Troubleshooting and solving signal noise on a 1989 JCM 800 2205

[Jquijano]

Tried several cables. I will do the swap test to see if it reduces this ac current noise.

[SoulFetish]

There is popular version of one of the 800 models that we get in on a regular basis. I apologize that I can't remember the exact one, but it's the one with the front panel red LED and uses the transistor array IC chip for the switching. I think it's the same as the model specified in this thread.
Anyway, the stock design suffers a noise problem that I believe is amplified and more audible in the overdrive setting. You can add additional filtering til you til you finally decide to send it on a Viking funeral, and it will not reduce the noise at all. The one way we have been able to drop the base level of noise significantly (particularly in the overdrive setting), is by limiting the current in the LED.
I'll try and find out what series resistor value we settle on as a compromise between noise and LED visibility. I'm pretty sure that what I'm describing above is audible once the amp is on and the tubes start conducting whether there is a guitar plugged in to the input, or not. I would tend to agree with the others that this problem sounds like a candidate for a bad preamp tube. You can try this if you have no spares. Turn the amp on with your guitar plugged in to the input. when you hear the noise, put it in standby; pull the V1 tube and take it out of standby. If the noise is still there, do the same thing with V2.
Or, swap V1 and V2. Some marshalls are sensitive in their V2 positions to noise depending on the tube installed.

[Jquijano]

Thanks. I do have some brand new mullard reissue ecc83 and could try with those ones and report. I would also like to mention that when i turn the amp off it draws some noise before it shuts off.

[pdf64]

Thanks. I do have some brand new mullard reissue ecc83 and could try with those ones and report. I would also like to mention that when i turn the amp off it draws some noise before it shuts off.

New shouldn't be equated to good, all valves need to be checked in a good amp.

So after the power is switched off, there's a second or 2 of the hum buzz, even if the guitar volume is turned down to 0?

[g1]

There is popular version of one of the 800 models that we get in on a regular basis. I apologize that I can't remember the exact one, but it's the one with the front panel red LED and uses the transistor array IC chip for the switching. I think it's the same as the model specified in this thread.

These are the 2205/2210/4210 like the schem. Tom posted in post #3. The early 80's versions had discrete transistors, but in the late 80's they went to the CA3046 array that you mentioned.
For the LED issue, can't you use something modern that is brighter at lower currents?

[Tom Phillips]

At this point in the discussion I think it would be beneficial if you could post an audio clip of the noise so that everyone can hear the exact noise that you are trying to eliminate.

[Jquijano]

New shouldn't be equated to good, all valves need to be checked in a good amp.

So after the power is switched off, there's a second or 2 of the hum buzz, even if the guitar volume is turned down to 0?

When i finish using the amp, i turn the stanby off and then the power off. When i shut the power off the amp generates a 2 to 3 second noise before shutting down.

[Jquijano]

At this point in the discussion I think it would be beneficial if you could post an audio clip of the noise so that everyone can hear the exact noise that you are trying to eliminate.

let me record a clip for you. Maybe this background noise is normal in this amp model.

[pdf64]

When i finish using the amp, i turn the stanby off and then the power off. When i shut the power off the amp generates a 2 to 3 second noise before shutting down.

How about if you forget about the standby switch and just turn the power off? ie does the noise stop immediately the switch is thrown?

[Grrrg]

let me record a clip for you. Maybe this background noise is normal in this amp model.

Well, you should know since you hat the amp for a few years. Was it always noisy or did that just start now?

[Jquijano]

Well, you should know since you hat the amp for a few years. Was it always noisy or did that just start now?

It always had that background noise which is more present in the overdrive channel.

[Tom Phillips]

It always had that background noise which is more present in the overdrive channel.

That statement on it's own could be considered normal for a JCM 800 2205. What is hard to know from a written discussion is the amplitude of the noise and if that level of noise is within the normal boundaries for a JCM 800 2205. One way to find out would be to compare your amp side-by-side with another stock JCM 800 2205. Can you do that in a music store or with a friend who has a JCM 800 2205?

[The Dude]

That is typical. More gain = more noise.

[Jquijano]

That statement on it's own could be considered normal for a JCM 800 2205. What is hard to know from a written discussion is the amplitude of the noise and if that level of noise is within the normal boundaries for a JCM 800 2205. One way to find out would be to compare your amp side-by-side with another stock JCM 800 2205. Can you do that in a music store or with a friend who has a JCM 800 2205?

I cant. Most people here are buying Friedman amps!