Got a question about the B-1 output capacitor. I have not read all 253 pages of this thread, so I apologize in advance if this has been discussed before. The standard BOM for the B-1 calls for a 10 mfd Axon capacitor. I actually used 15 mfd Axons in mine, because I had 2 left over from a passive speaker crossover. My B-1 feeds a Pass 6-24 crossover. The 6-24 article says that the input impedance is 12k ohms. Why such a big output cap on the B-1? Wouldn't a much smaller output cap give a suitably low 3db point? And does the output cap on the B-1 interact with the input cap (.1 mfd) on the 6-24? Do they combine in series to give an effective input cap to the 6-24 of something less than .1 mfd? The combination does sound fabulous, so I'm not complaining. Just trying to understand what is going on.
The cap takes care of DC, probably thumps too. I’d probably not remove it in this particular circuit, especially if it sounds ok.
Wait a minute. Are we talking about C1 or C2, or C201, iaw attached schem?
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Got it. I would not touch those values personally. The 10uF cap need to remove the DC voltage from the source, which can be very high - up to half the supply voltage. And the resistor after it protects the precious JFETs.
Regards,
Andy
I'm building the original B1 and I have a question about power supply.
I was going to use a 24v (PSK-10D-24-T) SMPS plus an allo CM board.
But then I wondered if it might be possible to power this thing with 6 ea. 18650 lithium batteries in series. But seems like there are mixed reviews of these batteries in audio applications.
Worth a shot, or stick with the SMPS + CM?
I was going to use a 24v (PSK-10D-24-T) SMPS plus an allo CM board.
But then I wondered if it might be possible to power this thing with 6 ea. 18650 lithium batteries in series. But seems like there are mixed reviews of these batteries in audio applications.
Worth a shot, or stick with the SMPS + CM?
Running off batteries doesn't justify the extra complexity, with or without a charging circuit. Nelson provided an excellent filter in the B1 circuit to eliminate noise from an SMPS or other types of power supplies.
E.g. I'm using a Meanwell SMPS (24V) + DC/DC converter adjusted to 18V to power my B1 (I know, not the best solution, but it was a newbie choice) and there is no noise coming through from the PSU. I didn't measure it, but I have 100dB speakers and it's dead quiet.
E.g. I'm using a Meanwell SMPS (24V) + DC/DC converter adjusted to 18V to power my B1 (I know, not the best solution, but it was a newbie choice) and there is no noise coming through from the PSU. I didn't measure it, but I have 100dB speakers and it's dead quiet.
Some time ago, I decided to upgrade the caps in the signal path (C100, C101, C200 & C201) to boutique caps and was rewarded with a substantial improvement in sound clarity. I chose ClarityCaps CSA series, but I suspect other good brands should yield good results too. Maybe it's just that I had originally used crappy caps, but the B1 is now my preferred preamp by far. Can't wait to build the Iron Pre, though.
Sure seems worth while. I will be building a B1 and will incorporate this improvement
help needed 
please
Finally the B1 was ready to play. And it played well for some hours - but next time I switched it on it burnt the fuse (100mA T) on the primary side of the transformer.
I thought that maybe the fuse was bad and replaced it. Same thing happened.
I disconnected the B1 and opened it.
i have tried attaching an ohm-meter to the + and ground (power input) and got a reading of 42 ohm. I think that should be a lot more?
should I look at the paralleled capacitors or the K170? Or do you have some good advice to the fault finding process?
pleaseFinally the B1 was ready to play. And it played well for some hours - but next time I switched it on it burnt the fuse (100mA T) on the primary side of the transformer.
I thought that maybe the fuse was bad and replaced it. Same thing happened.
I disconnected the B1 and opened it.
i have tried attaching an ohm-meter to the + and ground (power input) and got a reading of 42 ohm. I think that should be a lot more?
should I look at the paralleled capacitors or the K170? Or do you have some good advice to the fault finding process?
Information needed in order to trouble shoot your B1:
- Focused and well lit pictures of the B1, including shots of the whole build and individual shots of the boards
- Information about the power supply, including pictures and schematic if available, power transformer voltage and VA information too.
Looking at your power transformer, the 100mA fuse may be too small. Typically the minimum fuse size would be transformer VA/AC voltage, so fuse would be 50VA/230VAC = 0.217A. So I would suggest 200mA or 250mA fuse.
Since the preamp was working previously, there may be nothing wrong with it. But to be on the safe side, you can disconnect the powrer supply from the B1 board, install a new larger fuse, connect a volt meter to the power supply output and power up and see if the fuse blows. If you have a dim bulb tester, power up with it first to check to see if there is a problem.
Since the preamp was working previously, there may be nothing wrong with it. But to be on the safe side, you can disconnect the powrer supply from the B1 board, install a new larger fuse, connect a volt meter to the power supply output and power up and see if the fuse blows. If you have a dim bulb tester, power up with it first to check to see if there is a problem.
