Carver Crimson 275 Measurements

[paulbottlehead]

I tried posting this information to a different forum, and it caused a HUGE stir and got taken down very quickly, but I think this information is important to put out for public consumption and thankfully I saved a copy before it was removed.

OK, here we go! So a friend of mine brought one of these over just for me to check out casually along with a completely different project he wanted some help on. I would not have really considered even bench testing the amp, but when I picked it up, I nearly smacked myself in the face because I was expecting a lot more weight. I crinkled my brow a bit and got out my equipment to measure his amp, and the results were surprising. The results were unexpected enough that I decided not to publish them without collecting a little more data, so I asked around and managed to borrow a second Crimson 275 and I have a fresh quad of KT-120s from Jim McShane.

Let's review the specs from Carver:

These are really impressive. 75W at 20Hz and 1% THD is something I've only seen from much larger tube amps (The MFA M-120s I repaired somewhat recently could do that, but they were pushing out 130+ watts!).

Anyway, let's get into the meat of the post. What kind of power do these amps make? I'll measure these all with an 8 ohm dummy load, ARTA as the FFT, and an OWON SDS-7102 scope. These tools have accurately measured a dozen or so vintage Mac amps (which all do slighly better than their specs), as well as some larger amps over 100W.

For the unsigned amp with one channel driven:

Right Channel
0W at 20Hz 0.99% THD. At around 5.5W, the noise coming out of that poor output transformer is too unsettling to continue the test.
15W at 35Hz 0.99% THD. At this power level, the transformer rattling is just starting to happen.
16.8W at 1kHz 0.99% THD.

Left Channel
0W at 20Hz 0.99% THD. This output transformer did not exhibit the gnarly noises.
0.03W at 35Hz 0.99% THD. This is usually where I look for close to full power to quantify reasonable power bandwidth. (Note that a bad solder joint I later found and is pictured later contributed to this result and fixing that made the left and right channels almost the same)
15.7W at 1kHz 0.99% THD.

For the unsigned amp with both channels driven:

Right Channel
0W at 20Hz 0.99% THD.
11.7W at 35Hz 0.99% THD.
16.8W at 1Khz 0.99% THD.

Left Channel
0W at 20Hz 0.99% THD.
0.04W at 35Hz 0.99% THD.
15.7W at 1kHz 0.99% THD.

For the unsigned amp with brand new output tubes and the driver tubes from the other amp:

Right Channel
17.1W at 1kHz 0.99% THD.

Left Channel
16.8W at 1kHz 0.99% THD.

So tubes obviously aren't a problem here, but maybe this amp that doesn't have its face plate, is missing a signature on the cover, and has an output transformer that's prone to rattling just needs repairs and isn't a good sample? Well let's try the other one!

For the signed amp with one channel driven:

Right Channel
0W at 20Hz 0.99% THD. Unpleasant noises started happening around 9W.
17.4W at 35Hz 0.99% THD.
17W at 1kHz 0.99% THD.

Left Channel
0W at 20Hz 0.99% THD. Unpleasant noises also happening around 9W.
11.7W at 35Hz 0.99% THD.
16.8W at 1kHz 0.99% THD.

At this point I don't really think I need to try driving both channels on the second amp to see what/if anything improves.

Another question is what things look like if you push past 1% THD, and you can certainly get to 75W with this amp and THD is 2.5% at 1kHz. At 35Hz, this amp makes 37.5W at 55% THD hard clipped.

Here's a scope trace at 32W/35Hz, THD here is 27%.

Here's a scope shot at 8W/20Hz, THD here is around 22%.

I decided to also check the claim of the amp being flat from 20Hz to 20KHz and at 1W nominal the amp is -1dB at 16.5Hz and 20.2kHz.

Output impedance measured to 2.7 Ohms, not 1.7 Ohms.

At this point I was DYING to pull the covers off the iron on this thing, and so I did!

Seeing this is a little relieving in terms of what I've measured, as my numbers and Edcor's numbers agree pretty well. In the first picture of the center OT, one of the white wires was loose and this was causing measurement problems in one channel. Upon resoldering them I found the channels were pretty well matched.

I pulled the PT cover off too, and for the ~8A of heater current required for a 6.3V winding, 5.5A seems to be pushing things. Similarly, the power supply is a full wave doubler with around 110mA of DC current drawn between the output tubes and the driver stage. With 330uF doubler caps, estimated draw from the HV winding is 440mA AC. More current means more heat, and this is under a transformer shroud.

I have these loaners for a few more days, so if there are other measurements anyone is curious about, I'm happy to take them. I probably should evaluate output at 4 ohms, since the specifications also claim 75WPC is available in that configuration as well.

 

[warnerwh]

I can understand how your measurements may have rattled all of the owners. Thank you for your effort. And you're right this is good information to put out there. You may save some people from a serious mistake which I'm sure they will be grateful for.

 

[mhardy6647]

Thanks for your perseverance and for generating and sharing some data on these little amplifiers, @paulbottlehead
I need to (re) read & digest your review before commenting further.

I... umm... still would be curious to hear one. I mean, heck, it might be a great 15 wpc amplifier from an audiophile standpoint, although for that, it's a bit pricey.

 

[anmpr1]

Back in the day, one percent distortion was about what you expected from a decent tube amplifier. So the distortion measurements you provide at lower power are consistent with that. On the other hand, the wattage you measured is a lot less than what Carver is claiming. I have no idea about that. 75 watts at 55% THD?

In 1957, the Dyna Mk III was rated at 60 watts at 1% distortion, and 0.5% distortion at 'below' 50 watts. That said, Dyna watts were not FTC watts-- Carver is claiming FTC watts. [FWIW, Dave Hafler argued against the FTC rule for tube amps since, in his opinion, the rule had nothing much to tell the consumer when it came to tubes, as opposed to SS circuits, the latter which could more easily be stressed by the FTC schedule.]

A situation with tube gear, one that you highlight, is noise. Noise can essentially be done away with with SS designs. However, a noisy transformer is more of an outlier. Not uncommon, but not totally expected. If these are under warranty I'd get Bob on the horn and ask him about it.

During the transition in consumer gear from tubes to SS, Dave Hafler, the man responsible for selling more tube gear than I guess anyone, said that in his opinion there really wasn't much, if any, difference in perceptual sound quality between the two, at least for most people and for most systems. Likewise, I read an interview somewhere with Bob Carver where he stated that he honestly can't tell the difference, but that tubes are great at night, with the lights dimmed.

For me, tubes and SS are apples and oranges. The question I ask is whether each design takes advantage of 'the best' they can possibly offer, knowing all the while that tubes will never ever be 'the best' that can be offered within the overall context of audio circuits. To my mind it makes no sense to judge a tube amplifier next to a SS, on an absolute basis.

That said, tubes still have value for some, even if that value is not necessarily based on specs. An analogy: if you are trying to identify the swiftest feathered friend, you can bet that a chicken or a turkey will never fly as fast or as high as an eagle or vulture; but the chicken might taste better at dinner time. Even if the tube amp is a turkey.

 

[tomlang]

This is incredible. This wins the Audio Scam of the Year award for 2021. I guess this pic of Bob winding his "proprietary" transformers was in Edcor's basement.

Next year, I predict a new Webster's dictionary word "Carvered" to replace "fraud". Pathetic.

 

[anmpr1]

This is incredible. This wins the Audio Scam of the Year award for 2021. I guess this pic of Bob winding his "proprietary" transformers was in Edcor's basement.

Next year, I predict a new Webster's dictionary word "Carvered" to replace "fraud". Pathetic.

Before I'd go that far I'd make sure the gear is not broken. Bob has been known to use a lot of hyperbole. He's made a career out of it. But he also has a track record of delivering on his promises. If I was the owner of these, I'd contact Bob and ask him about it.

Just to be clear: I'm not saying that these examples are not representative of production. If they are, then that is certainly pathetic. But something doesn't appear totally right, and I'm willing to give Carver the benefit of the doubt until its sorted out.

I'm reminded of the ASR review on one of the Benchmark DACs. If I remember correctly, the measurements were not up to par. John Siau took the device back to his lab, measured it, and it was fine. meeting specs. Not equating Benchmark QC with a handmade Carver tube amp. I just would want to know more before I would say there is fraud.

 

[raindance]

15 watt Edcor output transformers certainly explains why the amps are so light.

Bob must have an interesting way of measuring power. Perhaps he has a special freezer that makes them super conduct?

The low frequency measurements also look like the output stage is seriously under-biased.

 

[tomlang]

Very under biased. That is why the tubes run so cold. Anymore bias and the poor 15w output transformer couldn't handle the quiescent current.

 

[Schollaudio]

15 watt Edcor output transformers certainly explains why the amps are so light.

Bob must have an interesting way of measuring power. Perhaps he has a special freezer that makes them super conduct?

The low frequency measurements also look like the output stage is seriously under-biased.

Yup, crossover distortion, however at 15watts it could be decent. With proper outputs and bias it could have made it's ratings.

 

[tomlang]

...and then you would have an even more dangerously undersized power transformer.

No reputable manufacturer exceeds the stated filament ratings and then top it off with overloading the HV winding as well. Even if this thing made spec the evidence right there is a lawsuit waiting to happen if it started a fire.

I wouldn't be surprised if Edcor issues a cease and desist using their products over rated values allowing them to be put dangerously into consumers hands. I doubt they want their name listed on the lawsuit even if they are held harmless.

 

[TriodeLuvr]

I predict Bob will pot his transformers in the future.

 

[anmpr1]

15 watt Edcor output transformers certainly explains why the amps are so light.

If I was using those, I'd cover them up, too.

Very under biased. That is why the tubes run so cold. Anymore bias and the poor 15w output transformer couldn't handle the quiescent current.

Bob advertises some sort of special circuit to keep the tube life up.

I've never read any independent review of his smaller amps. I have no way to judge. Bascom King (Audio 2/91) measured Bob's big one, the one costing as much as a small house: from that graph it looks like 300 watts into an 8ohm load with less than 1% THD, and much more wattage with commensurate distortion.

If these are not broken, and if they are representative of production, it is sad, at the very least. The fact that two amps sourced apart are similar to each other is not a good sign, for sure.

 

[tomlang]

I predict Bob will pot his transformers in the future.

Methinks someone smoked the 'pot' compound instead of pouring it into the container...

 

[anmpr1]

I tried posting this information to a different forum, and it caused a HUGE stir and got taken down very quickly, but I think this information is important to put out for public consumption and thankfully I saved a copy before it was removed.

Out of curiosity, on what forum did you post? And were you given an explanation of why your post was removed?

 

[tmtomh]

Let's review the specs from Carver:
View attachment 174164

I am not a technical expert so I could be missing something obvious here, but it seems that Carver's official specs say this amp is within +0/-3dB from 16Hz-35kHz, +/-0.25dB from 20Hz-20kHz, and yet the Power Bandwidth goes only as low as 24Hz. Isn't it impossible for all of those specs to be true at the same time?

It would seem that the "0 watts at 20Hz at .99%THD" measurements Paul took support the more limited power bandwidth spec rather than the broader frequency response spec, yes?

 

[anmpr1]

The more I think about this, the more perplexed I am. First, Bob has been in business long enough, and is smart enough to know that you can't advertise and sell a 15 watt amplifier as a 75 watt amp. Why would he do that? Why would he: a) risk all the good will he's built up over the years; b) risk dealing with an FTC complaint (is the FTC rule still in effect?) which could result in a large fine, or worse; c) risk some other state consumer agency complaint; d) totally ruin his current business and any future endeavors he might want to engage in? I certainly can't explain why he would do that.

I am frankly surprised that the OP was able to so easily find a second Carver amp to compare it with, since I understand they are a little on hen's teeth side of rarity. But I guess in some areas they are more common than in others.

The Carver site states that these have a five year warranty. They state the warranty is transferrable to a subsequent owner. Since this is an open forum, as since an allegation has been made, I'd want to know whether the owners of these two amps have contacted their dealer, or Bob directly, and if so, what did the dealer and/or Bob have to say about the situation? I'd definitely want to know that before I started making any conclusions about his current business practices.

Then, after that, let the chips fall.

 

[Martin]

Wow! Very surprising. I though Bob Carver was an amplifier guru. I have always loved the looks of these new Crimson amplifiers. I've lusted after his Crimson 350 Monoblocks. These measurements are a real kick in the gut. I'd think you got a hold of some knock-off amp except you separately sourced a second amp that validates your measurements... Another audiophile legend is exposed as a complete fraud. So sad.

Martin

 

[paulbottlehead]

Out of curiosity, on what forum did you post? And were you given an explanation of why your post was removed?

I am still awaiting an official ruling one way or the other on whether my post comes back or not. I actually asked a moderator about whether I could post this information or not and he said yes. In the discussion thread I let people know measurements were coming, and the site owner was present and replying to that thread.

If they do not put my post back, I will call them out here for it certainly.

 

[anmpr1]

Another audiophile legend is exposed as a complete fraud. So sad.

Can we say that? I've seen many measured reviews of Carver gear over the years, but never anything like this. What we know is that a new member of the forum, with no history, posts a very troubling review. Yet we have no background about the gear in question. Where did they come from, how were they bought, how old are they, was any attempt made to contact the dealer or the manufacturer? Many questions, few answers.

Again, if what we have been shown is representative of Bob's current product, then it's a very sad day indeed. Sad for Bob, his company, and consumers who trusted him over the years, and bought his gear. But we really don't know that for sure. Until the questions are answered, until we know more, I think caution is in order.

 

[paulbottlehead]

Can we say that? I've seen many measured reviews of Carver gear over the years, but never anything like this. What we know is that a new member of the forum, with no history, posts a very troubling review. Yet we have no background about the gear in question. Where did they come from, how were they bought, how old are they, was any attempt made to contact the dealer or the manufacturer? Many questions, few answers.

Again, if what we have been shown is representative of Bob's current product, then it's a very sad day indeed. Sad for Bob, his company, and consumers who trusted him over the years, and bought his gear. But we really don't know that for sure. Until the questions are answered, until we know more, I think caution is in order.

I posted my first name and my industry affiliation. I have been involved in DIY tube audio for about 22 years. I do not own these amplifiers. One was brought to me just to look at along with a completely unrelated/unfinished project that needed some help. The other amplifier I had to find on my own and ask if I could borrow it.

As I mentioned in my initial post, I am here because this may be the only place where this information can be posted without being taken down.

Here's an image off Canuck Audio Mart and you can see the four black screws between the PCB and the speaker binding posts holding in the channel frame output transformers in this amp.