BOSOZ balanced pre - for novice - questions

[andrea7617]

I would start the BOSOZ preamp.
Because I'm a novice, I have some doubt. I ask you!!!
First question is about the volume control. This is for me the most
difficult part of the project.
I use an unbalanced input (network player Pioneer N50) so I think I may use ALPS BLU RK27112 10K as input potentiometer (Pass calls it P1-P2 10 kohm)

I would do the simpliest solution, using only the input potentiometer.
Potentiometer P5
In this case, wich value of fixed resistor instead of potentiometer called
P5? The hole for this potentiometer are on board so I solder the resistance
in the hole (simple...)

Potentiometer P3-P4
This il the output potentiometer. If I don't use it, which resistor may I
use? Where in the board? Can I let the output without resistor?

Preamplifier gain.
I will use this pre with a diy Aleph 30 (that I'm building).
I can choose the gain of this pre using R15 value. Which is the best gain
for me. Default gain is 10. Is this the best value for my configuration?

Thank you for helping me!!!

 

[Zen Mod]

search

there is a recent thread with answers on same questions

 

[Russellc]

I still have this board unstuffed from back in the "Old Colony Sound" days...also the original Zen Amp board and matching Bride of Zen from the same source and era.

Once my Pumpkin Shunty is done, I may begin stuffing that one. Following.

Russellc

 

[Russellc]

Zenmod, is this the thread?

http://www.diyaudio.com/forums/pass-labs/296326-x-ccs-bosoz-need-more-gain.html

Russellc

 

[Zen Mod]

I believe it is some previous thread by Tony , or burst of his/our posts in previously existing thread

in any case - recent

 

[Cambe]

Maybe this one.
http://www.diyaudio.com/forums/pass-labs/3538-bride-zen-bride-son-zen-2.html

 

[Zen Mod]

yup

 

[andrea7617]

I found the question about potentiometer.
Ok, Zen Mod says not to use P3-P4 and replace with 5k resistors. Perfect! First question (novice question...) Where shall I put this resistors? Directly in the signal cables that connect the pcb board to xlr/rca output (out+ and out- for each channel)? Or may I use no resistors in the cable output and only replace R11-R12 with 5k resistors instead your original value 100 K?

Second question. P5. I read that it can be shorted but I can be use a 500 ohm trimpot. Sorry for this stupid question... Trimpot has 3 legs and on the board there are only 2 hole...How can I connect correctly trimpot?

 

[Zen Mod]

1. solder them on board

2. just in case , post your reference schm

 

[andrea7617]

An externally hosted image should be here but it was not working when we last tested it.

 

[andrea7617]

In the image there is the solution without P3-P4 using 5k resistors soldered on the board to XLR out.
P5 should be changed with fixed resistor that, added to R15, gives the gain.
In this case I may use only pot in the input.
Is it correct???

 

[Zen Mod]

post your reference schematic and proper picture of pcb

your sketch in #10 is not good interpretation of what I meant

imagine that these 5K fixed resistors are substituting 5K pots , set on max.

 

[andrea7617]

post your reference schematic and proper picture of pcb

your sketch in #10 is not good interpretation of what I meant

imagine that these 5K fixed resistors are substituting 5K pots , set on max.

Yes, 5K fixed resistors sobstitute 5K post. I understood it in this way.

 

[Zen Mod]

so that means - solder resistor on top and bottom pot pcb pads

take output signal from top pot pcb pad , or take it from wiper pad , but short wiper and top pads

as you sketched it , you're having 5K series (to signal) resistors ...... and that's wrong interpretation

 

[andrea7617]

An externally hosted image should be here but it was not working when we last tested it.

 

[andrea7617]

Thank you Zen Mod.
This should be correct...Each resistor has one leg soldered on top pcb and other leg soldered on bottom pcb. So each out signal hole is shorted with 5k fixed resistor.
Finally I solder the signal cable on the top (or bottom, it's the same) of the out connection on the pcb to the xlr. May I do the same thing (put 5k resistor) with the ground connection thar link pcb to xlr?

 

[Zen Mod]

you're getting it wrong

as I said :

post your reference schematic and proper picture of pcb

this way I can't help you , because I'm not familiar with that pcb and I can just guess what P5 is and what proper pcb pads are

 

[andrea7617]

I will use the same pcb of Nelson Pass https://www.passdiy.com/project/preamplifiers/balanced-zen-line-stage

 

[Zen Mod]

replace R11 and R12 with 5K values (instead of 100K)

connect +Out pcb pad to XLR Pin 2
connect -Out pcb pad to XLR Pin 3
connect GND to XLR pin 1

in place of P5 - you can temporary use either pot or trimpot , and when you set gain adequate for your needs , measure it and replace with fixed resistor(s)

 

[andrea7617]

replace R11 and R12 with 5K values (instead of 100K)

connect +Out pcb pad to XLR Pin 2
connect -Out pcb pad to XLR Pin 3
connect GND to XLR pin 1

in place of P5 - you can temporary use either pot or trimpot , and when you set gain adequate for your needs , measure it and replace with fixed resistor(s)

Great!!!
Thanks a lot!!!