The Fenton Project Final?

Here she is in her new home with her new best friend:

The Fenton Project VIII

The amp is assembled and we are doing the real testing.

The initial tryout was with a Marshall 2x12 cab and my Gibson Nighthawk.

This amp is a little screamer. Fat, blooming overdrive. Tons of gain! Too much? This is where you get questions that will drive you crazy. Perspective is everything. What I'm loving is that it does like to take off, just grab a note and feed it back if you let it. Nice. Hit a note, bend it up, let the feedback catch, then slowly bend back and it catches the octave harmonic and feeds that back. Sweet.

That Nighthawk has a huge bridge Pup and the neck I have in there is no softy either. Hmmm, it sounds good, maybe great, but ... Some clean is essential. This starts breaking up real early. But it all works and well and the sound is there. Time to try it with the speaker and cab it will live with and more typical guitars.

In the cab with a Tele. Now we're talking. I can dial in however much gain I want off the guitar. Just set the volume on the amp for however much max gain I'll want, set that tone control to be as bright as I'd ever want and work the controls on the guitar. The tone control is very interactive with the volume, much the way a "bright" switch has little effect when the volume is turned up. Not a very severe affect either, just dials in more or less treble and bass. Nice.

Tried it with my Strat with Duncan Classic Live Wire, active pickups. It liked that too. Same with the Hamer with Rio Grande Bastard P90-ish pickups.

The overall tone is very open and broad and strongly reflects the guitar. Some amps tend to homogenize things, this one just makes the guitar louder and adds however much gain and overdrive you like.

The acid test -- how's it play in church? Perfectly well behaved. Was mostly clean for this set and it handled it very well. The Volume on the amp was around 10 o'clock and the guitar was mostly down for the clean stuff and only got wound up for one song. It behaved very nicely on the edge of break up. Many amps tend to give you something like a clean tone, but with fur on it. This was just a clear crunching tone at that point.

All in all, I'm gruntled and the amp ships soon.

The Fenton Project VII

Everything is wired and time to test!!!!!

As with any new build or extensive overhaul it's best to power up slowly. A variac works well, to apply power gradually. I prefer the safety light approach. It reacts faster than I can read a current meter and it's more or less automatic. A 100 watt bulb will limit maximum current to something under one Amp and that is low enough that no serious damage would result from any problems.

Good thing I didn't trim the Output Transformer primary leads to length - as feared they were out of phase with the rest of the circuit and needed to be reversed. This is one of those things that are easier to identify with a function test than by pulsing the tranny and testing phase.

Now that everything works let's run it up on the scope and see what we get. Ooh, lots of gain. Bias check shows the power tubes dropping 13V across the 150 Ohm Cathode resistor; we've got 370V at the plate for a static dissipation of 15.5W per tube. A bit hot but no hotter than a lot of other EL84 amps. We'll run with this for now. Once we've got a baseline on the sound we'll see if cooling them off doesn't hurt.

Running it up into an 8 Ohm dummy load we get 18WRMS at 400Hz as the top and bottom of the waveform start to round off. Pretty much what you'd expect. Run a few different frequencies and some square wave to test the tone control. Time for a half power / one hour burn in. Everything appears solid and stable, nothing overheats and no extraneous noise appears on the 'scope.

Now for a real test - the test instrument is a Marshall 1936 2x12 cabinet. Plug in, power up, dead quiet. Turn everything up and there's the expected shhhhh of gain noise, but that's all there is no hum, sizzle or buzz. Now the guitar ...

The Fenton Project VI

We are close to the limits of my understanding of Roman Numerals (all of which is learned, like every American, from the Super Bowl) and my photographic limitations are taking a toll.

When we left off, I had connected the main power supply wiring, leaving the power cord for last so it wouldn't get in the way on the bench. Now it's time for the output transformer.


Early on, I was thinking to break out the wire lacing ribbon and go old-school HiWatt on it. However, the necessity of just getting this thing done sorta became a priority. The hand lacing is beautiful, but wire ties work too and since I'm only making one of these there isn't time to build the sort of wiring jig that would make lacing fast. You'll note that I left the primaries of the Output Tranny long enough to swap. Having had a painful formative experience with a mis-marked transformer I always do this until the phase is confirmed and then clean up the excess lead.


With the back of the amp wired up, now it's time to do the front. It's much easier to do this stuff without other things in the way. Yes, shielded wire on the low level stuff like from the input jack to the first stage and from the volume/tone controls back to the recovery stage. Why? Because I can. It doesn't cost much and could save time later. Anyone who has ever had to futz with the green wires in an old Marshall to get them exactly where they belong (just so high above the chassis, not near this, not too high) will understand.



So let's drop the board in and wire it up. Here is where the planning pays off. This part went fast and smooth enough I just got in a groove and neglected to take pictures.


A little front end detail.

Here she is ready for tubes and applied voltage.

There's the cute little back side. The stacked jacks are 4 Ohms. The only reason I could see for adding a pair of 8 Ohm jacks is to run a full stack. Doesn't look likely. But running this with an extension cab seems real probable so let's make it easy.


Pretty, isn't it. I like the big Alco knobs. I use them on everything. Great look and feel.

Next phase is to power up, do some testing and detailing on the wiring - then to fit it in the cab and rock out a little.

The Fenton Project III

Here's the populated board with all flying leads attached looking for a home. The circuitry for each stage follows in order and parallels the tube placement so there will be a minimum of crossing wires and nothing is close that can't run together.

In the interest of a neat layout nearly everything mounts to the board. The tone control network will mount on the back of the pots, very simple and neat and the signal from the tone and volume will run directly to the next tube stage through a shielded lead.

Grounds for the preamp section are all grouped and run together to the common buss at the main filter / decoupling cap.

Next we get the chassis drilled, hardware mounted and start with the off-board wiring.

The Fenton Project

This is an interesting project. Commissioned by a fellow TGP'er, I am building an amp inspired by the Fenton 110. This is a variant on the classic 2xEL84 theme. Everybody and his kid brother has a Marshall 18W alike or Vox AC15-ish amp - this was different enough to be interesting and right in line with my experience with EL84 practice.

I had never heard of this company before - NB, this is not the vintage Fenton Weill - rather a small and now defunct builder. My client had tried this amp for a time and liked it, and now wanted one for himself but has been unable to find one.



A couple of things stand out about this design, and there are a few changes in store. Since we aren't going to be using the low gain input jack, that component will be omitted, which should make for better reliability (I've worked on a lot of JCM 800s with the complaint of "lo gain input works, hi gain doesn't). We're also making a change to the power supply. Our build will use some extremely beefy AC15 type iron from Magnetic Components. This means a 6CA4 rectifier tube instead of the 5Y3. The original used a Fender Deluxe Reverb type output tranny so this should be a good bit more solid.

The client has a very nice 1x12 cab that was previously occupied by a heavily modded Epiphone Valve Jr that the new amp will be designed to go into.



Updates to follow shortly.

Been Busy

Been busy building and prototyping pedals and revising and updating the PCBs. Progress is sweet but slow.

In the meanwhile, go enjoy some FX pedal history. There you'll find the history of Fuzz as seen from the Country music perspective. Lots of great links to musical samples and examples.

GO! Now!

Hero Pedal with Down By Law - LIVE.

That last video was sweet. Now back to what we normally do around here. Rock out.

That was Sam with Down by Law in Brazil. Yeah, the video is a bit crude, but whaddya want, it still rocks.

More Dirt Removal

So, we've talked about preventing problems by exercising all the controls and jacks. We've turned all the knobs and flipped all the switches and run a plug in and out of all the jacks. So anything still not working right needs more than just exercise. Almost everything here applies to pedals and guitar electronics as well as to amps.

Mostly we're going to approach this from the point of view of solving a problem. You may not need to address everything discussed here. If you've got a noisy switch or a jack that hums when nothing is plugged in you might not want to do the whole amp, especially if it is otherwise clean and in good shape. But if you've got something that's been left in a shed or has a lot of obscure noises, get it all.

Let me introduce my favorite product in the world. Caig Deoxit D5.

You need a can of this. It isn't cheap, $12 - 18 for the size shown but it will last a long time and do a tremendous amount of good while it lasts. There are other worthwhile contact cleaners, but as long as I've been using this I haven't needed another. The one thing that does not work is WD40. Save that for cleaning bike parts and keeping your tools from rusting. WD40 leaves a lot of oil behind that dries into a hard and unpleasant varnish. If you use it on something you will need to use it again because of it. Then you'll need something else to flush out all the old WD40.

One other reason to use D5, it is completely benign to tolex, plastic, guitar finishes (even nitrocellulose lacquer) and, so far as I can tell, human beings. Don't drink the stuff, but I have gotten it in my eye and even that doesn't burn. Here's the MSDS.

So get your can of D5 and some tools if that is where this next phase takes us. Notice that the nozzle turns to adjust the spray, you'll want that at the lowest setting.

Tube Sockets and Grotty Tube Pins

For tube sockets, give a small small spray either directly at the socket or on the tube pins and run the tube in and out of the socket. Allow to dry before firing up the amp. Some tube pins tend to corrode in really ugly ways. The pins on small 9 pin tubes, like 12AX7s require some very fancy metallurgy. Because they go through the glass they have to expand and contract with heat in a way that is compatible with the glass. Normal metals won't do this, so corrosion resistant alloys are out of the question. Use a shot of Deoxit and a bit of 3M scotch brite to clean heavy corrosion. Sandpaper also works. Never use a file on a tube pin it, the vibrations will damage the tube.

We test for dirty pins by firing up the amp and listening while pushing the tube around a little in the socket. Start with the controls set low, no reason to blast yourself. If there's a problem it will be obvious. So, clean, let dry, power up and test. Just put a finger tip on the top of the tube and move it gently. If one cleaning does not do the job, repeat it.

Control Pots

We need access to the controls for this. It is rarely rewarding to try to clean a pot by spraying around the shaft and hoping the cleaner gets in. It's worth a try as a desperation move on a sealed pot, but not normally worth it. So open up the amp. All the normal safety warnings apply. Unplug and use a DC voltmeter to ensure that the voltages in the amp have drained. If you don't understand that, do not proceed.

With the amp open, look at the pot in the area where the terminals come out to be soldered to the wires or to the circuit board. Generally there will be window in the metal can around the terminals. Some pots will also have a hole in the case.

A short spray into either of these openings followed by exercising the pot will do the job. These do not get hot so you can feel free to test immediately. Do be sure the amp is correctly connected and safe before applying power. The usual rule is that a pot that does not operate cleanly after two cleaning attempts should be replaced. Do know that some controls will always be a little noisy, the "Presence" control on Marshalls is one example. Some pedals will also misbehave like that.

As a general rule any pot with DC current flowing through it will make noise. This can be an important diagnostic tool. If you find a pot that is noisy when turned that does not improve with cleaning and you notice that the noisy spots in the pots rotation never move when you spray or exercise it you likely have a DC voltage on that pot. This can help locate a leaky coupling capacitor or failing opamp.

Jacks

A quick spritz of Deoxit into the jack an running a plug in and out will solve most jack problems. Including dirt on the shorting leaf of the input jacks on an amp. This is the introductory course so we won't talk about the use of a burnishing tool for the ones that don't respond. Again, if repeated cleaning attempts fail, it is probably best to replace the jack.

Everything Else

In most modern amps you are going to find connectors like this:And this.

You'll find these push on connectors throughout many amps and almost always connecting speakers. It is good practice to clean them every few years, especially if you've got noise problems. Give the connector a short spray of D5 before removing it, this will make it a lot easier if there is any corrosion already there. Pull and push it back down a couple of times. On some amps, this could keep you busy awhile.

Be careful of any connectors that aren't indexed. Make sure everything goes back just as it was. Some multi-pin connectors will have a latch or catch on them. Don't just yank - look.

This is also where you will find if a connector has been poorly soldered. If the pin or post comes out of the circuit board, it isn't because you did something wrong, it is because it already had a problem.

Switches

I do not recommend cleaning a malfunctioning power or standby switch. Once those have gone the least bit bad, they arc and destroy the contacts in a way that no cleaner will fix. It may not hurt to clean a functional switch, but remember that Deoxit is flammable and we do not want any fires in the amp. You'll find that most such switches are sealed anyway.

Signal switches are another matter entirely. Find an opening. Sometimes the only path into the switch is straight along the actuator shaft, usually with a spring in your way. Even those often have a small cutout on the top. You'll see if you've gotten in there. It doesn't take much. One of the important things to know about Deoxit is that the less you use the better.

The Important Trick

Using heat from a lighter or other source you can soften the spray tube and bend it into a convenient shape. Don't melt it, and don't do this on the can. Let me emphasize that do not spray Deoxit near a heat source or flame. Bend the straw then mount it to the can. The bent straw will get in a lot more places than the straight one.

The Short Version
Find all the connections in the amp, give them a shot of Deoxit and move them through their range of motion. Let dry and add power.

Congratulations. You should now have a quieter, sweeter sounding amp.

My Thought for the Day

Price Point Engineering is the art, the craft and the science that serves marketing by ensuring that no customer buying a product ever gets more than he paid for.

Dirt Sounds Like Dirt

Dirt sounds bad. It doesn't even sound good in a bad / good dirty way. So let's talk about how to get the crud out of your amp. I intend for this to be the first of a series of posts on things a player can do to understand, maintain and improve his own equipment. Not that I don't want the work, you can always just send it to me or one of my colleagues around the country. We're always happy to do this stuff. Even if you do just send it in, now you'll know what we're doing and why, and why we charge what we do for it.

What is this crap and where did it come from?

Open up any well used guitar or bass amp and you'll usually be greeted by something far dirtier than its external appearance and conditions of use would have you believe. The short answer is that large positive voltages attract crap from the air. Notice how quickly dust finds its way to your TV or computer monitor, like that but slower because of the lower voltages. It isn't uncommon to look in something like an Ampeg SVT and see a trail of filth on the circuit board that outlines the path of the copper traces on the other side of the board.

Fans (like in that SVT) are a part of that. Along with the cooling air, they blow in all the contaminants and dust in that air. Ever play a bar that served food? The airborne grease from the deep fryer has found its way onto and into your amp. If you can smell something, food, cigarette smoke, stage fog it can end up in your amp.

Crud and filth also get into an amp through more obvious methods. At the end of a show, what do you do? Unplug the guitar, wipe it down and put it away (you do wipe it down, right), then you go to the amp, turn it off and start wrapping your cords. While you're standing there winding your cable watch the plug drag across the stage picking up spilled beer, bassist sweat, punk singer spit and just plain crap tracked in from the parking lot when you loaded in. That filthy plug will go back into your guitar or amp the next time you play and it will foul the jacks. (Guinness will totally mess up a plug, that's experience talkin')

Oh, and metal just plain tarnishes when you leave it alone in Earth's atmosphere. There are metal on metal connections from one end of your amp to the other, switch and jack contacts, wipers on control pots, every sort of Faston, Molex and pin connector known to man. Unless they're all gold plated, and they're not, they will tarnish or corrode. Oh, even the gold ones pick up crud same as everything else.

So what's so bad about this crud?

Some of this crud acts as an insulator that prevents signal from passing; some forms of crud, especially some of the corrosion found on contacts acts as a semiconductor. I've seen tarnished FX loop jacks that acted like a diode distortion circuit. How does that happen? Many jacks in guitar amps do more than just connect to the cable that you plug in. The input jacks almost always have some sort of switching contact that shorts the input to ground when nothing is plugged in. This is to quiet the amp when you aren't using it. When that shorting contact gets dirty the amp will tend to buzz or pick up radio stations when nothing is plugged into it. That wouldn't be so bad on an amp with only one input jack, but most amps have more and we don't use them all. So the unused jack is sitting there introducing noise and static while you're playing into the other.

Some amps have an FX loop or a set of jacks labeled "preamp out" "power amp in." Those are called looping jacks and have a set of switch contacts built in that bypass the jack when nothing is plugged in. When those tarnish or get dirty, the amp cuts out or distorts in really bad ways. If you have an amp that is cutting out that has any sort of looping jack the first thing to test is to plug a short cable between the in/out or send/return jacks and see if that fixes the symptom. Practice amps that have a "Headphone" jack can also suffer from this type of problem since the headphone jack is usually designed to kill the signal to the speaker.

What can I do about it?

There are two answers, one is preventative the other remedial. The most important preventative is exercise, that is use all of the jacks and controls on your amp. The guys who design the components are pretty smart and most switching contacts are what is called "self-wiping" which leaving out all potty references means they rub against one another when you use them abrading away tarnish and crud. At least once or twice a year make sure to exercise every switch, knob, control and jack. With the power off, flip every switch back and forth about ten times, especially the ones you never use. You shouldn't need to worry about the power and standby switches, but all those channels and stuff you don't use, exercise those switches. Turn every control pot back and forth about ten times, especially the ones you haven't touched since you got it. For those you can have the amp powered up with the master volume set sorta low and listen to see if they're noisy and if they clean up. For the jacks, again more exercise, run a plug in and out of each one about ten times. Don't feel awkward if you get a little excited doing this, it's only natural. And I do mean every jack, speaker jacks (with the power off, of course) FX loops, footswitch jacks, all of them. Again pay special attention to the ones you never use or just leave plugged in all the time, like the speaker jack in a combo amp.

The same thing applies to tube sockets. Partially pull each tube and push it back in two or three or four times. Careful with the big ones, you don't want to break the index pin, so be gentle. Just partially pull and re-insert each one.

For something like a mixing console this could take awhile. But if you don't do it, you will pay someone else to do it and that someone will charge between $50 and $125 an hour. Your call. This will prevent most of the problems that repair techs see in older equipment.

Summary.

Keeping your amp in clean, dry air helps. But that isn't where most of the gigs are. Wipe down the plugs on your cables before or after using them.

Exercising all of the jacks, pots, switches, every control on the front and back panel will prevent problems. Idleness does more harm than wear, so at least once a year run everything through its paces.

I'll be back next time with how to cure the problems that exercise alone doesn't fix.

Fancy Cables

This is a fairly hot subject and I've gotten into some ill-advised arguments over it in some forums. The arguing part seems unnecessary and I'm going to try to explain my opinion clearly and in a way that avoids stepping on anybody's toes.

A solid basic guitar cable made of reliable, quiet and relatively low-capacitance cable with reliable, high-quality plugs can be had for about $30 from any number of sources. This is all you need. Look for cable with Mogami or Canare wire and Neutrik or Switchcraft plugs. There are other brands, but these are the standard. And again, this is what you need, quiet, reliable, low-capacitance. Without that basic functionality a cable is not worth considering.

You can pay more and get additional features if you like, pretty jackets that do actually help protect the cable and gold plated ends are both popular and pretty. No reason to not have them if you like. But look at these as optional features that are added to what is essential; quiet, reliable, low-capacitance. If a cable lacks those things there is no added feature that will make up for it.

There are "premium" cables out there that are objectively, measurably, statistically and factually inferior in reliability. Some have terrible failure rates and a few have terrible failure modes.

Quick example that hit my bench, a customer using one "premium" cable had the tip of the plug come off inside the jack of his amp. Being a PCB mounted TRS Cliff jack there was no way to remove the tip without destroying and/or replacing the jack. The customer ended up with a repair because of this inferior cable with inferior plugs that had been sold to him for five times the cost of a cable that would never have had this problem. Sure the "lifetime" warranty of the cable got him a brand new one, just like the old one, but it sure didn't pay his repair bill or make up for the time without his amp.

This is unacceptable.

I don't want to hear the argument that these cables sound better - broke cables do not sound good. This industry has had reliable cables for about 30 years now. If someone presents a cable as being an improvement it must do everything those cables did, plus. Not instead.

That is all. Make sure that you are getting something that will get the job done. Then, if you can afford it and it sounds good to you upgrade however much you like. Just don't get suckered into thinking that because something is more expensive that it is automatically better. It has the potential to be better, but not all of them are.

That $30 cable I was talking about is better than what you heard on your favorite albums of the past. It really, really is good enough. And if someone wants you to pay more insist that he give you everything that you get in the low priced cable plus whatever added features he's advertising. There is no excuse for accepting less.

There are a lot of guys out there building fine cables at all price points. These are good guys selling a legitimate product. I am not criticizing them for offering something better and more expensive. On the other hand there are companies with nothing but a huge endorsement / advertising budget who sell unreliable gold-plated crap. You deserve better than that.