How to get more clean range

[Ranalog]

lots of thanks!

[Craig B]

Hi Ranalog,
I noticed that the NFB is connected in the wrong place. That will create a distortion/volume problem. The connection should go to the top of the 47 ohm resistor. Look at the fender Champ AA764 as an example.
Good luck!
Craig B

[roberto]

Yes, there was also that point in my first list on page one.

[roberto]

Small papers for big ideas!

[Ranalog]

well, I try it.

First I need to say that NFB was wrong in the draws I attached the construction is in the good place.

After that If I remove the 220k 500p resistor that join the plate and the grid resistor o the CF I lose lot of sound color.

The voltage diivider before the send Cap no afects to the sound.

what danger is put the 220k and 500p cap between the plate and grid (cf)

[roberto]

No danger. That was RG's suggestion!

[Ranalog]

How affects the nfb to clean range? If I up the NFB resistor I can get more clean?

[strelok]

NFB is a complicated thing. The simplest explanation is that NFB theoretically produces greater linearity in the stage, at the cost of output power. So the more feedback you have (lower resistor value) the cleaner the stage and the less power you will get out of it. Its not 1 for 1 so there is some ground to be had from doing so, up to a point. Your best bet would be to experiment with different values and see what suits you best. The other caveat is that when the stage does clip, it clips much harder that it otherwise would. Try experimenting with some lower values, say 2k or 1k5 and see what it does for you. Then maybe try a higher value 4k7 or so and see what you like better. The theory is quite a bit more complicated than most other aspects of amp design so swapping them out is the easiest way to find what works best.

[roberto]

Renalog, try one mod at a time.

[pdf64]

The simplest explanation is that NFB theoretically produces greater linearity in the stage, at the cost of output power

Surely NFB is better seen as reducing gain, rather than output power?
OK, if the system gain becomes insufficient to fully drive the linearised amp then one perspective may be that power has been reduced, but that's unlikely to be a problem with many guitar amp circuits.

[roberto]

...well, what about a dummy load and then reamp with a class D amp at the volume that you need?

[strelok]

The simplest explanation is that NFB theoretically produces greater linearity in the stage, at the cost of output power

Surely NFB is better seen as reducing gain, rather than output power?
OK, if the system gain becomes insufficient to fully drive the linearised amp then one perspective may be that power has been reduced, but that's unlikely to be a problem with many guitar amp circuits.

You're right, I should have said gain, not sure why I said power, lack of sleep maybe? lol. Also I second roberto's statements, both about not getting ahead of yourself and the dummy load idea.

I've used simple resistive dummy loads quite a bit, both to run a small amp into a larger poweramp to make it loud enough for gigs and to run a 100 watt marshall wide open into a slave amp to play with output tube distortion at a much more reasonable volume. The extra gear is really the only downside, however you have a perfect spot to insert various effects in between the dummy load and the poweramp.

[roberto]

I mean something like this one:
http://www.ebay.com/itm/110932793981

You can find all the info here:
http://sure-electronics.net/download/AA ... 1.0_EN.pdf

Together with something like that:
http://www.ebay.com/itm/231407089766