Simulcast/Broadcast Silicon Mod?

[airvian]

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

 

[Big Monk]

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

No reason you couldn’t.

 

[airvian]

No reason you couldn’t.

Any pointers on what could work well enough?

 

[Big Monk]

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.

 

[airvian]

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.

 

[Big Monk]

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

I would socket it and play around.

 

[airvian]

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.

 

[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.

 

[airvian]

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.

 

[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?

 

[airvian]

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.

 

[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.

 

[airvian]

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.

 

[airvian]

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

 

[MichaelW]

...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......

 

[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...

 

[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!

 

[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).

 

[TheHammer1982]

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

 

[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.