Hey, Gang! Let’s Design a DIY Amp!

Let’s not just talk about one-knob gear — let’s design some! Any interest in conspiring to create a minimalist DIY amp?

Frankly, the intensity of the reaction to my recent One Knob Manifesto startled me. I had a general sense there was a growing interest in minimalist gear, but I was no idea the sentiment was so intense. (Though I’d hesitate to draw too many conclusions based on a focus group of the obsessive geeks who hang out here.)

Now, don't get your hopes up — we probably won't create anything QUITE this awesome.

Now, don’t get your hopes up — we probably won’t create anything QUITE this awesome.

Since posting that piece, folks have been sending me info on relevant new products, like Henretta’s no-knob stompboxes and the Mill Hill Love amplifier, reportedly being used by Jonny Lang.

The limited edition Love amp fascinates me. Not its ornate furnishings, but the minimal controls: no tone stack, not even a volume control. It’s pretty much exactly what I was talking about when I expressed an interest in an amp with nothing but an on/off switch. That desire became even more focused last week when I reviewed a fabulous amp from a new Colorado Springs company called Toneville. (I’ll link to the Premier Guitar review when it goes live in a couple of weeks.) The Toneville Beale Street model I reviewed features a full compliment of blackface-style controls, but the tone controls are voiced so that the tone stack can largely be removed from the circuit, and there’s also a pot to remove the negative feedback loop for a more tactile/primitive response. As with some other ultra-high-end amps I’ve written about recently (like the Little Walter 50/22 covered here), the tone controls sound great wide-open, and it matters surprisingly little where you set the volume — you just drive it hard enough to warm things up, and then shape the tone from the guitar. With a nicely voiced and biased amp, you need far fewer controls than you might think. And the more crap you omit, more livelier the reponse and the more immediate the tone

The no-controls Mill Hill Love amp.

The no-controls Mill Hill Love amp.

So why don’t we collectively create something in this vein? A simple but great-sounding tube amp with nothing but an on/off switch? I’ve never designed anything such thing and have little relevant expertise beyond the knowledge that, unlike 9v stompboxes, AC-powered amps can kill you. But I’ve built enough kit amps to know that a one-knob head can be easy, potentially inexpensive (though you could invest in ultra-premium tranformers, vintage tubes, NOS parts, and so on), and it should sound stunning. If we come up with a plan, we can source the parts, create step-by-step instructions, and probably get a vendor to put together a kit for us. (I’m thinking out loud here, so bear with me.)

I’m not firm on many details other than these:

  • head-only design (at least initially)
  • low-wattage for home/studio use — something you can crank without self-evicting
  • should sound big and bad-ass (not a cheap, practice-amp sensibility)

Any interest, folks? And more important, any ideas? And more important, any ideas? What would make this fun, useful, and bitchin’?

66 comments to Hey, Gang! Let’s Design a DIY Amp!

  • Sam

    Given my oh-so-limited experience with amp design, I have little in the way of advice or tips. But, I CAN say I’m in!
    I really, really would love to be able to put together a killer little amp with the help of you and the rest of the builders here.

  • Jeremy

    I thought this was going to be a post about the BIAS! iPad app, which has been hyped to death all week for it’s ability to let users design/tweak their own amps!

    you idea of an ultra-simple non-virtual amp is much more fun though; for a long time I used to play through an old single valve record player, and that gave a much better tone than it had any right to!

    • joe

      Hey, some of my old friends are responsible for said hyping, and they’re good at their jobs! ;)

      I’m eager to check out BIAS — though experience suggests that iOS throughput isn’t really formidable enough to deliver seriously great results.

      • Jeremy

        In fairness, I didn’t say it wasn’t worthy of hype – and indeed it was the main reason for me upgrading to IOS7, which I’ve been trying to put off – but the hype has straddled the fine line between brilliant marketing and “not again!” for me. :)

        I’m on a now-lowly original iPad mini and it runs fine, so with the new chips in the Mini 2 and Air, I don’t think you need worry about IOS throughput.

        only thing is, as great as it sounds, BIAS isn’t as good for warming these cold winter nights as much as a real amp.

  • smgear

    I’m definitely in! I was mumbling ‘low wattage, low wattage’ as I read, so I was thrilled that it was in your requirements. I absolutely don’t know enough of the technical side to put circuitry to this petition, but I’d love for it to inherently drive hotter than ‘usual’ so that a fully opened volume pot is breaking up to a tasty degree, but it cleans up when you back off. I know there are endless shades of od flavors out there which all add special sauce, but I hate that I need od to wake up 90% of the amps out there. So I’d prefer if the ‘ratio’s’ were geared so that the natural state has some hair on it rather than having a nice clean that necessitates outboard gear to drive, if that makes sense. I’m not against pummeling that with more OD, but I’d like to be able to send some p90s straight into it and have it sing.

    Of course that would paint it further into a corner, but I love corners…

  • Shizmab Abaye

    I presume you’ve already checked out the AX84 projects over at http://www.ax84.com. Those are pretty stripped down.

    • joe

      No, I had not! Pretty interesting! What do you guys think of the ax84 stuff?

      An EL-84-based project might be a good call, because those tubes are cheap, plentiful, and sound good. Or as Hartley Peavey once cracked, “The EL-84 is the greatest sounding tube of all time, because I get them for 75 cents each.”

      • Oinkus

        Ax84 is a great place with some really serious folks that love amps. Low cost still might not reach the $1.50 I have to my name but you have to love something that doesn’t cost the proverbial arm and leg. EL-84s is as good a place to start with specs as any. I do love my little H&K 18 watt but more for the actual bells and whistles then the wattage. Built in power soak and zero watt out for silent recording plus 2 channels AND an OD on the footswitch. Oh yeah digital reverb too , price not so friendly.I would volunteer to thoroughly trash, I mean test your amps for you guys just send them to me and they will get a complete checkup !

  • thomas4th

    I’m definitely interested in such a project. I can’t say I know much about amp design, but I’m a fan of minimalism done well.

  • vami

    I’ve done a few minimalistic designs with only volume controls but since I often leave them at the same place (for in-house playing) the amps might as well be hard wired and only guitar controls used.
    I’m still indecisive what the best topology for good tone at low volume is. I’ve been experimenting recently with a simple push pull self splitting 12AU7 (nothing new, done long time ago) but I’ve also been working with real pentodes at lower voltages (also, nothing new).
    Unfortunately, most low voltage amps on the market are done by copy cats that use high driving voltages that enable tubes to utilize their full (totally unnecessary) power output.
    When I got hooked on the power scaling topology I was toying with an idea to make an amp with 3 different power settings (.25, 25 and 100% power) instead of a pot, as the only control. I abandoned the idea after actually building my first power scaller as the different power settings required tweaking of the tone stack and drive controls for optimum tone.

    • joe

      Oh man ‚ thanks for chiming in, vami, since you’re a lot further along with this thinking than I am.

      Do you think your switchable power idea might work better if there were no tone stack?

      And might variable input cap work as a crude tone control? Just to siphon off a few highs if things get too bright?

      • vami

        Joe, try to find an amp with a power scaling implemented, I read everything on the subject including Kevin O’Connor’s books but only when I actually experienced the topology I understood what it was all about. Lowering operating voltages scales the power down but it also changes the tone, so some tweaking is usually required to preserve (or get impression of) the original louder tone that you desire. This definitely works better than master volumes or brake boxes, but you would still need a master (and you’d definitely need it if only your power section and inverter are PS-ed down). PS is not the holy grail of low power tones but with a little bit of tweaking it can sound mighty good, depending on what you’re after. I play mostly clean so I don’t have to overdo it. One of the downsides is that I usually play with the tone (and master) settings more after changing guitars, something that I don’t usually do when amps are not PS-ed, but it could be just something in my head (?).
        Dana (Hall Amplification) sells a simplified kit (VVR3) at http://www.hallamplification.com/main.html?src=%2F#2,2. I never tried his kits but reviews are positive (I built everything myself). You can try the cathode version in your Champ (I believe you built one from a kit); that’d be a cheap entry into the field.
        Speaking about simple amps, someone is selling locally a matched guitar/amp set from ’65 (Epiphone The Professional). The amp has only one knob. Why? Because all amp controls are on the guitar :-)

  • joe

    Oh —and here’s a closer look at the guts of the no-knob Mill Hill Love amp: http://www.millhillaudio.com/Love-Circuit-Card.html

  • NotSoFast

    No experience here but I’d follow along at home. I’ve got a Reason Bambino amp with a 6AQ5 tube and NOS those run $3 on eBay. The Bambino sound great – without the extra circuitry it might be better.

  • I’ve got a pet theory that part of why big amps sound different from little amps is the difference in the circuit blocks used in the design. A Champ type design can sound great, but doesn’t sound entirely like a Twin, even with the AB763-type preamp circuit in common. Beyond the power of the output section, there’s the long-tailed pair phase inverter and there’s the fixed biasing.

    The things that make for cheap, small, easy to DIY amps, though, tend to be typical small-amp design features and not to be big-amp design features. It’s a weird balance to attack head on. So we tend to go single-ended and cathode biased. Doesn’t sound bad at all, just different.

    Hit a middle ground, I guess. Adapt an earlier octal-preamp tweed circuit for more common preamp tubes, and stick to a lower powered output pair. EL-84s are so common in cheap amps these days that if I were trying to save tube costs I’d go for Russian 6P1P tubes–6AQ5 equivalents an a nine-pin socket at a couple bucks a pop. They’re like 6V6′s with a lower voltage headroom and a bit less output, which is all to the good for the project.

    If you want less homework, just do a tweed Harvard (good enough for Steve Cropper) using half of a dual triode instead of the single triode for the first stage.

  • smgear

    fyi, the Mill Hill Summer is a 3.5 watt cathode base so you can swap tubes easily.

    I can’t find any samples or schems, but..
    http://www.millhillaudio.com/Summer_Main.html
    http://www.amptone.com/millhillsummer.htm

    That approach might be nice so you can customize it easily by swapping tubes

  • Sounds like a great way to spend a weekend. I’m in.

  • Dave

    I’ve just picked up a kay 504 (50s vibro-champ-ish) amp. It’s really very very nice for recording, simple circuit; breaks up easily; trem sounds lovely. It’s got an 8″ speaker which is actually lovely and I think marrying the speaker to the cicuit might actually be an important extension of the 1 knob manifesto. This thing has an old jensen ceramic in it that I think helps give the amp a distinct voice.

    For recording I’m not sure a larger speaker is necessarily better (I get some huge tones out of a 6″ speaker built into a tube tape recorder) but maybe a speaker out might be a good compromise?

    Anyway – the other observation I have is that the tone control doesn’t necessarily sound best all the way open. This particular amp uses the tone control as the on/off switch and I’ve found through lazy experientation that I tend to prefer it rolled off a touch. I don’t have a tone control on my tele though, as it’s wired ala a broadcaster. Anyway, the point here is I wonder if having a tone circuit that’s voiced for the amp / speaker combination might be better than either ‘wide open’ or variable?

  • joe

    Thanks Dave! What tubes are in the Kay?

    Man, I continue to be stumped by how the amount of lows a speaker moves so often seems to have little bearing on the speaker’s size. I’ve measured dozens and dozens of speakers of different sizes and ages, and the results never fail to surprise. The most bass-intensive speaker I’ve found is an 8″ from a 1950s Magnatone combo.

    I think that, initially at least, this project will be a head only. The upside is, if lots of folks build one, we can compare results with various configurations.

    • mwseniff

      Cabinet design has a huge effect on bass response. The infinite baffle can produce impressive bass from small speakers. An open back guitar cab is the simplest form of infinite baffle speaker cabs. As most folks have noticed using open back guitar amps that bass response varies dramatically due to placement of the amp. The only true way to measure a woofers response is with a standard cabinet and a well understood testing space. One of the cool things about building as a head for test projects is to use spkr cabs you know well for testing. But there are many things that control bass in a woofer like cone weight and material, surround design and material, spider, and even coil design and magnet specs.

      Besides a spkr cab can be the next project :-)

  • CroftyTTL

    I reckon this could wind up being quite an awesome project – I’ve wanted a tiny valve head for a while, just as a fun toy, and as a head it would be great.

    The smallest possible footprint would be nice to see too – I’m wondering if mounting the tubes sideways would be plausible? I’m not sure how much it would affect heat dispersion or travel safety though.

    Personally, as and when this is in place and ready to build, I’ll be finding a way to mount one inside of an old broken N64 I have knocking about.

    • joe

      Cool! I haven’t even started coming up with ideas for enclosures. There are so many fun possibilities!

      I haven’t tried the Toneville Rio Grande, which is built into a metal utility box. Maybe some kind of steel tool box? Anyone have good ideas?

  • Frank

    Joe,
    I live in France quite expensive to get any good amp at a reasonable price here unless you go to the UK, then the exchange rate will cost you, so I’m up for a do it yourself. I did come across a Trace Elliot 15w Velocette, was blown away by the sound of that little amp, with only a tone & volume and a hi-low switch. Apparently they are very similar to the Old Gibson Goldtones.

  • wrangle

    I don’t think I’ll be building an amp any time soon (I only just started doing some rudimentary soldering a week ago), but I’m a huge fan of minimalist equipment & really looking forward to seeing how this project progresses.

    For myself, I tend to like clearer, cleaner amps because I usually like to use a fuzz or similar device for dirt. Bearing this in mind, I was curious if anyone has ever designed a stompbox specifically to compliment a no-control amp?

  • Evil

    I’ve been pondering something similar as a low watt beast.

    Something to think about are those TV-oriented tubes that you can still get tons of cheap ($2 each-ish) – the ones that have captured my imagination are the 12FX5′s or 12CA5′s for power tubes – they should be able to work on the output of the quite common and cheapish 120v-12v transformers run back to back for power. You could put a quad of them in the amp at a (ballpark) output at 6W total and still get that gnarly complex pentode power tube swirl at relatively low wattage.

    Or contrariwise use just one of these pentodes for about a Watt and change of straight up Class A power output. Put a dual triode of your liking in the front end for a simple two tube amp, but lower output than the two tube EL-84 based amps that are so common. . .

  • Tonechaser

    If the pic shows up here is my favorite amp and it only has a vol. knob. It’s a very old supro and sounds like the bee’s knees. These old amps are relatively simple and sound great.

  • This is a great idea. I’ve done some solid state builds, but tube projects would be new territory, so it’d be great to learn. 6v6, EL84, less likely tubes…so many good tubes to choose from. (I seem to recall Zachary Vex demonstrating the ones in his Imp Amp were late-tube-period military surplus that would survive hammer blows…but if I had one, I wouldn’t try that.)

    Joe, I wonder if your observation on speaker bass response doesn’t have something to do with cone tensioning. I have absolutely no physics to back that up, but obviously diameter alone isn’t a predictor of bass extension. I do have experience with doing an audio installation for which all my sound reinforcement options fell through, so I brought a couple Klipsch powered computer speakers, and they really brought the bass–especially after I zip-tied them to paving blocks (to keep them from walking away during the installation). Granted, they were in a very reflective space (the former restroom of Cleveland’s subway station under the Detroit-Superior bridge), but they sure filled the room, on down to the 30-40 Hz range.

    • smgear

      yeah, for some reason, despite all the other factors that we musicians obsess about in the chain, we generally ignore the physics of the cab itself. Design of the cab, surfaces/materials, Q, ports, baffles, etc are often overlooked. In one regard, the ‘flaws’ of an open fender design define to the essential character of that ‘tone’, but if you want balanced, uniquely tuned, or more full range tone from a small speaker, then there is a lot you could do by intelligently designing the cab with respect to different speaker characteristics and desired ‘tone’. Then there’s some relatively new theoretical ‘advancements’ like current driving cones which could change the whole equation (maybe in a good way, maybe not). Anyways, perhaps that could be part two of this diy exercise – small cabs for home recording.

  • mwseniff

    Sounds like a great idea to me. I would have to go count them but I have a big stash 25L6′s that came from an old building a buddy was rehabbing they are all new but the boxes have a bit of water damage. These tubes have been sitting in my garage for 12 years or so in a box. I would contribute these to this project. The 25L6 was used in portable record players in a series filament design which we wouldn’t want to do but we would need a 25 volt filament supply (perhaps the other lower voltage filament tubes could use 3 pin voltage regulators for their filaments. These tubes produced 2-3 watts single ended and have more of a 6V6 sound than a 6L6 sound. For more power you could run them in single ended parallel or in P-P for 10 watts. If odd ball tubes were used it would make it a unique project. It could even be a series filament design if a isolation style xfrmr was used on the AC line.

  • Roger

    This does sound like a serioulsy good idea! I think I could learn a lot from this project. Hopefull I will be able to “build along” with you guys.

  • It doesn’t seem to me as though there is a lot of actual design work to do but I’d vote for using standard and readily available tubes. I would think it would not be too difficult to punch a chassis for both a 9 pin Noval base and an octal base for the power tube (or maybe just allow for an octal to noval adaptor). Then it might be possible to allow the option of using an EL84 a 6V6 or an EL34 for the output tube. Stick a 12AX7 in front and you are good to go. Since there are two triodes in the 12AX7 and there is not going to be a lossy tone stack in the way I would think there might be enough gain to even produce some overdrive. And no need for ridiculous boutique parts crafted from orichalcum and insulated with dried unicorn scrotum. Just good quality modern resistors and capacitors and ordinary copper wire.

  • NotSoFast

    Trying to think of something good for cases. Thought it would great if the case was a flight case – nothing to pack. But they aren’t very stiff and don’t have air openings. Then thought about those metal attaché cases… until I checked what they cost. Vintage luggage also lacks the air flow and stiffness. Then I thought about crates and… well, that’s been done!

    But then…. computer cases! They are varied, inexpensive or ornate, led lights. They have airflow. Fans if needed. They look good next to computers. Some are quite compact and luggable. Check this one:
    http://www.frozencpu.com/products/17613/cst-1349/BitFenix_Prodigy_Mini-ITX_Tower_Computer_Case_-_Midnight_Black_w_Bolt-On_Window.html?gclid=CJX-rpHzgbsCFUpBQgodURsAVg#blank

    There are metal ones. Plastic ones. Clear ones. Long ones, tall ones, short ones, brown ones. Google images show hundreds. Mass produced, cheap, tough, made for electronics.

  • NotSoFast

    Bonus points if the DVD tray can hold a beer.

  • Well you really have to build valve amps on a strong rigid metal chassis, so it’s not that difficult to use that as the frame and bolt a couple of wooden ends to it, with a bottom plate and a perforated screen over the top to protect and ventilate the valves. A two valve amp like this is not going to require a large case (I’d guess you could build it as 1 foot by 6 by 6 inches (in those quaint British Imperial measurements I believe you still use over there in the colonies) and I would suggest you want it to be as small and lightweight as possible.
    Often repurposing containers to house electronics they were not designed for is a lot of work and usually only worth doing for the quirk factor.

    • mwseniff

      I second the repurposing cabinet as a bad idea. A simple folded metal chassis would be best ideally non-magnetic steel flashed with copper on the inside of the chassis for a good low impedance ground plane. However a steel chassis doesn’t need to be that fancy. I wonder if we have enough interest to get the metal work done by a sheet metal fabricator that could punch the chassis for tube sockets and controls etc. it would be a lot safer for beginners to have a sturdy chassis with the transformers, tubes, controls and components all held in place rather than a rats nest of construction. Having a standard chassis would make troubleshooting over the blog much easier. I would like to see extra tube sockets for further experimentation.

  • stew

    I know nothing about amp building, but love the idea of a small, flexible vale amp as a kit suitable for beginners … watching!

  • NotSoFast

    Well I demonstrably do know nothing about building amps. I’ll listen and learn. Thanks!

  • NotSoFast

    …eyes old PowerPC Mac Pro case like a turkey before a feast… Oh, never mind. I will listen! I will!

  • Jason

    What about using something like an 11MS8 that has a triode and pentode in the same bottle and making it a one tube no knob amp? :satansmoking:

  • I really want to build an amp. I built a Fender champ type kit a few years ago, and recently bought a kit to build a 18 Watt type, which I haven’t started yet. This project sounds more interesting than the new kit.

    An obvious starting point would be to start from an existing design. Here’s a video that auditions a series of old time smaller amps. This might offer some ideas for a starting point.

    http://www.youtube.com/watch?v=NQfiw4F1Bv4

  • Shayne

    Apologies if I’m repeating something further up the thread, but there are a lot of DIY guitar amps out there – I think this site deserves something truly different. Germanium first stage, for one. And I think a static induction transistor for the output – very triode like, though somewhat hard to find. See http://www.firstwatt.com/sitintro.html ; I’m sure if we were to actually try to do a guitar SIT design the good folks who frequent diyaudio.com would be able to help find us the parts.

    • Interesting. Any commonly available SITs in current production or new-old stock in quantity? From the hifi perspective it looks to be about the advantages of triode output without the output transformer. I think some of us might actually prefer an output transformer for a guitar amp.

      • Shayne Hodge

        Well, you could probably use a transformer anyway – I know McIntosh does on their solid state designs. (Technically an autoformer, I think).

        I’m not sure of part availability. From the threads I looked at people buying fakes off ebay was a problem, but I’d have to imagine they can still be scrounged up.

        The SIT power amps I’ve seen are typically at 1-2% THD at 1 – 1.5W, which makes me wonder if one couldn’t get a really nice bit of distortion from them at 3-5W. They also have really simple circuits, which is nice.

    • smgear

      that SIT concept sounds well-worth a try. I’ll run it by a friend of mine next time I see him. He is a circuit encyclopedia and has a great stockpile of hard to find tubes and components.

  • Wade

    What I really would like is a very small tube amp. I have a Yamaha THR10 and I have a Lunchbox mini. Both are good and do certain things well. But I would like to have a small tube amp. I think this is what the market is missing. And it needs to do clean tones well. I think 1amp max and maybe even 1/2 amp is where I would like to see one. There are plenty of 8-16watt amps and of course these are good for practice as well as gigs — I love my Blues Jr w Bill M mods, but I think what is needed is a smaller version for playing when your kids are sleeping or travel or somewhere where you want that tube sound, but you can’t easily take your real amp.

    • Bebah Palulah

      Maybe it seems counter intuitive, but clean sounds need more headroom than overdriven sounds. It’s way easier to get overdrive out of these low wattage amps. So if you want low power AND nice clean sounds AND the ability to play well with single coils and humbuckers you’re almost inevitably going to need some type of compression or limiting which takes it right out of the “simple” category.

      That said, I’d love to be proven wrong!

  • glpease

    Some random thoughts:

    This could be a really fun project. I’ve done a few small, low power designs. There are a lot of tradeoffs, and it’s probably important to consider what’s wanted in the final outcome. All valves? As previously mentioned, good clean tones want headroom, and that means more watts, unless very low volumes are used. And, getting both good clean tones and good crunchy tones with a single knob is a challenge, and with NO knobs, it might be nearly impossible in most cases.

    For clean tones, I like good low end response, but when things get really crunchy, that same bass response can drive the small amp into the “farty” zone pretty quickly. In low power builds, I usually limit the low-end response to keep things lively, but with some guitars, this often comes at the cost of anemic clean tones. I experimented with some ideas to adjusts the low end response as the gain is increased, but so far, nothing really compelling has come of that. And, of course, the beauty of simple designs is transparency, so putting too much passive filtering in the signal path isn’t necessarily a “Good Thing.”

    In principle, I like Joe’s idea of a no-knob amp, but this presents even more challenges than a gain-only design. Depending on the guitar’s pickups and wiring, simply rolling the volume down can radically change its tonal characteristics. Volume pots with treble bleeds will further accentuate highs at low volumes, increasing shrillness, and emphasizing the potential for auditory anemia mentioned above. HBs with conventional wiring can lose too much treble as the pot heads anti-clockwise, choking the life out of the tone, further resulting in the phenomenon of the system sounding good only when wide-open, or close to it.

    Cranked big amps sound like they do partially because of the huge volumes of air they’re moving, and the influence of that air movement on the guitar itself. Killer sustain isn’t just the product of gain, but of SPL as well. Even my 15W amps sound better when they push the cones hard than they do at low volumes. MIc up a big amp and play from a different room for an idea of just how much interaction there is between axe and air. And, most of the small amps we’ve grown to love are in boxes that are far from rigid. The interaction between cabinet and speaker starts to be a significant factor in the amps “feel” only at higher volumes.

    Since the goal is a head, not a combo, speaker and cabinet choice will have a huge influence on the final tone. I hot-rodded a Champion 600 for a friend. The finished amp sounded remarkable played through a big cab, but dreadful through the tissue-paper stock speaker in its small, relatively rigid box. I put a Jensen in it which improved it a little, but not enough to make it something *I* wanted to play through.

    Finally, with a project like this, it’s hard to avoid the “committee syndrome.” With a lot of cooks, each adding their own spices, the soup may indeed get muddled. Getting all that sorted may well end up being part of the fun of the game, though. If this moves forwards, I’d love to play!

  • el reclusa

    Semirelated to this whole shebang, inasmuch as the idea of a 2 el84 amp with minimalist controls: just saw a kinda goofy, sorta-Decoish Fender amp called a “Pawn Shop Vaporizer” (huh?) that’s 2 x 10, 2 el84s and- get this- has a footswitchable mode that bypasses the volume and tone controls completely. And apparently it has reverb. For $400 new. I’m sure it’d gotta be cheap, Chinese, probably lots of surface-mount junk. Cool idea, at least…

    • mwseniff

      I have the Fender Pawn Shop Excalibur (2-6V6 w/15″ spkr), it sounds great. the one I have is the original one and there is a new version with a different spkr but they cost a bit more I haven’t heard one yet. I might replace the spkr in mine with an alnico spkr a vintage JBL D130 would be sweet if I could find an affordable one but that is unlikely. But I have to say the amp sounded great right out of the box it loves fx pedals. It works well in a band and it can get very loud.
      My buddy has a Greta and it sounds great even at low volume levels.

      • I’m eyeing the older brown model without the speaker upgrade. It’s getting cleared out for $200 from some places. For a 15″ alnico, I’ve had my eye on the Tungsten T15Q — 20 watter in Jensen style for $140. Best cheap source I hear for vintage alnico is pulls from old organs, hifis, etc., but those are often dinkier than guitar speaks and I don’t know how often 15s come up.

  • Paul Stacey

    I’ve heard some very impressive stuff from the Fender Greta – might be worth stealing.

  • el reclusa

    I reeeeally wanted a Greta for conversation-level playing, as we have a baby due in a little over 50 days now and I wanted neither to disturb her nor hafta only play through my plastic Marshall toy amp. Fortunately, I snagged a Jet City Picovalve a couple of months back when they were on clearance for peanuts, and the 2W setting is actually not too shabby at really low levels. Actually, for a cheap imported amp, it’s really not bad at all. I dunno how far I’d trust it to gig with on a regular basis, but for home use it’s a winner.

  • SFer

    makes me think of the noisey cricket from now defunct (?) beavis audio, at lesat as design inspiration?

  • Dan

    I made a little amp in Y2K using a variation of a Vox AC-4 schematic, some roofing copper and some oak for the sides. It has a tone control and a cathode bypass capacitor that can be defeated. I use it in my home studio all the time with a homemade speaker cab. The cab has two 10″ Weber alnicos, one open back and one closed. I can pick either speaker or both, series or parallel. Most of the time I leave the tone control out of the circuit. I probably record more with this little amp than any other amp I’ve got. It’s easy and doesn’t hurt my ears (as much).

    http://danharrisdesign.com/wp-content/uploads/2014/02/2014-02-11-09.12.26.jpg

  • I put this together this afternoon- had countless issues. You know how some days things just don’t come together? Well, this is some really poor playing, but at least the clean tones came up pretty well on my little amp. I’ll try to do another vid using my old Strat and my latest homemade guitar- the Halloween Guitar.
    Here’s a Youtube link to the demo-
    http://www.youtube.com/watch?v=nSsY3yn0tks

  • Basically it’s a Vox AC4 schematic, but I used what I had kicking around in the parts bin, added the defeat switches for the tone and cathode cap. I bought some NOS Canadian output transformers (I think I got 5 of them)and they sound really great- wish I could get more of them! They work fine looking at 4-16 ohm loads.

    I’ve been reading about your fuzz box experiments- thanks for all the research! I just ordered some germanium transistors and I might build in a switchable stage of gain using one of these. Gonna try to build one of your fuzzes- I discovered they are out of stock of kits.

    • Shizmab Abaye

      After my one class A amp rebuild, I looked at what it would take to reinvent the design with new off the shelf parts. From my brief research I’d have to say that the cost of the transformers is the limiting factor – the replacement output transformer for a 1 watt Blackstar amp from Mercury Magnetics will run you $55! That’s more than I spent on my vintage amp.

      I think there may be some price gouging on any transformer designs thought to have tube amp applications. Surely MM is not the bargain basement place to get transformers. Think about it – these things are made of wire, iron, glue, plastic and/or paper. Production does not require ridiculously expensive equipment.

      If you could convert an old PT Cruiser to a transformer winder using the odometer somehow to count turns, you might be in for a better deal.

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