modman

Freestompboxes.org rehosting

Fri, 03 Jul 2009 00:50:06 GMT

Hi everybody,

You might have seen that the website freestompboxes.org is down.

What happened, in short, is the following: we registered with a new hosting company 3ix.com, everything seemed to be fine and the people very helpful. Until this afternoon CET they just pulled the plug without any prior notice.

There was no explanation given and no illegal material pointed out by the provider, but as a matter of fact, the terms of service mention that in case of abuse they are allowed to take measures without any justification.

So we have learned a lesson, and no real harm was done. The forum will be back up by tomorrow 0am at the latest. Check here for updates....

freestompboxes@gmail.com
modman

Tweed Princeton + Dumble tonestack

Sun, 22 Jun 2008 16:40:03 GMT

I have been so busy the last few months that I didn't realize I forgot to rig up the second part of my report on the little Harley Benton 5W Blues Junior clone which is itself a tweed Princeton.

Well it's has grown...

Here are some interesting documents if you would like to work on a Harley Benton yourself:

See through Main PCB
See through tone control PCB
Harley Benton Stock Tone control schematic
Fender Princeton 5D2 schematic
Harley Benton - Circuit Description in French
Harley Benton - Circuit Description in English
Freestompboxes.org thread on this amp

I have done the following changes:

R1 = 1M pull down instead of the 68k
R2 = 33k that I could have lowered even down to 10k, but as analogguru points out, that heaps of gain in reserve, so figured I'd go with the Princeton Tweed value
R6 = jumper
R8 = 1k5
R9 = 2k2
C3 = 4.7uF
C4 = 4.7uF

Changed the tone pot to a master volume control:

Took the ROG Umble schematic and took out the tone stack:

Soldered up this little tone stack on a piece of perfboard:

And put the tone stack hidden at the back of the amp, as a secret weapon.

Although the tone stack could be improved, and there's the sound of pigs being slaughtered when both GAIN and MASTER are near to maximum, this is in no way a problem since the amp has so much more gain aboard then before. You can hear the amp now when it's turned on, which is normal for a fender type camp you expect at least also to get some nice clean tones from.
With the gain turned down and the master all the way up, it renders near to acoustic clean tones of the jazzier kind, especially since the the mid cut and bass control allow perfect fattening up of the clean tones without distorting. The other way around, gain maxxed out and master down, grittier tones arrive. Distortion you turn up the master volume, but also the tone stack may be useful in generation and shaping the disortion at lower volumes. With mid cut completely engaged, screaming distortion can be gotten at very basic levels. This is because the mid cut take a bit from your volume.
The amp is very sensitive to humbuckers, even a little too much to my taste, so I might have to work on the input, or adding another one with a higher in series resistor. Ir"s hard to keep the amp clean at any volume with humbuckers.

In short, it really has the ka-ching that I want from an amp and that I've yet to find in a commercial < 500 EUR amp. When I see a Harley Benton head on ebay, I'll bid again.

have fun,
modman

Harley Benton GA5: 5W Class A 8" combo

Fri, 28 Mar 2008 14:04:27 GMT

Now the 90s tube craze has gone full circle even budget brand are hitting the market hard with quality tube material. Many already went overboard when the Epiphone Valve Junior came out, but now thomann.de presents the Harley Benton GA-5 at 98 EUR, the ultimate beginner's amp mod kit has arrived. I don't think you could even buy a kit for a complete combo amp at this price -it retails at 98 EUR, the head version at 88 EUR

Harley Benton GA5 5W 8" combo

1. Compared to the Epiphone Valve Junior

The only advantage to the Epiphone are the stock 4, 8 and 16 ohm output jacks. The Benton only has 4 ohm output jack, but it does have a tone control. Here's an extract from an early review

"... that little Tone/EQ dial DOES have an important effect on your sound - not as a tone control, but as a 'texturiser', insamuch as it 'thickens' the mids only. With my Hofner archtop with humbuckers this is all too evident
as, using my toe to wind the knob up and down while playing continuously, brings out all sorts of harmonics without changing the overall tone. It does add a shade more volume at around 8-9 o-clock, (this dial strangely goes the opposite direction from normal tone dial's going from bright to bassy)."

2. Inside the GA5

I've heard the GA5 is assembled in the same factory as the Epiphone and looking at the construction, that is no surprise. PCB layouts seems to match and the HB even has the pcb to host three output jack though it only has one external out. This really seems to be our punishment for not buying an Epiphone, it seems, but we'll come back to that later.

The power tube was a half decent Sovet EL84, even date coded 06 07 and made in Russia. The Epi, I heard had Sovtek for the preamp too, but the Harley has a cheapo made in China 12AX7 hidden in the tube retainer:

The first move would be to replace the stock tubes with decent ones of your liking. To get the preamp tube out, gently push down and twist the tube container and it will pop right off (thanks Rob!).

3. Biasing the EL84 power tube

This in fact is really easy and something you can do if you have a digital multimeter, an alligator clip and some caution. The most simple and basic rule is - NEVER PUT BOTH HANDS IN AN AMP THAT'S TURNED ON. When working on a life amp as you will need to to bias the tube, always keep one hand in your pocket.

Even unplugged a tube amp might kill you because the capacitors are still charged even when unplugged. So tap them with a screwdriver that has a rubber or plastic handle. Or: with a guitar plugged in, just unplug the power cord (don't use the on/off switch) and keep playing until you hear no more sound from the amp.

First, get the chassis out: remove the four plastic covers on the top of the amp, they hide the screws holding the chassis in the cabinet. Make sure you unplug the speaker jack and then put the amp on its head so it rests on the transformers and you can look at the component side of the pcb.

Now reconnect the speaker (you don't want to damage the output transformer) and turn the amp on, let it warm up for some time. Make a cup of tea in the meantime...

Ok, now let's check the bias!

We will be needing four values to calculate the bias:

maximum anode dissipation of the power tube, EL84/6BQ5, which is 12W

cathode biasing resistor, R14, which is 220 ohm

cathode voltage to ground - cathode is pin 3 on the EL84

anode voltage to ground - anode is pin 7 on the EL84

You can go by the value indicated by the resistor colours, but you might as well measure it -- it can be measured in circuit. Mine was 217 ohm. Now connect an alligator clip to the black lead of your multimeter and connect it to the ground point top right on the chassis, various ground point join togeter on the chassis here:

Now measure the cathode voltage on pin 3 with DMM in the 20V range:

And the anode voltage on pin 7 with DMM on the HV range:

With this value, we can calculate the plate to cathode voltage, by subtracting the cathode voltage from the anode voltage:

308V - 9,33V = 298,67V

Take the cathode voltage 9,33V and divide by resistor value 217 ohm to get the cathode current:

9,33V / 217 ohm = 0,043 A

Multiply the cathode currect by the plate to cathode voltage to get the total dissipation

0,043 A * 298,67 V = 12,84 W

If you want to take into account the screen dissipation, you can take it at 10% of the cathode current and deduct that from the final dissipation. Like this:

0,0043 A * 298,67 V = 1,3W
12,84W - 1,3W = 11,24 W

This could be improved by decreasing the value of the cathode baising resistor, to get total dissipation up, but is actually not so bad. If the dissipation is much more that 12W, you should increase the value of biasing resistor R14 to get it closer to 12W.

Hey -- was that easy or what?

Soon more on the Harley Benton, but it seems like we will be missing out on the Epiphone "kill the noise"-mods ;-)

MIT Boss DS-1 Distortion: Keeley mods

Wed, 24 Oct 2007 00:50:04 GMT

I bought a wreck of a DS-1 about two years ago for close to nothing. It was in quite a sorry state: two knobs missing, worn out rubber grommet and no switch. Still distorted fine of course.

Over the last few days, I'm cleaning out stuff so this one was first up. Robert Keely is one of the stompbox modding pioneers and his mods are widely acclaimed and published on several websites:

RobertKeeley.com: a page on DS-1 by the man himself
Indyguitarist: a great printable, clear overview of the mods
Use this for reference layout and schematic
A blog about modding the DS-1

For now, I did all the mods except the switched in extra led in D5, but I will try something that clips even better. More later. I also replaced all other capacitors on the board by new higher quality caps. I used WIMA caps throughout.

In conclusion I should say that these Keeley mods are not really modification to the circuit at all, but simply give better fidelity, more dynamic response to playing and more gain. Replacing the caps might have had an overall effect on the sound clarity as well.

2001 Epiphone Les Paul fix up

Tue, 23 Oct 2007 14:13:17 GMT

I bought an Epiphone Les Paul with a defective pickup off ebay for little money. "Defective pickup' is always only the symptom, and hardly ever the problem. You've a lot of guitar banging ahead if you want to knock out a cased humbucker pickup.

Anyway, the guitar sounded fine acoustically so I didn't hesistate. The neck pickup position was fine and in the combined setting (neck + bridge pu) I got a very slight sound from the bridge pu if I turned the neck volume down. So I was sure that the problem was a short somewhere in the bridge controls.

Original wiring seemed messy and ground is always carried on the shield wire of the insulated cable used, so the ground path close to the signal path in several places. A very bad idea if you want to prevent problems. One contact and your signal goes down the ground drain....

Selector switch was a potential culprit, but turned out innocent after the continuity tests.

Had to remove most of the circuitry to find the short, here's the back of the humbucker

In the end, there was no short, but the volume pot was dead, had infinite resistance (no contact) to the signal. So I ripped up a volume and tone control setup on a breadboard, to test out different caps and pots:

I ended up swaying to mojo talk and using a fat 400V 0;022uF polarized Erofoil cap whch tested ok. After trying different pots, I got the best range in tone control with a 100K pot, which is very unusual for a Gibson Les Paul. Everybody uses 500k, but nobody uses their ears or I'm competely missing something.

True Bypassing a EH Micro Synth

Wed, 26 Sep 2007 15:18:18 GMT

You all probably know this outlandishly nice effect by Electro Harmonix, the guitar Micro Synth. Just because such a strange effect, it is very sad that it doesn't have a true bypass. It's typically an effect you won't be using the whole gig through.

So I went about True Bypassing this baby with a standard Carling DPDT switch, the led shows power, and isn't an effect on/off. There are great options to use a bicolor led turning green when the effect is engaged, but that's for later.

Let's have a look:

You can see there are only three poles on the SPDT standard switch, the input jack (yellow wire) is always connected to the effect board, and fed into a buffer that connect to the switch with the brown wire. When the effect is not engaged, the brown wire is connected to the blue wire going to the output jack. This buffer prevents the signal from loading onto the effect board because even when the effect is not engaged, the board is connected to the circuit. So the configuration of the old switch is:

1 brown (from buffered input) 2 blue (to output jack)
3 green (output effect board)

ON position 3 is connected to 2: input jack -> buffer -> effect board --> output jack
OFF postion 1 is connected to 2: input jack -> buffer -> output jack

1. So we firest unsolder the yellow wire from the input jack and solder on a new white wire that is long enough to reach the switch.

2. Now unsolder all (blue, brown and green) wires on the switch.

3. Here the configuration of the new switch

(1) white from input jack (4) green from board
+ jumper to (6) FX SIGNAL OUT
CLEAN SIGNAL IN

(2) brown from board (5) blue to output jack
TO FX BOARD FX SIGNAL OUT

(3) black to GROUND (6) jumper to (1)

In one postion 1 connects to 2 and 4 connects to 5
In the other 3 connects to 2 and 6 connects to 5

With the effect on input from guitar goes to fx board, output fx board goes to output switch. In the off postion the signal connects with a jumper to pole 6 and so directly to the jack. Meanwhil, in the bypass mode, the fx board input in grounded.

Here we go:

Luckily the ground tab on the chassis was close to ground the input while in bypass...

If you still got both brown and yellow wires still connected to the board, you can see if you hear a difference with buffer (connect yellow to switch) or without (connect brown to switch.)

PCB transfer with PLAIN laser copier paper!

Sun, 02 Sep 2007 12:11:23 GMT

Having troubles getting thick picture paper through that old stubborn laserwriter, so I thought, why not try and transfer a PCB layout from plain copier paper. Remeber, this paper as a shiny side and a softer side and you should always use the former to prevent the ink from running out.

You know I recommended picture paper of various kinds in other entries (see left for the links), forget it!

Tried a small portoin and when that seemed to work well, I just went for the rather larger Maestro Sample and Hold Filter layout by moosapotamus.

The procedure is the same as with picture paper, but it seems the punching of holes is not necessary.

Here are some pictures of te Maestro board:

cutout, clean board

iron on. use the higest setting on your iron and don't be affraid of overheating anything

soak in warm water (not cooking)

fix toner by adding cold tap water

the toner is sticking!

gently rub from center to sides using your thumbs to remove the excess paper

transfer done, paper removed

etching as usual, see my previous entries on the subject

etching done

Baja Trembulator tremelo

Fri, 31 Aug 2007 01:30:51 GMT

This is great and easy to make tremelo pedal, redesigned by Bajaman on the basis of the Demeter Tremulator. If you want to make this pedal, you'll find all you need to build this one right here.

It uses a vactrol device you can easily replace by whacking together an LDR and a LED.
Yes I am out of jack and only had this 24k golden jack left. Envisioned a slow/fast switch but there simply wasn't enough space in this box.

thanks Baja, you're great

Transferring the layout to the PCB, we've been through that before:

Let's Etch

Enclosure

Gut shot

the JaWarI: Tim Escobedo's sitar emulator guitar pedal thingie

Mon, 28 May 2007 20:22:28 GMT

Built this nice ciruit a while ago, in search of usable effects of the more unfamilliar kind. If you're a fan of original and amazing effects, Tim's Circuit Snippets are worth checking out.

It's a gain-controlled sitar emulator, but you will have more fun once you forget about trying to imitate a sitar. It really a is a recording pedal, that you might want to use very sparingly.

I used the GGG layout for the pcb. If you have trouble finding the appropriate transformer coil on the European mainland, check out Banzai's TM018.

The layout is the Indian god Ganesh, which I got somewhere on the web.Etched in aluminium as usual.

Germaniac Booster Project part I: the basic Germanium Guitar Booster

Sat, 14 Apr 2007 10:10:38 GMT

The idea is to develop a more full-fledged Germanium booster in the long run, but we will start with the most basic schematic first. Every update on the project will boil down to a workable booster, a modded clone of it's predecessors.

Introduction: Germanium?

Ever since the boutique pedal craze started to rage, everyone started going bananas on so called NOS germanium transistors because these were used in the very first guitar effects produced -- the original Arbiter Fuzz Face, the Dallas Rangemaster and the illusive Harmonic Percolator all used germanium devices.

The industry has, since the late 60s - early 70s switched over to silicon as the basis of semiconductors, because this proved more reliable. The only freak still interested in germanium are radio amateurs and guitar effect diy-ers. To cut a long story even shorter, there seems to be a general consensus that a well-selected germanium device does have is own particular sonic characteristics. Some has to do with the low gain of germanium in general, and it surely is possible to mimic a low gain device by piggybacking two silicons

Fuzz Face and Rangemaster schematics abound on the net, so the silence on the one stage germanium guitar booster is a bit strange. Back in the boutique, you realize that this is just another attempt to create a marketing hype on something even less complicated than a FF or a normal booster.

Dirty-Boy-Germanium-Boy-Multi-Frequency-Booster-Pedal $350
Electrolead GC �130

So let's get started

A Basic Germanium Booster setup

We will start out with the most basic setup that works (ie. boosts or overdrives) the input signal. My schematic drawing skills are not everything, so note the the output only connected to the collector of the transistor.

Now let's fill out the blanks:

Q1 is a low leakage Germanium NPN, I used 2SD352H with gain of hFE 115.

C1 is the input capacitor -- .022uF or 22nF would be a good starting point, but you can try values up to .1uF
C2 is the output cap - .047uF or 47n for starters, but try up to .1uF (100nF)
C3 is 47uF or higher for more extreme though less defined maximum gain. Connect the negative side to the ground.

R1 is the bias resistor, a 100k trimpot that regulated the voltage fed into the transistors collector. Use the variable resistor to put about 4.5V on the collector
R2 is the gain control, a 5k B potentiometer in series with C3 a electrolyte cap 47uF to ground.

To sum it up, put your guitar signal into the base through an input cap, connect collector through a biasing resistor to your 9V, connect the emitter to ground through an electrolyte and take the output signal from the collector after an output cap.

Your own Germanium Stash

The sonic quality of the result will be largely influenced by the quality of the transistor. You could of course also try PNP Germaniums, which are more common, just remember to switch +9v with ground and turn the electrolyte around. If don't want to go sifting through ebay and buy funky lots that were sifted through too many times, buy them at Smallbear or Aron's stompbox forum for the US and Banzaieffects in Europe (Germany)

I would advice to get a Rangemaster type Ge NPN transistor. hFE's of about 100 will be great, but you can experiment. Considering the single stage design, you might want to try out higher gain Ge's if you have them.

"For linear amplifying, the collector must be more positive than the base; the base must be more positive than the emitter by about 0.4 to 0.7V for silicon, and 0.0 to 0.3 for germanium; the emitter should be the most negative pin. The voltage difference between the collector and emitter is the biggest voltage that the transistor can swing linearly. If the collector is not a volt or more above the emitter, or the base is not a base emitter drop above the emitter as noted above, the transistor cannot be acting as an amplifier." R.G. Keen at Geofex.com

For the 2SD352H I used, I measured the following voltages using 8.9V as source

E = 0.3V
B = 0.3V
C = 4.6V

Well how does it sound? Well a very solid booster with a lot of drive that can overdrive at max gain settings. I do seems to recognize some of that fuzzy, rambling Germanium grit in the sound, If with this minimal parts count, you cannot hear the germanium at work, then when are you going to hear it.

Remember it's only a single stage booster with a gain control as yet. There is more to come, so if you're really interested, subscribe to the modman updates.

Next time we will start finetuning the booster and maybe indulge in some tone control experiments. I'm still developing this as we go along, who know where it'll end? Stay tuned!