18Watt.com

Between Ceriatone's layout, the 18watt.com Layout, and the 18watt Schematic there are three different values for the Negative Feedback Circuit!

1. Ritchie's layout shows a 47k resistor across the switch.
2. Ritchie's schematic (rev 5) shows a 27k.
3. Ceriatone's layout shows a 100k across the switch (with the 47k on the board).

I followed Ritchie's 4.5.06 layout with the 47k across the switch and am having problems when the NF switch is in the Off position (weird alien noises).

A little background: I had to reverse the PI's plate's wires to be able to the Master without squeal.

I'm going to try a 27k in place of the 47k in the meantime.

If this works, at least folks with similar problems will have a thread they can search/find

So...

Anybody got any thoughts on why I'm tuning into Martian mind control transmissions when my Negative Feedback is switched off?

Sounds like some sort of 80's computerized sound effect.

Run a wire from the ground on your output jack to the chassis and see if that helps.

Ken

Good evening,

I went through the same problem with my early prototype, had to lift speaker ground and reverse OT primary (brown/blue) to clear the problem.

Now my present version has the feedback switch, so I had to re-address this noise issue. This time I followed a tip from Ritchie, one star ground dedicated for the normal channel, and a separate bus ground for the TMB. OT secondary is grounded right at the chassis, OT primary is on the normal side (blue/brown), and the amp is now dead quiet at all settings.

Hope this helps

Claude

Got it all figured out...

I was used to hearing motorboating and high pitched squeal when it came to oscillation, not Alf channeling the homeplanet.

I had swapped the OT wires previously, but that was before I "fixed" something else.

I swapped the OT wires and got it hammered out now. I dig the sounds of both no NF and NF on.

I like the NF on the 36w, it tightens up the bass considerabley. Off is nice and raw.

I like FB and also the tone defeat options.

I've been tweaking my prototype chassis for almost a year, but was not satisfied with the previous tMB designs. Now I think I reached my goal with rev 5, will build my final version around it. Will be a head, and a 4x10 slant cab.

Claude