Metropoulos Forum

Hi guys,

Some cool info in this thread. I've got the Yeti. Just moved over the NFB to the 16 ohm tap (still with 39k) and I'm loving the tighter feel. Craploads of gain in this thing that I never use though. Two Q's on that.

Firstly, I told Nik I was chasing a bigger, more Malcolm Young feel. Along with the NFB change, he suggested trying out a lower value plate resistor. This will increase plate voltage yeah? I think I'll give it a go, some talk of this a few pages back, anyone got a follow up report?

Also, with the Zeners, can I safely change to LED's for something a bit different?

Cheers,
Nick

....

If anyone was unaware, Ceriatone have posted the layout for the 50w Chupacabra & Yeti:

http://www.ceriatone.com/images/layoutP ... hupa50.jpg" onclick="window.open(this.href);return false;

http://www.ceriatone.com/images/layoutP ... Yeti50.jpg" onclick="window.open(this.href);return false;

Somebody can upload the schematics? I can't see it.

Looks like they've updated their website. Go to the "Documentation" section at http://www.ceriatone.com/hot-rodded-ple ... acabra-50/

Alternatively, the new direct link is http://www.ceriatone.com/ceriatone/wp-c ... t-2015.jpg

I've built a bunch of these by now. Stock, modified, used the layout as the foundation for an Atomica and other Jose variations. I'd say the stock Chupacabra circuit really benefits from a few simple changes:

1. Add the missing 10K B+ dropper between PI and CF
2. Increase NFB resistor to 47K
3. Reduce slope resistor to 33K
4. Remove Pussy Trimmer and replace with typical 470K resistor as part of the voltage divider
5. Lower V1a plate load to 330K
6. Replace zeners with 18v on one side and either MPSA06 or 2N5401 on the other side
7. Remove all the bright caps and stuff on Gain 1. Either keep the 82K/150K voltage divider (hardwired) or go with 68K/68K to keep things tighter
8. Hardwire 4700pF cap on Gain 2

That's a good start. Plenty of other things could be done, like going with more traditional cathode arrangements (like 2K7/.68uF in the first two stages to make the amp punchier). I would also increase the grid leaks a bit to at least 150K. But if going with stock Marshall 220K value, I would reduce the PI output couplers as well. Too much bass being passed for no reason.

And ideally, I would up the voltages in the entire amp a bit. Stock, the Chupa runs like 97v on V1a plate, which is a bit loose and gainy. But the amp sounds good stock. It's just that after building a bunch of these things, those are the changes I've enjoyed. I like a PT spec'd for a higher secondary so the B+ is around 475v and you have at least 160v - 180v on V1a.

Some excellent suggestions for these builds, some I've already used in similar contexts, some I will use in the future - thanks!

it's a shame almost everything on this site is a broken link. can't see layouts or schematics on any past posts. Pretty useless.