This is for Georgehifi especially but others can chime in.
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Oh? You think 10kOhm is a great impedance for a source to be looking at? 99% of sources, Yes, Yes and Yes again, unless you have a tube source with massively high unacceptable 3kohm'ish output impedance. Just don't tell me how uncolored they are because that's a demonstrably false statement.You'll never know, with your low gain amps, and using 25kohm passives, you can take that to the bank. . Cheers George |
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kosst_amojanWhy do you keep assuming I've used a passive? I never have and I never will.Really!!! now this is a laugh, from statements like this below. kosst_amojanCan we clear something up? All passives basically suck. You really need to, with the right setup, and not using such a low gain amp as you have. Then you will have an ear opening experience, and will be enlightened. End of story. Cheers George |
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We're talking current delivery, and BJT's (bi-polars) will do current better than mosfets can. Ask the current amp kings EG: Krell, Gryphon ect why they use BJT's, and they don't have problems with thermal runway, because they are good designers, and don't get it, even with the massive Class-A bias they have. Your done. |
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I just can’t stand seeing BS put up, and have to give the truth. There is no such thing as an amp that can double it’s wattage the way he quoted. And if you believe Mosfets can do current better than BJT’s then your just as bad. As far as Ralph he great and we agree on many things, except for his instance on Zero auto transformers being a fix without any negatives, which they are far from, and are just a bandaid fix for a problem of not having the right amp for a given speaker. Cheers George |
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You two really need to update your semiconductor knowledge. Upvoted by, MSEE Electrical Engineering & Circuit and System, Master of Science in Electrical Engineering (2015) and M.S Electrical Engineering, University of Southern California (2017) Pros for BJT: "BJT’s at the same physical dimensions and price can usually give you a lot higher speed, as they have very little input capacitance. BJT’s can give you a lot higher gain. Just take a bunch of components and compare them, and you’ll find the BJT’s give you better gain characteristics and therefore require fewer gain stages. BJT amplifier stages are much more linear than MOSFET amplifier stages, as the gain doesn’t depend on the bias voltage. This gives better fidelity. BJT’s are capable of handling higher output currents for signal outputs and can have lower output impedance. In amplifiers intended to drive a low input impedance load or deliver significant amounts of power, this is a huge advantage. Many of the highest quality op amps are made with a BiCMOS process using a BJT pair for the output buffer stage." Cons for MOSFET: "Not as high of fidelity as BJT, since the gain will vary slightly as you increase the input voltage (that is, it will generate some very weak harmonics). Input capacitance. The higher the gain, the greater the input capacitance thanks to the Miller effect. Can’t drive a low-impedance load very well. Low gain per part, which often means more amplification stages are necessary for higher gain, even when using advanced design techniques. Each amplification stage adds noise -- that is, you can never, ever get a better signal-to-noise ratio at the output than at the input." I believe the OP has everything he needs, and doesn’t need the BS from the F5/Mosfet lovers, which I’ve heard and are great amps, if used within their comfort zone with preamps with high’ish gain and speakers not too low in EPDR load impedance’s and moderately efficient, because of wattage limitations. Hope you got everything you needed bubba12 Unfollowing this corrupted thread. Cheers George |
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bubba12 OP156 posts01-25-2018 6:37pmI need opinions on the Odyssey Stratos Extreme mono amps I’ve come across some Odyssey amps, a stereo and the mono-block version of it here in Australia, that a friend bought in who was going to be the Au agent for them. I can’t remember which ones they were but they were the upper end of the range. We listened to them, with a group of our audio society friends and were all in the opinion that the stereo version sounded better than the monoblocks, even through the very hard to drive Infinity Systems Renaissance 90 Signatures, oldie but a goody. After that listening session, we peaked under their skirts, and what I pointed out to the potential agent was that the monoblocks were just bridged versions of the stereo one. Now I don’t know if this bridging of the stereo ones for the monoblocks is done right through the range. But if you post a photo of the inside on one of the many free image hosting websites I can let you know, if they are just bridged stereo’s or true monoblock amps. Cheers George |
Yes, George raises an excellent question. Looking at the specs and descriptions of the stereo and mono versions of the Stratos Extreme, though, several things suggest to me that the mono version is not bridged, but instead parallels the two output stages and perhaps some of the other circuitry. Specs which point to that conclusion include the 8 ohm power rating of the mono version being only slightly higher than the rating of the stereo version (a 4 ohm rating is not provided for either amp); both amps are described as stable into 2 ohms; the output current rating of the mono version is twice as great as for the stereo version (yes, I realize that output current ratings are usually meaningless, in part because how long that current can be supplied for is not defined); damping factor is much greater for the mono version than for the stereo version; input impedance is specified as being the same (22K) for both versions of the amp. I note also that **both** versions have a statement saying "RCA & XLR (bridged) inputs." Not sure what the reference to bridged XLR inputs means. In any event, while the sonics of many bridged amps can be expected to be significantly compromised driving the 4 ohm nominal impedance of the Dynaudio C-1 Platinum, this appears to be a different (and presumably better) situation. Regards, -- Al |
I've noticed the same approach by a couple of other manufacturers and also found their stereo amps sound more musical than their comparably power monos. Yes a few disadvantages happens with bridging a stereo amp, while you get more 8ohm wattage the drive-ability into low impedance's is greatly diminished. The damping factor (output impedance) of the amp is raised, therefore not having as good control over the bass. And the other is the distortion of the amp increases, and I believe also the noise. Cheers George |
bubba12 Why not stick with the Devialet 400 which you have, or the Pass Labs you said you could get? BTW which Pass Labs was it? All are good. Cheers George |
I’ve sold the Devialet 400. Frankly,I didn’t like it. I may still buy the Pass Labs and it would probably be 260.8 mono with the xp-12 preamplifier. In the mean time I got a decent deal on the Odyssey gear and figured I would see how pleased I could be on the cheap. I’m pretty certain that the Pass Labs are the end game but damn! So much money. |
bubba12 OP160 posts01-26-2018 10:07amI’ve sold the Devialet 400. Frankly,I didn’t like it.Doesn’t surprise me, I’ve yet to hear a class-D yet that’s sounded right in the upper mids/highs, either too rolled off, soft, cold or harsh depending on the switching frequencies filter’s filtering characteristics. Great in the bass and upper bass though. Yes the XA25 is a little short on power, should sound very nice (being high bias Class-A series) from low to medium levels. Also it’s gain is only 20dB so an active preamp with bit of gain is needed to partner with it. The XA60.8 would be my pick for you, still the high bias series, and should have enough power for the Dynaudio C-1 's, and it's a higher gain than the XA25 at 26db so you could get away with a passive preamp and save a stack on money. Cheers George |
I love the sound of well made Class-A. Way back I built some very large pure 100w pure Class-A ones using 20 x Hirel EB/ED 204’s BJT’s per channel and a 5kva transformers 500,000uf per channel, that were a 3 man lift, they were water cooled because of the huge amount of heat that needed to be dissipated, and were size of a large coffee table. http://www.diyaudio.com/forums/parts/76846-whatever-hirel-transistors.html My preference is like Nelsons (if you delve into his past) for the sweetness and effortless sound of Class-A which will come from in a smaller way from the XA A/B amps. The XA series has more Class-A less Class-B The X series has less Class-A and more Class-B So it all comes down to which flavour of "Class" your drawn to. For me it would be for the XA’s. Cheers George |
PS: Love these older class-a monsters, Mark Levinson ML2 monoblocks, only 25w Class-A into 8 ohms, nothing more, but said to be able to do the "almost" doubling wattage act down to 1ohm https://ucarecdn.com/c5da1bf6-48bb-420e-b088-b6dbf0dceb7a/-/scale_crop/840x630/center/ http://4.bp.blogspot.com/-9uGHPSseR-w/U3aWYTrghsI/AAAAAAAB8yI/XxdvN_K7-jk/s1600/ML2a.JPG Cheers George |
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Bubba12: I have had 2 sets of Krell mono blocks and one set of Pass Labs. I had 2 Kma 160’s a set of Pass X250’s and now have a couple of Krell EV 600’s. I liked them all. Good class a bias and plenty of current. The KMA 160’s didn’t have enough juice for my then Martin Logan Monoliths. Bought some Wilson Max II,s and the Pass amps couldn’t get me where I wanted to go. Finally bought some Ev 600’s and have never looked back. They have all the current I desire and personally, I love the Krell sound. I would try to find a used Krell stereo amp-one of the older models that have had the caps replaced. IMO, you can never have too much power and there are occasionally good deals to be found on used Krell amps. Steve |
