2. amps-preamps
  3. 1233757559

Cayin A70T has bogus tube rectification?

I hate starting this thread. I am also a little hesitant because

a.) I bought the amp and hate the thought of its resale value after I post this

b.) I am not an electronics expert, so I have to rely on other experts for the facts.

Here is the basic story. I bought the amp from an audiogon member about a month ago. A friend of mine bench tested it and found a very large amount of crossover distortion on the scope. We unbuttoned the amp to look at the circuit and try and figure out what was wrong - but that is a side issue. The real issue is that there were four diodes strapped to the base of the 5AR4 which formed a solid state bridge rectifier. The bridge appears to completely bypasses the tube. The tube seems to just stands in the socket doing nothing but glowing. My friend had questioned this before I bought the amp because he says that a single 5AR4 is marginal for four KT88s. Usually you will see two.

I found a site (which I did not realize was in the Phillipines) where I blogged about this. There was some very good discussion there between very knowledgeable electronics guys and they came to a seemingly inescapable conclusion that the tube was there for show - as a marketing add-on to capitalize on the idea that tube rectification is better than solid state.

Here is the link to the thread on that forum (go to page 18)
http://pinoydvd.com/board/index.php?topic=29032.540

We are waiting for Cayin to respond to this issue, but they are in the middle of Chinese New Year (which last 15 days) and are not available for comment. If the evidence weren't so compelling, I would wait for their response before posting this.

There is a slight chance that we missed something in our analysis - but the fact that one of the contributors to the discussion actually pulled the rectifier tube with the amp turned on, and it kept running (now that I think about it, he didn't say how long he left it on, so he may have been running on capacitance) and the fact that a pretty critical analysis of the circuit does not reveal any function for the tube, I decided to post this on Audiogon in order to bring this issue to light in the USA and Europe.
ttbolad
rhljazz
1,250 posts
 
I just took a look at the Cayin website. The A70t in the photo has nine tubes but the description only lists 4 KT-88, 2 12AX7, and 2 12AU7. I don't see any claims made for tube rectification or any rectifier tubes specified in the owners manual. So, it does appear to be a styling gimmick only. Lots of products are sold on appearance versus performance. For the record I have not heard or seen a Cayin product. The appearance may be misleading but the published info on the website is factual.

Who told you it was tube rectified and where did they get their info? Maybe it was just assumption on someones part?

I don't see anything to get excited about. A safer bet would be VAC, Cary, Manley, Quicksilver, etc. You gets what you pay for IMHO.
trelja
3,223 posts
 
Without having a stock Cayin in front of me, I have no way of verifying the assertions in this thread. And, while I'd surprised (and disappointed, yet again), after dealing with the Chinese for the past couple of years, I have to say that I'd really not be all that surprised.

As has been pointed out, the Chinese transformers are of pretty high quality. Combine that with using good (or very good) coupling capacitors, and the implementation of classic tube amplifier designs from the 1920s - 1960s resulted in producing good sounding tube amplifiers. They also are capable of putting out some nice chassiswork, provided, in my opinion, it does not cross the line of being cloying.

North American and European customers have bought these products over the past decade because they've previously been inherently cheaper than domestically made products given that level of sound quality. Now that the cost advantage has all but evaporated, and the level of support and customer care (and, actually giving a flying flip) from the Chinese companies themselves has thus far been to put it kindly, indifferent, my opinion is that you are going to see a whole lot less of their stuff imported into our markets as time goes by. In fact, it's already become reality.

I don't want to say too much beyond that now. Suffice it to say that there were reasons for me feeling compelled to give up the line I represented.
sns
3,003 posts
 
I've been doing a bit of research into the marketing of this Cayin model. While I have yet to see any marketing that states tube rectification specifically, some spec. sheets at dealers specifically mention the 5A5R as a tube rectifier. Also, the Cayin AT-88T does not have this extra tube, SS rectification. Seems like at least some deception involved if this is indeed not tube rectified.

Having said that, my Cayin Phono-One is superbly assembled, very disappointed in parts quality, stock capacitors are a joke and stock resistors are garden variety. Replacing the stock caps with V-Caps and Jantzen Z Superior caps has resulted in a way better preamp. I will eventually swap out stock resistors as well.

If this theory of Cayin deception is true I will be very disappointed in Cayin, Steve at VAS seems like a good guy.
semi
649 posts
 
could not agree more with Rodman99999
captkhz
7 posts
 
I think I can speak for him when he brought the amp. to me for study, repair, he thought it was tube rectified because of the nice gz-37 tube there on the amp! I agree, Quicksilver a good option and even Dyna as well
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