Pass B1

[omishra]

Assembled the B1 and Pass BOZ today. Need some help to setup the ldr attenuator.
The procedure that omishra posted about finding R1, R2, R diff is not working the way it is should.
I wanna know that is the procedure to be followed when the the circuit is connected and powered or out of the circuit.

Please follow this in isolated LDR board.

another simple method of balancing Volume Pot. No soldering required for temporary connections.

1. LDR board is not connected to the circuit.
2. LDR board supplied 7.5-12V DC with correct polarity.
3. Connect two 3" wires from L-IN & R-IN on LDR board to 5V and L & R ground to 5V supply ground.
   • In my photo of LDR Vol Control, white wires in each channel are L-IN & R-IN on LDR board.
   • Rear left first pin hole at Volume Pot while holding Volume Pot towards you is 5V. PS ground is used as ground for measuring purpose.
4. Now measure Voltage at L& R output (where I earlier connected Blue and orange wires).
   This need to be same at any point of Volume level wrt ground (green wire in my last photo).
5. Vary Volume pot little 10% at a time from. Notice both the voltages at same position. Write down them for each position till you reach 90% of volume level.
6. Observe the difference in the voltages, ideally they should match equal.
7. Set Volume pot at your preferred listening level (e.g. 9'0 clock position if 7'0 clock position is zero volume).
8. Match output voltage at out pins equal towards middle of voltage difference. Out pins are 3rd from left in each channel when stereo pot shaft is facing you.
9. Remove this 5V supply wire and reconnect to PASS B1 wires. You are done!

This way it is always guaranteed that for same inputs you will get equal output in both channels. Verified by providing 5V input to both channels, and at desired position equal output from Volume Control.

 

[Audiodoc]

I have isolated the ldr board. Here are a few findings.

1. Voltage at the power in 0-24V after using resistor in series.
2. 5V regulator is not warm and output at pin 3 is 5.4V.
3. Both blue trimmers at 500 ohm.
4. the resistance between the in and out on both sides is in megaohms?

 

[omishra]

4. the resistance between the in and out on both sides is in megaohms?

It comes somewhere between 40E - 13K. It increases along with counter clock wise rotation of pot and vice verse.
Please look at 5V supply line if it is reached till LDR LEDs or not. It seems they are off.

 

[Audiodoc]

Will reflow the solder later and check for any dry joints and post some pictures. Thanks!

 

[Audiodoc]

Got it working will calibrate tomorrow.

 

[sachu888]

Got it working will calibrate tomorrow.

Congratulations Sir :clapping:,
waiting for pics.

Regards,
Sachin

 

[Audiodoc]

Pics are here. Calibrated listening sessions tomorrow. Even the Pass BOZ is ready though naked!

 

[captrajesh]

@Audiodoc,

I appreciate the way the caps have been connected to the B1 to enable the whole thing to fit into a slim cabinet. A noob question; would this way of connecting the caps through wires to the PCB not affect the SQ adversely?

 

[sachu888]

No effect in SQ,they are just power supply caps.One question to Doc Pass B1 has ground in 4 side holes of PCB.Did you ground your board with chassis as you have used plastic spacers for PCB mounting.
BTW nice placement of parts.I am very eager to hear this thing,waiting for cab



Regards,
Sachin

 

[Audiodoc]

The shortest path i.e direct pcb mounting is definitely better however I have used thick (1 mm diameter copper) and short wires and that was the only way to fit it in. I dont think the difference should be audible. Now I have matching cabinets for the pass B1 pre and MyRef Power.

 

[sachu888]

The shortest path i.e direct pcb mounting is definitely better however I have used thick (1 mm diameter copper) and short wires and that was the only way to fit it in. I dont think the difference should be audible. Now I have matching cabinets for the pass B1 pre and MyRef Power.

All your cabs look great.

Regards,
Sachin

 

[omishra]

The shortest path i.e direct pcb mounting is definitely better however I have used thick (1 mm diameter copper) and short wires and that was the only way to fit it in. I dont think the difference should be audible.

Hi Nice fitting.
Yes those wires wont affect anything though I am curios to know how they are fixed? Are they glued to side walls?

 

[sachu888]

Hi Nice fitting.
Yes those wires wont affect anything though I am curios to know how they are fixed? Are they glued to side walls?

I think by Two way tape.

Regards,
Sachin

 

[Audiodoc]

Yes a 1 x 1 cm square piece of two way tape. Passed the earthquake shake test.

 

[Audiodoc]

Tested the pass B1. Simply the most transparent preamplifier I have ever heard. Flat spectrum no coloration the way a preamplifier should be. Will test and compare the BOZ which has some gain as soon as I make an enclosure for it.

And in case someone is going for a group buy once more will luv to buy 2 more LDR volume controls.

Lot of projects at hand so no time to write long reviews a gaincard clone, a pass 5, a naim clone and a beyerdynamic A1 clone down the line!

 

[sachu888]

Tested the pass B1. Simply the most transparent preamplifier I have ever heard. Flat spectrum no coloration the way a preamplifier should be. Will test and compare the BOZ which has some gain as soon as I make an enclosure for it.

And in case someone is going for a group buy once more will luv to buy 2 more LDR volume controls.

Lot of projects at hand so no time to write long reviews a gaincard clone, a pass 5, a naim clone and a beyerdynamic A1 clone down the line!

Hi Doc,
Pass B1 is transparent and natural,every single review suggest that.
BTW: I will receive few sets B1+LDR+Power supply boards on Feb 2nd.I will have some extra sets.If anyone wants to get PCBs please post in this thread.
Members interested for 2nd group buy :

Doors
Magma
Svaze
Ravi_d

Regards,
Sachin

 

[Audiodoc]

I want two ldr kits coz getting components is not possible in chandigarh except for the resistors and capacitors.

 

[sachu888]

I want two ldr kits coz getting components is not possible in chandigarh except for the resistors and capacitors.

Hi,
Actually I have ordered 8 sets of b1+LDR+Power supply boards,with extra 2 oards of LSA.Extra LDR boards have been reserved by Ravi_D and Cmsajith,if anyone backs out I will send it to you.I can order more LDR boards if enough interest(10 or more members) is there.

Regards,
Sachin

 

[captrajesh]

Hi,
Actually I have ordered 8 sets of b1+LDR+Power supply boards,with extra 2 oards of LSA.Extra LDR boards have been reserved by Ravi_D and Cmsajith,if anyone backs out I will send it to you.I can order more LDR boards if enough interest(10 or more members) is there.

Regards,
Sachin

Hey Sachin, I want an LDR kit for my Tube pre. I didn't know about the second group buy; else would've ordered one.

 

[Audiodoc]

Everyone is loving the LDR kit. Much better than the best Blue velvet Alps pots I have used. Want to compare it with smd / through hole stepped attenuators.