Noob Q's about 18 watt

[Lindz]

Is it normal on an 18 watt TMB (Ceriatone layout) that with a guitar plugged into normal input, adjusting the TMB master volume will affect hiss on that channel, and vice versa, when I am in the TMB input, dialing up the Normal volume will affect the noise? Not using a jumper cable, I am literally plugging into one or the other channel

Does not affect the volume but quite definitely affects the hiss.

I noticed this because my TMB channel is quite hissy when turned up, and if I plug into to the Normal channel it is also hissy unless I turn down the TMB master. To a lesser degree the normal channel volume seems to add or subtract hiss on the TMB channel as well.

Did I wire something incorrectly or is there some interaction normally?

Q2 - chasing hiss on the TMB channel. Amp is VERY hissy when I really crank it - My Marshall 2203 when dimed is less hissy than the TMB channel with the master at 3. Super hissy when I crank it up - not much hum. Sounds great, just very hissy.

I've read a lot, and tried some simple tube swaps, changing a few carbon comps in places to metal film or metal oxide but still very hissy.

Being a noob I am kind of shooting in the dark - any suggestions?

Amp is a combo layout. pics below. There was originally mostly 1/2 watt carbon comps throughout but I have been changing many one at a time to see if it quiets down.

thanks in advance for any help

Lindsay

[martin manning]

This is normal since boith channels are fed into and mixed by the phase inverter at all times. If noise is generated within either channel, it will show up at the output and its level will be determined by the volume control for that channel. My recent experience with new production is that you'll have to try several tubes to find a quiet one.

[Gaz]

well, one reason the 18 watt has more hiss than the 2203 is because it has no NFB, which significantly reduces hiss IME.

[plexitone]

Replacing carbon comp resistors with CF or MF early in the circuit of both channels will reduce hiss. There's not any benefit to having them before the first gain stage.

CC's for plate resistors can cause noise too.

[Zippy]

Did I wire something incorrectly or is there some interaction normally?

From what you describe, it seems your channels are active whether a guitar is plugged in or not. I don't see the schematic at Ceriatone - does your amp use shorting jacks that go to ground when not in use?

[Weathered]

Did I wire something incorrectly or is there some interaction normally?

From what you describe, it seems your channels are active whether a guitar is plugged in or not. I don't see the schematic at Ceriatone - does your amp use shorting jacks that go to ground when not in use?

They do, but any noise introduced after the input stage will still be bled into the PI if your volume is up on that channel, even if it isn't used.

[Travst]

Did I wire something incorrectly or is there some interaction normally?

From what you describe, it seems your channels are active whether a guitar is plugged in or not. I don't see the schematic at Ceriatone - does your amp use shorting jacks that go to ground when not in use?

You can grab Ritchie's TMB schematic at 18watt if you're so inclined. I don't know whether it's kosher to repost it here.

[Phil_S]

You might try 1W rated plate load resistors to calm the hiss. Not sure it will work, but it's worth trying. The underlying thought is that heat will have less effect on a 1-watter.

[Lindz]

Thanks for the replies.

Yes the amp is active when no guitar plugged in - hisses as more as you turn up the volume(s). In fact I noticed today that it feedbacks slightly on the TMB channel (shrill microphonic) if it is dimed even with no guitar which kind of surprised me. Any suggestions on what might cause this and a layman's explanation on how to possibly address it?

the normal channel is SO much quieter that I think there must be some issue in the TMB circuit introducing a bunch of noise. I can't see the TMB being literally 10x noisier than my 2203 or the normal channel JUST because it lacks negative feedback - sure that would contribute but it is REALLY hissy but my uneducated attempts at chasing it down are getting me nowhere fast.

As I said above, it would be great if those of you with some troubleshooting skill to suggest a few likely places to look, or components to change in order to try and quiet it down (remembering I am pretty green) I can solder but am still learning the electronics and theory, etc. so it is helpful if any replies are simplified and do not assume I know much about electronics. It is a good learning experience

there is an Ceriatone 18 watt TMB layout here. My amp has a few subtle cap and resistor changes to Plexi values though they do not seem to be the hiss culprits as far as I can determine-
http://ceriatone.com/images/layoutPic/m ... iatone.jpg

[Gaz]

The feedback your hearing is most likely a monophonic preamp tube that only acts up with enough gain.

I personally can't think of a wiring error that would cause hiss, but a bad part yes. So maybe you've got a bad resistor in the TMB channel. Here's a good summation of what causes hiss.

http://www.geofex.com/ampdbug/hiss.htm

[Lindz]

OK - so swapped a few preamp tubes and got rid of the feedback with no guitar plugged in. Thanks - does not seem to help the hiss at all though

However I noticed an odd thing when powering up to try the different tubes - when amp is on standby I can still hear what I play faintly through the speaker cab. Not just for a few seconds where it will continue as it fades out after switching to standby like my other amps - but continuously at a very low volume. Does it on both channels - its a bit louder if I plug into the normal channel, but does it on the TMB too.

I would assume there should be no signal? Bad resistor? Grounding? other?

More noob questions...

thanks!