The Amp Garage

Any members on here with beginners advice, feel free to chime in. :) Hello, I have started KiCad in februari 2022 last year. I have created my first PCB for my JCM800. Although I still have a slight issue with the amp, the PCB I made is great! I started with these lessons: https://www.udemy.com/cou...

Maybe, I give it a try next time!
Thanks for the schematic

Thanks bepone, but I am fine like it is.

I just need to adjust de LM317 a little and it’ll be perfect.
It already works like a charm.

N.B.: Hum at the power line frequency (that is, 50Hz or 60Hz) is caused by the mains leaking into the audio path. This can be poor grounding, capaictive coupling, magnetic field coupling AC wall socket ground or neutral shifting, that kind of thing. Hum at twice the power line frequency (100 or 120...

Measure the voltage across the 4.1 ohms and calculate current to verify that you are getting what you want. It is due to the fact that I picked a standard transformer, which might not entirely match my calculations. The output voltage of the transformer winding for the heaters might have lowered a ...

This is the amp at the moment.

I used the pointers Merlin gave in his new power supply book.

Maybe I will put this preamp in a dedicated housing. But before I decide, I wil wait until I have used it with a guitar and see if it is worth the effort.

This is the PSU that I used for HT and DC heaters.

The heater supply's LM317 might need a little adjustment. Currently it is at 10.9v dc where it should be 11.4v dc at minimum for it to be optimal. 12.6v would be the goal.

Okay, that’s clear. but why is that responsible for the disappearing of the hum? It had already had a DC supply? A mystery to me. There is parasitic coupling between windings inside the transformer due to the way it is wound. Usually the 6.3VAC heater winding is the last thing added over the top of...

sluckey wrote: ↑Sun Jan 01, 2023 12:29 am It's not a matter of elevating the heaters. It's a matter of referencing (connecting) the heaters to ground.

Okay, that’s clear. but why is that responsible for the disappearing of the hum?
It had already had a DC supply? A mystery to me.

The heater circuit shouldn’t be left floating. It needs some sort of DC reference to prevent the heater to cathode voltage exceeding the limit, eg 180V. And the AC impedance between the heater circuit and circuit common needs to be low, eg not much higher than 100 ohms. Aah, great! It worked. First...

There is however I little bug still. There seems to be a 150hz hum present. Which is off course unwanted. The hum is there even when the input is grounded. I have been experimenting a little. By undoing the wiring for the heaters and re-wiring it for 6.3volts power supply. Initially The heaters were...

Yesterday I finished wiring up all the parts. And today I switched it on for the first time using the variac. At first I seemed to have made a mistake. As I was only hearing a loud humming sound, when I amplified it using my tiny lm386 chip amp. After investigating a little it must have been the wir...

Hello, I have been preparing and building the Valve Wizard’s Ultra High Gain Preamp the past weeks. After reading Merlin’s books I was so curious as to how it would sound that I had to try. I know there is an other forum post on this design but there have been no sounds posted. Years ago I ordered a...

I’m not certain where you are grounding your input wire shield. If it is on the preamp buss, try grounding the shield to its own chassis ground lug, and only at one end of the shield, of course. I have grounded the sleeve of the wire shield on the sleeve of the input jack, which in turn is the sing...

After an afternoon of desoldering an re-soldering en cutting wires and making a general mess of things. I have finally finished my amp again. The hiss issue in my amp is al down to the v1 grid stopper resistor. It seems to become less when I put in lower value as oppose to the 68k that was in there....