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.

First Look Ronsonic Diesel Driver

Here's the big, bad buffer. The Ronsonic Diesel Driver. Plug 9 - 18VDC into the jack at the top and your guitar into the jack you see on the side there.

The input impedance is matched to that of classic guitar amps. This will not load down your guitar. It also won't give it that unpleasant brittle, glassy top end that some buffers with extremely high input impedances do.

The goal here was transparency, as if nothing was added to your guitar and nothing taken away.

Then you go around to this side:

The top jack goes out to your tuner. It has its own buffer so nothing that happens there can affect your signal. Some tuners are infamous tone-hogs that will kill signal even off on a side chain. That won't happen here.

The next jack is the Send to your pedal board. This is buffered with a state-of-the-art opamp that can drive any load that will be encountered in the wild. Prototypes were built with more usual opamps that sounded good but didn't have these spec's, now we are way ahead of the bunch with great sound and impeccable technical spec's.

The third jack down is the Return from your board.

The bottom jack goes to your amp. Again this is seriously buffered and fully capable of driving huge runs of cable without signal loss. For large stages and ever more common isolation boxes this will get your signal to the amp intact and sounding great.

The switch can either bypass your pedalboard or work as a mute, silencing everything except the tuner out. Choose this option when you order. It can be changed with a simple soldered in jumper by any reasonably competent tech should you change your mind later. If you prefer, a user selectable jumper can be added at a slight extra charge. We don't recommend this as this should be a more or less permanent decision and even with the gold plated connectors we prefer the reliability of soldered connections.

Legends are hand marked on the bottom since we don't anticipate this being plugged and unplugged a lot. Mostly this will get installed on the board and forgotten except to step on it when it's time to tune. You can order top markings if you prefer in legible technician hand lettering.

We are taking orders now, no payment until we are ready to ship in 2-4 weeks. Price is $129 plus $8 flat rate shipping in the USofA.

Please email if you are interested in getting a free test run with the prototype.

The Boards Have Landed

The prototypes of the new PCBs for the Ronsonic Diesel Drive Buffer have arrived. They look good, very good. I'm building them up now and am already planning improvements for the production version.

It's funny you look at a schematic on the screen for months, study and craft the circuit board on screen and on paper for weeks and then you get the thing in your hands and improvements become obvious. The good news is that there are no errors to correct, only improvements in layout and assembly.

The Electric Guru and Hero boards are also in. These are a lot nicer than the original builds. I'll be assembling a couple of single and dual pedals to go off in a couple of Tour Boxes I'm planning. So be ready for the announcement.

The next couple of posts will discuss some of these pedals in a general way, the various types of buffers, history and use of treble boosters and like that. So stay tuned for some pedal geek goodness.

New Circuit Boards On The Way

Big news on several projects.

The big project for the last couple of months has been preparing the new Diesel Drive Buffer for production. This is the monster buffer project that I described previously. The original target price of $100 is now deemed hopeless, too many compromises would be necessary to get there. It would still be a better than typical product, but why do "better" when "awesome" is within reach. This does not use your usual twelve cent transistors or fifty cent ICs; it is all top shelf parts all the way. And this is an application that will reward the investment.

The order has been placed with the board house for prototypes of the new circuit board. They will be here in a couple of weeks and we'll get this thing off the breadboard and onto the pedalboard for some serious workouts. It's very hard to demonstrate a buffer pedal in a recording of video, but I've got a few ideas about how to show what this beast can do.

I am also revisiting a couple of classics. The Hero Overdrive and Electric Guru Treble Booster are also getting new circuit board designs. These boards will both speed production and produce a more reliable pedal. None of the existing pedals have had any circuit related failures, but these will just be that much more robust.

Thanks for checking in, I'll keep you posted on any new developments.

Update from the Bench

Things have been quiet on the blog here lately. Pedal and amp repairs are the priority, I don't get to play when I've got someone's gear setting there on my bench eager to go home and make music.

Tbe Big Bad Buffer with no name is coming along nicely. The design has made it off the breadboard and the prototype PCB layout is coming together. I still need a name for it, was thinking "Diesel Drive" but still looking for ideas. This is a fun project for me since it is one of the few where the published specifications are meaningful to the design. Most of the time with pedals we are torturing and abusing the technology to create interesting sounds. This is one of the few cases where we really want things like low distortion and huge, clean headroom.

On the back burner are the parts and drawings for my recreation of the legendary Roland AP-7 Jet Phaser. If you remember the Isley Brother's song Who's That Lady, you know the sound. It's a combination eight stage (yes, 8 stages, like double Phase 90s) phase shifter with an integrated distortion circuit (the "Jet" part of the name) to push it into a completely new range of sound. This is a remarkably complex device that has never been reissued or reproduced since back in the day. This is one of those things that I wanted and couldn't afford when I was a kid and for the collectors price they sell for now, well it's time for my clone. Here's another example of what this pedal can do by the great Larry Graham and a great wrap up to this post:

Rehousing Pedals, When I Do It, When I Don't

Almost every pedal builder does this at some point. Take a commercial pedal built in a cheesy, oversized enclosure with poor quality controls and jacks and rebuild it with boutique grade components. Usually smaller, but almost always more robust and reliable. Very often the electronic switching and buffering circuits are bypassed or removed as well and the pedal is recreated in a true bypass version.

I've done a few myself and have developed some opinions on the subject. Imagine that, me, with opinions. My experience has been that for simpler, analog pedals the player is better served to have a reproduction built or buying an original. Here's my breakdown on that. A decent rehouse will cost somewhere upward of $75. That plus the cost of the original pedal will cost very nearly as much as simply having most reproductions built. If we take something simple like the Dano French Toast, the cost of a pedal plus the rehouse is about the same as a clone of the Foxx Tone Machine of which it is a copy. And a Transparent OverDrive rehouse is outright silly (and borderline accessory to intellectual property theft) you can just order a Timmy for that money.

Yes, you can find a hobby guy who is just happy to have someone pay for the parts he experiments with. And that is definitely a good thing. Enjoy this hobby. That's what it is for, having fun. But, if you need a professional build quality, or if that pedal breaks down, as all things will, the pro build is going to be far better.

Some rehouses make more sense. Things like the Dano Chicken Salad, that are more complex give the player an option that he might not otherwise have. While a commercial Univibe clone like the MojoVibe (a personal favorite) would be better, it will be about twice the price of the rehouse. So it does let you get your Vibe on at a lower cost than a boutique clone, and sounds better and runs more reliably than the factory pedal.

Here's an example of not rehousing. A friend and regular customer called and asked about having me rehouse a Green Ringer into a foot-toy format for him. Instead, I suggested a scratch build that included some improvements and a much smaller footprint than could ever be possible with a rehouse.


No indicator LED. Thought about it, but things are a bit tight in there and there's never a question whether this little screamer is on. Oh, and this cost the same as just a rehouse.

On the Drawing Board - The Buffer

Got a couple of projects in the works I'd like to talk about a bit.

First, is the new buffer. This is actually a triple buffer designed to go onto a pedal board and fill all the buffer / driver / splitter needs anyone might normally have. The basic idea is, guitar goes in, there's a separate, isolated output for the tuner. This keeps the tuner off the signal path, some tuners are tone suck disasters, even when used in a branch off the signal path. This fixes that problem. There's a buffered output to the pedals, and a return. Then another buffer to drive the line to the amp.

Here's the jacks:
Guitar input
Tuner Out
Buffered Out to pedalboard.
Return from pedalboard.
Buffered Out to amp.
The stomp switch can be internally selected to either mute for tuning or bypass the pedalboard.

Technologically, this thing is a monster. It runs well on 9VDC, and even better at 18, and is safe anywhere up to 24 Volts. It uses some very serious modern IC technology instead of the usual buffers and antique opamps you see in other pedals. The dedicated Tuner Out uses a typical FET buffer stage since we don't really care what the tuner sounds like, we just want to isolate it from the rest of the signal path. Truth be told, you could run the Tuner Out into an amp or pedal and it wouldn't sound any worse than the other buffers on the market.

The design challenge now is developing this pedal to the point that we retain all the features in a compact format. Yes, this all fits in a standard "MXR" type box. And, I'm trying to keep the price under $100! as low as possible, right now we're looking at $129. There are other pedals with similar features, they are larger and vastly more expensive. Oh, except none of them give you the option of having a mute or bypass switch.