Getting a head of myself - Marshall 2204 JCM800 inspired build

[kuDo]

Now I just finished the rebuild of only the preamp section.

And I have finally defeated my “hiss” demon.

In the end It must have been the turretboard soldering, that plagued me.
I remember that I had a real tough time soldering it back then. I think I must have had a bad batch off turrets.
Can’t remember that I have ever had such a struggle with soldering as then.

Now I based my amp on the same schematic as back in this tread. This time I used a “tube town EZ board”
https://www.tube-town.net/ttstore/tube- ... -9333.html

It was a dream to work with. Solder, now, was as easy as the name of the board suggested

It now looks like this

[kuDo]

This afternoon I have hooked my pre-amp up to my EF80 power amp made recently.

I made a little recording with my I pad. It’s not a real good recording, but it’s something to illustrate.
The hum that is heard, is from my p90 pickup. When I drop down my guitar volume to 0. The amp is now silent and there is not even heater hum to be heard.

Don’t look at the video, just listen it is real nice recording of my floor

[kuDo]

This amp turns out to be quite the journey.

After my first attempt wasn’t quite perfect in terms of performance, I decided to rebuild it.
when the rebuild of the preamp was done, the amp is now noise free.

I had put a lot of effort into this amp build. I learned a thing or two. And that was all great.
But the end result wasn’t what I wanted it to be.

So Was thinking of rebuilding the amp once more, but this time as a PCB build.
There are a lot of these boards online that I would be able to use, but I would really like it if I was able to design my own.
So I have been following an online course to understand how to operate KiCad software.

After a lot of hours sitting behind the pc screen, I have finally received my own design PCB from the company the could make it for me.

I am very pleased with the results. I have just finished soldering the components.
So at this point I thought it would be nice to post an update.

[xtian]

Nice! Hope it sounds as good as it looks!

[kuDo]

Nice! Hope it sounds as good as it looks!

Thanks Xtian. I hope so!

Currently wiring it all up.

[kuDo]

I finished up the soldering and wiring of the amp. Version 2.0 is now working.
This time based on a PCB I designed. So things are more tidy which is nice.
All power supply capacitors are on the PCB, except for the first two filtering caps. Those are now placed in the outdoors.

But……

I still have a sssssssssssssssssss problem.
This hiss is gone when I pull out V1 out of its socket.
When the hiss is present I am not having a guitar connected .
The hiss is the same when the guitar is connected.
Once I start playing, it is no issue, but when I stop it is pretty irritating.

[bepone]

hiss like high frequency oscillations artifacts in hearing range , means that your layout and lead dress is not good!
pcb design is an art and you need to be experienced to make it hum, hiss free!
so probably after 10th attempt you will make good pcb. also important is the copper thickness , i bet you chose thinnest possible to save money and for pcb amp need to be max posible what you can afford.

also who knows what you did for the clearing from pads to plane ( ) did you respect rule of 3-5 mm from high voltage pad to the others?

ok. to cut the story. you cant change pcb now. remove all the wiring on V1. maybe you can fix something.
coax cables under the board not over.. wires on V1 also, put against the chassis not on the air and not in "X" like you have. remove heater wiring and find dc source , supply dc heaters from good source to eliminate penetration of noise through the cathode - heater line.
see if something better.
read little bit how to design high voltage pcbs also
good luck

[martin manning]

I still have a sssssssssssssssssss problem.
This hiss is gone when I pull out V1 out of its socket.

Did you try different tubes in the V1 spot? Maybe you have a noisy tube.

When the hiss is present I am not having a guitar connected .The hiss is the same when the guitar is connected.

So it's present with or without anything plugged into the amp? The source of the noise is inside the amp then, not getting in through the input. I would suspect the V1 tube, or a noisy component, resistor or cap, around V1. I think your PCB looks good. The components are nicely spaced, meaning far enough apart to avoid any problems.

[kuDo]

I still have a sssssssssssssssssss problem.
This hiss is gone when I pull out V1 out of its socket.

Did you try different tubes in the V1 spot? Maybe you have a noisy tube.

When the hiss is present I am not having a guitar connected .The hiss is the same when the guitar is connected.

So it's present with or without anything plugged into the amp? The source of the noise is inside the amp then, not getting in through the input. I would suspect the V1 tube, or a noisy component, resistor or cap, around V1. I think your PCB looks good. The components are nicely spaced, meaning far enough apart to avoid any problems.

Hello Martin,

I have tried a couple of different tubes. All of them seem to be very sensitive to poking. Almost as if the where microphones.
But I can't believe that al 3 of my pre-amp tubes would be bad. I have used 2 JJ's and a Tung-Sol.

Indeed, no guitar plugged in gives already a lot of hiss. I think I might build the first stage separate, just to test it.

[xtian]

Did you put V1a grid stopper resistor right on the tube socket (best practice)? Hard to tell in photo. What value is grid stopper?

[bepone]

Indeed, no guitar plugged in gives already a lot of hiss. I think I might build the first stage separate, just to test it.

did you try what i have suggested before? put all the wires against the chassis? first stage must be silent without guitar on max volume. all other problems what you have are related to lead dress and pcb..
it is easy , several hour job, remove all from V1 and do again.
dc heaters for V1 can also eliminate one possible cause.

[Littlewyan]

What if you plug into the low input? That would eliminate the first gain stage, does it still hiss? Could you upload a recording of it please?

[kuDo]

Did you put V1a grid stopper resistor right on the tube socket (best practice)? Hard to tell in photo. What value is grid stopper?

Hello xtian,

Thanks for the reply, somehowe I don’t get update notifications anymore so I didn’t see you reacted.

The 68k grid stopper is attached to the socket. And is fed by the input socket via a wire with a metal shield which I in turn is connected to ground on the input side only.

[kuDo]

did you try what i have suggested before? put all the wires against the chassis? first stage must be silent without guitar on max volume. all other problems what you have are related to lead dress and pcb..
it is easy , several hour job, remove all from V1 and do again.
dc heaters for V1 can also eliminate one possible cause.

Running the wires against the chassis didn’t do it unfortunately.
I think I will as mentioned earlier build the first stage separate, just to see if that works and wire it up again.

Heater hum doesn’t seem to be present. It has been elevated and balanced via a humdinger pot.
But if all else fails, I can try.

[kuDo]

What if you plug into the low input? That would eliminate the first gain stage, does it still hiss? Could you upload a recording of it please?

I don’t think the hiss is there anymore, when engaging the low input. But I will verify that.

I have tried to record it, but doing this with an Ipad doesn’t seem to yield good results.