Zhili Audio Cary Cad-40 based kit

[mhconley]

I've been searching for a tube monoblock kit to build as my first foray into tubes. I had pretty much settled on Dynakit's Mark IV kit when I ran across this ridiculously cheap kit on Ebay: KT88 /6550/EL34/6L6 Vacuum Tube Power amplifier MONO XLR Balanced DIY KIT by ZHI | eBay and KT88/6550/EL34/6L6 Tube Amplifier Power Amp DIY Kit America CARY cad-40 Circuit 574838478640 | eBay.

They are supposedly based upon the Cary CAD-40. They look pretty nice but I don't know much about this stuff so I am seeking your expert opinions.

I found a manual for the Cary CAD-40M amplifier. One of the sellers says they have chassis available. (I sent a request for more information.)

What do you think of the original Cary CAD-40M? Does this look like a decent kit? Is it worth $160 shipped?

Thanks,
Martin

 

[kevinkr]

It's a rip off of a Cary design using a registered trademark and on that basis I wouldn't recommend it whatever the technical merits might be.

The Dynakit stuff is solid both technically and ethically.

 

[audiowize]

At the risk of sounding like a racist (again), I'll list some of the cons of buying kits and parts of eBay sellers (mostly from China).

1. Fake/counterfeit parts. When you buy parts from Digikey or Mouser, they come shipped straight from the manufacturer. When you buy randomly from eBay, your 100uF/450V capacitor might have a 22uF/350V capacitor inside it. I've also had terrible experiences buying transistors and integrated circuits from eBay sellers in China. Often they are miles off on their specs and don't work. Another hint - look for the Nichicon 1700uF/450V snap-in capacitor which comes with that kit, do they actually exist??? If indeed those power supply caps are fake, what do you suppose is in the can?

2. The CAD-40 and similar designs are incredibly dependent on very high quality output transformers to work properly. These are not included (maybe a blessing?). If you go too low in quality, your amp could become an oscillator if it's designed for very high quality iron. If the amp is designed for low quality output iron, then you'll be wasting your money using quality parts. Do you believe the seller will be able to provide an answer one way or the other on this?

3. Mounting high heat octal and 9 pin tubes to a PC board is a bit of a dicey proposition. You need high a high quality board designed specifically for this.

4. So the seller has a chassis available, which transformers fit the chassis? Is a US transformer available? Is the US transformer made to work off 110V (bad) or 120V (good, but less common).

5. As Kevin mentioned, this is a rip-off from a company that's very much still in the business. If you want to buy a copy of a Marantz tube preamp that was last manufactured 50 years ago, go for it! It's a whole lot different to support someone ripping off very recent work in the industry.

 

[mhconley]

OK, OK, I get it. There’s a reason they’re $160. I’ll stick with the Dynakit Mark IV. Like they say, if it sounds to good to be true, it probably is.

Martin

 

[mhconley]

I have already posted that I am going with the Dynakit Mark IV kit but I wanted to follow up with some additional comments and the responses from the Ebay sellers...

1. Fake/counterfeit parts. When you buy parts from Digikey or Mouser, they come shipped straight from the manufacturer. When you buy randomly from eBay, your 100uF/450V capacitor might have a 22uF/350V capacitor inside it. I've also had terrible experiences buying transistors and integrated circuits from eBay sellers in China. Often they are miles off on their specs and don't work. Another hint - look for the Nichicon 1700uF/450V snap-in capacitor which comes with that kit, do they actually exist??? If indeed those power supply caps are fake, what do you suppose is in the can?

Not that I have found. Who knows whats inside it. Interesting thread on counterfeit parts on AudioScienceReview.com: DIY Audio: Counterfeit Parts | Audio Science Review (ASR) Forum. Amazing that the Chinese will counterfeit such cheap parts just to make a few cents. And that's not racist - it's a comment on Chinese copyright law (oxymoron) and business practices.

2. The CAD-40 and similar designs are incredibly dependent on very high quality output transformers to work properly. These are not included (maybe a blessing?). If you go too low in quality, your amp could become an oscillator if it's designed for very high quality iron. If the amp is designed for low quality output iron, then you'll be wasting your money using quality parts. Do you believe the seller will be able to provide an answer one way or the other on this?

4. So the seller has a chassis available, which transformers fit the chassis? Is a US transformer available? Is the US transformer made to work off 110V (bad) or 120V (good, but less common).

When I asked about transformers one seller cam back with a price of $725 for a set for two monoblocks. The other simply stated they had no 110v transformers in stock.

Lastly for chassis one supplied this link: MONO block Tube power amplifier Chassis for cary amp 500x150x60H mm | eBay which looks like photos of real Cary CAD 40M MK II monoblocks. The other simply provided one of the photos from that same auction. Prices were similar, $225 for the pair. I wonder what you'd actually get...

Anyway, at those all in prices $160 + $225 + $725 = $1,110 the Dynakit Mark IV kit is looking even more attractive. It's a no-brainer really...

Martin

 

[audiowize]

Yes, the Dynakit is easily the way to go. If you ever blow one up, you can just go to the Dynakit website and buy any replacement parts that you need too!

That video is chilling. His statement about never getting real integrated circuits is consistent with my experiences as well, though I have also had the same issue with single transistors too.

 

[Salectric]

Aside from the unfair trade practices, the parts kit linked in the OP’s first post uses a printed circuit board. The Cary 40M (which I used to own) was all point to point wiring. Also the 40M came with two very different input/driver circuits. Each used a single 6SL7 but the earlier version used a split-load phase inverter; the later one used a paraphase inverter. The schematic that used to be on the Cary website (don’t know if it is still there) was just the paraphrase.

The 40M was actually a very nice sounding amp. Its weaknesses were the solid state rectifiers (I prefer tube) and the big 1200uf electrolytics in the power supply.

 

[samb]

hello salectric
i also own a pair of cary M40
The sound is only OK not outstanding,it lacks details...
In my opinion this is for two reasons:
1.the output transformer
2.the minimalist design

There are at least 3 design problems:
1.at HTpower level there is only one capacitor before feeding the output transfo.This is the minimum,usualy you put at least two filter sections
(the two capacitors you see is only to split the 430 voltage beetwen them).
2.the EL34 auto cathode biasing is high, around 70 ma and this consume tubes kickly
3.at 6SL7 level the voltage beetwen cathode and heater is out of specifications
specs= max 90volts and then you need to set the heater at around 50 volts

And last,,, yes , two spliters have been used...

 

[Salectric]

Samb,

Sounds like our Cary amps were different versions. The B+ on mine was much higher than 430v. It was around 520v as I recall. And it ran the EL34s quite hot, right at the max dissipation if I am remembering right. I tried reducing the B+ and I also tried reducing the current in the EL34s by increasing the cathode resistor, but each of these made the amps sound less good so I left it in the original operating conditions.

 

[audiowize]

hello salectric
There are at least 3 design problems:
1.at HTpower level there is only one capacitor before feeding the output transfo.This is the minimum,usualy you put at least two filter sections
(the two capacitors you see is only to split the 430 voltage beetwen them).

In a class AB or class B push-pull amp, it's incredibly normal to have the OPT hooked up to the first power supply node.