First build crackle n pop.. benson monarch.

[johnnyreece]

The cause of the hiss may also be the presence of all those CC resistors in the signal path, as well. As was mentioned, you may just want to live with it. It's not like you can hear that when you're playing, or anything.

[TUBEDUDE]

If you must use CC resistors you will have more noise. If it becomes annoying, remember they are hygroscopic (absorb moisture). Leaving it on for a few hours to
cook out the water could help.
If not, replace the plate resistors with metal films. That is if you're not stuck on CC voodoo, i mean mojo.
Using metal films in the signal path, and reducing the value of Rg on your first triode will reduce your noise.

[unknowntome]

UPDATE: the crackle and pop has disappeared!! Amazing… I changed the 100k load resistor and that was it! All that’s left is a ‘shhhhhhhhhh’ white noise that I think I can tolerate although would love to be able to reduce it if possible… any ideas?? thank you so much for your help

Pull tubes one at a time like you did for the crackle pop. See if you can identify the source of the white noise. There may be another plate load resistor to replace. Or it may require using 1W plate load resistors. Or maybe something else. White noise can be more difficult to find and cure. You may want to just live with it.

So I just ran the experiment.

Pulled out V3 - shhhh persisted. Reinstalled.
Pulled out V2 - shhhh stopped. Reinstalled.
Pulled out V1 - shhhh stopped. Reinstalled.

Is there a specific plate load resistor I should be looking at next? I’ve got 1W carbon film resistors ready to go.

[unknowntome]

If you must use CC resistors you will have more noise. If it becomes annoying, remember they are hygroscopic (absorb moisture). Leaving it on for a few hours to
cook out the water could help.
If not, replace the plate resistors with metal films. That is if you're not stuck on CC voodoo, i mean mojo.
Using metal films in the signal path, and reducing the value of Rg on your first triode will reduce your noise.

Hey tubedude.. thanks for chiming in.. by Rg you’re referring to the 68k grid stopper resistor connected to V1? If so, is there a particular value you would recommend? Would changing from CC to CF (same value) help?
Cheers

[Colossal]

by Rg you’re referring to the 68k grid stopper resistor connected to V1?

The 1M to ground on the input jack and the 68k grid stopper resistor should ideally be metal film for the lowest noise. What goes in, gets louder and those two are of critical importance. If you can reduce that 68k to 33k (or lower), all the better.

[unknowntome]

by Rg you’re referring to the 68k grid stopper resistor connected to V1?

The 1M to ground on the input jack and the 68k grid stopper resistor should ideally be metal film for the lowest noise. What goes in, gets louder and those two are of critical importance. If you can reduce that 68k to 33k (or lower), all the better.

Thanks colossal! I think I’ll give these suggestions a go first before attempting to change plate resistors.. hopefully these two modifications make enough of a difference! I’ll report back..

[Phil_S]

Pulled out V3 - shhhh persisted. Reinstalled.
Pulled out V2 - shhhh stopped. Reinstalled.
Pulled out V1 - shhhh stopped. Reinstalled.

Is there a specific plate load resistor I should be looking at next? I’ve got 1W carbon film resistors ready to go.

Yes, the 56K on the first triode of V1. As Colossal says, it could be the 1M and 68K on the input jack. Change them one at a time.

[TUBEDUDE]

I'd replace the 68k with a 10k MF and install a small cap (10-100pF) from grid to ground. That will help with potential ultrasonic oscillations. The grid resistors Johnson noise is the dominant noise source. So lowering the value and getting carbon out of there will be the most effective strategy to reduce the noise.

[unknowntome]

Pulled out V3 - shhhh persisted. Reinstalled.
Pulled out V2 - shhhh stopped. Reinstalled.
Pulled out V1 - shhhh stopped. Reinstalled.

Is there a specific plate load resistor I should be looking at next? I’ve got 1W carbon film resistors ready to go.

Yes, the 56K on the first triode of V1. As Colossal says, it could be the 1M and 68K on the input jack. Change them one at a time.

UPDATE:

Ok, so I’ve changed the 1m with a 1W CF, the 68k with a 33k 1W CF, and the 56k with a 1W CF without luck.

Should I change the 10k load resistor on V1..? Or the 100k load resistors on V2? The attachment which shows another build has used CF in place of all of those as well as the 470k …

[Stevem]

You may just be hearing what is normal with any tube and it’s called shot noise.

Preamp tubes due to there potential large level of gain have more of this.

This sounds like faint little rain drops on a tin roof and is the sound of the electrons emitted from the tubes Cathode hitting the plate.

Unfortunately the stronger the tube is the more of this you will have.

If your going to drop those 68k resistors down a bunch smaller then add that cap mod so the first gain stage does not pick up radio stations and stray CB radio transmissions.

Years ago a buddy in the band I was in build a amp and he used it on the first gig the band played and loved it top to bottom.
On our second gig the bar we where at was 1/3 mile away from a radio broadcast tower and his amp was picking up its signal to the point that we could not even start to play until he raced home and got his old amp!

[unknowntome]

You may just be hearing what is normal with any tube and it’s called shot noise.

Preamp tubes due to there potential large level of gain have more of this.

This sounds like faint little rain drops on a tin roof and is the sound of the electrons emitted from the tubes Cathode hitting the plate.

Unfortunately the stronger the tube is the more of this you will have.

If your going to drop those 68k resistors down a bunch smaller then add that cap mod so the first gain stage does not pick up radio stations and stray CB radio transmissions.

Years ago a buddy in the band I was in build a amp and he used it on the first gig the band played and loved it top to bottom.
On our second gig the bar we where at was 1/3 mile away from a radio broadcast tower and his amp was picking up its signal to the point that we could not even start to play until he raced home and got his old amp!

Haha.. I’m not quite at the point of tuning in local community radio..!

There’s definitely more ‘shhhhh’ compared to my Marshall bluesbreaker and fender blues Deville (aside from the shhh it’s really quiet.. no hum or anything.. ).

The cap mod is a cap from pin 7 to ground?

Also, I’m wondering whether it’s worth changing all the plate resistors like the image above?

[unknowntome]

Another update: I've changed both the 100k V2 plate resistors from CC to CF.. I've also replaced a few wires with shielded wires (from the volume and tone pots)... neither of these changed the nature of the SHHHHH sound. I should add the the volume of the SHHHHH is only affected by the internal Phase inverter pot.. turning out down (CCW) almost gets rid of it completely and turning it the other way increases its volume... does this provide any clues??

[Stevem]

Your barking up the wrong tree by trying to cure a hiss issue with sheilded wire!

Your menipulation of the PI section is simply killing of some hiss due to phase canceling, which is by far not the right way to deal with it!

[pdf64]

…
So I just ran the experiment.

Pulled out V3 - shhhh persisted. Reinstalled.
Pulled out V2 - shhhh stopped. Reinstalled.
Pulled out V1 - shhhh stopped. Reinstalled.
…

It may be helpful to clarify that V3 looks to be the reverb circuit, rather than the phase splitter, which is not what might usually be inferred from the terminology.

[unknowntome]

Your barking up the wrong tree by trying to cure a hiss issue with sheilded wire!

Your menipulation of the PI section is simply killing of some hiss due to phase canceling, which is by far not the right way to deal with it!

I think I’m running out of trees to bark up at! i read it in some other thread and thought I’d try my luck. Any other suggestions..?

Again, the nature of the shhhhh isn’t impacted by anything else.. not by the tone knob or switch not by the volume. Doesn’t change when I chop stick the wires around..

It’s a 10k pot and I’ve got it sitting at 3k which is the beginning of the point where the shhhhh start to be more noticeable .. I think the consensus on the benson monarch thread is somewhere between 4 and 5.