Improving on X-BosoZ to mate the F4

[steenoe]

Thanks a lot Babowana Nice calculation. So this means that with SE input, the gain is too low. My BosoZ having 39k instead of 50k, has even a bit lower than 13dB gain then.
Hmmm, 13dB for unbal in. What if only used unbal out also? Which is the case with the F4. Do you get the full 13dB with singleended out?

Steen

 

[Babowana]

Reflecting on the whole thing, it came to mind that I didnt connect the Negative-OUT to ground when connecting the BosoZ to the F4. I just unplugged it from the A-X's, which runs balanced. Would that have any influence on the gain?

Yes, I think so.
With one input and one output, the gain is approximately,

20xlog(39K/10K) = about 12dB (gain of 3.9x)

 

[Babowana]

Which is the case with the F4. Do you get the full 13dB with singleended out?

Yes.

Try simple increase of 39K higher till your ears start detecting any distortion in sound ^^~

 

[Zen Mod]

Yes.

Try simple increase of 39K higher till your ears start detecting any distortion in sound ^^~

agree with

anyway-regarding jfet xccsschmack-whateversusy-bosssoz? it's already drawed somewhere;
I really don't remember which thread, but I remember that Babo was in it.....
Babo- -when I drew one of many schmtcs just for you, where you asked for version without sim supply........?

there is it....http://www.diyaudio.com/forums/showthread.php?postid=1153110#post1153110 .....lot's of mumbo jumbo,but few useful schmtcs
btw-each time I was pretty sleepy ,so my drawings must be carefully checked.......as always

 

[Babowana]

anyway-regarding jfet xccsschmack-whateversusy-bosssoz? it's already drawed somewhere;
I really don't remember which thread, but I remember that Babo was in it.....
Babo- -when I drew one of many schmtcs just for you, where you asked for version without sim supply........?

Do you mean the "Krazy"?
It was a jfet(J310) cascoded BOSOZ. It offered really great sound.
But, no one was intersted in the great sound ^^~

 

[Zen Mod]

Do you mean the "Krazy"?
It was a jfet(J310) cascoded BOSOZ. It offered really great sound.
But, no one was intersted in the great sound ^^~

nope..... who wants another preamp .....?

everyone expect another one ,radically changed comparing to any previous seen ..........

I edited my post- I found what thread was in question

 

[steenoe]

Thanks for the replies, Babowana. That helped a lot I beleive there is a little work to be done on the Twisted animal. But i guess the 20dB's will be out of reach without too much distortion, at least with SE input
Thanks for the link, Choky I will have a look.
Massimo, thanks for the offer. To be honest with you, I dont know when I will take the F4 apart for modifications. It sounds so great that I am very reluctant to fiddle with it. When I do, I will be happy to try them though. I will send you a mail.

Steen

 

[Zen Mod]

Thanks for the replys, Babowana. That helped a lot I beleive there is a little work to be done on the Twisted animal. But i guess the 20dB's will be out of reach without too much distortion, at least with SE input
Thanks for the link, Choky I will have a look.
Massimo, thanks for the offer. To be honest with you, I dont know when I will take the F4 apart for modifications. It sounds so great that I am very reluctant to fiddle with it. When I do, I will be happy to try them though. I will send you a mail.

Steen

btw-tell what your needs are and I'll try to think something........real jfet bosoz with cascodes and ccs-es etc.......

even if that's probably boiled water ,we just didn't searched 'nuff

 

[steenoe]

btw-tell what your needs are and I'll try to think something........real jfet bosoz with cascodes and ccs-es etc.......

even if that's probably boiled water ,we just didn't searched 'nuff

I imagine something like a 2SK389 input, cascoded and ccs'd with irf610's and 9610's. SUSY ofcourse. I am not the designer around here, but something along those lines, which will bring the J-fets sweetness and silky-smooth detailed topend to the table Ofcourse with enough drive to hold the F4 on a tight leash, so to speak

Steen.

 

[Zen Mod]

I imagine something like a 2SK389 input, cascoded and ccs'd with irf610's and 9610's. SUSY ofcourse. I am not the designer around here, but something along those lines, which will bring the J-fets sweetness and silky-smooth detailed topend to the table Ofcourse with enough drive to hold the F4 on a tight leash, so to speak

Steen.

preferenced PSU voltages ....or I can choose +/- 150V ?

 

[steenoe]

preferenced PSU voltages ....or I can choose +/- 150V ?

I am not sure the voltage needs to be very high, considering the J-fet being the main gain device? I know that mosfets needs to be run, "red hot" for increased linearity, but J-fet should be more civilized in that respect BTW YGM

Steen

 

[Zen Mod]

I am not sure the voltage needs to be very high, considering the J-fet being the main gain device? I know that mosfets needs to be run, "red hot" for increased linearity, but J-fet should be more civilized in that respect BTW YGM

Steen

it will be probably cascoded with BC little cuties-there is no need for IRF in that current range

preferred CCS ?
or I can use two-bjt CCS as in Babelfish?

edit:
you want dedicated thread for that,or we can proceed in "jfet bosoz" playground?

edit edit........follower stage(s) or not?

edit edit edit:
is it one day too much for this?
I have few other things to finish

 

[steenoe]

it will be probably cascoded with BC little cuties-there is no need for IRF in that current range

preferred CCS ?
or I can use two-bjt CCS as in Babelfish?

edit:
you want dedicated thread for that,or we can proceed in "jfet bosoz" playground?

edit edit........follower stage(s) or not?

edit edit edit:
is it one day too much for this?
I have few other things to finish

There is no hurry at all, take your time. I dont mind proceeding in the J-fet BosoZ thread, but I am not sure if it would be better with a dedicated thread, or keep it here? Its often difficult to search for things that are burried in other threads. After all, its a preamp for the F4, basically I guess. With a singleended gain of minimum 20dB, it will be a nasty thing hooked up to other amps with high sensitivity. You know; 9 o'clock at the volumeknob and the speakers beg for mercy

Steen

Oh, did you see the little YGM

 

[steenoe]

Yes.

Try simple increase of 39K higher till your ears start detecting any distortion in sound ^^~

Since the function is logarithmic, what value would be a good starting point, for lets say 16dB and 20dB gain? I have no clue how to calculate log values I probably knew once, but memory you know.... Furthermore, its not that I think the preamp can do 20dB but it would be fun to test Did anyone make a distortion versus gain curve?

Steen

 

[steenoe]

Since the function is logarithmic, what value would be a good starting point, for lets say 16dB and 20dB gain? I have no clue how to calculate log values I probably knew once, but memory you know.... Furthermore, its not that I think the preamp can do 20dB but it would be fun to test Did anyone make a distortion versus gain curve?

Steen

cviller? (Now that you are calculating, anyway ) I am sure you can do it I just took the lid off my BosoZ, I could have sworn that would never happen

Steen

 

[cviller]

Formula for dB is 20*log(amplification), So 10x is 20dB

 

[steenoe]

Yep, but is this the log part?? I give up then
http://www.formel.dk/matematik/simple_regneregler/logaritme.htm

Steen

 

[apassgear]

One thing is to get the correct gain on the xbosoz (whatever) pre for the F4 as everyone knows but could be other issues also.

Even though F4 has high input impedance and should present no matching problem with almost any pre there seems that some of the schematics I’ve seen such as the one posted by Steen on post 551 might have a high output impedance specially at high volume settings.

If I should have such problem the first thing I would do is to check output impedance of the pre at the end of the interconnect cable just to make sure I’m not throwing the gain through a high output impedance.

 

[Babowana]

Since the function is logarithmic, what value would be a good starting point, for lets say 16dB and 20dB gain? I have no clue how to calculate log values I probably knew once, but memory you know.... Furthermore, its not that I think the preamp can do 20dB but it would be fun to test Did anyone make a distortion versus gain curve?

Steen

Okay

R19/R14 = 4 then 20*log(4)= 12dB
R19/R14 = 5 then 14dB
6 then 15.6dB
7 then 16.9dB
8 then 18.1dB
9 then 19.1dB
10 then 20dB
11 then 20.8dB
12 then 21.6dB
13 then 22.3dB
14 then 22.9dB
15 then 23.5dB
16 then 24dB

Measure the drain voltage of Q3 and see whether the difference between the +rail voltage and the measured drain voltage is at least 20V. Then, try 16dB and 20dB gain ^^.

 

[steenoe]

Thanks for tuning in Tony Can I measure the impedance with a true RMS meter? Or do I need a scope for that? I had a supiscion all along, that the BosoZ might have a problem like that. I have experienced on several occasions that it is a bit "weak" so to speak. The more the volume is cranked up, the slower it increases. With low input sensitivity amps, its more pronounced.
But I always blamed it on the pot, wired at the output. Come to think of it, I read in the twisted bosoz thread about other people, complaining about the gain. I dont know whats wrong, but something is. Anyone with experience with the BosoZ are welcome to tune in As for now, I will try and hook up my crudely made test-standard BosoZ and see how it goes.

Steen

Edit, Thanks JH