SR45 amplifier
- Thread starter debk
- Start date
Paul Joppa
Moderator
Thanks, Aaron.
Not much yet, except I've shuffled the parts around quite a bit to simplify the wiring. There are still 16 or so wire bundles, mostly 2 wires each, of 4 different compositions - but at least they don't cross each other any more. And I put most of the parts in a BOM spreadsheet so I can guess about the cost.
Premium caps are EXPENSIVE! I may put all the PSU caps on a separate board, and let the tweakers make their own boards for fancier caps. Between the DC filaments and the turn-on delay logic, there's a lot mroe caps than usual. Incidentally, I'm keeping the critical caps off the board, it just has caps with no signal voltages.
Not much yet, except I've shuffled the parts around quite a bit to simplify the wiring. There are still 16 or so wire bundles, mostly 2 wires each, of 4 different compositions - but at least they don't cross each other any more. And I put most of the parts in a BOM spreadsheet so I can guess about the cost.
Premium caps are EXPENSIVE! I may put all the PSU caps on a separate board, and let the tweakers make their own boards for fancier caps. Between the DC filaments and the turn-on delay logic, there's a lot mroe caps than usual. Incidentally, I'm keeping the critical caps off the board, it just has caps with no signal voltages.
PJ is indeed out of town at the moment.
-PB
-PB
Paul Joppa
Moderator
Status? Same as when I left town. (Just got back last night :^) Ask next week - I hope to get some time on this project. There's a lot done in my head that isn't written down or sketched out yet.
Paul Joppa
Moderator
Got some time Thursday and today, and finally got a lot of my thoughts down as actual schematics with parts values (!). Four pages and counting. I've also tentatively laid out which functions go where on the new physical layout, so I can draw the actual wire bundles. Once that's done, I can start doing the detailed PC boards. (Don't worry, all the signal voltages are off the boards - it's just power supplies and sequencing logic.)
One of the things going into this design is an RFI filter at the power input; I'm following Buddha (the late John Camille) in using a commercial RFI filter followed by a homebrew lower-frequency filter that gets down to 2kHz. I've gone back and forth on how to do this, and how complex to let it get, but that's where I am now.
The power and protection sequencing was a bear since I didn't want to use digital counters. At this point there are four LV regulators and three relays in each amp. I had worked it out a month or two ago, but getting the details down on paper (and fixing my hand-waving!) was a chore.
One of the things going into this design is an RFI filter at the power input; I'm following Buddha (the late John Camille) in using a commercial RFI filter followed by a homebrew lower-frequency filter that gets down to 2kHz. I've gone back and forth on how to do this, and how complex to let it get, but that's where I am now.
The power and protection sequencing was a bear since I didn't want to use digital counters. At this point there are four LV regulators and three relays in each amp. I had worked it out a month or two ago, but getting the details down on paper (and fixing my hand-waving!) was a chore.
Paul Joppa
Moderator
Good progress this week - as usual, once I see the circuit and/or layout on paper, I make changes ... Hope to get some PC boards laid out this next week or two. I need to mock up the power supply to confirm voltages and delay-relay sequencing, before getting into the actual audio circuit - but I'm already looking at some options for the driver bias.
Paul Joppa
Moderator
No update today; too much real-life business.
Paul Joppa
Moderator
OK, a bit of progress finally. Today I ordered two chassis plates, on which to build the prototype pair. Since this required enough certainty in PC board layout to position the mounting holes, which in turn means finalizing the specific parts to be used, that's actually quite a bit of work - but Front Panel Express has a sale that I didn't want to miss! The plates were $180 on sale, FWIW.
I've started refining my horn system. Having had it off for a few weeks has helped me realize where a couple of improvements could be made, mostly positioning and crossover related. I will still modify the three pairs of Paramounts to use one Co, one Ni and one series feed with Ag primaries and secondaries with the WE. And when I install the horns back, hopefully early next year, they will be powered by three pairs of these new sr 45s!
Pd. Please Paul, when designing keep in mind my tl404s!
Pd. Please Paul, when designing keep in mind my tl404s!
Paul Joppa
Moderator
"I'm sorry, Xavier, I can't do that. Opening pod bay doors ..."
Seriously, the chassis is laid out for the OT-2 and OT-3; there's enough room for a TFA-204Senior but that's it. Since I don't have drawings for the TL-404, I can't say whether it will fit or can be oriented correctly.
Of course a custom chassis plate is always an option. Not an inexpensive option, since it would not be laser-cut, but an option. Let's get something working before we start to re-design it for different parts!
Seriously, the chassis is laid out for the OT-2 and OT-3; there's enough room for a TFA-204Senior but that's it. Since I don't have drawings for the TL-404, I can't say whether it will fit or can be oriented correctly.
Of course a custom chassis plate is always an option. Not an inexpensive option, since it would not be laser-cut, but an option. Let's get something working before we start to re-design it for different parts!
