Naylor Superdrive Presence and OT Tap

[Mr. Lime]

I tried increasing the 1n5 to 2n2 but that didn't help.

There's hardly a change in sound when turning the presence. Only in maximum position at 0.2ohm there's a sudden volume increase.
Maybe the tail R has to be changed as well or change the 5n to 3n3?

The resistance between the 8ohm tap and ground measures 0.3ohm. Is that normal?

[martin manning]

When the pot goes to zero resistance all the feedback is dumped, so no surprise you get a volume boost. Is your pot a log or linear? Which lugs are jumpered? I would use a log pot, and jump the center and clockwise lugs to bring the resistance up slowly.

[Mr. Lime]

The volume boost appears especially at low master volume.
With a Power Soak the effect isn't noticeable.

First i had a 5k linear pot and then I replaced it with 5k log, it doesn't matter which lug I used, it's always the same volume boost nearly at maximum pot turn without much of a tone change.
The tone stack bass also has very little effect on the overall sound. 44n as switchable bass cap didn't help either.

Without NFB the amp doesn't sound much different..

[martin manning]

Where in the circuit is your master volume? If you have added something to the posted schematic that may be changing the feedback ratio.

[Stevem]

The resistance of OT taps should be as follows.
4 ohm tap .5 ohm.
8 ohm tap, .71 ohm
16 ohm tap, 1 ohm

[Mr. Lime]

Thank you for the response.

Both 8 and 4 ohm outputs have 0.3 ohm resistance on my amp..

Mastervolume is exactly placed like in the schematic but it's 1M instead of 500k at the moment. I planed to add another switchable Mastervolume with 1M pot. So at the end they would be parallel resistances.

Maybe I have to try a resonance control with a typical feedback resistor to get the needed bass boost.
On the other hand I like the feel of the PA with very little nfb.

Any suggestions to get some bass?

[Tony Bones]

Both 8 and 4 ohm outputs have 0.3 ohm resistance on my amp..

I wouldn't get too worked up over that. Measuring very low resistance is difficult. Different meters will often give different results, and some meters are no good at all down there.

[martin manning]

No problem with that MV location, actually I missed it when I had a quick look before.

I can’t see why you’re not getting more effect out of it.

[Mr. Lime]

Tweaked my amp a bit and now i got massive bass.

I put a 47k feedback R infront of the 3n3 (1n5 original) cap and replaced the presence pot with a "scratchy Marshall style" 5k pot and 220n presence cap. The 10k and 5n came out because they were the reason for the bad range of the pot!
With 5n on the scratchy pot the range was very much better as well but I felt that the 5n cap was way to thin sounding for my liking. I also tried the Naylor style presence with 22u and 680n presence cap but it doesn't work. Maybe they had to go down to 5n to have some kind of effect?