Magic 5B

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audioferret

Magic 5B
« on: 19 Nov 2006, 04:21 am »
It works!  IT WORKS...IT WORKS!!!   aa

I feel like Doc Brown in "Back to the Future".  "You mean, I've finally built something that works!!"

I finished my Magic 5B.  My first try resulted in some serious buzzing and I had to go back to the drawing board.  It seems that I put the wrong resistors across V3a and V3b.  After replacing them, voltages appeared normal and it is sounding beautiful.  Almost no noise.

I will report more after letting it burn in more.  All three topologies sound great.

THIS IS SO COOL!!!!

-AF


steve k

Re: Magic 5B
« Reply #1 on: 19 Nov 2006, 05:06 am »
Congratulations!!!
I'm still tweaking mine and it just gets better and better. First I swapped a pair of Sonicaps for the Auricap output caps on the SRPP circuit. To me, the Sonicaps are more open and natural sounding than the Auricaps. Then I swapped out four resistors for Tantalum films that Doc recommended. The result--increased clarity and detail in the SRPP circuit. Finally, I switched in a pair of Blackgate VK 150mf/350V caps for the last two 100mf electrolytics in the PS circuit. They have about 250 hours on them now but I've noticed a definite tighter control over the bass and more overall detail. The 5B is really fun to play with and tweak and I still find myself switching back between the two active circuits depending on the music but overall I prefer the CF circuit.

I've also rolled a lot of tubes through the 6R7 output circuit but there are surprisingly little difference between them. Otherwise, I've stuck with the RCA 12SX7GT's elsewhere.

Give us a full report after it's burned in.
steve

ooheadsoo

Re: Magic 5B
« Reply #2 on: 19 Nov 2006, 08:47 am »
Can you guys describe the sonic differences between the 3 modes?

steve k

Re: Magic 5B
« Reply #3 on: 19 Nov 2006, 04:53 pm »
I can only tell you what it sounds like in my system. I don't use the passive stage because the output is way too low for my system. The CF circuit is more extended on top and bottom with lots of bass and midrange--a more traditional full bodied tube sound with a lot of texture. The presentation is detailed and warm. The SRPP circuit is more neutral and linear across the frequency range with less emphasis on the top and bottom than the CF circuit. Some have said it's a more "modern" sound--closer to a solid state sound but still with the rich texture of tubes. I'll use SRPP if the source material is overly bassy or muddy and also if the source is extremely bright--SRPP tends to clean things up better, whereas CF exaggerates these faults in the source material. CF has more slam and is more dynamic.

Keep in mind the outputs are different for all three topologies: CF produces 23.5 dB gain, SRPP produces 20 dB gain and Passive 0 dB. YMMV.
steve

Frihed91

  • Jr. Member
  • Posts: 280
Re: Magic 5B
« Reply #4 on: 19 Nov 2006, 06:15 pm »
Ask Doc, but rolling those tubes should not have much effect, esp in the CF mode.

steve k

Re: Magic 5B
« Reply #5 on: 19 Nov 2006, 06:38 pm »
I did, and he indicated his use of 100% negative feedback in the circuit would minimize the differences between tubes. Being curious, I still tried 5 or so varieties and did find some subtle differences. The 6R7's are so cheap to buy, its no big deal.
steve

ooheadsoo

Re: Magic 5B
« Reply #6 on: 20 Nov 2006, 11:06 am »
If it weren't for the joy of diy, would you guys buy a magic 5b as a finished product or the ultra 4a? 

steve k

Re: Magic 5B
« Reply #7 on: 20 Nov 2006, 02:02 pm »
In my case, I didn't need the phono pre since I already have one. Otherwise, I think I'd be happy with either the 4A or 2A models. They both use the cathode follower circuit.
steve