I want a little more loudness without distorsion, But only a little.
AlsoI know I a need mod the volume control becouse it opens very early. In other post I asked for a problem in this amp. I had strange noise in the volume control, and the solution was change the 250kA pot for a 25ka pot.
Now I havent any noise or CRACKKKK, but I 've a bad range.
But the more important to know isthe MORE LOUDNESS WITHOUT DISTORSION
Unfortunately to get a little more loudness, a lot more power is needed; 3dB is a small change but requires twice the power level, when 1dB is the normal resolution of human perception.
So, bigger transformers, more tubes etc.
Looks like you may have found your next project.
Alternatively, use a more efficient speaker.
If you are using one that is 98dB/watt, then changing to one that is 101dB/watt may be sufficient.
Or use 2 speakers, as acoustic coupling increases forward efficiency.
Last edited by pdf64 on Mon Apr 20, 2015 2:02 pm, edited 1 time in total.
Hi Ranalog,
This circuit does not look familiar to me. Did you design it yourself? I think it has too much gain to allow a clean sound. The new 25k volume pot helped somewhat by sending most of the gain to the ground. Changing the plate load on v1b to 100k also should have helped somewhat.
You could remove the 25 uf capacitors on the cathodes of v1b and v2b to reduce excess gain and clean up the sound. Then try putting the 250k volume pot back in and see how much control and clean sound you can get.
In my opinion, you have no need to make apologies for your English. I have had to ask much the same question of native speakers of USA English. That's why I knew to ask the question.
I have read your earlier thread and this one, and I have some general comments.
The circuit you are using is fairly unusual, especially in the circuits immediately before and after your effects loop jacks. A designer of "normal" amplifiers would not have done it that way, at least not without a long process of trial and error. This may be good, or bad, or more likely it is *both* good and bad. It gives you a sound you like, which is good, but then causes some difficulties in other ways.
It is very likely that some of the early distortion is coming from the cathode follower just before the volume control and effects loop. I have some comments about that, and some things for you to try. This may or may not make the sound have a tone quality you like. There is only one way to find that out - try them.
First: Your cathode follower before the volume control is self biased at a very low current. A more normal practice would be to connect its grid directly to the plate of V1b for biasing purposes. You could do this by putting a capacitor of 0.22uF or bigger (1uF would be fine) between the 10K and ground at the cathode follower's grid. This raises the grid enough to put a significant voltage across the 100K cathode resistor of this tube.
This may eliminate the sudden distortion all by itself. Try this and we can proceed with other things if this does not work.
roberto wrote:I would start from something easier.
Set the amp like that:
Gain stage - tone stack - gain stage - cathode follower - loop - recovery - power amp.
Connect the CF directly to the second gain stage.
I wrote up much the same thing, and erased it when I thought about his statement that he liked the sound.
I suggested what I did because of that. It preserves more of the original circuit. We still don't know *what* he likes about it. And can't - it's not a problem with languages, our languages don't have good and clear descriptions of tone.
Fairly certain that's what he is getting at. Though if you're willing to get rid of the 100k resistor and 500p cap (as shown in your updated schematic) you may as well get rid of the 10k resistor and added cap as well. Then you'll have a more conventional DC coupled cathode follower. It will change the sound for sure, but you might like it better, or maybe not.
It *may* help with your cleans as well, since you wont be attenuating the signal, you won't have to push the previous stage as hard to get enough signal to get the output stage at the volume you want. This assumes however that the preamp will start to overdrive before the output does. Which is something I couldn't tell you just from looking at the schematic.
That's not what RG suggested.
Ho suggested to polarize correctly the CF keeping the voltage divider before it.
The capacitor in that point is a bypass for the AC but keeps the grid voltage of the CF still high.
