Is my new amp TOO GOOD?

@orthomead I also went from a pair of 200iQ to pair of Master 300 iQ (prototype versions). I’ve noticed these amps all vary their sonic balance quite a bit in stereo versus mono, and also with tube type KT88 vs 120 or 150. 

A pair of 300 sound perfect with the stock KT88. With 120 it’s a bit too rich. However, in stereo mode the single 300 amp is a lot more forward. A LOT. I don’t like it at all with KT88, but it’s a really nice balance again with KT120. 

I do seem to recall the 200iQ in stereo was pretty well balanced with KT88 but there too I preferred KT120, and in mono mode the 2 tube sets were a close call. 150 will be darker than 120 with even more emphasis on bass.

In short I’d try popping KT120 or maybe even 150 in your stereo 300. A power conditioner or cables are not going to get the balance where you like it nearly as effectively as a tube swap.

being tube amps it’s hard to optimize one config for stereo, mono, 4 ohm, 8 ohm all at once. I use 8 ohm Tannoys btw (96dB)

@mulveling In the 200's I actually preferred the KT 170's over the 150's.  To me the KT88's sounded a bit anemic. The current sound is actually quite well balanced but there is a little too much sizzle on the upper end.  Some snare drums explode out of the speakers.  In truth, my ears have always been sensitive to upper frequencies though.  Also the dynamics are much more pronounced with the 300's, which is taking a little bit of getting used to.  I don't quite have 100 hours  on the tubes.  I did talk to Kevin and have changed the stock 6SN7's to my NOS RCA 5692's which has also helped somewhat.  I do like the idea of changing to KT120's but I don't have them anymore-they went with the 200's on the trade in.  I still have eight each of the KT 150's and 170's.  I guess I could change a row in each amp to see how that does. I would check with Kevin first. My speakers are early Magico S7's (89dB).  Appreciate your input.

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@mulveling I talked with Brent who confirmed that rolling should be done row by row.  Actually he said I could mix and match with no ill effects.  I switched the first row out with KT 150's.  Surprisingly little change.  Then I switched the back row out with 170's (my preferred tube in the VAC 200) and that took the majority of the shrill sound out, but it seemed overall a little "muddy".  I switched the first row back to the KT 88's and this seems to be the best compromise.  I've learned some things in this current upgrade.  Alll prior upgrades did nothing but add good to the system.  I could turn up the volume with impunity on almost all recordings. Everything sounded better. I believe this current upgrade shows the "truth" in the recordings and some recordings are just best not cranked.  The detail and staging is incredible  now and well worth the time and energy to sort it out.  I'm adding a Shunyata T30 Typhon and hoping that will also add further improvements.

Before you spend more money, try facing your speakers straight ahead (no toe-in) and placing your listening seat closer to the plane of the speakers compared to the distance between the speakers. That should reduce the treble energy you're hearing and may take care of your concerns. It will also enlarge the size of the soundstage, as a bonus!

@mojo771 Can you give us an update, did some break-in time resolve your issues?