Crate V3112 issues, Grounding and hiss in clean channel

[nickb]

I really think you should fix the voltage you noticed as top priority. That should not be happening. Something is causing the leakage and it can only get worse. Using yourself as a current meter is probably not the smartest thing to do...

The very first thing to check is for wanted very low DC resistance from the earth pin of your power plug to the chassis.

[Jazz P Bass]

The voltage itself should be measurable.

The schematic shows that the jack is isolated by capacitors.
One of which has a 45Vdc source.

Either a capacitor is leaking or you 'felt' a brief voltage that was caught between the two caps.

[iefes]

Hey all, sorry I've been away for a while but I have been quite busy the last days.
Thanks again for all your help and your suggestions!

@G-One:
I tried your suggestion regarding the OD channel. I discovered that the OD channel seems to be noisy as well. The difference is that the OD channel in general is a lot less trebly, so the hiss noise gets a bit dampened but it is definetely there.

I didn't feel any voltage from the amp in the last day. But I thought about my setup when this occurred: I was running the amp and the DI-Box from different power points in my room. So my Amp and my pedalboard was connected to one power point and the DI-Box and the recording unit was powered by another power point in my room. I thought this shouldn't affect the result but maybe it did?

@nickb:
I checked the connection between earth of the power plug and chassis and there is 0 resistance.

@Jazz P Bass:
I didn't feel the voltage again and wasn't able to measure something since it happened. Which jack do you mean that is isolated by capacitors? So I could check it.


I tried some other things in the last days. First of all I bought some Deoxit and cleaned all tube sockets and pins and the Volume-Pot of the clean channel. Next thing I tried was pulling one preamp tube at a time. By doing so I discovered that the hiss isn't present when V2 is pulled but it is present when V1 or V3 is pulled. So it seems like V2 is the culprit. I changed it with another tube but it didn't help. I also ordered some almost brand new tubes which I will try the next days.
I read the article on geofex.com about noise in tube amps. There is mentioned that the cause of the hiss is located before the Volume pot if it is affected by the volume control. When I turn up the Volume pot the hiss gets louder so the cause of the hiss should be somewhere before the pot. This is in contrast to the fact that it got better when I pulled V2.
My idea about this was as follows: Without V2 plugged in there is no way for signal to pass through to V3 so this helped with the noise. But the cause of the noise is probably related to V1. In this article it is mentioned that plate resistors can get noisy. Do you think I should try to swap it?

So, it seems like I can locate the issue somewhere between the Input and the volume control. There is just V1A as V1B just affects the OD channel. Additionally there are some resistors and caps. Do you have any idea which of these parts could cause the issue?

Or do you guys think my idea is wrong and the cause of the noise is located somewhere else?

Thanks a lot, next time I will try to answer more quickly! :-)

Edit: I forgot to mention that last time I played the amp there was some noise like crackling or "frying" but just rarely. And it was independent of the Volume. This might be a bad tube, right?

[nickb]

Hum - certainly using different sockets is likely to increase the area of the hum loop so it's best avoided. As an example, if I measure the AC current between )the earths of) two sockets on the opposite side of my workshop I used to get 26mA. I did some changes and got it down to 1mA.

Going back to the voltage you felt. Your amp sounds like it's correctly grounded so perhaps the problem is the DI box. Without the DI connected to the amp but powered up, measure the AC voltage between the DI ground and the amp chassis.

On the hiss, a certain amount is normal. Rather than pulling tubes since , as you have realized, that can break the signal path, try substituting one at a time. In any case you know the problem is, at least in part, before the volume control. That means only V1. It could well be it's plate resistor that is noisy.

[g1]

the hiss isn't present when V2 is pulled but it is present when V1 or V3 is pulled.

You need to verify that the tubes are physically laid out like you believe them to be from the schematic.
We are used to calling them out from left to right (viewing from front) but this is not always the case. What the schematic calls "J3" is the phase splitter. Pulling it should kill any hum from the preamp. I think what you called V2 may actually be J3.
You will have to verify by tracing the sockets and comparing to the schematic.

[Jazz P Bass]

Here is a block diagram from the OM.

V3112T_OM.pdf

And an amp pic.
V1 is at the input jack.

[iefes]

Hey again,

Thanks for the block diagram, this makes things a little easier to understand. I'm certain that V2 was the tube I pulled when the hiss disappeared. I checked on the PCB and the sockets are labelled with their corresponding description. On the picture provided by Jazz P Bass its from right to left V1-V3 (J1-J3).

I will take the PCB out when I have time and have a look at the solder joints around this stage. Maybe I will try to change the plate resistor.

[g1]

the hiss isn't present when V2 is pulled but it is present when V1 or V3 is pulled.

Can you verify that the hiss is still present when V3 is removed?
If so, the problem must be after V3 (J3).

[iefes]

Thank you G-One. I think I confused myself with all the testing last time. You are right, there is no more hiss present when J3 is pulled. The hiss gets a lot less when just J2 is pulled and stays the same when J1 is pulled. In the clean channel it's volume is adjustable when J1 is pulled but not when J2 is pulled. In the OD channel the hiss can be controlled with the OD volume pot (comes between J2 and the effects loop) when J1 is pulled and also when just J2 is pulled.

These observations confuse me as they don't suggest a certain loaction within the circuit. It seems like it's produced somewhere close to J1 but also J2 affects it. It's strange. Sorry for all the struggle, if you guys have more ideas, feel free to share them! Thanks!