BOSOZ Preamp

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Maurizio

Member
Joined 2003
#1
Hello everybody.

My name is Maurizio. I bought the BOSOZ pcbs and i'm preparing the list of components to buy in order to realize it.

I've one question abou the gain of the pre.

From the Nelson Pass documentation i could see that the r15 resistor is setting the line stage gain.

Using a 430 ohm value the gain should be around 10 db.

Which value should i use to have the gain=1 ?

Having the gain settled at 1 by the r15 resistor..may i consider to use the P5 pot as volume set?

Many thanks in advance and apologize for my unperfect english.

Maurizio
 
#3
Maurizio *may* mean:
https://www.firstwatt.com/pdf/art_bosoz.pdf

If so: in hi-Z loads the load at the top of Q1 Q2 is about 648 Ohms. For unity gain we want the same in the bottom. But there is already a lot of 750Ω resistors there. I figure R15 should be near 820Ω.

This is a lot of parts and heat for unity gain-- why do you need it?
 

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#4
IMHO Not recommended. It's a >20 yo design.
I have it, and it's not worth it at all that's why I am not using it. One of these days I will repurpose it for something more modern and better sounding. Like PRR said lots of parts and heat...sound? Not so good.
 
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#5
Hello thanks a lot for your feedback about.

Why i want to use it?

Because my amplifier accept balanced inputs, and i would like to use like this.

I was evaluating the B1 Preamp as well as i do not need lot of gain but i'm just looking for low output impendance.

Any suggestion ? Anything i could use instead of it with balanced inut and output?

Many thanks in advance.

Maurizio
 
#8
well, you can hardly expect building something simple as sole 9V battery , and getting HiEnd quality of sound

if I assume properly, that is intention 🙂

speaking strictly about comment of IP being complicated - that reveals fact that you're not aware of all elements being necessary for proper line stage construction - if you count that you need:

-selector
-attenuator
-active stage
-proper power supply for active stage and auxilliary circuits (selector, if made in that
way)

.......... then everything you choose to make is complicated

now - BOSOZ - years ago we made here some iterations of JFet BOSOZ ; even if I would make evrything different nowadays, that one is better than original BOSOZ, from various reasons
 
#9
Hi Zen.

Well of course i'm aware about that.

But i see on IP that a multitap transformer is present as well..am i right?

Is it mandatory to use that opt? Where i can find more informations about?

Jfet Bosoz was discusse here on diyaudio?

Many thanks in advance.

Maurizio
 
#14
Hello..i had a look already and seems that the pre is composed by different single blocks.

Would be possible to start with the two main BAL pcb adding the AVC board later on ?

I could not find much more details about the unit gain..output impedance and so on? Can you pass me that info?

Maurizio.
 
#15
I don’t really know what’s feasible (and sensible) and what not, but would have started the other way round: have an AVC with a buffer (volume control plus good I/O impedances, selector-switch being optional), and if you feel you need gain, add it…

ZM, is this far off?
 
#16
Maurizio said:
Hello..i had a look already and seems that the pre is composed by different single blocks.

Would be possible to start with the two main BAL pcb adding the AVC board later on ?

I could not find much more details about the unit gain..output impedance and so on? Can you pass me that info?

Maurizio.
Click to expand...

It is best for ZM to comment directly on his designs and intentions...

However, what I expect can be done is to build a Balanced Iron Pre with your choice of attenuation and change to AVC later making it "effectively" into an Iron Pumpkin based on how you choose to implement it. You could choose ZMs Iron Turtle AVC or other providers'. This has been done successfully with the Single-Ended Iron Pre. Can't speak to balanced.

However, if all you need is a balanced unity gain buffer / selector / attenuation - that also may be a bit complex.

I think there is a thread around a balanced B1. That may suit you?

Balanced B1 Buffer
 
#17
I don't want to comment or explain IP here, pretty much everything is explained in relevant threads and can be further detailed in same threads

What is important that OP learn in best and easiest way how to decide what is best option for him, for his levels of expertise and his wallet

regarding balanced attenuators - good luck finding one which isn't made of two SE attenuators stacked in same bundle/space/box

forget IP, what I wrote above is to explain importance of every functional block in preamp as whole apparatus...... you know saying what is strength of entire chain ......
 
#18
Good Morning.

I'm pretty convinced that the stepped opt is making the diffrence.

But i could start with a basic configuration and improve afterword step by step.

Is it possible to buy the main PCB only?

If you prefere i will contact by PM.

Many thanks for all the informations.

maurizio
 
#19
ItsAllInMyHead said:
It is best for ZM to comment directly on his designs and intentions...

However, what I expect can be done is to build a Balanced Iron Pre with your choice of attenuation and change to AVC later making it "effectively" into an Iron Pumpkin based on how you choose to implement it. You could choose ZMs Iron Turtle AVC or other providers'. This has been done successfully with the Single-Ended Iron Pre. Can't speak to balanced.

However, if all you need is a balanced unity gain buffer / selector / attenuation - that also may be a bit complex.

I think there is a thread around a balanced B1. That may suit you?

Balanced B1 Buffer
Click to expand...


Many Thanks.!!!
 
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