Problem with this fizzy sound

[pdf64]

If the the gain is turned up very high / max, then the 220k would put more loading on to the preceding circuit, and would probably act to roll off some bass, especially if the tone stack was switched out (boost switch?).
If you leave normally the tone controls switched in then I wouldn't bother (to replace the 1M with 220k), as there's a bass control.
I thought of this thread yesterday with my band, as my guitar tone has developed a nasty fizz as the note decays!
So take no notice of me.
Pete.

[J M Fahey]

Agree with the above post.
What I hear in your MP3 is a very nice clean sound, with a very weak background fizzyness, which anyway bothers because itīs ugly, but even more because itīs "fixed volume", meaning itīs relatively loud at lower volumes and gets swamped at higher levels.
I *think* itīs a layout (maybe even grounding or grounding path) problem.
"Something" crunches at an earlier stage, as I said .
Part of thas sound gets to the Power Tubes grids (and so gets amplified and heard) by parasite capacitance/parallel track inductive coupling/poor choice of grounding points.
Usually the higher frequency component gets through: ugly mosquito buzz.
Maybe if you listen to the "full", somewhat distorted signal itīs not even noticeable, but pass it through a treble heavy filter (the parasite capacitance) and the ugliest part gets through.
Bad news, itīs a PCB amp (I think), not much you can do.
If it were PTP or eyelet/turret built, you might move some wires here and there and solve it.
And certainly, for this kind of pesky problems you *need* a scope.
Maybe someday in the fiture.
For now, I would just live with that problem until equipped to tackle it.
Good luck.

PS: we are talking a low level feed-through buzz here, possible under any PI type used.
Cathodynes have their own problems, but I guess theyīll appear at higher drive levels.
This seems more f a preamp issue.
Or to be more precise: a PCB layout one.
May be wrong, of course.

[Chuck H]

This amp has a post PI master. So if the annoying crackle is of one fixed volume it's somehow injecting directly into the power tube grids. That, to my thinking, only leaves the ground scheme.

I'm actually thinking that the noise is just more apparent at lower volumes. And I still think it's a result of operating conditions in the preamp. I might try raising the preamp voltages, reducing the preamp plate loads a little and maybe changing the preamp cathode bias resistors to a slightly lower value.

[wokkel]

Hi all,

first post.

With great interest I follow this thread. I have a Lil' Night Train and this 2-watt version suffers from the same note decay problem.
As the LNT has, AFAIK, an 12AU7 in self-split mode as powertube. The preamp is different from its bigger brother in that there is no mid pot.
I have no idea how similar the layout and components are. But the note decay fizz is there

On other forums I read about a mod for the LNT that could take away some high end fizz: snipping C19.
C19 is a ceramic disk marked with 101 K. Its position is between the middle lug of the Gain pot and the Bright/Thick switch. (I.e. the same location as C19 on the
NT15 schematic (?)).
Snipping this one did not help. I was fairly disappointed, because other people really liked this mod. The note decay was not helped. And the amp got more prone to interference: I had more crackle on top of the notes. I soldered it back...

One more remark: since I have my LNT and the note decay, I have been listening more closely to my other overdrive generators:
- a D-type amp, the 44 watt D'Lite
- a zendrive copy
- a Wampler Plextortion
Though the LNT is the clear winner, all other overdrive sources have this in differing amounts.
Sometimes I fear that the LNT made me aware of an overdrive characteristic that is just there.

Harald

[Chuck H]

Sometimes I fear that the LNT made me aware of an overdrive characteristic that is just there.

Harald

Not every OD device or amp does this. It may be a really unfortunate coincidence that you have three that do. It ma also have something to do with the tpe of pickups your using in combination with devices that are prone to this problem.

[Lupinsansei]

Hello - thanks for your persistence

I also have the Lil' Night Train and it is infected with the same problem... I have swapped the tubes with a significant variety of different brands and types. The effect on tone is quite noticeable, but the 'note decay' is always present as soon as I turn up the gain. Yesterday, I removed the power tube (12AU7) and put in an ECC81. The clean tone sounded even better with the ECC81 but the awful buzz was more apparent. The buzz did not change, it just became relatively louder in the 'mix' - as if it had it's own channel in a mix and only it was increased. Oh, I also clipped C19 as well - no benefit whatsoever. Thankfully, even after clipping the cap, I am still not picking up the radio station that I was when I had the original tubes installed (I am in a relatively remote area of northern Japan and there are exactly 2 radio stations that I can hardly pick up with a receiver designed for the task...)

When I maximize the gain, I also get a strong phasing sound.

I have heard this noise in other amps and, frankly, it sounds like crap wherever I've heard it. I have an Egnater Rebel 30 that has none of this sound whatsoever, so I don't think it is just an unavoidable overdrive/distortion artifact.

Unfortunately, I know nothing of electronics and amp design. I know what caps, resistors, transformers, etc. are and I can operate a soldering iron - but that is about it. However, If someone is willing to hold my hand, I am willing to experiment. Sans this problem, this amp has a great sound, and as it is fairly popular, I imagine that any useful remedy will be appreciated by many.

[sickman82]

I ordered the bits needed to do the mods today. They're coming from Banzai Music in Germany, so it may not be until the end of the week before I can do anything. Looking forward to carrying out the mods and seeing the results now.

I've had a bit of time now with the PI valve. The JJ 12AT7 does help quite a bit with the problem I was experiencing with high gain pedals. I'd recommend that if anybody has the same problem (blocking distortion/cutting out) with using high gain fuzz/overdrive pedals with the NT, get a 12AT7 for V4.

[Silvio55]

Well after some time I have some news! I got the resistors three days ago and this weekend I had some time and started doing the mods.
I replaced:
R1 470ohm
R17 2.2k
R16 2.2k
R13 2.2k
R9 100k
R26 100k
and added a 10K gridstopper on V3A, so far these are the mods Iīve done. Well the sound changed a little, not that much, maybe a little less of that chimey voxy sound(or maybe itīs just me), but sounds real good, in bright mode it didīt loose any gain, maybe a hair more gain than before, but in thick mode it seems to have lost some gain (not a real problem for me). How about the infamous "fizz"?......mmmmmm itīs still there, just as always, maybe it really is layout problem (or maybe other mods could be tried ) What do you guys think?

[Chuck H]

How about the infamous "fizz"?......mmmmmm itīs still there, just as always

Grrrr...

[sickman82]

Damn. I thought we had it cracked.

My parts still haven't arrived.. My order was on back order for a week, and then the Deutsche post shipped my order to the USA! I'm not so bothered about receiving it now though.

I have been sending emails back and forth with the guy who did that list of mods I posted though. He is going to put together a demo for me, so I'll share it as soon as I get that. He basically made the NT as close to vintage Vox as he could, and altered voltages to match those of the 50's valve datasheets. He hasn't mentioned any fizz, but his mods are very extensive.. It would no longer sound like the NT if we followed his lead.

[Silvio55]

Grrrr...

And more Grrrrrrrrrrr!!!!

Damn. I thought we had it cracked.

Yes, let me say damn too

I donīt know, this amp sounds sweet but this fizz at lower volumes drives me crazy, maybe some day Iīll throw the pcb out of the window and make a handwired board for it, if I learn how to desing a layout.

[Jazz P Bass]

zhere is the opening statement from this 160 layer post.
"Hello! I have a vox nigh train 15, and have found this fizz as note decay when you play with the gain set at the point of breakup, (letīs say between 11 oīclock and 1 oīclock in bright mode) itīs not there when you play clean and when overdriven it becames a part of the sound so itīs not that noticeable."
When (I am not reading 160 posts, sorry) did the problem change from "at the point of breakup" to "low volume fizz"?
Understand, I am curious.

[Silvio55]

zhere is the opening statement from this 160 layer post.
"Hello! I have a vox nigh train 15, and have found this fizz as note decay when you play with the gain set at the point of breakup, (letīs say between 11 oīclock and 1 oīclock in bright mode) itīs not there when you play clean and when overdriven it becames a part of the sound so itīs not that noticeable."
When (I am not reading 160 posts, sorry) did the problem change from "at the point of breakup" to "low volume fizz"?
Understand, I am curious.

No, it didnīt, one thing doesnīt exclude the other, the problem is at low volume (the MV set low) and the point of breakup is the gain set between 10 and 12 oīclock, if you put the gain higher the fizz is still there, just becomes a part of the sound (it doesnīt sound good either) but maybe less noticeable, if you set the MV higher it desappears.

EDIT: Me bad! youīre right Jazz, I didnīt mention the low volume thing in the first post!!

[Jazz P Bass]

So what does "Between 10 & 12 o'clock" mean?
On a scale of 1-10.

[Silvio55]

So what does "Between 10 & 12 o'clock" mean?
On a scale of 1-10.

Between 3.5 and 5 (the NT doesnīt have a numbered scale from 0 to 10). Imagine the knob like a watch, 12 oīclock would be the knob pointing up, or just in the middle.