Raffler Amplifier Owners Manual

Version 1.0 for Amplifier Version 1.0

10/13/2004

Minnesota Amplifier Cooperative Table of Contents

Introduction...... 1 Project Background...... 1 Design and Build Goals...... 1 Raffler Features and Characteristics...... 1 Separate Clean and Distorted Channels...... 1 Great Components...... 2 Great Materials and Looks...... 2 Notes on the Circuit Design...... 2 Low Gain Channel...... 2 High Gain Channel...... 2 Preamp Pentode...... 3 Single-Ended Output Stage...... 3 Circuit Topology...... 3 Amplifier Settings...... 4 Master Volume...... 4 Low-Gain Channel...... 4 Clean Tones...... 4 “Chiming” Tones...... 4 Mild-to-Middling Distorted Tones...... 5 High Gain Channel...... 5 Heavy Distortion Tones...... 5 Cleaner Tones...... 5 Channel Switching Pedals...... 6 External Speaker operation...... 6 Allowable tube substitutions...... 6 Non-120Vac operation...... 7 Servicing...... 7 Warranty...... 7 Appendix A: The design team (Bios)...... 8 Appendix B: Schematic...... 9

i Introduction

Project Background The Raffler is a guitar amplifier design and development project involving five Minnesotan contributors to the “AX84.com” amplifier community. We wanted to learn from the design of the amp, have fun collaborating on the project, and develop a fantastic sounding and looking amp.

As we got going with the project the idea came up to raise money for charity by raffling-off the resulting first build of the amplifier, especially within the AX84 community. It was just the right idea, and we found Sweet Relief, a fantastic charity for musicians facing illness, disability, or age-related problems, who were willing to run the raffle and accept the donations. Hence the inspiration for the amplifier’s name: the “Raffler.”

Design and Build Goals The Raffler was designed with the following goals in mind:

1) Great clean sound with maximal “touch sensitivity” and “chime” 2) Superb overdriven and deeply distorted sounds at any volume 3) Exceptional hand-made appearance 4) Minimized build complexity 5) Reasonably compact and lightweight 6) Superb for home use, recording, and has just enough power for a gig.

We think we surpassed the design and build goals on every count, and we think you’ll agree. Raffler Features and Characteristics Toward achieving the above goals, we came up with the following features and characteristics “shopping list.”

Separate Clean and Distorted Channels We felt two separate channels would be needed. Using a single channel would result in compromises toward achieving the greatest clean and distorted tones we wanted. So instead, we decided on having two completely separate high and low gain channels that would allow us to design each to its best advantage. Two separate channels also lend themselves well to channel switching. Also, two channels are flexible: separate instruments or effects chains can be sent to either channel.

Listen to available sound clips and we think you’ll agree: the Raffler has superb clean, overdrive, and heavy distortion sounds at any amplifier volume, with or without power tube distortion.

1 Great Components Next to the design, the components make the biggest contribution to what an amp sounds like and to its long-term reliability. We’ve used great components: Chris Hurley’s Doberman/Heyboer output tranny, a WeberVST C12N type speaker contributed by Russ Shermer, the Jolida EL34, F&T and JJ filter caps, NOS American preamp pentode, metal-oxide resistors (in all but a few places), and orange-drop and “poly” coupling caps, just to name a few.

Great Materials and Looks Credit John Ward for how this amp’s appearance turned out. He has achieved superb results. The cabinet is finger-jointed yellow-pine, with a curly-maple front plate. The finish is danish oil to toughen the pine a bit and bring out the grain, followed by about 9 coats of #3 Bulls Eye shellac for its deep yellow glow. The baffle is 1/2" birch plywood. The cabinet handle and feet are from Jenkins Sound shop.

The 16x8x2 Hammond steel chassis was finished with Rustoleum appliance enamel. Laser printer decal labels (Smallbear electronics) were applied, followed by a couple of polyurethane clear coats. Internally, John’s custom made turret- board supports the point-to-point wiring.

A bit of materials contribution from Carl were the rear model/serial-number plate and the vintage control knobs salvaged from an old PA. They definitely contributed to the extreme hipness of the amp. Note the color coding on those knobs too! Notes on the Circuit Design

Low Gain Channel The low gain channel needed to have a great presence, and sparkle or chime, while using a minimum of tube stages. This led to an unusual tone stack design. The intent was to minimize the tone stack losses as in classic Marshalls, yet offer full-range tone control, ala the Fender “black-face” tone stacks. The resulting design was derived from the “T” notch filter topology used in many old Gibson “Whiteface” amps. It definitely achieved the “low-loss” intent, and the “full-range tone controls” were largely achieved. (Ideally, the bass control could stand a bit more range, but it has been tweaked for the right balance in the amp, making more range an “eh, probably don’t need it” issue)

High Gain Channel The distortion channel needed to use a minimal number of tube sections while sounding better than most all of the “preamp only” distortion and distortion pedals out there. Toward this end, the Raffler borrowed from the distortion channel design of the “Taz Tweed,” an amplifier that achieves some of the best

2 overdrived and heavily-distorted sounds according to our ears, despite only using two stages for distortion.

The sound of this channel is largely due to the circuit between its second and third stages. In this scheme, a resistively-coupled approach is used versus the usual capacitive-coupling. Careful attention is given to signal padding and low- frequency cut-off. The results: the Raffler’s high-gain channel goes from a great reasonably-clean sound to an excellent sounding super-heavy distortion sound.

Preamp Pentode We feel the Raffler has nailed a great “feel” for both clean and distorted playing. A considerable component of this is when its preamp pentode is properly tweaked-in for your guitar and playing style. When you push a pentode, it starts to “squash-up,” or compress. In the right amounts this really makes an amp fun to play, helping bring out the best in players. This pentode also helps achieve a considerable amount of “chime,” something often attributed to amps with preamp pentodes (e.g., some Vox, Matchless, and “boutique” amp designs).

Most other guitar amps with preamp pentodes have the pentode as an input stage. In the Raffler, the pentode was instead moved to the role of driving the output tube. This was partially because we heard the pentode lose character when followed directly by any type of tone stack. We could have put a buffer in to keep that from happening, but that would have raised tube count and circuit complexity. It was also moved because we wanted to get any “touch sensitivity” and/or “chime” applied to the distortion channel too. So, output of both channels is mixed together and amplified by the preamp pentode.

Single-Ended Output Stage We feel that the single-ended output adds significantly to the sound and feel of the amp. There’s a smoothness and warmth in the amp the EL34 single-ended (SE) helps impart at lower amp volumes, and a great grind that it gets at higher volumes. The SE output stage made an phase splitter irrelevant. Tube count (compared to a push-pull design) is reduced by at least one power tube and probably one-half of a preamp tube. Truth be told, that’s probably the real reason we used an SE output: reduced tube count and complexity. It’s a really great output stage borrowed from another AX84 project, the P1 Extreme, by Phil Rowley. Circuit Topology Understanding the amplifier settings below is easier if you understand a bit about the circuit topology of the amplifier. The two channels (low gain and high gain) are completely independent of each other.

The low gain channel has a single input stage going into a low-loss “treble-bass” tone stack, followed by a volume control. In itself this channel won’t distort, but it

3 can be made to get the following preamp pentode to distort, resulting in excellent overdriven tones.

The high gain channel has an input stage followed by two distortion generating stages. It has a tone control that limits the highs generated when distorting. It is followed by a 2kHz notch filter that helps contour the high-gain channel’s tone. Its tone knob has a push-pull switch that partially defeats this contouring filter when pulled. Pulled-out works better for some types of tones/pickups, pushed-in works better for others.

The two channels are mixed together before being amplified by the amp’s preamp pentode. The output levels of either channel can be set to keep this pentode completely clean, start to compress, or distort. The output of the preamp pentode is then limited by the “Master Vol” control before being amplified by the power tube. Amplifier Settings

Master Volume As mentioned above, the Raffler has an overall “Master Vol” control that limits the signal going to the power tubes. As such, both the low gain and high gain channel’s total volume are affected by this control. Typically, start with this control at about one-half of its maximum. For “bedroom” output levels, set this lower. For gigging levels, set it higher. See below for further ideas on how to use this control.

Low-Gain Channel The low gain channel was designed for warm to sparkling clean sounds, but it can also be set to get some great overdrive crunch from the preamp pentode and/or the power tube. Note that setting the amp’s “Master Vol” too low will limit the overall volume available from the amp.

Clean Tones Setting the Low-Gain channel’s “Vol” low, while keeping the “Master Vol” reasonably high will yield great clean tones with lots of presence. Use the “Treble” control to dial in smooth, warm jazz tones toward it’s lower range, chimey pop tones in the middle to upper ranges, and sparkling tones at it’s highest settings. The “Bass” control is used to set just the right bottom end from your guitar for the style you’re playing.

“Chiming” Tones As noted above, some of the amps best “chiming” tones are from the low-gain channel’s “Treble” control set at half up to two-thirds of max. The “chime” from the low gain channel can also be accentuated by pushing the preamp pentode tube a bit. This is done by going slightly toward the control settings for “Mild-to-

4 Moderate Distorted Tones” described below, backing-off to where the tone is still clean but more “chimey.”

Mild-to-Moderate Distorted Tones To get a bit of growl from the Low-Gain channel, set it’s “Vol” knob fairly high (more high for single coils, a bit less for humbuckers), and keep it’s “Treble” knob fairly high too. Then, to keep the overall amp volume from getting too loud, decrease the “Master Vol” lower until you get to the output volume wanted. Start the “Bass” fairly low and work upwards – increasing the “Bass” too much with distorted tones can lead to a “ratty” sounding blocking-type distortion (i.e., not the good type of distortion).

High Gain Channel The high gain channel is designed for great, heavy distortion sounds from it’s 2nd and 3rd stages. It can also deliver surprisingly good cleaner tones.

Heavy Distortion Tones Set the High-Gain channel’s “Vol 2” to about one-quarter to start ,and set the “Vol 1” and “Tone” to about two-thirds maximum. For heavier distortion increase “Vol 1,” although increasing it too far will cause a loss of tone definition - as if the sound is getting “out of focus.” However, this may be desirable if you are looking for “lo-fi” or “fuzz-face” sort of tones.

Humbucking pickups will generally not sound great with “Vol 1” maxed-out. Back “Vol 1” off for humbuckers until a heavy tone with good definition is achieved.

Lower output pickups (e.g. some single coil pickups) can sound good with maximum or near maximum settings on that control.

The “Tone” control can be pulled-out to increase the mid-trebles. Pulled-out settings are often better for “classic rock” guitar tones, while pushed-in settings can be great for the “heavier” stuff.

Once you get the tone to what you’d like, adjust “Vol 2” for the High Gain channel’s overall volume.

Note that you can further add distortion from the preamp pentode into this mix: set the overall “Master Vol” fairly low, then set “Vol 2” somewhat higher. This type of setting can add some great texture if “Vol 2” is not set too high. This approach is the way to get great distortion tones at bedroom volumes.

Cleaner Tones Getting cleaner tones from the high gain channel is done by reducing “Vol 1” to just above zero, and then setting the “Tone” and “Vol 2” controls to get your desired treble-bass balance and output level. Keep in mind that setting “Vol 2” too high will result in the preamp pentode beginning to compress or starting to

5 distort. For cleaner tones, you’ll want to avoid setting “Vol 2” too high. In general, increase the “Master Vol” if cleaner tones are desired from this channel: “Vol 2” can be set lower while achieving higher output volumes Channel Switching Pedals Being that the low and high gain channels are truly separate, an output switch pedal can be used to send your guitar into either channel. This type of setup can be used to switch between channels at the touch of your foot. Boss makes a great switching pedal that is extremely versatile and provides totally silent switching. External Speaker operation The speaker supplied with the S/N 001 Raffler is a WeberVST Ferromax 2 ohm model. Don’t use this speaker in parallel with another speaker. That would either create too low of an impedance (if the other speaker is 2 ohm also), or create a volume mis-match between speakers (if the other speaker is greater than two ohms). When combining speakers, make sure that only two to four ohm loads get applied to the “4 ohm” jack; or four to eight ohm loads get applied to the “8 ohm” jack, or eight to sixteen ohm loads get applied to the “16 ohm” jack. Allowable tube substitutions We’ve played around with many tube types before arriving at the following, which seem to give the most versatility and great sounds:

V1: 12AX7 V2: 12AX7 V3: 6SH7 V4: EL34

If you want to experiment, V1 and V2 can be swapped with any “12A_7” type tube (where the underbar is replaced by “U, V, X, Y, or Z” - note the 5751 is a slightly lower gain 12AX7 type). V3 can be substituted with a 6SJ7.

V4 could be substituted with a KT-77 type or a 6CA7, should you be so lucky as to have either of these old types. Don’t try a 6L6, KT-66, KT-88, or 6550 type without changing the cathode biasing resistor to an appropriate value.

Please note that V1, V3 and V4 are shared between the high gain and low gain channels. This means that if you replace any of those tubes, it will potentially affect the sound, level and distortion character of both channels. V2 can be replaced with a higher or lower gain equivalent to alter the distortion characteristics of the high gain channel. Changing V2 will have no noticeable affect on the low gain channel.

Any brand of replacement or substitute tube should be fine.

6 Non-120Vac operation If this amp is to be used on anything but 110Vac to 125Vac, then a voltage step- up or step down will be needed. Avoid any type of small solid-state “converter,” they won’t work. Instead, use a matching transformer or auto-former rated to 150 watts. The matching transformer or auto-former will be a decent sized, heavy things. The auto-former would be smaller/lighter than the transformer.

Servicing There are lethal voltages and currents inside the Raffler (as there are in all tube amps). If you are not experienced in servicing tube amplifiers, do not attempt to learn on this one. Warranty In the event of failure, this design team warrants parts and labor repairs to one year to the winner of the raffle. You pay shipping to us (insure it), we pay for it back to you (insured).

Any hacks or modifications to the amplifier (even by a skilled professional) will void the warranty. If you want changes, we recommend that you simply build a variation on this amp.

We can’t cover obvious misuse (e.g., plugging it into a 220V outlet, running it without a speaker), or obvious abuse (e.g., a guitar headstock through the speaker grill), but we will be fairly liberal in what constitutes “covered by warranty.”

7 Appendix A: The design team (Bios)

Carl Berger is a systems engineer by profession, electrical and software engineer by training, and an eclectic guitarist since learning to play, “Moby Dick” at the ripe old age of 13. He’s been a member of the AX84 community since its inception, and highly recommends well designed tube amps over any solid state contraptions that he has ever heard. Carl contributed to the design of the Raffler, built a prototype of the amp, and contributed to this manual

Russ Shermer is a physicist by training turned computer consulting professional. He played in a band after high school before college and career took precendence. It was the search for great cranked amp tone at living room volumes that led him to the AX84 community. “Building this amp with the co-op has been a great opportunity to give something back to the AX84 community, contribute to a worthwhile charity and learn from some very skilled amp builders, all at the same time.”

Ross Stites …

John Ward is a biologist with no formal training in engineering or music. "But I have a keen interest in both and building guitar amps has been a great hobby thanks to the AX84 community and especially the MN amp group."

Mark LeSage is a psychologist (behavior analyst to be specific) by training and a behavioral pharmacologist by profession. He took up guitar around age 12, at a time when he enjoyed playing air guitar while listening to Kiss Alive! He has no formal training in electronics. He discovered the AX84.com website in 2000, which prompted his foray into learning about electronics and building guitar amps. Despite the fact that he has built the AX84 P1 and High Octane amps, he remains extremely ignorant about electronics and circuit design compared to the other members of the Raffler team. As such, he has been relegated primarily to role of “amp tester” and web site designer 

8 Appendix B: Schematic

5 4 4 B B B Raffler Rev. 1.0 R4 R9 R13 Berger, Lesage, Shermer, Stites, Ward 81k C2 100k C6 100k C8 Volume 1 High-Gain V1a .0068 V1b .047 V2a .022 C10 Volume II Tone R2 R5 C3 C4 R11 R14 120p 1 M A 1 M A C9 68k .0018 .0068 330k R16 R6 R1 12AX7 R5 12AX7 12AX7 R15 1 M A 120p 1 M 1 M A R12 1 M A 470k R17 R36 C1 C5 22k C7 R3 R7 R8 R10 1 M A 470kC11 470k 1k 22/25 330k 1.5k 0.68/600 10k 0.68 .0022 180p

3 3 B Tone Stack B

Volume R38 2 R19 C26 C14 R23 220k B 220k 1 M A C16 C23 .047 5K-SE .0018 R39 V4 C15 500p 270p V3 C27 V2b 2.2 M Low-Gain 4 R20 R22 R27 R29 30p 500p R26 470k 8 68k R24 1 M A 330k 4.7k R40 R18 C25 EL-34 12AX7 220k 6SJ7 1 M A 16 1 M 1 0.1 B R28 R37 C24 R41 R42 C28 R21 C13 R25 C12 1 M 2.2k 470k 330/5 W 2.2k 22/25 2 M 33/35 150/50 .0022

270 - 0 - 270 120 mA 2 4 5 D1 B B B 1N4007 1 R35 D2 B 1k/5W 3 AC B B1 = 362 Vdc 1N4007 R34 R30 R31 R32 R33 B2 = 348 Vdc 6.3V - Heaters/Lamp B3 = 341 Vdc 100/5W 1k/5W 5.6k/2W 22k/3W 10k/2W B4 = 273 Vdc B5 = 262 Vdc 5V C22 C17 C18 C19 C20 C21 50/500 50/500 40/500 20/500 20/500 20/500