master volume hiss

[cruzthree]

Hi 18 watt gurus.

New to the forum, as I recently acquired an 18w TMB build put together by someone else. The original owner said it never worked. I've gone through and cleaned up some solder joints etc and got the clean channel working great.

But the problem I'm having is that if the master volume is open even a little bit, there is a hissing noise that comes through the amp. I've changed tubes, but still happens. Only goes away if I pull out V2.

The layout is the ceriatone 18w tmb

20231021_162251.jpg

Appreciate any suggestions. Thanks in advance.

[JMPGuitars]

Hi,

Welcome to the site!

There's a LOT going on in that build that could contribute to noise. I'd suggest reading the threads in my signature, especially those about ground schemes and soldering. Watch the videos too.

The first thing I would do is replace the input 1M resistors, and the grid stopper resistors with quality metal film resistors. Then replace the input wires with shielded wire.

If that amp came into my shop, I would strip it and start it over. I hate seeing cloth wire in guitar amps (besides all the other problems). You may be able to get it at least working without going that far, but to me, it would be less work to redo it correctly.

Thanks,
Josh

[cruzthree]

Thanks Josh! I appreciate you taking the time to get back to me. I have been looking at those threads and searching the forums prior to making this post. I'll continue reviewing and looking at what I can learn from those excellent resources.

I'll try the upgraded resistors and shielded wire, but I thought all the cool amps had cloth- look plastic covered wire? What is recommended as replacement?

I did think about pulling this apart but then I was able to get the normal channel to work by fixing a few poor solder connections. It's fairly quiet, too (as long as the master volume is on 0).

The TMB channel works but, it's only when the master volume is turned up that the amp gets noisy. I can have it open at 1/2 and use the volume pot to get a good sound. So the only problem with the way it functions, at the moment, is that hiss when the master volume is turned up. I feel like I must be missing something.

Cheers

[JMPGuitars]

PVC or PTFE insulated wire; personally I prefer the PTFE. I only use cloth wire in guitars.

The ground scheme the amp has is a problem, and it's covered in my signature threads that I mentioned. There's still a lot of solder problems, also covered there.

You might get lucky, making some fixes may get it to a playable place. For now. Bad soldering could fail in the future though, and become a whole new set of problems.

If you decide to try and fix it, but get stumped after replacing those resistors and adding shielded wire, you should post a sample of the noise.

[Bieworm]

Recently started using high quality cloth wire at the tube socket side. I really like it for its positioning properties.

[JMPGuitars]

Recently started using high quality cloth wire at the tube socket side. I really like it for its positioning properties.

PTFE has excellent positioning, and isn't easy to burn or light on fire. There are some decent cloth wires out there, but I'm skeptical of anything I don't know the source of.

[cruzthree]

Here's a clip of the noise it's making now.

https://youtube.com/shorts/JKLccU0kjak? ... eXHOmJSVLn

I'll replace the suggested resistors see how I go.

[JMPGuitars]

Maybe the clip downplays the noise, but it wasn't terrible. It certainly could be as simple as resistor hiss. Report back after changing those resistors.

[cruzthree]

Hi 18 watt gurus!

For those following along, I changed the 22k resistor on pin 2 of v1 to a carbon film. There was maybe a little bit of an improvement. Putting a guitar signal through the TMB channel seems to make the static less, or at least less noticeable.

Here is a YouTube video after if yer interested: https://youtube.com/shorts/tvl7kw0x2pI? ... uPWcTHLuxy

Also, here's a video showing the normal channel works beautifully and dead quiet, so long as the master volume is off! https://youtube.com/shorts/7EgUAoFxv8Y? ... dLIvpfjUp4

[JMPGuitars]

A small improvement would be expected. I haven't checked out the videos yet, but here's the way noise goes:

Carbon Comp: Noisiest
Carbon Film: Less Noisy
Metal Film: Much Less Noisy, maybe even...quiet!

I would still switch all input resistors to metal film. Think of it this way: the greatest noise potential is coming from the inputs. The inputs go through every amplification stage. If you're starting with noise, you're amplifying noise. That's why it's essential for those to be metal film.

[cruzthree]

Hi Josh

Thanks again! I see why you're called super duper admin. Really appreciate your comments.

I couldn't get the metal film resistors in 1 watt size or sheilded wire, so I haven't tried those changes yet.
In Australia, we have Jaycar that carries a bunch of components but not specifically for amps. I can order online but it's nice to go into a bricks and mortar shops to pick up what you need.

I found a similar issue in a thread from a few years back. Looks like lot's of component changes with tiny incremental improvements added up to addressing the problem satisfactorily for the OP (post is here if interested viewtopic.php?t=25142 )

Cheers

[JMPGuitars]

Ah yes, you'll see they also improved their ground scheme. However, that thread was actually older than better practices. For example, I stopped using Switchcraft #12 jacks on amps. I only use isolated jacks now. The ground scheme thread is superior to the advice in that thread.

Okay, so you're limited on what's locally available, and that's okay. Those resistors don't need to be 1W. You can usually go higher wattage without issue. 1/2W MF is also fine for those input resistors as long as they're good quality. I would prefer to go to 2W vs 1/2W though.

[Bieworm]

Josh is right about the wattage. I have experienced the same once with a noisy PI. While I used metal film resistors they were still noisy. I had put 1/4 watt resistors for the lack of bigger ones. After putting 1W there the noise was gone. I believe the theory is due to the larger physical size that the electrons have more room to move and collide a lot less. Those collisions add to the noise. Correct me if I explain this incorrectly.
Also, that shielded wire is arbitrary. I use excess amounts of shielded wire throughout my amps to avoid unexpected noise just in case.