WHY DO SOME AMPS "GHOST" MORE THAN OTHERS?

[RCGPNY1]

I had won a Marshall Super Lead 100watt RI some years ago. When I received it and cranked it up...it "ghosted" quite a bit. I don't beleive any of the original Super Leads I had(my first was a '71) ghosted at all..or so little I didnt notice. The reissue sounded like it had a ring modulator. I know the reissue is based on an earlier version, but I find the Ghosting annoying. Also can it be tamed in an amp that ghosts alot?

[Bob S]

Power string caps & resistors are a usual suspect.
I'd check the e-caps for drift first.

[joshdfrazier]

Hmmmm... What is "ghosting"?

[Reeltarded]

Its a note under the fundamental when the PS caps are worn out or a little to low a value.

[jelle]

Inability of power rail to decouple or filter sufficiently. Result is intermodulation distortion. Cause is too high ESR or bad grounds. Good luck.

[Stevem]

All plexy`s will pretty much oscilate due to wire layout they had if the volume is up high enough AND the presence it opened up enough.
Is this what you are hearing, or is it the unfiltered 120 hz power supply modulating your notes.
When you turn the presence down so that the amp has the least gain is the problem still there?

[RCGPNY1]

Actually...the amp I was currently thinking of wasn't a plexi, although I used it as an example. The particular Bruno UG30 I own ghosts at higher settings. It seems to be guitar/speaker dependant of course how much you hear it. As I understand the way the power supply is...is one of the reasons why it sounds so good at clean and on the brink tones. He claims it wouldnt sound as good to make the ghosting go away totally

[Reeltarded]

You might feel different than him.

Is it less than 50u mains? Strats hate too little on the mains and on the front pickup. A little more filtering can get you back the sustain by supressing that "almost an A".

[Leo_Gnardo]

What Jelle said. Boils down to insufficient filtering to keep the power supply charging peaks @ 120 Hz (in 60 Hz power line areas) or 100 Hz (in 50 Hz areas) from intermodulating with the signal when heavily overdriven. IF that's the "ghosting" you're talking about. It sounds like somebody's gargling along with your guitar especially if you're playing higher notes, say an octave or so up on the G and beyond. Grunting along, out of tune with your notes.

"Better" is subjective. If you're looking for an "authentic" gut bucket blues tone then you try to emulate the under-filtered power supplies that were in cheap amps of yore. I don't have any qualms about beefing up the hi voltage filtering for those who complain about the problem. Sometimes it can be fixed by increasing bias filtering too. Recently on a standard Fender Pro Reverb I was able to relieve the problem by adding a second bias filter cap across the range resistor - the one from the lowest voltage lug on the adjustment pot to ground. Background hum went silent, and gargling diminished to the point of acceptability, all for the cost of a 4.7 uF 50V cap. Pennies. Sometimes uncommon solutions work. And in amps with tube rectifiers you really are limited as to how much capacitance you can install on the primary B+ filter without distressing the rectifier tube, so other solutions must be sought.

Older Marshalls, where the bias supply ground is wired to the "bus wire" across the back of the pots, often have a hum that won't go away. Moving the grounding point to the same as the first or second hi V stage does away with this. Odd how they double-filter the bias, then dump the noise into the audio ground. Now that's not cricket. It can be fixed in just a minute with a piece of wire. Except for those who must have the authentic hum along with their notes. It takes all kinds...

[Roe]

usually ghosting in plexis has to do with:
- poor grounding scheme, including ground loop at pots
- weak filter caps on mains and screens
- underrated choke (not often)
Output tubes can also make a difference. sometimes one pair will ghost more than another

[Littlewyan]

If it has LCR Caps then that could be your problem, they aren't as good as say F and T Capacitors. Reason being they use an etching process for the capacitors to make them smaller (like Taiwan Made Capacitors), at low voltage that's fine you'll get the correct capacitance, however at a higher voltage you most likely won't. I also believe this is a very common issue with any 100w Marshall probably because of the increased PS filtering required, not heard of it being an issue on the 50W. Also the 100W uses capacitors in series.

Could be that with some amps you're lucky with the capacitors or you have a set of Output Valves that don't suck as much current so the amp isn't as affected. Easiest and cheapest thing to check first would be the grounding scheme and the soldering for the ground points. Or if you have another set of Output Valves it'd be good to try them.

Although like Leo said 'better' is a very subjective thing, some people actually like to lower the PS filtering in Amps to try and get a certain sound.