Double Cross Pilot Run Finished

by James Brown

Well, 1 week late ain’t too bad!  Yesterday we received the final parts we were waiting for so we could finish up the pilot run on the Double Cross amplifiers today.  So this morning we showed up early and began dealing with all the details remaining to tighten up all the processes and build up these amps so we can get some out there.

The day began with the vinyl covering of the amp cabinets.  This process requires a lot of careful trimming, stretching, and seaming of the vinyl so that the resulting amp is smooth and has no wrinkles…especially on the large cornerless radius on the front.

While the cabinets were drying, we began the process of burning in all the amplifier chassis.  We run all the amplifiers at nominal power for 1 hour, which usually is enough time for any problems to surface.  At the end of the process, the amplifiers are once again tested to make sure that they are still providing the appropriate output voltage.  Here our Assistant Engineer Randy Hampton loads the burn-in rack:

After the cabinets are dry, the stainless finished metal grills are mounted, and the rest of the cabinet hardware is installed like handles, corners etc., in preparation for the final chassis’ to be mounted.

After the burn-in is completed, and after a short cool down, the chassis are mounted into the cabinets.  Here Mechanical Engineer Scott Benson, who was responsible for all the mechanical designwork on the Double Cross, helps install the chassis’ and the tube protection grills on the back of the amplifier:

On the first pilot run of the amps, I get to do the fun job.  QA guy!  Man this thing really cranks.  I had made a last minute tweak to the overall volume the day before, and now it kicks serious ass. 

I’m drinking my celebration Bud Light as I post these pictures online, because it’s been a long road and I’m really satisfied with the amp’s tones, flexability, and I know everybody that plugs in will be excited as I am about what it’ll do.  It’s so chunky, yet heavy, so clear, yet still sustaining…..it cleans up awesome on the lead tones, and if you crank it, it’ll knock your d!&k in the dirt!

I’m happy:

by James Brown

Double Cross Pilot Run–Cabinet assembly

by James Brown

Yesterday the cabinet assembly portion of the Double Cross Pilot run was started.  Our cabinets are made of birch plywood, and here you can see how they are cut from a piece of that plywood using a router.  The result is a cabinet with very accurate dimensions, so the fit is much better than if it were cut using table saws and fixtures like most factories use.

After the pieces are all cut, they are glued and stapled.  Notice that all the inside cleats are mounted using routed ‘dado’s’  This technique insures that everything mounts properly, with little chance for gaps or fit problems.

Closeup of the birch plywood:

The radii on the front are added after the assembly is completed, so the fit between sides and top and front pieces can all be very tight glue joints.

Here’s 5 of the pilot run cabinets after assembly:

Tomorrow we’ll finish covering these, and we’ll finish up the final assembly part of the pilot run.  We should get some out tomorrow if all goes well.

Double Cross Delays

by James Brown

Well I guess it was inevitable that something would delay the completion of the pilot run today…..it turns out that due to some power outages at the transformer factory, we won’t receive the power and output transformers until sometime next week.

Secondly, the footswitch control circuit boards are also delayed.  In manufacturing, it only takes one missing component to prevent building something, but with two it’s even tougher to work around.  So we’ll have to postpone that final build.

As soon as we get the parts in, I will be completing the pilot run and I’ll post some pictures of that assembly process. 

In the meantime, I just uploaded a draft version of the owners manual to the regular location on kustom.com:

Double Cross Owners Manual

Thanks,

James

Double Cross Pilot Run Part II

by James Brown

The final step of the Double Cross electronic assembly is to curve the amplifiers against a standard.  This ensures that all the parts are correct and that the pot tapers are right, etc.  This may seem a little extravagent, but I like the fact that every amp that goes out is the same.

Here’s George McKale, a fellow amp engineer helping out with the testing.

This is a 100% quality check on each chassis assembly, and I receive a set of curves for each serial number amp that goes out.   Here’s the QA inspector performing the curve tests:

The frequency response curve that comes to me shows 3 different curves, one for each channel, and they match reasonably close.  These curves show the result of a very small signal going through the amp, with the effects of all the various eq points in the circuit, both pre and post eq.  If the curve is off more than a couple of dB, then there are bound to be wrong values accidently placed, a solder bridge, or some other variance.  Variation within a couple of dB is usually caused by the knob settings being off a tiny bit, so they’re acceptable.

Now if we’re lucky enough to get the rest of the parts in time, we should be finishing up the pilot run later this week……

Double Cross Pilot Run

by James Brown

Last week we began the pilot run for the Double Cross amplifier.  Some last minute parts arrived on Thursday, and we ran the amps on Friday and Saturday.  These electronic assembled chassis and grills will be installed into cabinets later this week to complete the first batch of amps.  Next week I’ll have to evaluate each one carefully to make sure they match the standard, and at that point we’ll begin shipping some to sales reps, artists, and retail stores.

Here’s some pictures of the process.  I didn’t get a chance to shoot the circuit board assembly before it was complete, but here is one of the chassis before installing the printed circuit boards.

Double Cross chassis prior to assembly

The circuit boards are installed into the chassis:

Chassis buildup

The input jack board is installed and the cables inserted into the main circuit board.

Installing input circuit board

Then the tube hardware, like the cover holders and clips to hold the 6L6s are installed:

Tube hardware is added.

Then the 20 ‘kustom’ designed knobs are installed.  The amp uses 2 sizes, a Kustom tradition, to help the user quickly find the volume and gain knobs which are larger.  The EQ and other knobs are all smaller diameter:

Knobs for Double Cross

One important issue was the grills for the front of the cabinet.  We received the pilot run grills but some were not quite good enough.  The finish had some small imperfections, so I requested revised versions be built with improvements.  These imperfect grills can be used, however, in the amps that go to the safety testing organization:

Pilot run grills arrive

The final assembly is scheduled for Thursday as planned, and barring some unforseen delay in parts, we should make it by the deadline.  I can’t wait to get some of these into our artists and reps hands, and to finally start shipping them to our customers.  I’m sure they’ll be well-received.

Double Cross Rear Panel

by James Brown

Recently I spotted a lot of questions on Harmony Central about the Double Cross, and in particular people wondering about the back panel.  So here it is:

This shows the final chassis, and you can see the added 12AT7 crammed in by the power amp tubes.  5-12AX7s, 1-12AT7s and 6-6L6’s(or EL34’s).

Here’s the Speaker Output system:

It has an impedance selector so you can switch to 16, 8 or 4 ohms and includes 2 parallel speaker jacks.

Here’s the Direct Out:

The DI was a lot of fun.  Using the same method as when we designed the Coupe DI, we positioned a Blue large diaphram studio mic about head-height, and made small adjustments until it sounded the same through headphones as live.  Our lab was designed on a separate slab from the rest of the building, and we have 12 foot ceilings to eliminate the possibility of creating weird resonances.  The resulting curve helped us figure out what to do for the direct output in order to simulate the speaker’s contribution.  Then we replaced the slant with the straight, and redid the curves.  I think it’s very effective, and we had a lot of excited artists at NAMM who were tired of roadies kicking over their carefully positioned ‘57 and ruining their whole nights guitar sound…..and it has the added bonus of being able to mix the sound.  I.E. you could use a slant so it cuts through on stage better, but still use the straight DI sound if you prefer that.

Here’s the Effects and Footswitch area.  The Effects loop is a tube driven effects loop, series connected, and it’s of course footswitch-defeatable.  There are separate Send and Return level controls, which lets you set the level of the loop between about -10dBV(0.3VRMS) and 0dBV(1VRMS)….and there’s sufficient overall gain to compensate up to 10dB for lossy effects!  This is very handy if you have some old delay you love, but you hate when you kick it in and the volume drops a tiny bit.  With this system you can easily make this up.

The Footswitch is a single 1/4″ cable(see the picture in my earlier posting), so it’s easy to replace in the field as opposed to DIN jacks or wimpy Ethernet cables or something like that.  The footswitch cable is usually a weak link of any amp system, so I wanted to make sure to toughen this up.

The MIDI system is very simple.  It works like this:  You plug a MIDI pedal into your effects rig, and the MIDI Out of the effects product into the Double Cross’ MIDI IN jack.  Now to program it, all you do is follow these 3 steps:

1) Send MIDI preset Number to amp.

2) Switch your Double Cross footswitch to the preferred setting.

3) Press and hold the Save button to store it.

Now every time that particular MIDI preset number is sent, the amp will respond accordingly.  You can then either leave your Double Cross footswitch at home, or more likely, you can still use it in conjunction with the MIDI system.  Most other manufacturer’s require you to use complicated MIDI mapping to get to all the footswitch combinations, but I hate that kind of stuff.  Of course it costs more to do it this way, but for this model the cost was of secondary importance to the functionality.

Hope this sheds some light.

 

Double Cross Footswitch System

by: James Brown

Well, I keep bringing up the footswitch, and I’ve made a bunch of headway on it.  It’s a complicated system that handles MIDI as well as provides a 5 button footswitch function via a single stereo cable….kind of like the one on the Coupe.  As a player, I’ve always hated relying on DIN jacks and things like that for a footswitch cables.  For one thing, they can get damaged easily, but also they’re hard to replace in an emergency.  So on the Defender, Coupes, and Double Cross all the footswitches use standard mono or stereo 1/4″ guitar cords.  It costs a little bit more and the technology takes a little bit longer, but ultimately it’s much better.

Here’s the first footswitch system patched into the NAMM 08 prototype.  It was a scary mess:

After I got it working with the rest of the amp, I had to get a new set of circuit boards with the extra transistors and things to drive the channel switching, effects loop, and boost relays properly.  Earlier this week, I received the ‘final’ circuit boards, and now I’m busy comparing them to the previous version to make sure I didn’t lose the tone in the process of implementing this.  So far so good.

The footswitch is pretty cool, and it’s all metal, so you won’t tear it up.  We made it so that it has a separate button for each channel, a boost, and an effects loop switch.  The channel buttons have a neat twist:  If you hit the channel you want, it will go there of course.  But if you hit it again, the amp toggles back to the previous channel.  This way you can use it to punch over to a channel and back real quickly without having to look down again.   So it works more like a stompbox in front of the amp would.

The MIDI part of the footswitch system allows you to access the channels, boost, and effects loop by sending a MIDI preset # to the amp.  If you have a MIDI pedal, all you have to do is patch it into your effects products, then from them into the Double Cross’ MIDI IN jack.  To set up a preset, you just step on the MIDI pedal preset (1 for instance) and your effects unit will go to that preset.  Then you channel select, select the Boost and/or the effects loop of the Double Cross using its normal footswitch.  Then you just press and hold the STORE button on the back of the amp.  From then on, when the amp receives that MIDI preset #, it will perform those footswitch functions.  AND, you can still use your amp’s regular footswitch too.

Double Cross Grill Development

by James Brown

After January NAMM 08, one of the first things we had to do was start tooling the actual metal grill.  Now that the amp was so well received, Scott put the finishing touches on the design, and sent it off to be tooled.  About 2 months later, we received the first rough version so we could check the fit and all the mounting holes and things.

After another month or so, we received a finished part.  The finish is a stainless steel look that really matches well with the rest of the parts on the amp.  This first sample looks awesome!  It has some minor imperfections that you can see when you’re up close, but at a distance I think it’s pretty striking!  …..one step closer to this hotrod hitting the streets.

What’s going on with that footswitch…….

January NAMM 08

by James Brown

 

Well, this time around, we really tried to present the amp in its full-blown glory.  I knew the footswitch circuitry wouldn’t quite make it, but we did the best we could to get the real amp to the show with all the other additional features. 

 

Direct Out:  I borrowed the same ’Blue’ microphone that we had used to develop the Coupe Direct Out circuitry, and proceeded to mic up our Vintage 30 cabinets.  I spent some time moving the microphone around until it sounded the same through a pair of nice Audio Technica headphones as it did listening to the amp.  Basically it was about head height so it wasn’t the typical close-mic in-your-face tone, but a more pleasant sound like you get when you’re standing by the amp playing.  This was used to develp the curves for the switchable DI….one curve for the 412 Straight and another for the 412 Slant.  

 

Footswitchable Effects Loop:  This circuit had to be tweaked a lot to make sure the levels were correct between active and bypassed.  This effects loop uses a True Bypass relay to bypass around it, but even when it’s active, it’s driven by a tube follower.  I spent a lot of time adjusting the gain of the Send and Return Level controls to make sure that you could drive a lot of different level effects without clipping or excessive noise.

 

Extra Gain Sw:  As mentioned on the last listing, it was tough to add this since it was more like traditional gain where it can get a little bit too compressed if you’re not careful….but I tweaked the amount of gain so that it couldn’t overpower the other added stages.  The result gives you a lot more gain, but you don’t lose the dynamics of the Tight and Thick switches.  And I guess it’s hard to argue with one more switch that gives you more gain!  Right?

 

LEDs on the faceplate:  This might seem like a lot of marketing or cosmetics, but I think it’s quite helpful to see what channel is active and to tell if the Effects loop and Boost are active.  Of course there’s a lot of circuitry involved to get that stuff to work, but I think the end result is worth it.

 

Rather than tool up a metal grill like this, we decided to spend some bucks on what’s called an SLA(Stereo Lithography Apparatus) version for the NAMM show.  It’s basically a plastic part made from a machine that ‘prints’ the part in a liquid by using to lasers that are computer controlled.  It builds it one layer at a time, and is pretty amazing as you can tell from these photos.  The nice thing is it allows you to fine tune the fit before you spend 10’s of thousands of dollars for tooling of a real metal grill.

 

Of course the reaction at NAMM was great!  We had a lot of interest in the amp, and took a bunch of orders on it.  This is always a good indication that it’s done right, since anybody could see that we had not cut any corners on the amp.  My motto has always been to try and make what I did last year sound bad.  I can definitely say that this is the best amp I’ve ever designed, and it definitely solves a lot of the subtle problems we’ve all fought with for years with high gain amps, in terms of their typical inability to stay dynamic once you add a ton of gain. 

 

Now if I can just get the footswitch in it and the grill finished……

Double Cross at Winter NAMM ‘07

by James Brown

When we showed the 1st real prototype of the Double Cross at Winter NAMM ‘07, we made no bones about it being just that.  The amp was really more of a test platform to bounce the idea of the Cross Switches off some of our various endorsers, and to get some feedback from the dealers as well.  In order to get it to the show, we had to have the grill made by a local hot rod builder named ‘Sarge’ who hammered the grill out of a flat piece of aluminum.  In his shop, he had a complete 40’s hot rod that he had built from scratch made of sheets of aluminum, which was wild to see!

 The response to the looks, features, and most of all the Cross Switches was phenomenal.  Since most amp companies put switches on lead tones that do dramatic EQ curves and junk like that, I was somewhat leary that folks wouldn’t be able to hear the subtle differences in distortion that we were playing with…..but luckily I was wrong.  Each day at the show I watched guys really get into the combinations of distorted tube tone you could get, and mostly they were all excited about how you could tell when they hit the strings harder or softer.  This is normally only possible with much lower gain amplifiers.

 

‘07 was spent making further tweaks to both the cosmetics and circuitry.  To make the power amp a little more robust, I decided to add a 12AT7 buffer tube between the phase inverter and power amp tubes.  This allows the use of lower bias resistors so that even a borderline power tube will run properly and never thermally run away.  I figured this would be a big benefit for a touring product like this, even with the added cost. 

 

Later in the year, our sales manager Bill Xavier suggested that maybe some people might want a tiny bit more gain.  I had to admit that it was tempting to add 1 more switch to each channel, but I had to carefully play with the amount of additional gain to avoid losing the delicate balance of distortion tones.  When it was all said and done, you could still easily hear each type of distortion and blending them together gave you the best of all.  Especially noticeable is how easily you can hear the G and B strings ring in a chord…even at these gain levels.

 

The last month or so of ‘07 was when we made the most progress toward finishing up this monster of an amplifier project.  Our new Industrial Designer, Matt Copley, made some final tweaks to polish up the grill and artwork, and Scott Benson proceeded to finalize the rest of the mechanical design.  I worked round the clock tweaking the DI to sound like our Vintage 30 cabs, and adding the extra Cross Switch to give you traditional ‘more gain’ in addition to the other 3 previously on the amp.  I just wanted to make sure it would go to 11.

 

Winter NAMM ‘08 was right around the corner………and we still didn’t have the footswitching stuff worked out…….