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Old 25th June 2007, 01:00 AM   #1
tinitus is offline tinitus  Europe
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Default Ultrapath line amp

Hi, I have no experience with tubes, so I want to ask you if it really can be as simple as this, or are there missing parts in schematic ?
What I think I have learned is that a single tube like this may have high gain ?
In article 2 tubes are shown .... I guess that would mean they only use half of the tube .... could they be wired different so that tubes could be shifted left to right when they wear out, or are other factor in play with tube wear ?

http://www.electra-print.com/ultrapath.php
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Old 25th June 2007, 01:29 AM   #2
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It really is that simple.

2 tubes are shown because Jack used single triodes (6J5). You could use both sides of one 6sn7 instead and only use one tube.

There is a fair amount of gain from the tube, but the output transformer will reduce that significantly.
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Old 25th June 2007, 01:20 PM   #3
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I built this preamp a few years ago using 12J5s and Electraprint iron... it seemed to be very sensitive to AC ripple so make sure to use a steady DC supply. I never really tweaked it too much (not much to tweak!) before it got replaced by another unit.
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Old 25th June 2007, 03:31 PM   #4
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Thanks guys, I am still considering a passive TVC but also remember when I had a tube pre with a single ECC81 and it had something very special
Should I go on and build this I could consider using regulated solidstate supply
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Old 25th June 2007, 03:49 PM   #5
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kstagger how did you like the sound?

Ever tried a different tranformer or tube?

I have been curious about this preamp and pondering transformer options. I know Sowter makes some line output transformers but don't know of much else capable of 20-25 ma to be able to experiment with different tubes...
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Old 25th June 2007, 06:04 PM   #6
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never swapped out the transformer... but I did check out different versions of the 12J5 (which is mercifully cheap)...

It's been awhile but I remember it was an all-around good performer - I used an outboard regulated Heathkit power supply supply/. But in the end I preferred some of latter creations and the line transformers were sold off to fund some other projects. Don't get me wrong - it wasn't a bad preamp at all and I sure wish I could hear it again with my (since then) upgraded system. If I was going to build it again, I would have used a stepped volume control pot and a different PS.

There are some pix on my website (behind my screen name) under Projects. It's a cruddy 'free webspace' so beware of the pop-ups.
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Old 25th June 2007, 08:04 PM   #7
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Question How good is it?

Quote:
Originally posted by kstagger
Don't get me wrong - it wasn't a bad preamp at all and I sure wish I could hear it again with my (since then) upgraded system. If I was going to build it again, I would have used a stepped volume control pot and a different PS.
So do you mean that if the power supply has been carefully taken care of then the amp is very good and enjoyable?

Would you describe the Ultrapath line amplifier as an outstanding device judged by the sound quality alone?
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Old 26th June 2007, 12:22 AM   #8
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Thinking about using this

http://www.supertube.de/RNT400/RNT400.htm
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Old 26th June 2007, 01:14 PM   #9
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Default Re: How good is it?

Quote:
Originally posted by Nikolas Ojala


So do you mean that if the power supply has been carefully taken care of then the amp is very good and enjoyable?

Would you describe the Ultrapath line amplifier as an outstanding device judged by the sound quality alone?
Sorry - it's been too long since I've heard it so I can't say anything very specific about the sound anymore... at the time I thought it was one of the best preamps I've ever heard - but (at least in my system) I ended up preferring some of my later designs - perhaps it's vanity. I would say try it out.
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Old 28th June 2007, 02:14 AM   #10
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Default A bit different solution

It seems that the beauty and fundamental idea of the Ultrapath amplifier is in minimizing this current loop:
Anode - Transformer primary winding - Capacitor - Cathode.
The way that was done in Ultrapath amp was by removing the bypass capacitor from the cathode resistor and reconnecting it to the positive high voltage, directly to the transformer. Thus the loop area was minimized. As we have been told, the principle works. I suppose that keeping all iron away from the loop would be good too. Choosing a good capacitor is another important part of the solution. But this Ultrapath solution caused a problem we allready know: The 120 Hz humming.

We should remember what was important:

1) Keep the current loop small.

2) Have good capacitors in the signal path.

That is the Ultrapath way. But what about the humming problem?

I think there is at least one more possible solution, different than the Ultrapath, but based on the same principle:

1) Keep the bypass capacitor, just like in most cathode biased amps, but let the capacitor be as good as you can get.

2) Take one more good capacitor and connect it from the Ground to the high DC source voltage. You get an AC current loop:
Anode - Transformer primary winding - (DC voltage here) - New capacitor - (Ground here) - Bypass capacitor - Cathode.

3) Take care that the current loop really is small and there are no iron parts inside or near the loop.

The schematics of this solution is nothing special. You can easily draw it. Actually there is nothing new. The new capacitor is just one more filter for the DC. But keep in your mind the original idea of the Ultrapath amplifier. Following the idea you should be able to get desired results.
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