The Amp Garage

Is this local negative feedback increasing headroom or that my imagination?

You need all that for detail but as I said, the 'do these component changes affect sound' you just need one person able to hear it blind. Then you can debate all you like whether it matters but not whether it exists.

Surely you only really need one listener to consistently identify component changes blind to disprove the doubters?

Can anyone point me to audio or video examples of acceptable levels of IM distortion in similar amps ie low filtering marshall type amps please?

Thanks guys. I'm going nowhere. Slowly.

You have a oscillation problem then and likely due to layout reasons. Just for S & G try reversing the output tube plate wires or the wires off the secondary side of the PT to the speaker jack, whichever is easier for you. I still don't understand this, do you mean reverse the output transformer wi...

maxkracht wrote: ↑Tue Feb 13, 2024 6:42 pm Are you sure the noise is coming from the power amp? Maybe you are getting partial cancellation of the noise when running PP. Any schematic/pictures of the amp?

Tried to pm you but its stuck in my outbox?

Hmm that's an interesting idea. It is definitely intermodulation distortion. Leaving a low string ringing and then bending notes above it you can hear the low harmonic out of tune bending in the opposite direction.

Yeah I thought so to but couldn't find any negative reports. I have the Paul ruby mod installed.

I called it pseudo SE, it's in a KOC book apparently, but its basically a mv for one side out of the phase inverter grounding the signal to 2 out of 4 tubes with a pot. I got it from the vajra schematic (pp-se mod) on 18watt.com there are various versions of it. I like it a lot except for excessive ...

I'm really confused now. Currently each pair has 220ohm shared resistor bypassed with 2200uf as stated. Case 1.Say I change that to 180 ohm bypassed plus 40ohm still shared then I've changed nothing except the bypassed portion of the cathode resistor. Case 2. If I make the non bypassed part individu...

Yes sorry I was going to run the extra resistors from each tube to the shared resistor on the board. Do I need to double the value of the non shared part of the resistance? Ie going from a shared 220 ohm to a shared 150 ohm I need to make up 70 ohms equivalent shared resistance. Am I looking for 70 ...

Apparently they are common on 18 watt marshall style circuits.

I have some unwanted IM distortion on my hodge podge mess (lite 11b with double power section running 4x 6p1p ) especially when running in pseudo SE mode with an mv on one half of the power section. I currently have 16v across 220 ohm 5w cathode resistor bypassed with 2200uf cap, shared between each...

You have a oscillation problem then and likely due to layout reasons. Just for S & G try reversing the output tube plate wires or the wires off the secondary side of the PT to the speaker jack, whichever is easier for you. Sorry I didn't fully understand this. I have no nfb if it makes any differen...