Side track : Reverb Tank

For a long time,  I didn't realize one of the coils in my Ruby reverb tank had broken at the terminal and was not functioning properly.  Fortunately the tank connects with a set of standard RCA connectors (R/W).

 Reverb Tank above.  Reverb I/O taped connectors down-left.

Due to the broke ass tank, I began theorizing the insertion of different effects in the reverb position of the amplifier's circuitry.  

The pictured piece of breadboard is an old tremolo circuit from the amplifier portion of an Allen Classic organ.  The reason I was interested in it at all, in the beginning, was the 'more random motion' switch, as it had it's own placard and switch on the facade of it's original housing.  Who wouldn't be.  Right now I'm hoping it wasn't simply a control for the lesle motor on the horns, but I'm fairly confident in the efficacy of the components, upon rebuilding.

After experimenting with low mix/slow phasing, as well as low mix/shallow depth/high speed tremolo for texturing; being able to use the independent channel and global mix controls for a nonstandard effect for the position gives me a big rubbery one.  

Especially if that effect had an on-board switch for more random motion. The Diablo already features a reverb cancel 1/4" jack, making remote termination of the effect (performance) possible.  This is again just from observation -I have in no way tested the reverb cancel feature on the amplifier.  Hopefully it acts as an toggle for yes/no.

I still have to place an order with mouser for the components to rebuild the tremolo.
After replacing the Power PCB in the Diablo, I haven't had any other components marked as bad, however, I haven't tested all of them.  My primary concern was with noise, and so far we have a lot more headroom than we did.
This is a sidetrack.
Expect new rails.  

Minused emulation circuit

Number one answer, survey says...
Cutting the cap and resistor result in transparency from the amp.
Sounds fuckin' beautiful.
Still trying to wrap my head around equalizing the signal from a potential four points in the signal chain, but I'm trying for the least amount possible.  Of course, some inter-signal equalization is needed to clean up the sound of whatever, but that's collusion.

Resolving all of the solder joints on the LED bar via suction pencil, removal of LED lights, and resoldering each light remedied the three-year flicker.  Sometimes you just have to throw the right amount of amphetamines at something before it will get done.

In summation, two successful tests run since this posting.  Test was with unbalanced 1/4" at -30db setting, which is almost too hot for the Avid eleven rack to handle without clipping.  This makes me eager to test with the balanced XLR out of the Diablo > 11R XLR in w/ pad switch engaged.  The in-line gain control should help mitigate the overwhelming volume.
The unbalanced and balanced inputs are unsurprisingly loud due to their position in the circuit.  The typical use for these outs is for mixer > PA or similar setup.  Hopefully the provided controls are able to accomplish what I'm hoping for.



Upcomming posts:
-Capacitor and resistor master lists written out, after several corrections.
You can't get high and be an accountant; you make a mistake and cost people millions of dollars.
-Intentions of posting scans of handwrites and ctrl-z-able computer lists.  More than likely this will be when I post individually hilighted versions of the schematics for Resistors and Capacitors.
-PCB connector mapping - interconnectors aren't labeled or defined on schematic.  Will aid in general reassembly.

XLR frequency emulation

[23DEC2015 UPDATE : Frequency emulation components are as follows : R20, R21, R22, and C7.
*More information contained within post Ground Force One

In the El Diablo user manual, you'll find an entry that goes something like "...the balanced XLR output on your head is frequency compensated to emulate the sound coming out of your speaker cabinet."

I didn't think anything of this until I wanted to record silently with the head --the main out of any given tube head is essentially the set of cabinet jacks that follow the power tube compliment in the circuit.

With this in mind, and after research for days, I built a small "cabinet load simulator" or "power soak." This device emulates a speaker cab in that it accepts the current the speakers normally would and dissipates that current as heat with a simple resistor circuit.  (Potential post on that device, in the future.)

Many market-side speaker cabinet simulators feature a headphone jack to utilize the rig (Head and cabinet sim) as a headphone amp.  While I could have achieved this, I wanted to keep the resistor circuit simple, making potential future troubleshooting easier.  Also, that signal chain would have made me super nerves.  

Power soak in hand, the next step was signal chain.  TED has so many fucking outputs, it couldn't be difficult. 

Partial wrongs. 

What I sometimes settled on was using the Global FX Send as the output of the head; this is after trying both the balanced out and the GFXS before and after stomp and rack effects.  My reasoning for trying both and not swearing by the XLR is that THE XLR OUTPUT OF THE HEAD IS FREQUENCY COMPENSATED.

This means that, regardless of what you put in to the head, it is going to limit and color the signal in a way you cannot manipulate conveniently.  Or at all, unless you have some serious brain knows.  Or know an electrical engineer.

After my recent and successful battle with signal chain noise, I decided to endeavor toward the balanced XLR out of the head.  That, and the realization that if I'm taking the signal from just after the preamp, it isn't being processed by the power tubes. 

Taking it straight from the GFXS is the signal from everything up to the end of the preamp --gain then eq, then FX send.  

So, I says to myself, Self, I says, let's find that goddamn frequency compensation circuit and eliminate it.  

If you don't know by now, I intend to run the head in to a speaker cabinet emulator.  This way, I need the output to be as transparent as possible, i.e. not pretending it is doing any good boosting or limiting any of the signal in a static manner, after the power tubes, for 'aesthetics.'  Because if I need to eq the signal, I will.  

Don't force it up my ass.  

With all of that out of the way, here is the solution.

Capacitor and resistor compose the frequency compensation circuit, as you can see in the included pictures.  Note that I cut R20 before I took the picture because I get excited easily.

updates with tests on xlr and 1/4" unbalanced sans emulation to follow.

Potentiometers

Here's a list of the pots:
01: 500K-A (warm gain)
02: 50K-A (warm volume)
03: 50K-B (low eq)
04: 25K-B (mid eq)
05: 50K-B (high eq)
06: 50K-B (warm reverb)
07: 500K-A (hot gain)
08: 100K-B (hot volume)
09: 250K-B (contour)
10: 50K-B (low eq)
11: 25K-B (mid)
12: 50K-B (high)
13: 50K-B (hot reverb)
14: 100K-B (attack)
15: 100K-B (reverb master)
16: 50K-B (master volume)

In the beginning

I begin this blog in hopes that other fanatic jacks, unable to find the information they are looking for, find me in their last throes.  

The item of my focus, now and forever, amen, the

Genz-Benz El Diablo 100 H

Granted, I'm sure the 60H and combo versions function on the same principles, but I haven't asked KMC for the schematics to those, because I don't own those, and I don't care.

Not even really sure where to begin here.

I want to provide as much information as possible, both functionally opinionated as well as technically factual, about the tube head model printed above.  

Having played guitar seriously through my early teens and being shit raking poor, I handled a lot of equipment.  Not just the penises of traveling underwear salesmen, I also refer to audio ... stuff.

Not going to gloss over that nonsense because this is what the destination happens to be.

Bought my Diablo in 2011, so by then that specific head was already five years old. (PCB date says 2004.)   I'm fairly certain it was either a lemon or someone spilled a beer directly in to half of the tube sockets and then rearranged all of the metal film capacitors.

I practiced, blew tubes, played shows, and made love to it set up this way for... three years.  Thinking back it was the source of a lot of frustration for a long time.  But when it was good, it was so great, you know, and it only hit me to let me know it loves me.  Just those six times.

Joking aside, all of the troubles with the amp were worth the way it sounded when it was working properly.  The clean channel alone is something only Jesus should be able to hear.

As Genz-Benz was purchased by fender, you are no longer able to purchase parts from the amplifier's manufacturer.  I can't, at least, since apparently everybody only gets one.

BTW

I'm a big fan of re-purposing things, and do not promote buying parts from the manufacturer, anyway.  If you're handy, there are infinite spare parts.  Except capacitors.  Fuck.  Anyway.