I finally finished the extended B1-R2 buffer I have been working on after receiving the chassis and finding the time to do the work.
For those not familiar, the B1-R2 is the Rev 2 version of the Pass B1 single ended buffer re-designed by Papa to work with a bipolar, rather than single ended, supply.
This build is for my office that also uses an ACA-Mini with boards created so it will mount in a more standard chassis with heat sink.
I modified the B1-R2 to use the output buffer pretty much as designed by Papa (Thanks Papa! 🙏) but I also added a few other things I wanted,
This one has an adjustable LM317/337 based power supply w/RCRC front end, a volume pot and a configurable gain stage on the same board.
The AC source is a 24V AC wall transformer connected by a standard 2.1 mm barrel connector.
It is laid out so the gain stage, which uses an LM4562 op-amp, can be omitted or the gain can be easily changed. The gain resistors and the op amp are all socketed and easily changed, bypassed or omitted. Or could be soldered in if no changes are expected.
The pot is an Alps RK27 at 20k Ohms. The next build will use a slightly wider chassis that will function the same but have an additional front panel 1/8" input, an LED power indicator and use a 10k pot with a higher input Z. Using that 20k Pot with 50k input impedance was pretty silly of me. The new build will go in the main rig.
So how does it sound? I think it sounds utterly fantastic! Really open, detailed and dynamic. My office stereo has never sounded this god. It's quite a change, But of course I may have builder's bias. 🙂
I created the board in KiCad. If anyone is interested and wants the design files or Gerbers I'd be happy to share. I can also share the chassis source at AliExpress. Drop me a PM if interested.
Attached is the schematic as built. I have a new rev with tiny improvements not yet built, And it probably never will be built. I ordered the five board minimum for the first build and expect to only build one or two more.
So
For those not familiar, the B1-R2 is the Rev 2 version of the Pass B1 single ended buffer re-designed by Papa to work with a bipolar, rather than single ended, supply.
This build is for my office that also uses an ACA-Mini with boards created so it will mount in a more standard chassis with heat sink.
I modified the B1-R2 to use the output buffer pretty much as designed by Papa (Thanks Papa! 🙏) but I also added a few other things I wanted,
This one has an adjustable LM317/337 based power supply w/RCRC front end, a volume pot and a configurable gain stage on the same board.
The AC source is a 24V AC wall transformer connected by a standard 2.1 mm barrel connector.
It is laid out so the gain stage, which uses an LM4562 op-amp, can be omitted or the gain can be easily changed. The gain resistors and the op amp are all socketed and easily changed, bypassed or omitted. Or could be soldered in if no changes are expected.
The pot is an Alps RK27 at 20k Ohms. The next build will use a slightly wider chassis that will function the same but have an additional front panel 1/8" input, an LED power indicator and use a 10k pot with a higher input Z. Using that 20k Pot with 50k input impedance was pretty silly of me. The new build will go in the main rig.
So how does it sound? I think it sounds utterly fantastic! Really open, detailed and dynamic. My office stereo has never sounded this god. It's quite a change, But of course I may have builder's bias. 🙂
I created the board in KiCad. If anyone is interested and wants the design files or Gerbers I'd be happy to share. I can also share the chassis source at AliExpress. Drop me a PM if interested.
Attached is the schematic as built. I have a new rev with tiny improvements not yet built, And it probably never will be built. I ordered the five board minimum for the first build and expect to only build one or two more.
So
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