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Old 9th November 2005, 11:55 PM   #11
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If you are a "dumb", then I'm the "dumber"

You got the blind NS10 schematic in your hands?
If you do, then here's what I do.

-First, I use symmetrical power supply, +/-25V with 0 gnd. So, I do not use R5, R6, R7 in the schematic. If you got only single supply 0/50V, then R7=200k, R5=R6=100k, C4=47uF.
- R13=20k potentiometer, for volume adjust. The wiper goes to left of C1 (470nF MKT), R12 is moved after C1. The bottom of VR13 goes to ground via additional 1k resistor, the upper is fed with input.
-The right of C1 connected to voltage divider (R6-R7), thus to R12=1k, and this R12 connects to gate of Q1, or if you got symmetrical supply, you can put the right of C1 with 100k to gnd (0V).
-R12=1k, is placed after the voltage divider (that is after C1) and before the gate of Q1 (2sk30y).
-I also put 470pf WIMA from gate to drain of Q1 (2sk30y).
-R4=10k, Q2=mpsA92, Q3=mpsA42, R8=470ohm, C2=C3=22uF non polar elko. R1=10k, R2=2k2 (makes gain=10k/2k2), R9=2k7 1/2watt.
- put base stopper at base of Q3, I use 1k there.
- R3 is for adjusting DC output, it is about 100k-470k, depends what device you use for Q1. I myself don't mind DC offset at left of C2, I got only 0V5 there, so I don't use R3. Sounds better without R3, even it has DC.
-R10=100ohm, R11=100kohm.

I tried various devices for Q1, MPSA06, MPSA42, 2n5401, BC550C, BC546, they sound differently. The best sound is 2sk30y (you can also buy 2sk30gr suffix).
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Old 10th November 2005, 12:16 AM   #12
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Old 10th November 2005, 02:56 AM   #13
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Hey Choky,

what's your favorite tube preamp design?
I have some 6922 and 6SN7 still in box.

Tom
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Old 10th November 2005, 03:56 AM   #14
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lumanauw,

I see a single stage (Q1) with level shifter followed by power stage (Q3). Very clever like JLH.

But what do you mean leave out R3?
This connects Q1 emitter to gnd and seems to be needed in my simulation.

If its as good as you say I will have to try it!

Tom

EE
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Old 10th November 2005, 05:36 AM   #15
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Hi, Tmblack,

I don't invent the schematic, it is NP who make it. So, I really don't know the values of each component and its main function.

From my backengineering (I don't use SIM, I go straightly to the real thing), it seems R3 is only for determining DC point at output, and in my real cct, it works without R3 at all, but it has slight DC. Sounds better too without R3.

Without R3 : Example Q1=bipolar with VBE=0V6. The current flowing through Q1 is 0V6/R4. I use R4=10k, so the current flowing is 6E-5A. Without R3, this current will flow from emitor of Q1 to R1 then to R9. This means if the base of Q1 is hold at 0V, and R4=R1=10k, then at the output (before C2) it will be -1V2.
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Old 10th November 2005, 07:18 AM   #16
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Quote:
Originally posted by tmblack
Hey Choky,

what's your favorite tube preamp design?
I have some 6922 and 6SN7 still in box.

Tom
hehe-just click at button bellow...
look for WOT

easily made with one 6922 per channel,with both sections paralleled

unsurpassed type of music presentation,if not anything else ...



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Old 10th November 2005, 03:59 PM   #17
tmblack is offline tmblack  United Kingdom
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Hi Lumanauw

you are correct, good job at figuring out the values.
I plan on trying it and Choky's preamp.

Tom

EE
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Old 10th November 2005, 06:00 PM   #18
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Here's the basic NS10 circuit.

Since the M1 is basically the same as the the SL10 MC input
stage, you can see it on the SL10 schematic which is posted
at www.passlabs.com/np
Attached Files
File Type: pdf ns10.pdf (8.8 KB, 826 views)
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Old 10th November 2005, 09:37 PM   #19
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Quote:
Originally posted by tmblack
Hi Lumanauw

you are correct, good job at figuring out the values.
I plan on trying it and Choky's preamp.

Tom

EE

like I say-use ECC88 or 6922,both sections in paralel;

Ua around 100V on top of your OPT ( OC3 is pretty handy there,even if I dont know exact current capacity in this moment (little bookie is not near me) so you;ll need maybe even two OC3 per channel ......

I suggest that you use grid stoppers of circa 100 ohms per each grid, both anodes tyed together with ferite bead right at base -as must ;I also always put that bloody 1M resistor from grid to ground,just because I can't trust to any pot to hold grid at gnd potential forever .......
both cathodes tye together and use one mutual resistor in range 43 to 51 ohms ,and you'll be in current range of some 25 to 30 mA per channel ;some 1000 micro/6V sh#ty BG cap or other (choice is yours) across cathode resistor is your choice also

you can also try NiCD (at least 4Ah/1V2 ,NiMH also) in cathode ( as battery charger instead of preamp hehe) but be prepared that some cells are bad for that use-oscillations can arise if you use "bad " accu .....

in final breadboarding try to rotate just secondary leads (rotate-swap, whatever you call it) -just because in one position capacitive parasitics in OPT are smaller than in other position.
loading secondary with some resistor can be usefull also (sonically wise) but that depends solelly of your particular OPT.....

I hope that some of this will help .......
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Old 10th November 2005, 09:52 PM   #20
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Quote:
Originally posted by Nelson Pass
Here's the basic NS10 circuit.

Since the M1 is basically the same as the the SL10 MC input
stage, you can see it on the SL10 schematic which is posted
at www.passlabs.com/np



just rename that *.zip to *.gif
Attached Files
File Type: zip sl10-sch.zip (75.5 KB, 530 views)
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