Thursday, 1 December 2016

Hudson Electronics Broadcast

Original info:
The Broadcast is a transformer coupled, discrete Class-A germanium pre-amplifier based on the classic broadcast consoles of the 1960s. In the low-gain setting, the Broadcast can cover everything from sparkling clean boost through to transparent overdrive, all with a healthy dose of volume available to push your amp. The Broadcast features a specially selected Triad steel-core transformer and a NOS germanium transistor. Advancing the gain on the Broadcast starts to saturate the transformer and the pedal’s discrete circuitry, giving rise to a gentle and dynamic compression coupled with subtle thickening of the midrange. With the gain switch in the high setting and the trim control wound up, the Broadcast starts to deliver heavier distorted sounds with a warm and fuzzy edge to them. The Broadcast covers a wide range of driven and distorted tones whilst remaining dynamic, responding well to pick attack and the subtle nuances of every player.

Thanks to Tipunk777 for reverse-engineering his own pedal in the Forum section.
There are 2 layouts:
one with a 24V charge pump and one without.
23/12/2016 Layout updated! Changed Gain Switch to On-Off-On and rotated OC71 180 degrees
Added a second layout with charge pump. It's the same as before but on the top of the layout to give more space to the transformer.




49 comments:

  1. Great job with the vero, Alex - thx for sharing. The lower gain tones on the video really shine.

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  2. Built the second layout. Used the wrong transformer. It works and sounds like the video, but my gain and low cut pots aren't doing anything yet. Just finished so haven't looked it over yet.

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  3. Found a soldering mistake and now low cut works.

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    Replies
    1. Thanks NDF!
      Do Gain and Low Cut work?
      Is it verified than?

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  4. Gain still isn't working. It got late so I stopped playing with it. In the schematic in the thread I think the 10 uf attached to gain 1 was 100uf ? Would that change anything?

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    Replies
    1. The 10uF is correct but there may be a mistake somewhere else:
      can you try to disconnect Gain 1 and connect it to row 7, right above Sw1? If it works you should reverse Gain 1 & 2 after.
      Please, let me know if it fixes it.

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  5. It's all working now. Did the layout change recently? I had been working from a screen cap of it and didn't have the cut on the bottom row.

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    Replies
    1. Yes Alex changed the layout as there was an error.

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  6. It sounds pretty cool. Better into a clean amp than a dirty one for me. I used a tm009 for the transformer. Not sure what sort of difference that has made

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  7. Where can I find these transistors? Are there alternatives I can use? Ta ~~

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  8. Replies
    1. and should the bs549c be bc549c? a silicon npn?

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  9. Yes I think it is bc549c instead, I used a bc549 and an sft 352 pnp germanium transistor. I have a bunch sorted by hfe and I just grabbed one with 70 or 80 hfe.

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    Replies
    1. Thanks, I'll keep looking around for this pnp... This pedal sounds great!

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  10. I always socket the transistors and try whatever I have, I've found most pedals aren't too picky if you use the right type. I imagine many npn silicons and pnp gemaniums would be fine for this circuit

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    Replies
    1. Hi NDF!
      Did you make the changes to Gain 1?

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  11. Does the original have the crarge pump?

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    Replies
    1. i think there have been 2 different versions, 1 with a charge pump and one without.

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  12. What would be a good hfe for the germanium transistor? 70-150 range? or under that?

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  13. Cheers Alex and Tipunk777, I've built the version without the charge pump, and it's working as per expectations, so you can probably tag that layout as verified. Low is pretty subtle, though and I had to make some substitutions of key components because I didn't have exactly the right stuff.

    So, the non-charge pump layout works with: 470R substituted for the 450R, 22k level pot instead of 25k, a different 1:1 centre-tapped transformer (which I think is a TM018) and a Russian PNP Ge transistor with a measured gain of about 40 that looks like a grey flying saucer.

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  14. Can anyone share how they mounted their transformer - bend the pins? on its side like in the production photo?

    Thanks!

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  15. I used a different transformer, but I just bent the mounting pins out of the way

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  16. Does anyone know if there are more versions of the gain switch? In most videos I have seen online the Pedal has a three position switch. This one seems to be a two position on-on?

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  17. For the transformer, could one use pins 2 and 5 for ground, instead of 3 and 4 as in the layout? If it's 1:1, then the windings should be the same, right?

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    Replies
    1. ...or do you only get half the windings with the center taps?

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  18. The center tap is a wire connected to the center of the winding. You don't really "get half the winding" from the centertap. It has half of the winding on one side of it, and half of the winding on the other side of it.

    But to answer your question, if you use the center taps (pins 2 and 5) instead of 3 and 4, it won't work the same as the original.

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  19. Built the version with the charge pump. Works nicely, except for the fact that it doesn't make an audible difference if the transformer is installed or not. Bridging the across the top row of where the transformer I'd supposed to go (or not making the cut) doesn't change the sound a bit. Checked it back and forth. Installing a different transformer with different impedances cuts a lot of bass, so it's not an error in the build or layout. Just another mojo myth debunked it seems! I would like to be wrong here. Has anyone made different experiences?

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  20. i own the original 9V Broadcast version in which i later installed an 18V charge pump so it runs on 18V now. upon inspection of your vero layout, one big error that i found is that you have the OC71's emitter and collector reversed. the collector is supposed to connect to a 5K6 resistor to ground and the emitter connects to a 4K7 to the V+.

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    Replies
    1. Thanks John!
      I've updated it.

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    2. right on. i also drew out my 9V original's vero layout. the thing is, they used vero-board with .133" spacing.

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  21. BTW, and LT1054 works fine for the 25V charge pump.

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  22. Can you tell me why there are two different layouts with charge pumps, both with the same components?

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  23. please read the original text. it explains it.

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  24. SORRY - I downloaded the images before I read the new bit of info about them.

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  25. So if the Gain switch is 'on-off-on', it is a 3 position spdt-switch then?

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  26. Yeah, but you could use a 3 position DPDT too though, and just use one side of it.

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  27. I have a strange problem with the finished build. I have checked my connections but the gain switch ain't working like it should. I get 'low gain' on middle position, 'medium gain' on the left position and 'High gain' on the right.

    What am I missing here?

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  28. Replies
    1. But in the demos of 3 position switch-model it goes from left to right? Low-mid-high.

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    2. You should be able to do the same by using an On-On-On DPDT switch.

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  29. Anyone know of easily accessible, reasonably priced replacements for the OC71? I'm not having any luck finding them.

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    Replies
    1. There are some available on ebay, but you can try any PNP Germanium, with hFE somewhere in the Rangemaster/FF zone, 70-120 Cheap alternative would be AC125 which supposed to be replacement.

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