Problem with this fizzy sound

[Chuck H]

If the input reads 220/230 volts I have to assume it's ratio is set for 225V. So, assuming 6.3V on the filaments with 225V in, if you actually have 210V input your filaments should measure 5.88V. Even if your PT primary is 240V, with 210V input your filaments should have 5.5V Not 5V to 5.1V Something's fishy.

Did you have your meter set to read high voltage when you measured the filaments?

Just for laughs, set your meter to read lower voltage and re-check. Also, check the filament voltage on the power tubes. hey're AC do you need to reset the meter.

EDIT: Looking at the schematic I see that the filamens are supposed to be at 6V. So, assuming 6V at 240V input you should get 5.25V on the filaments. That seems pretty close to a nominal voltage your reading!?!

What to do??? Not sure. The filaments are DC now (though I'm a little confused by the "X" termination for the filaments on one triode of each preamp tube.) There's a TON of filtering (about 10,000uf!). The diodes drop a little voltage. Just not much to do to get that voltage back up short of adding a filament transformer.

[Silvio55]

I checked the voltages of the filaments today and at 222 volts I got 5.5 volts AC at the power tubes and 5.80 volts DC at preamp tubes. The voltages I got earlier were all AC. Donīt know why I get higher DC voltages than AC. The AC voltages were measured at the two conectors labeled TAG 13 and TAG 14 and rechecked at pins 4 and 5 at the power tubes, the DC rectified were measured at pins 4 5 and 9, first between pin 4 and ground, pin 5 and ground (I got half the voltage that way) and then between pin 9 and 4, and pin 9 and 5 (where I got the 5,80 volts).

[pdf64]

Check for any Vac across the heater fuse FS2 clips and try re-seating it a few times.

[Silvio55]

Check for any Vac across the heater fuse FS2 clips and try re-seating it a few times.

I did that but I still get the same readings. Maybe itīs just my meter, it doesnīt have a setting for lower voltages in AC and perhaps itīs not that accurate in that range. The DC voltages seem ok, not very low, I think 5.5volts shouldnīt bring any problem.
Iīm believing that the voltages are not the cause of the fizzyness, I tried the amp today with the wall voltage at 230 and itīs still the same.

[Chuck H]

I'm thinking you have what amounts to a 240V primary that is blanket allocated for service by the manufacturer. This is a particular problem in your case where voltages may run as low as 210 volts regularly. Perhaps a Variac type transformer capable of lowering and raising voltages is needed in your case no matter what commercial amp you want to use. But it does seem particularly bad with this model due to the "universal" primary allocation. And though I don't think it's related to the OP topic issue I do know that I've heard amps with low filament voltages and they sounded bad. Sort of grubby and undefined. Like not all the sonic info was getting through.

[Silvio55]

Yes Chuck, it should have a 220V primary transformer instead of a 240V, but having played the amp at 230V I didnīt noticed much difference in the sound, and as you said, the voltage is probably not the cause of the fizzynes al low volume.

[Deltones]

that p.i. stage needs a complete redesign to get rid of the fizziness problem...

or you just need to turn up your master.

I just registered to this forum because I bought my Night Train a week ago have exactly the same problem as the OP and was trying to find out more about it. This response by diagrammatiks grabbed me so I will add that I run my Night Train via a Two Notes Torpedo VB-101, no cab proper. So basically, I run the NT at full on the Master volume and basically get the amount of clean/dirt volume I want via the gain knob for direct recording. The trail of fizz displayed in the OP's clip is there, even with the MV at max and the gain knob below 9 o'clock.

Hopefully, this will give you some more indications as to where the problem may or may not be. I love the sound I get with the Night Train, but that trail of fizz is definitely a mood and recording killer on cleans.

[Chuck H]

I run my Night Train via a Two Notes Torpedo VB-101, no cab proper

What are you using for a load?!? You can't just run a tube amp output into a typical high Z input safely.

[Deltones]

What are you using for a load?!? You can't just run a tube amp output into a typical high Z input safely.

The Torpedo VB-101 is a load box as well as a cab simulator for direct recordings.

[Silvio55]

The Torpedo VB-101 is a load box as well as a cab simulator for direct recordings.

I thought it was just a plugin for recording software!
Thatīs interesting because with a cab, and the master full up I canīt hear the fizz, but thereīs another issue with the master full up, I think itīs crossover disrtotion and sounds like this

http://www.unimind.us/fizz1.mp3

http://snowboardmaterials.com/tmb_fizzz.mp3

The first one is an EL84 plexi (plexi brown), playing palm mutes, the second is an 18 watter, and itīs the same with the night train, but the solution for this is clear: the "Paul Ruby mod" (as I have read because I didīt made this mod yet), or just put the master on 1 oīclock and donīt move it, īcause you get the fizz with lower volume and the crossover distortion at higher volume.

[Deltones]

I thought it was just a plugin for recording software!
Thatīs interesting because with a cab, and the master full up I canīt hear the fizz, but thereīs another issue with the master full up, I think itīs crossover disrtotion and sounds like this

http://www.unimind.us/fizz1.mp3

http://snowboardmaterials.com/tmb_fizzz.mp3

The first one is an EL84 plexi (plexi brown), playing palm mutes, the second is an 18 watter, and itīs the same with the night train, but the solution for this is clear: the "Paul Ruby mod" (as I have read because I didīt made this mod yet), or just put the master on 1 oīclock and donīt move it, īcause you get the fizz with lower volume and the crossover distortion at higher volume.

They do have a plugin but it's another product than the VB-101. I listened to your clip and it's not the same thing I have. What I get is exactly as the OP posted. I'll try and post a short clip later today for reference.

Oh, and I did test it with my cab to make sure it was not some digital artifact and with MV full and gain below 9 o'clock, the trailing fizz was there.

[Chuck H]

I think that, even though my method was less than ideal, we narrowed the trailing fizz to the preamp. Raise those preamp voltages and reduce the plate load resistors and see what happens. I think I outlined it above. Three resistors.

I did consider that it could be parasitic oscillation. The NightTrain has a funky layout that places the output of the amp near the input. But with the master low there is no change to the problem (though it does become more audible). With the master set low the power amp leads and components aren't creating the same radiant fields as when the amp is set high so there should be a change. So I've concluded that the trailing fizz is due to the gain structure, bias conditions and voltages in the preamp. The down side is that there's no way to change this without altering the basic tone of the amp at least a little.

[Deltones]

Ok gents, short clip put together to show the same problem as the OP. First part is just guitar and amp, and I did a segment with a tremolo because it puts forward the problem a little bit more. Master volume dimed, gain knob at 9 o'clock and EQ knobs at noon.

Vox Night Train Trailing Fizz Problem by Deltones on SoundCloud - Create, record and share your sounds for free

Unfortunately, I know SFA about electronics so even if you guys manage to fix the problem, I probably won't be able to fix it myself, but hopefully, what I posted will help in resolving the problem.

[jmaf]

I think that is just how a vox night train amplifier sounds....

[Steve Conner]

I agree It's probably designed to have a dirty, treble boosted sound reminiscent of the AC30. If you use a guitar with overwound, dark sounding pickups, that can come across as fizzy.