The Amp Garage

Last question (fingers and toes crossed). The bias pot. I'm using a 0-50k pot mounted in a DIY bracket in favor of the tiny, mechanically feeble, one in the kit that would go on the turret board. More robust and keeps fingers and screwdrivers at a distance. The pictorial wiring diagram shows it wire...

One question.

When you say "increase the negative bias at pin 5", do you mean make it more negative or more positve?

Thank you sir!

Thanks for that. I was aware that it was DDC causing the scratching, and was wondering if the cap would block the DC if put before the pot. The WD is shown above, repeated below. The cap is a 0.1 uF, attached between the pot middle lug and ground. The input goes to one outer lug and the third is gro...

"Keps", "keep" "lock nut", whatever.

PS.

This is a typical "keep nut". No nylon inserts involved. The serrated "washer" on the bottom is attached to the nut and bites into whatever is below:

I've moved all [/i] the grounds off the PT bolts now. The ground scheme is curretly as follows: 1. The mains ground goes to one #8 bolt and keep nut, near to, but separate from, the PT mounting bolts. This wire should be long enough that in the highly unlikely event that the mains plug sticks in the...

Yup.

And if you're in a highrise steel-framed building, it's probably being held up by bolts. Without locknuts, without any washers, let alone serrated ones, keep nuts, nyloc nuts...

Just friction.

Comforting that, isn't it

I've made the change. As it happened there is (well, was) a spare hole in the chassis already. I opened it put a bit and used a #8 machine screw and a keep nut. Your vid seems to show whoever built that amp hadn't heard of keep nuts, BTW. A bit of a right turn, but I am yet again reminded of my old ...

Fairy nuff. I can do that. Personally, I don't think using a separate bolt, equally (un)likely to come undone, is any different, but I can do it.

Anything else?

In the quest to remove the quite high 60 and 120 Hz hum from my JTM45 kit, I've reworked the grounding scheme, as shown below. The idea is to remove the ground bus wire from the pot casings, and to provide one ground bus for all the turret board grounds. It's extended to take in the Presence and Mid...

I reflowed all, and I mean all, the solder joints and the hums and ticking have gone. It must have been a bad joint or a bad ground (or a bad joint to a ground causing them.. There's still some hiss (white noise) with the volumes cranked right up, but I guess that's to be expected from a fairly simp...

Mojototone DR103 100 watt head. It's produces quite a noticeable mains hum, especially if the input volumes and master volume are set to max. Obviously this wouldn't be heard (much) when playing, but even at lower volumes its noticeable. The Amp sits in a metal chassis, and I added a grounded alumin...

Sorry, not the "Master" volume pot, but the Brilliant Channel pot.

It's about a year old Mojotone kit I built myself.

I've been going though it all day, and finally traced it to a duff master volume pot. No idea how that happened, but "stuff" does happen.

Now working fine.

Thanks everyone.