New DISPRE preamp, successor to previous popular version

[aparatusonitus]

Thank you PMA....One more question, THD and harmonics content, are they different with and without DC servo correction?

 

[PMA]

I can see no change in distortion after servo has been connected. The only difference is very low frequency rolloff.

 

[homemodder]

Hi PMA


Interesting circuit, i am currently building your first circuit after a friend of mine recommended it but am i bit confused on the operation. Is this vas a folded cascode ??
I have schematics of a amp (i think its russian) which uses the topology aparatusonitus shows. My buddy built it as well and says it sounds great, better than his stochino amp. What do you think of such a topology. I will post the schematic as soon as i find it again on my harddrive, but maybe on another thread not to hijack this one.

Alex

 

[AndrewT]

Open Loop and Closed Loop gain of the New DisPre :

why is the OLG flatter and wider than the CLG?

 

[aparatusonitus]

Hi PMA,

I've tried to sim your circuit, but failed to meet your OLG rolloff corner at 1MHz (mine is around 30-50kHz depending of how I size R7/8 and R21 resistors). What's the catch?

 

[MaxS]

> aparatusonitus

I'm not sure at all but you can try to swap Q11 and Q12 by BD139 and BD140.


PMA, nice project !

 

[aparatusonitus]

Hi MaxS,

Yes I know that, but they are not a solution to my question how PMA manages OLG at 1MHz.

 

[padamiecki]

Ahoj Pavel!
I am the one who will maybe chill you down.
GNFB is only 10 dB but I can guess that high order harmonics were growned after applying GNFB. Am I right?
PS I preffer your prevoius pre!

 

[PMA]

They lie below -140dB, which is both inaudible and unimportant. OLG vs CLG and transient response with same shape for any output voltage are very important.

You can make this pre without ANY global FB, by proper resistor choice and 1 added resistor. I have decided to make it this way, with slight feedback.

 

[crt]

halo,

what minimum and maximum supply voltage for dispre
first version?

what the value of pot (for volume control) for dispre pre-amp?

 

[PMA]

For first version, supply voltage was 2 x 15V to 2 x 18V. It could be higher, in case of change of component values. The pot for first version was 2 x 5k or 2 x 10k. The new one will accept value up to 2 x 50k.

 

[PMA]

I would like to display what I mean a "consistent step response". The attached image shows step response for 10V and 1V output step, in one image, 1V response 10x magnified. This is WITHOUT input RC filter. As one can see, there is no slew rate limitation visible.

 

[AndrewT]

I would like to display what I mean a "consistent step response". The attached image shows step response for 10V and 1V output step, in one image, 1V response 10x magnified. This is WITHOUT input RC filter. As one can see, there is no slew rate limitation visible.

Hi,
can you confirm that the plot shows about 0.2uS for a rise from 1.5V to 9.5V giving ~40V/uS (for that test signal) and still showing no sign of slew limiting.

 

[PMA]

I think I can say that Tr(10%-90%) is about 200ns, even for 10V step, as attached, with values plotted, and that the shape is RC-RC-RC like, not slew rate limited:

 

[PMA]

For this 10V step, slew rate derived at steepest part of the plot is about 95V/us, still not limited by charging of internal capacitances.

 

[Jan Dupont]

Very nice

 

[lgabco]

Pavel,

Could we know resistor values? My simulations are showing bit worse results than yours. My distortion is "only" double of yours.

Ladislav

 

[PMA]

I am not telling now. I am just building a prototype, resistor values will be released after tests and measurement.

 

[crt]

for BD 139 and 140. is the device need small heatsink?
for transistor, i saw the dispre have two version?
-with bc556/546
-with bc557/547
which one is the best?

sorry for stupid question.

 

[MaxS]

Hello everyone and especially crt,

To choose among BC5x6 and BC5x7, you have to define your rail voltage.

Max.