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PLLXO biamp + passive pre-amp on MMGs: a nice little surprise

69.65.69.236

JBen

Last week I borrowed a passive pre-amp model similar to what I may buy later on, just to test some parameters. There was a little surprise: improved bass "depth". Of all the better things that I expected, this was NOT one. I was already getting more bass low-reach than I thought possible (which allows me to avoid using a subwoofer for music). Yet, my ears kept telling me that it was delightfully increased. On Friday evening, the sweeps, shown at the bottom here, finally confirmed that my modded MMGs were, indeed, reaching further down. By adding more test music pieces, selected for the purpose, the reality of it became sweeter still.
There's a long story behind this but here's one aspect that may be of use to a few of you (the heavy tweakers and the adventuresome at heart):
-- The better SQ (including + bass & dynamics) came when using a passive pre-amp WITH a PLLXO bi-amped system.
These two are not exactly your typical signal boosters. Actually, they are "signal strength attenuators".
I've used the PLLXO bi-amp (passive line-level crossover, bi-amplification) for years, refining it to fit my own situation. Along the way, I had been taking deliberate steps towards the eventual adoption of a passive pre amplifier. Some of you may be able to do the same.
Happily, as I hoped, the PLLXO is not preventing the use of a passive-pre amp. All the expected additional SQ goodies are showing up. Yet, the last thing I expected was more bass depth. More surprising still, the passive preamp did not lose any dynamic slam (yes, Maggies can "slam") and, in some music pieces, it seems to have actually improved (subject to further evaluation listening).
So, together with a PLLXO -- or with an active XO -- a passive pre-amp can be an enabler of significantly better SQ in Maggies. Do not assume that the insertion losses will be detrimental. This may still happen in some systems but the output signal strength of modern playback gear is usually enough to 'keep things moving', even rockin'!

Edits: 08/10/14

Follow Ups:

RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - pistonengine 13:14:50 08/11/14 (1)
How do you make your measurements? And more to the point, how can I make those measurements with minimal investment?
- RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - JBen 13:48:18 08/11/14 (0)
  There are various types. However, REW (free software), a calibrated microphone and a PC/MAC can give you some solid footing. We are not talking "lab-grade" in many cases; our rooms can defeat this easily. The flip side is that the measurements are superbly practical, precisely because "it is in our own room". You can "see" better, as you make changes.
  
  Months ago I mentioned that in recent times the availability of calibrated microphones has increased while the prices have come down. I have tested several units and they fare well vs my more expensive ones, at least for all practical purposes. In fact, the Dayton Audio iMM-6 Calibrated Measurement Microphone is less than $20 and works well with REW on PC/Mac (though it was originally designed for iPhones & Android). Look it up at Dayton (link below).
  
  I wish I could offer a proper basic "how-to" but I am a bit short on time these days. I will still try to do so -- perhaps this week -- but count also on others who have similar experience to pitch in. You may also want to roam REW's forum on HometheaterShack.com
  
  I do plan to place more emphasis on some practical examples of what can be achieved with REW or similar packages. Folks tend to become more motivated to learn when they see the usefulness.
  
  Once they see how easy and practical it has become to measure, the real challenge is to remind them that some discipline helps achieve the best results.
  - http://www.parts-express.com/dayton-audio-imm-6-calibrated-m (Open in New Window)
RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - Davey 07:21:49 08/11/14 (19)
You're simply equalizing the speakers in a different (and variable) way than you were before. It's simply not possible to increase bass depth just by using a passive-preamp/PLL combination. Bass "depth" (I assume you're talking subjectively here) might be altered, but the mechanism is not as you conclude.

Sorry to burst your bubble. These kind of experiments can easily lead folks off on a tangent and yield wrong conclusions.

Cheers,

Dave.
- RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - old guy 42 09:40:16 08/11/14 (16)
  IMO...you owe inmate JBen an apology after reading your post.
  - RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - Davey 09:52:51 08/11/14 (15)
    Apology? You must be kidding.
    
    I always provide an objective commentary/opinion based solely on the technical aspects of whatever is experimented with. I completely discount subjective analysis because it can be very misleading/confusing. I've provided a plausible explanation to JBen's current experimentation......which he can either embrace/understand or completely discount. That's up to him.
    
    Anybody with even a passing familiarity with this forum knows my M.O.
    
    Dave.
    - RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - JBen 13:03:53 08/11/14 (13)
      Hmmm. What's gotten into you? Davey, you did not even ask what type of passive pre-amp I used. You forgot that I measure a lot of stuff whenever I can. You did not catch that I heard/perceived PLUS I measured it? Did the chart not show up? Clearly, you must have been affected by something.
      
      Your responses have taken me quite by surprise. So, I am going to leave it at this until you recover from whatever caused you say these things. I am suspecting that you are in one of those days that afflict us all from time to time. When I am in one of these, I myself appreciate other folks understanding.
      
      [BTW, read my posting again. There are things that I am saying and other things that I am NOT saying, mostly to keep it short. Please ask, if something is not clear.]
      - RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - neolith 07:49:55 08/12/14 (11)
        
        In Reply to: RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise posted by JBen on August 11, 2014 at 13:03:53
        
        JBen, I am a little lost here. I don't think Davey was slighting you or refuting your claim of improved bass response. He was just commenting on the physics of your setup. Just because it works for you, does not mean the use of a passive preamp and a PLLXO can be generalized to anyone's setup. Don't become like PG who had great success with his mods but didn't have a clue about the mechanism and took offense when his explainations were questioned. I really don't think Davey was in any way "dissing" you.
        BTW is the passive preamp using a constant output impedance design?
        �
        
        �
        
        Edits: 08/12/14
        
        RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - JBen 20:43:15 08/13/14 (7)
        
        In Reply to: RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise posted by neolith on August 12, 2014 at 07:49:55
        
        Neo, I must thank you for your attempt to defuse. The comparison to the former inmate, actually begs for an opportunity to clarify things that seem to have been missed. For one, PG never provided much in the way of objective indicators.
        To his credit, this did not stop some of his contributions from being very useful to inmates. That someone "demanded" from him explanations as to why these worked -- and he often delivered some made-up science instead -- does not diminish the value of the contributions. Human history is full of successful empirical and experimental approaches. Many yielded great benefits that engineering and pure science had to catch up with for explanations much later.
        As Davey would say: "Sorry, Mr Edison, your light bulb's physics need to be explained -- and in proper engineering terms -- before we can use that light." LOL! Luckily for Davey, I am not a genius like Mr Edison, or as smart as PG. But, I am not too much of an idiot either, just a little. Plus I have good hearing, much perseverance when it come to pursuing tweaks and honesty. I don't like too fool myself, much less others.
        I REPORT based on my perceptions and measurements in a real-world acoustical environment. I did not offer ANY explanations, since I am merely reporting at this stage and I also wanted to be brief. No matter, Davey simply pounced, claiming that I explained the workings of things wrongly. I explained NOTHING. So, in his first reply he took on the "bass" subject as if I had attemped to explain it. That's when the "dissing" began.
        Talk about his "straw man argument" phrase, which I just learned about...or red herring, as I know it! His true aim was the PLLXO/Passive-pre combo itself...a practical impossibility to him, it seems.
        I did make clear WHO this original posting was for: "heavy tweakers and the adventuresome at heart" , did I not? I further added that it works only in some cases. It does take some talent along with the opportunity, which further reduces the amount of people who would use it. A little teamwork can go a long ways. On this I am known to provide help and additional details when asked .
        The real issue is that Davey felt compelled to squash my unveiling of a working combination (PLLXO/Passive-pre) which he has trashed in the past. Asking me was "out of the question", LOL! Dumb me, expecting him to do so.
        In any event, we agree on something. The PLLXO/Passive-pre combo may not be the wisest thing to do in most cases. Like I stated originally, it may be only work for some "heavy tweakers and the adventuresome at heart".
        Finally, at this moment, PG must be happy as hell. Imagine, two of his harshest critics are now at odds with each other! I think we would be better off if he came back after all...Davey must be missing him that badly, LOL! Hmmm, Neo...was that strategic thinking on your part, bringing him up? : - ))
        
        Edits: 08/27/14
        
        RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - Davey 08:58:53 08/14/14 (5)
        
        In Reply to: RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise posted by JBen on August 13, 2014 at 20:43:15
        
        Back to some pesky facts regarding PLLXO's and passive preamps.
        
        I've posted regarding PLLXO's for many years on this forum and nearly always I've qualified my statements with something like...."PLLXO's variables must be understood.....", "you can't easily transfer to a different power amp combination......", "source resistance must be low.....", or various other qualifiers along those lines. That doesn't mean they won't work.
        
        If you can find a post by me where I declared a "PLLXO/Passive-pre combo a practical impossibility," I'd like to see it.
        For you to intimate that I'm not a fan of PLLXO's is simply silly. I lost count, but I think there are probably about fifty Maggies users out there who have successfully bi-amped their systems with a PLLXO I optimized for them.
        
        Dave.
        
        RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - JBen 11:38:49 08/14/14 (4)
        
        In Reply to: RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise posted by Davey on August 14, 2014 at 08:58:53
        
        Wow, I may have missed clarifying this! I have never intentionally said that you are against the PLLXO itself (alone). If I even implied it by omission, I apologize. Yes, I can see that some inmates may not realize that we are disagreeing ONLY about the combination of a PLLXO plus a Passive Pre-amplifier.
        
        Folks, for the record, we have both been always in agreement that a PLLXO (by itself) has it's well-earned placed as a crossover alternative. It is my preferred option whenever it is applicable and Davey has always done a terrific job of explaining its strengths and weaknesses. Thanks to his direct help, several inmates do indeed enjoy uncommon delights from their Maggies.
        
        Ok, let's clean up this mess, please. As for you influence in the past, I am not in the least bitter about it, at all. I made the decision. However, it was your insistence on the sensitivity of PLLXO's which convinced me to stay away from adding a passive preamp long ago.
        
        You really know your stuff. Many of us take it seriously, and for good reasons. I will submit that none of us can be right all the time but you tend to be more reliable than all of us here when it comes to the electronic engineering.
        
        So, I took the passive pre-amp off my priority list years ago. Meanwhile, I installed these devices for friends, who marveled at what their systems did as a result. Yet, I refrained from even trying to fit one at home with the PLLXO biamp. To be sure, had I done it too early, I would have crashed and burned. For a long time I merely walked to the system and hooked my PLLXO directly to the source for the additional sweet delights.
        
        It was not until later, when I had created several PLLXO implementations, that I began to see some opportunities for a passive pre to be added. PLLXO reactivity could be dealt with within an envelope of values; limited, but potentially useful. All my players/sources & DACs now had suitably high outputs. At that stage, I figured that I could make compromises and I made some adjustment for it. It is tricky. It certainly is not for everyone. Yet, when it can work, it is a genuinely worthwhile pursuit...if only for a few cats like me.
        
        Your own opinion on the whole matter of the combination was restated here in this thread. You've made it sound as if it is "practically impossible." But hey, by and large, I am not in disagreement with you at to how challenging it can be. This is stuff that works in a narrow range of opportunities. I was merely lucky that my system could already fit that range. Which really is luck, not smarts. Well, luck and the constant pursuit at experimental level, which helped.
        
        The sweeps I included yesterday show that EQ can stay stable after varying the volume at the passive pre. Yet, as you well know, something's gotta give for this to happen...and it varies from system to system. Because of the PLLXO, no "just add water" recipe can be made unless all componets are the same. However, there is a range of practical equipment combinations, I am beginning to suspect. Identifying these in the next few month may offer more practical choices....if it can even be called "choices".
        
        RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - Davey 12:19:37 08/15/14 (3)
        
        In Reply to: RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise posted by JBen on August 14, 2014 at 11:38:49
        
        Post the schematic of your PLLXO and your passive preamp specifications so we can all take a look and analyze.
        
        Dave.
        
        RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - JBen 22:03:40 08/15/14 (2)
        
        In Reply to: RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise posted by Davey on August 15, 2014 at 12:19:37
        
        I just got home and saw this after midnight.
        
        You know, even a "please" could have made a difference. Somehow, I don't react well to commands.
        
        Anyway, there will be a time when I will explain my own setup, months from now. It is not a spite. It is part of a larger plan in which the designs that I use can be seen in proper context.
        
        Therefore, I strongly suggest that we stop here for now. This will be my last: Please.
        
        RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - Davey 06:51:17 08/16/14 (1)
        
        In Reply to: RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise posted by JBen on August 15, 2014 at 22:03:40
        
        "Proper context." Huh?
        You've made claims.......I'd like to see the circuit and component values so I can simulate and then discuss.
        Send it to me off-line if you like.
        Please.
        Dave.
        
        Edits: 08/16/14
        
        My lunch break dessert - JBen 10:21:42 08/18/14 (0)
        
        In Reply to: RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise posted by Davey on August 16, 2014 at 06:51:17
        
        This lunch break gives me a chance to recollect the improved sweetness of the music that I barely had enough time to enjoy over the weekend. Its aftertaste remains strong in my mind and heart, almost like an amazing dessert after this quick meal.
        Yes, context. The "gestalt" of my whole setup is now far from any MMG-based system out there. My system is very different partly because my MMGs are different from most. Furthermore, I have ventured well off the beaten path, as well as the beaten formulas. There are ongoing efforts to see which of my tweaks may work with more current MMGs (or even other Maggies) and in other contexts.
        As for the combination of the PLLXO and a passive preamp, it will be a new addition to the ongoing refinement effort. I also need to buy one (I used a borrowed one).
        You called it a claim, which is fine. In this thread, I already added measurements to back up the claim. Again, it can be done. I don't sell this stuff, it will be free to all. In a few months, things will be presented in their full context at my home. After that, I will be mostly gone from this forum to help folks in other forums with their health issues.
        Meanwhile, I crave to listen and enjoy more of my music. The substantial distractions in argumenting can wait.
        
        Edits: 08/18/14 08/18/14
        
        RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - Davey 08:38:40 08/14/14 (0)
        
        In Reply to: RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise posted by JBen on August 13, 2014 at 20:43:15
        
        I'm glad you looked up the definition of straw man and red herring. You're employing them like a champ now. :)
        
        My goodness.
        
        Dave.
        
        RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - Davey 11:10:55 08/12/14 (2)
        
        In Reply to: RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise posted by neolith on August 12, 2014 at 07:49:55
        
        Neither a series or a shunt-configured attenuator will have a constant output resistance. Thus, the source resistance driving the PLLXO will change with attenuator position and this will also change the PLLXO operation.
        This kind of configuration is packed with interactions. (You may remember me commenting about these aspects/trade-offs starting many years ago on this forum.) I'm still not sure folks are appreciating the complicated interactions here. :) An active crossover scheme is much "simpler" in operation.
        
        Your comment about the PLLXO not being able to be generalized to anyone's setup is spot on.
        
        Cheers,
        
        Dave.
        
        RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - JBen 12:21:57 08/12/14 (1)
        
        In Reply to: RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise posted by Davey on August 12, 2014 at 11:10:55
        
        There you go again. Please do like Neo just did. He did precisely as should have been done: ask for clarification. Better still, he even thought "how can this be done?" Well, he figured it out all by himself. Hell, it took him less time to figure it out than it took me. That's basically how it is done. That's what I call being an open minded fella! He is being helpful and useful to others in the forum. When you assume things or misread things, you ain't as useful as you can brilliantly be.
        
        Ironically, my original posting was meant to set the record straight on a misdirection. One that you keep nurturing to this moment. My biggest issue is that you are among those discouraging experimentation in this area. Claiming that something is not possible -- when it is "merely harder" -- may prevent some folks from discovering sweet results. You words actually cost me YEARS of not trying because you said so: I ate it at cost and it cost me. Fine, my mistake. I corrected it and I am enjoying the fruits. Why should I not want to make others happy!
        
        BTW, now you say that measurements of the speakers are not good. Darn, I don't listen to impedances...and drivers never behave "by the book"...hmmm, there is actually no book on Maggies. So, I believe that one should learn what the REAL behavior of each of those drivers is by measuring each, live, under load. It is an acoustical imperative. In doing so, the impact of changes in the electronics is better understood also.
        
        Anyway, I had already erased many of the sweeps from last week. However, the chart below was done this morning in a rush before leaving for work. It is a different (experimental) PLLXO than used last Friday; so is the room configuration, and nothing is yet optimized for music listening purposes. No matter. The one thing that I wanted to test once again was the constancy of the EQ at varying passive pre-amp volume levels.
        
        The top 4 sweeps are taken at 4 volume settings in the passive pre. The actual SPL is compensated at the source so that it is roughly the same room-related interaction. There is also a -20db level (not all done at the passive pre) and a noise floor line. The latter is important for all my measurements, though I rarely bring it up in the forum.
        
        So, as you can see in this 12db spread -- presented as overlapped -- at 4 distinct settings, each 4db apart...the EQ remains virtually the same. I can actually go higher up or lower down before other factors intrude too much. Had I had the time, I would show the behavior of the individual drivers. However, it takes better control of the environmental noises to avoid their intrusion.
        
        RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - Davey 13:07:01 08/12/14 (0)
        
        In Reply to: RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise posted by JBen on August 12, 2014 at 12:21:57
        
        Dave throws his hands up. :)
        
        Now it's my fault you wasted years of valuable experimentation time?? What did I do.....come over to your house and padlock your experimentation toolbox?
        Show me where I ever said experimentation is not worthwhile. And also show me where I ever said "measurements of the speakers are not good."
        
        Straw man arguments/rebuttals really irritate me.
        
        This has become a surreal experience. :)
        
        Dave.
      - RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - Davey 13:51:19 08/11/14 (0)
        
        In Reply to: RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise posted by JBen on August 11, 2014 at 13:03:53
        
        It's very simple. Your passive preamp is adding source impedance relative to your active preamp. This yields a slightly increased action to the low-pass filter in the low-pass portion of your PLLXO.
        To measure/visualize it much more accurately, do not use an acoustic measurement, but rather a before/after measurement at your amplifier output....or even at the amplifier input (if your measuring equipment has very high input impedance.) Acoustic measurements introduce too many variables.
        The comment regarding me having "one of those days" is just silly.
        Cheers,
        Dave.
        
        Edits: 08/11/14
    - RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - old guy 42 10:04:21 08/11/14 (0)
      Re-read my last post!!..nuff said
- RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - JBen 09:28:07 08/11/14 (1)
  David, how on earth can I be "cheered" when I may have just been insulted?
  - RE: PLLXO biamp + passive pre-amp on MMGs: a nice little surprise - Davey 09:42:38 08/11/14 (0)
    Insulted? What on earth are you talking about?
    I provided you an explanation of what you experienced with your setup. I can't argue with your subjective evaluation, but by coupling a passive attenuator with a PLLXO you've created a complicated equalization interaction network.....and the EQ varies with volume control position. :)
    There's more going on there than intuitively you might think.
    
    I almost always sign my posts with "cheers." It means nothing more than have a good day. You should know that by now. :)
    
    Dave.
You can't do that :) - neolith 06:34:26 08/11/14 (1)
I am totally surprised (and also envious of the flat curve) that this works. The attenuation caused by the passive pre and the PLLXO is no biggy if your source is adequate - most CDP's put out 2V. However I would think that the variable load impedance on the PLLXO with changes in the passive attenuation would play havoc with the crossover points. Did you alter your PLLXO to account for the change in the load impedance caused by changing pre's?
In any case, so much for theory and congratulations on one more step up the never ending ladder of tweaks.

�

�

Edits: 08/13/14
- RE: You can't do that :) - JBen 07:50:19 08/11/14 (0)
  Neo, you are exactly right, which is why I had to be cautious. While modern playback units, including CDPs, SACD & DACs now have tons of output, the PLLXO could have reacted with variable responses.
  
  Yet, it seems like the only sacrifice that I'll have to make is to use 1st/1st order slopes. I prefer 1st/2nd in these ancient MMGs (that is what they came with, at speaker-level). However, the 6db extra insertion loss in the PLLXO...would be a killer with some recordings done a very low levels.
  
  That said, I am still going to try achieving it with the PLLXO in 1st/2nd order mode...just to see what can be done. The 1st/2nd slopes actually work beautifully in some "direct configurations", where I can vary the volume in some Oppo and USB DAC units. With these, the only need would be for an "input selector" box. Of course, I could still build an active xo. The newer opamps leave very little to be desired

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