Peeking inside a Carver Crimson 275 Tube Amplifier


So, I just had to pop the hood on the Carver Crimson 275 tube amplifier. I was so curious as to how this little guy weighs so little and sounds so lovely.

  • The layout is simple and clean looking. Unlike the larger monoblocks (that cost $10k), this model uses a PCB.
  • The DC restorer circuit is nicely off to one side and out of the way. It doesn’t look all that complicated but I’m no electrical engineer. Why don’t more designers use this feature? It allows the power tubes to idle around 9.75w. Amazingly efficient.
  • The amp has very good planned out ventilation and spacing. No parts are on top of each other.
  • Most of the parts quality is good. There’s a host of Dale resistors, what look like Takmans, nice RCA jacks, heavy teflon hookup wire, and so on.
  • Some of the parts quality is questionable. There’s some cheap Suntan (Hong Kong mfr.) film caps coupled to the power tubes and some no name caps linked to the gain signal tubes. I was not happy to see those, but I very much understand building stuff to a price point.
Overall, this is a very tidy build and construction by the Wyred4Sound plant in California is A grade. I’m wondering a few things.

Does the sound quality of this amp bear a relationship to the fact that there’s not too much going on in the unit? There are very few caps--from what this humble hobbyist can tell--in the signal chain. And, none of these caps are even what many would consider decent quality--i.e. they aren’t WIMA level, just generic. This amplifier beat out a PrimaLuna Dialogue HP (in my room/to my ears...much love for what PrimaLuna does). When I explored the innards of the PrimaLuna, it was cramped, busy and had so much going on--a way more complicated design.

Is it possible that Bob Carver, who many regard as a wily electronics expert, is able to truly tweak the sound by adding a resistor here or there, etc.? Surely all designers are doing this, but is he just really adroit at this? I wonder this because while some parts quality is very good to excellent, I was shocked to see the Suntan caps. They might be cheaper than some of the Dale resistors in the unit. I should note that Carver reportedly designed this amp and others similar with Tim de Paravicini--no slouch indeed!

I have described the sound of this amp as delicious. It’s that musical and good. But, as our esteemed member jjss [ @jjss ] pointed out in his review, he wondered if the sound quality could be improved further still. He detected a tiny amount of sheen here and there [I cannot recall his exact words.] even though he loved it like I do.

I may extract the two .22uF caps that look to be dealing with signal related to the 12at7 gain tubes and do a quick listening test.
128x128jbhiller
Thank you for being the voice of reason Don!

jjss and Oz, thanks for making me laugh! 
I hope to do the surgery this week; waiting on parts. 
Status Update--

I have all of the power tube coupling caps in, which consist of 4 .68uF and 4 .1 uF Clarity CMR caps.  I have yet to touch the two .22uF caps near the gain/phase section of the circuit--arguably those could do more to signal preservation (I'm waiting on VCap CuTFs to arrive for that section).  

I also replaced the four resistors linked to the larger .68uF coupling caps with Kiwame 5watts, .39kohm and .36kohm.

I'll spare you the audiophile shopworn terms, and we are only 8 hours into break in.  

The new caps make things sound more relaxed and less tense.  I don't mean relaxed in the sense of more laid back, but rather less uptight.  I know this amplifier, very, very well.  With the cap swap, on Johnny Hartman's "I Just Dropped by to Say Hello," things don't sound as intense.  There's a bit of strain in those old caps (Suntan, brand anyone?).  

The Clarity's are clearly more detailed and it's easier to pick out the space around instruments and voices.  Piano sounds like the recording was voiced better--mics placed more correctly--when it's the same recording. 

The originals had more a feeling like we were driving at breakneck speeds and while we never drove off the guardrails, a sense that we could was there.  That made the amp exciting, and even though it was pretty darn smooth, I'm now seeing where it wasn't. 

Here's a summation--

Old/Suntan Caps (<$1 ea) and Bargain Resistors (~pennies):  
  • Fun, exhilarating sound
  • Big soundstage
  • Powerful, fast
  • Slight electronic hash on the top end and bass could be a touch more defined. 
  • Overall, pretty nice gestalt. 

New Clarity CMRs (~$225 upgrade) + 4 Kiwame Resistors on the Coupling Caps: 
  • Presentation seems at ease with more mature stature. 
  • Things are relaxed--less uptight--but still dynamic.
  • Detail is improved.
  • Gone is the slight hash and tizzy sounds that can occur on the upper mids and highs. 
  • Overall, things sound more elegant.  There's no loss in dynamics and power, while the sound of space around things makes things more seductive. 
We can debate confirmation bias or placebo effect etc.  I think I know my amp and my ears.  When tuning a guitar by ear you develop quite the sense of nuance for timber and when notes properly engage each other with overtones that naturally must come with when the frequencies of them ring together properly.  I'm not claiming I'm a golden ear--there's tons of stuff I cannot hear.  I can hear this.  And, I have done upgrades in the past where I readily admitted that the improvement was marginal or non existence or not worth it. 

From a subjective estimation perspective, I think this makes things sound 5-10% better and break-in has just begun.  

Notes for DIYers or Techs: 

Holy cow--I'd never desoldered lead free solder or at least like this.  I had my Hakko up to 890 degrees and there were times I couldn't melt the stuff.  I obviously used audio-dork solder (Cardas Eutectitc solder), which is way easier to work with and looks great.  

I actually had to carefully drill out some of the through holes on the PCB (not my first choice), as whatever is in the solder used by Wyred4Sound in construction is insane.  

There is virtually no room on the board to install these caps.  I was sensitive to size when selecting.  There are way larger options.  After break in, I'll be adding silicone to adhere the caps down, and I may add some bracing to hold them. Honestly though, they are so snugly fitted that they aren't moving now. 

This was a tough surgery for me.  I'm no hack, but I'm no pro either.  I've built one point to point EL34 amp, 3 kits, and done plenty of mods in the last 5 years.  This required a bit more patience.  

Carver could easily draw the board bigger as there's room in the chassis for this, which would accommodate bigger parts.  He has massive real estate on the board for the big resistors but virtually none to upgrade those Suntan caps.  

Now, I cannot wait to do the VCaps and get through equipment break in and subjective break in.  

PS. Voltages measured better with the new caps too--for the objectives out there!  There were spots where it looked like some DC was slipping through a cap on its output.  Not much, but it was there.  None with the Clarity Caps.

Many more hours of listening to go though.  I'm happy.   
One more EARLY listening note....

On Walter Wolfman Washington's "Lost Mind" from the album "My Future is My Past" (opening track): 

The opening soliloquy where he's pouring a glass of bourbon (presumably) sounds creepily authentic. I can hear the room he's in much more.  I had to listen to it many times out of curiosity and pleasure. 

The acoustic guitar now sounds to recorded properly. Before I thought it was buried a bit too much and not defined enough.  Now it's right there. 

Let's hope these caps don't make anything sound worse--especially poorly recorded stuff. ;)
@jbhiller

ok jb i am sending you my crimson and booze to say thanks

single malt? porto? veuve cliq? bordeaux?  :)
jjss, I think you deserve MVP of Audiogon's forums!  You have great knowledge, are a team player, and oh-so-hilarious!  

I used to be single malt guy.  Now bourbon and a touch of the green scene.  

But, Sir, (assuming you are a sir), this was a tricky little upgrade!  I would take 2X the time if I was doing this on someone else's amp!  

I actually called a woodworking friend to see about making a sub-unit plinth so I'd have more room.