HUDSON: Sidecar Overdrive

I did a layout for the Hudson Sidecar a couple of years ago, and I retraced my steps recently and found a few things that needed to be updated.  The Sidecar is a progression of the 999 Overdrive, which is Hudson's version of a 'green box' overdrive, made for people like me that don't like the green box.  

There's also another variation out there called the Motorcycle, which sounds like the same circuit that's been retuned for a bit more low drive, with the addition of an output transformer, not unlike the Broadcast.  My guess is the 470n / 1k off the inverted input stage has been adjusted, maybe a tweak to the bass side of the active eq???.    

Plenty of great pics on FSB  Schematic on PedalPCB

The layout below should be pretty close to a version of the original from 2017.   0.15" vero, so a tin can IC is a must.

HUDSON SIDECAR  -  0.15" VERO LAYOUT

Note that there are minor variations out there, depending on how Hudson was making them at the time.

HUDSON ELECTRONICS: Broadcast, Peach Guitars Version

This is the Peach Guitars version of the Hudson Broadcast, as traced by V1nce69 and posted on the Guitar FX layout forum.  Others also did work on tracing in this thread, so sorry if I left anyone out.  Lots of great gut shots and a bunch of measured voltages there too.

The layout is basically a redraw of the original, which used 0.15" vero - but without the charge pump daughter board (I'm not a big fan of using charge pumps, as most pedal power supplies have high voltage outputs these days).

You can't use these layouts on standard vero, or if you do, you'll have a hell of a time getting it all to fit.

HUDSON BROADCAST - 0.15" VERO LAYOUT

Note: The gain switch can be either ON-ON or ON-OFF-ON.  Stock is ON-OFF-ON

HUDSON BROADCAST - LTSPICE

This is trickier than usual to model, as a germanium transistor and a transformer are involved.  LTspice doesn't have a transformer model library (which is annoying), so you have to model your own using inductors.  I measured the inductance and resistance of a TY-141-P transformer, so hopefully, the model is close.  Same with germanium transistors - they can be different enough individually, let alone simulating one.

Anyways, here it is.

If you like more bass, decrease R13.  I found changing the 330n capacitor moves the mid-range peak in conjunction with the lo-cut control.  Increasing to 1u brings the peak lower, at the cost of some high frequencies elsewhere.

The overall response can be quite gain dependent, as it appears to have a bit of a mid hump at its highest gain setting (no bass cut)

Same again but with gain fixed at 100% and the locus sweeping a few values.

And again, but with a 330n and 1u cap to show the change in peak.

The output stage forms a high-pass filter with the transformer - I think this is mainly what the transformer is adding to the mix.  I'm sure it does a little bit more, but perhaps not a lot.

The first time I built one, I didn't have the correct value transformer, and the difference in inductance changed the low-frequency response too much (not enough bass in my case).  I had to remove resistors to make it sound close to the original.

The Hudson Electronics Broadcast is a great little pedal - while now overshadowed by the Dual Broadcast, which has the high and low gain settings on a foot switch with individual level controls, it's essentially the same under the hood.  

I never thought a lo-cut pot would be so useful until trying this pedal.  It has a decent range to it, from clean through to near fuzz.  It can get quite nasty too with the lo-cut.

This runs at 24v, so you will need to build a seperate charge pump, unless you have 18v or 24v outlets on your pedal power supply (which is what I do).   Otherwise you can always run it at 9v.  It works, it's just not as dynamic - and maybe sounds a little flat by comparison to running at 24v.

HUDSON ELECTRONICS BROADCAST - POINT TO POINT LAYOUT

Note:  If you use a different isolation transformer, you may need to make adjustments to the 15k / 33k resistors before the transformer.  The resistors and one half of the transformer form a RL high pass filter - I had this issue and could not for the life of me work out what was happening until someone more experienced than I pointed this out.  I couldn't work out why I had a full range signal coming from Q2 and the coupling cap, but it disappeared at the transformer. 

HUDSON ELECTRONICS BROADCAST - CIRCUITLAB SIMULATION

Follow the link to Circuit Lab to play with a simulation of the Broadcast - at least until they lock you out and ask for a subscription.  

https://www.circuitlab.com/circuit/43q3t2mjg3ev/hudson-electronics-broadcast/

I quite liked the single Hudson Electronics Broadcast; the Dual is just that little bit more practical.  It can run from clean through to downright nasty tones.   The low-cut is really great too.

You will need to build a 24v charge pump for this or run the entire thing at 9V - which does work, albeit with a slightly different tone.  Anything in-between also works - 12V and 18V are also OK if you have either option on your power supply.

If you want to build this as the original Hudson Broadcast, just remove the second volume control and adjust the switching to suit (I'm sure you can work it out).  If you have taken one look at this and thought, nah, might stick to vero, there are some great layouts on Guitar FX Layouts, including the original layout used by Hudson, which also includes transistor voltages from an original unit.  The original used a larger vero board, so it will be a bit cramped on standard .1 pitch vero.

HUDSON ELECTRONICS DUAL BROADCAST - POINT TO POINT LAYOUT

HUDSON ELECTRONICS DUAL BROADCAST - WORK IN PROGRESS

It's passing signal, just need to do some further testing with the guitar before adding the transformer etc, and making sure I'm happy with Q2 (currently an OC45).

Then I got bored and decided to start fresh and rework things....   it now has external pots instead of trimmers, and I made some minor tweaks to the layout.  For some reason, I also thought it would be a good idea to twist wires together to give it more of a vintage look.   

I have stuck with an OC45 as Q2.  I tested a few different options, it didn't really like anything high gain, and while the Soviets were pretty good, they were just missing something compared to the OC45.  I can see why they use them in production units, as they're cheap and readily available, unlike OC45s or equally hard-to-come-by parts.   

As you can see, I'm not one who does incredibly neat internal wiring.  I've seen worse, but it's not going on Instagram is it.  

HUDSON ELECTRONICS DUAL BROADCAST - MODS

Transformer

The transformer is not essential by the way.  If you wanted to, you could quite easily change the entire configuration coming off the emitter of Q2 to something a little more normal without substantially altering the tone and feel of the pedal (the 100uf running into the 15k / 33k resistor and the transformer).  Being a point-to-point layout, there are plenty of opportunities for experimentation available.

Note:  If you use a different isolation transformer, you may need to adjust the 15k / 33k resistors before the transformer.  The resistors and one-half of the transformer form a RL high pass filter - I had this issue and could not for the life of me work out what was happening until someone more experienced than I pointed this out.  I couldn't work out why I had a full range signal coming from Q2 and the coupling cap, but it disappeared at the transformer.  

Trimmers

Take one or both of the internal trimmers and make them external pots.  While the extra knobs are a little annoying, I like the added functionality.  

NOTE:  One trimmer sets the overall gain of the pedal (bottom left), and the other trimmer sets the boost level.  So if they are both cranked, there will not be much boost.   Set the low-gain first, then adjust the boost.  Adjusting the low-gain, will also change the other channel.  

Single channel

If you're never going to use both channels, why not make it a single and save a switch.  If you're feeling really minimal, the Broadcast could quite happily be trimmed down into a two-knob beast.  Just the High setting and no lo-cut.  

Tone controls

A treble pot could be added to the output stage, if you really wanted to go nuts with extra knobs.  As there's already a lo-cut control, a simple low-pass filter would do the job nicely.  It's mostly not needed, but on some settings the tops could be tamed a little.   I tried this, and it worked pretty well.  I can't remember what values I used; it was quite mild, I remember that much.  

While I like the lo-cut, to remove it, just join the two points that connect to the pot.  

Transistor

I've listed an OC71 as that was on the schematic, but I have seen photos of this with a Soviet MN20.  Make sure it's a low-gain PNP germanium transistor, and you will be close.  I'd recommend testing a few if you have that option.