The pot on the output is just plain bad design. I would seriously question the credentials of anyone who suggested using such a thing there. In the days of Yore, they would tie a global feedback loop from the output down the line, all the way back to the input. That's done here (mark a red X in my little black book) and a lower value would substantially drop the gain. 15 to 15dB is easy. I am not a fan of global feedback at all, unless it encompasses two stages, no more. The problem with it is that it tries to correct something that happens in the past, not recently. In fact, it is wide spanning GF that gave audiophiles the notion that all feedback as an entirety was supposed to be bad, which isn't true at all. We still read such nonsense today. SY made a worthy suggestion to reduce the feedback, but why it is spanning three stages is beyond me. This design is terrible, where did you find this? Is this an old Conrad Johnson, because it's a lot like one? The second 6N4 should be powering the 12AU7's from its cathode, not anode, and as merlinb noted the drive setup is incorrect for the arrangement. What is the purpose of this preamp? The average user only needs 3dB of gain for common modern amplifiers, and a bit more for some tube amps. I don't have any 6N4 tubes in my library, or I would have completely modified this design to better suit fidelity and livability. I am going to check and see if I can find this tube.
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Different tubes have different specified workpoints.
Don't swap tube types!
Get a basic book about electron tubes and how to choose the correct workpoint.
Wow - it's been 7 years since this thread was started and you're still trying to fix this preamp??
Is this a commercially produced preamp or a DIY project? Is it built using point-to-point or a circuit board?
If you don't need gain, it doesn't make much sense to design something that has a lot and then try to figure out how to get rid of it.
As has been pointed out, a "passive preamp", which is just a volume pot or stepped attenuator, is all you really need to drive your amp to full power. Have you tried doing that during the past 7 years?
Sometimes a little bit of gain and some "tube flavor" is desirable. In that case, start with a low gain tube and build something simple. I did just that last year and the only tubes I considered had a mu less than 10.
Even a 12AU7 (mu 20) and others with similar mu (6SN7, 6CG7, 12BH7) probably has more gain than you really need. But there are many preamps that use these tubes. If you're still using a SS amp, find a design that uses one section as a gain stage and the other as a cathode follower.
Perhaps they will respond. . . but that poster has not been active here for about a year and a half.
I still have this preamp, and have found it in dust.Thinking try to listen again the sound is oke only the gain is to high i read on the internet the the gain for ecc 82 us lower then the ecc83. And I tested the ecc82 instead of the ecc83. But I hear distortion. I have change the 100k on the input to 47k mutch better.
Just try to use it after 7 years
Thanks
Just try to use it after 7 years
Thanks
The schematic you posted shows 12AU7 / ECC82 (and 6N4s, which I'm not familiar with). So why are you using ECC83 / 12AX7s?
The ECC83 (12AX7) has an amplification factor (mu) of 100, while the ECC82 (12AU7) has a mu of 20. So a 12AX7 will give you more gain, not less. I thought you needed less gain. While they do have the same pinout and heater voltage/current, everything else about them is different. They are not considered direct subs.
Again, is this a commercially produced preamp or a DIY project? Is it built using point-to-point or a circuit board? Maybe you could post a pic.
And, did you ever try using just a simple volume control / passive preamp as was suggested 7 years ago?
I try again, in this board they use ecc83 as first and ecc82 as second stage. Woensdag i charge this the sound is mocht beter but but still at higher frequency distortion. So I replace the 100k resistor into 47 but still sometime distortion. Could you please draw what I can do. Sorry I have not enough money to buy a other one.
Thanks
Thanks
It's a volume pot, it's adjustable. Need more drive, turn it up. Need less, turn it down.
You never did answer the questions I posted earlier:
Just to be clear, the suggestion that was made 7 years ago, to try a simple volume control / passive preamp would involve removing the preamp entirely from the system and replacing it with a volume control.
Most amps do not require more than the nominal 2v output from most sources in order to reach full power output. While a preamp might offer other advantages, such as multiple inputs, tone controls or improved dynamics, the extra gain is typically not needed.
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