Does anyone know anything about this amp?
Dec 16, 2008 at 5:04 AM Post #2 of 16
Little Dot.
wink_face.gif
 
Dec 18, 2008 at 5:44 AM Post #5 of 16
Do you plan to run speakers with it, too? It's an integrated, with 5W and 8 ohm taps. So it probably has output transformers for that. My guess is that it has a resistor or two to step down the output for headphones.

I'm wondering if they put the output transformers next to the power/filament transformer under the box at the rear. If they did, that's not the best design. It can be done, but the output transformers should be as far away as possible from the power transformers. Get them too close together and you're going to get noise. I don't know what's under the hood here, though.

I'm not sure why they put the 6E2 in there. It's a variant of a "magic eye" display tube. I think it displays bars, probably along with the output. If you like that sort of thing, great. I don't like putting gimmicks or anything unnecessary on amps, but that's just me.

The 12AX7 is a common tube, usually used in guitar amps. I don't like them much for audio applications, though some do. They are inexpensive and widely available. I'm not familiar with the 6P14; I think it's a Russian variant of the EL84. The EL84 is another tube widely used in both audio and guitar amps. I haven't heard an EL84, but there are some nice looking DIY projects that use them.

For construction, it looks like the tube sockets are mounted on a PCB under the chassis. Personally, I'm not crazy about PCBs with tubes. Tubes give off more heat than solid state does (generally) and PCBs don't always hold up to heat very well. That depends on the PCB quality and I don't know what they're using.

It could be a good amp. Thing is, do you want to risk $400 on something that might not be?
 
Dec 18, 2008 at 6:25 AM Post #7 of 16
Quote:

Originally Posted by moodyrn /img/forum/go_quote.gif
I also saw this amp on pacific valve. They have pics of the inside that shows it's hand wired. There is no pcb board. Would 5 watts be enough to power efficient tower speakers?


Internals can be found herehttp://pacificvalve.us/images/MC_84_C07_Insides.JPG


How efficient are your tower speakers? Your speakers would have to be around 96dB or higher for 5W of output.
 
Dec 18, 2008 at 7:13 AM Post #9 of 16
Sounds like a Woo or Little-Dot would serve you better. If you got one with an output then you could add a power amp later for your speakers. Small desktop tube amps are probably not going to work well with the towers you have. The Woo 3 and some of the LD's have an output and could be used as a preamp, that would be my recommendation.
 
Dec 18, 2008 at 7:19 AM Post #10 of 16
I'm not crazy about the layout. First, that's the power and filament transformer in the bottom chassis. You can see the wires from the IEC jack going to it and it hooked to the power switch on the side. The output transformers must be under the cover on the top.

The power transformer looks like it has a partial aluminum shield over it, but it's still awfully close to the output taps. I would have put the output taps on the back of the top cover, to keep them away from the power supply. Also, you'll see the RCA jacks in the upper right corner of the photo. The input leads pass right by the power transformer and on/off switch. You're supposed to keep the inputs as far away as possible from the power supply. If they're close, they can pick up noise from the transformer. I don't think the input leads are shielded, either, since I don't see shielding over the wires where they connect to the input selector.

For the good parts, the filament leads are twisted, which is good. I like the ceramic sockets and the work looks clean. The grounding bars and ground point look done well and I think those are Nichicon and Elna capacitors in the power supply - they're good ones. The resistors look like 1/2W or 1W metal film - those are good.

The thing that bothers me is that the input and output run close to the power transformer. You can get away with that for a speaker amp, since you won't hear hum unless your ear is right up against the speaker. Even then, speakers aren't nearly as sensitive as headphones are. But with headphones, you're going to hear any noise the amp is making since a very sensitive driver is 1cm from your ear.

I can't say for sure whether it'll make noise - they could have tweaked it all out. But the amp I'm building has the power transformer on the opposite side of the chassis from the input/output sections and I put in two bars of 3/4" aluminum between the power supply and the amp circuit. That's complete overkill, but I had a bit of a 3/4" bar around and it does block power supply noise.
 
Dec 18, 2008 at 9:18 PM Post #12 of 16
Well...just to give an alternate opinion:

I have one, and really like it. Sounds excellent when driving high-impedance headphones. Prone to some hum with lower impedance cans, though. But with my AKG K340's or 600 ohm Beyers, it sounds GREAT. I use Mullard EL84's and a Mullard 6HU6/EM87 "Cat's Eye" tube, and JAN 5751 input tubes. VERY smooth and nuanced sound.

Also, it's beautiful to look at:

DSC01585.jpg

DSC01517.jpg
 
Dec 18, 2008 at 11:35 PM Post #13 of 16
Wow the pics on ebay don't do this any justice. That thing is beautiful. I notice some very nice amps in your signature. How does it compare to some of those, or maybe a woo audio 3?
 
Dec 19, 2008 at 2:07 PM Post #14 of 16
With high impedance headphones, I prefer it over the Woo3, but it does have a "tubier" sound due to the sonic signature of the EL84 tube.
 
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