# Simulcast/Broadcast Silicon Mod?



## airvian

Has anyone tried swapping the Ge OC71 (or similar) for a silicon transistor?


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## Big Monk

airvian said:


> Has anyone tried swapping the Ge OC71 (or similar) for a silicon transistor?



No reason you couldn’t.


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## airvian

Big Monk said:


> No reason you couldn’t.


Any pointers on what could work well enough?


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## Big Monk

airvian said:


> Any pointers on what could work well enough?



I would imagine a PNP device between 70-100 hFE would do. 

You could put a pF range cap across base and collector to smooth things out if you feel it needs it.


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## airvian

Big Monk said:


> I would imagine a PNP device between 70-100 hFE would do.
> 
> You could put a pF range cap across base and collector to smooth things out if you feel it needs it.


Guess I'll just try my way through a bunch and see what works.


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## Big Monk

airvian said:


> Guess I'll just try my way through a bunch and see what works.


I would socket it and play around.


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## airvian

Big Monk said:


> I would socket it and play around.


Yeah that's the plan. Really want to try and play around with the transformer that's in the pedal too.


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## mdc

As far as my understanding goes, that transformer is doing essentially nothing aside from lookin' cool. I've read a few comments scattered around from folks who've built it with the transformer on a switch and can't hear much of a difference with it in and out of the circuit.


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## airvian

mdc said:


> As far as my understanding goes, that transformer is doing essentially nothing aside from lookin' cool. I've read a few comments scattered around from folks who've built it with the transformer on a switch and can't hear much of a difference with it in and out of the circuit.


Yeah, that's what I've read too. Seems like snake oil. They're pretty expensive as well. Neve seems to really swear by transformers though, so maybe that's why it was included in the original design.


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## mdc

The transformers in actual transformer-coupled mixing consoles are absolutely doing important things and (can) have a big effect on the sound; those units are also using much larger, higher quality iron running at much higher voltages. But yeah, just putting an audio signal that's already pretty distorted through a teeny 1:1 transformer seems like it isn't going to do much of anything. Maybe some bandpass filtering?


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## airvian

mdc said:


> The transformers in actual transformer-coupled mixing consoles are absolutely doing important things and (can) have a big effect on the sound; those units are also using much larger, higher quality iron running at much higher voltages. But yeah, just putting an audio signal that's already pretty distorted through a teeny 1:1 transformer seems like it isn't going to do much of anything. Maybe some bandpass filtering?


True. What I was wondering: Hudson advertises a different transformer in their Broadcast AP model. However, they seem to be identical in impedances and ratio. So I am led to believe that the biggest difference between the two circuits is the use of a silicon transistor instead of the OC71.


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## airvian

FYI: I now tried out several different transistors in both positions. As a silicon replacement for the OC71, the only PNP silicon transistor I found working consistently was the 2N4033. For the NPN silicon one, I found several BC-type silicon transistors passable. The ones that had the most useable sounds were the BC107A and the BC547A/B/C. However, I think many others would work well too. The best sound was achieved by using a 2N4033 and the stock BC549C though. Next step will be trying to get a treble trimpot in that thing.


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## airvian

thewintersoldier said:


> In any instance I have also heard that the transformer doesn't do much except drive up the price and the hype. I also know someone who is putting out a transformer less all silicon dual version in a 125b for those so inclined to be patient.


Yes. It feels like it does basically nothing.


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## airvian

thewintersoldier said:


> Most of the boutique game is just marketing, guitar gear junkies are so easy to manipulate especially when you have endorsements from players who serve to that niche market.


very true. when you know how little it takes to build that fuzz you really don't feel like spending the money


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## MichaelW

thewintersoldier said:


> ...guitar gear junkies are so easy to manipulate...


Ok, you pegged me....and to think I pay big bucks for counseling and we've never gotten to this level of truth......


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## dan.schumaker

For reference, here is one I made up using a SI transistor (just a 2N3904) and sans the transformer.  I still think it sounds pretty decent...


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## daeg

You guys are all correct. The transformer is for mojo points. A $1 part that makes the guitarist think there is magic inside the box.

There was a thread on DIYSB about transformer saturation, and a few guys much smarter than myself made convincing arguments that transformer saturation does occur at very high current levels, but there is no guarantee it even sound good!


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## daeg

https://forum.pedalpcb.com/threads/broadcast-ap-schematic.9119/post-85103

@bowanderror said:


> I looked in to it a while back and it's the same circuitry as the Broadcast, but with a silicon 2N4033 transistor in place of the Ge transistor, and an OEP Z1643E transformer instead of the TY-141P (both 10K:10K CT transformers).


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## THeHammer82

I wondered if that transformer actually did anything when I built my Broadcast. Sounds like it was a waste of $10.


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## HamishR

What's with the filtering? Why use a string of 10µF caps separated by resistors? I'm not being snarky! I just don't know why you would do that, and there is probably a very good reason of which I am unaware.


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## giovanni

We had a discussion about a similar filtering on the Marsh fuzz on another thread. Basically there is no reason for that…


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## jesuscrisp

HamishR said:


> What's with the filtering? Why use a string of 10µF caps separated by resistors? I'm not being snarky! I just don't know why you would do that, and there is probably a very good reason of which I am unaware.


It's how the charge pump works.


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## giovanni

jesuscrisp said:


> It's how the charge pump works.


On second look, I only see R13 as potentially “extra”. The rest of the resistors are for voltage dividers and the caps for filtering. Debatable whether you need all of the caps but certain design decision also depend on the way the original PCB was laid out. And btw the charge pump does not use resistors so I don’t think @HamishR was referring to that section.


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## jesuscrisp

giovanni said:


> On second look, I only see R13 as potentially “extra”. The rest of the resistors are for voltage dividers and the caps for filtering. Debatable whether you need all of the caps but certain design decision also depend on the way the original PCB was laid out. And btw the charge pump does not use resistors so I don’t think @HamishR was referring to that section.


I think I misread that but also I don't really see a string of resistors and caps.


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## HamishR

Sorry - got confused. Easily done for me. I've been looking closer at the schematic and now realise that the"string of resistors and caps" was indeed the diodes and caps for the charge pump. Don't mind me - I can be really thick sometimes!🤪

Time for a ride on my bike to clear my head.


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## HamishR

I've been drawing up a Vero layout to test this circuit without the transformer. It's ended up bigger than I like but it's quite tricky to fit into a Vero. Now to try it.


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## Chuck D. Bones

Those little transformers have crap bandwidth and are rolling off some of the top and bottom-end.  But I agree, as-designed it's 99% hype.

Hudson missed an opportunity to isolate the secondary from ground so that the Broadcast could also be used to break ground loops.


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## Dan0h

I am a recent convert myself. I totally was a sucker for the transformer magic, until I built the Heavy water clone and realized the “magic” was not the transformer in the Hudson after all. The Magic is when the circuit is just right and gels with the rest of your gear.


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## giovanni

Dan0h said:


> I am a recent convert myself. I totally was a sucker for the transformer magic, until I built the Heavy water clone and realized the “magic” was not the transformer in the Hudson after all. The Magic is when the circuit is just right and gels with the rest of your gear.


What does the heavy water sound like?


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## Dan0h

giovanni said:


> What does the heavy water sound like?


To me, on my set up, it sounds like the Hudson as a clean boost but with the clarity turned up. And less the fuzz at max settings. Still over drives the tubes and has a really nice crunch when maxed. Arche.


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## HamishR

I built a Heavy Water and was totally underwhelmed. But that's ok - most pedals are designed for somebody who is not me, I suspect. I didn't really go for the Hudson at first, but it does have something... As a boost the Broadcast is excellent, whether with the transformer or not. As Chuck suggests I suspect that the transformer is having a slight affect on the bandwidth - maybe it should have more effect because the Broadcast I built without the transformer sounds very similar to the stock form. I wish it rolled off a tad more high end!

The Heavy Water has little to no character of it's own through my setup. Whereas the Broadcast has a kind-of treble boost flavour that I seem to like. Everyone has their own take - maybe on a different day I would have liked the Heavy Water better.


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## HamishR

FWIW I have ordered some 2N4033 transistors. If I can get a similar tone with silicon I will be happy - one less variable. I love the sound of Ge transistors but prefer consistency. And then to address that high end... Daeg's idea of the cap across base and collector of the BC549C works. I'm wondering if increasing the size of C2 might help?


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## THeHammer82

The only real gripe I have about my Hudson clone is that the highs are a little overwhelming.


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## HamishR

At times I don't notice the highs and at other times they do grate! I think I'll have to try making C2 bigger.


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## dawson

Bumping this ol' thread:

If one were to build a Simulcast/Duocast circuit without a transformer on the existing PedalPCB board, would they need to install any jumpers on the PCB to bypass the transformer, or just leave a big gaping hole there?
I'm looking at the schematic, but not really understanding how transformers work, I'm unable to form any sort of hypothesis.  Thanks for any help!


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## szukalski

THeHammer82 said:


> The only real gripe I have about my Hudson clone is that the highs are a little overwhelming.


+1 If anyone has improved this then do share!


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## Chuck D. Bones

On the Simulcast, simply jumper T1-1 to T1-6.  T1-1 connects to R14.  T1-6 connects to pin-3 of the LEVEL pot.

Same thing with the Duocast.

I have some ideas on how to tame the highs, but have not tried them.

1. Increase C7.  Will have the strongest effect at high GAIN settings.
2. Connect a cap from B to C on Q2.  Start with 1nF.  Too dark - make it smaller.  To bright - make it larger.


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## dawson

Chuck D. Bones said:


> simply jumper T1-1 to T1-6.  T1-1 connects to R14.  T1-6 connects to pin-3 of the LEVEL pot.



Thanks, @Chuck D. Bones, I appreciate it!


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## THeHammer82

I picked up a Source Audio EQ2 a few weeks ago and it’s been fantastic. I was easily able to tame the highs on the Duocast with it.


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## HamishR

I followed Chuck's advice this time and put a cap across the base and collector of the 2N4033 transistor I have in one of my Broadcast clones - this one doesn't have the transformer yet still sounds wonderful! I used an 820pF MLCC because it was nearly 1nF and it fit better. And it seems to have reduced the highs a perfect amount for how I used the pedal.

Previously I did something similar on Q1 in another Broadcast on Daeg's advice and it worked there too. There are clever people here.


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## harmaes

The guts from the AP version from an Andersons video:





From around 11:20 in this video:


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## K Pedals

Yeah the new ones have circuit boards and they switched to the 2N404 for the transistor…


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## harmaes

The resistor colors are somewhat hard(er) to read. It seems like some 560R resistors instead of 5,6 or 56k? Overall it seems close the original with a 2n4033 or similar and Z1643E. *I think building the Simulcast with these mods could get me close?*

In general I don't really like the bridge tone Ariel is getting in this video. The neck pickup sounds better IMO.
I have 2 guitars setup with this string gauge and this requires more high end than with "normal" strings. That's probably the reason this pedal is behaving more as a treble boost which suits his guitars.


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