stormin Posted January 5, 2007 Share Posted January 5, 2007 I noticed in the PLX2 range that the 1802 's output circuitry is AB, while the 2502 is 2-tier class H. What the difference and what is typically preferred? Also are rge PLX2 (second generation) that much better than the PLX (first generation) amps? Anyone know? Thanks inadvance. There have been some say that the class H with its switching is inferior for some reason or another. My QSC is an SRA 2422 and it also is 2-tier class H. My ears are attracted to sound which comes from this amplifier. Thats really all that matters to me. I have no idea of the science involved I just understand that it switches over 230,000 times a second and the class H design is intended to keep the heat down and less current draw from such a high powered amplifier. If you notice all the big QSC's seem to run 2-tier or 3-tier class H. But then again the class AB designs could be at another level sonically I just dont know. Quote Link to comment Share on other sites More sharing options...
stormin Posted January 5, 2007 Share Posted January 5, 2007 Actually I believe Tigerwoodkhorns has owned both designs so maybe he will chime in on what his perception of the difference was. Quote Link to comment Share on other sites More sharing options...
Arky Posted January 5, 2007 Share Posted January 5, 2007 I noticed in the PLX2 range that the 1802 's output circuitry is AB, while the 2502 is 2-tier class H. What the difference and what is typically preferred? Also are rge PLX2 (second generation) that much better than the PLX (first generation) amps? Anyone know? Thanks inadvance. JB QSC has a tech forum in case you didn't know, Bob is the designer. It is under the support link. qscaudio. Quote Link to comment Share on other sites More sharing options...
Rivendell61 Posted January 11, 2007 Share Posted January 11, 2007 I do that all the time, but it rarely works with a low enough noise floor for the home - the only thing I haven't tried is that one resistor trick to create the impedance match, but it doesn't make up for the huge loss in gain. What's the point of having 200+ Watts available if you can only drive the amp to 20W? DrWho, The only reason the interconnect I described gets the nod in unbalanced to balanced is because it is more likely to maintain signal integrity (SNR, etc) than the alternatives. Now....if you're getting increased noise using that balanced connection then I would look at your gear. Is the interconnect wired properly? Or, more likely, the ground/circuitry (of the unbalanced or balanced side) may be less than desired (i.e., screwed up). Might be worth looking into. Re power--it should be a non-issue. Again, the lack of a perceived problem is why the 1:1 option gets the nod over the 1:4. The PLX has a gain adjustment for the very reason of matching the input. OTOH.....this is all very gear/situation dependent. While that interconnect is going to be best in most (studio or home) cases there may certainly be situations where the amp is not capable and/or the signal quality issues are not paramount, etc. Mark Quote Link to comment Share on other sites More sharing options...
mas Posted January 11, 2007 Share Posted January 11, 2007 See attached... Connecting Balanced&Unbalanced lines.pdf Quote Link to comment Share on other sites More sharing options...
Arky Posted January 11, 2007 Share Posted January 11, 2007 If anyone is interested, there is a tremendously long thread active over at AVS discussing some of these issues, specific to Crown & QSC, including the cleanbox & fan replacement. Bob Lee of QSC answers a lot of questions. Thread is "new amp is making me grin from ear to ear". I trust you guys more than AVS, but Bob should know of what he speaks. Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted January 11, 2007 Share Posted January 11, 2007 arky can you post the link cause I am trying to find it to no avail. Quote Link to comment Share on other sites More sharing options...
Arky Posted January 11, 2007 Share Posted January 11, 2007 arky can you post the link cause I am trying to find it to no avail. Good luck http://www.avsforum.com/avs-vb/showthread.php?t=418666&highlight=qsc+amplifier. Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted January 11, 2007 Share Posted January 11, 2007 holy crap 123 pages? Quote Link to comment Share on other sites More sharing options...
Arky Posted January 11, 2007 Share Posted January 11, 2007 It started in ' 04! I just searched Bob Lee & read his posts, mostly. I really like the QSC. Quote Link to comment Share on other sites More sharing options...
DrWho Posted January 11, 2007 Share Posted January 11, 2007 lol Quote Link to comment Share on other sites More sharing options...
Rivendell61 Posted January 12, 2007 Share Posted January 12, 2007 See attached... Bill Whitlock is the man re interconnect/grounding issues! If you are familiar with his writing (ideally more recent than the one you linked) you will no doubt recognize that my post above to DrWho was essentially a paraphrase of Whitlock's positions. He strongly advises against use of step-up transformers when going -10 to +4. And he advocates the interconnect I described as normative saying: "For all intents and purposes, using [that interconnect] is the correct way to connect an unbalanced component to a balanced one". Whitlock is particularly handy because he carries some authority, for several reasons, not least of which is that he participates on the AES task group on interconnection standards. Mark Quote Link to comment Share on other sites More sharing options...
DrWho Posted January 12, 2007 Share Posted January 12, 2007 I'm confused... "2.1 - "MINIMAL" is an Adapter Cable" "2.2 - "BETTER" uses an Output Transformer to Improve Balance" "2.3 - "BEST" uses an Input Transformer to "Fix" the Input Stage" "2.4 - A Simple Alternative" Quote Link to comment Share on other sites More sharing options...
Rivendell61 Posted January 12, 2007 Share Posted January 12, 2007 I'm confused... "2.1 - "MINIMAL" is an Adapter Cable" "2.2 - "BETTER" uses an Output Transformer to Improve Balance" "2.3 - "BEST" uses an Input Transformer to "Fix" the Input Stage" "2.4 - A Simple Alternative" Hmmm.... Somehow I don't think you are trying very hard here...... :-) All the clues are in my post (and there is really little mystery) i.e., read Whitlock's more recent papers on the subject (heck, I've even linked those to you before). It's a bit late but I will try.... Essentially in the paper mas cited Whitlock is simply listing connections in the order of ascending noise rejection ability. In later papers he answers the more specific question of what is the 'correct' (his term) way to connect unbalanced to balanced--which is not the same thing. He answers: via the described interconnect (see my quote from him in the post above). In other words, since most homes/studios do not have huge 'noise' problems and can manage to derive full signal integrity even with unbalanced connections (on occasion...). The 'correct' interconnect he describes adds c. 30dB of additional rejection above that. So there is rarely going to be a reason to resort to a transformer--and best signal quality will be preserved by using the simple cable option sans transformer (remember he sells transformers so he is being a good guy here). Going balanced to unbalanced is another matter..... Mark Quote Link to comment Share on other sites More sharing options...
DrWho Posted January 12, 2007 Share Posted January 12, 2007 So why would he provide methods that use transformers and call them better? / best? Also, I'm not talking so much about the noisefloor as much as the signal strength... It is very "difficult" for consumer gear to drive the pro gear to its full potential (ya, lame pun) [] But seriously, when running a subwoofer system of sensitivity 92dB, there's 10dB of gain to be made up to match the sensitivity of 102dB speakers. Then throw in a 12dB loss from going unbal to bal using the cable adaptor and now you need 22dB of gain. Even with the best noise rejection, you're still going to be raising the already existing noise floor with the extra gain (I think it'll only be +12dB not +22dB though). Most receivers only give you up to +12dB on the subwoofer channel and a max of -12dB on the mains...that's a lot of compensation just to get the levels matched - and it still doesn't change the fact that you're going to overdrive the preouts from the receiver when the volume goes up (especially with movies). Running the adaptor for the main LR amp isn't as big of a deal because the efficiency of the speakers means you don't have to run the amp as hard. However, you still won't realize the full potential of the amp - even if you crank the receiver up all the way. Your 480W / channel amp is now only 30W / channel [] I'm all for the cable adaptor when it works because it's cheap. However, it doesn't work all of the time and no article can undo those awful experiences (unless of course it explains why it was awful). So my advice would be to try the adaptor - if it doesn't work, then get the converter box. For what it's worth, right now I'm running an unbal out of a mixer into my crown amp with no problems - but running the subwoofer preout from my receiver into the crown amp is a most awful sound. The sub pre out through a passive transformer was better than the adaptor, but the mixer is extremely better than both of them. I'm led to believe that unbal pro gear is able to drive at higher voltage levels than consumer unbal gear. Quote Link to comment Share on other sites More sharing options...
mas Posted January 12, 2007 Share Posted January 12, 2007 Mike, Bill Whitlock is da man regarding interconnect/grounding issues. That is why I posted that article as well as several others of his regarding troubleshooting noise and hum issues in other threads. And you have pretty well answered your own question. Even I can't think of anything to debate with you (for now!!). That has to be worth something!** [][] **On the other hand, that could serve as impetus for you to go back, re-examine, and toss out everything you have said! [][] Quote Link to comment Share on other sites More sharing options...
DrWho Posted January 12, 2007 Share Posted January 12, 2007 And you have pretty well answered your own question. Perhaps you could do me the favor of pointing it out, lol [] Quote Link to comment Share on other sites More sharing options...
mas Posted January 12, 2007 Share Posted January 12, 2007 [:'(] If you can go direct, by all means.... (I guess that I am way out on a limb preferring to avoid the extra noise of additional unnecessary gain stages - and heaven forbid other fascinating toys with which others are enamored...) But if you can't, there are a number of options. I would start with the least expensive and least intrusive method - and the adapters work well in most cases. When they were needed, I have encountered few cases where they have ever proved in any way prohibitive. And if one has such a case in a home environment, I might suggest that they might benefit from taking a step back and taking a larger look at exactly what they are doing... [] Quote Link to comment Share on other sites More sharing options...
Rivendell61 Posted January 12, 2007 Share Posted January 12, 2007 So why would he provide methods that use transformers and call them better? / best? Answered above...... DrWho, It has been said several times that there will be some circumstances where equipment or situation demand another solution. I know nothing of receiver/subwoofer issues--that may be one of those situations. No one has said it will always be best. There are no doubt many situations where power needs overwhelm quality concerns. Whitlock is writing from an assumption that most are trying to maximize signal quality first--and only compromise on that when there is no other option. That cable is used everywhere as first choice but only seems to have a hard time with one individual... :-) You might read Whitlock's objections to the 1:4 boxes. You can also just look at the specs of the box mas suggested to see reason to avoid it. Re the QSC PLX amp Bob Lee (QSC engineer) has stated that the consumer step up should be no problem in most cases--turn up the gain if needed (he also suggests everyone read Whitlock.....). Again.....the cable solution is preferred by Whitlock, and others, not because it is cheap--but because it works best in the sense of best signal quality. It is SOP in most 'critical' unbal => bal situations. Here is an example from the manual for a DSD/SACD analog to digital converter (perhaps the best ADC extant) where absolute signal quality is obviously paramount. No transformers in sight! And do you recognize that cable? Quote Link to comment Share on other sites More sharing options...
Rivendell61 Posted January 12, 2007 Share Posted January 12, 2007 [:'(] If you can go direct, by all means.... (I guess that I am way out on a limb preferring to avoid the extra noise of additional unnecessary gain stages - and heaven forbid other fascinating toys with which others are enamored...) But if you can't, there are a number of options. I would start with the least expensive and least intrusive method - and the adapters work well in most cases. When they were needed, I have encountered few cases where they have ever proved in any way prohibitive. And if one has such a case in a home environment, I might suggest that they might benefit from taking a step back and taking a larger look at exactly what they are doing... [] Hey......I am in complete agreement with mas here! I only would note that when the term 'adaptor' is used it be understood that the cable wired as above and called an 'adaptor' is fine but the actual plug adapters should not be used. Mark Quote Link to comment Share on other sites More sharing options...
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