Bride of Zen, Bride of Son of Zen

[darrr]

what about 6k18 series on input?

 

[AndrewT]

I don't know what minimum source impedance this amplifier needs.
6k18 is unusually high, but that alone does not exclude it.

 

[darrr]

Ups..replacing r107 to 100k caused increased gain.There is no possibility to mute to 0 by pot -quietly but I can hear cd source and slight movement causes a large increase in volume

 

[AndrewT]

too much system gain !

 

[darrr]

I did what you adviced me -"put back 100k on r107". now what should I do? Change back to 1k5?

 

[AndrewT]

Remove gain stages that are not required.

 

[darrr]

Remove gain stages that are not required.

Ok. Can you explain me how to do it?
6k18 on input and 1k5 in r107 this configuration play much better

 

[mjf]

boz is a preamp with a lot of gain .........around 8 times.
made for pass zen amps and so on.
if you use the boz with normal hifi-amps (e.g. 1V sensitivity), you have more
gain/output signal than you need.

you can attenuate the signal at the input
and/or at the output.
and/or lower the gain (increasing the source res 100ohm up to 150ohm or so.....)

 

[darrr]

In my BoZ, someone used the third solution to reduce gain? see how it looks in the attachment. Is this also possible?
If you can look at my earlier post you will see that the measured values ​​after the 1k / 3W resistor differ from the diagram by about 7V. Should I worry about that?

 

[mjf]

......that is the first solution: attenuating the signal at the input. that is nothing else than a voltage divider - some kind of volume pot - at the input. this does not change the gain of the boz.

changing the irf510 source res( 100 ohm ) make a difference in gain.......

 

[darrr]

Thanks a lot Which solution is the best? what about voltages on drain?

 

[mjf]

......best solution?
there could be a few "best solutions".

perhaps an example:
boz with gain around 5 times:
input att. res 6.8k (do not use a bigger one - or the treble can drop down...)
source res 150ohm


the 10k pot (connected via 100k to the gate of the irf510) changes the current
through the transistor and the drain volts too........

 

[darrr]

super Is 5,6v not so much? Originaly 4v.

 

[mjf]

annother res......gives different volts.

have a look at the current:
original 4V/100ohm = 40mA
modified 5,6/150 = 37mA..........close to 40

 

[darrr]

I'll try 150R with 6k19 and will replace 1k5 to originally 100k. thanks a lot

 

[darrr]

one more thing worries me. measured voltages on r104. if I counted well, 3W is not enough.

 

[mjf]

P (heat) = V(volts) x I(current) on the res.
e.g. I=40mA .......= 0,04A
V= 60 - 20 = 40V (voltdrop across the res)
40 x 0,04 = 1,6W heat dissipation........so 3W should work (if the ambient temperature is not too high )

 

[darrr]

I have made changes and now the measurements look like this. there is less gain but I would like to have lower gain and remove the 6k19 attenuator at input. What max value can I increase r108? R104 is very hot.

 

[mjf]

why do you want to remove the 6.18k res? it helps - it lowers the input signal
a little bit.

yes,the 1k drain res is hot.......there are around 1,5W heat dissipation in it.

what pot do you use at the output of the boz?

some years ago i built my boz - with a drain res of 180 ohm.......

 

[darrr]

I have selector 3 inputs and one of them working without 6k18 for comparison. Pot is stereo 10k Alps