The Amp Garage

Another improvement: The 1uF bypass on the FET's source ("cathode") was a mistake. I just cut it out and left the 1K2 resistor unbypassed. This removed some mid-high harshness. The FET is sounding like a fine choice as a preamp. The only oddity I've noticed is that, when playing a power chord during...

Last step required to manage gain was to replace both 12AX7s with 12AT7s. Very happy now. Playing thru an EVM12S. Amp can be way too bright—can't turn on bright switch, and Presence is too much. But tone stack controls are really responsive. This demo is recorded with: Treble 3, Mid 3, Bass 5. This ...

I changed that 150K to 33K, and changed gNFB resistor from 100K to 50K. Still way too bright. I'll have to spend more time tweaking.

I'm getting 12 watts into 8R with these Fender OEM transformers. Can only imagine the mayhem with solid Trainwreck iron!

I have 3M double sided, 1mm thick tape holding the reservoir cap down--it's very firmly attached. When I build an amp for NASA, I'll meet the spec. Until then, I do it my way, baby.

Appreciate the advice about the 150K grid ref. I'll mess with that tomorrow.

Build finished, fired up successfully. 316v plates – 10.3 cathode = 306v plate-to-cathode, 10.3v across 130R cathode resistor = 80mA, or almost exactly 100% dissipation, so that's nice. I have a LOT of noise at idle. It's not the gNFB, it's just a huge amount of gain following the Volume pot. If I g...

Nice looking chassis! Are you cutting slots on the tablesaw as well? Part of me wants to make this jig, part of me is fine with Hammond chassis... https://www.youtube.com/watch?v=yrb1Oh0aJM4 Bottom line is, I only fab my own chassis if I'm working for myself. It took about two hours for this exampl...

Thanks, Guy. But the cap at the input is for safety, not noise.

As suggested, I'd like to employ a DC blocking cap between input jack and LND150. I need a rating of 300vDC, but what capacitance, to avoid affecting the guitar signal ? And do I need non-polar, or can I get away with electrolytic? The only caps I have on hand that are small in size are a pair of 10...

Yes, this is my first Liverpool-ish build.

I knocked out the chassis today, from 0.080" aluminum with 1/4"-20 rivnuts. I found the Blues Jr's PT's 20-0vAC tap is perfect for powering a 28v dial lamp.

ViperDoc wrote: ↑Sat Mar 09, 2024 4:31 amAlso, did you consider placing the LND150 in the second vs. the first gain stage? I'm curious as to the difference that would make, if any.

No. I don't want to hear distortion from the FET.

I swap an old carbide blade on the table saw to cut 0.080 aluminum. Works fine, but I lack a full face shield, and deflecting aluminum chips with my face is always refreshing...

Updated layout in post #1. Trimmed some fat (empty space), aiming for a compact amp: 15"w x 6"d x 2.5"h

cdemike wrote: ↑Fri Mar 08, 2024 2:07 amBased on the other thread, I take it that the input cap is to protect the MOSFET from DC on the input?

It's more to protect against the LND150 shorting and sending 200+ volts to the guitarist.

Ten Over wrote: ↑Thu Mar 07, 2024 6:28 pmWhat is the two-tone brown thing on the Source?

Bypass cap, value to be determined at runtime.

Ten Over wrote: ↑Thu Mar 07, 2024 6:28 pm50pF seems a little skinny for the treble capacitor.

That 50p value is on both the layout and the schematic, from the Dumble Files section...