Problem with Rogue Medusa Amp (I need advice)

Thanks for your reply. I have the Egglestonworks original Rosa speakers. They sound great with the Pharaoh integrated, but not with the Medusa. Right now the Medusa has the JJ tubes that came with the amp, but I get the problem with any tubes I use.

If it has a negative feedback problem, does that point to a specific electronic part that might have gone bad in the amp? Is there any way I can test for a negative feedback problem or do I have to send it back to Rogue to have it checked out?

Will ask the obvious, have you contacted Rogue and discussed what you are hearing with them? Might get to the heart of the matter quicker

sounds like a gain miss match between your preamp and the medusa.
i just read online about people with your preamp having difficulties with edgy sound because of the very high gain of the mfa magus.
if you cant adjust the gain there are inline gain attenuators available, i have never used them.

https://www.diyaudio.com/forums/tubes-valves/77149-schematic-mfa-magus-5.html?s=b8b8a461bc471ad57fd0...
as others have mentioned you can email rogue and they will get back very quickly. go to their site for the contact link.

Just superficially from google images, a Pharaoh bypassing its very mediocre Alps RK27 volume pot (i.e. unity inputs) looks a LOT like the Medusa topology - both have a pair of the same Hypex UcD 400 modules (older than nCore in the new Dragon), a couple large coupling caps, and a pair of 12AU7 tubes. But there appears to be different kinds of coupling caps used over the years in both models. Your Pharaoh, being a current product, may utilize the better (at least more expensive) Mundorf EVO caps that don’t seem to appear in the Medusa (those look like Solens, but without the usual label). It’s quite possible that your system favors one cap over the other. Second, the Medusa very clearly sports input transformers (again, maybe CineMag or Jensen depending on vintage). The Pharaoh DOESN’T show input transformers, unless they’re hidden under the front board which is unlikely. The input transformers alone could be elements that don’t gel with your system - for example, I strongly suspect the Lundahl in+out transformers in the current VAC preamps may be the reason they don’t totally gel with my Tannoy system, whereas the VAC amps (no Lundahls) do spectacular work. So it’s entirely possible that the Pharoah is a much better match for your system, confirming your listening results.

So how did you arrive at the conclusion that a Medusa would be an upgrade? The Pharaoh is a more recent Rogue design, and at a similar price-point to the Medusa, so I think it’s unlikely someone at Rogue would recommend that move. The Dragon has replaced the Medusa, and THAT would be what you’d have wanted to consider for an upgrade. It uses the newer and improved nCore modules, which are measurably higher power and lower distortion. The Medusa has absolutely no power/distortion advantage over Pharaoh.

And sure, you could probably tame harshness and glare with Mullard 12AU7 (especially NOS, but maybe also Russian re-issues which have become quite good), but that will be more like a band-aid if you’re trying to correct for a downstream problem or mismatch. Mullards are warm and smooth with a slightly muted top-end, and some audiophiles abuse them for this reason ;)

One last thought - I always hated the 12AU7 tube in general, and with any Rogue gear I've owned (since they like to use that tube), I immediately replace them with 12BH7. But 12BH7's draw twice the heater current (0.6A vs. 0.3A), and I think Rogue says "not to" do that sub anymore lol. 

Thanks for all this technical information, which may be the reason that the Pharaoh is a better match for my Magus than the Medusa. But, I did try running the Pharaoh preamp through the Medusa amp and heard the same problem. I do a little more troubleshooting before I decide what to do. It is possible that there is a malfunction with the amp, so in the end I might send it to Rogue for evaluation just to make sure. I also, know someone selling a Rogue RP-5, which I can't afford to get, but it would be interested to hear that paired with the Medusa to see if I hear the same problem.

I assumed that the Medusa would be a substantial upgrade over the Pharaoh, because even though they are at the same price point, the Pharaoh includes a phono section and preamp section, so I assumed that the Medusa, being an amplifier only would be of a much higher quality, since all of the manufacturing and design costs are going into creating as good an amplifier as possible, as opposed to having to create an integreated amp with three different functions.

Mulveling, what changes in sound did you get when you replaced the 12AU7 with the 12BH7's? Did you end up having any problems, since they draw twice the current.  Why do you dislike the 12AU7's so much?