Opera Audio Consonance M500S Monoblock 300B Parallel Single-Ended Power Amplifiers.

Posted by mgrissom (A) on April 15, 2002 at 00:40:36


I bought a pair of Opera Audio Consonance M500S to drive my Lynn Olson designed ME-2 loudspeakers. The ME-2s are between 90 and 92 db efficient, are an easy load to drive, and were designed to be used with amps having a damping factor of 5 to 10. I had been using the Welborne Labs Laurels IIX Ultimates, which I liked very much, however they did not have quite enough power. So I posted on the AA to find out what my options were for a Push Pull 300B amp with 20 watts per channel and a 4-ohm tap. I believe I found all that were available and there are only 6 OR 7, most of them were expensive in the $6000.00 to $10,000.00 price ranges. The least expensive was a French model that was on sale for $2500.00 however when I called them they were not exporting. Ivan 303 posted a reply suggesting I take a look at the Opera Audio Consonance M500S that is a Parallel DHT 300B has 18W, and a 4 and 8 ohm tap. They are of a similar design topology to the Laurels, and Consonance M500KIT/Billies and people have commented that they liked Opera Audio M500KIT / Billies. After some e-mail back and forth with Stanley Chu of Time Telecom Limited, H.K., and a little studying I bought the M500S.

Because no one has posted that they have heard the M500S I decided I would review them. I feel this Parallel 300B is a good alternative for anyone interested in a higher power 300B based amp to power medium efficiency speakers. At only slightly more expensive than a Single 300B based amp, (in some cases cheaper) these make my speakers sing. I don't believe they deserve the bad press they have gotten.

There are some comments on the AA from Brian Cherry of DiyHiFiSupply, explaining why he doesn't carry them in kit form. I didn't see his comments until after I bought mine and I'm glad I didn't.


Before I even hooked them up I took the bottom off and took a look inside. The parts while maybe not being the very best quality are of very high quality. Electrolytics by Nippon, Rubycon, Black Gate and a couple that were labeled Maroon. Film Caps by Multicap (PPFXS) this is tin foil and polypropylene. I haven't seen the S suffix before, but was told it stands for tin. I won't write much more about this as most of it is covered in their web site. The amps also have a wide-open layout with lots of room that makes it easy to change parts. You can also see inside the unit on their site.

Build quality is good. The amps are long, from front to back just over 19 inches if you don't count the connectors, and they don't fit well in my rack. They hang 2 inches over the front and back, which I don't like. (I just got through adding 3 inches to the back of the shelf the amps are sitting on and now they look pretty cool.) The body is made of brushed stainless steal, some will like the way they look some will not.

The Sound

My first listen, I thought, this is what I've been looking for. These amps would play louder than my Laurels; in fact they play my speakers louder than I do care to listen. What I noticed was how well these amps reproduced voices. This is one of the best amps I can remember hearing for voices. Both male and female voices were almost magic. (I'll get to this later.)

The M500Ss are quiet! Quieter than either of the other amps I have. Also my Audio Research Classic 60, and Laurels required a Rat Shack ground loop isolation thing on my TV to pre amp connection to eliminate hum! The M500S doesn't need it. (I don't know why this should be, but it is what it is.) No ground loops.

The bass while not being as powerful as the Laurels was as deep. In stock form I preferred the Laurels tonal balance to that of the Consonance M500S.

I like both female and male vocals on the M500S better than either of my other amps. I could more easily tell who the singers are, while being individual, voices in a choir are blended better, and although voices are pure they don't have any overemphasized sibilance or break up.

To summarize the amp plays loud enough in my system, voices are great, they are quiet, and for us tweaks easy to work on. Did I fail to mention they are reasonably priced? These are the least expensive amps I've seen in this category and Stanley Chu has been a pleasure to deal with.

What I didn't like.

It didn't take long before I was hearing a metallic sound coming from the lower midrange. (It was also audible on some male vocals, which as noted is otherwise a strong point on these amps in my system.) I heard this metallic sound more on some music than on other but once I heard it, it was a nuisance. My girlfriend stopped over and her reaction to the amps was just like mine at first she said wow those sound good and then she heard the metallic sound and mentioned what is that, that doesn't sound right.?
(I don't like obvious negative additive stuff that detracts from the music.)

You may or may not hear it in your system. However after I bought these amps I noticed that Thorsten has posted much about the Consonance Billie. He mentions that the stock tubes sound brash, rough and unsophisticated. He goes on to say that on relatively flat speakers the upper midrange and lower treble is strongly tilted up. I didn't hear this on the stock M500S, however I have changed tubes and believe that while the TJ Mesh Plate 300B tubes minimize the metallic sound I hear, there is a compromise. In my system some of the midrange magic is gone. I should also note that I tried the Ken Rad VT-229 tubes in place of the stock Jan Phillips 6SL7. These tubes increased the power of low bass however they did little to eliminate the metallic sound. I liked having greater power in the bass and feel that this improved the tonal balance so I have left the Ken Rads in only going back to the JANs once or twice for comparison.

During the process of trying to tune out what I call a metallic sound by changing parts, I've changed almost every electrolytic cap in the amps except the Black Gate Cathode Bypass and (2) 10,000uf/10V 300B heater caps, to Elna Cerafines. This has made little difference and I've changed the big 390uf/400V Nippon Filter caps back from the Elna 220uf/500V caps I tried, as I think the Nippon sound smoother. (I didn't expect this.)

The following has resulted in what I feel are improvements to these amps.

One change that has moved the metallic sound lower in frequency (out of the range of male vocals) and slightly improves bass impact was replacing the 10,000uf/10V 300B DC heater supply filtering caps that are across the legs of the bridged rectifiers with (2) 4700uf/16V Black Gate caps. (I had these on hand from trying them in my Laurels where I didn't really like them.)

Next I replaced the 100uf/10V Black Gate 6SL7 driver cathode bypass cap with a 100uf/100V ZEN (Huge 1.75 inch D x 3.5inch L) metalized polypropylene from North Creek as I had these on hand from a speaker crossover project. (I may also try (2) paralleled 47uf/250V SCRs) This has made the biggest change/improvement; the metallic sound is all but gone. Everything is smoother and more dynamic.

Note after making this change the Tj 300B Mesh Plates now sound much better than the stock tubes in every respect. And the stock tubes do sound as Thorsten describes them.

One other note If you decide to try the SRPP to MU modification mentioned at the end of this article then save the $50.00 you will spend for this mod. As these caps will be removed for that mod.

I have also replaced the 0.47uf/400V Multicaps with my favorite speaker cap the Crescendo 0.47uf/600V polypropylene film and aluminum foil from North Creek. (These are said to have a sound somewhere between the Hovlands and Jenson PIO. Having tried all three in my speaker crossover I would have to somewhat agree. In my speaker crossovers I prefer the Crescendos to anything else I have tried.)

The jury is out on this last change. Yea it changes the sound. Both the stock 300Bs and the Tj Mesh Plates now sound good again. Every thing sounds mellower. I just don't know which way I like it better. I will probably change back to the Multicaps. I really think I could be happy either way, however I think I like the Midrange better with the Multicaps and the Low Frequencies slightly better with the Crescendos.

I would recommend these amps to anyone with speakers in the 88-95 db/spl range that are looking for the single ended 300B experience. (I plan on trying them with my 86/87db Borealis speakers, I suspect they will drive them, however it's a hassle moving them, when I do I will post the results.) The Consonance M500S may delight you right out of the box (and with some speakers in some systems I believe they will) if not a few small changes may do it for you as it has for me. The parts changes I recommend are 1st change the 100uf/10V-bypass cap to a metalized polypropylene type like the SCR/Solen 47uf/250V; you need two in parallel. (Note that if you make this change you may be like me and not like the stock 300B tubes this way also if you are planning the SRPP to MU stage mod these caps will be taken out and of no use.) Listen to them with the TJ Mesh Plate 300B and you may be done here. If not, 2nd replace the 10,000-uf/10V 300B heater caps that are across the legs of the bridged rectifier with (2) paralleled 4700uf/16V Black Gates. (Note: there are 2 of these 10,000uf/10V caps for each 300B (one is soldered to the tube socket and the other to the rectifier, I only changed one of them.) You may want to try this change first, as it does not seem to adversely affect the sound of the stock tubes. Again this might end it. 3rd change the .47uf/400V Multicap to your favorite i.e.: Jensen PIO, Hovland, or Teflon etc.

P.S. For me the midrange won out.
I've changed back to the Multicaps with the Tj mesh plate 300B tubes. After listening this way for a while I will say the Crescendos are more polite.

This is the best I have been able to achieve so far. The more I listen the better I like them.

OK, even though I'm pretty happy I have to try the modifications that Stanley Chu has e-mailed me, these were intended for the Billies however they will also work on the M500S amps and are highly recommended by Thorsten, and others. They are as follows:

1. Convert the 6SL7 driver stage from SRPP to MU stage. This modification will be available as a kit from DIYHIFISUPPLY. For this mod one cap is replace, two resisters, and one cap added. This mod is said to further clean the sound of the amps and remove the metallic sound of the SRPP. (It is interesting that Thorsten used the word metallic, as this is the way I described it and I feel it is almost gone now.) I will definitely be trying this mod in the future.

2. Adding a grid Choke. This is said to increase dynamics among other things. This modification requires modifying the box. (Some standoffs or spacers between the amp body and bottom plate, as the chokes are a little large. I don't think this will be a big deal on this chassis.) I'm sure I will also try this one.

My system consists of the following:

Front End: Grado Sonata Cartridge, SME IV.5i tone arm, RPM Turntable, Ah Tjoeb CD player with all the upgrades, and an Audio Research SP9-MKIII pre-amp. Interconnects are DIY made from Beldon 89259 and Cardes RCA connectors. Speaker cable is Nordost Super Flatline Bi-Wire terminated with North Creek Big Spade Jr. I also have a pair of DIY transmission line subwoofers that are electronically crossed over at 45 Hz. Driven by some sand amps. I run the ME-2 full range.

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