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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

Showing 3 responses by atmasphere

atmasphere's avatar
atmasphere
11,588 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.

atmasphere's avatar
atmasphere
11,588 posts
 

It's a video of a Suntan cap blowing up.

Those are electrolytics, quite different from what is used for coupling caps in tube gear!

 

atmasphere's avatar
atmasphere
11,588 posts
 

A little birdie told me that the amps subject of ASR’s testing were, in fact, $600 kit amps--differing in quality from actual units sold with serial numbers.

@jbhiller Do you have any evidence to support this claim?

I’ve been in the industry for about 47 years. @mulveling has an excellent point, one which I’ve also found troubling. I’m a big fan of the Harmon Kardon Citation 2 which is a stereo 60W/channel amplifier. It weighs about 3 times more. But its made of the same materials. We make a 60 watt monoblock amp that lacks the weight of an output transformer and it weighs about 25 pounds while employing an aluminum chassis.

IMO something doesn’t add up. Put plainly, prior to the Carver amp, no stereo or monoblock tube amps capable of 75 watts that weighed so little were ever made! Since this spec comes from the Carver website: https://www.bobcarvercorp.com/copy-of-crimson-raven-features-spec

I’m inclined to think one of two things. (Using Occam’s Razor...); one explanation is that the weight is a typo. The other explanation, the weight is correct, requires too many other things (some quite wild) such that the answer is for too complex to be correct.

The problem here is that a 19 pound amp would also very coincidentally be about the same weight as a tube amp capable of about 17 watts per channel. I don’t like it when coincidences like that pop up- it makes me think something is fishy.

You are in a position to shed some light on this, and apparently possess the required skills to do what needs to be done, as evidenced by the work you talked about prior on this thread.

I’ve become quite curious and am holding all explanations in abeyance. Could you weigh your amplifier and relay to us that value? Could you remove the output transformer cover and show us what the output transformer looks like? If the ASR review is not of the same amp they are doing a disservice IMO.

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