Your high gain approach?

[chipaudette]

Hi All,

I've seen a lot of talk on this site on building/modding/debugging amps based on the classic designs -- especially tweed through blackface Fenders and plexi-ish Marshall configurations. It's all super-interesting and really educational. But, there's not much talk about the high-gain side of the amp world.

What kind of high-gain amps have people here had success building or modding? What kind of topology have you had success with?

Some classic topologies I can think of are the all-tube varieties (Mesa Boogie MK I, Boogie MK II-IV, Marshall/Soldano/Recto/Bogner), the hybrid varieties (Marshall Jubilee, Marshall JCM900), and the all solid-state varieties (short list...GK?).

I personally have modded my Fender Deluxe Reverb Reissue into something approximating a Boogie Mk 1. It functioned but didn't sound all that good. I then pulled that out and wired it instead to be more like the configuration used for Mk IIC through Mk IV. That required adding relays and stuff, but the mod ended up being much more successful than my attempt at a Mk I. For the last few months, I've been really enjoying my new sound. Now, I'm toying with ideas on how to cram in some version of the Boogie graphic EQ to really complete the sound.

What have you folks done? What are some of the issues you've had (and hopefully overcome)? I wanna hear the stories!

Chip

[Steve Conner]

The Ninja Toaster was an oddball high-gain amp that I designed years ago when I was studying EE and listening to a lot of metal.

http://scopeboy.com/toaster.html

I came up with the gain structure and voicing by experiment, and used a parametric EQ instead of the Boogie's graphic. (To this day, I'm still not sure exactly how my parametric EQ circuit works, but it does.) The gain structure is switchable with three levels from clean to full-on shredding distortion, and on clean, it actually works OK as a bass amp too.

I currently use it with a closed back 1x12 loaded with an EVM12L reissue. The mid scoop setting I used to use never sounded right with this speaker, and boosting the upper mids around 4kHz worked out a lot better. But with other speakers I've tried, I could get a real aggressive chunking, mid scooped sound. What the forum leaders here call a "Wanker woofie drone" or "can of bees" which is one reason why you won't see much discussion of high-gain amps here: they're not cool.

To be honest though, that scooped tone just never works at a gig: you need lots of midrange to cut through the mix, and decreased bass to save your amp's power for making that midrange.

As for sound clips, I used the amp a lot at gigs and on my own recordings, but I don't have much that shows off the high-gain tone, except one mp3 of me playing Always With Me, Always With You

[Enzo]

The more complex, the more sophisticated, the more gain you have, the harder it is to pull off. Guys here do build Marshall and SOldano type amps. But when you start into higher gain amps, the layout starts to matter a lot more, circuit stability issues are more intense, etc. So there is less of it.

A novice can build a 5E3 with reasonable expectation of success. A Mk4 or a 5150, not so much. And cost is a factor. COmpare the transformers needed for a 5E3 to those for some high gain 100 watt head.

I am all for someone tackling a tough build, but it is beyond a lot of people.

That said, I'd be interested in other's experiences as well.

[loudthud]

Two amps you didn't mention are disscussed in detail at:

http://ampgarage.com/forum/

You'll have to sign up to gain access to most of the good stuff but it's well worth it.

Some have built SLO100's but I'm not sure if there is a forum that focuses on those amps. Another is London Power's Standard. There is some discussion of that here and it's well documented in KOC's books.

I think what holds many people back is lack of test equipment and the knowledge to use it. Many things become critical in high gain designs that can be ignored in Tweed and Blackface clones.

[daz]

I spent months trying to get a high gain pre sounding right and i finally nailed it pretty good by closely copying the AX84 site's high octane pre with 2 gain pots and a voltage divider after each pot. It made a big difference from the endless stream of designs and changes that came before. It's not perfect tho and i have come to the conclusion that the right way, and i have read this several places, is to add even more gain stages and add a little gain at each one verses more gain at fewer stages. This allows you to add more tone shaping stages and to keep the chance of oscillation and blocking distortion low. If i built another hi gain amp i'd use 3 triodes this time for a total of 4 including the PI.

[chipaudette]

Steve,

Your remark about the impact of speaker choice caught my attention. With my DRRI, I've only been able to use the Jensen that came stock. It's the only speaker that I have, so I can't check out the sound of my modded amp through anything else. Does anyone have an opinion of how the stock Jensen should color my sound vs other speaker choices?

I would characterize the sound of the overdrive in my modded amp as very midrange...almost no low-end metal chug and very little high-end sizzle. It's great (for me) for leads but the amp's sound doesn't have the frequency extension necessary to do hard-rock/metal riffs with kick-to-the-stomach authority.

Might a speaker swap have a more dramatic impact that a post-gain EQ?

Chip

[Steve Conner]

Uh, I don't exactly associate the stock speaker and open-back cab of a Deluxe Reverb with "kick-to-the-stomach authority". More like being nuzzled by a kitten. It's nice, but it's not metal.

If you want metal chug and sizzle, you should swap it out for a Vintage 30 or something, and even then it's not going to chug that hard in an open-backed cabinet.

[chipaudette]

Enzo,

I certainly agree that higher-gain amps have a lot more squeeling problems (my own amp included). Squeeling is pretty much what sunk my attempt at a Boogie MK I preamp in my DRRI. I don't have nearly the squeeling probelm in my current pre-amp layout.

As for your comments about building a high-gain monster, I offer two comments as a reply...

First, building from scratch is indeed tough...but what about modding an existing amp? Half of the traditional Fenders out there have two sides to its preamp ("Normal" and "Vibrato"). I know that it's a somewhat common mod to simply cascade the two sides, but that sounds crappy...I know, I tried. Still, one could be a little more sophisticated than blindly cascading. One could try putting in the proper voltage dividers and tone shaping caps to get a better overdrive tone. It's all about fiddling (or stealing from other high-gain schematics). By modding an existing amp, no expensive components required...it's all there waiting for a soldering iron. With so many of these Fender amps out there, I'm curious why I don't hear more about such experiments.

As for my second comment to your reply, I also agree that building powerful 100W amps requires expensive (and big and heavy) transformers. They're also loud as hell. Who wants that?!? As we all know, lower power amps (EL84 / 6V6 / 6L6 SE) require much cheaper components and are easier to fit in a reasonably sized chasis. For the type of playing that most of us do, I'm surprised that there's not more talk in the home-brew community of pairing a high-gain pre-amp with low-power power amps. Sure, there's some amount of talk of this out there...but not much on this forum.

If one starts from a classic low-power amp design or amp kit, what expensive components need to change to add an extra 12AX7 or two to the pre-amp? Do the transformers need to get bigger (ie more expensive)? Heater current is, what, 300 mA per tube? Is the transformer in a typical amp build driven by the total heater current for the amp, or is it driven by the high-voltage supply capacity for the power tubes? I'm very curious to know...

Thanks!

Chip

[Steve Conner]

Well, a lot of metal is appreciated by younger players who'd never think of building with tubes. Maybe they don't understand them, or maybe they can't afford them, but the effect is the same: If you go over to runoffgroove.com you'll find a dozen Mesa clones made out of JFETs.

My first two amps were solid-state and sounded like crap, I was only converted from the dark side when I found a 50 watt tube PA in a dumpster. I could never have afforded a 50w transformer set at the time.

I'm sure older amp builders think that tubes are wasted on the high-gain tones, but I get a wicked feeling cracking open the throttle, sorry, guitar volume knob on a cranked high-gain tube amp, that no combination of stomp boxes, rackmounts, solid-state PA amps and PODs has ever duplicated. I'm not a biker, but I imagine it's the same kind of auditory experience as doing a burnout on a Harley with bare pipes. If you're unlucky, it even smells the same.

[chipaudette]

Daz,

I concur with the "little bit over many stages" philosophy.

In my first several months of looking at the mesa boogie schematics, I thought that the "distortion" happened in one or two gain stages. For the Mk IV schematic below, I thought that the distortion was created by overdriving V3A and V3B in the "lead stages" shown on page 2.


http://www.schematicheaven.com/boogieamps/boogie_mkiv.pdf

But, after re-arranging my pre-amp to look like the Mk IV, I realized that a critical part of the sound comes when the "lead circuit" joins back up with the signal path on page 1. Note that the lead signal comes back into the circuit and then hits V2A. In the old Fender design on which all these Boogie amps were based, this V2A was the make-up/mixer tube for the reverb. I had assumed that this gain stage was just a hold-over from those days and was superfluous to the overdrive sound. Wrong! This last stage does indeed get overdriven and it is an important part of the overall overdrive sound in these amps.

So, for this amp, there are 5 pre-amp stages before the master volume. The first one stays clean, but in my opinion, the next four all contribute to the overdrive. I'd say that that qualifies as "a little bit over many stages".

Chip

[chipaudette]

Steve,

"If you're unlucky, it even smells the same." Man, that cracked me up so bad. Damn funny! The "nuzzled by a kitten" thing was a riot, too.

Thanks for brightening up my work day. Wait...I'm supposed to be working?

Chip

[chipaudette]

Steve,

Your first builds were solid state, huh? Did they have high gain channels? Did you design them from scratch (I know that you're that kind of guy) or did you base them on an existing solid state design? Did you ever get them sounding decent?

For a solid state amp distortion that I respect, I have a buddy who has a GK 250ML (the tiny little stereo amp from the 80s with the 2 x 6.5" speakers). What a tiny little thing! Plugged into an external speaker cab, though, this thing rocks! It's got thrust! Sure, I can only make it do the high-gain thing, but I've never had so much fun doing pinch-harmonic squeelies.

Are you familiar with it? I've not investigated its schematic but do you have any thoughts as to why its solid-state overdrive might work so well? (at least for me it works well)

Thanks,

Chip

[MattT]

I've only built two 'high-gain' amps...one of which is a Dumble ODS-type which isn't really high-gain in the metal sense. The other was an amp similar to a SLO but with a Bogner Ecstasy Lead channel...and the clean is different...but the architecture and switching is similar to a SLO.

The only thing I can add is that if I'm building a high-gain amp...it MUST have an effects loop. I can get high-gain tones from a goosed Marshall...but that doesn't have any good way to put time-based effects on it. So if I'm going to all the trouble of building I really have to have a loop. That won't be the case for everybody but for me it is a must.

Ironically, I built the Bogner-ish amp before the ODS but I used a Dumbleator effects loop in it (slightly modded). My ODS build uses the same loop. I think the loop actually makes both amps sound better...kind of fattens the tone a little and lops off a tiny bit of fizz.

[chipaudette]

Matt,

In your view, how is the SLO pre-amp different than the Ecstacy pre-amp? My memory is that they both use the same number of gain stages with a post-gain, marshall-style tone stack. My memory is that they're both in the same family of high-gain pre-amps which also includes the Dual Rectifier and the Marshall 30th anniversery. What do you think are the critical differences between the SLO and the Ecstacy? Do you have a link to the schematics that you borrowed from?

As for effects loops, I'm also considering putting one into my DRRI. I'd love to put a little bit of delay into my sound and I'm tossing around a couple different effects loop configurations. I'm not familiar with the Dumbleator effects loop. Is it buffered on both send and receive or just on receive? Did you do the buffering with tubes or (say it quietly) solid state? Do you have a link to a schem?

Thanks,

Chip

[MattT]

The SLO and Ecstasy preamps are similar:
Gain Stage - Volume - Gain Stage - Gain Stage with big, unbypassed cathode resistor - Gain Stage - Cathode Follower - Tone Stack. The last Gain Stage - Cathode Follower - Tone Stack is the same as you'll find in any ole Marshall.

The values are different...the Ecstasy values just scream 'Marshall'. Like; 2.7k/.68uF cathode on V1, 470k/470k voltage dividers, etc. The schematic floating around online is extremely close to the Red (lead) channel...but the voltages/power supply have to be right or it will sound really bad (I had built it once before and it was horrible). The Blue channel in an Ecstasy is basically the 2204 preamp. I'm afraid I can't tell you exactly how to get it to sound good...because I just don't know...I got lucky I think.

Go to The Amp Garage and register and you can go into the 'Dumble Files' section and there's a ton of Dumble info there. But it's very disorganized...by design perhaps. The D'Lator is all-tube (the Klienulator is a SS version of the D'Lator thjat was developed by an Amp Garage member...it supposedly sounds very good). SEND is buffered (it's a cathode follower) and the RETURN is just a regular gain stage...it's very basic/simple.