Hudson Electronic Broadcast

[Alex]

I've drawn mine on paper (looks like crap) and my scanner wasn't working.
It's pretty much the same but I've used 100uF caps instead of 120uFs.
There are a few differences:
On the top left where the 5K6 resistor meets the 56K and the 1K there is a 100uF (120uF) cap going to ground.
From the BC549C emitter there's a 100uF cap instead of 10uF and the 1uF from its negative side should be a 1nF.
I could not read values from the pictures. I've used Tipunk777's layout values.

[Ciaran Haslett]

Good man Alex.  I'll get those changed tonight.  I used his layout values as well (but obviously didn't input them correctly lol).

Looking at the 120uF caps....they seem far too big physically to be that value no?  I assumed 220uF based on that.  I could be wrong though...and they're just filter caps at the end of the day.

Cheers again

[Alex]

That's what I've thought but 120uF is not a "regular" value and I'm not sure how big they could be.
As you've said the circuit may come from a radio or something and he may have used 450V caps (or similar) which could explain the size.
I think they've just been used for filtering in audio equipments but 100uF would be enough in a pedal (may be completely wrong here).

[rocket88]

I was thinking the same thing when I sat down to trace it. I went looking for 120uF caps to get an idea about size, and the ones on the board look about the same size as 400v 120uF caps. I do wonder why they used an odd value all over the circuit though, I mean it all can't be for filtering, can it?

[Alex]

They should be for filtering.
There are 2 x 120uF caps going to ground on the main board.
One is straight after the 10R resistor and one after the 1K connected to V+.

[Neil mcNasty]

Just built this, and it "almost" works.
It works fine and sounds really great for about 10-20 seconds (after it is fed power) and then "buckles under/whimpers out", as if it is not getting enough current, as soon as all the caps are charged up.
This is just my theory based on the symptom I get and the fact that when I unplug the power, then wait a short while to let the caps drain out, and then plug the power back in. It works fine for another 10-20 seconds, before buckling under again.

I used a 42TM018 transformer while waiting for the correct one, but I do not suspect that to be the issue, as it should mainly just limit the frequency response to 3.4KHz instead og 15KHz.
- I therefore suspect that the circuit uses a bit more current then the charge pump can provide, but I could be wrong... Have not looked at the 1054 specs yet and it looks like the original uses a charge pump as well, so I am in a bit of a doubt on that thought...
- Another thought that strikes me is: if the 120uf caps actually should be 220uf.
Could this then cause issues like this when using 100uf? Indicating that the caps are draining faster then they are being charged up when you start playing/loading the circuit...?

I checked over it for any faults in my build, but could not find any. Will have a second look tomorrow.

[Ciaran Haslett]

It sounds more like a bad cap/cold solder to me lad.  This circuit will be pulling single figure mA at the most.  

[Alex]

Did you manage to fix it, Neil?

[Neil mcNasty]

Not completely Alex. But I think I'm on to something...
First I replaced most of the electrolytic caps, reflowed solder, knife the gaps, you know... the usual stuff... but no difference.
I also tried several OC45 trannies to make sure they were ok.
But then I noticed that I had connection issues with the transformer as the sound drops out when I wiggle it.
It has been recycled from a previous build and I had to solder on some extension leads to get it mounted, so there is clearly some connection issues going on. Maybe it also has become a bit overheated and damaged in the process...
The 42TM018 is also a bit to big for this layout, making a short to the +v power link a potential problem.
The transformer also picks up some high pitch whine that I suspect is because of this link running a bit close to the transformer. But I have not boxed it yet either, so that could explain it as well...
Could it be a good idea to rearrange the layout so that this link is as far away from the transformer as possible? Transformers are known to be more prone to noise from power leads...

I'm waiting for the correct transformer in the mail, and it will probably arrive sometime next week.
I have a strong feeling that it will fix my main issue.
When it sounded correct, it also sounded amazing, so I think the trace is good as far as I can tell...

[velouriafx]

Thanks for the answer, Neil. I will wait your build before I try this. In Brazil, I didnt find this transformer.

[Neil mcNasty]

velouriafx: on a second thought after looking at the schematic, it seems like the transformer is essential as it sits between the Gain Trim pot and the Volume pot.
Meaning that the Gain Trim sets the transformer distortion/coloration.
So without the transformer you will just end up whit two Volume pots in series.
This does not mean that it will sound bad, but that it will sound very different, and that the Gain Trim and Volume will have the same function.

I got my transformer at ebay from a UK seller that ships worldwide.
Do a search for TY-141P and it will be among the 2 or 3 top results.
I'll report back as soon as I get the transformer!

[velouriafx]

Neil: I found it in Small Bear too, but, in Brazil, the custom service is slow. I have a 3PDT order from Germany that is taking more than 50 days. So I'd rather wait for your feedback to order the transformer. Thank you very much for your attention. Keep us informed. Cheers

[rocket88]

i just ordered one too, so i'll be ready once it gets here. i see some nice potential for modding in this circuit too.

[Alex]

Not sure the link next to the transformer would cause noisy but there you go:

[Sergio]

Hallo Neil, have you been able to try your Helios Preamp layout? It was a mic instrument pre with ge transistor in it, right? Maybe these two are more or less the same? an slightly driven pre? or are they completely different? Thanks a lot

[Neil mcNasty]

Sergio: Not yet... Yes. it is a Mic Preamp Section from a Helios Console, but it is all Silicon design.
It is a lot bigger and complex than this kind of preamp.
That's an old layout by the way. It could really need a second look before anyone start building.
Something looks fishy about it...

I do have a couple of simple old RCA and other vintage Germanium preamp layouts that has some similarities to this kind of design.
But I need to dig out some schematics and check the layouts first.
I'll post them in the contribution section as soon as I've had the chance to look at them...

[Sergio]

All right Neil, thanks a lot for your work! very inspiring too

[tipunk777]

Oops! I leave you a week and now everything is done! Thank you all for your contributions, it is really very motivating to propose something else afterwards.

[Alex]

Found a mistake!
Gain 1 is connected to the wrong place. It should be connected to the other side of the 1n capacitor, where it connect to 1K, 5k6 and the 2 100uF caps.
I've changed the layouts.

[Ciaran Haslett]

High res HERE


Updated Q2 orientation.  Cheers John