Need advice on channel switching issue

[Planobilly]

Hi,

I am finishing up a new build two channel 100 watt high gain guitar amp.One channel is like a EVH 5150 and the other is like a Fender Bassman. The amp is working normally.

I built simple a 5V DC power supply powered from the heater supply. I have a 4700uf filter cap and a 7805 voltage regulator. This powers a relay. Everything works as expected except it introduces unacceptable hum into the circuit when powered up.

The relay is connected between the pre amp channels and the phase inverter.


Two questions.

Is there a better place to break the circuit?

Will I need to design a better system usings transistors?

Thanks,

Billy

Pre Amp drawing

 

[Enzo]

You did not include the rest of the circuit. Are your heaters center tapped and grounded the tap? Or a pair of resistors? Or elevated?

HOW did you derive the repaly supply from the 6vAC? I suspect that is the problem. Disconnect your 5v supply circuits from the amp. Tack a couple wires to the relay drive circuit, and use a 9v battery to click the relay back and forth. Now does it still hum?

 

[AquaTarkus]

I found it usually works better to get a separate small AC transformer and use that (rectified and smoothed) to power your channel switching system. You can take the transformer out of a cheap "wall wart" power supply.

BTW those two 470k resistors after the channel volume pots are probably going to kill off some of your high end. Not sure why you need them there.

Sent from my phone with Tapatalk. Please excuse any typpos.

 

[Planobilly]

Thanks Enzo,

I just got back to the project. The 6 volt AC from the transformer is connected to the DC rectifier then to the last tube. At that point I have two 100 ohm resistors going to ground. The connection may need to be made past the 100 ohm resistors....
I will do the testing you suggested.

Here is the rest of the schematic. Disregard the the power supply as it is not built like the schematic,

Perhaps this photo is better

Thanks AquaTarkus...actually I had in mind to use a separate transformer at some point. Perhaps something to produce 16V. I have not come to a final decision for other switching requirements and LED indicator lights. I will experiment with the 470K as I am looking at it now, I also am not sure why it is there.

Thanks,

Billy

Billy

 

[Planobilly]

Powering the relay with a battery solved the issue. I will power the relay with another transformer and get it off the heater circuit.

I have found a much bigger issue to solve. The audio signal is getting to the output tubes with the preamp circuit disconnected. I have to take the circuit board out of the amp and verify all the jumper wires on the bottom of the board. There is also the possibility/probability that something is coupling somewhere.

In the beginning I had two input jacks and did not notice the issue.

Fun stuff...lol

Thanks,

Billy