sound while on standby?

[Lindz]

Chasing a few issues with my 18 watt kit. See my other post about 18 watt noob questions

Just noticed that 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 fade out after switching to standby like my other amps - but continuously at a very low volume as long as the power is on. Does it on both channels but is louder on the Normal channel -

I would assume there should be no signal getting through when on standby?

suggestions?

thanks!

[selloutrr]

path of least resistance.

somewhere you have a short or an improper solder point or part.

post some pics so we can look

if you have a layout / schematic compare them for errors. then trace all parts thru the circuit to proper connections.

is this your build or are you troubleshooting it for someone else? has it ever worked properly?

[Lindz]

These pics were posted in my other 18 watt noob questions thread but might as well not send people looking for them. It is a Ceriatone combo chassis that I bought mostly assembled. Finished it and fired it up a couple weeks ago and it seemed to be working OK though I did not really run it much before I started tinkering with it.

Found a thread at the Trinity amps site "brown plexi mods" and sort of went through my amp changing caps and resistors mimicking the layout they came up with. It was not until I really started cranking it up after those changes that I noticed a few issues, a lot of hiss on TMB channel (abnormal I think), a weird buzz trailing notes (when it is cranked) and now this sound while on standby issue. Possible they were there before, perhaps I introduced them - I did not even notice the sound on standby issue until today, as I had not been strumming my guitar while plugged in and on standby before. The really hissy TMB channel I did not notice that much until I was diming the amp - when I first fired it up I was playing it more quietly and the hiss was not as apparent

Very possible I messed up something layout wise, got something too hot, poor soldering etc. but as a newbie I am not sure where to start looking, hence my posts. The board was looking a bit more clean before but now is a mish mash of carbon comp, metal film, metal oxide and various caps etc as I have already been trying to quiet it down and chase my issues by changing various parts - but I am shooting in the dark

Any help would be much appreciated

Lindsay

[Lindz]

would it not have to be related to the standby switch or resistor/cap on it?

[Phil_S]

Show a picture of the switches, please.

[Structo]

You are much better off having those 68K grid stoppers right on the tube socket, less hiss and better performance.

Do you have a capacitor or resistor across the standby switch contacts?

[surfsup]

Yes my thoughts as well do you have a resistor across the standby switch? Your pictures omit the switches.

[Gaz]

If you are using a center-tap interrupt type standby, as well as series reservoir caps with the CT connection at their junction you will get exactly what you are describing. Here's a quick schem.

[labb]

The design for the 18 watt marshall has the standby switch in the B+ line just after the rectifier. It shuts off all power to the tubes except for the heaters. For you to get sound out of the amp with it on standby you have to be by passing the stand by switch some way. Un plug the amp and start checking for continuity across the switch. It can be high resistance. Your volt meter is your best friend.

The Ceriatone layout for his 18 watt shows a 0.047uf cap and a 100K resistor across the terminals of the standby switch..Most likely the problem is in one of these connection...I have built three versions of the Marshall 18 Watt and only used the standby switch, not switch with the cap and resistor. If you can't find a problem with one of these components I would just cut them out.

[surfsup]

There's some info on the R in parallel with the standby here if you want to read a bit:

http://www.freewebs.com/valvewizard1/standby.html

[labb]

and the schematics for the 18 watt marshal can be found at www.18watt.com

in the "downloads" section.

[Lindz]

thanks for all the input!

pic below of the standby switch in my amp

Ceriatone layout shows .047uF 630v cap, 100k 3w resistor - see scem and pic below.

If I understand surfsup's comment and link this "leakage" may be designed into the standby??

Quote from Valve wizard:

"However, if we are willing to forgo the complete muting facility we can instead redesign the standby switch for a 'soft start' to truly help extend component life (especially the rectifier, whether valve or solid state). If we arrange the switch to allow the anode current to increase very gradually at the same time as the heaters warm up, then both inrush surge and cathode poisoning can be completely avoided. This can be done simply by placing a resistor in parallel with the switch... Once the capacitors are fully charged and the valves warmed up the amp will remain on standby, allowing a trickle current to flow at all times (so the amp will not be totally muted; there may be the faintest of strangled sounds if we tried to play). "

If I am following things correctly then this may be normal because of the resistor used on the switch?? If so what is the purpose of the cap? dumb noob question... but it seemed odd that I can hear faint guitar on this amp while on standby and I thought it had to be some dumb mistake I had made while soldering or something

thanks again for all the input - I appreciate it and am learning a lot

Lindsay

[Structo]

There you are.
That is why you are getting signal when in standby.

[Reeltarded]

thanks for all the input!

If so what is the purpose of the cap?

Lindsay

Those switches have bald spots.

[Structo]

The cap helps prevent popping when switching.

That is a common circuit that Merlin recommends.

It does not mute the signal all the way.