Hi folks
I've built a B1 buffer to use as a preamp. I got the board from ebay (I know, but this was months ago, before I even knew DIYAudio existed) and have had it sitting around for ages before I got around to building it. This is the board:
I managed to obtain a matched quad of real 2SK170s to use with this B1. I've used Russian caps - K77-1 and K75-10 PIOs bypassed with FT-1 Teflons, the electrolytics are Rubycon BXA 10000uF. Power supply is a simple LT1086 regulator board from eBay that I built myself - no dodgy fake components! A 90VA 26V toroidal trafo made in Germany by Schaffer is perhaps overkill, but it's what I had at hand that was suitable.
I've mounted it in a chassis recycled from a broken Cambridge Audio CDP and have a few questions I need to work out before I can complete the build.
1. I use a pair of power amps to biamp a pair of Linn Index speakers, currently I use a pair of y-splitter cables to connect these to my Yamaha preamp. With my B1 preamp, I'd like to have two sets of outputs to avoid the Y cables. How to implement this?
2. Volume control. The board has a 25K pot silkscreened on it, but I've soldered on a set of wires to run to a pot mounted on the front of the chassis. Will a normal 25k stereo pot suffice or is there a better solution such as a stepped attenuator? I don't know what options there are or the pros and cons.
3. Inputs, I only need 3 - computer, tuner, CDP, but I figure four is sensible in case I add something else to my hifi setup in future. How to implement four inputs? Obviously, a rotary switch is needed, but what else - relays, capacitors, etc?
I think that's it, I'd like to keep this as simple as possible with minimalistic circuitry, in keeping with the Pass Labs ethos that createdthe B1 itself.
I've built a B1 buffer to use as a preamp. I got the board from ebay (I know, but this was months ago, before I even knew DIYAudio existed) and have had it sitting around for ages before I got around to building it. This is the board:
I managed to obtain a matched quad of real 2SK170s to use with this B1. I've used Russian caps - K77-1 and K75-10 PIOs bypassed with FT-1 Teflons, the electrolytics are Rubycon BXA 10000uF. Power supply is a simple LT1086 regulator board from eBay that I built myself - no dodgy fake components! A 90VA 26V toroidal trafo made in Germany by Schaffer is perhaps overkill, but it's what I had at hand that was suitable.
I've mounted it in a chassis recycled from a broken Cambridge Audio CDP and have a few questions I need to work out before I can complete the build.
1. I use a pair of power amps to biamp a pair of Linn Index speakers, currently I use a pair of y-splitter cables to connect these to my Yamaha preamp. With my B1 preamp, I'd like to have two sets of outputs to avoid the Y cables. How to implement this?
2. Volume control. The board has a 25K pot silkscreened on it, but I've soldered on a set of wires to run to a pot mounted on the front of the chassis. Will a normal 25k stereo pot suffice or is there a better solution such as a stepped attenuator? I don't know what options there are or the pros and cons.
3. Inputs, I only need 3 - computer, tuner, CDP, but I figure four is sensible in case I add something else to my hifi setup in future. How to implement four inputs? Obviously, a rotary switch is needed, but what else - relays, capacitors, etc?
I think that's it, I'd like to keep this as simple as possible with minimalistic circuitry, in keeping with the Pass Labs ethos that createdthe B1 itself.
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1) Can't see why bridging between the sockets wouldn't suffice? Feed outputs to one, link to the other.
2) A stepped attenuator is a good way to go. I use Khozmo stepped attenuators in my builds. Any stereo pot will work if budget is to be watched
3) 4 way 2 pole switch. Or 6 way 2 pole and leave a couple disconnected. Might be cheaper. I use Elma switches. Hard to beat. No caps, resistors required.
Good luck with the build.
2) A stepped attenuator is a good way to go. I use Khozmo stepped attenuators in my builds. Any stereo pot will work if budget is to be watched
3) 4 way 2 pole switch. Or 6 way 2 pole and leave a couple disconnected. Might be cheaper. I use Elma switches. Hard to beat. No caps, resistors required.
Good luck with the build.
Cheers, that's answered my questions nicely. I think I'll use a 25k pot for the time being and perhaps upgrade to a stepped attenuator later, just so I can get the thing up and running as I have a DAC I've built that I need a preamp to be able to use properly and I'm getting impatient!
I'll post some pics tomorrow of how things are progressing thus far.
I'll post some pics tomorrow of how things are progressing thus far.
The input selector should be a non-shorting type.
The switched volume control must be shorting.
1. Just link the outputs
2. I bought Alps pots from some ebay source, stereo, and no possibility to adjust channel balance. (If building the NuTube variant or the 170/74 (n- and p-channel) variant in the future, i will reconsider.)
3. I built my B-1 with six inputs (via ELMA rotary switch). In reality I have two analogue sources, one DAC and one RIAA. The DAC selects between disk player, DAB+ tuner and a PC for FLAC file playing. So Nelson Pass' original approach with a simple two position C&K switch in reality suffice.
2. I bought Alps pots from some ebay source, stereo, and no possibility to adjust channel balance. (If building the NuTube variant or the 170/74 (n- and p-channel) variant in the future, i will reconsider.)
3. I built my B-1 with six inputs (via ELMA rotary switch). In reality I have two analogue sources, one DAC and one RIAA. The DAC selects between disk player, DAB+ tuner and a PC for FLAC file playing. So Nelson Pass' original approach with a simple two position C&K switch in reality suffice.
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