CORSA AMPLIFIERS

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Design Philosophy

My design journey for the Corsa began with a desire to build a simple, reliable amp that sounded great and still allowed some flexibility for fine-tuning the sound to the guitarist's personal taste. My goal was to create an amp with a seamless transition between clean and distorted tones. I felt that too many amps accomplished this transition rather harshly. That design journey led to the creation of the 18/00 Series amps, which have evolved into the Corsa. I'm proud of the way that this amp responds to picking attack and higher volume settings with increasing harmonic richness and complexity rather than breaking harshly and suddenly into distortion.

The Corsa amp is based around a quad of EL84 output tubes and produces 30 watts of output power (26 watts with 5AR4 rectifier installed.) A half-power switch allows you to shut off two of the tubes for smaller gigs and recording. The power amp section is driven by a two-channel preamp, with a single tone control for each channel. The preamp circuit is designed to accept different tube types to produce different gain structures and variations of the basic tonal characteristic. This allows you to personalize your Corsa to complement your playing style. Contact me for information about tube options.

Channel Link Switch: Years ago, many guitarists discovered that they could get additional gain and overdrive by linking their channels with a patch cable and balancing the two channels' volume controls to get the tone/overdrive desired. The Link switch on the Corsa allows you to do this without the patch cable, using both channels simultaneously regardless of which input jack you choose. The combination of the two differently-voiced channels allows quite a bit of tonal variation. Both tone controls remain active when using the Link switch.

FAQ

What controls are on the Corsa? It's kind of hard to make them out in the picture.

The Corsa amps have two channels: Normal and Bright. Each channel has a volume control, a tone control, and an input jack. There's also a Link switch that hooks you into both channels at once, regardless of which input jack you're using. The two channels are voiced differently from each other in a complementary fashion. By using the link switch, the two volume controls, and the two tone controls, you have a tremendous amount of control over the tone and gain of the amp. Since you can also change the gain and voicing with preamp tube selection (see below), it is easy to tweak the amp to work with your style and setup.

At the right side of the front panel, you'll find a power switch, standby switch, pilot light, and half-power switch.

The back panel has two speaker jacks and an Output Impedance selector switch, with 2-, 4-, 8-, and 16-ohm settings. This allows for lots of flexibility in speaker cabinet selection. Two fuse holders (HV and AC) are also on the back panel.

What's the difference in sound between the 18- and 30-watt settings?

Common sense would seem to suggest that the 30-watt is louder, with more headroom. This is true, but perhaps not to the extent to which you might expect. When you double your output power, you don't double the volume. Yes, the 30-watt setting is louder, but there is more of a tonal variation than a headroom change. Customers have described the 18-watt setting as being "silkier" and the 30-watt setting as being "meaner." This has to do with the way the power supply works and also with how the output section works with the speakers. When running a 5AR4 rectifier, the power levels drop to about 26 and 15 watts on the high- and low-power settings, respectively.

So just how loud is the Corsa on half power?

With a 1x12 cabinet it is about the same volume as a Deluxe Reverb.

What's the tube setup in the Corsa amps?

The Corsa comes with selected NOS JAN-Type 5751 twin triodes in the preamp and phase inverter positions. I chose these tubes for their sweet tone and moderate gain structure. The circuit will accept any of the RCA 9A-based twin triodes in any combination in these two sockets, allowing you to choose from some of the most popular twin triodes around: 12AX7, 12AY7, 12AU7, 6201, 5751, 7025, 5814, 6072, and the like. These choices allow you to adjust the amp's gain characteristics to suit your guitar and playing style. No adjustments are required when changing preamp tubes; just plug 'em in and play.

The output stage uses a quartet of hand-matched EL84 miniature pentodes. I've tried many types of EL84/6BQ5/7189 tubes in the amp, and each type produces its own characteristic tone. The J/J EL84s sound consistently great in this circuit, and I've chosen those as my standard offering. Other types are sometimes available - inquire if you'd like a different type. I can sometimes provide NOS JAN/Phillips 6BQ5s (at extra cost) for those seeking a bit more clean headroom and punch. Please inquire, as supplies are limited.

The Corsa amps can use a 5AR4 rectifier or a solid-state rectifier plugin.

What about bias adjustments?

Since the amp is cathode-biased, it requires no adjustment or re-biasing when you install a new, properly-matched set of output tubes.

Wait a minute. I've read that you can adjust bias on a cathode-biased amp. What gives?

Yes, it is possible to change the bias point of a cathode-biased amp. In the Corsa circuit, however, I've found that local feedback tends to normalize the output, allowing for tube pairs with widely-differing transconductance values and bias sensitivities to produce extremely similar operating points. Technical discussion aside, as long as the quartet of tubes is well matched for idle current, you shouldn't have any problems - plug 'em in and play.

Why didn't you include reverb/tremolo/effects loops?

When I built the original 18/00 (on a DuKane P.A. chassis, in case you were wondering) I wanted to strip things down to the bare essentials as a kind of technical exercise in amp voicing. My goal was to really understand what sonic (rather than technical) consequence was linked to each component change, and I spent an enormous amount of time tweaking the sound into the rich voice of today's Corsa. Once I had arrived at sonic nirvana, I found that any attempts to embellish the circuit traded away some small part of that hard-won tone. My recording (read: more talented than me) clients loved the amp in its pure form, and insisted that I not change a thing. That became the inspiration for me to continue building the circuit in its original minimalist glory.

What kind of construction is used for the circuitry?

The circuitry is assembled on custom-built G-10 epoxy turret boards, and connections are made with Teflon-insulated, silver-plated stranded copper wire. There are no printed circuit boards; all wiring is point to point, and all connections are made with silver solder. It's very labor-intensive, but I believe that it's what's necessary to make the amp sound as good as it does.

Hold it; are you telling me that wire and solder type really make a difference?

Well, everything makes a difference. Some are tiny differences; others are big. If you've ever compared a standard guitar cable to one of the premium ones, you probably found that you could hear a difference. Now, whether that difference sounds better or worse to you is really a matter of personal taste. The tone of any amp is the result of a large number of choices, some subtle and some not so subtle.

It's a little like fine cuisine, in that the difference is often in the details. Does it really matter that your bouillabaisse has teaspoon of crushed red pepper? It's a nuance, but a true connoisseur can tell the difference.

Similarly, you have to find combinations that work: simply combining the "best" of each component won't necessarily make the "best-sounding" amp. To continue with the cooking metaphor, the world's finest olives dipped in the world's finest chocolate probably won't make the world's finest dessert. In my opinion, anyway.

I guess the moral here is to be wary of any blanket statements about topology or component choice. Trust your ears.

Do you subcontract any of the work?

I have an experienced shop do all of my custom transformer winding, and have the panel engraving done by a small local engraver (who has his own $20k laser-engraving machine). I'm getting ready to farm out the chassis sheet metal work for better accuracy and consistency. I do everything else myself, from cutting the wood and finishing the cabinetry to staking the turret boards and wiring the amps. I'll only choose to sub out tasks which can be done better elsewhere; these shops need to meet or exceed my personal standards for quality and consistency.

What kind of speakers should I use with the Corsa head?

The obvious answer would be, "Mine!" Seriously, though, we started out playing the original 18/00 head through a 2 x 12" cabinet from a very well known boutique amplifier company, and it sounded great. Then I hooked it up through my old tweed amp's 12" speaker and it sounded just awful! Man, I was confused; that speaker just killed with the tweed amp. I set out to discover just what was going on. I gathered up about 15 different 12" speakers and auditioned them with the amp (using a few 'golden-ears' studio folks as my barometer.) I was astonished to hear just what a huge difference speakers can make, and how some speakers just seemed to work well with the amp, while other great speakers didn't. That 50's-voiced Alnico 12" that sounded so sweet with my tweed sounded like a cardboard box with the 18/00 Series! Finally, I was able to come to a kind of generalization: to my ears, the 18/00 sounded 'best' with British-voiced speakers. They seemed to have the clarity, chime, and mid- to upper-frequency response that really allowed the amp to shine in all of its harmonic glory. Once I had narrowed the field, we held another audition to choose the best raw speakers to pair up with the amps. My search revealed a clear winner in the WeberVST C12B (Ceramic Blue Dog) speakers (their P12B Alnico Blue Dog sounds great, too!) Ted Weber then went so far as to customize the C12B for my amps, resulting in a unique speaker: the WeberVST C12AC, available only with amps and cabinets from The Audio Cage.

My advice to any guitarist is to try as many different speakers and cabinets as possible with your amps. You'll probably be amazed at the differences, and it's a really economical way to broaden your tonal choices!

Does the amp work well with pedals?

Some of my effects-happy customers claim that the amp is very pedal-friendly. I really like it with clean-boost pedals, but I've heard the amps with some pretty intense distortion pedals and it sounds pretty nice. I like to do it all with pick attack and the guitar volume control, and the amp is really responsive to that kind of manipulation.

I don't like the black and red color scheme. Can you do other colors?

I'm trying to stay with "family" color schemes for the amps, but yes, different color schemes are available at additional cost. I did an outrageous all-red-elephant head for a fellow in Nashville. I nicknamed it 'El Diablo.' If you really don't like any of the standard color schemes, write or call about custom coverings and I'll do what I can to work with you. By the way, the 'TR' suffix on the red and black amps stands for tavola rossa, Italian for 'red panel.'

So how can I hear one?

CAGE amps aren't available in stores; I sell them directly to customers in order to keep the price down. I realize that this makes it kind of tough to try one out, so I have a couple of demo amps that are available for audition. If you're seriously interested in an amp and would like to check one out, contact me via e-mail or phone and we'll go from there.

The demo amps, by the way, are ugly. They are the test mules that I used for development, and bear no physical resemblence to the real deal. Some are even in unfinished cabinets. They do sound identical to production amps, though, so consider them to be sonic demos rather than visual ones!

How long does it take to get one of these things?

All of the amps are built to order (I can't keep stock on hand!) and the lead time varies with my backlog. Typically, it has been running about about twelve weeks from order to shipment, but call or write for current info.

So how do I order one?

Call or write so that we can discuss what you want and I can understand your needs. I'd love to sell everyone an amp, but sometimes there are other choices that might suit you better, and I won't hesitate to steer you elsewhere if I think you'll be happier with something else. Once we come to terms, I'll ask you to send a 50% deposit. Then I'll send you a confirmation letter with your assigned serial number and approximate delivery time. When your amp is nearing completion, I'll write or call to let you know. You can then send me the payment balance, and then I'll ship your amp directly to you.

What if I don't like it?

I want all of my customers to be totally happy with my amps, so there's a 1-week grace period on all purchases. If you're not totally happy, call me to make arrangements for return. Once I've received the amp in as-new condition, I'll send you a full refund.

Do I get a warranty?

Officially, I offer a two-year warranty on parts and workmanship, and ninety days on tubes. Beyond that, if the amp develops a problem that's a result of a problem with design or construction, I'll take care of it.