Pumpkin preamp - ordered by Steen , official making thread

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#2,784
yggdrasil said:
Do you think it will get too hot?

I know the first series regulation of the shunty gets too hot, and will need more aluminium.

I am also thinking of a slow fan.
Click to expand...

you really need some holes (plenty of them ) in that bottom plate , same as in cover plate

fan is not necessary then

anyway - that's still just preamp ....... holes are sufficient and simple solution ( necessity)
 
#2,786
The top already has 12mm holes every 5x5 cm. Will see what I can do with the bottom.

I measured the temperature on the heat sinks. The small ones was up 35-40 degrees C with the top off. The larger ones was only up 25-30 degrees C.

The volume controllers are DS1882.
 
#2,787
Hi Zen Mod🙂,

can shunty be driven only on the two outer voltage points +36 v and -36 V so that I get 72 V for an experiment or must the current always go over the midpoint "ground" and shunty will be damaged by my try to get 72 V?

I do not fire up until your answer!
 I´ll drink coffee!
Or can I use the two 470 R, I used to adjust the voltage and nevertheless suck my 72 V at the outer points?

will be very nice to get an answer from you!:spin:
 
#2,788
well - ground is state of mind :rofl:

you want 72V for som stage ?

OK - Shunty with xformer is giving ya +36, gnd , and -36

then connect just two wires for your next stage :

+36 is +Ub

-36 is gnd

leave Shunty's gnd not connected to next stage

it's same as that you are using two batteries in series , without connecting mid point to outer world

edit:

be sure that programmed Shunty's current is enough for load demands
 
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#2,793
X 0.2

BDP said:
I have both shunty and pumpkins running. The output offset is very sensitive to air currents and causes a number of volts negative offset when cooled. The culprit is the constant current source transistor Q9.

My question I have is about stabilizing the offset using the same techniques used on the Aleph-X where a resistor is placed between the output and returned to the source of the differential pair Q1 and Q2. If this would work what values might be appropriate. Another technique used was a resistor from the outputs to ground. On the pumpkin R2 and R4 seem to provide this function.

Any ideas

BDP
Click to expand...

If you had seen Pass X0.2 preamp, thay used 10K resistor from Drain of output mosfet Q5,Q6 - Q7,Q8 connected to Drain of Q10 to cancel DC Offset 😉

Thanks
Anadigit
 
#2,794
ANADIGIT said:
If you had seen Pass X0.2 preamp, thay used 10K resistor from Drain of output mosfet Q5,Q6 - Q7,Q8 connected to Drain of Q10 to cancel DC Offset 😉

Thanks
Anadigit
Click to expand...
That's a really good advice. I have made this modification, and the DC offset drifting is now much smaller.

A bonus was that with single ended source and balanced output THD was reduced to ~1/8 of the previous measurement.

Have not had time to listen to the results yet...
 
#2,795
Happy happy

yggdrasil said:
That's a really good advice. I have made this modification, and the DC offset drifting is now much smaller.

A bonus was that with single ended source and balanced output THD was reduced to ~1/8 of the previous measurement.

Have not had time to listen to the results yet...
Click to expand...

Glad to hear that !!!
I used this method to control X0.2 with non capacitor output 😀

Thanks
Anadigit
 
#2,798
Hi Zen Mod,

<<in any case - good goal for programming CCS-es in Shunty is 2x load current , so 50% will be burnt in Shunty itself ; that way your circ will be fed with authority ...>>

thanks Zen Mod for your answer😀, I hope you don´t mind I put your answer here, maybe someone else can profit from your explanations!

I will look what current I need for Aleph P 1.7 and for my other preamp and I give you one of the current values and you may tell me the modification needed in CCS for one case.

The next change I will try to make myself....😱

O.K.?
 
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