Simulcast gain "issue"

[Jonathan]

I put issue in quotations because it's working fine, I'm just curious what hfe you all put in and if it's behaving like it should? I don't have any experience with the Hudson broadcast, I'm only going by demos, but my build doesn't quite get as fuzzed out on the highest gain setting. It sounds great but it doesn't get that saturated, sagging nasty sound that I seemed to hear in videos, it's more of a high OD. I tried a few germanium pnps and the highest gain I have is about 225 hfe. I tried some silicon pnps and got either similar results or crazy feedback and oscillation as soon as I put it in.

Anyone else find that, or am I just wrong about what I think it's supposed to sound like? Is it the actual transistor? I don't have any oc71 on hand, could that be the issue more than hfe? I used an sft 323 I think.

 

[Jovi Bon Kenobi]

Now that you mention it I can see what you mean. Mine sounds about the same as what you describe, though I also love it. One thing I can think of is that there were a few different versions of the Broadcast built, some with an internal charge pump, earlier ones without. The Simulcast has the charge pump (18v?) so it's going to have a lot more headroom than the 9v. That might explain not getting as nasty as some of the earlier demos.

 

[Jovi Bon Kenobi]

would it be possible to negate the charge pump and run it from a power supply that goes lower than 9v to test? If I recall correctly there are some power supplys that have this function. And, I used a oc71 in mine btw.

 

[Jonathan]

would it be possible to negate the charge pump and run it from a power supply that goes lower than 9v to test? If I recall correctly there are some power supplys that have this function. And, I used a oc71 in mine btw.

I imagine it would be possible. I found it easier to just put a boost in front. I built a mosfet boost into the circuit and gets a very similar oversaturated sound. I had to modify the boost to make it less bright because it was getting too shrill but overall I'm happy with it.

 

[Robert]

If you pull out the charge pump IC and power it on 9V it will run at around 7.5V because of the circuit design.

 

[Jonathan]

Well, that's the answer. I was sure I'd seen videos of it running on higher voltage where it sounded fuzzy. But either way, running without the charge pump makes it sound the way I wanted. It loses a little bass response on lower voltage, but it also doesn't get as spiky and shrill when the bass cut is all the way up, which is nice. I wish I'd know just pulling out the ic would work before I spent all that time trying to find the right boost, haha. But at least now I have a lot of options and tweakability. Love this pedal.

 

[adam]

Thanks for this thread. I finished a Simulcast last week, and was really pleased with the sound. But today I was listening to Dan & Mick playing one and thinking “don’t think mine does that.” I tried it this evening and still liked it, but sure enough it won’t fuzz out. I’ll have to try popping the IC. Wonder if the charge pump could just be made switchable. Presumably, with the charge pump, you couldn’t sag the input voltage enough, right?

 

[Jonathan]

I believe that the sagging voltage is the issue. I'm sure the charge pump could be made switchable, I never looked into it because I just like it better without it, but I'm assuming if you connect a few points on the IC to a dpdt switch or something you could switch it in and out. I've done that with an IC on the clarinot clone to get rid of the fuzz. I'm just not sure which legs need to be taken out of the circuit but it should be pretty clear from the schem.

 

[caiofilipini]

I'm glad I found this thread. I built a Duocast a while back (build report here) and never managed to get it to sound close to the original. Until now. I pulled the charge pump (I used a TC1044SCPA) out, fed it 18V and it sounded much closer! It's a little fuzzier, but less muddy overall. Sounded better to my ears, at least.