High gain channel comparison questions

[wittyjeff]

I'm planning to have a high gain channel in my next build that is capable of some death metal shredding so to speak (without a push from a pedal).  The tone I'm going for should be similar to what is able to be produced by the OD channel of a Bogner Ecstacy and/or Uberschall (what my guitarist friend suggested/likes).  I was looking at Merlin Blencowe's "Ultra High Gain" channel on page 260 of his book: Designing Tube Preamps for Guitar and Bass.  That circuit seems like a straighforward, efficient high-gain design.  ...but will be it "high gain" enough? 
I see that both of the Bogner circuits I've mentioned have an additional gain stage compared to Merlin's.  Some other high gain amps (like some Peaveys) have 6.  Since I'm not an EE and don't have years of experience building amps... I'm worried that Merlin's definition of "Ultra High Gain" might not meet a shredder's definition if you know what I mean.
I've attached the schematic of the Merlin channel I was thinking of using, plus the two Bogner OD channels that I think might produce the distortion I'm looking for.  Could someone give me a rough comparison as to the gain produced by the Bogners in comparison to the Merlin circuit?  Seems like the Bogner circuits use higher grid stops and some other complexities... I imagine there's a reason for those.
I haven't started the build yet so all options are still on the table.  I'd hate to add an extra tube to the build only to use half of it, but there is room if needed.
Thanks in advance for your insight and advice.

[sluckey]

Here's another to muse over...

     http://sluckeyamps.com/misc/Aro_Project.pdf

[wittyjeff]

I like the straightforward looks of that Aro circuit.  Thanks!   Are you thinking that Merlin might be one tube short of an "Ultra High Gain" circuit?

[pdf64]

Does the ubers 3rd stage really have a 1k anode load resistor?

The Aro looks terrifying - you may need to strap the guitar down to a large solid object, to prevent lift off!

I think that Merlin’s preamp should achieve a similar degree of overdrive to those Bognors.

[T Wilcox]

https://ampgarage.com/forum/viewtopic.php?t=31272
Was just reading the above thread last night
Mark is the only one I know of that's built this one and he says its pretty gainy

Keep in mind there is an error that Merlin posted the errata on his website
The 4th stage cathode resistor should be 820 not 1k5

[wittyjeff]

Mr. T Wilcox,  Thanks for that thread link and for making me aware of the errata.  That could have caused me some problems that would have taken awhile to figure out, so dodged a bullet thanks to you. I'm hoping Mark will post some sound files.  It seems to be that different people have different definitions of what "high-gain" means.  I'm hoping for some Godsmack, Collective Soul, Alter Bridge, Alice In Chains, Judas Priest, Green Day, Limp Biscuit, Slip Knot, Slayer, take your pick type of distortion and tone.  I'd hate to build this and find out I'll need to rip it all apart again and add a tube or stage.  If the Merlin circuit could work, and I tend to think Merlin is a solid source of info, it would make for a nice efficient layout with enough room for the isolation that Merlin recommends.  I see that Mark had some problems, but I notice that in his layout/build, his first two stages are laid right next to the second two and Merlin specifically stated that there should be at least 8cm between them or oscillations would result. Mark has essentially zero space between them and mentioned he was getting oscillations.  I can only squeeze out maybe 6cm and crossing my fingers.  Thoughts?

[wittyjeff]

Does the ubers 3rd stage really have a 1k anode load resistor?

The Aro looks terrifying - you may need to strap the guitar down to a large solid object, to prevent lift off!

I think that Merlin’s preamp should achieve a similar degree of overdrive to those Bognors.

PDF, Thanks as always for your insight.  You've never steered me wrong in the past.  I have no idea on that anode load resistor as I'm not familiar with the Bogner circuit other than what I downloaded from Hoffman's library. 
I'll admit those 6-stage high gain circuits make me nervous as far as stability and other potential issues, but obviously they are out there and seem to work.  I'm sure Sluckey has built that Aro and had good results with it, so that's definitely an option although I'd like to avoid squashing in the extra tube and components unless there's a solid reason. 
So, you're saying that Merlin's maxed-out 4 stages can produce the same gain/distortion that those other 5 or 6-stage circuits produce?  I know there's a lot of devil's details like where the clipping occurs, biasing of the various preamp stages, how the cathode bypasses change the tone, ad infinitum... but it would be ideal for my actual build/layout if I could use Merlin's 2-tube circuit and end up with some metal-worthy distortion.  The guitarist I'm building to make happy is enamored with those two Bogner sounds, so I'm hoping it's somewhat close.
Your thoughts?

[sluckey]

I'm sure Sluckey has built that Aro

No. That's not my style of amp. I just stitched that together for a long gone member named Aro.

[pdf64]

With Merlin’s, every stage adds gain.
That’s not the case with the Bognors.

[wittyjeff]

Steve,  ...got it.  In that case, I might take the more conservative approach and stick with the Merlin.   I think if it's not close in tone I can add some tweaks later to adjust a bit.  The gain has to be there though.

Pdf, ...that's kinda what I was thinking, seems like the Bogner circuits add gain, the subtract, then add again.  I'm sure that adds some important subtleties and I reckon I'll find out why those are there later, but, again, I think if I can get the gain to that level... I'm hoping that some of the nuance can be teased out by other means after the fact (i.e. bass freqs/cathode bypass, high bypass filters, etc).
...agreed?

[T Wilcox]

Mr. T Wilcox,  Thanks for that thread link and for making me aware of the errata.  That could have caused me some problems that would have taken awhile to figure out, so dodged a bullet thanks to you. I'm hoping Mark will post some sound files.  It seems to be that different people have different definitions of what "high-gain" means.  I'm hoping for some Godsmack, Collective Soul, Alter Bridge, Alice In Chains, Judas Priest, Green Day, Limp Biscuit, Slip Knot, Slayer, take your pick type of distortion and tone.  I'd hate to build this and find out I'll need to rip it all apart again and add a tube or stage.  If the Merlin circuit could work, and I tend to think Merlin is a solid source of info, it would make for a nice efficient layout with enough room for the isolation that Merlin recommends.  I see that Mark had some problems, but I notice that in his layout/build, his first two stages are laid right next to the second two and Merlin specifically stated that there should be at least 8cm between them or oscillations would result. Mark has essentially zero space between them and mentioned he was getting oscillations.  I can only squeeze out maybe 6cm and crossing my fingers.  Thoughts?

Well I love the heavy stuff so heres what I've done so far. I'll use some of your examples
I wanted AIC dirt tone, I built a Ceriatone Molecular which got pretty close but then found on SLOclone forum the schem for Jerry's Bogner modded 800 "the snorkler" and built it as a preamp. It nails that tone. that being said i would not use that for green day, godsmack or most of the others listed.
The thrashiest one I've built so far is a clone of the Langner DCP-1(my definition of high gain changed after this build).It has 5 gain stages and was a challenge to tame but is by far the fastest circuit I've played.  It will slay if playing thrash like Exodus, Slayer and even some early metallica but I would hard pressed to get a good AIC tone out of it.
there are still a lot of circuits I'd like to build up and compare such as Diezel vh4, fryette deliverance, Engl and a few others i cant think of atm
There are also SLO derivatives like the 5150, 6505, some Mesas etc. which are whole other type of high gain maybe due to the cold clipper arrangement that have a completely different feel to me.
I am considering the Merlin ultra high gain as an upcoming build since it appears unique compared the others mentioned just to see.
I'll probably end up with a different build for every band/genre I like which is okay bc it feeds my building addiction
It's gonna suck once I've done em all, I might actually have to start practicing guitar again

[ShoemanGB]

I'll pitch in my .02.. having built Merlin's medium gain pre, it was more "modern" or hairier than I expected based on his description.  I was expecting a "classic rock" thing, like Page, Kossoff early '70's thing, but it to my ears (and with my later stages/gear) it does EVH or (your fave pointy guitar spandex band here) way better than it does Zep 1. 
 So if his descriptions are consistent his High gain will really be high gain plus some.   But I'm in my late '50's and have never heard most of the modern bands and sounds you guys are talking about emulating 
But I did see SRV live three times, so I got that going for me.

[wittyjeff]

I'm right there with ya Shoeman.  I'm just mentioning the tone my guitarist is looking for.  That's why this really high gain stuff is new for me.  Your comments do make me feel more confident.  If Merlin means high-gain when he says high gain... then this circuit should work well.

[wittyjeff]

Thought you guys would get a kick out of the attached meme if you haven't seen it already.

[thetragichero]

any reason not to have at least one dirt pedal on front? to my ears a little silicon adds something that the amp alone can't do (and on the case of sabbath/doom metal stuff, something emphasizing the higher frequencies more going into a bass-heavy old orange really balances things out)

[pdf64]

Yeah, the philosophical goal of achieving mega overdrive without the assistance of a pedal seems a bit pointless to me. Because for any serious playing scenario, does anyone really plug straight in, without even a tuner pedal?

[d95err]

does anyone really plug straight in, without even a tuner pedal?

I keep a tuner on top of the amp and simply unplug the amp and into the tuner when I need to tune.

I use a pedalboard and a pedal tuner too sometimes, but nothung beats the simplicity of guitar-cable-amp.

[SILVERGUN]

In 2014, (as a wee lad armed with just enough information to be dangerous) I studied the available Uberschall schematics, tweaked it on the breadboard and came up with this. I built a 2x12, 50W combo with EL34s using a 100W Marshall PT and a 50W OT, with about 500V plates and the attached sound clips are what I came up with. One thing that was new to me at the time was the use of the NFB circuit to enhance the low end and I remember sweating pretty hard trying to copy the circuit from the schematic, partially because of trying to find a correct inductor, and not really understanding why. I just trusted that Bogner knew many things that I didn't. I wound up with a 'way too big' inductor, but oh well, it worked.

The girl I was building/tweaking the amp for wanted a darker tone and we were chasing a bit of the modern metal guitarists squeal-ability.

I'm no metal guitarist and definitely not a shredder so, no guarantees, but this is what I got:
AK47demo2 by SILVERGUN | SoundClick

[SILVERGUN]

Here are the other 2 schematics I was working off of. Sorry, I don't remember where I got them.
I do remember using this power amp schematic with "resonance" type NFB almost note for note.
And again, I used a Marshall 100W PT with a TON of filter cap UFs

[sluckey]

Before you lock in on any particular circuit google "staalhoofd mod". Could be interesting.

[wittyjeff]

Yeah, the philosophical goal of achieving mega overdrive without the assistance of a pedal seems a bit pointless to me. Because for any serious playing scenario, does anyone really plug straight in, without even a tuner pedal?

It may be sacrilegious to say, but I'm no guitarist, ...so I just go by what my guitarist friend says.  He says that earlier in his career he relied on pedals primarily to shape his tone but much less so in later years.  He has an arsenal of pedals and effects gear (as well as just about every significant amp and cabinet set up you might expect a professional studio guitarist to have).  ...and yes, he does often uses pedals to adjust the amount and type of crunch etc.  However, he says that pure tone from the amp is the ideal to strive for.  He said the Bogner Uberschall was one of the best amps for that purpose that he's ever played through or owned. Naturally when playing a performance set that consists of a wide variety of styles and genres... well, there's no way a single amp would be able to do that without pedals.  At least that's what my limited knowledge tells me at this point and what you guys seem to concur with.  I tend to defer to your more extensive experience.  I'm just hoping to build amps that have the ability to offer a wide range of tones and distortion.  I'm hoping with my next build to be able to extend my range into some high-gain-capable-of-metal distortion.  I guess we will see how it goes.

[wittyjeff]

any reason not to have at least one dirt pedal on front? to my ears a little silicon adds something that the amp alone can't do (and on the case of sabbath/doom metal stuff, something emphasizing the higher frequencies more going into a bass-heavy old orange really balances things out)

It seems like the Uberschall in particular uses some heavy grid-stops but bypasses them with caps.  I'm assuming the 100W heaviness provides the deep boom and gut punch/thump on the low-end... but the bypassing of the signal with caps through the grid stops at several points along the way keeps the high-end sizzle in there.  I'm exhausted just thinking about building all of that... so yes, it would be a heck uv a lot easier to just simply do it with a pedal.  Would give more adjustment opportunity too.

[wittyjeff]

Here are the other 2 schematics I was working off of. Sorry, I don't remember where I got them.
I do remember using this power amp schematic with "resonance" type NFB almost note for note.
And again, I used a Marshall 100W PT with a TON of filter cap UFs

Thanks for these schematics.  They will help a lot!  I love the sound of that AK47 amp demo.  Definitely going to study and consider these.  I might just do the Merlin Ultra-High Gain this time around for curiosity's sake and since it fits in with the other Marshall switchable channel better space-wise, and then after, build a single channel metal machine and base it off the Uberschall but simplified, similar to the AK and others.
Again, my thanks.

[SILVERGUN]

One other tip...since you're gonna build something
I remember that when I was doing the final tweaking of this amp I found that a 12AT7 made a "better" phase inverter choice because it just handled the high gain preamp better IMHO

[pdf64]

Merlin also suggests the 12AY7 http://www.valvewizard.co.uk/acltp.html

[wittyjeff]

One other tip...since you're gonna build something
I remember that when I was doing the final tweaking of this amp I found that a 12AT7 made a "better" phase inverter choice because it just handled the high gain preamp better IMHO

Great suggestion.  I've had to do that on some other builds.  Also putting a 12AU7 or 12AY7 in some of the other stages to calm them down if they get unruly can be useful from what I'm reading.

[wittyjeff]

Before you lock in on any particular circuit google "staalhoofd mod". Could be interesting.

Steve, thanks for that tip.  I spent the last hour or so reading through the various results of that search.  Learned a lot and found a number of helpful schematics.  I have a lot to digest.  I'm thinking I might go ahead with this planned build with the Merlin preamp just to see how it pans out.  I like the second channel based on your switchable Plexi/JCM800 idea.  It should allow for some classic Marshall crunch and with the Merlin channel, produce some higher gain and hopefully metal distortion.  I'd say that will result in a versatile amp regardless.  After that, I might try to build a one channel 5 or 6 gain stage amp just to see how far to the edge I can wander.

[T Wilcox]

any reason not to have at least one dirt pedal on front? to my ears a little silicon adds something that the amp alone can't do (and on the case of sabbath/doom metal stuff, something emphasizing the higher frequencies more going into a bass-heavy old orange really balances things out)

I havent tried the Merlin circuit so I cant say whether pedals would be beneficial, but with the 5 gain stage Langner circuit I threw together any dirt pedals in front of the amp seem to only muddy up the distortion and also add to the noise floor so I never use them with it. It is a different animal than the typical Jose modded Marshall thing you see everywhere these days which I really appreciate since I've grown bored with that sound personally.
I am no purist and absolutely use pedals for great sounding overdrive/distortion with most of the other circuits I've built up ranging from AB763 deluxe, plexi, dumble, and even the hot rodded Jose Marshall types benefit depending on the sound you are going for.

[Tone Junkie]

If you do his high gain amp pay close attention to the tube placement. on one of them if you don’t have the proper distance. You will have problems with feedback . Talked to a gentleman on different forum when I was researching this circuit. He had to move a tube to fix the problem. In the book Merlin tells which one . I’m at work or I’d pull it up  out and give you the info.

[wittyjeff]

If you do his high gain amp pay close attention to the tube placement. on one of them if you don’t have the proper distance. You will have problems with feedback . Talked to a gentleman on different forum when I was researching this circuit. He had to move a tube to fix the problem. In the book Merlin tells which one . I’m at work or I’d pull it up  out and give you the info.

That's great advice.  I did read that part from Merlin.  He says the first two stages/first section (i.e. V1) needs to be at least 8cm away from the second (V2).  I have been able to do that on my layout. I've also tried to keep the board components of those two sections/tubes away from each other, but only managed to get about 4cm... but at least there's some air there between them.  Hope it's enough.
Thanks again.  I'm hoping that something else doesn't pop up and bite me after the fact.  Better to get everything now while it's just on paper that's for sure.

[T Wilcox]

I'd suggest running shielded straight from input jack to the grid stopper tied directly onto V1a grid with as little exposed as possible or it will be oscillation city.
My first attempt at a pcb build I neglected this and put the grid stopper on the board an inch away and it squealed with the gain knob above 9'oclock
You can see in the pic where the grid stopper was removed from the board and I re-ran the shielded straight to the tube which cured the squeal
That first run in a high gain circuit is like a very sensitive antenna for noise

[wittyjeff]

I'd suggest running shielded straight from input jack to the grid stopper tied directly onto V1a grid with as little exposed as possible or it will be oscillation city.

Duly noted.  I'm using all shielded cable, but the resistors were almost 2 inches away on the board on my layout.  I'll run them straight in like you did just to reduce the chances for problems.  ...another bullet dodged.  Thanks!

[Bieworm]

Yeah, the philosophical goal of achieving mega overdrive without the assistance of a pedal seems a bit pointless to me. Because for any serious playing scenario, does anyone really plug straight in, without even a tuner pedal?

Without a tuner you're soon going to have all the extra harmonics without modding the amp 😄😄😄😄