I'm at a point where i am confident in this board design, at least for the SRD-7. I have minimal interest in commerce and i know there's not much money in this, but i did order a stack of 30 boards.
It's largely a distillation of the official schematic for the SRD-7 MkII and modifications recommended by a few other tinkerers, so i don't really take credit for the circuit itself, just the board design. I'm using the same kind of cockroft-walton voltage multiplier as Stax used for the bias supply. Ballast resistors are 4.7M. Optional bias reserve caps moved to *before the ballast resistor. Noisy PTH devices replaced by regular power resistors. Room enough to reuse vintage resistors or to use whatever boutique power resistors you want.
It can also be used to convert a self-biased energizer to wall-powered bias. It *may be able to give you a self-pro-bias energizer out of an old SRD-4 but I haven't tested this yet and i may need to revise the design for that. I also haven't tested fitment in the SRD-6 yet and at a minimum it needs another hole drilled, or some foam mounting tape, as i hadn't realized that the mounting brackets in the SRD-6 are 100mm center to center.
I've also tested it in an SRD-5.
In an SRD-7, you basically desolder wires from the original board and solder them to the same position on the new board. The exception is that I've provided a position for a fuse when adding wall power (or upgrading an SRD-5).
The BOM is less than $10 from mouser for one board.
$10 plus postage, will come in a padded envelope with a short length of 2.85mm black 3d printer filament that you can use to plug the center hole on the socket you upgrade to high bias.
If i have enough parts left over when i am done testing and upgrading the energizers i have on hand, i may offer one or two fully populated boards. I Really don't want to upgrade your energizer for you. The SRD-7 pictured below is actually an earlier prototype layout, for full disclosure.
It can also be used to build a fully DIY energizer with high-quality transformers from Lundahl or similar, or whatever push-pull output transformers you got (must have a center tap on the HV side).
I'm not tryin'a be in business, I'm just proud to have produced it. You don't have to spend hundreds of dollars on a direct-drive amp for any modern staxen - you can modify a good old SRD-7 and use it with whatever amp you got. Dip a toe in and see what 'stats are like. Even the ancient ones are good, and yes the modern ones are mostly better.
Standard disclaimers apply - uses wall power and generates high voltages so exercise due care. Applying too high of a bias voltage to your electrostatic headphones may destroy them.
It's largely a distillation of the official schematic for the SRD-7 MkII and modifications recommended by a few other tinkerers, so i don't really take credit for the circuit itself, just the board design. I'm using the same kind of cockroft-walton voltage multiplier as Stax used for the bias supply. Ballast resistors are 4.7M. Optional bias reserve caps moved to *before the ballast resistor. Noisy PTH devices replaced by regular power resistors. Room enough to reuse vintage resistors or to use whatever boutique power resistors you want.
It can also be used to convert a self-biased energizer to wall-powered bias. It *may be able to give you a self-pro-bias energizer out of an old SRD-4 but I haven't tested this yet and i may need to revise the design for that. I also haven't tested fitment in the SRD-6 yet and at a minimum it needs another hole drilled, or some foam mounting tape, as i hadn't realized that the mounting brackets in the SRD-6 are 100mm center to center.
I've also tested it in an SRD-5.
In an SRD-7, you basically desolder wires from the original board and solder them to the same position on the new board. The exception is that I've provided a position for a fuse when adding wall power (or upgrading an SRD-5).
The BOM is less than $10 from mouser for one board.
$10 plus postage, will come in a padded envelope with a short length of 2.85mm black 3d printer filament that you can use to plug the center hole on the socket you upgrade to high bias.
If i have enough parts left over when i am done testing and upgrading the energizers i have on hand, i may offer one or two fully populated boards. I Really don't want to upgrade your energizer for you. The SRD-7 pictured below is actually an earlier prototype layout, for full disclosure.
It can also be used to build a fully DIY energizer with high-quality transformers from Lundahl or similar, or whatever push-pull output transformers you got (must have a center tap on the HV side).
I'm not tryin'a be in business, I'm just proud to have produced it. You don't have to spend hundreds of dollars on a direct-drive amp for any modern staxen - you can modify a good old SRD-7 and use it with whatever amp you got. Dip a toe in and see what 'stats are like. Even the ancient ones are good, and yes the modern ones are mostly better.
Standard disclaimers apply - uses wall power and generates high voltages so exercise due care. Applying too high of a bias voltage to your electrostatic headphones may destroy them.
Attachments
Last edited: