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?
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?
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.
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.
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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.
"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.
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.
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...
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...
No. The ECC88 is far too linear for the CF version, and has far too high gm for the common cathode circuit. The OP actually wants a little distortion. Used correctly, the ECC82 can provide mainly second-order - that is why it was used as a high-performance mixer in a GEC naval receiver in the 1960s.
At first, ECC82 is my tube choice because of low mu and gm, and by using ECC88 I would have to put massive amounts of feedback which would question the use of a tube as a preamp. But, so far, the tube buffer in the Gainclone looks most promising to me, and I think ECC88 here could do the job.
Thank you for all your answers, I think I'll make a plain common cathode preamp using ECC82 with separate HT power supply followed by transistor buffer driving an inverting opamp.
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I don't understand why you want a transistor buffer - seems redundant. Just use a tube preamp and deliver the output from that into your chipamp.
Well, I meant to put that buffer as some sort of additional isolation between tube and [expensive] SS stage, combined with protecting diodes, but maybe I'll just go without it. I don't know yet, I'm still in the phase of thinking, still have to put schematic and some numbers on paper.
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Also, is it needed to lower the high output impedance of the tube with buffer? Because opamp will be connected as inverting.
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