DIY biamp 6-24 crossover

[elwood625]

The bias resistor on Q2 sets the current to a value lower than Idss of the fet. It is optional. The bias resistor for Q1 is optional and only trims the DC setting. If I revise the board in the future I will probably drop the Q1 resistor and also replace the Q2 with the much less expensive J113 or similar.

Thank you.

 

[Franz Gysi]

I would like to add a volume pot and a buffer in front of my 6/24 xover.

Is this sketch correct, will it work?

 

[elwood625]

Here is my completed 6-24 active crossover in an integrated line stage. BA2018 line stage with Salas I-select input with Academy Audio VCU Muse volume control. The power supply is remote with a VRDN set to +18 -18vdc and a Meanwell hospital grade 24v SMPS with an SMPS filter in the power supply housing and another under the 6-24 PCB. Both power supplies have voltage adjustments, which I set under load. There is a +15 -15vdc regulator for the I-selec, VCU and Mute relay. The 6-24 has 24 postion 50K pots for low and high level, it uses 2SK170BL JFETs for the buffers. I used 6 matched pairs where the matching is left and right channels. I raised the 6-24 PCB and made a clear plexiglass cover with holes for the 6-24 adjusting pots.

 

[elwood625]

More pics.

 

[Rewind]

More pics.

Wow. I wish I van go back to not knowing how complicated this project is.
Why do you have both an smps and smps filter and a linear power supply in the same box?

 

[elwood625]

Why do you have both an smps and smps filter and a linear power supply in the same box?

To reduce noise, the BA2018 line stage seems sensitive to noise and hum.

 

[rif]

@elwood625 did you do all the casework yourself? It's impressive and very beautiful.

 

[elwood625]

did you do all the casework yourself? It's impressive and very beautiful.

I drilled all the holes, Front Panel Express did the lettering. Wish I had a machine like that.

 

[gadut]

Here is my completed 6-24 active crossover in an integrated line stage. BA2018 line stage with Salas I-select input with Academy Audio VCU Muse volume control. The power supply is remote with a VRDN set to +18 -18vdc and a Meanwell hospital grade 24v SMPS with an SMPS filter in the power supply housing and another under the 6-24 PCB. Both power supplies have voltage adjustments, which I set under load. There is a +15 -15vdc regulator for the I-selec, VCU and Mute relay. The 6-24 has 24 postion 50K pots for low and high level, it uses 2SK170BL JFETs for the buffers. I used 6 matched pairs where the matching is left and right channels. I raised the 6-24 PCB and made a clear plexiglass cover with holes for the 6-24 adjusting pots.

with this sophisticated build, i can only suggest to replace smps with linear supply like Salas BiB

 

[Franz Gysi]

Here with a better drawing again my questions:

1. can I add for overall volume control an additional frontend to the existing front end (marked with yellow marker)?
2. can I remove the coupling caps and the connections to VREF in the existing front-ends (red circles)?

Thanks for your feedback.

 

[adason]

If you will have small voltage on the buffer output, it may cause scratchy sound in the volume pots. I would suggest to use one cap on the buffer output. Just like B1.

 

[Franz Gysi]

If you will have small voltage on the buffer output, it may cause scratchy sound in the volume pots. I would suggest to use one cap on the buffer output. Just like B1.

I think this is irrelevant, as these to pots are trimmers to be set once.

 

[Franz Gysi]

But now I got aware, that on the first buffer stages from the xover VREF is missing . You are right, I need a cap on the output of my new buffer and I also need connections to VREF (the red circles in the schematics of post #1010).

Like this:

 

[Nelson Pass]

You.could conceivably use vref for the pot grounds.

 

[Franz Gysi]

Boahh, yeah! Thanks for the very good suggestion, Nelson!

This way?

Or add 1MEG between VREF and the pots?

 

[Zen Mod]

except In Pot

leave it as is

 

[Franz Gysi]

Ahh, yes! Adding 1 Meg between the pots and VREF would disable low volume levels for the channels, as it would completely change the voltage divider for volume control.

 

[Franz Gysi]

One more question: what value for the bias resistors, when I have 2SK170 with IDSS of 9 mA?

 

[Zen Mod]

none or few ohms

10R as max - you probably don't want to decrease Iq too much

of course - take care that paths "low pass filter" and "high pass filter" are AC coupled ( there is cap to block present DC)

 

[Franz Gysi]

Did I understand you correctly, ZM. This way?