Preamps

Discussion in 'Preamps' started by sphinxvc, Sep 21, 2016.

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  1. sphinxvc

    sphinxvc Gear Master East

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    I figure this is timely with RMAF right around the corner. So we don't go in circles in this thread, I'm posting links to 4 threads on preamps from SBAF and Changstar below, along with a couple of notable posts. The posts I brought over focus on implementation, not specific products. Also, in some cases I combined two successive posts from the same person into one quote.

    Let's move on and discuss...

    THREADS --
    SBAF: Dedicated Preamps vs Headphone Amps, Passive Volume Control for DACs/Sources
    Changstar: Volume Control for DACs or How to Get 20bits out of Yggdrasil, Advantages of Passive Preamps / What to Buy?

    What is behind 'pre-outs' makes all the difference. Is it just taps from pot? Or actual amp output routed there ? Or maybe some earlier stage ? I think I have seen all three. FWIW best pre-s I have heard are 2A3 tube amplifiers, or steppers. It depends on what needs to be driven and what is input to the pre. With Yggy to 50k power amp, I might choose passive. With Soekris 1021 with it's 625 ohm output to 10k power amp, I'd rather have 2A3 beefing up the signal. [separate post] I have seen many hp amplifiers having pre outs just spreading the pot two ways. This is passive pre, often shit one. Active monitors usually have lowish input |z|, passive might not cut it. My Genelecs with 10k work ok, still I prefer buffering. If the hp out is the same as pre out, then impedance matching is likely not a problem.
    IMO on paper a passive pre is going to beat out an active pre. In practice it's probably more rig dependent. The active pre is only going to muck up the signal with added distortion and higher noise floor; this sounds terrible on paper but can potentially sound better in person. Then you have things like impedance mis matching which could make things worse all around. [Separate post] I don't have much experience with active monitors but a passive pre will probably fare better, the noise floor of active monitors I've used is not great to begin with.
    I can tell you a high end dedicated pre will sound better than ever is built into that headphone amp. It's a very important component in a system that most headphone listeners have completely dismissed.

    The best sounding pre I've heard has been an active. I think the whole added distortion and noise floor argument is blown way out of proportion. [separate post] Transformer or autoformer volume control sounds amazing - AMAZING.
    Rex Aeterna said: “it's not true that actives add distortion or add noise.”

    They always do. Every amplification device essentially copies the input signals and sends out a copy. It is, however, debatable, how much of an influence on the overall system performance will the preamp noise and distortion add. [separate post] Passives have the disadvantage of potential impedance mismatch. Resistor thermal noise is a non-issue.

    And yeah - tranny volume controls. Good ones are made out of money.
    Rex Aeterna said: “if that is the case so, do passives. they might not have no transistors and a transformer in place to buffer the signal but, do have couple of components as well in the chain that can cause as much noise as anything else. guess it's a lose lose situation we got here.”

    No they really don't. Resistor thermal noise will be a hell of a lot lower
    If the bit-perfect nature really is the reason the Yggy sounds great then software volume control or any sort of digital attenuation should be in the trash
    Take a look here. http://www.diyaudio.com/forums/anal...ve-preamp-133.html?postid=1520215#post1520215

    I know that Nelson Pass is less-than-loved in some circles, but his measurements are interesting.
    Pro's to using a passive - extremely simple signal path, zero contamination from AC supply, power supply, or anything else. Single input versions amount to little more than connectors, some wire, and some type of pot or stepper. It doesn't get simpler than that. Con's - passives are poor at driving long lengths of cables. If the source has low output voltage (usually not a problem for balanced sources which generally have 4-6V output) a passive can have trouble.

    The major con though, and the reason why passives are generally niche devices, is that they can overly soften the sound and/or limit bass response. That, and passives generally work best if they are designed to work with the input and output impedances of the components they are being used with, rather than being "one fits all" as most active pres are. Remote control is also pretty rare among passives because you're obviously not going to have some sort of chip driven VC like a lot of modern pres. You need a moving part, and therefore a motor to drive it, which will obviously have to be electrically powered, defeating some of the purpose.

    One fairly clever pre that attempts to bring the best of both worlds is the W4S STP-SE. You get a remote, full display, balance control, and just about everything else that a typical active pre has. The volume control is resistor ladder, and the actual preamplification is passive, until the gain level reaches a certain point, and then the active gain stage kicks in, making it a semi-active design. I haven't heard it myself, but supposedly it's quite good.

    If you have other Audio-GD components and if Krell CAST is compatible with Audio-GD, that might be a good match. Otherwise I wouldn't recommend Krell, well I wouldn't recommend Krell anyway, but if you have to use the SE or XLR jacks instead of CAST, I really wouldn't recommend Krell.
    Quote from: mickeyvortex on June 06, 2015, 02:44:52 AM: “I was under the impression that active preamps are a remnant of the past where line level signals were very weak (turntables). signals of a digital origin are considerably more powerful. For eg, most DACs should output up to 2 vrms.”

    Not really. If you're using a low output MC, your phono pre may need to apply 60dB of gain, maybe even more than that, before the signal is strong enough to be sent on to any active linestage. No preamp without a dedicated MC phono input can deal with tiny signals like that, regardless of whether its active or passive.

    The reason why preamps in general are starting to fall out of favor is that fewer and fewer people need to be able to switch among 4 or 5 analog sources. Multiple sources are now being handled by the DAC, which may also have its own volume control.

    Actives still definitely have their uses though. A passive pre that can handle 7 inputs, a tape loop, and drive SE and balanced out simultaneously like the 326 I don't think would be possible.
    People say potentiometer quality doesn't really affect sound much other than channel imbalance at low volume and impedance causing issues. The resistor based attenuators seem to not have the imbalance problems. I think the Schiit sys uses a small alps pot
    uncola said: “People say potentiometer quality doesn't really affect sound much”

    Well others might disagree ;)
    mtoc the whole "more power = more dynamics/bass" is a fallacy that people say disappears when you compare two things after using a mic to perfectly volume match them. it's really just the louder/higher gain active device being at a louder volume total rather than having any sonic advantage. at least that's what I've read objectivists say :p and passive volume controls since they have no active parts don't have the potential to color the sound the way active preamps do, that's the theory. they can have high frequency rolloff if there's an extreme impedance mismatch though. The other real use active preamps have.. is if your source doesn't have enough voltage output to reach your amps max volume level because the input sensitivity is like 2.5Vrms to reach 100% volume but your dac only gives out 2.0Vrms etc.

    I've been trying a few passive preamps and my dacs digital attenuation and honestly I can't hear any disadvantage to the digital attenuation despite mentally knowing it destroys some bits of resolution. Maybe my vi dac just has a really good digital attenuation implementation. It's really nice not having a third device in my chain and not having to use a preamp
    I'd look for source input impedance ten times lower (or even less that that) than an amp's input impedance. Sometimes you need a preamp for power amps. Solid-state power amps tend to have lowish input impedance on the order of 10k ohms. A lot does depends on the source. Some sources (and it seems more and more, especially in the DAC arena) will have hefty output stages (and built in volume control / preamp functionality).

    uncola said: “mtoc the whole "more power = more dynamics/bass" is a fallacy that people say disappears when you compare two things after using a mic to perfectly volume match them. it's really just the louder/higher gain active device being at a louder volume total rather than having any sonic advantage. at least that's what I've read objectivists say :p and passive volume controls since they have no active parts don't have the potential to color the sound the way active preamps do, that's the theory.”

    In some cases where the source output is weak and the amplifier inputs are more difficult to drive, an active preamp can sound more dynamic with more bass heft. When it comes down to it, it's all about transfer of power, except on a smaller signal scale. The active preamp serves as a buffer and if necessary a voltage amplifier. Really not much different in terms of function from say an output stage of a DAC or a phonostage.

    Ironically, these differences in dynamics (when they do exist) are easier to discerne when gear is level matched. The problem with "objectivists" is that they have no data, no measurements, and have not performed any their proposed level matched blind tests themselves, much less have heard any of the gear and combinations thereof.
    Bottom line is the more stages (active or passive) you're chaining together, the more things are going to deteriorate. People should be smart about their gain staging rather than using going overboard with excessive gain and having to use near equal amounts of attenuation.
    LDR Preamps seems to be all the buzz nowadays, but there are some that say there is some major distortion inherent to the LDR type pot which makes the sound artificially warm making it pleasing to the ear. Others say that this is the best way to make a preamp if the goal is to achieve a colorless sound. Who's lying?
    It's all about keeping a clean signal path right? So instead of a pot, I'm gonna use some unstable resistors whose values change depending on the amount of light they receive. Those light sources are unstable and their output varies depending on the signal fed to them. That signal is likely controlled by a pot...

    ... and if there were concerns about electrical noise and other wibbly wobbly things, that noise is going to affect your light sources anyways. Yay!
    All TVC are bandwidth limited (to both sides of the audible spectrum) and add measurable amounts of distortion.

    The fact that this is not heard as such (limited) and sometimes a limited bandwidth could even be a blessing is another matter.

    Plus side... a TVC can actually amplify the input voltage level where the other options can only attenuate.

    LDR volume controls are not bandwidth limited but are non linear (in a distortion kind of way) and add measurable amounts of distortion.

    This is because an LDR isn't a 'normal' resistor but its a semiconductor that changes its properties depending on the amount of light on it AND the voltage across it.

    The music signal across the LDR is a varying voltage and thus distortion is added.

    Having 2 LDR's instead of 1 in one channel alleviates some of the non linearities when set at 50% volume drop.

    The fact that this is not heard as distortion, or sometimes even preferred over other volume controls is another matter.

    AVC's are NOT bandwidth limited (I never found one that deviated between 0Hz and 1MHz) and are linear components, thus can not add distortion /coloration even if they wanted to.

    This is true for both stepped as 'normal' potmeters and is only valid (the distortion thing) if contacts inside are operating normally.

    Still, some prefer TVC, LDR, or steppers over 'normal' potmeters...

    Me ... I don't care one bit... but do prefer not to use TVC or LDR's myself because of their technical limitations.
    I tend to agree with your sentiment. While I have not tested TVCs in my system, we all know how hard it is to find good magnetics that can be truly called "transparent" (if we can even define that term in the first place). The only application I would consider using a TVC was if I wanted to utilize the advantage of a transformer coupled input anyway (either for balanced/unbalanced conversion or phase splitter or CMRR) or if I wanted to get a bit more gain into the first stage.

    I would add that all "normal" pots are not created equally. Different resistive elements can definitely add measurable amount of distortion, with the precision metal film (as used in the GoldPoint steppers) resistors being the most linear and lowest noise available. All traditional (taper) pots will either use conductive plastic or a carbon track element, which will not quite be on the same of performance. Whether that distortion is below the threshold of ours senses or playback chain (or even measurement thresholds) is a different question. I guess smartphone's volume nub buttons sound ok...... :eek:
    To clear up a bit of the confusion:

    http://www.goldpt.com/attenuator_types.html
    LOL, the Melos SHA-A Gold head/pre amp had a photoresistor! Anyone who even did the smallest mods on the SHA-1 got rid of it. I'm not sure the reasons, but it may been reliability or lack thereof.

    If you want colorless, I would avoid autoformers and active stages if possible. Listen to @OJneg. I've been through three different pairs of MC transformers and all of them sound colored. The best ones are the least colored, but still colored, in a "good" way. While autoformers (no gain) will probably have less of an effect on the sound than MC transformers, my hunch is that they will not be totally transparent. (There's a Moth autoformer preamp lying around that I should check out sometime.) Same thing with active stages - they will color the sound.

    If you want to the least amount of coloration, go with a quality stepper with custom cables made as short as possible. This is assuming the drive ability of your source is sufficient, otherwise go with an active preamp. We have a Khozmo switcher in the lab and it's really nice. We would probably never offer it because it does need some maintenance in terms of adjusting and tightening up the nut in the back. The electronic resistor ladder switch things that I think @OJneg has is another approach. Bottom line is that if you want transparent to the source, nothing is going to beat two resistors. Go with a 50jk or 100k pot. This is consumer stuff and 50k to 100k will provide you with the best future compatibility.

    That being said, you may want to consider the active or transformer options which have been suggested - they do bring other things to the table.

    $100 Preamps - BH Quickie (tube active), Schiit SYS (passive)
     
    Last edited: Sep 25, 2016

  2. Pyruvate

    Pyruvate Friend

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    Thanks for making this. As you already know, I recently acquired a power amp and have since devoted the SYS to preamp duties. The past couple days, I've literally searched every mention of "preamp" on both websites in hopes of learning more, especially where to go from here. Oh boy, what a can of worms I've opened!

    I'm currently checking out the used market for some good vintage actives so I can compare with my passive SYS.
     
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  3. Armaegis

    Armaegis Friend

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    I'm curious to see Schiit's takes on preamps, especially for balanced users. If I'm going balanced, I want that stupid ground out of the equation entirely. I don't want my signal being treated as 4 separate channels all divided with reference to ground then smushed back together. That's the big advantage of TVCs for me, at least in theory.
     
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  4. spwath

    spwath Friend

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    Will read this when I have time. Always good to get more knowledge, thanks for putting this together. I
     
  5. sphinxvc

    sphinxvc Gear Master East

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    SYS is a beast, @Pyruvate. Good luck, vintage actives.

    Curious as well, @Armaegis. I think we can rule out TVCs and LDRs though, LDRs for obvious reasons and TVCs because good trannies are expensive. Since Schiit has a history of disrupting the market and pushing it forward at the same time, maybe they’ve come up w. a way to solve the primary weakness of passives: “…passives generally work best if they are designed to work with the input and output impedances of the components they are being used with…” (DaveBSC on Changstar). Impedance adjustability maybe? The Tortuga passive LDR is adjustable impedance, IIRC. Alternatively, maybe they’ve figured out a way to do volume control right in the digital domain. Alternatively alternatively, maybe it’s just a small signal pivot point active.

    The Raggy vs. SYS comparo we did a few months ago at a minimeet revealed to me that passives are “truer” to source when you’re “rolling” power amps (rolling as in trying out a new power amp). Or at least that it was true in that particular comparison. :D SYS also thoroughly trounced the Valhalla 2 in the transparency dimension. For the sake of being able to use the pre w. multiple power amps though (both Schiit and non-Schiit), I hope they’re working on a passive of some kind. Few things make you feel more like an audio dweeb than matching “voicing” and “synergy” of multiple gain stages. :rolleyes:
     
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  6. Wfojas

    Wfojas Friend

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    Which ones are you looking at @Pyruvate ? Budget?
     
  7. thegunner100

    thegunner100 Hentai Master Chief

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    Thanks for the collection of posts! We still need to compare Sys vs Jotun on your Stratos somehow after you make the move. Or if @SteelCannon gets his uber Stratos, we could use that instead. But it's totally possible that by the time either of these are complete, Schiit will have their pre's and powers.

    Yes, I agree that the Sys did sound better than the Ragnarok but the problem is that we didn't play enough with the gain settings and we don't know the output impedance on its pre-out. If the circolotron circuitry on SE is holding back the Rag's pre-out, that could be a cause too.
     
  8. Pyruvate

    Pyruvate Friend

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    Looking at a couple Parasounds from the 90s, the ones built by John Curl. Budget being $300. Getting a taste before I commit to something better.
     
    Last edited: Sep 22, 2016
  9. Armaegis

    Armaegis Friend

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    This would be my guess if Schiit were doing an active pre. Configure it with variable gain rather than pots in the signal chain perhaps? That's just armchair wizardry on my part though.
     
  10. Pyruvate

    Pyruvate Friend

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    Could this be part of the Manhatten Project? Regardless, if Schiit figures this out, they could make passives obselete.
     
  11. Wfojas

    Wfojas Friend

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    Great choice. Look at the Motif by Conrad Johnson, if you can find one. They will also have a very good phono section like the Parasounds.
     
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  12. Pyruvate

    Pyruvate Friend

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    Fuck it, pulled the trigger on a Parasound P/LD 1100 recently. Couldn't pass up the remote control, Class A topology, and headphone output (hoping it'll be halfway decent). Need to reward myself for passing boards anyway. I read everything I could about it on audiogon/audioasylum/avsforum and came to a conclusion that it'll be a good fit for my system. Plus it was made to pair with the HCA-1000a I got a week ago.

    I realize Schiit is coming out with a Pre in a couple weeks, but it'll most likely be more than what I'm comfortable spending at the moment. Anyway, this should arrive within the week and with the Joti loaner incoming mid October, I'll try to do a three-way shootout between the SYS vs Joti vs Parasound.

    I'll go on a upgrade hiatus after this (sure, let's see how long before I eat my words), but I've been meaning to get into DIY and learning more about electronics, so I have tons of reading to do.

    [​IMG]

    [​IMG]
     
    Last edited: Sep 24, 2016
  13. thegunner100

    thegunner100 Hentai Master Chief

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    Looks nice! Enjoy! :D
     
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  14. Pyruvate

    Pyruvate Friend

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    If there are any big parasound fans out there with deeper pockets than me, there's a P/LD-2000 balanced preamp on sale on craigslist near Burbank, CA. MSRP was once $1500 in the 90s, and it was their flagship preamp before getting "replaced" by the Halo JC2 preamps (which costs about $4k today).

    https://losangeles.craigslist.org/sfv/ele/5788904489.html
     
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  15. Wfojas

    Wfojas Friend

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    Wow, anyone wanting a solid state preamp should definitely look this up. I remember this having a slug of premium parts in the build.
     
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  16. Pyruvate

    Pyruvate Friend

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    Indeed it does. She's a real beauty.
    [​IMG]
    Taken from http://www.parasound.com/vintage/pld2000.php

    John Curl has outdone himself with his latest preamplifier design. Audiophile balanced design and pure class A balanced discrete circuitry means you get the cleanest, clearest signal path from input to output. You simply can't buy a better preamplifier at this price range. Dual Mono Topology, Complementary MOSFET drive stage, 6 high level inputs: Direct coupled, Balanced inputs and outputs with XLR jacks, 100% discrete Class A circuitry, Switched by precision gold contact relays, High current dual mono headphone circuit, Polarity invert from handset, Fully remote controlled, External IR input.

    FEATURES

    • Complementary MOSFETs
    • Gold-Plated Audiophile Jacks
    • Noted John Curl Design
    • All Relay Switching
    • 20 Gold-Clad Precision Relays
    • Gold-Clad FR4 Circuit Boards
    • Audiophile-Grade Capacitors
    • 92,000 uF Filter Bank
    • Dual-Mono Topology
    • Pure Class A Discrete Circuit
    • Direct Input Function
    • Silver-Plated Wiring
    • DC Servo Direct Coupled Circuit
    • High Current Design
    • Fully Remote Controlled
    • IEC Removable AC Cord
    • Motorized Alps Volume Control
    • Pure Silver XLR Input Wire
    • Balanced Inputs and Outputs
    • 0-180 deg Polarity Invert Control
    • Vishay Resistors in Critical Areas
     
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  17. OJneg

    OJneg The Most Insufferable

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    Have had a bit of time with the BH Quickie now. Pretty damn good active solution. I'd assume/hope that the higher end BH pres are equally good.
     
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  18. sphinxvc

    sphinxvc Gear Master East

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    How's it compared to your δ1?
     
  19. OJneg

    OJneg The Most Insufferable

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    delta1 has been confiscated for a different, unrelated project.
     
  20. uncola

    uncola Friend

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    great OP, sphinx. When my new preamp arrives I'll take some glamour shots for this thread
     

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