didit wrote: ↑Sat Jun 22, 2024 4:01 pm
...Assumption has been HiFi but perhaps you want the HiTHD of a Champ et al.
This, plus a built-in resistive attenuator, and pseudo balanced line-out. The idea is to have the option to mic the 8" speaker, use it for a reactive load, or go silent into a DAW. The cab is standard Champ dimensions; just had to widen the control cutout a bit. Pretty cute.
didit wrote: ↑Sat Jun 22, 2024 4:01 pmWith a fair B+ voltage coupled to solid primary filtering (100uF), and perhaps even choke-based PI filter, you will get the low-end bandwidth and solid damping needed to achieve HiFi profile at around clean 7W.
I've included a choke for B+ ripple reduction. The OT is a Champ replacement, but I could swap that for a larger unit at some point.
didit wrote: ↑Sat Jun 22, 2024 4:01 pmYou've the EE chops and tooling to run a pre-build design exercise, though you'll really need to think about how to model chosen SE OPT as manufacturers are sparse with the necessary inductance and impedance details to do so in a fulsome way. That is, unless you have a specimen you can place into a test harness.
I have it in hand, but thanks to Hammond's detailed data sheets I was able to model the OT for the design. I'm also planning to experiment with a feedback loop from the speaker back to the power tube grid.
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angelodp wrote: ↑Sun Jun 23, 2024 5:33 am
Looks great Martin. So with the standard Champ cab, it will be a 10" speaker at best, or can you somehow get a 12" in there?
Thanks! There is no way a 12 would fit, maybe not even a 10 since the PT is an upright mount.
martin manning wrote: ↑Sat Jun 22, 2024 9:28 pm
Thanks for the input, Ian.
didit wrote: ↑Sat Jun 22, 2024 4:01 pm
...Assumption has been HiFi but perhaps you want the HiTHD of a Champ et al.
This, plus a built-in resistive attenuator, and pseudo balanced line-out. The idea is to have the option to mic the 8" speaker, use it for a reactive load, or go silent into a DAW. The cab is standard Champ dimensions; just had to widen the control cutout a bit. Pretty cute.
didit wrote: ↑Sat Jun 22, 2024 4:01 pmWith a fair B+ voltage coupled to solid primary filtering (100uF), and perhaps even choke-based PI filter, you will get the low-end bandwidth and solid damping needed to achieve HiFi profile at around clean 7W.
I've included a choke for B+ ripple reduction. The OT is a Champ replacement, but I could swap that for a larger unit at some point.
didit wrote: ↑Sat Jun 22, 2024 4:01 pmYou've the EE chops and tooling to run a pre-build design exercise, though you'll really need to think about how to model chosen SE OPT as manufacturers are sparse with the necessary inductance and impedance details to do so in a fulsome way. That is, unless you have a specimen you can place into a test harness.
I have it in hand, but thanks to Hammond's detailed data sheets I was able to model the OT for the design. I'm also planning to experiment with a feedback loop from the speaker back to the power tube grid.
Does look cute. Doubtless you'll find it works as expected assuming not pushing the power stage hard and the speaker is a modern efficient 8" rather than the flimsy floppy kind that Fender issued back in the day. Look forward to hearing your conclusions and results.
Hey Martin, Just wondering... I'd love to build this... any chance you might post some details? Like your usual detailed build docs or a schematic? (FET gerbers or maybe I could buy a board from you?).
Looks great!
Still slow progress on this after abandoning the original custom chassis sizing. It's ready to go, now, though. Most recently, I picked up a new set of mini-toggles for the front panel. Short-bat types look much better at this scale. I have a detailed layout drawing, but it's still untested. After assembly and testing I will post more. I also have a stack of FET booster boards.
