Signal bleed at Master Volume 0

[psychepool]

Recently I made a Bogner Ecstasy clone.
It is not a 1:1 clone, it is simplized by omitting some functions.

Even when the drive channel is set to master volume 0, the volume is leaking a little.
This leaking sound responds to several preamp knobs, such as the gain knob, EQ knob and other toggles.

In fact, the sound level is so small that it is not annoying at all even if the gain knob is set at 10, so it is not a problem for use.
However, I was asked if this symptom might reveal that there was a problem with other parts.

I switched to another volume pot that has same value, but there was no change.

For ground connection, the OT center and the output tube screen power supply cap were connected to the star ground point near the power transformer.
The power supply caps of the front stages (PI ~ preamp stages) were connected to the chassis around the input with the PI and preamp ground. (I used JJ 40/20/20/20 multicap)

I try to the ground of the multicap remove from the chassis and connect to the preamp end of the board (cathode follower or PI ground tap), nothing changed.

Please let me know what I should check.

[Stevem]

With an issue like that it's a sure bet that the amp will go into oscillation at high enough volume levels.

Build wise all of your grid wires should be shielded and grounded at only one end, with that grounded end landing at the gain stages Cathode resistor grounding location.

Also build wise all grid wires need to be as short in length as possible since they are like a high impedance antenna to gathering up other signals from down stream gain stages in the amp.
Basic good build rule of Thumb is short grid wires and to get where they need to go plate output wires to the next gain stage can be long if need be.

Also coupling caps have what can be called a input and output side to them.
In regards to most new caps if you hold them with the lettering on them facing you then the input side will be on the right, with the output on the left end.
Installing these coupling caps the right way will help shield the down stream grid of the next gain stage.

[psychepool]

Here's some pictures of my build.

01.jpg

02.jpg

Although it may be difficult to identify clearly because it was built in a small space, all of the point you mentioned (wire to pin 2, 7, wire from coupling cap out, wire 2, and pin 3 of Gain and MVpots) used shield cables.

The shield was came out from only one side and connected to the preamp ground line, and is connected where each stage cathode resistance is installed.

The shield connected to the pot connected to the pin 1 of each pot. The wire connected to pin 1 is also connected to the ground line corresponding to the stage.
While all of the shields are connected to the recommended points, but does the wrong shield wiring point makes this matter?

And it's the first time I've heard that the coupling cap has a direction.

I checked the picture again and it happened that they were all mounted in the same direction.

Is the current state in the right direction?
All coupling caps are a Mallory 150 series.
The upper direction of the picture connected to the plate, and the lower side is the signal out.

It seems that the content you mentioned is almost applied.

Is it a problem that the shield cables are concentrated?
As a test, I removed all shields from the ground, but nothing changed.

Is there any other point to check other than the one mentioned?

[ChopSauce]

While reading this

... CTS seems to have a better "off" position, usually measuring close to 0 Ohms to ground while Alpha's (1MA's anyway) measure about 100R to ground fully CCW. No big deal unless a customer complains that they can still hear their guitar with the volume turned off.

I remembered that issue. So, maybe you can measure the pot resistance when fully turned down (CCW)?

[Doug R.]

ChopSauce makes a good point. Does your amp sound good at stage levels...any issues that occur when played loud ? If you short the wiper to ground does the signal disappear ?

[psychepool]

I remembered that issue. So, maybe you can measure the pot resistance when fully turned down (CCW)?

Is it necessary to remove the pot from the amp to check if the resistance value is 0 when fully turned CCW?
In the short test, it is confirmed that pins 2 and 1 are shorting when fully turned CCW.

ChopSauce makes a good point. Does your amp sound good at stage levels...any issues that occur when played loud ? If you short the wiper to ground does the signal disappear ?

It is mentioned in the text, but there is no problem in using it. I haven't used it on the stage, but there is no problem in using it in a very quiet house.
However, since it is not normal, it may be a clue that the other part has a problem.



I did one test.

I changed the earth point.
Using the multi-cap with only one ground in the preamplifier section (40/20/20/20uF), I was wondering if the stage separation was not working properly.

I couldn't separate them anyway, so I thought about what if I just put all grounds together in one place.
Remove the preamp ground from the chassis near the input,
and solder a wire the other end of the preamp ground line,
along with the preamp filter cap ground, attached it to the ground of the power supply of the output tube screen and connected to the star ground.

Oh... the volume leak is disappeared.
However, it seems that some other problems have occurred.
There wasn't enough time to check what the problem was, but it seems like some hiss noise has been added.
And when the power is turned off, the discharge seems to be slow with a strange oscillation

I will check the status in more detail later in the day.