Problem with this fizzy sound

[diagrammatiks]

man so jealous about the two-note.

I kinda want one really bad.

If I'm reading Merlin's chapter on cathodynes correctly, it appears that there is always going to be a little fizzy/cross-over thing going on with a cathodyne unless it has a few changes to the design.

The thing is, if you put the master all the way up into a load box or a speaker and then turn the gain up, the PI is still going to distort when it gets enough input signal.

I'm gonna read that chapter again and look over that night train schematic.

[jmaf]

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.

Yeah, agree AC30 is an influence there. First few notes I heard I thought "this sounds like Tiny Terror"....

[sickman82]

Back to reality today! The festive season is over. I hope you guys had a good one.

This amp is nothing like an AC30 Both in design and tonality. It couldn't sound any more different if it tried! I agree with the treble boosted sound though, it has that vibe to it. However, the problem isn't in the nature of the tones that this amp produces. There is a distinct, 'fizzy', secondary decay to the note being played which, as we have narrowed down so far, is probably being produced by the preamp. With the master cranked, the breakup from the power section masks it. Now if I was designing an amp, and it produced this sound, I would see it as a problem.. Not part of the overall nature of the amp. But, that's just me.

I'm interested to see the results of Chuck's suggestions, so much so that I might go back on what I said and have a go this week. If anything, it will be part of a learning experience. I'll check back over the previous posts for exact details.

I had some new valves delivered today.. JJ EL84's, EHX ECC83's and a JJ ECC81. I'll let you know how they work out once I get chance to try them out. By the way, my 'mystery guy' never replied to my last email.

[Deltones]

However, the problem isn't in the nature of the tones that this amp produces. There is a distinct, 'fizzy', secondary decay to the note being played which, as we have narrowed down so far, is probably being produced by the preamp. With the master cranked, the breakup from the power section masks it.

No it doesn't. You'll hear the same trailing fizz with MV cranked in the clip I posted above, just in case you missed it.

[Silvio55]

Hi Sickman! It´s sad that you didn´t get response from your mistery guy.

No it doesn't. You'll hear the same trailing fizz with MV cranked in the clip I posted above, just in case you missed it.

That´s interesting, Sickman and I were experimenting the same fizz issue, but it became less noticeable with the MV up, not even close to your clip with the MV dimed, in fact I get that kind of fizz with the volume quite low. Maybe it has something to do with using a load box instead of a speaker.

[jmaf]

You'll hear the same trailing fizz with MV cranked in the clip I posted above, just in case you missed it.

If you could post a sample focused just on that fizz you mention it'd help immensely, even Chuck H who has carried the piano trying to help you out I just stepped in to say that sample sounds normal for that amp.

So unless I'm missing something, that sample seems like a normal Vox Night Train to me. You're not going to get a Twin tone out of one even if you got Keith Richards to play it.

PS. My speakers are not top notch, admitedly, so I don't know if you're referring to something subtle that I am not hearing, so apologies in advance if that's the case. I've listened to the sample twice more just to make sure, I don't hear what you're saying on these speakers at all.

[Silvio55]

If you could post a sample focused just on that fizz you mention it'd help immensely, even Chuck H who has carried the piano trying to help you out I just stepped in to say that sample sounds normal for that amp.

So unless I'm missing something, that sample seems like a normal Vox Night Train to me. You're not going to get a Twin tone out of one even if you got Keith Richards to play it.

PS. My speakers are not top notch, admitedly, so I don't know if you're referring to something subtle that I am not hearing, so apologies in advance if that's the case. I've listened to the sample twice more just to make sure, I don't hear what you're saying on these speakers at all.

I do think that´s how a normal night train sounds, all night trains sound like that, but that doesn´t mean it´s right, something is not OK with this amp, and I don´t mean it should sound like a 5000 dollars amp, it´s just that annoying fizzynes you get. I like how it sounds, but hate that fizzy sound.

[Deltones]

Maybe it has something to do with using a load box instead of a speaker.

That's why I did check the result with my cab with the same settings. That trailing fizz was still there. Unfortunately, as others have mentionned it seems that this trailing fizz is one of the characteristics of the Night Train and that the research you guys are doing to resolve the problem may change the basic tone of the amp, which would be a shame as it sounds good already.

So at this point, I have to ask the question. Would any recording engineer and/or producer accept this cameo appearance by Run DM Fizz on any recordings? In context with other instruments, my guess is that the trailing fizz would probably be masked. But in solo, evidently it would not be.

[Deltones]

Ok, Lucky 7 post. Having the Torpedo does permit me to test different settings of Master Volume without destroying my neighbours or my hearing. So, with the same settings I used previously i.e gain at 9 o'clock and EQ knobs at noon, I found a sweet spot where the trailing fizz is not exactly gone, but it's at least subdued enough so that I could go and record without having me tear my hair out. The bad news is that the Master Volume is still around 1:30, 2 o'clock so that probably is not a volume you'd go for casual practice at home with your cab. Take note that these settings only apply with my guitar and amp.

Re-introducing any pedal that boosts the signal does bring back the trailing fizz though, so basically, it's back to square one. This or rent a time machine to go back to the 50's and play only with a cable between your guitar and your amp.

[diagrammatiks]

gah every time I do analysis on one of these "modern" budget tube amps I'm left feeling so confused.

I'm convinced that no-one who actually knows tube theory had a hand in designing these things.

fender's hot rod deluxe is the worst in that regard. space ship worthy flyback protected, regulated, transistor driven relay network, textbook perfect op-amp circuits for the fx loop. tube signal circuit could have been drawn on toilet paper with a magic marker by a monkey.

[diagrammatiks]

Man they might as well have just biased this amp into class A saturation. I can't believe someone actually did AC analysis on the loadlines and thought it was ok.

Starting from the power section - 2 watt resistors at least
R1 470ohm
R17 2.2k
r16 2.2k
r13 2.2k

Signal path

R21 Jumper
R23 2.2k
r26 parallel with 100pf 400vdc+
There needs to be a grid stopper on v3a of at least 10k
r35 - parallel with 220pf remove or increase for more upper harmonic distortion
r10 2.2k
c10 .01uf 400vdc+


you can also
replace r30/r31 with 100k
r29 with 3.9k
r19 with 470k

[Chuck H]

Not to poo poo your great work, but...

Do all tube circuits need to be run at their optimum bias according to the load line? How can the SLO100 be such a respected design if that is the case??? I figure that WRT guitar amps we intentionally create working conditions that manipulate the particular distortions we think should be implemented.

That's a lot of changes you propose. Wouldn't even be the same amp. I'm pretty sure the guys (and gals) who buy the Vox Night Train did listen before buying. Some things other than the basic tone do come into evindence post purchase. That's why we're trying to squash the trailing ratty fizz without drastic alteration.

I'm beginning to think that you just really don't like this amp Have you seen chassis shots? You'll really like this amp when you see how it's layed out.

Stop trying to make the OP cry. No one wants to see that.

[Steve Conner]

What on earth is "Class A saturation"? It makes no sense, isn't the Night Train a single-ended amp, so every tube in the thing must operate in Class A.

In my experience, all distortion effects will have "trailing fizz" to some extent. You hear it when a stage that clips hard is just falling out of clipping. It's most noticeable in simple tube circuits that try to make a lot of gain in a few stages, or solid-state distortion effects like the Tube screamer series.

If you want to get rid of it, the best way is a high-gain Mesa or SLO type circuit that builds up the distortion gradually over several stages. There is no single hard clipping point and you get smooth sustain with hardly a hint of fizz.

If your guitar doesn't have much treble output, it makes the fizz seem worse, because there are no string harmonics to mask the electronic ones. When that fizz starts to bother me, I know it's time for new strings. Also, a metal guitar could have very high output and drive the amp into areas that the designer never explored (they probably test their creations with a standard issue Strat and Les Paul)

Anyway, my point is, there are classic amps and effects that have the fizzy distortion, and you can hear it on records. Maybe not metal ones.

[frus]

Anyway, my point is, there are classic amps and effects that have the fizzy distortion, and you can hear it on records. Maybe not metal ones.

that's true, listen to this:

Neil Young Down By The River - YouTube

the decaying chord at 7:01, sound familiar?

there are other places, for instance listen to the right hand guitar at 5:52, you can hear he strums the chord gently, trying not to enter the fizzy distortion, but you can still hear traces of it

anyway, I think I found the cause (at least one of them) for this kind of behavior on concertina-PI amps, I'll try to record a video that shows (on the scope) what's happening.

on the other hand, I use the attenuator quite a bit, and found that all amps (some more, some less) feature a kind of fizz described here, until you turn it up a bit and the speaker starts moving, then it masks most of it. my 5F4 clone seems to have an extra helping of fizz, though

[EFK]

I've been following this thread with a lot of interest. I've worked a lot on some Supro amps that had this problem as well as some of my own Supro-inspired builds; my own were modeled after some of the 'gain-ier' Supro circuits, and I've probably lost a lot of hair trying to track down this annoying fizz. Over the course of time, I have some to the conclusion that it usually is a convergence of a number of issues, not just one; in other words, I have yet to find a single "A HA!" source of it. One thing I have *definitely* found is that as Steve C noted above, "It's most noticeable in simple tube circuits that try to make a lot of gain in a few stages..." VERY TRUE! One way I have fixed the issue is to cut back on the gain of each stage so that the amp gets pushed into high distortion territory (not like metal distortion, more like a cranked plexi 50W level of gain or maybe just a hair more) more slowly. Building up a huge amount of gain early on and then slamming all of that smack into a phase inverter seems to usually guarantee this problem. Also, with cathode biased amps, adding big value cathode bypass caps (10uf-100uf) often contributes. Long grid wires add to parasitic conditions that contribute (i.e., the reason at lot of old Supros have 500pf - 1000pf bleeder caps to ground all over the place). Bright speakers REALLY can contribute to this - in some amps, simply switching to a warmer speaker goes a long way towards cutting this fizz way back. Certain preamp tubes noted for being brighter or glassier aggravate it - old RFT 12AX7 seem to help cut it back, and they are known for being aggressive but darker tubes. I guess what I'm trying to say, in my non-professional experience, is that I've run into this problem a good deal and the only way I ever seem to be able to fix it is by stepping back, taking a breather (and maybe a drink or two...) and revisiting the amp - *all of the amp, not just the wiring or a single resistor or capacitor value* - in its entirety.