Bosoz or another line stage in front of crossover with B1 buffers

[Harolda]

In some threads you can find information/discussions on a project i am working on. It is difficult to combine all issues into one thread, so here is another one.

I am currently running a crossover which is build like this:

10K pot-B1 buffer - LP filter(1st) - LP filter (2nd) B1 Buffer - pot - B1 buffer - LP out

10K pot-B1 buffer - HP filter (1st) - HP filter (2nd) B1 buffer - pot - B1 buffer - HP out

The complete setup is balanced so all circuits are double. I am very happy with the results, but i want to add:
1) a Baffle step control and a gain stage to compensate for the loss of the filters which are PLLXO.
2) single ended to balanced conversion

The gain stage can be tubes, but i was thinking of the Bosoz in some form. I read it is suitable for single ended to balanced conversion, but is it realy good? ad how does this work in the circuit? Who has experience with this?

What is the output impedance of the Bosoz, i could use for the shelving filter (baffle step control). This filter is balanced, so it would like something like this:

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

So R1 would be the output impedance of the Bosoz or another suitable line stage and R2 would be a pot.

An comments on this or advise on a suitable line stage. Would i need the coupling caps of the Bosoz, as i have coupling caps in the last B1 buffer stage of the LP and HP. By the way all B1 buffers have symmetrical PSU's

 

[dms]

B1 Crossover BOSOZ

I too plan to combine these components, much in the same way. I plan to use sallen and key filters, using B1's for current gain, and making up the voltage loss with the BOSOZ or an aleph preamp, which may sound better than the BOSOZ. How tightly did you match your passive components in the balanced version of the passive crossovers? I was thinking of using the aleph or bosoz to provide the unbalanced to balanced conversion, if my filters are unbalanced. Right now, I am using a single capacitor and resistor for a single pole high pass, and a marchand opamp 24 db as a low pass, and I am fairly pleased with the sound. I want to try balanced since my cd player is balanced out. The BOSOZ output impedance is basically the pot value after the gain stage, which is 500 ohms in Nelsons design.

 

[Harolda]

Hello Don,

i used russian silver-mica's which are very close tolerance of +/- 0.5%! They are big and i had to put 2 in parallel to get the correct values. I will probabaly change to Vishay MKP 1830/1837 for the final version, only because they are smaller.

If the output impedance is 500Ohms, than the Rod Elliot Baffle step compensation should work. I think i will just have to try.

Can the aleph take care of the unbalanced to balanced conversion. My complete setup is now balanced, except for two sources which are single ended. Or i have to build a dac with balanced outs and run everything over the dac --> another diy project, why not.

regards

Harold

 

[Harolda]

I too plan to combine these components, much in the same way. I plan to use sallen and key filters, using B1's for current gain, and making up the voltage loss with the BOSOZ or an aleph preamp, which may sound better than the BOSOZ. How tightly did you match your passive components in the balanced version of the passive crossovers? I was thinking of using the aleph or bosoz to provide the unbalanced to balanced conversion, if my filters are unbalanced. Right now, I am using a single capacitor and resistor for a single pole high pass, and a marchand opamp 24 db as a low pass, and I am fairly pleased with the sound. I want to try balanced since my cd player is balanced out. The BOSOZ output impedance is basically the pot value after the gain stage, which is 500 ohms in Nelsons design.

Hello Don,

i had again a look at the BOSOZ circuit on the PASSDIY page, but i see now that the pots after the gain stage are 5K and not 500Ohms!

 

[dms]

BOSOZ output impedance

Harolda,
You are correct! I was thinking of the gain pot, which I believe is 500 ohms. Sorry for the mis information. I will have to re-read the writeup. I bought 5 of these boards, planning to build a multi-channel preamp for my combined surround/stereo system. I got bogged down with other projects including 3 aleph 30's, and an aleph 4. I was planning to use the BOSOZ after a B1 style crossover since my amps are balanced input and are some distance from the preamp. I am still some months away because I have a few projects to finish first. Keep posting your findings.
Don

 

[Harolda]

That is going to cost you a fortune on heatsinks!

 

[jupiterjune]

The gain stage can be tubes, but i was thinking of the Bosoz in some form. I read it is suitable for single ended to balanced conversion, but is it realy good? ad how does this work in the circuit? Who has experience with this?

What is the output impedance of the Bosoz, i could use for the shelving filter (baffle step control). This filter is balanced, so it would like something like this:

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

So R1 would be the output impedance of the Bosoz or another suitable line stage and R2 would be a pot.

Harolda-

The BOSOZ is a very good unbalanced to balanced converter. There is a modified circuit posted by Metalman in a very old thread. I think it has a active current source instead of a resistor to feed the sources of the complementary pair, and the gain devices are cascoded if I recall correctly. That is the circuit to use. Nelson's article about the BOSOZ tells how the output impedence is set. I think it is by the resistors located between the drains of the gain devices and the positive power supply. 500 ohms or less should be attainable if you are looking for unity gain from the circuit.

JJ