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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
atmasphere's avatar
atmasphere
11,616 posts
 

I'm just not sure how this thing could test out near 75w with that 15w Edcor OPT in mine from MusicDirect.

It won't.

As far as I can tell from the photos, that output transformer is a custom unit.

But its still a 15 watt device and will saturate when pushed beyond that level. The laminations in the transformer play an important role in how much power it can pass. The laminations are the magnetic core of the transformer and determine when it will saturate (no greater magnetic effect can occur). The wire plays a role too- it has to be able to handle the current at the power levels involved. But its mostly the laminations that say what power the OPT will be able to make. That is why higher power transformers are bigger and heavier.

jbhiller's avatar
jbhiller OP
1,361 posts
 

I wouldn't think so, but Bob has a PhD in physics.  His response suggests it will.  I'd bet it won't, but who am I? 

It will be sad if he goes into retirement making this representation--that it, it will exceed 75 w per channel, both channels driven at 8 ohms.

The question I have is this-- if this thing can only put out 15w per channel at 8 ohms, wouldn't we hear of folks finding they have little headroom before the thing starts getting blurry and smeary?  Was the room where they demonstrated it with KEF Blades so small that 15 watts was enough to get the KEFs singing? 

grovergardner
6 posts
 

jbhiller, don't swap out those resistors.  They provide "current feedback" from the output transformer, you won't gain anything by changing them.  To the contrary, some feel the amp might be improved by bypassing them.  Many amps in the 50's offered a similar arrangement, except with a variable resistor, to adjust the "damping factor," a way to "loosen" the amp's grip a bit to accomodate speakers with poorer bass response.

jbhiller's avatar
jbhiller OP
1,361 posts
 

Thank you @grovergardner !   Great intel!  I'm wondering if I could make a switch to adjust the damping factor as a project.  Hmmm...

ozzy62's avatar
ozzy62
2,847 posts
 

@funky54 

No 75 wpc tube amp is going to deliver into a 3 ohm load and 86 db sensitivity. Especially in a room like you described. It just shows how foolish you are to consider it.

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