trem 5/17/2017 1:20 PM
Modern "High-Gain" Amps
I only see the few amps that some Local/Young musicians bring to me for "normal" fix and maintenance stuff.
But it seems like a lot of these "high-gain" amps run their power tubes pretty cold. It seems like:
Mesa
PV
and now Marshall
all like to do this.
When i say "cold" i mean in the 30%-50% range of dissipation for a class A/B amp.
But this Marshall JVM 410 (2x12 combo) is really cold. These tubes are drawing about 30 mA at 460 VDC. and that is for a pair, not for one tube.
I do not have a calculator, what is that about 8-9 Watts.?
I have NO IDEA when these tunes were installed or who biased them, but it is kind of what i have seen.
Anyway.....Finally to my question. Is there any reason i should not set these EL34 to the more "typical" range of 60% bias at idle.?
Thank You
 
Enzo 5/17/2017 1:42 PM
Same reason those OEMs went for cool. Longer tube life and better reliability. Mostly they are relying on the preamp for the tones.

And the alternate question: why SHOULD you do it?

The 5150 from PV if found often had idle current in the 11-15ma range.

You have a calculator on your computer by the way.
 
nsubulysses 5/17/2017 1:47 PM
People will probalby say to view it on a scope and if theres no crossover notch there's no problem. Cold bias means easier on the tubes which means less warrantee issues when new amps are sold. So you could see why companies favor this so their amp can make it past its 3 year warrantee or whatever.

People will also probably say to listen to the amp. Does it sound bad biased so cold. Does it sound any different or better biased at 60%?

SOme amps that are high votlage like ampeg V4 need to be biased cold or they will probably fail prematurely. I doubt any of these new gains amps you're seeing are 540V B+ but they probably just want to make it easy on their tubes so their warrantee department can get less phone calls. It should just be biased warm enough that there is no crossover notch. That may fall below the average 50-70% plate dissipation range that people always talk about. It is only a suggestion though. The sound of the amp and the reproduction of the test signal are more important than the calculations, I would guess, as long as it runs in a safe territory, which basically just means any bias setting that's not excessively hot bias for no reason, which may cause problems.
 
Justin Thomas 5/17/2017 2:01 PM
And given the reputation of new tubes, why should anyone take any chances? Those big companies are probably among the biggest buyers of tubes in the world, and they're businesses, not just in it for the art. They use a lot of tubes, and if this saves them money, they'll do it.

I don't know if it was a super-cold bias, but Music Man used a few "unconventional" tricks to eke out every last minute of use from their power tubes, and Peavey followed suit with the Mace/Deuce, correct? I don't know the mechanism, but saving tubes through extremely conservative measures isn't that new. And I'd imagine the tube engineers would be proud.

And would anyone notice crossover distortion at the ridiculous gain levels and (comparatively) low actual volumes these amps are often used at?

Justin
 
nsubulysses 5/17/2017 2:17 PM
FWIW, I've heard people even say things like, "crossover distortion is part of the 5150 sound." not really sure if that's true because I never cared to check it out and mess with different bias settings.

Some customers have asked me to put the bias in a "normal" range on 5150 amps and I have. Pretty minimal listening difference sitting in my tiny workspace with a 100W amp going through a 2x12 under my bench. But the customers said it "sounded better." It probably did slightly. But also they probably played their backup amp for a few weeks then got back to their main rig, "normal" bias setting and all, possibly new power tubes as well, and were pleased with the results
 
Jazz P Bass 5/17/2017 3:36 PM
Hotter bias messes with the 'resonance' control.
 
trem 5/17/2017 3:40 PM
Right.....i understand all of that, but i do not play guitar, so i always wonder.
Every time i have seen an amp like this, i have just kind of figured that The Manufacture has Designed/Set it that way, and i have simply followed their lead.
But not being a player.....i have no idea if a Marshall JVM sounds better when its EL34 are idling at 8 watts or 15 Watts.
To be honest, i sort of do not understand the purpose of an amp like this. There are 4 modes, and two of those are switchable for 3 sounds. Orange, Yellow, Green or whatever colors they are. To my ear, most of these options sound awful, but i guess i am kind of old fashioned at this point.
Thanks For All The Input
 
Justin Thomas 5/17/2017 4:52 PM
Quote Originally Posted by trem View Post
To be honest, i sort of do not understand the purpose of an amp like this. There are 4 modes, and two of those are switchable for 3 sounds. Orange, Yellow, Green or whatever colors they are. To my ear, most of these options sound awful...
I think half of the reason most of them sound "awful" is that people think a Master Volume makes any amp a bedroom amp... Gain 10 Master 1 = AWESOME BONE-CRUSHING METAL TONE!!! Not... Hear those amps in a proper context, at a proper volume (loud aggressive drummer, etc.), and I bet they don't sound so "awful!"

Well, I hear an awful lot of awful players making awful sounds on all those "awful" channels, too...

Justin
 
J M Fahey 5/17/2017 5:08 PM
Quote Originally Posted by trem View Post
But it seems like a lot of these "high-gain" amps run their power tubes pretty cold. It seems like:
Mesa
PV
and now Marshall
all like to do this.
Maybe there is a reason most (all?) amp *manufacturers* , who *designed* them and then proceed to build tens of thousands do things that way.
When i say "cold" i mean in the 30%-50% range of dissipation for a class A/B amp.
"Cold" ????? can you grab those tubes with your bare hands?
But this Marshall JVM 410 (2x12 combo) is really cold.
To you maybe, clearly not to Marshall.
These tubes are drawing about 30 mA at 460 VDC. and that is for a pair, not for one tube.
So?
I do not have a calculator, what is that about 8-9 Watts.?
???????????????
I have NO IDEA when these tunes were installed or who biased them, but it is kind of what i have seen.
Does the word "Factory" ring a bell?
Anyway.....Finally to my question. Is there any reason i should not set these EL34 to the more "typical" range of 60% bias at idle.?
1) "typical" for whom?
Factory or Gurus/Forumites?
2) Just considering averages, since tens of thousands amplifiers leave Factories being used as-is , while maybe 1% of them get rebiased "hot" following Forum lore, Statisttics say that average/normal way is the Factory way.
 
trem 5/17/2017 5:22 PM
Quote Originally Posted by Jazz P Bass View Post
Hotter bias messes with the 'resonance' control.
How does it effect that.?
I see the pot on the front panel schem, but i cannot really follow it after that.
Thank You
 
Jazz P Bass 5/17/2017 11:12 PM
http://music-electronics-forum.com/t43369/#post441793
 
Chuck H 5/17/2017 11:45 PM
I suppose I could participate in the cold bias with preamp distortion/hotter bias with power tube distortion debate... I have been on both sides of that one a few times. I'll just say that when I finally get around to designing my own uber gainer it will have a "relatively" cool bias and rely primarily on preamp distortion. I don't think I'd bias at 15%! Or even 20%. But I will be setting the amp up to make maximum power with relatively little clipping from the power tubes. So that's the sort of standard you're seeing with the colder biased, uber gain guitar amps. The preamps are set up as signal processors and the power amps only have the job of making it louder. No or little power tube clipping intended. For better or worse, depending
 
Enzo 5/18/2017 12:40 AM
I look at it this way also: you get the designed tone of the amp at a wider range of volumes. You don't need to crank the amp.

You CAN modify these cooler amps to run hotter, but you still have to be pretty loud to get power tube distortion. So then you either have to play loud or get into attenuators and stuff for that part of the tone.
 
trem 5/18/2017 12:51 AM
Quote Originally Posted by Chuck H View Post
I suppose I could participate in the cold bias with preamp distortion/hotter bias with power tube distortion debate... I have been on both sides of that one a few times. I'll just say that when I finally get around to designing my own uber gainer it will have a "relatively" cool bias and rely primarily on preamp distortion. I don't think I'd bias at 15%! Or even 20%. But I will be setting the amp up to make maximum power with relatively little clipping from the power tubes. So that's the sort of standard you're seeing with the colder biased, uber gain guitar amps. The preamps are set up as signal processors and the power amps only have the job of making it louder. No or little power tube clipping intended. For better or worse, depending
Is there a Mathematical relationship between bias and the power output of an amp.?
That is to say.....if Marshall says that amp XYZ is a "100 Watt Amp"...running 4x EL34...but the power tubes are idling at 8 Watts, is it still a 100 Watt Amp.?
Or are those just round numbers that most manufactures use based on the potential of whatever power tubes a certain amp uses.?
Thank You
 
trem 5/18/2017 12:53 AM
Jazz P -
I see, interesting.
Like i said, i just follow what the factory does. Though all these years later, that can be hard to ascertain without input from them. I shot an email to Marshall and asked them what kind of bias number(s) they use when these amps are new. Perhaps they will respond.
I went ahead and biased these power tubes a few mA more than the old tubes were, but nowhere near what i would with a circa 1968 Fender/Marshall/Vox.
Thanks Again.....i appreciate the info
 
Enzo 5/18/2017 1:09 AM
No.

Idle dissipation is just a static amount, not related to audio power. I think my best analogy is idle speed on your car engine. My truck idles at about 500rpm. But if I were to goose that up to 700 or 1000 rpm, it would have zero affect on how fast the car can drive or the horsepower it could generate.

I don't want to spark the same tired debate, but there are ways to look at amp power. Ultimately the power rating is a measure of how much audio power it can put into a speaker load. This comes from the power supply fundamentally, but also is influenced by the tubes involved, and the circuit. The debate? Some want to measure power like hifi: how many watts into the load without distortion. My position? What if the amp is distorted all the time? Does it put out zero power? I consider it the amount of energy the amp can put into a speaker. I will let others worry, "they SAY it is a 120 watt amp but it only puts out 96 watts."
 
trem 5/18/2017 10:22 AM
Yes...Thanks.
I understand what you are saying.

So back to these "high-gain" amps. What i keep reading is that the amp designer is getting All/Most of the tone and character of his amp from the preamp, and the power tubes are simply there to drive the speakers and make the amp audible.
This Marshall JVM for example. Would it make just as much sense then to do away with the power tubes and OT and simply use a Solid State Power Amp.?
Or are they still benefiting from the "interaction" of tubes and a Output Transformer to develop the sound they are after.
Thank You

and i guess you would also ditch the PI tube.?
i suppose this would all start to take its toll on the sound of the amp, wouldn't it.?
Thanks Again

p.s. I am on a fairly "old" computer. It DOES have a calculator, but no matter which button you select, it wants to add everything.
 
eschertron 5/18/2017 10:32 AM
Quote Originally Posted by trem View Post
Yes...Thanks.
I understand what you are saying.

So back to these "high-gain" amps. What i keep reading is that the amp designer is getting All/Most of the tone and character of his amp from the preamp, and the power tubes are simply there to drive the speakers and make the amp audible.
This Marshall JVM for example. Would it make just as much sense then to do away with the power tubes and OT and simply use a Solid State Power Amp.?
Or are they still benefiting from the "interaction" of tubes and a Output Transformer to develop the sound they are after.
Thank You
While line out-to-mixing console tends to leave people unimpressed, my crystal ball shows the "modern amp" has a tube tone/distortion generator in front, and a SS power section. There's quite a bit of understanding on how tube output impedance affects the sound, and quite a bit of engineering on how to mimic it with SS components. It's going that way

Quote Originally Posted by trem View Post
and i guess you would also ditch the PI tube.?
i suppose this would all start to take its toll on the sound of the amp, wouldn't it.?
Thanks Again
My understanding is that the PI is part of the power amp. Especially when there's a loop insert after the Preamp and before MV/PI.
 
Enzo 5/18/2017 1:49 PM
yes, the PI is part of the power amp.
 
eschertron 5/18/2017 8:29 PM
Quote Originally Posted by trem View Post
and i guess you would also ditch the PI tube.?
i suppose this would all start to take its toll on the sound of the amp, wouldn't it.?

I think part of the appeal of 'tweed' and other older pre-MV amps is that the sweet spot involves a bit of PI and power tube distortion. It's not easy to build a circuit with preamp tubes that mimics this behavior, from sag to the sound of pentodes in push-pull. But this is not the 'high-gain' sound, as the preamp does most of the tonal coloring.
 
nosaj 5/18/2017 9:02 PM
Quote Originally Posted by eschertron View Post
I think part of the appeal of 'tweed' and other older pre-MV amps is that the sweet spot involves a bit of PI and power tube distortion. It's not easy to build a circuit with preamp tubes that mimics this behavior, from sag to the sound of pentodes in push-pull. But this is not the 'high-gain' sound, as the preamp does most of the tonal coloring.
makes me think of Ray Wylie Hubbard's Snake Farm. It just sounds nasty.

nosaj
 
Justin Thomas 5/18/2017 9:07 PM
Fender's Prosonic was an uber-gain (for the time) amp, and you could leave it at a nice tube-rectified hot-cathode-biased setting, and crank the Gain & Volume knobs on 10... I won't say whether it was pleasing or not, but, it was... errrr, interesting? But it definitely had all of the above! If you could take it. I could.

Justin
 
The Dude 5/18/2017 10:04 PM
Ah yes, the "Zinky". You could get a lot of different tones out of those because of the way the controls interacted. IMO, a pretty versatile amp- not just a gain monster,...... although it could do that too.
 
Chuck H 5/18/2017 11:32 PM
Bruce Zinky picked apart that design for years. So much so you'd think he didn't like it. I read his postings on more than forum stating things like the amp only sounds good with certain speakers or the plate to grid caps should be removed, etc. I had one. I was impressed enough that Bruce became a minor hero of mine WRT design. I met him at the 2009 winter NAMM show and it turns out he's sort of weird. Not in a bad way. Just one of those guys that's really smart but lacks social skills. He was alone in his Supro booth and just seemed nervous, most of what he said was a little odd and keeping a conversation on topic was impossible.
 
Zozobra 5/19/2017 6:10 AM
Quote Originally Posted by trem View Post
Yes...Thanks.
I understand what you are saying.

So back to these "high-gain" amps. What i keep reading is that the amp designer is getting All/Most of the tone and character of his amp from the preamp, and the power tubes are simply there to drive the speakers and make the amp audible.
This Marshall JVM for example. Would it make just as much sense then to do away with the power tubes and OT and simply use a Solid State Power Amp.?
Or are they still benefiting from the "interaction" of tubes and a Output Transformer to develop the sound they are after.
Thank You

and i guess you would also ditch the PI tube.?
i suppose this would all start to take its toll on the sound of the amp, wouldn't it.?
Thanks Again

p.s. I am on a fairly "old" computer. It DOES have a calculator, but no matter which button you select, it wants to add everything.

Depends on the amp and what tone the user wants, but some stuff sounds fine without the PI and power amp. This is an Engl backmore recorded using the FX loop send for example:
https://soundcloud.com/tjore/engl-bl...direct-in-test

Here is the Engl E530 preamp straight into an interface.
https://www.youtube.com/watch?v=7YjGal6ABqg
https://www.youtube.com/watch?v=-lKlcymOgb4

Both recordings use impulses/speaker sims and sound pretty much how I would expect them to if they'd mic'd up the cab.
Now of course neither of these preamps are all that subtle in their mangling of the input signal to say the least which helps.

More traditional marshall tones don't fair as well but they certainly aren't bad when the PI/PA are omitted

JVM: https://www.youtube.com/watch?v=o1bBYv-7pPE
DSL: https://www.youtube.com/watch?v=CuaZxmf_ddM

So we've established that with a bit of trickery that a tube pre can sound more than passable.

One notable hybrid amp that springs to mind is the Verellen Kalaloch. I can't find any good demos of it at the moment but that is two independent amps in one box. There are two clean tube pres, most likely fender derived circuits, for pedal use that each feed a 700W class D module. It's quite the thing.
 
eschertron 5/19/2017 4:46 PM
Quote Originally Posted by nosaj View Post
makes me think of Ray Wylie Hubbard's Snake Farm. It just sounds nasty.

nosaj
Well, I guess there's no better time than a Friday night to fall into a previously undiscovered oevre filled with greasy swamp boogie. Thanks, Jason!
 
nosaj 5/19/2017 5:43 PM
Quote Originally Posted by eschertron View Post
Well, I guess there's no better time than a Friday night to fall into a previously undiscovered oevre filled with greasy swamp boogie. Thanks, Jason!
Tell me what you think of him. I like his music a lot.
nosaj
 
nosaj 5/19/2017 6:59 PM
Quote Originally Posted by nosaj View Post
Tell me what you think of him. I like his music a lot.
nosaj
Also Ry Cooder is good and for something different try Honky (bassist from Butthole Surfers)
nosaj
 
eschertron 5/19/2017 7:13 PM
Quote Originally Posted by nosaj View Post
Tell me what you think of him. I like his music a lot.
nosaj
I like the 'cleverness' of his songs. There's a great deal of songwriters who simply drape the lyric over a music bed; here I get the sense of stylistic unity, it feels sincere. And regardless of the band lineup, he's got a great groove!

Quote Originally Posted by nosaj View Post
Also Ry Cooder is good and for something different try Honky (bassist from Butthole Surfers)
nosaj
Ry has been around, I probably need to catch up on what he's done in the last 30+ years
Honky? OK, down the rabbit hole again...
 
TimmyP1955 5/24/2017 4:46 PM
Quote Originally Posted by Zozobra View Post
Here is the Engl E530 preamp straight into an interface.
https://www.youtube.com/watch?v=7YjGal6ABqg
https://www.youtube.com/watch?v=-lKlcymOgb4



More traditional marshall tones don't fair as well but they certainly aren't bad when the PI/PA are omitted

JVM: https://www.youtube.com/watch?v=o1bBYv-7pPE
DSL: https://www.youtube.com/watch?v=CuaZxmf_ddM

D module. It's quite the thing.
I like 530 #1, though only the Marshall with the green box sounds bad.