Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: raza on January 15, 2021, 04:55:10 am

Title: GND problems- 2.3Volts to chasis.
Post by: raza on January 15, 2021, 04:55:10 am

Hello
This past month I made an amp that had a lot to do with it.

own design with 3 channels.
fender deluxe / plexi and LEAD.

The case long ago I made the Plexi / LEad channel and it works great. 0 noises!

now I have wanted to work a little more I have made a PCB board and such.

I have also made an external plate for the switching of the channels using optocouplers and arduino. It works perfect.

The only problem is that I have a lot of background noise. I have put shielded cable in all the necessary places, and I no longer know what to do.

The problem that I expose is the following:
On the switch board I feed it with the 6.3V of the filaments and using a 7805 low loss arduino feed to switch the channels.
Well, between the GND of the switch board and the chassis, I have a voltage difference of 2.3V.
obviously the switching board has the GND loose.

Could it be one of the noise problems? How would you solve the connection of the GND of the switching board to the amplifier chassis?

greetings and thanks.

Title: Re: GND problems- 2.3Volts to chasis.
Post by: sluckey on January 15, 2021, 05:29:41 am

It's fine to have a floating ground for your 5V power supply. In fact it is preferred when you use the filament AC to power the 5V supply. I doubt that is a factor for your noise problem. If you really want to ground the 5V supply to chassis use a separate 6.3V transformer.

Title: Re: GND problems- 2.3Volts to chasis.
Post by: pdf64 on January 15, 2021, 06:04:07 am

Please provide a schematic.
Note that it’s not possible to reference both the ac and dc sides of a full wave bridge rectifier to the same circuit node.

Title: Re: GND problems- 2.3Volts to chasis.
Post by: Williamblake on January 15, 2021, 11:45:48 am

Where does your filament gets its DC reference? Sounds like center tap to ground? I dont think it is the culprit but maybe to be sure lift it once to check out? What noise are you getting exactly?

Title: Re: GND problems- 2.3Volts to chasis.
Post by: acheld on January 15, 2021, 09:06:23 pm

What are you using for your Arduino power supply?

Title: Re: GND problems- 2.3Volts to chasis.
Post by: raza on January 16, 2021, 02:06:31 pm

problem solved

I have installed an external source since the 5V DC was taken out of the 6.3V Ac of the filaments.

So I have achieved that the difference of the GND is 0V and I have been able to connect them.
0 Noises. I've never played a high gain amp this quiet.


Thanks!