BOSS: DC Power Filtering

While I was looking at a few Boss circuits recently, I was reminded of some of the DC filtering they use.  I thought I might try it in LTspice for a look, as my oscilloscope is pretty basic, so I can't test it properly on the bench.

So if you are ever having trouble with power supply noise, give this a try.  You sacrifice close to 1 volt, but you also lose a lot of noise.

It's a capacitance multiplier, so basically, take the current gain of the transistor and multiply it by the capacitor attached to the base, and you have the capacitance of the cap.  So for a 47u cap and 2N3904, that's going to provide a really large capacitance in the filter...  way bigger than you could possibly fit in a small enclosure or afford to buy.

BOSS DC POWER FILTER

The green line shows ripple before the transistor, and the blue is post-transistor, which has almost no ripple.

BOSS: OD-1 Overdrive

A classic Boss overdrive - the one that started it all for Boss guitar effects, originally sold from 1977 to 1985.   This is one of the later designs that does not use the quad opamp.

Kind of curious that after this, many designs used the Boss version of a discrete opamp that can be seen in several different designs.  

BOSS OD-1 OVERDRIVE - VERO LAYOUT

BOSS OD-1 OVERDRIVE  SCHEMATIC

BOSS OD-1 OVERDRIVE - VIDEO DEMO

Not strictly speaking a straight demo of the OD-1, but I like Wampler's videos, and this does have a good comparison of the SD-1 and OD-3. 

MARSHALL: Blues Driver / Boss Discrete Opamp

If you've read any recent posts, you may have noticed that I'm experimenting with discrete opamps - specifically replacing standard opamps with simplified discrete opamps - I've only played with the Joe Davisson diode compression opamp so far (with some success).

While I was checking out DIY Stompboxes, I saw Rob Strand was experimenting with the Boss discrete opamp that's used in the Blues Driver.  I've occasionally looked at it but have never gotten around to playing with it.  

Anyway...  it appears to work as a drop-in, and I thought a Blues Driver / Blues Breaker hybrid might be fun.  They are totally different circuits by the way - similar in name only.

More to follow on the Boss discrete opamp.  Feel like I need to spend some time playing with this and the Blues Driver.  I have an interesting idea in mind for the Blues Driver; I'll post it if it's successful.  

MARSHALL BLUES BREAKER X BOSS BLUES DRIVER DISCRETE OPAMP

It looks like a Blues Breaker on LTspice.  But I'm always a little suspicious of anything using JFETS on spice as they're notoriously variable beasts in real life.

BOSS BLUES DRIVER SCHEMATIC - OPAMP MARKED

Here's the Blues Driver schematic, with the discrete opamp marked. A good analysis can be found here if you are interested in further reading.  

BOSS: FZ-3 Fuzz

Initially I wasn't sure about doing a layout for the Boss FZ-3, as it isn't the most popular fuzz out there - then looking at the schematic, it appears to be quite tweakable, so I thought why not make a start, and see where this goes.   

It has elements of a Tone Bender, a silicon Fuzz Face at its core, with a BMP type tone control.  Boss when next level on power filtering with this one too.

  

Details here on Aion FX.

BOSS FZ-3 FUZZ VERO LAYOUT

FZ-3 VIDEO DEMO

BOSS: Modded DS-1, Diode Compression Opamp

A somewhat polarising classic - the Boss DS-1, with a slight twist, as this has the Joe Davisson discrete diode-compression opamp onboard instead of an IC.

BOSS DS-1 DIODE COMP OPAMP - VERO LAYOUT

BOSS DS-1 DIODE COMP OPAMP - WAMPLER STYLE JCM MODS

This is what I ended up being happy with on the breadboard - it's basically the Wampler JCM mods, but I used a germanium and silicon diode in series for hard clipping rather than two silicon.  The combined forward voltage brings it up around the same level as the original diodes used in the DS-1.   

I also increased the size of the resistor on the emitter from 22 to 470 ohms to reduce gain in the first stage.  You could happily go a bit smaller than this, as the discrete opamp has less gain than a real opamp.  I may have taken a tad too much away - so maybe have a play with that yourself if you plan on trying this.

The most important change in terms of sound is the replacement of a resistor in the tone section, which really changes the character of the sound (mids return).  

So with all of these changes - it sounds like a nice distortion with some character, but not much like a DS-1.  

BOSS DS-1 DIODE COMP OPAMP SCHEMATIC

Some common mods included - minus diode clipping mods, as I'm sure we all know what this involves.  I've kept mostly stock values on the schematic while I test mods.  The only exception is the clipping diodes, where I have two on each side in series, as I just discovered the original diodes had quite a high forward voltage (0.92v typical, 1.2v max), which is close to 2 x 1N4148 in series.  

ORIGINAL BOSS DS-1 SCHEMATIC

 

ON THE BREADBOARD

Looks like a mess... and no input or output buffers at this stage.  Speaking of buffers, I may even try one between the tone and volume control to stop the interaction between the two.

 

ON THE SCOPE / FFT

Straight from the boost section - this is actually pulled back a bit, using a smaller resistor than the stock one, as it's normally distorted before it even hits the opamp (this is a common mod)

The next shot is the op-amp output and then at the clipping diodes. I need to change the diodes, as the original diodes have a forward voltage of about 0.9v, which is a decent step up from a standard 0.6v.  This certainly explains why the output was a bit lower than expected.

Caution - start with low levels.  Adjust the gain control, then tone - trace taken at the output of the tone section.   440hz sine wave