JTM 45/100 build, pics, clips and some questions on ghosting

[VintageCharlie]

Hi guys!

I finally cut together some bits to showcase the ghosting issues. In between are a couple of (SLOPPY!) riffs to give an idea of how the amp sounds.
Sorry, it's a bit long - a "showcase" of the ghosting starts at 2:30. Here the amp was dimed: Bright channel Hi input V: 10, P: 6, B: 0, M: 10, T: 7
On the second clip the EQ is set the same, but volume is at 3 or 3.5 - i can hear some minor ghosting from over 2 on the hi input volume.
If i increase the bass or if i go into the normal channel the ghosting increases a bit. It doesn't increase much when increasing the volume however.

At some spots i turn the volume down and you almost couldn't notice that the amp is on even though it's dimed, when turning up the volume, even humbucker's (potted) background hiss is much louder than the amps noise - despite the economy lamps, the computer i'm sitting right next to, etc. I suppose all this MIGHT be an indication for really good grounding? Or is there still a chance that the ghosting might be grounding related, even if the amp is aalmost dead-silent?

With a Les Paul i can't get out these oscilating squeals when putting the guitar right next to the head, but i can make that happen with a strat, if i stand at a certain spot (this can happen when the volume and mids are dimed and treble/presence are set rather high. But if that's nothing unusual, then that doesn't bother me at all.

Yes, the head case has an aluminum plate at the bottom - so that shouldn't be the cause.

[VintageCharlie]

2nd clip with same settings, but volume on 3.5

[passfan]

Is the amp plugged into the same circuit with the lights and computer ? The last bit of the first recording when you ran scales sounded like an odd harmonic coming up behind you. Computers generate 5th ordered hash onto the power line. I would get as far away from that as possible.

[Structo]

Weird, if it only did it with the Strat I would say it was wolf tones from having the pickups too close.

It's almost like a third interval from the base note.

The tone is very nice except for the ghosting.

That would bug the crap out of me!

Can you diagram your grounding scheme?

Well start with the best guess which is the Erie.

[Lynxtrap]

Have you tried running it through other speakers? Just to rule out that possibility.

[VintageCharlie]

Thanks for the input guys!

No, the amp is on a separate contact (don't know if they are connected internally somewhere though). But either way, i have tried the amp in other places, without a computer nearby, no eco-lights, etc. - same thing.

This recording was done WITHOUT any speakers of any sort - it was a line out signal taken from my hot plate, which was set on "load" setting, the signal went directly into my soundcard and i applied an IR cab simulation (3 mics, which doesn't sound as good as one or two, but for this purpose i wanted more frequencies to come through, in case that might help spot the cause for the ghosting) + some room reverb. It probably has some effect on the amps tone, but the ghosting appeared also when i ran it through real speakers. To eliminate the possibility of the hot plate being the cause for this (i have to use it as my 4x12 cab has only 2x 30w speakers in it at the moment), i ran it with 2 tubes and without the attenuator: same result in regard to the ghosting.

In regard to the wolfetones - that shouldn't be the cause - i was about 4-5 meters away from the head and there was no sound coming out of the speakers.

I will probably open it up and talk to the guy who built it at the end of december and will go through the easiest possible causes first and then proceed to others - just wanted to gather some tips and info beforehand. If the easiest solutions won't help, we will do a grounding scheme and pics under the boards, etc. Though, the scheme that was used is what they call "Larry-Grounding" at the Metro forum - which is a multiple star grounding scheme that Larry (a pro builder) uses in his amps and which he had explained into detail for the application in Marshall circuits on the forum.


And it is bugging the crap out of me! Especially because i love the tone of this beast - without the ghosts it would be exactly the Marshall tone i had hoped to get from this build.

Btw. is the amount of breakup that i get with a les paul at 3-3.5 on the Hi Bright volume normal (you can hear that in the second clip)? (though the mids are dimed and treble/presence are at about 14:00, which boosts it even earlier into breakup).

[VintageCharlie]

p.s. thank you very much for all the tips guys! I really appreciate it.

And one more thing i wanted to add about the amp - it sounds quite a bit cleaner and more open live through the real cab. When either miced up close through my sm57 or ran through a cab sim, the breakup and compression become far more audible. I like it in both situations - to me it was a new revelation though, as i didn't have almost any experience with recording.
The only way to capture a halfway convincing reflection of the amps real tone would be by a room-mic, or at least by mcing it up further away, but my attempts at that haven't been very successfull, as that is much more complicated than getting a decent close-miked tone + the amp is in an attic, in a room that is kind of triangle-shaped, which i don't suppose is good for the room sound.

[John_P_WI]

In regard to the wolfetones - that shouldn't be the cause - i was about 4-5 meters away from the head and there was no sound coming out of the speakers.

What Tom - Structo- was referring to is a problem that happens when single coil pickups are adjusted too close to the strings.

Maybe try backing off the pickup a little.

Good luck.

[VintageCharlie]

oh, ok, thanks for clearing that up for me. I knew of Wolftones only in connection to resonances in the guitar wood.
Nah, that's not the issue - i don't plan to stand with a strat 1m away from a cranked 100w Marshall with cranked presence and treble Actually, the pickups on it are already very low, as i prefer the tone this way

[Reeltarded]

It HAS to be the filtering. It's not an unworkable number, the part is bad. Gotta be.

Nice amp! (btw)

[VintageCharlie]

Thanks! I hope you're right - that would be the easiest thing to fix - checking lead dress and grounding would be a pain in comparison (= the boards have to be taken off and for that quite a few solder joints have to be lifted). May i ask, why you are so confident that the ghosting is caused by a filter cap - anything in the behaviour or the point where it starts, etc.? Would like to learn something about troubleshooting such things.

[pdf64]

Decreasing henries might reduce ghosting

No, decreasing the choke inductance value would lead to an increased tendancy to ghosting (ie 120Hz modulation).
3H should be sufficient though.
The filter caps are likely suspects, maybe a new one has high esr?
Suggest each power supply filter cap is bridged in turn by a known good one.
Pete.

[VintageCharlie]

Sorry, i actually meant increasing the henries But that would have a similar effect as adding more filtering - it would become stiffer, right?

If a faulty filter cap causes ghosting, what spec about the cap is the one that actually causes the ghosting? Does it have something to do with ESR?
All of the caps were tested for ESR and they all were good, including the old one - btw. the ESR ratings of the nos Erie and the new RIFAS were almost identical.

[overtone]

Hi Karlis,

I like the core amp sound and it is a great build. To see this passion for detail is quite compelling. Re. ghosting: I'm really not familiar with the circuit, but my first guess would also be filtering. A few things cross my mind so I will throw them out to the forum:

1. why does the circuit not have, what I call "balancing", resistors in parallel with the series mounted reservoir and filter caps? Could that freak the Rifas out?

2. the filtering currently is 33uf > 3H > 16uF right? You could try increasing the filtering value slowly in stages to see if it helps and go from there.

Maybe a combination of both, anybody have any thoughts?

Best, tony

[bluesfendermanblues]

Had a similar issue with an old Laney 100w from 1972. Its the same circuit. The original PSU caps had dried out. Changing them with new ones solved the issue.

So either your Rifa's are to old - could have been in stock for years before your bought them - or the are defect. Try four new ones and you'll be fine.

You might consider FT's or TAD's