B1 Buffer Preamp

[Salas]

Originally posted by crt


and for R1 = 220K still in use ?
270K-330K ? where i put this resistor ? can you draw me a simple schematic please.

Today i have replace the old 25K stepped attennuator with 22K value.
recalculate all the resistor again, that's pain but FUN!

I am talking about R1 always. I just say it may be 10-15X your pot value, and always there, especially with a switch pot. The moment there is no gate reference to ground, 4VDC can appear at the output.

[crt]

Originally posted by Salas


I am talking about R1 always. I just say it may be 10-15X your pot value, and always there, especially with a switch pot. The moment there is no gate reference to ground, 4VDC can appear at the output.

I've got it.
so it would be better to put that R1 on the volume switch or at PCB of B1 ?

sorry for my stupid question Salas.
i'm newbie about electonics.

Thank's
La Ode

[Salas]

Better near the JFET on pcb.

*There exist no stupid questions. Only silly problems if simple questions haven't been asked.

[crt]

Originally posted by Salas
Better near the JFET on pcb.

*There exist no stupid questions. Only silly problems if simple questions haven't been asked.

now i'm ready to design the PCB layout.
i will use LM317/337 too for voltage regulator (like in your schematic)
BUT can i stick with (1ohm, and 15000uF) after the reg ? like in original B-1. {see attachment}

picture

Thank's
La Ode

[Salas]

It can work, but it would work better if the big capacitors are before the regulators and the 1000uF ones after.

[jean-paul]

15.000 uF will be a little overkill but I could be wrong in the eyes of many. Better use two 2200 or 4700 uF caps with a resistor or coil in between. Everything before the regs of course. After the regs 100 uF and a 0,1 uF MKT/MKP. Some regs do oscillate with 1000 uF at the output.

I would advise to use separate supplies for the 2 channels. It could be wise to provide pads for shorting the input and output caps. Just in case the source has a DC component you can remove the jumper and you will have a coupling cap. Just an idea that adds functionality that could be useful.

Maybe I am old fashioned but if you provide board space for a RK27 potentiometer you could add an input RC filter before the potentiometer to avoid RF straying in. A -3db point of 40 to 50 kHz would be enough. You never know with all the RF garbage in the air. The B1 has a bandwidth of 10 MHz if I am not mistaking.

The icing on the cake would be 4 or 5 relay switched inputs. That would be a PCB for "B1 Deluxe" everyone will want

me too...

[crt]

Originally posted by Salas
It can work, but it would work better if the big capacitors are before the regulators and the 1000uF ones after.

Originally posted by jean-paul
15.000 uF will be a little overkill but I could be wrong in the eyes of many. Better use two 2200 or 4700 uF caps with a resistor or coil in between. Everything before the regs of course. After the regs 100 uF and a 0,1 uF MKT/MKP. Some regs do oscillate with 1000 uF at the output.

I would advise to use separate supplies for the 2 channels. It could be wise to provide pads for shorting the input and output caps. Just in case the source has a DC component you can remove the jumper and you will have a coupling cap. Just an idea that adds functionality that could be useful.

Maybe I am old fashioned but if you provide board space for a RK27 potentiometer you could add an input RC filter before the potentiometer to avoid RF straying in. A -3db point of 40 to 50 kHz would be enough. You never know with all the RF garbage in the air. The B1 has a bandwidth of 10 MHz if I am not mistaking.

The icing on the cake would be 4 or 5 relay switched inputs. That would be a PCB for "B1 Deluxe" everyone will want

me too...

Thank's for advice Salas and Jean-Paul.

now, the layout about 60% to finished
and maybe on saturday i can bought my layout to the PCB maker and take 4-5 days to finished.

I can not wait any longer to build this one too.

La Ode

[jacq.]

How critical is the 1uf. cap tolerance for C2, C100 and C200?

Thank you all for this wonderful tread.

Jacq.

[timothyshields]

I am nearly done building my B1 preamp, thanks to Colin at DIY Pass and those who kindly responded. That said, I'm not quite sure where I choose to use the preamp. In one set up I can utilize the unbalanced RCA outputs, but in another the amplifier requires balanced XLR inputs.

I have seen some discussion of this topic before, albeit I am unsure on how to proceed. Any suggestions would be much appreciated.

Timothy

[Diomedian]

Originally posted by jacq.
How critical is the 1uf. cap tolerance for C2, C100 and C200?

+/- 25% should do. :-)

-j