el84's fizzy?

[dinglehopper]

Finished an 18watt lite IIb build. amp sounds great clean to moderately driven, but when the volume gets past 3/4's up, there's an unpleasant fizzy sheen to the high end. thought it was maybe problems with the build, so cranked up aiken tomcat (also el84's) and there it is, again. not as pronounced, but definitely there. cranked up 5e3 (6v6's) and haze 40 (el34's), and it's not there. more pronounced through celestion gold, less through vintage 30.

Admittedly a small sample to draw conclusions from. Anybody with more experience have any insights/comments? (I tried the tgp search and a google search, didn't turn up much). If it is something intrinsic to el84's, is there a way to futz with the circuit to remove the fizz?.

thanks

 

[cratz2]

Hrmm... hard to say. Are the speakers new or very well worn in?

And what EL84s are you using?

I have a Carmen Ghia 2x10 and regularly play through the stock 2x10s and I've played it through an Avatar 2x12 with a G12H30 and a Blue Dog. I know the Carmen Ghia, if anything, is a bit dark, but there's nothing that I would call fizz anywhere in it.

I did buy mine used and it came with the original Groove Tubes EL84s that were very well used (~2 years old, gigged regularly) and I replaced them with TADs then JJs and both sounded considerably less good to my ears. More top end and just a more... modern sound, I guess. I put the original tubes back in and have played the amp like that for the last year and a half.

 

[dinglehopper]

The mojo greenback style speaker in the tomcat is well worn in (years . . .). the gold's been played for ~ a year (sounds fine with the 5e3). vintage 30 is well worn in (sounds fine with the 5e3 and marshall).

I'm using mullard RI el84's in the 18watt, assorted NOS in the tomcat.

"I did buy mine used and it came with the original Groove Tubes EL84s that were very well used (~2 years old, gigged regularly) and I replaced them with TADs then JJs and both sounded considerably less good to my ears. More top end and just a more... modern sound, I guess. I put the original tubes back in and have played the amp like that for the last year and a half."
This is interesting - I'm guessing that the older tubes have dulled a bit and likely lost some top end, which the newer tubes have not lost. which would lean toward "el84's fizzy". what, btw, did you mean by "modern sound".

thanks

 

[cratz2]

what, btw, did you mean by "modern sound".

thanks

Well... the Carmen Ghia sounds pretty similar to an 18W Marshall but a bit darker in general and is a little faster to crunch up. Throw in a dash of AC15... I like those qualities and they are what attracted me to the amp over my AC15s and over a desire to get a specific 18W Marshall clone.

With the newer tubes, esp the JJs, it just sounded more like a modern Marshall that just happened to get crunchy pretty quick.

Who knows... maybe I'll get a new set of Groove Tubes and not likes those either and go on a 'well used EL84' buying spree.



I'll put the JJs back in and do a comparison now that I've had over a year on the old tubes. Maybe they were 'fizzy'. I just remember them sounding less 3D and less open and less natural, I guess.

 

[RocksOff]

Sometimes.
18 watt marshalls can get pretty gnarly in those frequencies. As a general rule, I turn the tone knob up at lower values.
If able to play it at higher volumes, I begin to turn the tone knob down.

As a side note: I find Celestion Gold speakers to be fizzy in Marshall and Vox type circuits.

 

[KWCabs]

Personally I hear a little fizz in el84 tubes in general. Some people don't hear it or don't mind it, it's always bothered me a touch, and I can hear it in the best of them, including vintage AC30s that people remark as amazing. I've tried lots of different types, new and old, and I hear it with all of them. The V30s also have a pronounced high mid range, which is right where the fizz usually is, so that might exaccerbate the problem. Try them with a mellower speaker possibly and see if it lessens, and or think about a smoother preamp tube setup, maybe a nice 12at7 in v1 instead of 12ax7s. Might help might not, good luck.

 

[TomOlsen1]

Hi there

The fizz issue in 18 watt style amps is well documented, and requires only four diodes to fix. Here's the doc outlining it all:

www.18watt.com/storage/18-watter_buzz_info_311.pdf

Essentially, it's a crossover distortion issue, if you really want to dive deep check out the following

http://www.aikenamps.com/CrossoverDistortion.htm

You can also try a zobel filter, and maybe changing your PI tail resistor value from 47k to 56k. I found all three fixes solved the issue on mine.

Seriously though, it's also worth registering on 18watt.com or PPwatt. They live and breathe this stuff there and have been extremely helpful to me.

Regards,
Tom

 

[alexandergj]

I believe Dr Z implements a conjunctive or zobel filter in at least some of his el84 amps, which might explain cratz2's experience.
In my experience of my lite 2b, which is vvr scaled and run at low voltages, the best de-fizz result came from disconnecting the bypass cap on the el84s' shared cathode resistor. Apparently the lack of a bypass cap reduces their gain with a little local feedback. I can now use any combination of vvr and volume without the swooshy fizz on the decay of the note, and this is at distortion levels well in excess of AC/DC ZZ Top land.

 

[ZZ-383]

Heres a common "fizz" sound that is familiar to the EL84 amps that I own.
I have both an older 1994 tweed Pro jr and a newer Blues Jr (both 15 watts) and they both display some of the unpleasant sound heard at about 3:40 and again at 8:55 in this clip when I push them hard.

After much tweaking, tube swapping and even trying different output transformers I still haven't found any way to get rid of it short of keeping the volume at lower levels.

 

[rmconner80]

I think I hear that fizz / fuzz / unfocused artifact in almost any non master volume amp that I turn up well past the sweet spot. Some amps (Lead circuit marshalls) actually have that sweet spot up to 10 on the volume, but most don't.

EL84s seem to have it but it could be the amp circuit. Another offender is the 6L6 based BF Fenders. Turned up past the sweet spot they lose focus and get buzzy, but not in a good "cheap-amp-turned-up-so-low-it-sounds-like-it-is-falling-apart" tone. I think the frequency / topology / gain structure particulars of certain amps make it less prominent or even part of the tone while the particulars of other amps make it is easier to hear.

In both situations this may be the sound of grid blocking distortion.

 

[Mysterionn]

Personally I hear a little fizz in el84 tubes in general. Some people don't hear it or don't mind it, it's always bothered me a touch, and I can hear it in the best of them, including vintage AC30s that people remark as amazing. I've tried lots of different types, new and old, and I hear it with all of them. The V30s also have a pronounced high mid range, which is right where the fizz usually is, so that might exaccerbate the problem. Try them with a mellower speaker possibly and see if it lessens, and or think about a smoother preamp tube setup, maybe a nice 12at7 in v1 instead of 12ax7s. Might help might not, good luck.

I would have to agree here. There is a little bit of fizz (not much) but definitely there in most all el84 tube amps. My AC30 (which I love) has a small amount of that quality when using the amps drive instead of a pedal. I use pedals so I don't get that too much, but when using any amp drive on a el84 amp I hear a bit of that fizz in the mix.

 

[dinglehopper]

thanks for all the comments, all very helpful. the link to the ruby article was really interesting, although I can't say I completely understood all of it. it seems that part of the problem is crossover distortion as the increased clipping results in a zone of interrupted power tube output, resulting in class b operation. this would fit with the suggestion to alter the cathode bias to reduce output tube gain.

So, rather than undertake the more tedious route of rewiring the amp, I put an NOS GE 5751 tube in the preamp position, and a balanced 12ax7 in the PI position. Drastic improvement. I assume that this isn't much different than avoiding turning the initial 12ax7 preamp all the way up. also, I tried running a boost into the amp, and the fizziness returned.

so, it seems that the "problem" is too much gain at the el84's with the way the circuit is currently wired. amp sounds great, now. thanks, again.

 

[ken374]

My vox is clear as a bell!

 

[Rock City]

I believe Dr Z implements a conjunctive or zobel filter in at least some of his el84 amps, which might explain cratz2's experience.
In my experience of my lite 2b, which is vvr scaled and run at low voltages, the best de-fizz result came from disconnecting the bypass cap on the el84s' shared cathode resistor. Apparently the lack of a bypass cap reduces their gain with a little local feedback. I can now use any combination of vvr and volume without the swooshy fizz on the decay of the note, and this is at distortion levels well in excess of AC/DC ZZ Top land.

Hello first. I have been reading The Gear Page a lot and it also helped me few times. This is my first post and I just wanted to write down something:
I bought 18w head, 1974x clone with ss rectifier and Russian 6N2P-EV preamp tubes. I sold mine JCM800 from 1981. which I used for almost 20 years because I wanted more classic rock tone. I didn't buy JTM 45 RI since I couldn't play it in my apartment. So I took 18w which is pretty loud, but breaks up early and got that sweet non-master volume drive. I play it through 2x12" V30.
At first it was the best amp I have ever played. I use Gibson LP and Fender Telecaster in a punk / rock and roll band.
Using it on gig level, I have noticed "fizz" which I didn't like.
And I read A LOT, changed few preamp tubes (I had to wire amp differently) like ecc83, ecc82 and ecc81 and even power tubes.
But nothing happened in solving "fizz" problem, just some changes in amp character. Preamp tubes with "small gain" made amp sounding with little or none break up at all which was not cool. Who needs 18w clean sounding Marshall?
Then, I took out cap which was mentioned in a post above and volia! I really don't know what that funny little piece of electronics does in my amp but it sure spoils the fun. Now I have great sounding and cheap amp which I adore. Even my bass player played bass thru it and it sounded awesome.