When I recently started using the 16 ohm tap I found the NFB2 setting best. However after adding the Symposium Rollerblock HDSE footers and the RCA 805 tubes I actually find NFB1 sounds best. There is simply such little distortion even on the 16 ohm taps that I just don't need the feedback to give me the detail, separation, and tight sound that formerly required either added feedback or a drop to the 8ohm taps to present. In the end the dialable flexibility is fantastic to have.
I had done mini shootout among Acme, RCA and United 805(1940's). Melz 1578, RCA 5691 and Acme 300b are also used to drive Lansche 4.1 I played Eva Cassidy Autumn Leaves Mussogorsky's Pictures at Exhibition Land of forever (New Age music) and Tristan and Isolde (Wagner opera, introduction and second aria) Acme 805 overwhelmed RCA and United in refinement, texture. But RCA and United matched Acme in details and soundstage depth, width. United give slightly fuller bass than Acme or RCA. RCA is slightly more transparent than either Acme or United. The conclusion is that RCA and United are close to Acme in overall performance but I still prefer Acme in my system by slight margin. They are all nice wines which taste different. I may take turns between those tubes to save tube life. My Acme 805 had not shown any signs of failure ( it reached 120mA bias without boost)yet after 3500 hours.
In my system the RCA 805 clearly bests the Acme 805. Resolution and transparency are better. You get the concomitant increased details, texture, clarity into the backstage and inner details. Bass is more tuneful and the music can take on a faster pace if called for better than the Acmes. These tubes have shown the Acmes to have some coloration to it that I initially wasn't aware of. The RCAs are utterly uncolored, so be sure to add that elsewhere if that is what you seek.
Thanks for the reviews guys. Given you can find a pair of used but well measured RCA for USD 3-400. It's pretty good value.
I have a question related to this. The Legacy Calibre XD can be bi-amped with the 500w internal Ice amp running the low end. I wonder how the 508 IA would perform and sound with 48 watts driving the mids and highs?
Glad you guys are enjoying your RCA 805s like I am. Took a little more work but clearly, the result is obvious and superior.
I love it when a more affordable option is superior. I've gone from Elrog 300Bs to Acme 300Bs, which were superior in this amp. Now going from the more costly Acme 805s to RCA 805s is sonic improvement with wallet savings. $70 RCA 5691 clobbers most others. As audiophiles, we're often accused of favoring more expensive options due to placebo. Where's the placebo now? Lol
I bought my 508IA used from a guy who used it to drive the top half of his Legacy Aeris. So I think 508IA will be enough to drive the Calibre XD. He also claims that he cannot tell the diff between the 508IA and his Benchmark AHB2... but that's another story. non-amped Calibre has a [email protected]/4Ohm efficiency. A bit low but you don't need to drive the woofer. I drive my [email protected]/4Ohm Mezzo full range and it is just enough.
Hello Thomas How do you find the United 805 vs the Cossor 805 valves? I have a couple of pairs of Psvane 805 AT-II as a back up for my ACMEs and one of those AT-II pairs sounds very good. In fact, I will compare them to the ACMEs in a few days to see how far are them in sound quality as the ACMEs cost almost 4 times more. If I found the AT-II close enough to the ACMEs, I will have to think about if it's worthwile for me spending so much on a pair of valves. The problem with United and RCA 805 is that most sellers ship them AS IS with no warranty and at a bigger price than Psvane Cossor or AT-II, wich I can buy from sellers I can trust. So, as ACMEs are pretty expensive and I'm looking for an option, do you believe United or RCA are considerably better options than Cossor 805?
My 508 is driving a pair of Q Acustics Concept 500 floorstanders wich are 90 Db efficient and have a minimum of 3.8 ohms. It does it with ease and dynamics at volume levels much higher than safe ones for hearing issues. Much more dbs than I need. Even at low volume levels, the music is dynamic and very enjoyable. In fact, for me my 508 has more grip and balls than a Hypex NC500 based class D amp I also have at home. Not to mention better texture, smoothness and 3D sound.
Pedro, how big is your room and what type of music do you listen to? I have a 400 sq ft room and I listen to a lot of symphonic music. I find that 508IA has barely enough headroom for it. It clips quite often actually. If I listen to easier music like jazz or smaller scale music it is totally OK. Symphonic music is really tough on the setup. As for the clipping. I find that the upgrades I did to the power supply vastly reduced the clipping. The extra headroom from the larger and better capacitors just push it above what the room/speaker demand from the 508IA.
Since you are located in Argentina, it is too much risk to order United or RCA old tubes as is. My Acme had lasted 3500 hours no problem. Since you also have some other backup tubes, you can just enjoy the music not bothering about 805 tubes.
Well, My room has an L shape. The straight part of the L is about 470 sq feet and the side of the L is about 150 sq feet. I listen mostly to classic rock, but also some pop, chill out, folk, electronic, etc, but not symphonic music. I also like to listen at low to medium levels most of the time. Sometimes I crank up the volume, but not often. I do it for a couple of reasons, to preserve my hearing and because I believe hearing is like any other sense and it can get easily saturated. I prefer quality over quantity. If you drink a 1.000 dollar wine glass you do it zip by zip, not in two seconds. Otherwise, after the third glass You won't distinguish the good wine from the bad one. Thats just my opinion of course. On the other hand, I use a couple of subwoofers, wich I believe are somehow properly integrated with my mains speakers. They work about 60 hz and below and only to help un the sub base frequencies, taming the base modes somehow and providing better 3D image, but I guess they also may help pressurazing the room.
For 400 sqf 40W per side from 508ia (I actually measured it, output is 40W at 5% distortion from each channel) is not enough. You will need at least 500W, if not 1kW of power to fill room with sound from modern below 90dB/W speakers. Though if you use large horn loaded speakers, that will change.
Well, if you want to recreate concert or orchestral levels, may be not, but I get BIG soundstage, plenty of dynamics and slam with the 508, even before I had the subs. For my situation and the way I like to listen to music, it's far more than enough. In fact, even at my highest listening levels, I much prefer it over my Hypex NC500 class D amp wich has 700 wpc on 4 ohms.
@AP1 respectfully disagree about 500W-1kW. that will overpower the room too much. I have used a 1.2kW amp (Crown class D) and it overly powers the room. I probably only using a fraction of it. I regularly use a 150W class D amp and that does control the woofer better than the 508IA but loses out on the treble and imaging and pretty much everything else. If the argument is to stick to the low distortion side of the power range, there might be some case for that, but then a 1kW amp won't be SET and won't have the sound that we are looking for here. Finally, @Pedro Guillemain mentioned concert level. I happened to have measured and compared a classical concert sound level to my listening level at home. At home I am listening at pretty consistently 5-10dB louder. In the hall I measured from row 9 from the orchestra so it is very optimal. Granted that this is classical concert, a rock concert it will be vastly different where I never attend but I read stories that ppl will need to wear earplugs there.
btw, I used to own a pair of NC400. If you look at the actual Hypex datasheet, the NC500 is rated only 100W continuous. 700W is peak which is not very representative.
My room is 300 sqf and when I try to play rock at close to concert level (105dB+), I am pushing my Bryston (300W x 2) close to the limit. My speakers are 89dB/W efficient. I am Ok with 508ia playing acoustic small scale music like jazz trio or women vocal plus piano. But I cannot force it to play AC/DC or Judas Priest as they should be played.
Well, I don't enjoy music that loud. In fact, I feel my ears, after a few minutes at loud volume levels, start to feel pain and/or get saturated and my hearing capabilities and enjoyment decrease. Not to mention how room modes get over excited and they affect and distort the sound reproduction. It's fair to mention that when I crank up the volume, once in a while, some pieces of furniture and windows start to resonate. How much louder than that is it necessary? It's just too much for me. What I mean is that, for me, and I believe for most audiophiles, the 48 wpc of the 508 are more than enough, even with not too efficient speakers (90 Db or so). Unless, you need concert levels.
certainly if u want to push 105dB with 89dB/W speakers it won't be enough. Assuming symphonies at ~95-100dB level, I am ~8-12dB lower in requirement compared to yours. which happens to translate to below 40w. So I think we are consistent with each other, just that the speaker efficiency and target dB level are not the same.
I know it's somewhere in these 78 pages, but what are the differences between the 508ia and the 805ia?
Just got the EML 300B-XLS tubes today. Only have 1 hr on them so far but noting more extended and fuller bass along with a smoother presentation. Very complimentary to the RCA 805's. Looking forward to putting 50 hrs on them. Thanks to @Strat-Mangler for the recommendation .
You're quite welcome. Glad you're enjoying them. Don't forget to register them when you can. Easy to get distract by their wonderful sound.
