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Trafo Head One or Zana Deux T ? - Page 2

post #16 of 20
Thread Starter 
HI-JACKED THREAD

all I wanted was some help making a hard choice

if you are not addressing the OP's questions, your personal issues don't belong here

EOT = end of thread
post #17 of 20
OP, a "simple" description of Parafeed compared to series feed can be found here.
post #18 of 20
three cheers for Parafeed!
Hip Hip Hooray!
Hip Hip Hooray!
Hip Hip Hooray!

I would just ignore everything Regal said, and only read past Parafeed's first or second post if you care to understand circuit design a hair better, or the lack of other peoples understanding as the case my be.

Quote:
Originally Posted by budx3385 View Post
Parafeed - SIR - won't you please tell me what a "parafeed amp" is ? pretty please ?
Parafeed is a play on words.

If you look at a "classic" tube amplifier where the transformer is directly connected to the tube with DC current flowing in it, this is called "series feed." The transformer is in series with the tube.

Parafeed is a play on words. When you look at the schematic the output transformer looks like its in parallel with the tube, rather than series. In a parafeed amp there is a very high impedance load for the tube (such as a big fat resistor {nobody does this, but they could!} a specially designed choke/inductor or a transistor CCS) and then an output cap, and the transformer (or autoformer) to ground. In a parafeed amp no DC current flows through the transformer.

Now for some debate & all that.

Both topologies have their advantages and disadvantages & some people clearly prefer one over the other, but at the end of the day a talented designer (or even an average one who takes his head out of his butt long enough to design and test the thing) can make either sound very good.

Series feed has an advantage in that the amps are much simpler. There are 2 fewer parts directly in the signal path (in a very simple example) than a parafeed amp.

The disadvantage to series feed is that the transformer passes DC current. This requires a "gap" in the transformer core so that the transformer does not saturate. The problem with that gap is that it reduces bandwidth (the highest and lowest frequencies the amp can reproduce within some reasonable tolerance) which could get to the point where the loss of bandwidth is audible if care is not taken.

Another disadvantage to series feed is that the amplifier has lower noise rejection. This can be overcome, but it requires much more meticulous power supply design.

The parafeed amp has a few advantages as well.
The transformer on the parafeed amp does not pass DC current, and does not need to be gapped, and can accordingly be made with VERY wide bandwidth.

Another advantage of parafeed is that because of the "really high impedance load for the tube" (the big resistor, choke, or CCS) the parafeed amp generally has better power supply noise rejection than a series feed amp, and accordingly its easier to make a parafeed amp with very very low noise on the output.

The disadvantage to parafeed comes from the fact that the circuits are inherently more complex than series feed.

I would say its a difference rather than a clear cut advantage or disadvantage but the 2 amps do differ in that parafeed requires a cap very directly in the signal path where series feed does not. Depending how deep into the problem you dig, you could very easily argue that series feed puts power supply caps in the signal current loops where parafeed does not, and thus in the signal path. As much as series feed guys love to bash the concept of film caps in the signal path they dodge the concept of electrolytics hiding away in a corner waiting to ear-rape you.

At the end of the day, either amp topology can and often does sound great. Each one just has its own strengths & weaknesses which must be taken into account and the amplifier must be designed around them.




Edited/added:
Although I have not heard either of those amps much, they dont sound like what you are looking for. EEh, I would lean towards a 6sn7 & (I dont know what, perhaps an DHT) if you are looking for a smooth slightly warm sound.

You say that the 6sn7 dont match your ears, but it could be the amp as much as anything. i would check out the Woo5.
post #19 of 20
Quote:
Originally Posted by budx3385 View Post
sawindra -- how long are you going to have to wait? why did you choose the trafo?
Wait is 4 weeks, 6moons.com review pretty much helped. Elegant and classic design, class A, point to point wiring, can be used as a preamp and low heat.They say that fullrange single driver speakers are a good match with SET match, basically i am just applying it here
post #20 of 20
Thread Starter 
nikongod, that was clear, intelligible, and highly informative. Classy, actually. Thank you.

sawindra, sounds like you made a highly informed choice. I wish I felt so knowledgable.

I just learned that Rudi Stor has upgrade his tube amp to the RP8. Four 12ax7 drivers, apparently under low voltage since the enclosure is closed, with discrete silicon output amps. Hmm. Might be what I'm looking for. The specs look amazing. People have sniped at his quality, but he took care of the little problems I encountered asap. nikongod, if you drop by again, I'd appreciate hearing your thoughts.
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