the VRE-1 as either a unity gain unit, or with 6dB gain through the high-end Lundahl transformers he uses. Most order the +6dB version as Steve believes the differences between the 0 and +6dB gain versions are virtually undetectable. I have tried both in my (very similar to VRE-1) unit and own a 0dB gain version. With 1.5M balanced cables to my monoblock amplifiers, I cannot hear any loss of signal, bass, dynamics, staging, or anything, compared to the +6dB version.
Regarding Steve’s McCormack amplifiers, I believe all of them originally had a 100K ohm input impedance, up to the DNA-500, which was designed with a 10K ohm input impedance. The upgraded/revised versions which have balanced inputs, all have a 10K ohm input impedance, which would generally be difficult for an unbuffered passive volume control to drive without some sort of signal abberation. My own trials with passive and autoformer preamps have mostly been into my Clayton amplifiers that have 100K input impedance, and the result has always been similar....an attractive purity but also a flatter, less dynamic, less full-sounding, somewhat bass-shy, and overall less satisfactory sound compared to what I hear through my active buffered (unity gain) preamp. BTW, I heard Steve does an outstanding job modifying/upgrading the Micro Line Drive unit so you could consider that. He also works magic on the TLC-1! |
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The Tortuga looks interesting. I tried their buffer when it was "on tour" and it was not bad at all. The combination of my Goldpoint passive and the buffer sounded quite good but not at the level of my SMc buffer/preamp. I would have liked to have tried the Tortuga passive + buffer but only had their buffer and not the passive. I asked them why they don't offer the buffer integral with their passive preamp (it should fit in the big box version they offer) but I think they are just not there yet. |
