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

Power problems are apparent here.  Less than 2W available at less than 1% THD over 5kHz.  The 20Hz trace is also not so great.

Self-explanatory.

A 1kHz burst tone can let almost 75W out, but a 1-2 second tone cannot. 

The Carver amplifier manufacturer should simply come forward and revise their power outage specifications. Present what is accurate and factual.

Charles

To be fair, the ASR measurements show it performing a lot better into 8 ohms: 60 Watts/ch sustained at 1kHz, and at less than 1% THD. The really bad numbers, where it greatly underachieves its rated power (< 20 Watts/ch), are into 4 ohms. Without multiple taps this amp can only be optimized for one load, and it looks like it’s 8 ohms.

It did better than I expected at 8 ohms, but then 60 is still clearly under rated power, and it blew a fuse on top of that. And power bandwidth is clearly a big shortcoming here, probably much more than with other tube amps. 

It’s probably not filling any necessary market slot with this performance.

Is it 60W sustained if that blew the fuse?

Does 60W at 1% THD/1kHz matter when you're looking at single digit power at 1% THD above 5kHz and down in the bass?

Does 60W at 1% THD/1kHz matter when you're looking at single digit power at 1% THD above 5kHz and down in the bass?

We know the rational answer 

Charles