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Old 10th December 2013, 01:46 AM   #1
MilosC is offline MilosC  Serbia
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Default LM3886 + ECC82/12AU7

Hello,
I'm building an amplifier based on LM3886 IC and I want to add some tube "warmth" to it, but only using available power supply at about 60V. My question is will ECC82 as a preamp operated at such anode voltage (maybe driven with constant current source) produce characteristic tube distortion or it will sound "metallic" like plain solid state amp?
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Old 10th December 2013, 07:35 AM   #2
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cathode follower. And yes, 60v will work.
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Old 10th December 2013, 07:37 AM   #3
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Tubes & The Gainclones
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Old 10th December 2013, 08:52 AM   #4
MilosC is offline MilosC  Serbia
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Yes, that's exactly what I'm looking for. I wasn't aware of the sonic differences between series and shunt feedback before reading this. Why the input buffer and the opamp have different supplies? I believe it's to eliminate positive feedback.
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Old 10th December 2013, 09:38 AM   #5
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Quote:
Originally Posted by MilosC View Post
...produce characteristic tube distortion or it will sound "metallic" like plain solid state amp?
There are so many wrongs within this sentence...

A tube buffer (cathode follower), by design using massive feedback, will be a very linear element within the audio-path. If you just like the idea of using tubes or are in for a new project, that's awesome, but if you're trying to cure perceived sterility by slapping a tube in front of a SS stage, you'll be disappointed.

Last edited by funk1980; 10th December 2013 at 09:52 AM.
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Old 10th December 2013, 10:06 AM   #6
MilosC is offline MilosC  Serbia
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Originally Posted by funk1980 View Post
There are so many wrongs within this sentence...

A tube buffer (cathode follower), by design using massive feedback, will be a very linear element within the audio-path. If you just like the idea of using tubes or are in for a new project, that's awesome, but if you're trying to cure perceived sterility by slapping a tube in front of a SS stage, you'll be disappointed.
I like tube amps (I designed and built some) and this is my first excursion in design of HI-FI solid state amps... Maybe my sentence seems a bit stupid, but my idea was to use as much as possible linear SS amp and to introduce some even harmonics using tube as a preamp. I know that cathode follower has inherent feedback, and my first idea was to use classic common cathode amp, but as far as I understand, addittion of BJT as an anode load solves this problem (in the posted link). Of course, I'm open to suggestions.
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Old 10th December 2013, 10:52 AM   #7
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I think you are looking for this!


SuperTriode
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Old 10th December 2013, 11:13 AM   #8
DF96 is offline DF96  England
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"Characteristic tube distortion" is not characteristic of tubes, but only tubes put in circuits deliberately or carelessly designed to add distortion. Running a cathode follower from a fairly low supply rail voltage is one way of doing this. As a cathode follower has so much negative feedback and so 'wants' to be linear you have to either design very carefully or very incompetently to get much distortion from it.

An alternative to consider is a common cathode amplifier with anode load resistor roughly equal to 1/gm. This will give similar gain and similar output impedance to a CF, but much more distortion. However, at line level it might still sound OK. ECC82 would be a good valve to try for this as it can cope with large grid signals - it was based on putting two EC90/6C4 power triodes into one envelope.
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Old 10th December 2013, 12:23 PM   #9
MilosC is offline MilosC  Serbia
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Originally Posted by DF96 View Post
"Characteristic tube distortion" is not characteristic of tubes, but only tubes put in circuits deliberately or carelessly designed to add distortion. Running a cathode follower from a fairly low supply rail voltage is one way of doing this. As a cathode follower has so much negative feedback and so 'wants' to be linear you have to either design very carefully or very incompetently to get much distortion from it.

An alternative to consider is a common cathode amplifier with anode load resistor roughly equal to 1/gm. This will give similar gain and similar output impedance to a CF, but much more distortion. However, at line level it might still sound OK. ECC82 would be a good valve to try for this as it can cope with large grid signals - it was based on putting two EC90/6C4 power triodes into one envelope.
I'm looking for moderate compression, just to add that "warmth" to the sound. All sugestions look interesting, but I'm mostly interested in firsthand impressions, if someone has listened some hybrid amps with similar topologies, just to make sure that it's worth putting a tube in front of an opamp.
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Old 10th December 2013, 05:42 PM   #10
Cassiel is offline Cassiel  Libya
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Attention!! Warning!! The ECC82 tube sucks...big time! Do it with the ECC88.

By the way, I have a LM3886 amp and a 12AU7 preamp so I could easily check if it adds 'warmth' or not. I'm almost certain it will add dullness...
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