Best BOSOZ preamp parts selection thoughts

[hifimaker]

Thanks again for everyone's help in a prior thread selecting the BOSOZ preamp to tackle as a first hifi DIY project.

I'm new to DIY hifi, but have an ancient background in digital circuits and can fabricate, solder, and assemble very well.


As a foundation, I already have Kristijan's BOSOZ preamp board, w/2 PSU boards http://web.vip.hr/pcb-design.vip/ to get started.

3 Questions:

1) Are there well established or obvious parts substitutions to consider from the start?

2) What are some of the key "newbie" pit falls or traps folks fall into?

3) For attuenation, I'm considering either the APOX relay http://www.apoxcontrols.com/apox2.htm or take the Resister ladder approach as used in the DIY Taiwan site http://babelfish.altavista.com/babe...=104&gid=7&gid2=&Sort=&Price=&lp=zh_en&tt=url
Any thoughts here would be appreciated as well.

If possible I'd like to leverage as much collective wisdom here as possible, and avoid the common mistakes and gain the obivious sonic improvements with the right parts.

I appreciate any and all suggetions, ideas, or experiences anyone is willing to share.

Thanks again!!!

-David

 

[moe29]

i built the BZLS using the parts as described in the article, and it
sounds great... so you don't need to substitute stock parts with
"better" exotic parts for excellent sound.

the stock pots are fine, just a little cumbersome when adjusting
the volume. Balanced pots for each channel would be nice. If you
can swing the Apox setup - that would be pretty sweet.

have fun! good luck - you won't be dissapointed.

 

[sianturi]

How bout using this as the attenuator (DACT)? It has 4 ganged of potentio suitable for balance preamp. Saves you lots of trouble synchronizing Left & Right channel volume.


Now the question:
Which potentio works best as Volume control?
P1& P2 or P3&P4 ?

Also, if I were to choose P3&P4 as volume control, is it better for me to use high quality *fixed value* resistor for the P1&P2? I don't want some cheap potentio getting into the way of signal path, so how do you guys deal with it?

I know Mr. Pass wrote these in his article:
"Once you have obtained the optimal gain and input level, adjusting the output level with P3 and P4 will give you an effective volume control which attenuates circuit noise as well as level," but I'd like to hear other people experiences.

 

[Peter Daniel]

Pardon me for barging in at this point, not having read most
of the previous posts, but the general recommendation is
that you use both input and output attenuators on both the
BOZ and SBOZ. Inputs of 25-50 Kohm pots and outputs of 5
-10 Kohm are typical. In actual practice, this has worked quite
well for the vast majority of systems.

Forgive me also for repeating for the 100th time:

With the output pots all the way up, set the input pots for the
highest level you are likely to want. Then use the output pots
for day-to-day volume controls.

You don't have to do it this way, of course, but it's a good start.

Sianturi,

I posted this quote from the other thread as it explains a lot. After setting the input pots, I would replaced them with fixed resistors and this would be the end.

The Elma switchers seem to be a good choice, but pretty expensive too. Why not try this guy instead? http://www.diyaudio.com/forums/showthread.php?s=&postid=270652#post270652

 

[cowanrg]

im building a bosoz, and thats what i will use (see peter's post)

 

[sianturi]

Helo Peter Daniel,

Thanks a lot! That answers my question.

Cheers,

 

[Mad_K]

I am VERY happy with DACT CT2-10K*4 as input attenuator in my XBOSOZ (No outputatt. in this design)

 

[sianturi]

I am VERY happy with DACT CT2-10K*4 as input attenuator in my XBOSOZ (No outputatt. in this design)

hello Mad_K,

How do you connect your DACT attenuator to your circuit? Did you use CT-conn1 (Connector unit for CT1/2/4/5, incl. 3 x 300mm (3 x 12") wires) ? Or did you make custom footprints for the attenuator in your PCB (solder directly to PCB)?

Thanks!

 

[Mad_K]

hello Mad_K,

How do you connect your DACT attenuator to your circuit? Did you use CT-conn1 (Connector unit for CT1/2/4/5, incl. 3 x 300mm (3 x 12") wires) ? Or did you make custom footprints for the attenuator in your PCB (solder directly to PCB)?

Thanks!

They are mounted like this;

http://www.diyaudio.com/forums/showthread.php?s=&threadid=9765&highlight=bzls

but I have since done lots of mods to it, the most significant was x-ing it.. (and a lot of tidying up wiring etc)

 

[kevyjo]

Are you doing the BOSOZ or x-BOSOZ?

 

[till]

2) What are some of the key "newbie" pit falls or traps folks fall into?

My only problem was heatsinks got to hot. Use large enough heatsinks.

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

 

[Variac]

Since we are substituting fixed resistors for the input pot, one could put the resistors before the input selector switch.That way each input could have a different vaue to compensate for different outputs of source components.

 

[gchrist]

Why not use the sfrenice p11, cermet pot. It is cheap compared to other pots and sounds good.?

George

 

[kevyjo]

I wanted to ask, Mr Pass said he's seen many of these preamps tweaked with different pots/caps/resistors, but none with upgraded transistors, and he'd be interested to see that. I'm having a hard time locating much of any info on appropriate transistors, let alone "impoved" ones, any thoughts?

 

[hifimaker]

BOSOZ Attenuation

I decided to go ahead with the Taiwan attenuators, http://www.diyaudio.com/forums/show...0652#post270652 from this thread. It's a 10K resister network for both input and output.

Question is: Should both the input and output sides be attenuated the same and synced concurrently, or should the input side be fixed like suggested in Peter's quote of Mr. Pass above?

Which is preferred if both options are as easily feasiable?

kevyjo's question on which transistors to consider upgrading and with what type is also of interest.

Thank you,

-David

 

[hifimaker]

Hi kevyjo, The BOSOZ based on Kristijan's preamp board.

-David

 

[sianturi]

Re: BOSOZ Attenuation

Question is: Should both the input and output sides be attenuated the same and synced concurrently, or should the input side be fixed like suggested in Peter's quote of Mr. Pass above?

Which is preferred if both options are as easily feasiable?

I vote for Peter's suggestion.
Attenuating and sychronizing both input and output requires 4 ganged pot for mono, meaning 8 ganged pot for (balanced) stereo. This makes a high economy solution for a poor guy like me. Besides synchronizing 8 pots (ie: 2 piece of 4 ganged pots sync) involves elaborate mechanical construction. Just have a look at Stefano's Blue BoSoZ (I forgot the thread... Search for Blue Bosoz)

Cheers,

 

[moe29]

the thing about the transistors was tongue-in-cheek... of all the
things in a circuit, the transistors have the most effect on sound
quality, and we're using the best available right now.

attenuate as Mr. Pass suggests and you will get the most out of
the circuit... he designed it that way for a reason.

 

[hifimaker]

Thanks Moe29,

I kindof assumed that selecting a Ladder resister network with 10K value was a decent choice, or is 25K better?

85% of my listening is sourced from a CD and the remaining 15% from an FM tuner for background music.

What values have others selected to atuenate the BOSOZ's output?

Thanks,

-David

 

[kevyjo]

silly me