My Take on Threshold NS10

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Russ White

Russ White

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Joined 2005
twistedpearaudio.com
#1
Hello all,

Tony and others have asked me to look over the NS10, so I did. I managed to find Nelson's schematic, but it is lacking values and ratings for parts. So I just threw something together hoping Nelson and the rest of you could help fill in the blanks.

Some questions:

1) What should the PS be.

2) What are the part values.

3) What other design factors should I consider.

So to get things rolling I submit what is likely a completely flubbed up layout:

Cheers!
Russ
 

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#3
Russ White said:
Hello all,

Tony and others have asked me to look over the NS10, so I did. I managed to find Nelson's schematic, but it is lacking values and ratings for parts. So I just threw something together hoping Nelson and the rest of you could help fill in the blanks.

Cheers!
Russ
Click to expand...

Good you did open this thread, you won me but I'm glad you did.

I wanted to post a GUESS WORK schematic with some values to gather some interest and maybe having others like Blues running a virtual test. Of course we would like Nelson throughing in all his knowledge and memory of it, unfortunately he does not have the original schematic.

One thing for sure, Nelson has tiped that the NPN devices should now be MPSA18 (On-Semi). I check on this and it is a modern replacement of the original MPS6571 same low noise and equal in most parameters with the added benefit of a higher voltage rating, VCEO and VCBO up to 45.

😎
 
#5
Ok I found lumanauw's excellent instructions:

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).
Click to expand...

And I have attempted to do a bipolar schematic, but I am affraid I have botched it. Especially I am worrind about what should be connected to the negative rail.

Please bear with my ignorance. This is a learning expedition for me. 🙂

Cheers
Russ
 

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#12
gentlemans-my modest (and verry clever 😉 ) proposal is that we merge this in just one thread......not sorta Krell clone thread but.....

besides -even if NS 10 is JUST preamp ,I think that this preamp deserves clonnin' thread ........hehe

just notice- I always have strange way in making system for particular room-I choose first speakers for room,then preamp,and then amp ;
Am I weird or what -preamps are offten bigger fetish for me than amps ,mebbe just because I always have more than one good amp .....
 
#13
Hi, Russ,

About the schematic in post #5 :
- If you use single supply (only + and gnd), this schematic is lacking the pull up section (R5,R6,C4 in NP's sch). If the Q1's base voltage is not defined (near middlle of the rail, usually), I'm afraid the whole thing won't work.
-RBS (of Q3) is not attached to ground, but in series with the base (ordinary base stopper configuration)

For using symmetrical power supply, then your schematic in post#5 can have the input section like that (without R5,R6,C4),
-R13 is connected to GND (to define 0 point for Q1)
-R3 is connected to -rail (adjusted in value until you get 0V on output),
-The end of C3 is also connected to GND
-R9 is connected to -rail
-R11 connected to GND

I don't advise the following, but I do this : I pick up transistors with lower gain (HFE) in position of Q2 and Q3. I use MPSA42 and MPSA92 there. I don't use R3. If you trace oscilation in the whole cct, you can put pF capacitor between B-C of Q1.

PS :

Mr.Pass, is it alright to make this schematic using symmetrical power supply? I hope I'm not Hi-Jacking your NS10, it is just because I don't have the original component values
 
#14
lumanauw said:
Hi, Russ,
For using symmetrical power supply, then your schematic in post#5 can have the input section like that (without R5,R6,C4),
-R13 is connected to GND (to define 0 point for Q1)
-R3 is connected to -rail (adjusted in value until you get 0V on output),
-The end of C3 is also connected to GND
-R9 is connected to -rail
-R11 connected to GND

I don't advise the following, but I do this : I pick up transistors with lower gain (HFE) in position of Q2 and Q3. I use MPSA42 and MPSA92 there. I don't use R3. If you trace oscilation in the whole cct, you can put pF capacitor between B-C of Q1.
Click to expand...


Thanks!

My question, and that schematic is for dual supply (bipolar).

You have helped me greatly.

Cheers!:drink:
Russ
 
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