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Post by ruger9 on Nov 22, 2007 8:32:49 GMT -7
I posted this here, rather than in the RxJR forum, for 2 reasons: 1) it seems like an "expert" question, and 2) I've had this happen on other amps before. Basically, the way I use my tube amps AT HOME, I always use attenuators to bring the volume down. For example, with the RxJR I have been turning the MV up full, then using an attenuator as the MV. With the volume on the RXJR up at about 6-7, I'm pushing the amp pretty hard. HOWEVER, what I'm about to describe also happens WITH NO ATTENUATOR in the circuit. I think I have crossover or blocking distortion, and I'd like to see what you guys think about this. I've got a soundclip (not mine, but it is EXACTLY what my RxJR is doing) below, as well as a link to the page that gives the technicals behind it (supposedly.) I guess what I'm trying to find out is, is this a NORMAL occurance when pushing a tube amp "too hard"? Because if it is, I'll have to re-think the way I have my rig, because the sound drives me nuts. I didn't spend $$ on a great amp to deal with this. (Keep in mind I'm not blaming the AMP- I've had other amps do this as well, and I'm suspecting that my METHOD of bringing the volume down with an attenuator is making the amp volume quiet ENOUGH to make this crossover or blocking distortion apparent, whereas at gig volumes it would still be there, but be masked by the sheer volume.) Please chime in... I just want to get a consensus of what I'm dealing with here, and what I can do about it... [glow=red,2,300] EDIT:[/glow] I've added an update below discussing the possibilty that what this could be is BIAS-SHIFT distortion, not crossover or blocking distortion... Here's the soundclip: jonanderson.mn.googlepages.com/phase.mp3Here's the page: www.paulamps.com/18watterbuzz.html
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Post by dixiechicken on Nov 22, 2007 10:43:20 GMT -7
DC here!
Dunno - kind of hard to tell from your link - the graphs showing - seem pretty similar to me.
But the sound clip is completely off - that constantly sizzling/frying bacon sound doesn't belong. Rest of the sound doesn't sound too good either rather flabby and fuzzy.
World of difference if you compare it with my own clips I've done from my Route66 in the Sound section.
Contact Doc and/or Brent and ask their advice too.
Cheers: Dixiechicken!
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Post by ruger9 on Nov 22, 2007 10:50:16 GMT -7
Keep in mind that's NOT MY soundclip, just a soundclip I found that sounds like what I'm hearing, that was described as "blocking distortion". I would describe it as a "buzziness", almost like a fret buzz... on the wound strings, especially when hit hard. But it's not a fret buzz, it's definitely in the amp.
And it's not just about my RxJR, as I've other amps do it too...and other amps that DO NOT. I'm just suspicious that this may be something "normal" that happens when you push a tube amp pretty hard (RxJR MV dimed, Volume at 6-7, tele bridge pickup)
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Post by dixiechicken on Nov 22, 2007 16:39:02 GMT -7
DC here! Yes I got that (not your soundclip) but I don't think I have that buzzing fenomena i my Route66. (I'll check next time down in the rehearsal studio) You shouldn't really have crossover distortion in en el84 based class AB amp - especially if it's biased hot. This distortion usually occurs when you bias too cold and the crossover points between negative and postive halves of the signal don't align up properly. ( i.e. one powertube cuts off before the other open up to take up the slack - as it were) To me it sounds more like the power supply can't keep up with demand and maybe the filtercaps leave a bit of ripple left in the voltage going out to the plates. ( just speculating - it's gone 35 years since I studied this - elecrical stuff ) Cheers: Dixiechicken! Cheers: Dixiechicken!
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Post by dixiechicken on Nov 24, 2007 11:52:42 GMT -7
Hi "ruger9" - DC here!
Hit the rehearsal studio today with my "Lester" and Route66.
Dimed everything - really putting it through it's paces - it just sounds great - nothing at all like that sizzling strange sound in your example clip.
Even if the treble is too much for liking it really doesn't sound shrill - just bright.
Cheers: Dixiechicken!
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Post by benttop (Steve) on Nov 24, 2007 12:55:09 GMT -7
I listened to the clip, and looked over the web site referenced, but I have to admit I'm somewhat flummoxed here. The web site analysis certainly goes into much detail, but unfortunately each path taken is based on the previous conclusion, which means one wrong conclusion and the whole thing is off in the weeds.
My observation is that much of what you hear is based on the tubes you have in your amp. I recall years ago when I was using a DigiTech 2120 as my preamp, I replaced the two preamp tubes in that unit with JJ's and just about everything you could call tone had changed. The EQ envelope was different, the character of the distortion was different, the dynamics were different - it had utterly transformed that preamp into something different. This is when I realized just HOW DIFFERENT every tube is, and how they all bring something different to the overall tone equation.
In the case of that web site with all those scope pictures, I think I could make just as large a change as his Zener mod just by changing out the PI tube. And yeah, I know he says he did that, but how persistent was he, and how biased was his investigation? It is very difficult to say.
I suggest you try a good number of tube swaps before you ever consider a mod, and enlist some help from the Doc as well as Myles for specific suggestions relating to the types of tones you're looking for and which tubes are more likely to send you along in that direction.
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Post by ruger9 on Nov 24, 2007 20:20:17 GMT -7
I never even thought it could be the tubes, because I've had two very different amps do this (a Peavey Classic 50 and now the RxJR). However, the ONE THING both of those amps had that were the same type... JJ EL84s (or GT EL84S, same difference.)
I would never mod the RxJR. I would just sell it if I decided it didn't suit my needs. I do hope maybe the Doc or Myles could chime in here, because I'd like to get to the bottom of this. The reason I'm thinking it's not a "problem" per se is because 2 different amps have done it. I'm really thinking it's some kind of natural artifact that isn't normally noticeable at the volumes it occurs at (LOUD), but when attenuated down, becomes VERY noticed because of the overall volume drop.
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Post by dongiesen on Nov 24, 2007 20:50:33 GMT -7
Did you send a personal message to the Doc or Brent where they'll be sure to be made aware of your dilema?
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Post by ruger9 on Nov 25, 2007 7:07:36 GMT -7
Not yet, because I don't think this is a problem with the amp... I've had another amp other than a Z do it. I'm just trying to get to the bottom of the phenomena and don't want to "bother" Doc with something that isn't a warranty issue. If I thought there was something WRONG with the amp, I would've called him already.
DC - so, you had the 66 dimed & attenuated? Rehersal volume is still pretty loud I would think... if you get a chance, try diming the amp (ANY amp, but especially an EL84 amp if you have one) then bring it down to BEDROOM level, or maybe one click up from that, and let me know if you hear anything resembling that soundclip. Because I think the sound becomes alot more noticeable under heavy attenuation.
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Post by Strato on Nov 25, 2007 8:31:06 GMT -7
I am pretty sure that if any amp is cranked and the tubes are clipping, there will always be some crossover distortion. Class A operation has the least crossover distortion, while class AB has more, which is what the RX Jr is, correct?. I guess the only thing to do if you cant stand the tone but need the gain is to turn the amp down and use an overdrive?
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Post by dixiechicken on Nov 25, 2007 9:11:00 GMT -7
"ruger9" - no unfortunately I don't have an el84 amp - I'd like a Stangray though. "Strato" - slight correction true class A operation in an power amp does not have any crossover distortion. It can have the usual clipping distortion and compression effect. Class AB has crossover distortion and class B of course. (more or less). Cheers: Dixiechicken!
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Post by ruger9 on Nov 25, 2007 9:37:44 GMT -7
The RxJR is indeed Class AB. And I'm thinking that is the "problem"... since I'm diming the MV and pushing the normal volume up to 6-7, then attenuating down to a "loud home level" (which is about 50% or so on my Weber attenuator), the drop in volume makes the crossover distortion readily apparent, whereas at gig levels it would be largely masked by the sheer volume, as well as bass, drums, etc.
I was just hoping to maybe get someone who KNOWS to sort of verify that, because that would tell me how I can and can't use my attenuators at home (as far as getting the tone I want to hear out of my amps)... if I knew this was a "natural artifact" of pushing a Class AB amp "too hard", then I would have learned something about AB amps, what wattage amp I need, how to use attenuators to get the tone I want, etc...
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Post by dixiechicken on Nov 25, 2007 11:45:01 GMT -7
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Post by ruger9 on Nov 25, 2007 12:37:47 GMT -7
I've been doing some more digging... What might be happening here ...maybe... is [glow=red,2,300] BIAS-SHIFT DISTORTION.[/glow] I found this digging thru piles of papers from the LAST time I experienced this, with one of my previous amps... "For years I've described bias-shift distortion in the output stage as 'springy mosquitoes'. This type of distortion is affected by output load impedence, so it doesn't surprise me at all to find it exaggerated (or reduced for that matter) depending on what's connected to the amp's output, and I also find it more noticeable at reduced volumes from attenuators. Basically, what happens is that when your power stage is driven hard, it self-biases itself colder- sometimes MUCH colder- while a note is being played, then returns (or attempts to return) to the normal bias level between notes. It's assymetric in that the bias shift is only in the negative (colder-bias) direction. If you have enough range in your bias control, you can actually bias your amp cold enough that it sounds this way all the time, not just when cranked up loud- I've done this a few times to exaggerate this distortion when people had a hard time hearing it." Whaddya' think?
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Post by ruger9 on Nov 25, 2007 12:41:57 GMT -7
DC - you have your MV cranked, but where is your normal volume at? You're playing pretty clean. Cleaner than I play when I hear this sound.
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Post by dixiechicken on Nov 25, 2007 16:12:47 GMT -7
If you to my clips in the sounds section - scroll down to the YELLOW Section where I compare the 2 cabs with both my Telcaster and my Les Paul.
I have every control on the Route66 at thre o'clock - the volume and tone control on both guitars dimed using the bridge pickup of both guitars. This applies to the first four clips in the yellow section.
I don't really use more crunch or dist than that - prefer to play pretty clean - but to me in those clips - that is NOT clean. However even when I dime the everything on my Route - that sizzling frying sputter is absent.
Cheers: Dixiechicken!
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Post by bluzman on Nov 25, 2007 22:49:01 GMT -7
What speakers, settings guitar etc and Airbrake settings. I will see if I can reporduce it. I use mine live dimed and airBraked and I love it!! Get back at me!
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Post by ruger9 on Nov 26, 2007 4:53:29 GMT -7
I don't have an airbrake, I use a Weber Mini-Mass. But keep in mind the amp also does this without an attenuator, it's just WAY more noticeable when the volume is lowered using an attenuator.
MV: 10 Bass: 2 Mid: 6 Treble: 4 Volume: 7 Mini-Mass: any setting, the more you attenuate, the more you hear the anomally. Even at minimum attenuation. Especiialy on the E & A stings. Give F#(note) a good wack & hold it...
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