My Take on X-BOSOZ

Jump to Latest
#844
Test results

OK, so i decided to sleep on it and test the preamp this morning with R5 value of 10K. It worked like a champ, and that area and R5,C1,D1 is now considerably cooler than it was. 🙂

I would still like some validation from others that what I have done here makes sense. but one thing for sure. It works. 😀

Cheers!
Russ
 
#846
still4given said:
It akes sense that 221R would run a lot hotter than 10K. Why was it changed from the value that Metalman used?

Brian,

Thanks again for the kind offer. I have I have some 10K resistors on hand but not Dales.

Blessings, Terry
Click to expand...


As I already explained a few posts ago it is because 221 was the value of R5 on the first schematic which was given to me(not mine, came from Kari's thread). It wasn't until later that I saw Terry's actual circuit. And not until last night that I made the connection that R18 is equivalent to R5 in my circuit.
 
#847
Russ White said:



As I already explained a few posts ago it is because 221 was the value of R5 on the first schematic which was given to me(not mine, came from Kari's thread). It wasn't until later that I saw Terry's actual circuit. And not until last night that I made the connection that R18 is equivalent to R5 in my circuit.
Click to expand...


Hi Russ,

You're right of course. I remember that post now that you reminded me. :cannotbe: I wonder why the 221R worked in Kari's circuit. Are there other differences as well?

Thanks for all you hard work on htis.

Blessings, Terry
 
#848
still4given said:



Hi Russ,

You're right of course. I remember that post now that you reminded me. :cannotbe: I wonder why the 221R worked in Kari's circuit. Are there other differences as well?

Thanks for all you hard work on htis.

Blessings, Terry
Click to expand...


Thanks Terry,

I think we have it nailed down now. It was only that which was causing me to scratch my head. The amp was always working, even with the 221R R5 resistor. Mine never smoked or anything, just got that area of the PCB really warm.

Cheers!
Russ
 
#850
I had the same problem that Russ had. It just got really really warm. I figured I would try for a higher value and 1.5k was the first think I picked up. I was not sure how this would affect the circuit. It seems to be working fine with much less heat🙂
 
#851
So just to be sure I was not nuts, I went back to Kari's thread and checked, and indeed Kari used 221R for R5. But then I looked atthe neg rail, which is ONLY 9 VOLTS!!!!!

http://www.diyaudio.com/forums/attachment.php?s=&postid=615082&stamp=1112960648

So this is a situation where I really didn't know much about the circuit when I was choosing values and basically just copied what I had been handed verbatum. Lesson learned.

I think Terry Aben's 10K (his R18) there is a much better choice for the higher rails we are running.

In Kari's circuit he calls for 9V neg rail the drop accross the 6.8V zener is only 2.2V!!! So at 221 ohms R5 would only have to dissipate .02W, Now with our 20V neg rail its clearly a different (and I think better) beast (painfully obvious now). We drop 13.2V accross the zener which with 221R is a whopping .78W!!! Yikes! not really what we intended now is it!

So just to satify my need to understand I have changed the PS zener values on the neg rail to get around 9V (I got 9.3V) and I put the 221R R5 back in. And sure enough things stayed nice and cool, but the amp does not sound anything near as good!!! Metalman (our man Terry Aben) was dead on that the rails should be a minimum of 12V or so and I think our 20V rails are actually a good site better. Hiss and all around distortion just seemed much worse with the lower neg rail.

The lessen I learned is that the value of R5 must be adjusted for the negative rail. The impedance of the QX gate is very high, so you only need a tiny amount of current, so the 10K value I tested seems completely sane, and it sounds just marvelous.

So to wrap things up, the BOM has been corrected and future kits will include the 10K R5 also as Brian said we will happily send 10K resistors to anyone who bought a kit and needs one. Any good 10K metal film resistor should do fine. You could actually use any value from 1.5K to 10K or so. The value is not really critical, just make sure you stay below .15W or so dissipation to keep it running cool. 🙂

Anyway I learned a lot lot doing this exercise and I appreciate all the support.

Cheers!
Russ
 
#859
Russ White said:
So just to be sure I was not nuts, I went back to Kari's thread and checked, and indeed Kari used 221R for R5. But then I looked atthe neg rail, which is ONLY 9 VOLTS!!!!!

http://www.diyaudio.com/forums/attachment.php?s=&postid=615082&stamp=1112960648

So this is a situation where I really didn't know much about the circuit when I was choosing values and basically just copied what I had been handed verbatum. Lesson learned.

I think Terry Aben's 10K (his R18) there is a much better choice for the higher rails we are running.

In Kari's circuit he calls for 9V neg rail the drop accross the 6.8V zener is only 2.2V!!! So at 221 ohms R5 would only have to dissipate .02W, Now with our 20V neg rail its clearly a different (and I think better) beast (painfully obvious now). We drop 13.2V accross the zener which with 221R is a whopping .78W!!! Yikes! not really what we intended now is it!

So just to satify my need to understand I have changed the PS zener values on the neg rail to get around 9V (I got 9.3V) and I put the 221R R5 back in. And sure enough things stayed nice and cool, but the amp does not sound anything near as good!!! Metalman (our man Terry Aben) was dead on that the rails should be a minimum of 12V or so and I think our 20V rails are actually a good site better. Hiss and all around distortion just seemed much worse with the lower neg rail.

The lessen I learned is that the value of R5 must be adjusted for the negative rail. The impedance of the QX gate is very high, so you only need a tiny amount of current, so the 10K value I tested seems completely sane, and it sounds just marvelous.

So to wrap things up, the BOM has been corrected and future kits will include the 10K R5 also as Brian said we will happily send 10K resistors to anyone who bought a kit and needs one. Any good 10K metal film resistor should do fine. You could actually use any value from 1.5K to 10K or so. The value is not really critical, just make sure you stay below .15W or so dissipation to keep it running cool. 🙂

Anyway I learned a lot lot doing this exercise and I appreciate all the support.

Cheers!
Russ
Click to expand...
Let me just make this clear. In order to get higher voltage on the negative rail with Kari's board ONLY element that neds change is R5 from 221 to 10K ? Is that right - or there is any other change. What about positive rail? Kari suggests 60V and I see you guys are suggesting 70V. I am running negative rail off 18V transformer and getting 9V out. There were many posts about negative rail voltages, so lets make this clear.
Thank you
AR2
 
#860
Hi Russ,

Are we getting closer to having the boards for the attenuator? I'm really start to chomp at the bit to finish up this preamp.

Are you going to offer this as a kit or should we source the parts ourselves. If the latter, would you mind posting the BOM so I could be about gathering what I will need?



Blessings, Terry
 
You must log in or register to reply here.
Top Bottom